Metagenomic insights into the microbiota profiles and bioaugmentation mechanism of organics removal in coal gasification wastewater in an anaerobic/anoxic/oxic system by methanol

Metagenomics revealing biomolecular insights into the enhanced toluene removal and electricity generation in PANI@CNT bioanode

Microbial fuel cells (MFCs) have significant potential for environmental remediation and energy recycling directly from refractory aromatic hydrocarbons. To boost the capacities of toluene removal and the electricity production in MFCs, this study constructed a polyaniline@carbon nanotube (PANI@CNT) bioanode with a three-dimensional framework structure. Compared with the control bioanode based on graphite sheet, the PANI@CNT bioanode increased the output voltage and toluene degradation kinetics by 2.27-fold and 1.40-fold to 0.399 V and 0.60 h-1, respectively. Metagenomic analysis revealed that the PANI@CNT bioanode promoted the selective enrichment of Pseudomonas, with the dual functions of degrading toluene and generating exogenous electrons. Additionally, compelling genomic evidence elucidating the relationship between functional genes and microorganisms was found. It was interesting that the genes derived from Pseudomonas related to extracellular electron transfer, tricarboxylic acid cycle, and toluene degradation were upregulated due to the existence of PANI@CNT. This study provided biomolecular insights into key genes and related microorganisms that effectively facilitated the organic pollutant degradation and energy recovery in MFCs, offering a novel alternative for high-performance bioanode.

Electrocatalysis coupled heterogeneous electro-Fenton like treatment of coal gasification wastewater using tourmaline as catalyst: process parameters and response surface

Coal gasification technology is essential for realizing clean and efficient conversion of coal, as well as for reducing carbon emissions. However, coal gasification technology is accompanied by a large amount of coal gasification wastewater that is biodegradable. In this work, tourmaline was applied as a catalyst in electro-Fenton like process for treating coal gasification wastewater. The optimal applied parameters of coal gasification wastewater were investigated as follows: current density of 90 mA cm-2, tourmaline dosage of 8 g L-1, electrode gap of 1 cm, and temperature at 25 °C; the COD removal ratio reached 91.24% after 240-min treatment. In addition, the current density and tourmaline dosage were further optimized by response surface method. The result was about current density with 82.4 mA cm-2 and catalyst with 7.57 g L-1; the predicted COD removal efficiency was 86.91%. Under the optimal parameters the actual COD removal efficiency was 88.25% a little high than the predicted value. To explore the reusability of tourmaline as Fenton reaction catalyst, five cycles of experiments were carried out. The result demonstrated that tourmaline could be used as catalyst for treating coal gasification wastewater by electro-Fenton like process.

Overview of enhancing biological treatment of coal chemical wastewater: New strategies and future directions

Coal chemical wastewater (CCW) is a type of refractory industrial wastewater, and its treatment has become the main bottleneck restricting the sustainable development of novel coal chemical industry. Biological treatment is considered as an economical, effective and environmentally friendly technology for CCW treatment. However, conventional biological process is difficult to achieve the efficient removal of refractory organics because of CCW with the characteristics of composition complexity and high toxicity. Therefore, seeking the novel enhancement strategy appears to be a favorable solution for enhancing biological treatment efficiency of CCW. This review focuses on presenting a comprehensive picture about the exogenous enhancement strategies for CCW biological treatment. The performance and potential application of exogenous enhancement strategies, including co-metabolic substrate enhancement, biofilm filler enhancement, adsorption material enhancement and conductive mediator enhancement, were expounded. Meanwhile, the enhancing mechanisms of different strategies were comprehensively discussed from a biological perspective. Furthermore, the prospects of enhancement strategies based on the engineering performance, economic cost and environmental impact (3E) evaluation were introduced. And novel enhancement strategy based on "low carbon emissions", "resource recycling" and "water environment security" in the context of carbon neutrality was proposed. Taken together, this review provides technical reference and new direction to facilitate the regulation and optimization of typical industrial wastewater biological treatment.

Mechanism of quinone mediators modified polyurethane foam for enhanced nitrobenzene reduction and denitrification

The nitrobenzene (NB) reduction and denitrification performance of the immobilized biofilm (I-BF) reactors based on 9,10-anthraquinone-2-sulfonyl chloride (ASC) modified polyurethane foam (PUF-ASC) carriers were investigated. Experiments demonstrated that the quinone mediators enhanced NB reduction and denitrification performance. The NB reduction rates increased by 1.46, while the NO3--N removal rates increased by 1.55 times in the PUF-0.1ASC system. The quinone mediators promote extracellular polymeric substances (EPS) secretion. Electrochemical tests indicated that quinone mediators enhanced the electron transfer of biofilm systems. NADH generation was accelerated and microbial electron transport system activity (ETSA) was promoted. The abundance of genera with electrochemical activity, NB degradation and denitrification ability (Pseudomonas sp., Diaphorobate sp., and Acinetobacter sp.) increased. Metabolic pathways relating to NO3--N and NB reduction were uploaded. In conclusion, electron acquisition by NO3--N and NB was facilitated, bacterial community structure and metabolic pathways were affected by the quinone mediators.

Diverse and distinct bacterial community involved in a full-scale A/O1/H/O2 combination of bioreactors with simultaneous decarbonation and denitrogenation of coking wastewater

Taking into account difficulties in exhaustive simultaneous decarbonation and denitrogenation in biological treatment of coking wastewater (CWW), a novel full-scale CWW biological treatment sequentially combining anaerobic, aerobic, hydrolytic, and aerobic reactors (A/O1/H/O2) was designed performing excellent removal of carbon-containing pollutants in the bioreactors A and O1, while the nitrogen-containing compounds in the bioreactors H and O2. To provide an effective tool for the CWW treatment monitoring and control, the succession of microbial community in this unique toxic CWW habitat should be established and characterized in detail. The results of 16S rRNA genes revealed Acidobacteria dominating in the unique CWW habitat. The dominant groups in bioreactors A and O1 include Proteobacteria, Firmicutes, and Acidobacteria, while Proteobacteria, Acidobacteria, Nitrospirae, and Planctomycetes dominate in reactors H and O2. The genera of Rhodoplanes, Bacillus, and Leucobacter are rich in genes responsible for the xenobiotics biodegradation and metabolism pathway. The Mantel test and PCA results showed the microbial communities of A/O1/H/O2 sequence correlating strongly with SRT, and COD load and removal. The co-occurrence network analysis indicated decarbonation and denitrogenation driven by two network modules having the keystone taxa belonging to the Comamonadaceae and Hyphomicrobiaceae families. The results significantly expanded the knowledge on the diversity, structure, and function of the CWW active sludge differentiating the relationships between bacterial communities and environmental variables in CWW treatment.

