Influence of fermentation liquid from waste activated sludge on anoxic/oxic- membrane bioreactor performance: Nitrogen removal, membrane fouling and microbial community

Bacterial community and filamentous population of industrial wastewater treatment plants in Belgium

The discharge of industrial water requires the removal of its pollutants, where biological wastewater treatment plants (WWTPs) are the most used systems. Biological WWTPs make use of activated sludge (AS), where bacteria are responsible for the removal of pollutants. However, our knowledge of the microbial communities of industrial plants is limited. Understanding the microbial population is essential to provide solutions to industrial problems such as bulking. The aim of this study was to identify at a high taxonomic resolution the bacterial population of 29 industrial WWTPs using 16S rRNA amplicon sequencing. Our results revealed that the main functional groups were dominated by Thauera and Zoogloea within denitrifiers, Dechloromonas in phosphate-accumulating organisms, and Defluviicoccus in glycogen-accumulating organisms. The activated sludge characterization indicated that 59% of the industrial plants suffered from bulking sludge, with DSVI values of up to 448 mL g-1. From the bulking cases, 72% corresponded to filamentous bulking with Thiothrix as the most abundant filament; meanwhile, the other 28% corresponded to viscous bulking sludge in which Zoogloea was the most abundant genus. Furthermore, the bacterial population did not share a core of taxa across all industrial plants. However, 20 genera were present in at least 50% of the plants comprising the general core, including Thauera, Ca. Competibacter, and several undescribed microorganisms. Moreover, statistical analysis revealed that wastewater salinity strongly affected the microbial richness of the industrial plants. The bacterial population across industrial plants differed considerably from each other, resulting in unique microbial communities that are attributed to the specificity of their wastewaters. KEY POINTS: • The general core taxa of industrial plants were mostly made up of undescribed bacterial genera. • Filamentous bacteria constituted on average 4.1% read abundance of the industrial WWTPs. • Viscous bulking remains a significant type of bulking within industrial WWTPs.

Mixotrophic denitrification of waste activated sludge fermentation liquid as an alternative carbon source for nitrogen removal: Reducing N2O emissions and costs

Heterotrophic-sulfur autotrophic denitrification (HAD) has been proposed to be a prospective nitrogen removal process. In this work, the potential of fermentation liquid (FL) from waste-activated sludge (WAS) as the electron donor for denitrification in the HAD system was explored and compared with other conventional carbon sources. Results showed that when FL was used as a carbon source, over 99% of NO3--N was removed and its removal rate exceeded 14.00 mg N/g MLSS/h, which was significantly higher than that of methanol and propionic acid. The produced sulfate was below the limit value and the emission of N2O was low (1.38% of the NO3--N). Microbial community analysis showed that autotrophic denitrifiers were predominated in the HAD system, in which Thiobacillus (16.4%) was the dominant genus. The economic analysis showed the cost of the FL was 0.062 €/m3, which was 30% lower than that in the group dosed with methanol. Our results demonstrated the FL was a promising carbon source for the HAD system, which could reduce carbon emission and cost, and offer a creative approach for waste-activated sludge resource reuse.

Membrane reciprocation and quorum quenching: An innovative combination for fouling control and energy saving in membrane bioreactors

Membrane bioreactors (MBRs) play a crucial role in wastewater treatment, but they face considerable challenges due to fouling. To tackle this issue, innovative strategies are needed. This study investigated the effectiveness of membrane reciprocation and quorum quenching (QQ) to control fouling in MBRs. The study compared MBRs using membrane reciprocation (30 rpm) and QQ (injecting media containing 100 or 200 mg/L BH4) with conventional MBRs employing different air-scouring intensities. The results demonstrated that combining membrane reciprocation (30 rpm) with QQ (200 mg/L BH4) significantly extended the service time of MBRs, making it approximately six times longer than conventional methods. Moreover, this approach reduced physically reversible resistance. The reduction in signal molecules related to biofouling due to QQ showcased its critical role in controlling biofouling, even under high shear caused by membrane reciprocation. However, the impact of QQ on microbial community structure appeared relatively insignificant when compared to factors such as operation time, aeration intensity, and membrane reciprocation. By combining membrane reciprocation and QQ, the study achieved a remarkable 81 % energy saving compared to extensive aeration (103 s-1 in velocity gradient), in addition to the extended service time. Importantly, this combined antifouling approach did not negatively affect microbial characteristics and wastewater treatment, emphasizing its effectiveness in MBRs. Overall, the findings of this study offer valuable insights for developing synergistic fouling control strategies in MBRs, significantly improving the energy efficiency of the wastewater treatment process.

Effect of predatory bacterial mixtures on biolysis of waste activated sludge to improve dewatering performance

The generation of surplus sludge during biological wastewater treatment has become a prevalent issue, necessitating the development of a dewatering approach that is efficient, economically feasible, and ecologically sound. Bdellovibrio-and-like organisms (BALOs) are obligatory parasitic bacteria that prey on an array of bacteria. In this study, different BALO strains were isolated and purified from waste activited sludge (WAS). Anti-predation host strains were applied to screen the BALO strains with different host-range to minimize the overlap of the biolysis prey spectrum. In addition, the BALO strains with different host preferences were mixed for sludge biolysis treatment efficiency comparison. The results indicated that the capillary suction time and the bound water content in the WAS treated with the mixed BALOs were significantly decreased by 25.9% ± 1.7% and 5.2% ± 1.2%, respectively, compared to those treated with the single BALO strain. The soluble chemical oxygen demand concentration in the mixed BALOs treated group was increased by 31.2% ± 0.7% than that treated with the single strain. The findings indicate that the mixed strains used in the treatment process resulted in a notable enhancement of both sludge dewatering performance and lysis degree. In addition, the abundance of Proteobacteria treated with the BALO mixtures decreased by 69.1% than the single strain treated one which demonstrated that the BALO mixture expanded the sludge host lysis spectrum. This study revealed the different effects of single and mixed strains on sludge community structure, suggesting that the BALO host range expansion is crucial to further improve sludge dewatering performances.

