A review: Driving factors and regulation strategies of microbial community structure and dynamics in wastewater treatment systems

Biological degradation of organic micropollutants in GAC filters-temporal development and spatial variations

The capacity for organic micropollutant removal in granular activated carbon (GAC) filters for wastewater treatment changes over time. These changes are in general attributed to changes in adsorption, but may in some cases also be affected by biological degradation. Knowledge on the degradation of organic micropollutants, however, is scarce. In this work, the degradation of micropollutants in several full-scale GAC and sand filters was investigated through incubation experiments over a period of three years, using 14C-labeled organic micropollutants with different susceptibilities to biological degradation (ibuprofen, diclofenac, and carbamazepine), with parallel 16S rRNA gene sequencing. The results showed that the degradation of diclofenac and ibuprofen in GAC filters increased with increasing numbers of bed volumes when free oxygen was available in the filter, while variations over filter depth were limited. Despite relatively large differences in bacterial composition between filters, a degradation of diclofenac was consistently observed for the GAC filters that had been operated with high influent oxygen concentration (DO >8 mg/L). The results of this comprehensive experimental work provide an increased understanding of the interactions between microbial composition, filter material, and oxygen availability in the biological degradation of organic micropollutants in GAC filters.

External carbon source as a viable tool for controlling antibiotics and antibiotic resistance genes (ARGs) in effluent: Influence on antibiotic removal and ARGs dissemination

Fluoroquinolone antibiotics and antibiotic resistance genes (ARGs) regarded as emerging contaminants were poorly removed in conventional wastewater treatment plants (WWTPs). Nitrogen-containing heterocyclic organics were found to be biodegraded through denitrification co-metabolism. The feasibility to enhance antibiotics removal efficiency in WWTPs through denitrification co-metabolism needs to be further verified. Meanwhile, due to significant correlation between ARGs profiles and nitrogen removal that was previously observed, the dissemination of ARGs during denitrification was worthy of in-depth understanding. Herein, the antibiotic removal and ARGs dissemination in denitrification co-metabolism condition were investigated with different denitrifying consortiums that acclimated under different conditions in terms of carbon source and the exposure of Ofloxacin (OFL). The results suggest that the removal of OFL can be enhanced by the denitrification co-metabolism. The tolerance to OFL is different among various denitrifying communities. For the denitrifying consortiums acclimated with methanol, long-term exposure to trace OFL (1 μg/L) could reduce the capabilities of removal and tolerance to OFL. On the contrary, those acclimated with sodium acetate (NaAc), the capabilities of removal and tolerance to OFL, were enhanced by long-term exposure to trace OFL. According to the quantitative determination to 384 target genes with high-throughput quantitative PCR, the abundance of ARGs in consortiums greatly increased when exposed to OFL at the concentration of comparable to sewage, which was also much larger than that acclimated with methanol. It can be confirmed and supported by DNA sequencing results that the antibiotic removal and the dissemination of ARGs were determined by microbial community that could be shaped with carbon source. These conclusions suggest that selecting the right external carbon source can be a useful strategy for WWTPs to control antibiotics and ARGs in the effluent. From a new perspective on mitigating ARGs dissemination, NaAc was not an appropriate carbon source.

Microbial consortia-mediated arsenic bioremediation in agricultural soils: Current status, challenges, and solutions

Arsenic poisoning in agricultural soil is caused by both natural and man-made processes, and it poses a major risk to crop production and human health. Soil quality, agricultural production, runoff, ingestion, leaching, and absorption by plants are all influenced by these processes. Microbial consortia have become a feasible bioremediation technique in response to the urgent need for appropriate remediation solutions. These diverse microbial populations collaborate to combat arsenic poisoning in soil by facilitating mechanisms including oxidation-reduction, methylation-demethylation, volatilization, immobilization, and arsenic mobilization. The current state, problems, and remedies for employing microbial consortia in arsenic bioremediation in agricultural soils are examined in this review. Among the elements affecting their success include diversity, activity, community organization, and environmental conditions. Also, we emphasize the sensitivity and accuracy limits of existing assessment techniques. While earlier reviews have addressed a variety of arsenic remediation options, this study stands out by concentrating on microbial consortia as a viable strategy for arsenic removal and presents performance evaluation and technical problems. This work gives vital insights for tackling the major issue of arsenic pollution in agricultural soils by explaining the potential methods and components involved in microbial consortium-mediated arsenic bioremediation.

Effects of operational parameters on bacterial communities in Hong Kong and global wastewater treatment plants

Wastewater treatment plants (WWTPs) are indispensable biotechnology facilities for modern cities and play an essential role in modern urban infrastructure by employing microorganisms to remove pollutants in wastewater, thus protecting public health and the environment. This study conducted a 13-month bacterial community survey of six full-scale WWTPs in Hong Kong with samples of influent, activated sludge (AS), and effluent to explore their synchronism and asynchronism of bacterial community. Besides, we compared AS results of six Hong Kong WWTPs with data from 1,186 AS amplicon data in 269 global WWTPs and a 9-year metagenomic sequencing survey of a Hong Kong WWTP. Our results showed the compositions of bacterial communities varied and the bacterial community structure of AS had obvious differences across Hong Kong WWTPs. The co-occurrence analysis identified 40 pairs of relationships that existed among Hong Kong WWTPs to show solid associations between two species and stochastic processes took large proportions for the bacterial community assembly of six WWTPs. The abundance and distribution of the functional bacteria in worldwide and Hong Kong WWTPs were examined and compared, and we found that ammonia-oxidizing bacteria had more diversity than nitrite-oxidizing bacteria. Besides, Hong Kong WWTPs could make great contributions to the genome mining of microbial dark matter in the global "wanted list." Operational parameters had important effects on OTUs' abundance, such as the temperature to the genera of Tetrasphaera, Gordonia and Nitrospira. All these results obtained from this study can deepen our understanding of the microbial ecology in WWTPs and provide foundations for further studies.

IMPORTANCE

Wastewater treatment plants (WWTPs) are an indispensable component of modern cities, as they can remove pollutants in wastewater to prevent anthropogenic activities. Activated sludge (AS) is a fundamental wastewater treatment process and it harbors a highly complex microbial community that forms the main components and contains functional groups. Unveiling "who is there" is a long-term goal of the research on AS microbiology. High-throughput sequencing provides insights into the inventory diversity of microbial communities to an unprecedented level of detail. At present, the analysis of communities in WWTPs usually comes from a specific WWTP and lacks comparisons and verification among different WWTPs. The wide-scale and long-term sampling project and research in this study could help us evaluate the AS community more accurately to find the similarities and different results for different WWTPs in Hong Kong and other regions of the world.

Isolation of Enterococcus Bacteriophages from Municipal Wastewater Samples Using an Enrichment Step

Municipal wastewater, as an aggregate mixture of household and industrial effluents, harbors a highly diverse population of bacteria and their associated bacteriophages. Accordingly, it is a commonly used source of bacteriophages against many human-associated bacterial pathogens. Here, we describe a method for bacteriophage isolation from municipal wastewater with several optional enrichment and concentration steps.

A systematic review of industrial wastewater management: Evaluating challenges and enablers

The study provides a systematic literature review (SLR) encompassing industrial wastewater management research from the past decade, examining enablers, challenges, and prevailing practices. Originating from manufacturing, energy production, and diverse industrial processes, industrial wastewater's handling is critical due to its potential to impact the environment and public health. The research aims to comprehend the current state of industrial wastewater management, pinpoint gaps, and outline future research prospects. The SLR methodology involves scouring the Scopus database, yielding an initial pool of 253 articles. Refinement via search code leaves 101 articles, followed by abstract screening that reduces articles to 79, and finally 66 well-focused articles left for thorough full-text examination. Results underscore the significance of regulatory frameworks, technological innovation, and sustainability considerations as cornerstones for effective wastewater management. However, substantial impediments like; inadequate infrastructure, resource constraints and the necessity for stakeholder collaboration still exist. The study highlights emerging research domains, exemplified by advanced technologies like nanotechnology and bioremediation, alongside the pivotal role of circular economy principles in wastewater management. The SLR offers an exhaustive view of contemporary industrial wastewater management, accentuating the imperative of an all-encompassing approach that integrates regulatory, technological, and sustainability facets. Notably, the research identifies gaps and opportunities for forthcoming exploration, advocating for interdisciplinary research and intensified stakeholder collaboration. The study's insights cater to policymakers, practitioners, and researchers, equipping them to address the challenges and capitalize on prospects in industrial wastewater management effectively.