Low-concentration methanol effect on the microorganisms, nitrogen removal, and recovery of the completely autotrophic nitrogen removal over nitrite

Methanol has a significant effect on the performance of the completely autotrophic nitrogen removal over the nitrite (CANON) process. In this research, the effect of low-concentration methanol on the functional microorganisms and nitrogen removal and recovery in the CANON system is investigated. The result shows that the anaerobic ammonium-oxidizing bacteria (AnAOB) was suppressed with low-concentration methanol addition, and the phylum Planctomycetes was hidden. The genus Candidatus Brocadia was restrained, and the relative abundances reduced from 25.5 to 15.0% in the upper biofilm and from 20.3 to 14.3% in the bottom biofilm, respectively. However, low-concentration methanol promoted the nitrifying oxidizing bacteria (NOB) activity. This phenomenon reduced the average ammonium nitrogen removal rate from 95.0 to 70.7%, and the average total nitrogen removal rate decreased from 81.3 to 43.6%, respectively. The results demonstrated that the low-concentration methanol as an organic carbon matter harmed the CANON process. Fortunately, the CANON system had an excellent self-healing ability when the methanol was stopped, with the average ammonium nitrogen removal rate and total nitrogen removal rate returning to 95.5 and 80.9%, respectively. This research supplies a reference for practical engineering design and application by improving the understanding of the effects of low-concentration methanol on CANON process performance.

Microbial mechanisms of refractory organics degradation in old landfill leachate by a combined process of UASB-A/O-USSB

A combined process of anaerobic digestion (UASB), shortcut nitrification-denitrification (A/O), and semi-anoxic co-metabolism (operated by an up-flow semi-anoxic sludge bed; USSB) was constructed for the treatment of old landfill leachate (>10 years). The performance and mechanism of refractory organics degradation by the combined process (UASB-A/O-USSB) were investigated. The results showed that the semi-anoxic co-metabolism contributes 57 % of the totally degraded refractory organics. Specific microorganisms and their corresponding metabolic functions drive the degradation of refractory organics in each unit of the UASB-A/O-USSB process. In detail, organics with simple molecular structures were preferentially degraded by anaerobic digestion and shortcut denitrification, whereas those with complex structures were subsequently degraded in the oxic tanks and USSB reactor by shortcut nitrification and semi-anoxic co-metabolism. The structural equation model showed that the combined process of shortcut nitrification and semi-anoxic co-metabolism had a better effect on the degradation of recalcitrant organics than the single process. These findings provide information on how refractory organics are metabolically degraded in a combined process.

Bioaugmentation of quinoline-degrading bacteria for coking wastewater treatment: performance and microbial community analysis

Ochrobactrum sp. XKL1, previously found to have the ability to efficiently degrade quinoline, was bioaugmented into a lab-scale A/O/O system to treat real coking wastewater. During the bioaugmentation stage, the removal of quinoline and pyridine of the O1 tank could be enhanced by 9.88% and 7.96%, respectively. High-throughput sequencing analysis indicated that the addition of XKL1 could significantly affect the alteration of microbial community structure in the sludge. In addition, the relative abundance of Ochrobactrum has demonstrated a trend of increasing first followed by decreasing with the highest abundance of 7.87% attained on the 94th day. The bioaugmentation effects lasted for about 14 days after the strains was inoculated into the reactor. Although a decrease in the relative abundance of XKL1 was observed for a rather short period of time, the bioaugmented A/O/O system has been proven to be more effective in the removal of organic pollutants than the control. Hence, the results of this study indicated that the bioaugmentation with XKL1 is a feasible operational strategy that would be able to enhance the removal of NHCs in the treatment of coking wastewater with complex composition and high organic concentrations.

Formation of anaerobic granular sludge (AnGS) to treat high-strength perchlorate wastewater via anaerobic baffled reactor (ABR) system: Electron transfer characteristic, bacterial community and positive feedback mechanism

Anaerobic granular sludge (AnGS) was cultured to treat high-strength perchlorate (reaching to 4800 mg/L) wastewater by an anaerobic baffled reactor (ABR) system with five equal-volume compartments (C1-C5 compartments). Inoculated sludge completely granulated on day 104 with granule size of 0.50-0.75 mm and perchlorate removal efficiency reaching to 97% (influent perchlorate of 2000-4800 mg/L). The Cyclic voltammetry (CV) capacitance increased from 487.5, 465.8 and 407.8 μF to 576.5, 552.4, 549.6 μF in C1, C3 and C5 compartments of ABR system, respectively, suggesting the electron transfer capacity was enhanced under high-strength perchlorate stress. Meanwhile, adenosine triphosphate (ATP) value and electron transport system activity (ETSA) increased to 25.05, 22.87, 20.43 and 6.22, 4.87, 3.95 of C1, C3 and C5 compartments, respectively. The results suggested that high-strength perchlorate stress improved the microbial metabolic activity, which promoted secretion of extracellular polymeric substances (EPS). The more EPS could facilitate the formation and stability of AnGS under high-strength perchlorate stress. In addition, more reasonable metabolic division of labor in functional bacterial (Thauera and Comamonas) was beneficial to AnGS formation, which achieved high-strength perchlorate efficient removal. Finally, a positive feedback mechanism between AnGS formation and high-strength perchlorate removal was established through EPS, microbial metabolic activity and electron transfer characteristic in ABR system. However, excessive perchlorate (5800 mg/L) would exceed the treatment capacity of AnGS, which resulted in the deterioration of removal performance. This work provided an effective information for AnGS application to treat high-strength perchlorate wastewater.