Application and improvement methods of sludge alkaline fermentation liquid as a carbon source for biological nutrient removal: A review

Alkaline fermentation can reduce the amount of waste activated sludge and prepare sludge alkaline fermentation liquid (SAFL) rich in short-chain fatty acids (SCFAs), which can be used as a high-quality carbon source for the biological nutrient removal (BNR) process. This review compiles the production method of SAFL and the progress of its application as a BNR carbon source. Compared with traditional carbon sources, SAFL has the advantages of higher efficiency and economy, and different operating conditions can influence the yield and structure of SCFAs in SAFL. SAFL can significantly improve the nutrient removal efficiency of the BNR process. Taking SAFL as the internal carbon source of BNR can simultaneously solve the problem of carbon source shortage and sludge treatment difficulties in wastewater treatment plants, and further reduce the operating cost. However, the alkaline fermentation process results in many refractory organics, ammonia and phosphate in SAFL, which reduces the availability of SAFL as a carbon source. Purifying SCFAs by removing nitrogen and phosphorus, directly extracting SCFAs, or increasing the amount of SCFAs in SAFL by co-fermentation or combining with other pretreatment methods, etc., are effective measures to improve the availability of SAFL.

Under-loaded operation of an anaerobic-anoxic-aerobic system in dry and wet weather dynamics to prevent overflow pollution: Impacts on process performance and microbial community

Effects of low hydraulic loading rate (HLR) in dry weather and high HLR in wet weather on pollutant removal, microbial community, and sludge properties of a full-scale wastewater treatment plant (WWTP) were extensively studied to explore the risk of under-loaded operation for overflow pollution control. Long-term low HLR operation had an insignificant effect on the pollutant removal performance of the full-scale WWTP, and the system could withstand high-load shocks in wet weather. Low HLR resulted in higher oxygen and nitrate uptake rate due to the storage mechanism under the alternating feast/famine condition, and lower nitrifying rate. Low HLR operation enlarged particle size, deteriorated floc aggregation and sludge settleability, and reduced sludge viscosity due to the overgrowth of filamentous bacteria and inhibition of floc-forming bacteria. The remarkable increase in Thuricola and the contract morphology of Vorticella in microfauna observation confirmed the risk of flocs disintegration in low HLR operation.

Effect of thermal hydrolyzed sludge filtrate as an external carbon source on biological nutrient removal performance of A2/O system

Thermal hydrolyzed sludge filtrate (THSF) rich in biodegradable organics could be a promising external carbon source for biological nutrient removal (BNR). The use of THSF can effectively reduce wastewater treatment plants operating costs and recover bioresources and bioenergy from the waste activated sludge. In this study, the effect of THSF on the BNR process was investigated using a lab-scale anaerobic/anoxic/oxic (A²/O) system. Total nitrogen (TN) and total phosphorus (TP) removal efficiencies of 74.26 ± 3.36% and 92.20 ± 3.13% at a 0.3% dosing ratio were achieved, respectively. Moreover, 20.42% of the chemical oxygen demand (COD) contained in THSF contributed to denitrification, enhancing nitrogen removal efficiency from 55.30 to 74.26%. However, the effluent COD increased by approximately 36.80%, due to 18.39% of the COD contained in THSF discharged with effluent. In addition, the maximum denitrification rate was approximately 16.01 mg N g VSS^-1 h^-1, while the nitrification rate was not significantly affected by THSF. Nitrosomonas, a common chemoautotrophic nitrifier, was not detected after the introduction of THSF. The aerobic denitrifier Rubellimicrobium was stimulated, and its relative abundance increased from 0.16 to 3.03%. Moreover, the relative abundance of Dechloromonas was 3.93%, indicating that the denitrifying phosphorus removal process was enhanced. This study proposes an engineering application route of THSF, and the chemical phosphate removal pretreatment might be a means to suppress the phosphate recirculation.

Machine learning reveals the complex ecological interplay of microbiome in a full-scale membrane bioreactor wastewater treatment plant

Membrane bioreactor (MBR) systems are one of the most widely used wastewater treatment processes for various municipal and industrial waste streams. The present study aimed to advance the understanding of ecologically important keystone taxa that play an important role in full-scale MBR systems. A machine-learning (ML) modeling framework based on microbiome data was developed to successfully predict, with an average accuracy of >91.6%, the operational characteristics of three representative full-scale wastewater systems: an MBR, a conventional activated sludge system, and a sequencing batch reactor. ML-based feature-importance analysis identified Ferruginibacter as a keystone organism in the MBR system. The phylogeny and known ecophysiology of members of Ferruginibacter supported their role in metabolizing complex organic polymers (e.g., extracellular polymeric substances) in MBR systems characterized by high concentrations of mixed liquor suspended solids and a high solid retention time. ML regression modeling also revealed temporal patterns of Ferruginibacter in response to water temperature. ML modeling was thus successfully employed in the present study to investigate complex/non-linear relationships between keystone taxa and environmental conditions that cannot be detected using conventional approaches. Overall, our microbiome-data-enabled ML modeling approach represents a methodological advance for identifying keystone taxa and their complex ecological interactions, which has implications for the sustainable and predictive management of MBR systems.

Effect of nitrite on hydrolysis-acidification, biogas production and microbial community in semi-continuous two-phase anaerobic digestion of sewage sludge

Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests. In this study, the effects of nitrite on hydrolysis-acidification, biogas production, volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated. The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%), and causes an increase in the VS degradation rate during the AD process (+8.7%). The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process. High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite. Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively. These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semi-continuous two-phase AD system.