The perfluoroalkyl substances influenced the distribution of bacterial communities and their functions from source water to tap water

Perfluoroalkyl substances (PFASs) and antibiotic resistance genes (ARGs) in drinking water are environmental issues that require special attention. The objective of this study was to know the effects of PFASs on microbial communities and their functional genes from source water to tap water. PFASs were detected by mass-labeled internal standards method, and the microbial communities and functional genes were analyzed by metagenomics. Our results indicated that the concentration of total PFASs in the water ranged from 47.7 to 171.4 ng/L, with perfluorobutanoic acid (PFBA) and perfluorooctanoic acid (PFOA) being the dominant types. The PFASs concentration decreased slowly from source to tap water in some months. PFBA, PFOA, perfluorooctane sulfonic acid (PFOS) and perfluorohexanoic acid (PFHxA) influenced the functional genes related to two-component system, bacterial secretion system and flagellar assembly of Aquabacterium, Methylobacterium, and Curvibacter, which contributed significantly to macB and evgS. Therefore, the bacterial communities enhanced adaptation to fluctuating environments by upregulating some functional genes under the PFASs stress, with concomitant changes in the expression of ARGs. Moreover, PFASs also promoted the expression of functional genes associated with human diseases, such as shigellosis and tuberculosis, which increased the risk of human pathogenicity. The bench scale experiment results also suggested that PFOA and PFOS in drinking water can promote the ARGs proliferation and induce microbial risk. Therefore, it is necessary to take measures to prevent the risks caused by PFASs and ARGs in drinking water.

Linking the shifts in the metabolically active microbiota in a UASB and hybrid anaerobic-aerobic bioreactor for swine wastewater treatment

Due to the high concentration of pollutants, swine wastewater needs to be treated prior to disposal. The combination of anaerobic and aerobic technologies in one hybrid system allows to obtain higher removal efficiencies compared to those achieved via conventional biological treatment, and the performance of a hybrid system depends on the microbial community in the bioreactor. Here, we evaluated the community assembly of an anaerobic-aerobic hybrid reactor for swine wastewater treatment. Sequencing of partial 16S rRNA coding genes was performed using Illumina from DNA and retrotranscribed RNA templates (cDNA) extracted from samples from both sections of the hybrid system and from a UASB bioreactor fed with the same swine wastewater influent. Proteobacteria and Firmicutes were the dominant phyla and play a key role in anaerobic fermentation, followed by Methanosaeta and Methanobacterium. Several differences were found in the relative abundances of some genera between the DNA and cDNA samples, indicating an increase in the diversity of the metabolically active community, highlighting Chlorobaculum, Cladimonas, Turicibacter and Clostridium senso stricto. Nitrifying bacteria were more abundant in the hybrid bioreactor. Beta diversity analysis revealed that the microbial community structure significantly differed among the samples (p < 0.05) and between both anaerobic treatments. The main predicted metabolic pathways were the biosynthesis of amino acids and the formation of antibiotics. Also, the metabolism of C5-branched dibasic acid, Vit B5 and CoA, exhibited an important relationship with the main nitrogen-removing microorganisms. The anaerobic-aerobic hybrid bioreactor showed a higher ammonia removal rate compared to the conventional UASB system. However, further research and adjustments are needed to completely remove nitrogen from wastewater.

Stress response and signalling of a low-temperature bioaugmentation system in decentralized wastewater treatment: Degradation characteristics, community structure, and bioaugmented mechanisms

Low temperatures present challenges for stable wastewater treatment operations in cold regions. Low-temperature effective microorganisms (LTEM) were added as a bioaugmentation strategy at a decentralized treatment facility to improve performance. The effects of a low-temperature bioaugmentation system (LTBS) with LTEM at low temperatures (4 °C) on organic pollutant performance, microbial community changes, and the metabolic pathways of functional genes and functional enzymes were studied. To explore the bioaugmentation mechanism of LTBS based on stress response and signalling. The results showed that the start-up time of the LTBS (S2) with LTEM was shorter (8 days) and that it removed COD and NH₄⁺-N at higher rates (87 % and 72 %, respectively) at 4 °C. LTEM effectively degraded complex macromolecular organics into small molecular organics, and decomposing sludge flocs and the changing the extracellular polymeric substances (EPS) structure removed more organics and nitrogen. LTEM and local microbial communities (nitrifying and denitrifying bacteria) improved the ability of organic matter degradation and denitrification of the LTBS and formed a core microbial community dominated by LTEM (Bacillus and Pseudomonas). Finally, based on the functional enzymes and metabolic pathways of the LTBS, a low-temperature strengthening mechanism consisting of 6 cold stress responses and signal pathways under low temperatures was formed. This study demonstrated that the LTEM-dominated LTBS could provide an engineering alternative for future decentralized wastewater treatment in cold regions.

Model-based fractionation of biomass in a biological nutrient removal system and its effect on the removal efficiencies

Fractionation of active biomass in a five-stage Bardenpho process was accomplished using an MS Excel wastewater treatment plant modeling tool based on Activated Sludge Model No. 3 extended with a bio-P module. The biomass fractions within the treatment system were predicted as autotrophs, ordinary heterotrophs, and phosphorus accumulating organisms (PAOs). Several simulations were performed in a Bardenpho process using various C/N/P ratios in primary effluent. Biomass fractionation was obtained from steady-state simulation results. The results suggest that the mass percentage of autotrophs, heterotrophs, and PAOs in active biomass range from 1.7 to 7.8%, 5.7-69.0%, and 23.2-92.6%, respectively, depending on characteristics of primary effluent. Results of principal component analysis showed that TKN/COD ratio in primary effluent determines the population of autotrophs and ordinary heterotrophs whereas PAO population is mainly a function of TP/COD ratio.

Research on microbial community structure and treatment of dye wastewater with the enhancement of activated sludge by magnetic field at low temperature

This study characterized the effect of different magnetic field (MF) intensities (10-40 mT) on the degradation of dye wastewater by activated sludge and the diversity of the microbial community at a low temperature (5 °C). The examined MF range promoted the degradation of dye wastewater by the microorganisms in the activated sludge at a low temperature. It was found that the optimal degradation performance was achieved at 30 mT. Additionally, the maximum degradation efficiency of COD and chromaticity (66.30% and 60.87%, respectively) were also achieved at 30 mT and the peak TTC-dehydrogenase activity (TTC-DHA) was 9.44 mg TF g^-1 SS. Furthermore, it was revealed that MF enhancement increased the richness and diversity of activated sludge microorganisms, thus promoting the growth and reproduction of activated sludge microorganisms at low temperatures. Bacterial taxa known to effectively participate in the degradation of pollutants by activated sludge were enriched at 30 mT. The dominant bacteria under 30 mT were Flavobacterium, Hydrogenophaga, Gemmatimonadaceae, Zoogloea, Saprospiraceae, Pseudomonas, and Geothrix.

How anaerobic sludge microbiome respond to different concentrations of nitrite, nitrate, and ammonium ions: a comparative analysis

High concentrations of ammonium, nitrite, and nitrate always induce inhibition in anaerobic wastewater treatment. Due to the complexity and vulnerability of the microbial community (especially methanogens) in anaerobic sludge, little is understood about its underlying microbial mechanism under such inhibition. In this study, the shifts of microbial communities in anaerobic sludge under increasing levels of nitrite, nitrate, and ammonium ions were compared. Results show that although half maximal inhibitory concentrations (methanogenesis) were different for nitrite, nitrate, and ammonium ions with EC₅₀ values of 12, 30, and 3000 mg N/L, respectively, bacteria genera Kosmotoga and Brooklawnia dominated in all of the three high-stress inhibitory systems. Network analysis and redundancy analysis (RDA) of the microbial community showed the treatments with nitrate and nitrite ions decreased the modularity of anaerobic microorganisms. RDA showed that specific methanogenic activity was positively related to coenzyme F₄₂₀ under nitrite inhibition (r_p = 0.833, p < 0.05) and closely correlated with viability under nitrate inhibition. Gram-positive and nonmotile Brooklawnia genus showed a negative correlation with physiological characteristics in the ammonia treatments, suggesting its high resistance to ammonia.