Microbial community composition and function prediction involved in the hydrolytic bioreactor of coking wastewater treatment process

The hydrolytic acidification process has a strong ability to conduct denitrogenation and increase the biological oxygen demand/chemical oxygen demand ratio in O/H/O coking wastewater treatment system. More than 80% of the total nitrogen (TN) was removed in the hydrolytic bioreactor, and the hydrolytic acidification process contributed to the provision of carbon sources for the subsequent nitrification process. The structure and diversity of microbial communities were elaborated using high-throughput MiSeq of the 16S rRNA genes. The results revealed that the operational taxonomic units (OTUs) belonged to phyla Bacteroidetes, Betaproteobacteria, and Alphaproteobacteria were the dominant taxa involved in the denitrogenation and degradation of refractory contaminants in the hydrolytic bioreactor, with relative abundances of 22.94 ± 3.72, 29.77 ± 2.47, and 18.23 ± 0.26%, respectively. The results of a redundancy analysis showed that the OTUs belonged to the genera Thiobacillus, Rhodoplanes, and Hylemonella in the hydrolytic bioreactor strongly positively correlated with the chemical oxygen demand, TN, and the removal of phenolics, respectively. The results of a microbial co-occurrence network analysis showed that the OTUs belonged to the phylum Bacteroidetes and the genus Rhodoplanes had a significant impact on the efficiency of removal of contaminants that contained nitrogen in the hydrolytic bioreactor. The potential function profiling results indicate the complementarity of nitrogen metabolism, methane metabolism, and sulfur metabolism sub-pathways that were considered to play a significant role in the process of denitrification. These results provide new insights into the further optimization of the performance of the hydrolytic bioreactor in coking wastewater treatment.

Insights into removal of sulfonamides in anaerobic activated sludge system: Mechanisms, degradation pathways and stress responses

The fate of antibiotics in activated sludge has attracted increasing interests. However, the focus needs to shift from concerning removal efficiencies to understanding mechanisms and sludge responding to antibiotic toxicity. Herein, we operated two anaerobic sequencing batch reactors (ASBRs) for 200 days with sulfadiazine (SDZ) and sulfamethoxazole (SMX) added. The removal efficiency of SMX was higher than that of SDZ. SDZ was removed via adsorption (9.91-21.18%) and biodegradation (10.20-16.00%), while biodegradation (65.44-86.26%) was dominant for SMX removal. The mechanisms involved in adsorption and biodegradation were investigated, including adsorption strength, adsorption sites and the roles of enzymes. Protein-like substance (tryptophan) functioned vitally in adsorption by forming complexes with sulfonamides. P450 enzymes may catalyze sulfonamides degradation via hydroxylation and desulfurization. Activated sludge showed distinct responses to different sulfonamides, reflected in the changes of microbial communities and functions. These responses were related to sulfonamides removal, corresponding to the stronger adsorption capacity of activated sludge in ASBR-SDZ and degradation capacity in ASBR-SMX. Furthermore, the reasons for different removal efficiencies of sulfonamides were analyzed according to steric and electronic effects. These findings propose insights into antibiotic removal and broaden the knowledge for self-protection mechanisms of activated sludge under chronic toxicities of antibiotics.

Application oriented bioaugmentation processes: Mechanism, performance improvement and scale-up

Bioaugmentation is an optimization method with great potential to improve the treatment effect by introducing specific strains into the biological treatment system. In this study, a comprehensive review of the mechanism of bioaugmentation from the aspect of microbial community structure, the optimization methods facilitating application as well as feasible approaches of scale-up application has been provided. The different contribution of indigenous and exogenous strains was critically analyzed, the relationship between microbial community variation and system performance was clarified. Operation regulation and immobilization technologies are effective methods to deal with the possible failure of bioaugmentation. The gradual expansion from lab-scale, pilot scale to full-scale, the transformation and upgrading of wastewater treatment plants through the combination of direct dosing and biofilm, and the application of side-stream reactors are feasible ways to realize the full-scale application. The future challenges and prospects in this field were also proposed.

Effects of polyurethane foam carrier addition on anoxic/aerobic membrane bioreactor (A/O-MBR) for coal gasification wastewater (CGW) treatment: Performance and microbial community structure

Coal gasification wastewater (CGW) is a typical toxic and refractory industrial wastewater with abundant phenols contained. Two identical anoxic/aerobic membrane bioreactors (with (R2) and without (R1) polyurethane (PU) foam) were carried out in parallel to investigate the role of PU foam addition in enhancing pollutants removal in CGW. Results showed that both systems exhibited effective removal of chemical oxygen demand (>93%) and total phenols (>97%) but poor ammonia nitrogen removal (<35%) constrained by ammonia oxidation process. GC-MS analysis revealed that aromatic and other refractory intermediates were dramatically reduced in R2. Moreover, the PU addition had negligible influence on the total soluble microbial products and extracellular polymeric substances contents but significantly alleviated membrane fouling with the operating time 33% prolonged. Microbial community revealed that Flavobacterium, Holophaga, and Geobacter were enriched on PU. Influent type might be a main driver for microbial community succession.