Enhanced mesophilic fermentation of waste activated sludge by integration with in-situ nitrate reduction

This study investigated the reduction of nitrate in a mesophilic waste activated sludge (WAS) fermentation system and determined the effect of nitrate reduction on the hydrolysis, acidogenesis and acetogenesis. Experimental results showed that the initial nitrate concentrations of 100, 200 and 400 mg/L were completely reduced in 1, 2 and 7 days, respectively. The destruction of volatile suspended solids was 1.2, 1.8 and 2.8 times, respectively, that without nitrate, demonstrating nitrate promoted the release of organic matter in sludge and enhanced the biodegradability of sludge organics. Moreover, batch tests using model substrates illustrated nitrate reduction promoted sludge hydrolysis and acetogenesis, but slightly inhibited acidogenesis. This study offers a feasible method to address two major problems currently faced by biological wastewater treatment plants, i.e. the overabundance of WAS and the lack of carbon sources for the denitrification process.

Impacts of bio-carriers on the characteristics of cake layer and membrane fouling in a novel hybrid membrane bioreactor for treating mariculture wastewater

Membrane fouling is generally considered as a major bottleneck to the wide application of membrane bioreactor (MBR) for high saline mariculture wastewater treatment. Though numerous researches have investigated the membrane fouling of MBR combined with bio-carriers, few studies reveal the impacts of bio-carriers on the characteristics of cake layer and the mechanism of bio-carriers alleviating membrane fouling. In this study, two systems, namely carriers-enhanced MBR (R1) and conventional MBR (R2) were parallel operated, drawing a conclusion that bio-carriers effectively improved the characteristics of cake layer, thus mitigating membrane fouling. Fluorescence excitation emission matrix (EEM) analysis indicated that bio-carriers reduced the adhesion of proteins and humic acid-like materials on membrane surface. Molecular weight (Mw) distribution suggested that soluble microbial products (SMP) with small Mw (6-20 kDa) and biopolymers in extracellular polymeric substances (EPS) (50-300 kDa) was easier to accumulate on membrane surface in R2. The above results indicated that the presence of bio-carriers could effectively reduce the attachment of these organics on membrane surface, contributing to a larger porosity of cake layer and thus mitigating membrane fouling. Meanwhile, gas chromatography-mass spectrometry (GC-MS) clarified that more components were present in R2 than R1. Moreover, the majority of compounds in the SMP were present in both systems, while only 14 compounds in the EPS were the same between R1 and R2. Noticeably, certain aromatics only existed in R2, suggesting that bio-carriers effectively reduced the accumulation of recalcitrant materials, especially aromatics. These results revealed that bio-carriers shifted the precise composition of cake layers.

Nitrogen removal and microbial mechanisms in a novel tubular bioreactor-enhanced floating treatment wetland for the treatment of high nitrate river water

A novel tubular bioreactor-enhanced floating treatment wetland (TB-EFTW) was developed for the in situ treatment of high nitrate river water. When compared with the enhanced floating treatment wetland (EFTW), the TB-EFTW system achieved 30% higher total nitrogen removal efficiency. Further, the average TN level of the TB-EFTW effluent was below the Grade IV requirement (1.5 mg/L) specified in Chinese standard (GB3838-2002). Microbial analysis revealed that both aerobic and anoxic denitrifying bacteria coexisted in the new system. The relative abundance of aerobic and anoxic denitrifiers were 42.69% and 22% at the middle and end of the tubular bioreactor (TB), respectively. It is reasonable to assume that effective nitrogen removal can mainly be attributed to the addition of solid carbon source and the spatial difference in DO distribution (oxic-anoxic areas in sequence) inside the TB. The initial investment cost and operating costs associated with the TB-EFTW system are approximately 14,000 and 3500 yuan per 1000 m3 river water, respectively. Considering its low cost, minimal maintenance requirements, and effective nitrogen removal, this newly developed system can be regarded as a promising technology for treating high nitrate river water. PRACTITIONER POINTS: A novel TB-EFTW system was developed to upgrade traditional in situ treatment techniques. The TB-EFTW could achieve 30% higher nitrogen removal efficiency than EFTWs. Both aerobic and anoxic denitrifying bacteria coexisted in the system. The system shows better technical and economic performance compared with routine techniques.

Petrochemical and municipal wastewater treatment plants activated sludge each own distinct core bacteria driven by their specific incoming wastewater

Microorganisms in activated sludge from wastewater treatment plants (WWTPs) form complex networks to convert a wide variety of pollutants, thus ensuring water purification and environmental protection. In this study, activated sludge samples were collected from three full-scale WWTPs: a petrochemical WWTP (PWWTP), a municipal WWTP treating domestic wastewater (MWWTP_D), and a municipal WWTP treating a mixture of domestic wastewater and multiple industrial effluents (MWWTP_I+D). These samples were analyzed by high-throughput sequencing of 16S rRNA gene PCoA and CPCoA indicated that the samples from three WWTPs were separated, suggesting that each WWTP had unique microbiome characters (P < 0.05). This was also evidenced by the different predominant bacteria (PDB), biomarkers, and key nodes of co-occurrence network in the three WWTPs. Microorganisms with all three above mentioned characteristics were defined the core bacteria, specifically: Georgfuchsia, Thauera and GP4 in PWWTP, Phaeodactylibacter and Hyphomicrobiuml in MWWTP_D, and Otheakwangia, Terrimonas, Phenylobacterium, etc. in MWWTP_I + D. Furthermore, in accordance with the functional profile prediction, the functional groups in PWWTP metabolized aromatic compound, sulfur compounds and heavy metal typically present in petrochemical wastewater. In contrast, the microbiome in MWWTP_D was represented by the population breaking down macromolecular biodegradable organic matter and the nitrogen nutrients that constitute the vast majority of domestic wastewater pollutants. Both functional groups coexist in MWWTP_I + D. These results revealed that the specific composition of incoming wastewaters produced distinct ecological niches and modulated the ecological structure of activated sludge microbial communities in real-world WWTPs. However, the generalization of the results of this study will require further research.

