Microbial community structure and pharmaceuticals and personal care products removal in a membrane bioreactor seeded with aerobic granular sludge

Nitrate input inhibited the biodegradation of erythromycin through affecting bacterial network modules and keystone species in lake sediments

Antibiotic contamination and excessive nitrate loads are generally concurrent in aquatic ecosystems. However, little is known about the effects of nitrate input on the biodegradation of antibiotics. In this study, the effects of nitrate input on microbial degradation of erythromycin, a typical macrolide antibiotic widely detected in lake sediments, were investigated. The results showed that the nitrate input significantly inhibited the erythromycin removal and such an inhibitory effect was strengthened with the increased input dosages. Nitrate input significantly increased sediment nitrite concentration, indicating enhanced denitrification under high nitrate pressure. Bacterial network module and keystone species analysis showed that nitrate input enriched the keystone species involved in denitrification (e.g., Simplicispira and Denitratisoma). In contrast, some potential erythromycin-degrading bacteria (e.g., Desulfatiglandales, Pseudomonadales, Nitrospira) were inhibited by nitrate input. The variations in dominant bacterial groups implied competition between denitrification and erythromycin degradation in response to nitrate input. Based on the partial least squares path modeling analysis, keystone species (total effect: 0.419) and bacterial module (total effect: 0.403) showed strong association with erythromycin removal percentage. This indicated that the inhibitory effect of nitrate input on erythromycin degradation was mainly explained by bacterial network modules and keystone species. These findings will help us to assess the bioremediation potential of antibiotic-contaminated sediments suffering from excessive nitrogen discharge concurrently.

Promising bioprocesses for the efficient removal of antibiotics and antibiotic-resistance genes from urban and hospital wastewaters: Potentialities of aerobic granular systems

The use, overuse, and improper use of antibiotics have resulted in higher levels of antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs), which have profoundly disturbed the equilibrium of the environment. Furthermore, once antibiotic agents are excreted in urine and feces, these substances often can reach wastewater treatment plants (WWTPs), in which improper treatments have been highlighted as the main reason for stronger dissemination of antibiotics, ARB, and ARGs to the receiving bodies. Hence, achieving better antibiotic removal capacities in WWTPs is proposed as an adequate approach to limit the spread of antibiotics, ARB, and ARGs into the environment. In this review, we highlight hospital wastewater (WW) as a critical hotspot for the dissemination of antibiotic resistance due to its high level of antibiotics and pathogens. Hence, monitoring the composition and structure of the bacterial communities related to hospital WW is a key factor in controlling the spread of ARGs. In addition, we discuss the advantages and drawbacks of the current biological WW treatments regarding the antibiotic-resistance phenomenon. Widely used conventional activated sludge technology has proved to be ineffective in mitigating the dissemination of ARB and ARGs to the environment. However, aerobic granular sludge (AGS) technology is a promising technology-with broad adaptability and excellent performance-that could successfully reduce antibiotics, ARB, and ARGs in the generated effluents. We also outline the main operational parameters involved in mitigating antibiotics, ARB, and ARGs in WWTPs. In this regard, WW operation under long hydraulic and solid retention times allows better removal of antibiotics, ARB, and ARGs independently of the WW technology employed. Finally, we address the current knowledge of the adsorption and degradation of antibiotics and their importance in removing ARB and ARGs. Notably, AGS can enhance the removal of antibiotics, ARB, and ARGs due to the complex microbial metabolism within the granular biomass.

The fate of sulfamethoxazole and trimethoprim in a micro-aerated anaerobic membrane bioreactor and the occurrence of antibiotic resistance in the permeate

This study investigates the effects, conversions, and resistance induction, following the addition of 150 μg·L-1 of two antibiotics, sulfamethoxazole (SMX) and trimethoprim (TMP), in a laboratory-scale micro-aerated anaerobic membrane bioreactor (MA-AnMBR). TMP and SMX were removed at 97 and 86%, indicating that micro-aeration did not hamper their removal. These antibiotics only affected the pH and biogas composition of the process, with a significant change in pH from 7.8 to 7.5, and a decrease in biogas methane content from 84 to 78%. TMP was rapidly adsorbed onto the sludge and subsequently degraded during the long solids retention time of 27 days. SMX adsorption was minimal, but the applied hydraulic retention time of 2.6 days was sufficiently long to biodegrade SMX. The levels of three antibiotic-resistant genes (ARGs) (sul1, sul2, and dfrA1) and one mobile genetic element biomarker (intI1) were analyzed by qPCR. Additions of the antibiotics increased the relative abundances of all ARGs and intI1 in the MA-AnMBR sludge, with the sul2 gene folding 15 times after 310 days of operation. The MA-AnMBR was able to reduce the concentration of antibiotic-resistant bacteria (ARB) in the permeate by 3 log.