Enhanced phenols removal and methane production with the assistance of graphene under anaerobic co-digestion conditions

Coal gasification wastewater (CGW) contains high concentration phenols which lead to poor anaerobic biodegradability and resource utilization. In this paper, new insights to improve synthetic CGW anaerobic degradation with the help of graphene under co-digestion conditions were investigated. Batch tests showed that with the addition of graphene dosage of 10 g/L and glucose as a co-substrate with chemical oxygen demand (COD) concentration of 2000 mg/L, the average COD concentration decreased from 3995 mg/L on day 1 to 983 mg/L on day 12. The average total phenol (TP) concentration decreased from 431 mg/L on day 1 to 23 mg/L on day 12. The cumulative methane production for 12 days was about 200 mL. Long-term experiments showed the average effluent COD and total phenol reached 1137 mg/L and 200 mg/L, respectively. While methane production stabilized at 500 mL/d. In addition, the coenzyme F₄₂₀ concentration increased from 1.075 μmol/g/VSS to 2.3 μmol/g/VSS. The analysis of microbial community structure indicated that the performance of phenols removal and methane production was related to the main microbial flora. The enriched Clostridium, Pseudomonas and species from Firmicutes and Chloroflexi participated in the stages of hydrolysis and acidogenesis. The electrogens Pseudomonas and archaea Methanosaeta were likely the major groups taking part in the direct interspecies electron transfer (DIET). The results obtained in this paper provide a theoretical basis for high-efficiency anaerobic degradation of CGW in practical engineering applications.

A Review and Bibliometric Analysis on Applications of Microbial Degradation of Hydrocarbon Contaminants in Arctic Marine Environment at Metagenomic and Enzymatic Levels

The globe is presently reliant on natural resources, fossil fuels, and crude oil to support the world’s energy requirements. Human exploration for oil resources is always associated with irreversible effects. Primary sources of hydrocarbon pollution are instigated through oil exploration, extraction, and transportation in the Arctic region. To address the state of pollution, it is necessary to understand the mechanisms and processes of the bioremediation of hydrocarbons. The application of various microbial communities originated from the Arctic can provide a better interpretation on the mechanisms of specific microbes in the biodegradation process. The composition of oil and consequences of hydrocarbon pollutants to the various marine environments are also discussed in this paper. An overview of emerging trends on literature or research publications published in the last decade was compiled via bibliometric analysis in relation to the topic of interest, which is the microbial community present in the Arctic and Antarctic marine environments. This review also presents the hydrocarbon-degrading microbial community present in the Arctic, biodegradation metabolic pathways (enzymatic level), and capacity of microbial degradation from the perspective of metagenomics. The limitations are stated and recommendations are proposed for future research prospects on biodegradation of oil contaminants by microbial community at the low temperature regions of the Arctic.

Microbial community and function evaluation in the start-up period of bioaugmented SBR fed with aniline wastewater

An enhanced sequencing batch reactor (SBR) system was developed to treat synthetic wastewater rich in 600 mg/L aniline. The aniline degradation efficiency was almost 100%, and the total nitrogen (TN) removal rate was more than 50%. Metagenomics technology revealed the community structure, functional genes and metabolic mechanism during the start-up of the enhanced reactor. Sequencing results showed that Proteobacteria, Bacteroidetes, Chloroflexi and Actinobacteria were dominant phylum. The proportion of degradation of aromatic compounds function increased gradually, but the proportion of nitrogen metabolism function changed little. Functional genes involved in aniline degradation including benA-xylX and dmpB/xylE were detected. The functional genes of nitrogen metabolism were involved in complete nitrification, traditional denitrification, assimilation nitrate reduction and dissimilation nitrate reduction. The functional contribution analysis and network analysis showed that the cooperation and competition of Thauera, Delftia, Diaphorobacter, Micavibrio and Azoarcus ensured the effective removal of aniline and nitrogen.

Impact of electrical stimulation modes on the degradation of refractory phenolics and the analysis of microbial communities in an anaerobic-aerobic-coupled upflow bioelectrochemical reactor

An electrically stimulated anaerobic-aerobic coupled system was developed to improve the biodegradation of refractory phenolics. Expected 4-nitrophenol, 2, 4-dinitrophenol, and COD removals in the system with aerobic cathodic and anaerobic anodic chambers were approximately 53.7%, 45.4%, 22.3% (intermittent mode) and 37.9%, 19.8%, 17.3% (continuous mode) higher than that in the control system (26.0 ± 6.4%, 30.7 ± 7.1%, 49.8 ± 3.0%). 2, 4-dichlorophenol removal in the system with aerobic anodic and anaerobic cathodic chambers was approximately 28.5% higher than that in the control system (71.4 ± 5.7%). The contribution of the aerobic cathodic/anodic chambers to the removal of phenolic compounds was higher than that of the anaerobic cathodic/anodic chambers. The species related to phenolic biodegradation (Rhodococcus, Achromobacter, PSB-M-3, and Sphingobium) were enriched in the cathodic and anodic chambers of the system. These results showed that intermittent electrical stimulation could be a potential alternative for the efficient degradation of refractory phenolics.

Diversity and functional prediction of microbial communities involved in the first aerobic bioreactor of coking wastewater treatment system

The pre-aerobic process of coking wastewater treatment has strong capacity of decarbonization and detoxification, which contribute to the subsequent dinitrogen of non-carbon source/heterotrophic denitrification. The COD removal rate can reach > 90% in the first aerobic bioreactor of the novel O/H/O coking wastewater treatment system during long-term operation. The physico-chemical characteristics of influent and effluent coking wastewater in the first aerobic bioreactor were analyzed to examine how they correlated with bacterial communities. The diversity of the activated sludge microbial community was investigated using a culture-independent molecular approach. The microbial community functional profiling and detailed pathways were predicted from the 16S rRNA gene-sequencing data by the PICRUSt software and the KEGG database. High-throughput MiSeq sequencing results revealed a distinct microbial composition in the activated sludge of the first aerobic bioreactor of the O/H/O system. Proteobacteria, Bacteroidetes, and Chlorobi were the decarbonization and detoxification dominant phyla with the relative abundance of 84.07 ± 5.45, 10.89 ± 6.31, and 2.96 ± 1.12%, respectively. Thiobacillus, Rhodoplanes, Lysobacter, and Leucobacter were the potential major genera involved in the crucial functional pathways related to the degradation of phenols, cyanide, benzoate, and naphthalene. These results indicated that the comprehensive understanding of the structure and function diversity of the microbial community in the bioreactor will be conducive to the optimal coking wastewater treatment.