Reproducibility of Aerobic Granules in Treating Low-Strength and Low-C/N-Ratio Wastewater and Associated Microbial Community Structure

Long-term stability of the aerobic granular sludge system is essentially based on the microbial community structure of the biomass. In this study, the physicochemical and microbial characteristics of sludge and wastewater treatment performance were investigated regarding formation, maturation, and long-term maintenance of granules in two parallel sequencing batch reactors (SBR), R1 and R2, under identical conditions. The aim was to explore the linkage between microbial community structure of the aerobic granules, their long-term stability, as well as the reproducibility of granulation and long-term stability. The two reactors were operated with a COD concentration of 400 mg/L and a chemical oxygen demand to nitrogen (COD/N) ratio of 4:1 under anoxic–oxic conditions. It was found that although SVI30, sludge size, and distributions in R1 and R2 were different, aerobic granules were formed, and they maintained long-term stability in both reactors for 320 days, implying that a certain level of randomness of granulation does not affect the long-term stability and performance for COD and N removal. In addition, a significant reduction in the richness and diversity of microbial production was observed after the sludge was converted from inoculum or flocs to granules, but this did not negatively affect the performance of wastewater treatment. Among the predominant microbial species in aerobic granules, Zoogloea was identified as the most important bacteria present during the whole operation with the highest abundance, while Thauera was the important genus in the formation and maturation of the aerobic granules, but it cannot be maintained long-term due to the low food-to-microorganisms ratio (F/M) in the system. In addition, some species from Ohtaekwangia, Chryseobacterium, Taibaiella, and Tahibacter were found to proliferate strongly during long-term maintenance of aerobic granules. They may play an important role in the long-term stability of aerobic granules. These results demonstrate the reproducibility of granulation, the small influence of granulation on long-term stability, and the robustness of aerobic granulation for the removal of COD and N. Overall, our study contributes significantly to the understanding of microbial community structure for the long-term stability of aerobic granular sludge in the treatment of low-COD and low-COD/N-ratio wastewater in practice.

Tetracycline removal in granulation: Influence of extracellular polymers substances, structure, and metabolic function of microbial community

Tetracycline is a potentially hazardous residual antibiotic detected in various sewages. High concentration (mg/L) of tetracycline is found in pharmaceutical/hospital wastewater and wastewater derived from livestock and poultry. So far, only antibiotics in μg/L level have been reported in granulation of aerobic sludge during wastewater treatment, but its effects in high concentration are rarely reported. In this study, the influence of tetracycline in high concentration (∼2 mg/L) on the formation of granular sludge, structure, and metabolic function of the microbial community during the granulation of aerobic sludge was investigated to improve the understanding of the aerobic granular sludge formation under high-level of tetracycline. The role of extracellular polymers substances (EPSs) derived from granular sludge in the granulation and tetracycline removal process was also investigated, showing that tetracycline improved the relative hydrophobicity, flocculability and protein/polysaccharide ratio of EPSs, accelerating the granulation of sludge. Succession of microbial communities occurred during the domestication of functional bacteria present in the sludge and was accompanied with regulation of metabolic function. The addition of tetracycline lead to an increase of tetracycline-degrading bacteria or antibiotic resistance genus. Those findings provide new perspectives of the influence of tetracycline on aerobic sludge granulation and the removal mechanism of tetracycline.

High removal efficiencies of antibiotics and low accumulation of antibiotic resistant genes obtained in microbial fuel cell-constructed wetlands intensified by sponge iron

Using microbial fuel cells with constructed wetlands (MFC-CWs) for eliminating antibiotics has recently attracted extensive attention. However, antibiotic removal efficiencies in MFC-CWs must be enhanced, and the accumulation of antibiotic resistant genes (ARGs) remains an unmanageable issue. This study tries to enhance the antibiotic removal in synthetic wastewater and reduce ARGs by adding sponge iron (s-Fe⁰) and calcium peroxide to the anode and cathode of MFC-CWs, respectively, and/or simultaneously. The results demonstrated that adding s-Fe⁰ and calcium peroxide to MFC-CWs could improve the removal efficiencies of sulfamethoxazole (SMX) and tetracycline (TC) by 0.8-1.3% and 6.0-8.7%. Therein, s-Fe⁰ also significantly reduced 84.10-94.11% and 49.61-60.63% of total sul and tet genes, respectively. Furthermore, s-Fe⁰ improved the voltage output, power density, columbic efficiency, and reduced the internal resistance of reactors. The intensification to the electrode layers posed a significant effect on the microbial community composition and functions, which motivated the shift of antibiotic removal, accumulation of ARGs and bioelectricity generation in MFC-CWs. Given the overall performance of MFC-CWs, adding s-Fe⁰ to the anode region of MFC-CWs was found to be an effective strategy for removing antibiotics and reducing the accumulation of ARGs.

Biological mechanism of alleviating membrane biofouling by porous spherical carriers in a submerged membrane bioreactor

In this study, porous spherical carriers were fixed around the hollow fiber membrane module to mitigate membrane biofouling. Two MBRs (R1 without carriers, R2 with carriers) were operated for 31 days under identical operating conditions to investigate the effects of the carriers on the reactor performances, the production of extracellular polymeric substances (EPS), the level of N-acyl-homoserine lactones (AHLs), and the microbial communities. The results showed that the presence of carriers in MBR was conducive to nitrogen removal and decreased the total membrane filtration resistance by about 1.7 times. Slower transmembrane pressure (TMP) rise-up, thinner bio-cakes, lower EPS production, and fewer tryptophan and aromatic proteins substances on the membrane surface were observed in R2. The polysaccharides secretion of EPS in bio-cakes was mainly regulated by C4-HSL and 3OC6-HSL in the presence of carriers. The microbial community analysis revealed that carriers addition reduced the relative abundance of EPS and AHL producing bacteria in the membrane bio-cakes and enriched the accumulation of functional bacteria conducive to nutrient removal in the mixed liquor. This study provided an in-depth understanding for the application of porous spherical carriers to alleviate membrane biofouling.