Environmentally relevant level of perfluorooctanoic acid affect the formation of aerobic granular sludge

The growing increasing occurrence of perfluorooctanoic acid (PFOA) in wastewater has raised concerns about its potential impact on the environment. Nevertheless, the impact of PFOA at environmentally relevant level on the formation of aerobic granular sludge (AGS) is still a 'black box'. This study thus aims to fill this gap by comprehensive investigation of sludge properties, reactor performance and microbial community during the formation of AGS. It was found that 0.1 mg/L PFOA delayed the formation of AGS, causing relatively lower proportion of large size AGS at the end of operation process. Interestingly, the microorganisms contribute to the reactor's tolerance to PFOA by secreting more extracellular polymeric substances (EPS) to slow or block the entry of toxic substances into the cells. During the granule maturation period, the reactor nutrient removal especially chemical oxygen demand (COD) and total nitrogen (TN) were affected by PFOA, decreasing the corresponding removal efficiencies to ∼81.2% and ∼69.8%, respectively. Microbial analysis further revealed that PFOA decreased the abundances of Plasticicumulans, Thauera, Flavobacterium and Cytophagaceae_uncultured, but it has promoted Zoogloea and Betaproteobacteria_unclassified growth, which maintained the structures and functions of AGS. The above results revealed that the intrinsic mechanism of PFOA on the macroscopic representation of sludge granulation process was revealed, and it is expected to provide theoretical insights and practical support for direct adoption of municipal or industrial wastewater containing perfluorinated compounds to cultivate AGS.

Comparative study on the treatment of swine wastewater by VFCW-MFC and VFCW: Pollutants removal, electricity generation, microorganism community

Swine wastewater, characterized by high organic and nutrient content, poses significant environmental challenges. This study aims to compare the effectiveness of two treatment technologies, namely Vertical Flow Constructed Wetland-Microbial Fuel Cell (VFCW-MFC) and Vertical Flow Constructed Wetland (VFCW), in terms of pollutant removal, electricity generation, and microorganism community dynamics. The results showed that the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen (TN), total phosphorus (TP) and sulfadiazine antibiotics (SDZ) by VFCW-MFC were as high as 94.15%, 95.01%, 42.24%, 97.16% and 82.88%, respectively, which were all higher than that by VFCW. Both VFCW-MFC and VFCW have good tolerance to SDZ. In addition, VFCW-MFC has excellent electrical performance, with output voltage, power density, coulombic efficiency and net energy recovery up to 443.59 mV, 51.2 mW/m³, 52.91% and 2.04 W/(g·s), respectively, during stable operation. Moreover, the microbial community diversity of VFCW-MFC was more abundant, and the species abundance distribution in cathode region was more rich and even than in anode region. At phylum level, the dominant microorganisms in VFCW-MFC included Proteobacteria, Bacteroidota, Firmicutes and Actinobacteriota, which showed good degradation effect on SDZ. Proteobacteria and Firmicutes are also involved in electricity production. Chloroflexi, Proteobacteria and Bacteroidota play a major role in nitrogen reduction.

Fate and removal of iodinated X-ray contrast media in membrane bioreactor: Microbial dynamics and effects of different operational parameters

Iodinated X-ray contrast media (ICM) are mainly used in medical sector, and their presence in environmental waters is a cause of concern as they are capable of forming highly toxic iodinated disinfection byproducts. In the present study, the removal mechanisms of the three ICM- iohexol, iopromide, and iopamidol were elucidated in a lab-scale aerobic membrane bioreactor (MBR). At steady-state operation (solids retention time (SRT)- 70 days, organic loading rate (OLR)- 0.80 KgCOD/m³-day, nitrogen loading rate (NLR)- 0.08 KgNH₄-N/m³-day, hydraulic retention time (HRT)- 12 h), the average removal of iohexol and iopromide was found to be 34.9 and 45.2 %, respectively, whereas iopamidol proved to be highly recalcitrant in aerobic conditions of the MBR (removal <10 % in all phases of the MBR operation). Further, through batch kinetic studies and mass balance analysis, it was observed that ICM were primarily biotransformed in the MBR system and biosorption (K_d < 10 L/Kg) was negligible. The biodegradation rate coefficient values (K_biol) of the ICM were found to be <0.65 L/g-d which indicate that biotransformation rate of ICM was slow. Increased OLR (1.60 KgCOD/m³-day) and reduced SRT (20 days) were found to negatively affect the removal of the ICM. Further, the removal of ICM was found to depend on its initial concentration, and the increment in the ammonium loading (0.16 KgNH₄-N/m³-day) did not favor its removal. The dosing of ICM altered the microbial dynamics of the mixed liquor and reduced the microbial diversity and richness. Bdellovibrio, Zoogloea, and bacteria belonging to TM7-3 class, Cryomorphaceae and Hyphomonadaceae families may contribute in ICM biotransformation.