Treatment of coking wastewater in biofilm-based bioaugmentation process: Biofilm formation and microbial community analysis

Coking wastewater (CWW) containing complicated organic compositions and strong toxicity cause potential hazards to natural water bodies as well as human health. The aim of this study was integrating newly isolated Comamonas sp. ZF-3, biofilm-based bioaugmentation and fluidized bed reactor into an anoxic filter-fluidized bed reactor (AF-FBR) system to treat actual CWW. The results showed that 93 % of chemical oxygen demand (COD) and 97 % of ammonia nitrogen (NH₄⁺-N) removal efficiency were achieved with hydraulic retention time of 70 h. The main pollutants including phenolic compounds, heterocyclic compounds and polycyclic aromatic hydrocarbons could be removed via biofilm-based process in AF-FBR. The formation of carrier biofilm was consistent with the system performance as well as the biofilm community evolution, during which the microbial community was gradually dominated by some functional genus (e.g., Comamonas, Thiobacillus, Pseudomonas and Thauera), meanwhile, ammonium-oxidizing bacteria Nitrosomonas, nitrite-oxidizing bacteria Nitrospira and denitrifiers (e.g., Pseudomonas, Thiobacillus and Bacillus) coexisted in biofilm to form a microbial community for biological nitrogen removal. Such microbial community structure explained the observed simultaneous removal of COD and NH₄⁺-N in the AF-FBR.

Coupling of Fe-C and aerobic granular sludge to treat refractory wastewater from a membrane manufacturer in a pilot-scale system

A novel pilot-scale system based on aerobic granular sludge (AGS) as a biological treatment step was proposed to treat refractory wastewater from a membrane manufacturer. The components of the system included a microelectrolysis Fe-C filter, a hydrolysis acidification bioreactor (HA), sequence batch reactor 1 (AGS SBR1), sequence batch reactor 2 (AGS SBR2), and a membrane bioreactor (MBR). The Fe-C filter effectively improved the biodegradability of the wastewater components and introduced some byproducts (such as Fe²⁺, Fe³⁺, and Fe minerals) that are beneficial for the cultivation and stability of the AGS. Ideal conditions for aerobic granulation were maintained in the SBR, such as alternating feast and famine conditions. A selection pressure, including a hydraulic shear force and settling time, was also created therein. The results showed that the AGS was formed successfully in both SBR1 and SBR2, the sludge volume index after 30 min (SVI₃₀) and mean particle size reached 34.2 mL/g and 720 µm, and 36.7 mL/g and 610 µm, respectively, and a satisfactory nutrient removal capacity was achieved in the system. During the entire experimental period, the microbial community changed significantly; enrichment of microbes with the secretion of extracellular polymeric substances (EPS), granule stabilization functions in the AGS, and the differentiation of microbes corresponding to the function of each unit were observed. The use of Fe-C, application of SBRs, and use of dewatered sludge as an inoculant played key roles in the cultivation and stability of the AGS.

Metagenomic Insights Into the Mechanisms for Biodegradation of Polycyclic Aromatic Hydrocarbons in the Oil Supply Chain

Petroleum is a very complex and diverse organic mixture. Its composition depends on reservoir location and in situ conditions and changes once crude oil is spilled into the environment, making the characteristics associated with every spill unique. Polycyclic aromatic hydrocarbons (PAHs) are common components of the crude oil and constitute a group of persistent organic pollutants. Due to their highly hydrophobic, and their low solubility tend to accumulate in soil and sediment. The process by which oil is sourced and made available for use is referred to as the oil supply chain and involves three parts: (1) upstream, (2) midstream and (3) downstream activities. As consequence from oil supply chain activities, crude oils are subjected to biodeterioration, acidification and souring, and oil spills are frequently reported affecting not only the environment, but also the economy and human resources. Different bioremediation techniques based on microbial metabolism, such as natural attenuation, bioaugmentation, biostimulation are promising approaches to minimize the environmental impact of oil spills. The rate and efficiency of this process depend on multiple factors, like pH, oxygen content, temperature, availability and concentration of the pollutants and diversity and structure of the microbial community present in the affected (contaminated) area. Emerging approaches, such as (meta-)taxonomics and (meta-)genomics bring new insights into the molecular mechanisms of PAH microbial degradation at both single species and community levels in oil reservoirs and groundwater/seawater spills. We have scrutinized the microbiological aspects of biodegradation of PAHs naturally occurring in oil upstream activities (exploration and production), and crude oil and/or by-products spills in midstream (transport and storage) and downstream (refining and distribution) activities. This work addresses PAH biodegradation in different stages of oil supply chain affecting diverse environments (groundwater, seawater, oil reservoir) focusing on genes and pathways as well as key players involved in this process. In depth understanding of the biodegradation process will provide/improve knowledge for optimizing and monitoring bioremediation in oil spills cases and/or to impair the degradation in reservoirs avoiding deterioration of crude oil quality.

Simultaneous wastewater treatment and energy harvesting in microbial fuel cells: an update on the biocatalysts

The development of microbial fuel cell (MFC) makes it possible to generate clean electricity as well as remove pollutants from wastewater. Extensive studies on MFC have focused on structural design and performance optimization, and tremendous advances have been made in these fields. However, there is still a lack of systematic analysis on biocatalysts used in MFCs, especially when it comes to pollutant removal and simultaneous energy recovery. In this review, we aim to provide an update on MFC-based wastewater treatment and energy harvesting research, and analyze various biocatalysts used in MFCs and their underlying mechanisms in pollutant removal as well as energy recovery from wastewater. Lastly, we highlight key future research areas that will further our understanding in improving MFC performance for simultaneous wastewater treatment and sustainable energy harvesting.