Full-scale activated sludge transplantation reveals a highly resilient community structure

Well-functioning and stable microbial communities are critical for the operation of activated sludge (AS) wastewater treatment plants (WWTPs). Bioaugmentation represents a potentially useful approach to recover deteriorated systems or to support specific AS processes, but its application in full-scale WWTPs is generally problematic. We conducted a massive transplantation (in one day) exchanging AS from a donor to a recipient full-scale WWTP with similar process type (biological removal of nitrogen and phosphorus) and performance, but with differences in microbial community structure. The treatment performance in the recipient plant was not compromised and the effluent quality remained stable. The AS community structure of the recipient plant was initially very similar to the donor AS, but it almost completely restored the pre-transplantation structure approximately 40 days after transplantation, corresponding to 3 times the solid retention time. Most of the unique species of donor AS added to recipient AS disappeared quickly, although some disappeared more slowly the following months, indicating some survival and potentially a time limited function in the recipient plant. Moreover, the addition in higher abundance of most species already present in the recipient AS (e.g., the polyphosphate accumulating organisms) or the reduction of the abundance of unwanted bacteria (e.g., filamentous bacteria) in the recipient plant was not successful. Moreover, we observed similar abundance patterns after transplantation for species belonging to different functional guilds, so we did not observe an increase of the functional redundancy. Investigations of the microbial community structure in influent wastewater revealed that for some species the abundance trends in the recipient plant were closely correlated to their abundance in the influent. We showed that a very resilient microbial community was responsible for the outcome of the transplantation of AS at full-scale WWTP, potentially as a consequence of mass-immigration from influent wastewater. The overall results imply that massive transplantation of AS across different WWTPs is not a promising strategy to permanently solve operational problems. However, by choosing a compatible AS donor, short term mitigation of serious operational problems may be possible.

A Review of Basic Bioinformatic Techniques for Microbial Community Analysis in an Anaerobic Digester

Biogas production involves various types of intricate microbial populations in an anaerobic digester (AD). To understand the anaerobic digestion system better, a broad-based study must be conducted on the microbial population. Deep understanding of the complete metagenomics including microbial structure, functional gene form, similarity/differences, and relationships between metabolic pathways and product formation, could aid in optimization and enhancement of AD processes. With advancements in technologies for metagenomic sequencing, for example, next generation sequencing and high-throughput sequencing, have revolutionized the study of microbial dynamics in anaerobic digestion. This review includes a brief introduction to the basic process of metagenomics research and includes a detailed summary of the various bioinformatics approaches, viz., total investigation of data obtained from microbial communities using bioinformatics methods to expose metagenomics characterization. This includes (1) methods of DNA isolation and sequencing, (2) investigation of anaerobic microbial communities using bioinformatics techniques, (3) application of the analysis of anaerobic microbial community and biogas production, and (4) restriction and prediction of bioinformatics analysis on microbial metagenomics. The review has been concluded, giving a summarized insight into bioinformatic tools and also promoting the future prospects of integrating humungous data with artificial intelligence and neural network software.

Monthly dynamics of microbial communities and variation of nitrogen-cycling genes in an industrial-scale expanded granular sludge bed reactor

Introduction

The expanded granular sludge bed (EGSB) is a major form of anaerobic digestion system during wastewater treatment. Yet, the dynamics of microbial and viral communities and members functioning in nitrogen cycling along with monthly changing physicochemical properties have not been well elucidated.

Methods

Here, by collecting the anaerobic activated sludge samples from a continuously operating industrial-scale EGSB reactor, we conducted 16S rRNA gene amplicon sequencing and metagenome sequencing to reveal the microbial community structure and variation with the ever-changing physicochemical properties along within a year.

Results

We observed a clear monthly variation of microbial community structures, while COD, the ratio of volatile suspended solids (VSS) to total suspended solids (TSS) (VSS/TSS ratio), and temperature were predominant factors in shaping community dissimilarities examined by generalized boosted regression modeling (GBM) analysis. Meanwhile, a significant correlation was found between the changing physicochemical properties and microbial communities (p <0.05). The alpha diversity (Chao1 and Shannon) was significantly higher (p <0.05) in both winter (December, January, and February) and autumn (September, October, and November) with higher organic loading rate (OLR), higher VSS/TSS ratio, and lower temperature, resulting higher biogas production and nutrition removal efficiency. Further, 18 key genes covering nitrate reduction, denitrification, nitrification, and nitrogen fixation pathways were discovered, the total abundance of which was significantly associated with the changing environmental factors (p <0.05). Among these pathways, the dissimilatory nitrate reduction to ammonia (DNRA) and denitrification had the higher abundance contributed by the top highly abundant genes narGH, nrfABCDH, and hcp. The COD, OLR, and temperature were primary factors in affecting DNRA and denitrification by GBM evaluation. Moreover, by metagenome binning, we found the DNRA populations mainly belonged to Proteobacteria, Planctomycetota, and Nitrospirae, while the denitrifying bacteria with complete denitrification performance were all Proteobacteria. Besides, we detected 3,360 non-redundant viral sequences with great novelty, in which Siphoviridae, Podoviridae, and Myoviridae were dominant viral families. Interestingly, viral communities likewise depicted clear monthly variation and had significant associations with the recovered populations (p <0.05).

Discussion

Our work highlights the monthly variation of microbial and viral communities during the continuous operation of EGSB affected by the predominant changing COD, OLR, and temperature, while DNRA and denitrification pathways dominated in this anaerobic system. The results also provide a theoretical basis for the optimization of the engineered system.

Deciphering the microbial community structures and functions of wastewater treatment at high-altitude area

Introduction: The proper operation of wastewater treatment plants is a key factor in maintaining a stable river and lake environment. Low purification efficiency in winter is a common problem in high-altitude wastewater treatment plants (WWTPs), and analysis of the microbial community involved in the sewage treatment process at high-altitude can provide valuable references for improving this problem. Methods: In this study, the bacterial communities of high- and low-altitude WWTPs were investigated using Illumina high-throughput sequencing (HTS). The interaction between microbial community and environmental variables were explored by co-occurrence correlation network. Results: At genus level, Thauera (5.2%), unclassified_Rhodocyclaceae (3.0%), Dokdonella (2.5%), and Ferribacterium (2.5%) were the dominant genera in high-altitude group. The abundance of nitrogen and phosphorus removal bacteria were higher in high-altitude group (10.2% and 1.3%, respectively) than in low-altitude group (5.4% and 0.6%, respectively). Redundancy analysis (RDA) and co-occurrence network analysis showed that altitude, ultraviolet index (UVI), pH, dissolved oxygen (DO) and total nitrogen (TN) were the dominated environmental factors (p < 0.05) affecting microbial community assembly, and these five variables explained 21.4%, 20.3%, 16.9%, 11.5%, and 8.2% of the bacterial assembly of AS communities. Discussion: The community diversity of high-altitude group was lower than that of low-altitude group, and WWTPs of high-altitude aeras had a unique microbial community structure. Low temperature and strong UVI are pivotal factors contributing to the reduced diversity of activated sludge microbial communities at high-altitudes.

Influencing Factors of Stereotypes on Wastewater Treatment Plants- Case Study of 9 Wastewater Treatment Plants in Xi'an, China

As an indispensable part of cities, wastewater treatment plants play an important role in environmental protection and urbanization. However, the promotion of wastewater treatment plants has been consistently hindered by residents' negative stereotypes and rejections, which is called "Not-In-My-Back-Yard" (NIMBY) effect. This study collected the first-hand data with the residents residing within 3 kilometers of 9 wastewater treatment plants in Xi'an, China through a survey. Keyword co-occurrence network analysis was conducted and the results illustrate that residents have stereotypes toward wastewater treatment plants. There are two types of residents' stereotypes toward wastewater treatment plants: positive and negative. The positive stereotypes of wastewater treatment plants in turn can be subdivided into the three categories of treatment technologies, treatment results, and social impacts. But the negative stereotypes didn't demonstrate meaningful categories. We also tried to identify the influencing factors that cause residents' stereotypes. The distance from residents' residence to the wastewater treatment plants has impacts on the stereotypes of residents' who reside within 1000 meters of the wastewater treatment plant: the farther from the wastewater treatment plants their residence is, the more positive their stereotypes are. We also found that the more educated the participants are, the more positive stereotypes of wastewater treatment plants they have. Moreover, residents' stereotypes toward wastewater treatment plants are more influenced by formal education. Non-formal education and informal learning probably have less influence on the promotion of wastewater treatment plants. Therefore, we propose to incorporate environmental education for sustainable development into formal education to increase residents' acceptance of wastewater treatment plants.

Characteristics of the colony structure of A2O processes under different ultraviolet conditions in plateau areas

In this text, a laboratory-scale A²O was performed in Linzhi City at a 3000-m altitude. During the test operation, the UV irradiation was carried out in oxic tank for 0, 5, 10, 30, and 180 min. The 16SrRNA gene sequencing was performed on the activated sludge in anaerobic, anoxic, and oxic tanks, and the colony structure characteristics of phyla, genera, and species classification levels in the sludge were analyzed. There were significant differences in the numbers of genera and species (p ≤ 0.05). The community richness, uniformity, diversity, and other indicators differed to some degree compared with those of other regions. The analysis of composition of bacterial colonies revealed different levels. The significance test of the difference between the groups, the significance of the dominant species, and the mechanism of UV was analyzed. A CCA diagram was used to verify that UV is an important factor in the colony structure composition, and the correlation heatmap diagram was used to analyze the microorganisms that are significantly related to UV. A sample hierarchical cluster analysis showed that the time of UV exposure can be divided into two categories, and the effects of UV exposure increase sequentially as the time of exposure increases. A comprehensive analysis found that the enhancing and inhibitory effects of UV affect the composition of the colony structure in the sample, and the time of irradiation will affect the enhancing or inhibitory effect, that is, the colony structure from the samples that were irradiated for different amounts of time differs greatly.