Humic acid removal and microbial community function in membrane bioreactor

A membrane bioreactor with humic acid substrate (MBR-H) was operated to investigate organic removal and membrane performance. Approximately, 60% of chemical oxygen demand removal was observed in MBR-H. The biosorption capacity reached to the maximum value of 29.2 mg g^-1 in the experiments with various activated sludge concentrations and the amount adsorbed on the newly produced microbes was limited. To understand key functions of microorganisms in the biodegradation of humic acid, the microbial community was examined. The dominant phylum was changed from Actinobacteria at the raw sludge to Proteobacteria at the MBR-H. Especially, great increases of β-, γ-, and δ-Proteobacteria in the MBR-H indicated that those class of Proteobacteria played a vital role in humic acid removal. Investigation at the genus level showed enrichment of Stenotrophobacter in the MBR-H, which indicated the presence of metabolites in the proposed humic substance degradation pathway. In addition, the bacteria producing extracellular polymeric substances were increased in the MBR-H. Substantial variation of microbial community function was occurred in the MBR to degrade humic acid. Operational parameters in MBRs might be sought to maintain water permeability and to obtain preferable condition to evolution of microbial consortia for degradation of the refractory organic matter.

Triclosan weakens the nitrification process of activated sludge and increases the risk of the spread of antibiotic resistance genes

The usage of triclosan (TCS) may rise rapidly due to the COVID-19 pandemic. TCS usually sinks in the activated sludge. However, the effects of TCS in activated sludge remain largely unknown. The changes in nitrogen cycles and the abundances of antibiotic resistance genes (ARGs) caused by TCS were investigated in this study. The addition of 1000 μg/L TCS significantly inhibited nitrification since the ammonia conversion rate and the abundance of nitrification functional genes decreased by 12.14%. The other nitrogen cycle genes involved in nitrogen fixation and denitrification were also suppressed. The microbial community shifted towards tolerance and degradation of phenols. The addition of 100 μg/L TCS remarkably increased the total abundance of ARGs and mobile genetic elements by 33.1%, and notably, the tetracycline and multidrug resistance genes increased by 54.75% and 103.42%, respectively. The co-occurrence network revealed that Flavobacterium might have played a key role in the spread of ARGs. The abundance of this genus increased 92-fold under the addition of 1000 μg/L TCS, indicating that Flavobacterium is potent in the tolerance and degradation of TCS. This work would help to better understand the effects of TCS in activated sludge and provide comprehensive insight into TCS management during the pandemic era.

Responses of microbial structures, functions and metabolic pathways for nitrogen removal to different hydraulic retention times in anaerobic side-stream reactor coupled membrane bioreactors

Synchronous sludge reduction and nitrogen removal have attracted increasing attention, while the underlying mechanisms of diverse nitrogen metabolism within the complicated processes remain unclear. Four anoxic/oxic membrane bioreactors, three of which were upgraded by anaerobic side-stream reactors (ASSR) and carriers (APSSR-MBRs), were operated to determine effects of hydraulic retention time of ASSRs. APSSR-MBRs achieved more significant nitrogen removal and higher nitrate uptake rate because of more denitrifying bacteria and the supernumerary release of secondary substrates. Ammonia uptake rate showed the diverse Nitrospira preceded over anaerobic decay and sulfide inhibition in the ASSR, and made the reactor exhibit higher nitrification capacity. Metagenomic analysis indicated that APSSR-MBRs showed higher abundances of genes related to nitrogen consumption processes, and higher abundances on the carriers, confirming their pivotal roles in nitrogen metabolism. This study provided novel perspectives to build a bridge between process model and nitrogen metabolism in the sludge reduction system..

Phosphate substances transformation and vivianite formation in P-Fe containing sludge during the transition process of aerobic and anaerobic conditions

Excess sludge was considered as a promising raw material for phosphorus recovery. In this study, the P-Fe containing sludge came from the aerobic membrane bioreactor with electrocoagulation (EC), which was refluxed to the anaerobic unit for iron reduction. Under anaerobic condition, the ORP and pH maintained at -350 mV and 7.5, which exactly met the conditions for vivianite formation. According to the analysis of X-ray polycrystalline diffraction (XRD) and field emission scanning electron microscopy (FE-SEM), the final product of the sludge after anaerobic condition was mainly vivianite. Microbial analysis showed that there were iron reducing bacteria (IRB) in sludge before and after anaerobic process, including Dechloromonas, Desulfovibrio. Aeromonas and Methanobacterium. During the transition process of aerobic and anaerobic conditions, amorphous phosphate substances in P-Fe containing sludge could be transformed vivianite just with long term standing, which could promote the recovery of phosphate resource from wastewater.

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).

Effect of operational strategies on the rapid start-up of nitrogen removal aerobic granular system with dewatered sludge as inoculant

In both sequencing batch reactors with dewatering sludge as inoculant, the strategies by step-feeding (R1) or step-feeding combined with low aeration (R2) were performed under alternating anoxic/aerobic condition to discover superior methods launching nitrogen removal aerobic granule system. Interestingly, two reactors accomplished granulation at day 0, two days later, possessed prominent settling performance (SVI < 45 ml/g. MLSS) and denitrifying ability (TIN > 80%). Thereinto, R2 had lower crushing rate, larger granules, higher biomass and better pollutant removal performance owing to low aeration and more filamentous bacteria on AGS surface. Moreover, effluent NH₄⁺-N was used as indicator of excess filaments due to its quick response for the filaments. After effluent NH₄⁺-N exceeded 5 mg/L, causative filaments Sphaerotilus were effectively inhibited and eliminated by enhancing pH value to 8.0 ± 0.2. As a result, this study provides a new insight into rapid start-up nitrogen removal granule system by promoting and limiting filaments in proper period.