Mechanism of downward migration of quinolone antibiotics in antibiotics polluted natural soil replenishment water and its effect on soil microorganisms

Reclaimed water is widely concerned as an effective recharge of groundwater and surface water, but trace organic pollutants produced by traditional wastewater treatment plants (WWTPs) would cause environmental pollution (water and soil) during infiltration. Therefore, the effects of reclaimed water containing ofloxacin (OFL) and ciprofloxacin (CIP) in antibiotics polluted natural soil (APNS) were investigated by simulating soil aquifer treatment systems (SATs). The experiment results showed that OFL and CIP in water were adsorbed and microbially degraded mainly at 30 cm, and the concentration of OFL and CIP in soil increased with depth, which were mainly due to the desorption from APNS. Concurrently, the change in replenishment water concentration also significantly affected OFL and CIP in pore water and soil. Although OFL and CIP inhibited the diversity of soil microbial community, they also promoted the growth of some microorganisms. As the dominant bacteria, Proteobacteria and Acidobacteriota can effectively participate in the degradation of OFL and CIP. The degradation effects of soil microorganisms on OFL and CIP were 45.48% and 42.39%, respectively, indicating that soil microorganisms selectively degraded pollutants. This experiment was carried out on APNS, which provided a reference for future studies on the migration of trace organic pollutants under natural conditions.

Formation, application, and storage-reactivation of aerobic granular sludge: A review

It was an important discovery in wastewater treatment that the microorganisms in the traditional activated sludge can form aerobic granular sludge (AGS) by self-aggregation under appropriate water quality and operation conditions. With a typical three-dimensional spherical structure, AGS has high sludge-water separation efficiency, great treatment capacity, and strong tolerance to toxic and harmful substances, so it has been considered to be one of the most promising wastewater treatment technologies. This paper comprehensively reviewed AGS from multiple perspectives over the past two decades, including the culture conditions, granulation mechanisms, metabolic and structural stability, storage, and its diverse applications. Some important issues, such as the reproducibility of culture conditions and the structural and functional stability during application and storage, were also summarized, and the research prospects were put forward. The aggregation behavior of microorganisms in AGS was explained from the perspectives of physiology and ecology of complex populations. The storage of AGS is considered to have large commercial potential value with the increase of large-scale applications. The purpose of this paper is to provide a reference for the systematic and in-depth study on the sludge aerobic granulation process.

Removing nutrients from wastewater by constructed wetlands under perfluoroalkyl acids stress

Constructed wetlands (CWs) are often used to treat wastewater discharged from wastewater treatment plants (WWTPs), while emerging contaminants (such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)) have been commonly discovered in WWTPs. However, no research has examined whether PFOA/OS (i.e. PFOA and PFOS) affects the performance of CW. Therefore, this study compared the nutrient removal efficiencies of four CWs with varied configurations under PFOA/OS and no PFOA/OS stress conditions. We found that CW containing plants or/and iron-carbon had higher removal efficiency for nutrients (except NH₄⁺-N) than conventional CW in stable operation under wastewater without PFOA/OS. Plants or/and iron increased the nutrient removal efficiency by plant uptake, chemical reaction, and co-precipitation of iron hydroxides. In contrast, the iron-carbon inhibited the nitrification of nitrifying bacteria by consuming dissolved oxygen, converting NO₃^--N to NH₄⁺-N. Although the removal efficiencies of nutrients by CWs differed after introducing PFOA/OS, the removal order was consistent with those before adding PFOA/OS. Plants or/and iron-carbon effectively increased CWs' resistance to PFOA/OS loading and toxicity, and the function of iron-carbon was superior to the plants. In addition, PFOA/OS reduced the abundances of microbes Hydrogenophaga, Pseudomonas, Sphingomonas, Nitrospira, and Candidatus_Accumulibacter that contributed to nutrient removal.

Enzymatic integrated in-situ advanced anaerobic digestion of sewage sludge for the removal of antibiotics and antibiotic resistance genes

Antibiotics and antibiotic resistance genes (ARGs) in sewage sludge can cause high ecotoxicological risks in the environment and public health concerns. The aims of this study were to establish enzymatic integrated in-situ advanced anaerobic digestion (AAD) by adding cellulase and papain as well as the two enzymes combined with zero valent iron (ZVI) directly into the anaerobic digesters to explore the removal of antibiotics and ARGs under the mesophilic condition (35 °C). The methane production potential during in-situ AAD was effectively improved. Papain and cellulase at 30 mg/gTSS were most effective in improving antibiotic removal. The removal of sulfamerazine (SMZ) and sulfadiazine (SMR) could reach 89.10 % and 71.75 %. Combined enzymes with ZVI also enhanced the removal of all target antibiotics, especially roxithromycin (ROX), SMZ and SMR most significantly. Except for sul1, tetA and tetB, the removal of ARGs by papain reached 6.33 %-82.15 %. The addition of cellulase effectively improved tetA removal. The combination of biological enzymes further enhanced the removal of qnrS and ermX. The tetG, tetB, sul3, ermX, ermT, qnrS, and aac(6')-IB-CR by combined enzymes with ZVI could even not be detected after digestion. Addition of papain, cellulase, and ZVI caused variations in the dominant bacteria. All target antibiotics presented significant positive correlations with the genera norank_f__Bacteroidetes_vadinHA17, norank_f__norank_o__SJA-15, norank_f__norank_o__Aminicenantales. Redundancy analysis showed archaea Methanosaeta and Candidatus_ Methanoacidiosum genera greatly contributed to antibiotics removal with the combination of enzymes and ZVI. Co-occurrence network analysis indicated the removal of ARGs was mainly based on the changes of existence of host bacteria.

Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes

Studies on antibiotic removal during wastewater treatment processes are crucial since their release into the environment could bring potential threats to human health and ecosystem. Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms (AOMs) has received special attentions due to the enhanced removal of antibiotics during nitrification processes. However, the interactions between antibiotics and AOMs are less well-elucidated. In this review, the recent research proceedings on cometabolic biodegradation of antibiotics by AOMs were summarized. Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) played significant roles in both nitrification and cometabolic biodegradation of antibiotics. Antibiotics at varying concentrations might pose inhibiting or stimulating effect on AOMs, influencing the microbial activity, community abundance and ammonia monooxygenase subunit A gene expression level. AOMs-induced cometabolic biodegradation products were analyzed as well as the corresponding pathways for each type of antibiotics. The effects of ammonium availability, initial antibiotic concentration, sludge retention time and temperature were assessed on the cometabolic biodegradation efficiencies of antibiotics. This work might provide further insights into the fate and removal of antibiotics during nitrification processes.

Effect of alkaline treatment on the removal of contaminants of emerging concern from municipal biosolids: Modelling and optimization of process parameters using RSM and ANN coupled GA

The current study aimed in enhancing the efficiency of alkaline treatment for CECs remediation in biosolids through the application of RSM and ANN. Due to the seasonal variation of CECs in biosolids, a complete CECs profile over a period of three years were performed. Out of 64 targeted CECs, 13 PhACs (70.1 μg/kg) and 10 pesticides (57.2 μg/kg) were detected in biosolids. In order to enhance the remediation efficiency of CECs by alkaline treatment, process parameters - pH (9.0-13.0), time (3.0-12.0 h) and biosolids age (1-28 days) were optimized by statistical modelling. Using Box-Behnken design, experiments were designed and the resultant data was employed as input for model building using RSM and ANN. The developed mathematical model for alkaline treatment of biosolids using ANN predicted CECs removal with 3.2-fold lower MSE and exhibited high regression coefficient (R² > 0.99) than the conventional RSM model. Further, the multiparameter model was optimized for achieving maximum of 95.7 % CECs removal using ANN-GA. On analyzing the acute toxicity of alkaline treated residual biosolids under the optimized conditions, a reduction in LC50 by an average of 2.1-fold than initial biosolids was observed. This study not only established the application of statistical modelling in the development of an efficient remediation strategy for biosolids, which can be further applied for large-scale remediation process, but also proved the reliability and efficiency of ANN-GA.

Influence of selected antibiotics on respirometric activity of activated sludge

The main topic of this study is to determine the effect of selected antibiotics on the respirometric activity of sewage sludge microorganisms. Within the practical part of the work, several respirometric measurements were performed with activated sludge from a wastewater treatment plant, while the influence of three selected antibiotics — sulfamethoxazole, sulfapyridine, and ciprofloxacin, on sludge activity was monitored. The aim of the work was to point out the inhibitory effect of all monitored compounds on sludge activity and to quantify the inhibitory effect. For sulfamethoxazole (in the concentration range of 0.142—1.42 mg·L−1), the determined inhibition was in the range of 9.67—27.7 %, depending on the concentration of the test substance and the type of respirometric measurements. For sulfapyridine, inhibition values ranged from 1.13 % to 31.9 % for the concentration range from 0.134 to 1.34 mg·L−1. Ciprofloxacin inhibited the activity of activated sludge microorganisms in the range of 4.55 % to 28.8 % (at CPX concentrations from 0.104 to 1.04 mg·L−1).

Insights into the acute effect of anti-inflammatory drugs on activated sludge systems with high solids retention time

The increase in the occurrence of the pharmaceuticals in the environmental compartments is becoming emerging concern as it reflects their inefficient treatment in the wastewater treatment plants which are the main sources of these micropollutants. Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most commonly prescribed and frequently detected pain medications in wastewater treatment plants. A lab scale sequencing batch reactor (SBR) was operated for seven months and acute inhibitory effect of NSAIDs on activated sludge was tested with respirometry. Culture amendment with different concentrations of NSAIDs in the presence as well as absence of nitrification inhibitor resulted in considerable variation in the oxygen uptake rate (OUR) profiles. The decrease in OUR and nitrate production rate governed with reduced heterotrophic and nitrification activity. The kinetics of half saturation for growth and maximum autotrophic growth rates are determined to be affected negatively by the acute impact of anti-inflammatory pharmaceuticals even at the environmentally relevant concentrations. High removal of tested NSAIDs was observed even for the first time introduce with these compounds.