Bioaugmentation with Acinetobacter sp. TAC-1 to enhance nitrogen removal in swine wastewater by moving bed biofilm reactor inoculated with bacteria

To enhance the performance of moving bed biofilm reactor (MBBR) inoculated with heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria, bioaugmentation with Acinetobacter sp. TAC-1 was firstly employed and then the treatment performance for real swine wastewater was presented in this study. Results indicated that NH₄⁺-N and TN removal rates of bioaugmented reactor were significantly improved from 16.53 mg/L/h and 16.15 mg/L/h to 24.58 mg/L/h and 24.45 mg/L/h, respectively. The efficient removal performance (NH₄⁺-N 95.01%, TN 86.40%) for real swine wastewater was achieved within 24 h. Microbial analysis indicated that the composition of functional bacteria varied with the introduction of Acinetobacter sp. TAC-1, especially the abundance of Acinetobacter, Paracoccus and Rhodococcus related to the nitrogen removal. Furthermore, bioaugmentation with Acinetobacter sp. TAC-1 increased abundance of enzymes and functional genes (nirS, nirK and norZ) corresponding to denitrification that may be responsible for the enhanced nitrogen removal performance.

Spatial Variation of the Microbial Community Structure of On-Site Soil Treatment Units in a Temperate Climate, and the Role of Pre-treatment of Domestic Effluent in the Development of the Biomat Community

The growth of microbial mats or “biomats” has been identified as an essential component in the attenuation of pollutants within the soil treatment unit (STU) of conventional on-site wastewater treatment systems (OWTSs). This study aimed to characterize the microbial community which colonizes these niches and to determine the influence of the pre-treatment of raw-domestic wastewater on these communities. This was achieved through a detailed sampling campaign of two OWTSs. At each site, the STU areas were split whereby half received effluent directly from septic tanks, and half received more highly treated effluents from packaged aerobic treatment systems [a coconut husk media filter on one site, and a rotating biodisc contactor (RBC) on the other site]. Effluents from the RBC had a higher level of pre-treatment [~90% Total Organic Carbon (TOC) removal], compared to the media filter (~60% TOC removal). A total of 92 samples were obtained from both STU locations and characterized by 16S rRNA gene sequencing analysis. The fully treated effluent from the RBC resulted in greater microbial community richness and diversity within the STUs compared to the STUs receiving partially treated effluents. The microbial community structure found within the STU receiving fully treated effluents was significantly different from its septic tank, primary effluent counterpart. Moreover, the distance along each STU appears to have a greater impact on the community structure than the depth in each STU. Our findings highlight the spatial variability of diversity, Phylum- and Genus-level taxa, and functional groups within the STUs, which supports the assumption that specialized biomes develop around the application of effluents under different degrees of treatment and distance from the source. This research indicates that the application of pre-treated effluents infers significant changes in the microbial community structure, which in turn has important implications for the functionality of the STU, and consequently the potential risks to public health and the environment.

Modification of expanded clay carrier for enhancing the immobilization and nitrogen removal capacity of nitrifying and denitrifying bacteria in the aquaculture system

In aquaculture systems, the treatment of nitrogen pollution has always been a center of attention due to its impact on productiveness. The bioremediation method based on simultaneous nitrification and denitrification was often used to effectively remove ammonium, nitrite, and nitrate compounds. In addition, the attachment and biofilm formation of the nitrogen-converting bacteria on carriers had superior removal efficiency over the suspended bacteria. Thus, this study focused on the fabrication of a porosity floatable expanded clay (EC) carrier that provided the basic structure for the immobilization of the nitrifiers Nitrosomonas sp., Nitrobacter sp., and the denitrifier Bacillus sp. The EC was also coated with alginate and essential nutrient to support the cohesion and growth of bacteria. Especially, the selected Bacillus sp. previously proved was able to reduce nitrite/nitrate in aerobic conditions. The co-immobilization of these three aerobic bacteria on the prepared carrier would simply the treatment process in practical use. Initial results showed that the integration of essential nutrients (N, P, K) on alginate coated EC (EC_Alg_N) increased bacterial density to (57 ± 3) × 10⁷ - (430 ± 30) × 10⁸ CFU/g, which then led to the enhancement of removal efficiency up to 91.62 ± 0.67% in the medium containing initial nitrogen content of 60 mg-N/L. The nitrogen removal efficacy of bacterial immobilized EC_Alg_N remained at 83.95 ± 0.15% after being reused for 6 cycles. In conclusion, the bacterial immobilized EC_Alg_N could be a potential material for nitrogen polluted wastewater treatment in aquaculture systems.

The effect of rhizosphere and the plant species on the degradation of sulfonamides in model constructed wetlands treating synthetic domestic wastewater

The effects of and main contributors in rhizosphere and plant species on the degradation of sulfonamides (SAs) in constructed wetland (CW) models for the treatment of domestic wastewater are currently unclear. To investigate the degradation and key rhizosphere factors of mixed SAs with sulfadiazine (SDZ), sulfapyridine (SPD), sulfamerazine (SMZ1), sulfamethazine (SMZ2), and sulfamethoxazole (SMX) at millimeter distances from the root surface, a multi-interlayer rhizobox experiment planted with Cyperus alternifolius, Juncus effusus, Cyperus papyrus, and an unvegetated control was conducted. There was a higher O₂ saturation and dissolved organic carbon (DOC) content and a lower SA content in the rhizosphere and near/moderate-rhizosphere (0-3 and 3-8 mm from rhizosphere) than the far/non-rhizosphere (8-40 and 40-90 mm from rhizosphere). Bacterial abundance and community composition was indicative of the microbial degradation of SAs. Both the O₂ and DOC contents promoted total bacterial abundance in different zones from CW rhizoboxes. The relative abundance of the most dominant bacteria was significantly correlated with O₂, DOC, and SAs, except SMX, which also indicates other dissipation processes for SMX in the rhizosphere. Furthermore, more metabolites and aerobic SA-degrading bacteria were observed in the rhizosphere and near/moderate-rhizosphere than in the far/non-rhizosphere zones, suggesting that the effect of O₂ in the rhizosphere is important in the degradation of SAs in CWs.

Model construction and application for effluent prediction in wastewater treatment plant: Data processing method optimization and process parameters integration

Wastewater treatment based on the activated sludge process is complex process, which is easily affected by influent quality, aeration time and other factors, leading to unstable effluent. Facing increasingly stringent sewage discharge standards in China, it is necessary to build a prediction model for early warning of effluent quality. In this study, nine machine learning algorithms were adopted to construct models for the prediction of effluent Chemical Oxygen Demand (COD). In order to improve the prediction accuracy of the models, model optimization was conducted by introducing the hysteresis condition [Hydraulic Retention Time (HRT) of 18 h], data processing method (K-FOLD) and process parameters [dissolved oxygen (DO), sludge return ratio (SRR) and mixed liquid suspended solids (MLSS)]. Results showed that both K-Nearest Neighbour (KNN) and Gradient Boosting Decision Tree (GBDT) displayed excellent prediction effects, the best results of MAPE, RMSE and R² were 7.34%/1.29/0.92(COD, KNN). The optimized models were further applied to the prediction of effluent total phosphorus (TP), total nitrogen (TN) and pH. The MAPE/RMSE/R² were 7.43%/0.92/0.93(TN, GBDT), 17.81%/0.19/0.99(TP, KNN), 0.53%/0.16/0.99 (pH, KNN) respectively, indicating high prediction accuracy. The change and comparison of modeling conditions provide a new insight to wastewater prediction models. In addition, this study is close to the actual application scenario of WWTPs operation and management, also laying a foundation for the reverse regulation of energy saving and consumption reduction of wastewater treatment plants (WWTPs).