Effect of steel slag in recycling waste activated sludge to produce anaerobic granular sludge

The amount of waste activated sludge (WAS) has grown dramatically in China. WAS is considered as a problematic and hazardous waste, which should be disposed in a safe and sustainable manner. In order to recycle WAS to an anaerobic granular sludge (AnGS) process for anaerobic digestion, Fe powder and steel slags (rusty and clean slags) were used to enhance the granulation process. The results demonstrated that both rusty and clean slags encouraged the development of granular sludge. Adding 10 g/L clean slags could increase AnGS granulation rate by 37%. In the presence of clean slags, extracellular polymeric substances (EPS) concentration in granules increased noticeably to 715 mg/g mixed liquor suspended solids (MLSS). High throughput sequencing analysis exhibited more diversity and higher abundance of functional microbial communities in the batch bottle with 10 g/L clean slags. This study suggested that adding clean slags at 10 g/L dosage was a sustainable and effective method for the sludge granulation.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Effects of exogenous N-acyl-homoserine lactones on nutrient removal, sludge properties and microbial community structures during activated sludge process

This study investigated the effects of exogenous N-acyl-homoserine lactone (AHL) signal molecules, N-hexanoyl-_l-homoserine lactone (C6-HSL) and N-octanoyl-_l-homoserine lactone (C8-HSL), on treatment performance, sludge properties and microbial community structures in activated sludge systems. Results showed that the nitrification and denitrification efficiencies were enhanced with the addition of signal molecules. The particle size, irregularity, and internal mass transfer resistance of activated sludge flocs (ASFs) increased, primarily because dosing AHLs led to a content increase and chemical composition variation of extracellular polymeric substances (EPS) in sludge. Microbial analysis indicated an increase in both the bacterial richness and diversity of the systems. The relative abundances of the key functional groups, including bacteria related to C and N removal and EPS production, varied correspondingly. This study presents an insight into the comprehensive understanding of the effects of AHL-based quorum sensing on activated sludge treatment process.

Fate of typical endocrine active compounds in full-scale wastewater treatment plants: Distribution, removal efficiency and potential risks

In this study, the distribution, removal efficiency, and potential risks of 9 typical endocrine active compounds (EACs) in two full-scale wastewater treatment plants (WWTPs) were investigated. The EAC concentrations ranged from 0.2 to 7394.2 ng/L in influents. The source of influents was a critical factor in determining the EAC levels. EACs were primarily removed in the secondary biological processing units, with removal efficiencies fluctuating from 13.7% to 98%. The biological treatment processes and operating parameters (i.e., HRT and SRT) influenced the EAC removal efficiency. Bisphenol A (BPA) and estriol were mainly removed by biodegradation, while antidepressants were primarily eliminated by sludge adsorption according to the distribution patterns and mass flow of EACs in WWTPs. Novosphingobium, Saprospiraceae, etc. were the core functional bacteria for EAC biodegradation. In addition, sertraline in effluents and dewatered sludge may pose medium environmental risks, while the other EACs pose low environmental risks.

Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution

This study investigated the effects of radial oxygen loss (ROL) of three different plants on nitrobenzene (NB) wastewater treatment and bioelectricity generation performance in constructed wetland-microbial fuel cell (CW-MFC). ROL and root biomass from wetland plants showed positive effects on NB wastewater compared to unplanted CW-MFC. Scirpus validus exhibited higher tolerance to NB than Typha orientalis and Iris pseudacorus at 20-200 mg/L NB. As NB concentration reached 200 mg/L, the CW-MFC with Scirpus validus had relatively high DO (2.57 ± 0.17 mg/L) and root biomass (16.42 ± 0.18 g/m²), which resulted in the highest power density and voltage (19.5 mW/m², 590 mV) as well as NB removal efficiency (93.9 %) among four reactors. High-throughput sequencing results suggested that electrochemically active bacteria (EAB) (e.g., Geobacter, Ferruginibacter) and dominant NB-degrading bacteria (e.g., Comamonas, Pseudomonas) could be enhanced by wetland plants, especially in CW-MFC with Scirpus validus. Therefore, Scirpus validus was a good option for simultaneously treating NB wastewater and producing bioelectricity.

Effect of temperatures and alternating anoxic/oxic sequencing batch reactor (SBR) operating modes on extracellular polymeric substances in activated sludge

In order to investigate the effect of temperatures and operating modes on extracellular polymeric substances (EPS) contents, three sequencing batch reactors (SBRs) were operated at temperatures of 15, 25, and 35 °C (R_{15 °C}, R_{25 °C}, and R_{35 °C}, respectively), with two SBRs operated under alternating anoxic/oxic conditions (R_A/O and R_O/A, respectively). Results showed that higher contents of tightly bound EPS (TB-EPS) and total EPS appeared in R_{15 °C}, while loosely bound EPS (LB-EPS) dominated in R_{35 °C}. In all three kinds of EPS (LB-EPS, TB-EPS and total EPS) assessed, protein was the main component in R_{15 °C} and R_{25 °C}, while polysaccharides dominated in R_{35 °C}. Moreover, compared with R_O/A, R_A/O was favorable for the production of the three kinds of EPS. Furthermore, three kinds of EPS and their components were augmented during the nitrification process, while they declined during the denitrification process under all conditions except for R_{35 °C}.