Efficiency of sulfamethoxazole removal from wastewater using aerobic granular sludge: influence of environmental factors

The effects of adsorption, sulfamethoxazole (SMX) content, chemical oxygen demand (COD), and dissolved oxygen (DO) are recognized to be crucial for SMX removal in the aerobic granular sludge (AGS) system. Therefore, we investigated the impact of adsorption and these three different environmental factors on the SMX removal loading rate and removal efficiency of an AGS system, and determined the differences in microbial community composition under different environmental conditions. Adsorption was not the main SMX removal mechanism, as it only accounted for 5% of the total removal. The optimal SMX removal conditions were obtained for AGS when the COD, DO, and SMX concentrations were 600 mg/L, 8 mg/L, and 2,000 µg/L, respectively. The highest SMX removal efficiency was 93.53%. Variations in the three environmental factors promoted the diversity and changes of microbial communities in the AGS system. Flavobacterium, Thauera, and norank_f_Microscillaceae are key microorganisms in the AGS system. Thauera, and norank_f_Microscillaceae were sensitive to increases in SMX concentrations and beneficial for degrading high SMX concentrations. In particular, Flavobacterium abundances gradually decreased with increasing SMX concentrations.

Aerobic Granular Sludge-Membrane BioReactor (AGS-MBR) as a Novel Configuration for Wastewater Treatment and Fouling Mitigation: A Mini-Review

This mini-review reports the effect of aerobic granular sludge (AGS) on performance and membrane-fouling in combined aerobic granular sludge-membrane bioreactor (AGS-MBR) systems. Membrane-fouling represents a major drawback hampering the wider application of membrane bioreactor (MBR) technology. Fouling can be mitigated by applying aerobic granular sludge technology, a novel kind of biofilm technology characterized by high settleability, strong microbial structure, high resilience to toxic/recalcitrant compounds of industrial wastewater, and the possibility to simultaneously remove organic matter and nutrients. Different schemes can be foreseen for the AGS-MBR process. However, an updated literature review reveals that in the AGS-MBR process, granule breakage represents a critical problem in all configurations, which often causes an increase of pore-blocking. Therefore, to date, the objective of research in this sector has been to develop a stable AGS-MBR through multiple operational strategies, including the cultivation of AGS directly in an AGS-MBR reactor, the occurrence of an anaerobic-feast/aerobic-famine regime in continuous-flow reactors, maintenance of average granule dimensions far from critical values, and proper management of AGS scouring, which has been recently recognized as a crucial factor in membrane-fouling mitigation.

Zero-valent iron enhanced in-situ advanced anaerobic digestion for the removal of antibiotics and antibiotic resistance genes in sewage sludge

The in-situ advanced anaerobic digestion (AAD) enhanced with zero-valent iron powder (ZVI) under mesophilic condition was investigated to remove 5 antibiotics (sulfamerazine (SMR), sulfamethoxazole (SMZ), ofloxacin (OFL), tetracycline (TC), and roxithromycin (ROX)) and 11 antibiotic resistance genes (ARGs) (AAC (6')-IB-CR, qnrS, ermF, ermT, ermX, sul1, sul2, sul3, tetA, tetB, and tetG) in sewage sludge. The effects of different ZVI dosages, antibiotic concentrations, and solid retention time (SRTs) on the removal were explored. Also, the correlation coefficient of antibiotics and ARGs, microbial community structure, biogas production and methane yield were analyzed. All conducted treatments operated stably, and the modified Gompertz model described the cumulative methane yield well. The antibiotics, with the exception of OFL, were effectively removed in the sewage sludge at a dosage of 1000 mg/L ZVI, SRT 20 d, and an antibiotic concentration of 20 μg/L during AAD. The removal rates of SMZ, SMR, TC, and ROX reached 97.39%, 74.54%, 78.61%, and 56.58%, respectively. AAC (6')-IB-CR and tetB could be effectively reduced during the in-situ AAD. Through the redundancy analysis, AAC (6')-IB-CR, ermT, ermX, sul2, tetB, and tetG had strong positive correlations with the antibiotics in the reactor. The principle component analysis revealed that the community structure was similar when the SRT was 10 d and 20 d at the same amount of ZVI and antibiotic concentrations in the sludge. Under the operating parameters of 1000 mg/L ZVI dosage, SRT 20 d, and an antibiotic concentration of 20 μg/L, Erysipelotrichia, Verrucomicrobia, Clostridia, Caldiserica, and Alphaproteobacteria of the class were dominated microorganisms in the anaerobic digestion.