Towards better process management in wastewater treatment plants: Process analytics based on SHAP values for tree-based machine learning methods

Understanding the mechanisms of pollutant removal in Wastewater Treatment Plants (WWTPs) is crucial for controlling effluent quality efficiently. However, the numerous treatment units, operational factors, and the underlying interactions between these units and factors usually obfuscate the comprehensive and precise understanding of the processes. We have previously proposed a machine learning (ML) framework to uncover complex cause-and-effect relationships in WWTPs. However, only one interpretable ML model, Random forest (RF), was studied and the interpretation method was not granular enough to reveal very detailed relationships between operational factors and effluent parameters. Thus, in this paper, we present an upgraded framework involving three interpretable tree-based models (RF, XGboost and LightGBM), three metrics (R², Root mean squared error (RMSE), and Mean absolute error (MAE)) and a more advanced interpretation system SHapley Additive exPlanations (SHAP). Details of the framework are provided along with a demonstration of its practical applicability based on a case study of the Umeå WWTP in Sweden. Results show that, for both labels TSS_e (Total suspended solids in effluent) and PO4_e (Phosphate in effluent), the XGBoost models are optimal whereas the RF models are the least optimal, due to overfitting and polarized fitting. This study has yielded multiple new and significant findings with respect to the control of TSS_e and PO4_e in the Umeå WWTP and other similarly configured WWTPs. Additionally, this study has produced two important generic findings relating to ML applications for WWTPs (or even other process industries) in terms of cause-and-effect investigations. First, the model comparison should be carried out from multiple perspectives to ensure that underlying details are fully revealed and examined. Second, using a precise, robust, and granular (feature attribution available for individual instances) explanation method can bring extra insight into both model comparison and model interpretation. SHAP is recommended as we found it to be of great value in this study.

Denitrifying bioreactor microbiome: Understanding pollution swapping and potential for improved performance

Denitrifying woodchip bioreactors are a best management practice to reduce nitrate-nitrogen (NO₃ -N) loading to surface waters from agricultural subsurface drainage. Their effectiveness has been proven in many studies, although variable results with respect to performance indicators have been observed. This paper serves the purpose of synthesizing the current state of the science in terms of the microbial community, its impact on the consistency of bioreactor performance, and its role in the production of potential harmful by-products including greenhouse gases, sulfate reduction, and methylmercury. Microbial processes other than denitrification have been observed in these bioreactor systems, including dissimilatory nitrate reduction to ammonia (DNRA) and anaerobic ammonium oxidation (anammox). Specific gene targets for denitrification, DNRA, anammox, and the production of harmful by-products are identified from bioreactor studies and other environmentally relevant systems for application in bioreactor studies. Lastly, cellulose depletion has been observed over time via increasing ligno-cellulose indices, therefore, the microbial metabolism of cellulose is an important function for bioreactor performance and management. Future work should draw from the knowledge of soil and wetland ecology to inform the study of bioreactor microbiomes.

Ecological Insights Into Community Interactions, Assembly Processes and Function in the Denitrifying Phosphorus Removal Activated Sludge Driven by Phosphorus Sources

The microbial characteristics in the wastewater treatment plants (WWTPs) strongly affect their optimal performance and functional stability. However, a cognitive gap remains regarding the characteristics of the microbial community driven by phosphorus sources, especially co-occurrence patterns and community assembly based on phylogenetic group. In this study, 59 denitrifying phosphorus removal (DPR) activated sludge samples were cultivated with phosphorus sources. The results suggested that homogeneous selection accounted for the largest proportion that ranged from 35.82 to 64.48%. Deterministic processes dominated in 12 microbial groups (bins): Candidatus_Accumulibacter and Pseudomonas in these bins belonged to phosphate-accumulating organisms (PAOs). Network analysis revealed that species interactions were intensive in cyclic nucleoside phosphate-influenced microbiota. Function prediction indicated that cyclic nucleoside phosphates increased the activity of enzymes related to denitrification and phosphorus metabolism and increased the α-diversity of microorganism but decreased the diversity of metabolic function. Based on these results, it was assumed that cyclic nucleoside phosphates, rather than inorganic phosphates, are the most available phosphorus source for majority microorganisms in DPR activated sludge. The study revealed the important role of phosphorus source in the construction and assembly of microbial communities and provided new insights about pollutant removal from WWTPs.

Simultaneous mineralization of 2-anilinophenylacetate and denitrification by Ru/Fe modified biocathode double-chamber microbial fuel cell

A double-chamber microbial fuel cell (MFC) with Ru/Fe-modified-biocathode was constructed for simultaneous mineralization of 2-anilinophenylacetate (APA) and denitrification. The factors on performance of simultaneous APA degradation and denitrification were explored. The contributions of ROS to APA degradation were evaluated by EPR and quenching experiments. The microbial community of Ru/Fe-modified-biocathode was determined by high-throughput sequencing. Results showed that low resistance accelerated APA degradation by Ru/Fe-modified-biocathode, while higher initial APA concentration inhibited microbial activity of the biocathode. The optimum ammonia concentration was 50 mg L^-1, while too high or too low ammonia concentration did not favor APA degradation. The APA degradation efficiency of Ru/Fe-modified-biocathode-MFC was higher than that of other modified-cathode-MFCs. The APA degradation process confirmed to the pseudo-first-order kinetic model, and APA degradation kinetic constant, the maximum removal efficiency of TOC, ammonia and TN were 2.15d^-1, 59.70%, 99.20% and 44.56% respectively, signifying a simultaneous APA mineralization and denitrification performance of Ru/Fe-modified-biocathode-MFC. The coulombic efficiency decreased with APA concentration increase. OH was the primary radical in APA degradation progress. Eight kinds of intermediates were measured, and two APA degradation pathways were proposed, among which APA hydroxylation was the main pathway. The microbial community of Ru/Fe-modified-biocathode was dominated with Nitrosomonas at genus level, and enriched with various APA-degraders, nitrifiers, and denitrifiers such as Pseudomonas, Nitrospira, Nitrobacter, Paracoccus, Thermomonas, Dechloromonas, and Clostridium_Sutra_stricto_1. COG analysis showed the redox reaction of Ru/Fe might affect signal transduction and environment adaptation, while FAPROTAX analysis suggested that Ru/Fe-modified-biocathode exhibited higher nitrification activity than that of carbon-felt-biocathode. The synergistic mechanism of simultaneous APA mineralization and denitrification was mainly redox reaction of Ru/Fe and supplemented by aerobic biodegradation.

Comprehensive insights into core microbial assemblages in activated sludge exposed to textile-dyeing wastewater stress

Microorganisms in activated sludge are widely recognized for their roles in wastewater treatment. However, previous studies were mainly concerned with the diversity and driving factors of microbial communities within domestic wastewater treatment, and those of domestic wastewater treatment systems mixed with industrial wastewater are poorly understood. In this research, three different full-scale aerobic activated sludge (AS) wastewater treatment systems fed with municipal, textile-dyeing, and mixed wastewater, respectively, were monitored over the operation course of three months. 16S rRNA amplicon sequencing analysis revealed that the microbial communities in textile-dyeing wastewater activated sludge (AS) exhibited significantly lower richness and diversity (p < 0.01, Adonis) compared to those fed with municipal wastewater. In contrast, textile-dyeing derived AS selectively enriched microbial taxa with aromatic degradation and denitrification potentials. Further, FARPROTAX and metabolomics indicated the inhibition of 72.5% metabolic functions (p < 0.01) in AS from the system fed with textile-dyeing wastewater, including the pathways of pentose phosphate metabolism, purine metabolism, and glycerophospholipid metabolism. Overall, this study corroborates textile-dyeing wastewater is a novel microbial niche and could suppress sludge performance by inhibiting microbial activity and metabolism, raising concerns on AS-based systems for industrial wastewater treatment.

Biological treatment of coke plant effluents: from a microbiological perspective

During coke production, large volume of effluent is generated, which has a very complex chemical composition and contains several toxic and carcinogenic substances, mainly aromatic compounds, cyanide, thiocyanate and ammonium. The composition of these high-strength effluents is very diverse and depends on the quality of coals used and the operating and technological parameters of coke ovens. In general, after initial physicochemical treatment, biological purification steps are applied in activated sludge bioreactors. This review summarizes the current knowledge on the anaerobic and aerobic transformation processes and describes key microorganisms, such as phenol- and thiocyanate-degrading, floc-forming, nitrifying and denitrifying bacteria, which contribute to the removal of pollutants from coke plant effluents. Providing the theoretical basis for technical issues (in this case the microbiology of coke plant effluent treatment) aids the optimization of existing technologies and the design of new management techniques.

Toxic Effect of Ammonium Nitrogen on the Nitrification Process and Acclimatisation of Nitrifying Bacteria to High Concentrations of NH4-N in Wastewater

The aim of the conducted research was to assess the effectiveness of the nitrification process, at different concentrations of ammonium nitrogen, in biologically treated wastewater in one of the largest municipal and industrial wastewater treatment plants in Poland. The studies also attempted to acclimate nitrifying bacteria to the limited concentration of ammonium nitrogen and determined the efficiency of nitrification under the influence of acclimated activated sludge in the biological wastewater treatment system. The obtained results indicate that the concentration of ammonium nitrogen above 60.00 mg·dm−3 inhibits nitrification, even after increasing the biomass of nitrifiers. The increase in the efficiency of the nitrification process in the tested system can be obtained by using the activated sludge inoculated with nitrifiers. For this purpose, nitrifiers should be preacclimated, at least for a period of time, allowing them to colonize the activated sludge. The acclimated activated sludge allows reducing the amount of ammonium nitrogen in treated sewage by approx. 35.0%. The process of stable nitrification in the biological treatment system was observed nine days after introducing the acclimated activated sludge into the aeration chamber.