Biodegradation of phenolic compounds in high saline wastewater by biofilms adhering on aerated membranes

High saline phenolic wastewater is a typical toxic and refractory industrial wastewater. A single membrane-aerated biofilm reactor (MABR) was used to treat wastewater containing phenol, p-nitrophenol and hydroquinone under increasing phenolic loading and salinity conditions. More than 95 % of phenolic compounds were removed, and a removal efficiency of 8.9 g/m² d for total phenolic (TP) contents was achieved under conditions with 32 g/L of salt and 763 mg/L of influent TP contents. The microbial diversity, structure and function of a biofilm exposed to different conditions were investigated by high-throughput 16S rRNA gene sequencing and metagenomics. Salinity and specific TP loading substantially affected the bacterial community. Gammaproteobacteria, Actinobacteria and Betaproteobacteria contributed more to initial phenolic compound degradation than other classes, with Pseudomonas and Rhodococcus as the main contributing genera. The key phenolic-degrading genes of different metabolic pathways were explored, and their relative abundance was strengthened with increasing phenolic loading and salinity. The diverse cooperation and competition patterns of these microorganisms further promoted the high removal efficiency of multiple phenolic contaminants in the biofilms. These results demonstrate the feasibility of MABR for degrading multiple phenolic compounds in high saline wastewater.

Effects of substrate fluctuation on the performance, microbial community and metabolic function of a biofilter for gaseous dichloromethane treatment

Dichloromethane (DCM) is a harmful volatile organic compound that usually originates from pharmaceutical industry. In this study, the treatment of gaseous DCM in a biofilter was investigated by gradually increasing the DCM inlet concentration. Nearly 80% of DCM could be removed when the inlet concentration was lower than 0.30 g m^-3. The maximum elimination capacity of 26.6 g m^-3·h^-1 was achieved at an inlet loading rate of 38.4 g m^-3·h^-1. However, with the increase in the inlet concentration to more than 0.60 g m^-3, the removal efficiency obviously decreased to about 40%. After a starvation period of 2 weeks, the biofilter rapidly recovered its performance. The Haldane model including a substrate inhibition term was applied to describe the kinetics of the biofilter. High-throughput sequencing indicated that DCM-degrading genera, such as Rhodanobacter sp., Hyphomicrobium sp., Rhizomicrobium sp., Bacillus sp., Pseudomonas sp., and Clostridium sp., were dominant in the biofilter in different operation phases. The microbial communities and diversities were greatly affected by the DCM concentration. Microbial metabolic functions were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The results indicated that xenobiotics biodegradation and metabolism, carbohydrate metabolism, and amino acid metabolism were the three most abundant metabolic pathways of the microbes. The abundances of these metabolic functions were also altered by the DCM concentration.

Performance and microbial community of a novel combined anaerobic bioreactor integrating anaerobic baffling and anaerobic filtration process for low-strength rural wastewater treatment

A novel combined bioreactor integrating anaerobic baffling and anaerobic filtration process was developed and operated for 210 days to treat low-strength rural wastewater. The effects of hydraulic residence time (HRT) and organic loading rate (OLR) on chemical oxygen demand (COD) removal and methane (CH₄) production of the combined bioreactor were investigated. The combined bioreactor can start up successfully in 25 days and achieve enhanced performance. The COD removal rate and CH₄ yield were influenced significantly by HRT and OLR. The influent COD was removed effectively through the synergistic effects of the anaerobic baffling and anaerobic filtration. The baffle zone played the main role in the degradation of the pollutants, and the filter zone mainly contributed to improve the resistance to shock loading. High-throughput sequencing technology was used to analyze the bacterial and archaeal community structure and diversity. Clostridium_sensu_stricto, Longilinea, Acetoanaerobium, Arcobacter, and Acinetobacter were found to be the dominant bacteria. While Methanothrix and Methanoregula were the dominant archaea, which were responsible for methane generation. This study not only highlights the good energy recovery and resource utilization potential of the combined bioreactor but also presents significant guidance for the application of the combined anaerobic process for low-strength rural wastewater treatment.

Temperature modulating sand-consolidating cyanobacterial biomass, nutrients removal and bacterial community dynamics in municipal wastewater

Cultivating sand-consolidating cyanobacteria using wastewater has unique advantages on both nutrients recycling and ecological restoration by transferring excessive nutrients from wastewaters to desert areas. Although previous study showed that sand-consolidating cyanobacterium well adapted to synthetic domestic wastewater, no study has been carried out on actual wastewater. This study aims to investigate the sand-consolidating cyanobacterial biomass production and nutrients removal by cultivating Scytonema hyalinum in the municipal wastewater under different temperatures. The results showed that biomass accumulation increased with temperature from 20 ℃ to 30 ℃, while severely depressed at 35 ℃. More than 81.63% sCOD, 90.64% TDN and 97.08% TDP were removed by day 30 under each temperature except for 35℃. The inoculation of S. hyalinum strongly regulated the native wastewater bacterial community. These results indicated that sand-consolidating cyanobacterium S. hyalinum well adapted to municipal wastewater and temperature had remarkable effects on cyanobacterial biomass accumulation, nutrients removal and wastewater native bacterial community dynamics.

New insights of enhanced anaerobic degradation of refractory pollutants in coking wastewater: Role of zero-valent iron in metagenomic functions

Coking wastewater (CWW) has long been a serious challenge for anaerobic treatment due to its high concentrations of phenolics and nitrogen-containing heterocyclic compounds (NHCs). Herein, we proposed and validated a new strategy of using zero-valent iron (ZVI) to strengthen the anaerobic treatment of CWW. Results showed that COD removal efficiencies was increased by 9.5-13.7% with the assistance of ZVI. GC-MS analysis indicated that the removal of phenolics and NHCs was improved, and the intermediate 2(1H)-Quinolinone of quinoline degradation was further removed by ZVI addition. High-throughput sequencing showed that phenolics and NHCs degraders, such as Levilinea and Sedimentibacter were significantly enriched, and the predicted gene abundance of xenobiotic degradation and its downstream metabolic pathways was also increased by ZVI. Network and redundancy analysis indicated that the decreased oxidation-reduction potential (ORP) by ZVI was the main driver for microbial community succession. This study provided an alternative strategy for strengthening CWW anaerobic treatment.