Non-surface Attached Bacterial Aggregates: A Ubiquitous Third Lifestyle

Bacteria are now generally believed to adopt two main lifestyles: planktonic individuals, or surface-attached biofilms. However, in recent years medical microbiologists started to stress that suspended bacterial aggregates are a major form of bacterial communities in chronic infection sites. Despite sharing many similarities with surface-attached biofilms and are thus generally defined as biofilm-like aggregates, these non-attached clumps of cells in vivo show much smaller sizes and different formation mechanisms. Furthermore, ex vivo clinical isolates were frequently reported to be less attached to abiotic surfaces when compared to standard type strains. While this third lifestyle is starting to draw heavy attention in clinical studies, it has a long history in natural and environmental sciences. For example, marine gel particles formed by bacteria attachment to phytoplankton exopolymers have been well documented in oceans; large river and lake snows loaded with bacterial aggregates are frequently found in freshwater systems; multispecies bacterial "flocs" have long been used in wastewater treatment. This review focuses on non-attached aggregates found in a variety of natural and clinical settings, as well as some recent technical developments facilitating aggregate research. The aim is to summarise the characteristics of different types of bacterial aggregates, bridging the knowledge gap, provoking new perspectives for researchers from different fields, and highlighting the importance of more research input in this third lifestyle of bacteria closely relevant to our daily life.

Accumulation of sulfonamide resistance genes and bacterial community function prediction in microbial fuel cell-constructed wetland treating pharmaceutical wastewater

Microbial fuel cell constructed wetlands (CW-MFCs) with different circuit operation conditions and hydraulic retention time (HRT) were constructed to evaluate their ability to remove and accumulate pharmaceutical and personal care products (PPCPs) (sulfadiazine (SDZ), carbamazepine (CBZ), naproxen (NPX) and ibuprofen (IBP)) during four months running process. The abundance level of corresponding sulfonamide antibiotic resistance genes (ARGs) was also investigated. The results showed that closed circuit operation of CW-MFC contributed to the decrease in mass loading of COD, NH₄⁺-N, PPCPs, and wastewater toxicity in the effluent. Additionally, closed circuit operation with low HRT contributed to enhancing selected PPCP mass accumulation on electrodes by electro-adsorption, and thus the higher sulfonamide ARG abundance was detected in the electrodes and effluent. Moreover, the composition of bacteria was greatly influenced by the mass accumulation of PPCPs revealed by redundancy analysis results. Procrustes analysis results further demonstrated that bacterial community contributed greatly to the ARGs profiles. Therefore, ARGs with their host bacteria revealed by network analysis were partially deposited on electrode substrates, and thus ARGs were effectively accumulated on electrodes. Function analysis of the bacterial community from PICRUSt predicted metagenomes revealed that closed circuit mode enhanced the abundances of the function genes of metabolic and the multiple ARGs, suggesting that closed circuit operation exhibited positive effects on metabolic process and ARG accumulation in CW-MFC system.

Interaction between perfluorooctanoic acid and aerobic granular sludge

The increasing use of perfluorooctanoic acid (PFOA) raises concerns about its potential toxicity to the environment. However, the interaction between PFOA and aerobic granular sludge has never been documented. This work therefore aims to provide such support through investigating the fate of PFOA at environmentally relevant levels in aerobic granular sludge systems and its impact on aerobic granular sludge. Experimental results showed that 32.0%∼36.4% of wastewater PFOA was removed by aerobic granular sludge in stable operation when PFOA concentration was ranged from 0.1 to 1.0 mg/L. Mass balance analyses and X-ray photoelectron spectroscopy survey scan revealed that the removal of PFOA was dominated by adsorption rather than biodegradation, and sorption kinetic analysis indicated that inhomogeneous multilayer adsorption was responsible for this removal. The adsorbed PFOA deteriorated the settleability of granular sludge and biological nitrogen and phosphorus removal significantly. Experimental results showed that 1.0 mg/L PFOA inhibited anaerobic phosphate release, aerobic phosphate uptake, nitrate reduction, and nitrite reduction processes by 60%, 50%, 13.1%, and 5.8%, respectively. It was observed that PFOA induced large amounts of filamentous villus growing on the surface and increased the extracellular polymeric substances of granular sludge. Fourier-transform infrared spectra and X-ray photoelectron spectroscopy spectrum showed that several function groups in extracellular polymeric substances such as hydroxyl groups, amides and polysaccharides were affected by PFOA. It was also found that PFOA inhibited the cyclic transformations of polyhydroxyalkanoates and glycogen. Microbial community analyses showed that PFOA decreased the abundances of Nitrosomonas, Nitrospira, Accumulibacter, and other function microbes such as Rhodospirillaceae, Thauera, and Azoarcus.