A machine learning framework to improve effluent quality control in wastewater treatment plants

Due to the intrinsic complexity of wastewater treatment plant (WWTP) processes, it is always challenging to respond promptly and appropriately to the dynamic process conditions in order to ensure the quality of the effluent, especially when operational cost is a major concern. Machine Learning (ML) methods have therefore been used to model WWTP processes in order to avoid various shortcomings of conventional mechanistic models. However, to the best of the authors' knowledge, no ML applications have focused on investigating how operational factors can affect effluent quality. Additionally, the time lags between process steps have always been neglected, making it difficult to explain the relationships between operational factors and effluent quality. Therefore, this paper presents a novel ML-based framework designed to improve effluent quality control in WWTPs by clarifying the relationships between operational variables and effluent parameters. The framework consists of Random Forest (RF) models, Deep Neural Network (DNN) models, Variable Importance Measure (VIM) analyses, and Partial Dependence Plot (PDP) analyses, and uses a novel approach to account for the impact of time lags between processes. Details of the framework are provided along with a demonstration of its practical applicability based on a case study of the Umeå WWTP in Sweden involving a large number of samples (105763) representing the full scale of the plant's operations. Two effluent parameters, Total Suspended Solids in effluent (TSS_e) and Phosphate in effluent (PO4_e), and thirty-two operational variables are studied. RF models are developed, validated using DNN models as references, and shown to be suitable for VIM and PDP analyses. VIM identifies the variables that most strongly influence TSS_e and PO4_e, while PDP elucidates their specific effects on TSS_e and PO4_e. The major findings are: (1) Influent temperature is the most influential variable for both TSS_e and PO4_e, but it affects them in different ways; (2) PO4_e depends strongly on the TSS in aeration basins - higher TSS concentrations in aeration basins generally promote PO₄ removal, but excess TSS can have negative effects; (3) In general, the impact of TSS in aeration basins on TSS_e and PO4_e increases with the distances of the basin from the merging outlet, so more attention should be paid to the TSS concentration in the third or fourth aeration basins than the first and second ones; (4) Returning excessive amounts of sludge through the second return sludge pipe should be avoided because of its adverse impact on TSS_e removal. These results could support the development of more advanced control strategies to increase control precision and reduce running costs in the Umeå WWTP and other similarly configured WWTPs. The framework could also be applied to other parameters in WWTPs and industrial processes in general if sufficient high-resolution data are available.

A novel pilot-scale IFAS-MBR system with low aeration for municipal wastewater treatment: Linkages between nutrient removal and core functional microbiota

In this study, we proposed a novel IFAS-MBR with low aeration for the treatment of real municipal wastewater. With biocarriers packed in the anoxic tank, the pilot-scale IFAS-MBR operated with average dissolved oxygen concentrations of 0.56 mg/L in the oxic tank. Over 110 days of operation, highly efficient nutrient removal was achieved with the total nitrogen (TN) and phosphorus (TP) removal efficiencies of 78.1 ± 7.2% and 93.7 ± 5.8%, respectively. The average effluent concentrations of TN and TP reached 5.4 and 0.26 mg/L, respectively. Meanwhile, the removal efficiency of COD reached 95.3 ± 1.3% in the system, and the concentrations of COD decreased from 31.9 ± 3.7 (sludge supernatant) to 12.7 ± 1.6 mg/L (permeate) after membrane filtration. Microbial community analysis showed that Nitrosomonas (0.32%) and Nitrospira (1.85%) in activated sludge were the main drivers of the nitrification process, while various denitrifying bacteria in activated sludge and biofilms were responsible for nitrate reduction in the anoxic tank. Candidatus Accumulibacter (0.34%) and Dechloromonas (1.31%) primarily contributed to denitrifying phosphorus uptake in the anoxic tank. Furthermore, these organisms (i.e., core functional microbiota) exhibited stable levels over the entire operation. The highly enriched hydrolytic fermentation bacteria drove community succession, and the remarkable functional robustness of microbial communities in activated sludge and biofilms favored nutrient removal. Overall, the novel IFAS-MBR system provides an energy-efficient MBR alternative owing to its highly efficient performance and low operating costs enabled by low aeration rates and the absence of an external carbon source.

Microbial community in biofilters for water reuse applications: A critical review

The combination of ozonation (O₃) and biofiltration processes has become practical and desirable in advanced water reclamation for water reuse applications. However, the role of microbial community and its characteristics (source, abundance, composition, viability, structure) on treatment performance has not received the same attention in water reclamation biofilters as in other applications, such as in drinking water biofilters. Microbial community characterization of biofilters used in water reuse applications will add evidence to better understand the potential microorganisms, consequent risks, and mechanisms that will populate drinking water sources and ultimately influence public health and the environment. This critical review provides insights into O₃-biofiltration as a treatment barrier with a focus on development, structure, and composition of the microbial community characteristics involved in the process. The effect of microorganism seeding by the influent before and after the biofilter and ozone oxidation effects are explored to capture the microbial ecology interactions and environmental factors affecting the media ecosystem. The findings of reviewed studies concurred in identifying Proteobacteria as the most dominant phylum. However, Proteobacteria and other phyla relative abundance differ substantially depending upon environmental factors (e.g., pH, temperature, nutrients availability, among others) gradients. In general, we found significant gaps to relate and explain the biodegradation performance and metabolic processes within the biofilter, and hence deserve future attention. We highlighted and identified key challenges and future research ideas to assure O₃-biofiltration reliability as a promising barrier in advanced water treatment applications.

Nitrogen species control the interaction between NO3--N reduction and aniline degradation and microbial community structure in the oxic-anoxic transition zone

Contrary to the fact that NO₃^--N can serve as electron acceptor to promote organics degradation, it was also found NO₃^--N reduction does not necessarily promote organics degradation. We speculate nitrogen (N) species may control the interaction between NO₃^--N reduction and organics degradation via shifting related microbial community structure. To prove the hypothesis, oxic-anoxic transition zone (OATZ) microcosms simulated by lake water and sediment were conducted with the addition of N species (NO₃^--N, NO₂^--N, and NH₄⁺-N) and aniline as typical organics. High-throughput sequencing was used to analyze the microbial community structure and functional enzyme in the microcosms. Results show that, NO₂^--N inhibited NO₃^--N reduction while enhanced aniline degradation. For NH₄⁺-N, it promoted NO₃^--N reduction when NH₄⁺-N/NO₃^--N concentration ratio ≤ 2 and inhibited aniline degradation when NH₄⁺-N/aniline concentration ratio ≥ 0.5. The presence of NO₂^--N or NH₄⁺-N weakened the interaction between NO₃^--N reduction and aniline degradation, which might be caused by significant changes in the diversity and abundance of microbial communities controlled by N species. The microbial mechanism indicates that NO₂^--N weakened the interaction by affecting both denitrification enzyme activity and electron transfer capability, while NH₄⁺-N weakened the interaction mainly by affecting electron transfer capability. These results imply that N species, as well as other electron acceptors and donors, in the contaminated OATZ should be fully considered, when performing in situ remediation technology of NO₃^--N reduction.

Enhanced low-temperature denitrification by microbial consortium using solid-phase humin

Reducing the use of liquid organic carbon electron donors during biostimulation of heterotrophic denitrification is critical for sustainable groundwater remediation. Solid-phase humin isolated from natural sources can provide a cost-effective alternative to classical electron donors. In this study, the low-temperature denitrification capacity of an acetate-fed microbial community was enhanced using humin at 20 °C and 10 °C. These enhancements were not caused by faster acetate consumption and greater bacterial growth with the addition of humin. Estimation of the electron balance and first-order kinetics suggested that the enhancement in denitrification occurred mainly after acetate exhaustion. Humin may therefore have acted as an additional electron donor for the denitrifying microbial community, with the reduced quinone group in humin potentially responsible for electron donation. The addition of humin increased the richness and diversity of the denitrifying microbial community, in which Dechloromonas spp. played a critical role. Given the prevalence of humin and denitrifiers using humic substances, our results have important implications in the bioremediation of nitrate-contaminated groundwater using less liquid organic carbon electron donors.