Sustainable remediation of diesel-contaminated soil by low temperature thermal treatment: Improved energy efficiency and soil reusability

Thermal treatment can effectively remediate diesel-contaminated soil, but is considered unsustainable because of its energy-intensive nature and potential to damage soil properties. Here, we used low temperature thermal treatment (LTTT) as an energy-efficient technique to remediate diesel-contaminated soil. The impacts of LTTT on the physiochemical and ecological properties of soils were investigated to evaluate the reusability of heated soil. Heating at 250 °C for 10 min reduced the concentration of the total petroleum hydrocarbons from 6271 mg/kg to 359  mg/kg, which is lower than the Chinese risk screening level of 826 mg/kg. After LTTT, most soil physiochemical properties were nearly unchanged, and the NO₃^--N and NH₄⁺-N contents increased. Moreover, LTTT-remediated soil was favorable for the germination and early growth of wheat. The microbial community changed substantially, but recovered after being mixed with uncontaminated soil. Finally, exploration of the mechanisms of LTTT revealed that pyrolysis was the dominant mechanism of diesel removal. A biochar-like pyrolytic carbon was formed, which improved the soil reusability.

Structure and function of microbial community involved in a novel full-scale prefix oxic coking wastewater treatment O/H/O system

A novel full-scale prefix oxic coking wastewater (CWW) biological treatment O/H/O system had been operated steadily six years with the effluent quality meeting national discharge standard. Comparing to the traditional CWW biological treatment process, which usually have an anaerobic unit at the start of the process, here the O/H/O system has obvious advantages in COD removal, total nitrogen removal and reduced energy consumption. It is very necessary to illustrate the structure and function of the microbial community involved in different bioreactors of the O/H/O system. High-throughput MiSeq sequencing was used to examine the 16S rRNA genes in this system. Results revealed a contrasting microbial composition among the activated sludge samples of three sequential bioreactors: the β-Proteobacteria related sequences dominated in the O₁ activated sludge with the relative abundance of 56.44% while 7.53% of the sequences were assigned to Thiobacillus; Rhodoplanes related sequences dominated in the bioreactor H and O₂ activated sludge with relative abundance of 8.86% and 8.92%, respectively. The physico-chemical characteristics of CWW were analyzed by standard methods and the operational parameters were routinely monitored to examine their effects on the microbial communities. The bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was used to predict the microbial community functional profiling and found three dominant genera of Rhodoplanes, Lysobacter and Leucobacter enriched the xenobiotics biodegradation and metabolism pathway. The diverse and distinct microbial community involved in biological treatment processes of CWW treatment indicating that water characteristics and operational parameters determined the microbial community composition. These results significantly expanded our knowledge of the biodiversity and population dynamics of microorganisms and discerned the relationships between bacterial communities and environmental variables in the biological treatment processes. Moreover, in this study, we proposed a comprehensive biodegradation model of CWW treatment and defined as O/H/O system.

Simultaneous sulfide removal, nitrogen removal and electricity generation in a coupled microbial fuel cell system

A coupled microbial fuel cell (MFC) system, consisting of a nitrifying sulfide removal MFC and a denitrifying sulfide removal MFC, was assembled to simultaneously treat ammonium and sulfide in wastewater. It provided a promising approach to recover electricity from wastewater containing sulfide and ammonium. Considering both substrate removal and electricity generation performance, the desirable feeding S/N molar ratio was deemed as 3 and the optimal temperature was found to be 30 °C. Under this condition, the coupled MFC achieved a sum coulomb production of 554.8 C/d, a total nitrogen removal efficiency of 58.7 ± 1.3% and a sulfur production percent of 27.4 ± 0.4-33.3 ± 0.9%. The introduction of nitrifiers and electroactive oxic microbes from the oxic-cathode chamber into the anoxic-cathode chamber favored nitrogen removal.

Effect of low-intensity direct current electric field on microbial nitrate removal in coal pyrolysis wastewater with low COD to nitrogen ratio

The coupling of bioelectrochemical system with the biological denitrification process (R1) was constructed for nitrate removal in coal pyrolysis wastewater (CPW) and the effect of low-intensity direct current electric field was investigated. Compared with control reactor (R2), the total nitrogen (TN) removal efficiency in R1 at the optimized voltage of 0.9 V was 94.20 ± 2.14%, which was 14.42% higher than that in R2. The biofilm on the cathode of R1 enhanced the nitrate reducing, however, nitrite was only reduced by bacteria in suspended activated sludge, which was confirmed by cyclic voltammetry measurement (CV). Microbial community network analysis revealed that exoelectrogenic bacteria of Pseudomonas was enriched on the anode of R1, and the "small world", including Zoogloea, Pseudomonas and Arenimonas, was established under the stimulation of voltage. Therefore, Pseudomonas transferred electron to anode, and Arenimonas could utilize electron from anode to reduce nitrate, which enhanced TN removal in R1.

Structure and function of microbial community associated with phenol co-substrate in degradation of benzo[a]pyrene in coking wastewater

Coking wastewater (CWW) contains high contents of phenols and other toxic and refractory compounds including polycyclic aromatic hydrocarbons (PAHs) with the most carcinogenic benzo[a]pyrene (BaP) among them. The mechanism of PAHs/BaP degradation in activated sludge of CWW treatment with phenol as co-substrate was studied. For characterizing the structure and functions of microbial community associated with BaP degradation with phenol as co-substrate, high-throughput MiSeq sequencing was used to examine the 16S rRNA genes of microbiology, revealing noticeable shifts in CWW activated sludge bacterial populations. Major genera involved in anaerobic degradation were Tissierella_Soehngenia, Diaphorobacter and Geobacter, whereas in aerobic degradation Rhodanobacter, Dyella and Thauera prevailed. BaP degradation with phenol as co-substrate induced bacterial diversification in CWW activated sludge in opposite trends when anaerobic and aerobic conditions were applied. In order to predict the microbial community functional profiling, a bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was run to find that some dominant genera enriched in the BaP pathway may own the ability to degrade PAHs/BaP. Further experiments should focus on testing the dominant genera in BaP degradation at different oxygen levels.