Biodegradation of pharmaceuticals and personal care products in the sequential combination of activated sludge treatment and soil aquifer treatment

Soil aquifer treatment (SAT), applied after activated sludge treatment (AST), has been widely used for wastewater reclamation. AST and SAT show potential for removing micropollutants, including pharmaceuticals and personal care products (PPCPs). However, the role of sequential combination of AST and SAT on the biodegradation of PPCPs was not clear in previous studies. In this study, the removal characteristics of PPCPs in AST and SAT were evaluated to assess the legitimacy of sequential combination of AST and SAT. SAT showed effective removals of antibiotics (> 80%), including fluoroquinolones and macrolides by sorption, but poor removals of amide pharmaceuticals (i.e. carbamazepine and crotamiton) were observed in both AST and SAT. Additionally, biodegradation contributed to the effective removal of carboxylic PPCPs (i.e. ketoprofen and gemfibrozil) in both ASTs and SAT, but effective biodegradation of halogenated acid and polycyclic aromatic compounds (i.e. clofibric acid and naproxen) was observed only in SAT (82.1% and 81.8%, respectively). Furthermore, the microbial substrate metabolic patterns showed that amino acids, amines, and polymers were biodegradable in SAT, which was fit for the biodegradation characteristics of PPCPs in SAT. For microbial communities, Proteobacteria were dominant in AST and SAT, but Acidobacteria and Actinobacteria were more abundant in SAT than AST, which could contribute to the effective removals of halogenated acid in SAT. Considering PPCP biodegradation and substrate metabolism, SAT displays a wider range on the biodegradation than AST. Therefore, we conclude that these two processes can complement each other when used for controlling PPCPs.

Prevalence of Antibiotic Resistance Genes and Their Association with Antibiotics in a Wastewater Treatment Plant: Process Distribution and Analysis

Effluents from wastewater treatment plants has been identified as a main point-source of antibiotics and antibiotic resistance genes in natural water environments. In this study, a typical municipal sewage treatment system in south China was taken as the research object to investigate the effects of each treatment unit on eight target antibiotics (sulfamethoxazole, sulfamethazine, tetracycline hydrochloride, oxytetracycline dihydrate, norfloxacin, ofloxacin, clarithromycin, roxithromycin), 17 antibiotic resistance genes (ARGs) and class 1 integron genes in the system using Accelerated Solvent Extraction-Solid phase extraction-Ultra high Performance Liquid Chromatography-Tandem mass spectrometry (ASE-SPE-UPLC-MS/MS) and real-time fluorescent quantitative PCR (qPCR) and the correlation between them. Seven antibiotics (mainly sulfonamides and tetracyclines, 4.19–141.97 ng·L−1) were detected in the influent, while only sulfamethoxazole, sulfamethazine, ofloxacin, and clarithromycin were detected in the effluent (3.11–16.61 ng·L−1). The tetracycline antibiotics in the wastewater treatment plant (WWTP) were transferred to the sludge phase by adsorption, in which tetracycline hydrochloride and oxytetracycline dihydrate were mostly removed in the aerobic and anaerobic stages, while sulfamethoxazole was mainly removed through biological transformation. Sul I was the most abundant resistance gene, but the WWTP had no obvious effect on its removal. Anaerobic treatment was found to play an important role in tetA, tetQ, and tetX removal. Moreover, correlation analysis revealed that the relative abundance of tetX was significantly correlated with clarithromycin (p = 0.039) and ofloxacin (p = 0.028), while that of tetQ was significantly correlated with sulfamethazine (p = 0.007) and sulfamethoxazole (p = 0.001), and that of tetC was significantly correlated with the class 1 integron gene (p = 0.014). Overall, the results presented herein provide a reference for improving the antibiotics and ARGs removal efficiency of WWTPs in south China.

Effect of hydraulic retention time on micropollutant biodegradation in activated sludge system augmented with acclimatized sludge treating low-micropollutants wastewater

This research investigates the effect of hydraulic retention time (HRT) on micropollutant biodegradation of two-stage activated sludge (AS) system augmented with acclimatized sludge treating low-micropollutants wastewater. The experimental wastewater was a mixture of landfill leachate and agriculture wastewater, and HRT was varied between 24, 18, and 12 h. The results showed that, under 24 h HRT, the micropollutant biodegradation efficiencies were 87-93% for bisphenol A (BPA), 2,6-di-tert-butyl-phenol (2,6-DTBP), di-butyl-phthalate (DBP), di-(ethylhexyl)-phthalate (DEHP); 75-81% for carbamazepine (CBZ), diclofenac (DCF); and 88% for N,N-diethylmeta-toluamide (DEET). The degradation efficiencies were similar under 18 h HRT: 87-93% for BPA, 2,6-DTBP, DBP, DEHP; 75-80% for CBZ, DCF; and 80% for DEET. However, the efficiencies substantially declined under 12 h HRT: 71-93%, 55-60%, and 50%, respectively. Importantly, the findings revealed that HRT plays a crucial part in micropollutant biodegradation of bioaugmented AS system. More specifically, too short an HRT (12 h) results in low micropollutant removal efficiency, and too long an HRT (24 h) contributes to low daily throughput and high treatment operation cost. As a result, moderate HRT (18 h) is operationally and economically optimal for bioaugmented AS system treating low-micropollutants wastewater.