Core activated sludge communities are influenced little by immigration: Case study of a membrane bioreactor plant

Microbial immigrants arriving with influent wastewater may influence activated sludge (AS) ecosystems. However, the extent to which immigration impacts AS communities is still debated. To explore the intensity of immigration impact, we used sequencing technology to track the raw wastewater and AS communities from a membrane bioreactor plant over a 12-month period. We first distinguished core populations from peripheral ones in both raw wastewater and AS based on their occurrence frequency and abundance. The results showed that core OTUs (≥ 80% occurrence frequency) made up a large fraction (> 90%) of total sequences, while peripheral OTUs composed the majority of all detected OTUs but merely occupied a few sequences. A significant difference in core communities between the influent and AS was found, as well as between the compositions of core and peripheral populations. Additionally, the persistent functional bacteria of AS, although not numerically dominant, accounted for 96.24% of the total sequences related to nutrient turnover, suggesting the presence of a small number of longstanding and core functional bacteria in the AS ecosystem. Importantly, 64% of the 5188 OTUs in AS, which accounted for 91.51% of the sequences, exhibited positive growth rates, which suggested that their apparent abundances were due to growth within the plant, not from immigration. Taken together, these results demonstrated that the impact of influent populations on core AS communities was limited. Overall, this work provides quantitative insights into the impact of immigration, which is expected to advance our understanding of the AS community assembly.

Carbon availability shifts the nitrogen removal pathway and microbial community in biofilm airlift reactor

This study investigated the response of nitrogen removal performance and microbial community to different carbon composites in biofilm airlift reactors for wastewater treatment. Three reactors were filled with poly (butylene succinate) and bamboo powder composite at the blending ratio of 9:1, 1:1 and 1:9. Increasing the component of bamboo powder in the carrier reduced the carbon availability and had an adverse effect on nitrate removal efficiency. However, bamboo powder improved the ammonia removal rate which mainly through autotrophic nitrification. Three reactors exhibited distinct microbial compositions in both bacterial and fungal diversity. High inclusion of bamboo power decreased the relative abundance of denitrifiers Denitromonas and increased the relative abundance of nitrifiers, including Nitromonas, Nitrospina and Nitrospira. Moreover, correlation network revealed a competitive interaction between the taxa responsible for ammonia removal and nitrate removal processes. Those results indicated the feasibility of steering nitrogen removal pathway through carrier formulation in wastewater treatment.

Effective abatement of 29 pesticides in full-scale advanced treatment processes of drinking water: From concentration to human exposure risk

This study investigated the occurrence and removal of 29 pesticides in 4 drinking water treatment plants (DWTPs) with conventional and advanced treatment processes (i.e., ozonation + biological activated carbon, and ultrafiltration) in Shanghai, China from 2018 to 2019. The concentration levels of target pesticides in raw waters ranged from below the limit of quantification (<LOQ) to 2391.3 ng L^-1, whereas in finished waters significantly decreased to a range of <LOQ to 269 ng L^-1. The application of the advanced treatment process could effectively remove target pesticides. For example, the highest removal of isocarbophos after the advanced treatment process reached 94.6%, whereas its removal after the conventional treatment process was just 42.6%. The estimated daily intake level of target pesticides in finished water, which were pretty lower than acceptable daily intake levels in finished water, could be reduced by 67% if combining the conventional and advanced treatment processes. Although the multiple pesticides in raw waters were effectively removed by advanced treatment process, their synergistic toxic effects induced by the residual pesticides and their degradation by-products on human health deserve further attentions.

Who put the film in biofilm? The migration of a term from wastewater engineering to medicine and beyond

Sessile microorganisms were described as early as the seventeenth century. However, the term biofilm arose only in the 1960s in wastewater treatment research and was adopted later in marine fouling and in medical and dental microbiology. The sessile mode of microbial life was gradually recognized to be predominant on Earth, and the term biofilm became established for the growth of microorganisms in aggregates, frequently associated with interfaces, although many, if not the majority, of them not being continuous "films" in the strict sense. In this sessile form of life, microorganisms live in close proximity in a matrix of extracellular polymeric substances (EPS). They share emerging properties, clearly distinct from solitary free floating planktonic microbial cells. Common characteristics include the formation of synergistic microconsortia, using the EPS matrix as an external digestion system, the formation of gradients and high biodiversity over microscopically small distances, resource capture and retention, facilitated gene exchange as well as intercellular communication, and enhanced tolerance to antimicrobials. Thus, biofilms belong to the class of collective systems in biology, like forests, beehives, or coral reefs, although the term film addresses only one form of the various manifestations of microbial aggregates. The uncertainty of this term is discussed, and it is acknowledged that it will not likely be replaced soon, but it is recommended to understand these communities in the broader sense of microbial aggregates.

The call for regional design code from the regional discrepancy of microbial communities in activated sludge

Discerning the differences in activated sludge (AS) microbial community due to geographic location and environmental and operational factors is of great significance for precise design and maintenance of wastewater treatment plants (WWTPs). Hence, in this study, 150 AS samples collected from WWTPs in South China and North China were analyzed by 16 S rRNA gene sequencing. In general, AS microbial community in North China had lower diversity, higher proportions of stochastic assembly (35.7% v.s. 15.8%) and more network keystone species (19 v.s. 5) compared with southern AS community. Conductivity and SRT had significant effects on AS community in both regions. Latitude, annual mean temperature, and influent BOD, COD, and ammonia influenced South China community significantly, while pH and influent total phosphorus affected North China community. To achieve stable performance, southern WWTPs should carefully monitor fluctuations in wastewater characteristics, while northern WWTPs should monitor AS communities for shifts in the dominant taxa from immigrant strains brought in through the influent. Additionally, WWTPs in North China should be aware of the need to proactively control sludge bulking because of the high abundance and occurrence of Haliscomenobacter in these AS communities. MAIN FINDING: The call for regional design based on the regional discrepancy of microbial communities in activated sludge is uncovered and according suggestions were given.

Tropical and temperate wastewater treatment plants assemble different and diverse microbiomes

The diversity and assembly of activated sludge microbiomes play a key role in the performances of municipal wastewater treatment plants (WWTPs), which are the most widely applied biotechnological process systems. In this study, we investigated the microbiomes of municipal WWTPs in Bangkok, Wuhan, and Beijing that respectively represent tropical, subtropical, and temperate climate regions, and also explored how microbiomes assembled in these municipal WWTPs. Our results showed that the microbiomes from these municipal WWTPs were significantly different. The assembly of microbiomes in municipal WWTPs followed deterministic and stochastic processes governed by geographical location, temperature, and nutrients. We found that both taxonomic and phylogenetic α-diversities of tropical Bangkok municipal WWTPs were the highest and were rich in yet-to-be-identified microbial taxa. Nitrospirae and β-Proteobacteria were more abundant in tropical municipal WWTPs, but did not result in better removal efficiencies of ammonium and total nitrogen. Overall, these results suggest that tropical and temperate municipal WWTPs harbored diverse and unique microbial resources, and the municipal WWTP microbiomes were assembled with different processes. Implications of these findings for designing and running tropical municipal WWTPs were discussed. KEY POINTS: • Six WWTPs of tropical Thailand and subtropical and temperate China were investigated. • Tropical Bangkok WWTPs had more diverse and yet-to-be-identified microbial taxa. • Microbiome assembly processes were associated with geographical location.

Modeling of photosynthesis and respiration rate for microalgae-bacteria consortia

In this article, the influence of culture conditions (irradiance, temperature, pH, and dissolved oxygen) on the photosynthesis and the respiration rates of microalgae-bacteria consortia in wastewater treatment was analyzed. Specifically, some short photo-respirometric experiments, simulating outdoor raceway reactors, were performed to evaluate the response of microalgae, heterotrophic bacteria, and nitrifying bacteria to variations in environmental parameters. Results demonstrate that irradiance is the most dominant variable to determine microalgae photosynthesis rates. However, reduction in microalgae activity was not observed at higher irradiance, ruling out the existence of photoinhibition phenomena. Related to heterotrophic and nitrifying bacteria, their activities were strongly affected by the influence of temperature and pH. Moreover, the effect of dissolved oxygen concentrations on microalgae, and bacteria activities was studied, displaying a reduced photosynthetic rate at dissolved oxygen concentrations above 20 mg/L. Data have been used to develop an integrated model for each population (microalgae, heterotrophic bacteria, and nitrifying bacteria) based on considering the simultaneous influence of irradiance, temperature, pH, and dissolved oxygen. The models fit the experimental results in the range of culture conditions tested, and they were validated using data obtained by the simultaneous modifications of the variables. These individual models serve as a basis for developing a global biologic microalgae-bacteria model for wastewater treatment to improve the optimal design and management of microalgae-based processes, especially outdoors, where the cultures are subject to variable daily culture conditions.