New insights into pollutants removal, toxicity reduction and microbial profiles in a lab-scale IC-A/O-membrane reactor system for paper wastewater reclamation

In this study, an internal circulation-anoxic/aerobic (IC-A/O) process followed by ultrafiltration (UF) and reverse osmosis (RO) system was applied for paper wastewater reclamation. The IC-AO system presented a stable and efficient performance, achieving high removal of chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) with methane production rate of 132.8 mL/d. Acute toxicity to Daphnia magna (D. magna) was reduced significantly (83.2%) and the spearman's rank correlation analysis indicated that the toxicity of effluents from each reactor were positively correlated with COD and TOC. Hexadecanoic acid, octadecanoic acid and benzophenone were the main toxic contributors for biological effluent. Microbial community revealed that Anaerolinea was significantly related with organic pollutants. The UF-RO system further removed pollutants and toxicity with the final effluent COD, TOC, ammonium nitrogen (NH₄⁺-N) and TN of 32.6, 18.8, 0.3 and 9.2 mg/L, respectively, which proved that it was feasible for paper wastewater reuse. This study presented an efficient, practical and environmentally competitive system, and paved a foundation for the treatment and reuse of paper wastewater.

Enhanced nitrogen removal of coal pyrolysis wastewater with low COD to nitrogen ratio by partial nitrification-denitrification bioprocess assisted with polycaprolactone

The purpose of this study is to investigate the enhancement of polycaprolactone (PCL) on total nitrogen (TN) removal of coal pyrolysis wastewater (CPW) with low COD to nitrogen ratio by partial nitrification-denitrification bioprocess (PNDB) in one single reactor. With the innovative combination of PCL and PNDB, the TN removal efficiency in the experimental reactor (signed as R1) was 10.21% higher than control reactor (R2). Nitrite accumulation percentage (NAP) in R1 was 82.02%, which was 17.49% higher than R2 at the dissolved oxygen (DO) concentration of 0.9-1.5 mg/L, for the reason that the extra DO was consumed by PCL biodegradation at the aerobic period. Gel permeation chromatography (GPC) results demonstrated that organics with the molecular weight of 185 Da, which could serve as additional carbon sources for denitrifiers, were generated during the PCL hydrolysis process at the anoxic period. PCL was hydrolyzed by extracellular enzymes with the break of the ester bond which was confirmed by FT-IR spectrometer. Microbial community analysis revealed that Ferruginibacter was the dominant hydrolysis bacteria in R1. Nitrosomonas were the main ammonium-oxidizing bacteria (AOB) and Hyphomicrobium were the denitrifiers in this study.

A novel phenol and ammonia recovery process for coal gasification wastewater altering the bacterial community and increasing pollutants removal in anaerobic/anoxic/aerobic system

Coal gasification wastewater (CGWW) is a typical toxic and refractory industrial wastewater. Here, a novel phenol and ammonia recovery process (IPE) was employed for CGWW pretreatment, and the coupled system assemble by the IPE process with A²/O system (IPE-A²/O) were operated to enhance the treatment performance of CGWW. The results showed that the IPE pre-treated effluent had a higher BOD₅/COD ratio and lower refractory compounds compared to a typical process (MIBK). Subsequent A²/O biological treatment indicated that the A²/O-p system (A²/O system followed IPE process) obtained a higher average COD removal of 92% compared to 87.7% of the control (A²/O-m, A²/O system followed MIBK). The GC-MS analysis suggested that the content of alkanes in the IPE-A²/O effluent was lower than that of the MIBK-A²/O. The high-throughput sequencing revealed Levilinea, Alcaligenes, Acinetobacter, Thauera and Thiobacillus were the core genera in A²/O system. The genera Alcaligenes, Acinetobacter, Thauera and Thiobacillus in the degrading consortium were enriched in the A²/O-p system, leading to increased removals of organic pollutants and TN. These results suggested that the IPE process was a feasible pretreatment method, and the coupled IPE-A²/O system was an alternative technique for treating CGWW.

Exploring bacterial communities and biodegradation genes in activated sludge from pesticide wastewater treatment plants via metagenomic analysis

Activated sludge (AS) has been regarded as the main driver in the removal of organic pollutants such as pesticides due to a high diversity and abundance of microorganisms. However, little is known about the biodegradation genes (BDGs) and pesticide degradation genes (PDGs) harbored in the AS from wastewater treatment plants (WWTPs). In this study, we explored the bacterial communities and BDGs/PDGs in the AS from five WWTPs affiliated with pesticide factories across four consecutive seasons based on high-throughput sequencing. The AS in pesticide WWTPs exhibited unique bacterial taxa at the genus level. Furthermore, a total of 17 BDGs and 68 PDGs were explored with a corresponding average relative abundance of 0.002-0.046% and 2.078-7.143% in each AS sample, respectively, and some BDGs/PDGs clusters were also identified in the AS. The bacterial communities and BDGs/PDGs were season-dependent, and the total variations of 50.4% and 76.8% were jointly explained by environmental variables (pesticide types, wastewater characteristics, and temperature). In addition, network analysis and distribution patterns suggested that the potential hosts of BDGs/PDGs were Thauera, Stenotrophomonas, Mycobacterium, Hyphomicrobium, Allochromatium, Ralstonia, and Dechloromonas. Our findings demonstrated the linkages of bacterial communities and BDGs/PDGs in the AS, and depended on the seasons and the pesticide wastewater characteristics.