Evaluating influence of filling fraction of carriers packed in anaerobic side-stream reactors on membrane fouling and microbial community of the coupled membrane bioreactors

An anoxic/oxic membrane bioreactors (AO-MBR) and three identical anaerobic side-stream reactor coupled with anoxic/oxic membrane bioreactors (ASSR-MBR) were constructed and operated in parallel to investigate the appropriate filling fraction of carriers packed in ASSR, influences on pollutants removal, sludge reduction, membrane fouling and microbial community of ASSR-MBR. Inserting ASSR achieved efficient COD removal and nitrification, and packing carriers in ASSR obtained the highest sludge reduction efficiency of 50.5 % at filling fraction of 25 %. Compared to AO-MBR, inserting ASSR without carriers induced the release of viscous components in extracellular polymeric substances (EPS) and the formation of calcium carbonate-related bacteria on membrane surface, and thus deteriorated membrane fouling. Packing carriers with 25 % filling fraction promoted the hydrolysis of soluble microbial products and EPS, whilst reduced the viscoelasticity of sludge flocs. Higher filling fraction of 50 % increased the shear forces to the biofilm and biomarkers related to membrane fouling, and thus showed little improvement to alleviate membrane fouling. MiSeq sequencing revealed that although it enriched in the bulk sludge of conventional ASSR-MBR and the coupled reactor with filling fraction of 50 %, the floc-forming, hydrolytic and fermentative bacteria were more inclined to attach on the membrane surface and alleviate fouling process.

Performance and microbial community of the CANON process in a sequencing batch membrane bioreactor with elevated COD/N ratios

In this study, the effects of elevated chemical oxygen demand/nitrogen (COD/N) ratios on nitrogen removal, production and composition of the extracellular polymer substances (EPS) and microbial community of a completely autotrophic nitrogen removal via nitrite (CANON) process were studied in a sequencing batch membrane bioreactor (SBMBR). The whole experiment was divided into two stages: the CANON stage (without organic matter in influent) and the simultaneous partial nitrification, anaerobic ammonia oxidation and denitrification (SNAD) stage (with organic matter in influent). When the inflow ammonia nitrogen was 420 mg/L and the COD/N ratio was no higher than 0.8, the addition of COD was helpful to the CANON process; the total nitrogen removal efficiency (TNE) was improved from approximately 65% to more than 75%, and the nitrogen removal rate (NRR) was improved from approximately 0.255 kgN/(m³·d) to approximately 0.278 kgN/(m³•d), while the TNE decreased to 60%, and the NRR decreased to 0.236 kgN/(m³•d) when the COD/N ratio was elevated to 1.0. For the EPS, the amounts of soluble EPS (SEPS) and loosely bound EPS (LB-EPS) were both higher in the CANON stage than in the SNAD stage, while the amount of tightly bound EPS (TB-EPS) in the SNAD stage was significantly higher due to the proliferation of heterotrophic bacteria. The metagenome sequencing technique was used to analyse the microbial community in the SBMBR. The results showed that the addition of COD altered the structure of the bacterial community in the SBMBR. The amounts of Candidatus 'Anammoxoglobus' of anaerobic ammonia oxidation bacteria (AAOB) and Nitrosomonas of ammonia oxidizing bacteria (AOB) both decreased significantly, and Nitrospira of nitrite oxidizing bacteria (NOB) was always in the reactor, although the amount changed slightly. A proliferation of denitrifiers related to the genera of Thauera, Dokdonella and Azospira was found in the SBMBR.

Evolution of Antibiotic Resistance and the Relationship between the Antibiotic Resistance Genes and Microbial Compositions under Long-Term Exposure to Tetracycline and Sulfamethoxazole

The removal of antibiotics and widespread of antibiotic resistance genes (ARGs) have received continuous attention due to the possible threats to environment. However, little information is available on the evolution of antibiotic resistance and the relationship between ARGs and microbial communities under long-term exposure to sub-inhibitory concentrations of antibiotics. In our study, two laboratory-scale anoxic-aerobic wastewater treatment systems were established and operated for 420 days to investigate the evolution of antibiotic resistance under exposure of 5 mg·L⁻¹ tetracycline (TC) or 5 mg·L⁻¹ TC and 1 mg·L⁻¹ sulfamethoxazole (SMX). The average removal rates of TC and SMX were about 59% and 72%, respectively. The abundance of the main ARGs responsible for resistance to TC and SMX increased obviously after antibiotics addition, especially when TC and SMX in combination (increased 3.20-fold). The tetC and sul1 genes were the predominant genes in the development of TC and SMX resistance, in which gene sul1 had the highest abundance among all the detected ARGs. Network analysis revealed that under antibiotic pressure, the core bacterial groups carrying multiple ARGs formed and concentrated in about 20 genera such as Dechloromonas, Candidatus Accumulibacter, Aeromonas, Rubrivivax, in which intI1 played important roles in transferring various ARGs except sul3.

A novel pilot-scale tubular bioreactor-enhanced floating treatment wetland for efficient in situ nitrogen removal from urban landscape water: Long-term performance and microbial mechanisms

In order to strengthen in situ nitrogen removal of urban landscape water, a novel pilot-scale tubular bioreactor-enhanced floating treatment wetland (TB-EFTW) was constructed, and the long-term performance and responsible microbial mechanisms were investigated in this study. The results showed that the system could remove 81.5% nitrogen from the landscape water after 240 days' operation. Moreover, the contribution rate of plant absorption to nitrogen was low (8.3%), which indicated that microbial biotransformation rather than plant absorption played a more key role in nitrogen removal in TB-EFTW system. The declining dissolved oxygen (DO) concentration along the axial direction of tubular bioreactor (TB) resulted in the sequential bacterial community of nitrifying, aerobic denitrifying, and anoxic denitrifying bacteria in the front, middle, and final part of TB. High-throughput sequencing results demonstrated that the internal environment of the system realized the coexistence of nitrifying, aerobic denitrifying and anoxic denitrifying process. The reason was mainly because that oxic-anoxic (O-A) areas were formed in sequence along the axial direction of tubular bioreactor. Overall, a unique advantage in nitrogen removal was achieved in TB-EFTW, which could provide important references for in situ treatment of urban landscape water. PRACTITIONER POINTS: TB-EFTW strengthened nitrogen removal for in situ urban landscape water treatment. Microbial conversion played a key role in nitrogen removal of the TB-EFTW system. The unique distribution of oxic-anoxic (O-A) areas was formed in sequence along the TB. Nitrification, aerobic, and anoxic denitrification were synergistically involved in the TB.