Effects of hydrodynamic shear stress on sludge properties, N2O generation, and microbial community structure during activated sludge process

Sludge properties are critical to the treatment performance and potentially correlate with nitrous oxide (N₂O) generation during activated sludge processes. The hydrodynamic shear stress induced by aeration has a significant influence on sludge properties and is inevitable for wastewater treatment plants (WWTPs). In this study, the effects of aerobic induced hydrodynamic shear stress on sludge properties, N₂O generation, and microbial community structure were investigated using three parallel sequencing batch reactors (SBRs) with identical dissolved oxygen (DO) concentrations. Results showed that with a shear stress increase from 1.5 × 10^-2 N/m² to 5.0 × 10^-2 N/m², the COD and NH₄⁺-N removal rates were enhanced from 89.4% to 94.0% and from 93.9% to 98.0%, respectively, while the TN removal rate decreased from 66.0% to 56.5%. Settleability of the activated sludge flocs (ASFs) also increased with the enhancement of shear stress, due to variation in sludge properties including particle size, regularity, compactibility, and EPS (extracellular polymeric substances) composition. The increase in shear stress promoted oxygen diffusion within the ASFs and mitigated NO₂^--N accumulation, leading to a decrease in the N₂O-N conversion rate from (4.8 ± 0.3)% to (2.2 ± 0.6)% (based on TN removal). Microbial analysis results showed that the functional bacteria involved in the biological nitrogen removal was closely related with shear stress. The increase in shear stress favored the enrichment of nitrite oxidizing bacteria (NOB) while suppressed the accumulation of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB).

Impact assessment of bioaugmented tannery effluent discharge on the microbiota of water bodies

Effluents are commonly discharged into water bodies, and in order for the process to be as environmentally sound as possible, the potential effects on native water communities must be assessed alongside the quality parameters of the effluents themselves. In the present work, changes in the bacterial diversity of streamwater receiving a tannery effluent were monitored by high-throughput MiSeq sequencing. Physico-chemical and microbiological parameters and acute toxicity were also evaluated through different bioassays. After the discharge of treated effluents that had been either naturally attenuated or bioaugmented, bacterial diversity decreased immediately in the streamwater samples, as evidenced by the over-representation of taxa such as Brachymonas, Arcobacter, Marinobacterium, Myroides, Paludibacter and Acinetobacter, typically found in tannery effluents. However, there were no remarkable changes in diversity over time (after 1 day). In terms of the physico-chemical and microbiological parameters analyzed, chemical oxygen demand and total bacterial count increased in response to discharge of the treated effluents. No lethal effects were observed in Lactuca sativa L. seeds or Rhinella arenarum embryos exposed to the streamwater that had received the treated effluents. All of these results contribute to the growing knowledge about the environmental safety of effluent discharge procedures.

Nitrifying and Denitrifying Microbial Communities in Centralized and Decentralized Biological Nitrogen Removing Wastewater Treatment Systems

Biological nitrogen removal (BNR) in centralized and decentralized wastewater treatment systems is assumed to be driven by the same microbial processes and to have communities with a similar composition and structure. There is, however, little information to support these assumptions, which may impact the effectiveness of decentralized systems. We used high-throughput sequencing to compare the structure and composition of the nitrifying and denitrifying bacterial communities of nine onsite wastewater treatment systems (OWTS) and one wastewater treatment plant (WTP) by targeting the genes coding for ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ). The amoA diversity was similar between the WTP and OWTS, but nosZ diversity was generally higher for the WTP. Beta diversity analyses showed the WTP and OWTS promoted distinct amoA and nosZ communities, although there is a core group of N-transforming bacteria common across scales of BNR treatment. Our results suggest that advanced N-removal OWTS have microbial communities that are sufficiently distinct from those of WTP with BNR, which may warrant different management approaches.

Sludge retention time affects the microbial community structure: A large-scale sampling of aeration tanks throughout China

Microbial communities in activated sludge (AS) have a significant influence on the functions and stability of aeration tanks in wastewater treatment plants (WWTPs). The microbial community structure is affected by various factors, among which operational parameters outcompeted as the key factors in shaping its structure. However, as an important operational parameter of aeration tank, the mechanisms by which sludge retention time (SRT) affect community properties remain unclear. In this study, 144 AS samples from aeration tanks of 48 full-scale WWTPs operating under different SRT conditions were examined via high-throughput Illumina-MiSeq sequencing technology. The results indicated that SRT significantly affected the diversity, composition, assembly, and co-occurrence patterns of the microbial community in aeration tanks. Moreover, our results provided clear evidence that the microbial communities in aeration tanks operating under SRT of 10-20 days have the highest biodiversity, the lowest stochastic processes influence, the more stable molecular ecological network structure, the lowest risks of filamentous sludge bulking and enhanced nitrogen removal potential. The microbial communities could be more stable and resilient to disturbance when aeration tanks were operated under this SRT condition. The findings of this study provided a reference for the optimization of aeration tanks from an of microbial community perspective.

Biogeography and Assembly of Microbial Communities in Wastewater Treatment Plants in China

Scientific understanding of microbial biogeography and assembly is lacking for activated sludge microbial communities, even though the diversity of microbial communities in wastewater treatment plants (WWTPs) is thought to have a direct influence on system performance. Here, utilizing large-scale 16S rRNA gene data generated from 211 activated sludge samples collected from 15 cities across China, we show activated sludge microbes, whose growth and metabolism can be regulated followed with the metabolic theory of ecology with an apparent Ea value (apparent activation energy) of 0.08 eV. WWTPs at a lower latitude tend to harbor a more diverse array of microorganisms. In agreement with the general understanding, the activated sludge microbial assembly was mainly driven by deterministic processes and the mean annual temperature was identified as the most important factor affecting the microbial community structure. The treatment process types with similar microbial growth types and functions had a distinct impact on the activated sludge microbial community structure only when WWTPs were located near each other and received similar influent. Overall, these findings provide us with a deeper understanding of activated sludge microbial communities from an ecological perspective. Moreover, these findings suggest that, for a given set of performance characteristics (e.g., combined nitrification, denitrification, and phosphorus removal), it may be difficult to employ common engineering levers to control additional aspects of community structure due to the influence of natural environmental factors.

The seasonal changes of core bacterial community decide sewage purification in sub-plateau municipal sewage treatment plants

The decline of sewage purification efficiency in winter is a frequent problem in sub-plateau municipal sewage treatment plants (MSTPs). Understanding the links between activated sludge (AS) bacterial community and sewage purification is crucial for exploring the cause of this problem. In this study, Illumina high-throughput sequencing technology was applied to investigate the seasonal changes of AS bacterial community in sub-plateau MSTPs. The sequencing result indicates that the bacterial community OTU number, diversity, and relative abundance in winter are significantly lower than that in summer samples. The discriminant linear effect size analysis (LEfSe) reveals that Proteobacteria and Chloroflexi members were enriched in summer AS, while Actinobacteria and Firmicutes were enriched in winter AS. The results indicate that different core bacterial community assembly was developed in summer and winter, respectively. The changes in bacterial community may be the reasons for the lower sewage purification efficiency in winter. Furthermore, redundancy analysis (RDA) shows that temperature and dissolved oxygen (DO) are the principal factors that drive the seasonal changes in the core bacterial community diversity, richness and structure in sub-plateau MSTPs. Thus, the sub-plateau AS selects for a unique community assembly pattern and shapes the particular AS ecosystem. These results expand previous understanding and provide insight into the relationship between bacterial community and performance of sub-plateau MSTPs.

Identifying the link between MBRs' key operating parameters and bacterial community: A step towards optimized leachate treatment

A MBR treating compost leachate was studied in order to link the operating parameters (solid and hydraulic retention time) to contaminant's specific bacterial catabolic activity. In this context, a lab-scale aerobic membrane bioreactor was operated for 200 days, at solid retention times (SRT) of 30 and 45 days and four different contaminant load rates. Results showed that increasing the food to microorganism ratio (F/M) by increasing the contaminant load rates lessened the selectivity pressure, which allowed the proliferation of subdominant operational taxonomic units (OTU) (relative abundance >3%) that were otherwise inhibited by highly adapted dominant OTUs (relative abundance >10%). Subsequently, increasing the SRT resulted in a lower species richness and the selection of two dominant types of bacteria: 1) genera with low growth rates that feed on non-limiting substrates or substrates with few competitors, and 2) genera with metabolisms that are highly specific to the available substrates and that can outcompete the other genera by using the substrate more efficiently. The bacterial population evolution observed during this study suggests that the mixed liquor population diversity and structure can be modulated with the operating conditions for the bioenhancement of contaminant specific catabolic activity. Identified dominant and subdominant genera were linked to the MBR's NH₄⁺ and COD removal performances. Interestingly, nitrification performances were unaffected by the organic load rate and the Nitrosomonas relative abundance.