Enhanced aerobic granulation by inoculating dewatered activated sludge under short settling time in a sequencing batch reactor

The effect of dewatered activated sludge on aerobic granulation was investigated in a sequencing batch reactor (SBR) under short settling time. The results showed that dewatered sludge accelerated aerobic granulation and the granulation was completed within 5 days. On day 5, the aerobic granules were regular, compact, fast-settling and high granular strength and possessed excellent removal performance of carbon and nitrogen. The change trend of extracellular polymeric substances (EPS) was basically consistent with granular strength and granulation rate, indicating that EPS in granules played a vital function for granulation. Microbial community succession was investigated by pyrosequencing. In 5 days, microbial diversity was reduced and certain strains were rapidly enriched in the granules to become dominant species, serving on a crucial role in rapid granulation and pollutant removal as they could secrete excess EPS and possess the excellentability removing carbon and nitrogen pollutants.

Enhancing the digestion of waste activated sludge through nitrite addition: insight on mechanism through profiles of extracellular polymeric substances (EPS) and microbial communities

Extracellular nitrite has been used to improve the digestion of waste activated sludge (WAS). However, the underlying mechanism remains largely unknown. In this study, WAS was treated with 0.2 gNO₂^--N/gVSS for 7 days and its performance was compared to that of aerobic and anaerobic treatments. The addition of nitrite had a distinct effect on the reduction of VSS/SS and the accumulation of soluble organics compared to the control reactors. As evident by the variations of extracellular polymeric substances (EPS), nitrite addition had a positive effect on decreasing protein. In particular, the decrease of protein mainly occurred in tightly bound EPS (TB-EPS), which caused sludge disintegration and enhanced sludge reduction. Additionally, the decrease of microbial diversity with nitrite addition was significant compared to the control reactors, accompany with a decrease of live/dead cells ratio and an increase of supernatant DNA concentration. This suggests that nitrite could cause cell death and lysis, resulting in sludge degradation. Thus, nitrite addition enhanced sludge treatment through the combined effect of TB-EPS disintegration and cell lysis. These findings will be useful for the optimization of sludge treatment process based on nitrite addition.

Effects of biomass pyrolysis derived wood vinegar on microbial activity and communities of activated sludge

The effects of wood vinegar (WVG) on microbial activity and communities of activated sludge were investigated in a sequencing batch reactor (SBR) process. Results showed that the optimal WVG concentration was 4 μL/L when the pollutants removal efficiency and microbial activity were promoted by a WVG dilution factor of 1000. WVG could reduce the increase in microbial species richness, which led to a more notable variety of microbial species diversity. The enhanced microbial activity and communities were addressed to the promotion of 7 main classes of microbes in Proteobacteria, Bacteroidetes, Acidobacteria, and Nitrospirae phyla. The growth of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and main genera of denitrifying bacteria (DNB), phosphorus-accumulating organisms (PAOs), and glycogen-accumulating organisms (GAOs) could be promoted by WVG, which improved the sewage treatment effectiveness in a SBR.

Alkaline fermentation of waste activated sludge with calcium hydroxide to improve short-chain fatty acids production and extraction efficiency via layered double hydroxides

Ca(OH)₂ addition was proposed to improve short chain fatty acids (SCFAs) production via alkaline fermentation of waste activated sludge (WAS), with CO₃^2- and PO₄^3- being removed simultaneously, so that the SCFAs extraction efficiency could be improved. Alkaline fermentation of WAS with Ca(OH)₂ and NaOH addition were performed respectively, and the efficiencies of SCFAs extraction from the fermentation liquids via in situ layered double hydroxides (LDHs) were investigated. The results showed that, the SCFAs production was much more improved with NaOH addition than that with Ca(OH)₂ addition. However, the SCFAs contents in the synthesized SCFAs-LDH were 6.7 ± 0.4 mg COD/L (control), 12.4 ± 0.5 mg COD/L (with NaOH addition) and 17.4 ± 0.4 mg COD/L (with Ca(OH)₂ addition), respectively. This means that Ca(OH)₂ addition is an effective way to improve SCFAs extraction from fermentation liquid of WAS.

Pretreating anaerobic fermentation liquid with calcium addition to improve short chain fatty acids extraction via in situ synthesis of layered double hydroxides

In situ synthesis of layered double hydroxides (LDHs) was proved to be an effective way to extract short chain fatty acids (SCFAs) from anaerobic fermentation liquid (AFL) as carbon source for biodenitrification, but the SCFAs content in SCFAs-LDH was unsatisfactory because of the existence of much carbonate in AFL. Pretreatment of AFL with calcium addition was investigated to remove carbonate and improve SCFAs extraction via LDHs synthesis. Results of batch tests showed that, the carbonate removal efficiency was as high as 76.6% when the calcium addition was 0.06 mol/L at pH 12. When using the optimal SCFAs/Al³⁺ ratio of 3.0, the total SCFAs content in SCFAs-LDH with pretreatment was improved to 46.5 mg COD/g LDH, which was 4.5 times of the control (10.4 mg COD/g LDH). These results suggest that adding calcium to AFL was an effective way to eliminate the negative effect of carbonates on SCFAs-LDH synthesis.