The bacterial community structure of submerged membrane bioreactor treating synthetic hospital wastewater

The pharmaceuticals are biologically active compounds used to prevent and treat diseases. These pharmaceutical compounds were not fully metabolized by the human body and thus excreted out in the wastewater stream. Thus, the study on the treatment of synthetic hospital wastewater containing pharmaceuticals (ibuprofen, carbamazepine, estradiol and venlafaxine) was conducted to understand the variation of the bacterial community in a submerged membrane bioreactor (SMBR) at varying hydraulic retention time (HRT) of 6, 12 and 18 h. The variation in bacterial community dynamics of SMBR was studied using high throughput sequencing. The removal of pharmaceuticals was uniform at varying HRT. The removal of both ibuprofen and estradiol was accounted for 90%, whereas a lower removal of venlafaxine (<10%) and carbamazepine (>5%) in SMBR was observed. The addition of pharmaceuticals alters the bacterial community structure and result in increased abundance of bacteria (e.g., Flavobacterium, Pedobacter, and Methylibium) reported to degrade toxic pollutant.

Insights into the Fate and Removal of Antibiotics in Engineered Biological Treatment Systems: A Critical Review

Antibiotics, the most frequently prescribed drugs of modern medicine, are extensively used for both human and veterinary applications. Antibiotics from different wastewater sources (e.g., municipal, hospitals, animal production, and pharmaceutical industries) ultimately are discharged into wastewater treatment plants. Sorption and biodegradation are the two major removal pathways of antibiotics during biological wastewater treatment processes. This review provides the fundamental insights into sorption mechanisms and biodegradation pathways of different classes of antibiotics with diverse physical-chemical attributes. Important factors affecting sorption and biodegradation behavior of antibiotics are also highlighted. Furthermore, this review also sheds light on the critical role of extracellular polymeric substances on antibiotics adsorption and their removal in engineered biological wastewater treatment systems. Despite major advancements, engineered biological wastewater treatment systems are only moderately effective (48-77%) in the removal of antibiotics. In this review, we systematically summarize the behavior and removal of different antibiotics in various biological treatment systems with discussion on their removal efficiency, removal mechanisms, critical bioreactor operating conditions affecting antibiotics removal, and recent innovative advancements. Besides, relevant background information including antibiotics classification, physical-chemical properties, and their occurrence in the environment from different sources is also briefly covered. This review aims to advance our understanding of the fate of various classes of antibiotics in engineered biological wastewater treatment systems and outlines future research directions.

Biodegradation aspects of ibuprofen and identification of ibuprofen-degrading microbiota in an immobilized cell bioreactor

An enrichment process was employed by applying high ibuprofen concentration in an immobilized cell bioreactor in order to favor the ibuprofen-degrading community present in activated sludge. Experimental data showed the ability of the immobilized cell bioreactor to achieve high ibuprofen removal efficiencies (98.4 ± 0.3%), the tendency of the enriched biomass to acidify the treated liquor, and the inhibition of the nitrification process. Illumina sequencing revealed a massive increase in the relative abundance of Alphaproteobacteria and Gammaproteobacteria (from 29.1 to 80.8%) and a dramatic decrease in the proportion of Bacteroidetes, Planctomycetes, and Verrucomicrobia (from 42.7 to 2.1%) when pure ibuprofen served as the sole carbonaceous feeding substrate. This shift in the feeding conditions resulted in the predominance of Novosphingobium and Rhodanobacter (25.5 ± 10.8% and 25.2 ± 3.0%, respectively) and demonstrated a specialized ibuprofen-degrading bacterial community in activated sludge, which possessed the selective advantage to cope with its degradation. To the best of our knowledge, this bioreactor system was capable of effectively treating the highest ibuprofen concentration applied in wastewater treatment plants.

Impact of current density on the function and microbial community structure in electro-bioreactors

The assessment of bacterial communities in wastewater electro-bioreactors has garnered attention to improve efficiency of wastewater treatment plant (WWTP) processes. This study evaluated the effects of applying different current densities on the function and microbial community structure of an electro-bioreactor by measuring nutrient removal efficiency and analyzing 16S rRNA gene high-throughput sequencing. The electro-bioreactors at current density of 3, 5 and 7 A/m² resulted in an enrichment of operational taxonomic units belonging to distinct functional bacterial families such as (Nitrospiraceae: 8.5, 12.5 and 12.6% relative abundance, respectively) and (Rhodocyclaceae: 8.1, 8.8 and 9.7% relative abundance, respectively), leading to efficient N-removal (>98%) and P-removal (>98%) higher than the control bioreactor (9.6 and 5.0%, respectively). Applying different electric currents proved to affect microbial community composition in electro-bioreactors. The results reported here could prove to be valuable for process control, optimization and improving WWTPs design and operation.

Treatment of 17α‑ethinylestradiol, 4‑nonylphenol, and carbamazepine in wastewater using an aerobic granular sludge sequencing batch reactor

This study quantifies the removal of a mixture of commonly detected emerging contaminants, 17α‑ethinylestradiol (EE2), 4‑nonylphenol (NP), and carbamazepine (CBZ) from synthetic wastewater using aerobic granular sludge in a sequential batch reactor. The emerging contaminant concentration in the influent wastewater was maintained near 500 μg/L for the duration of the experiment. Removal of EE2, NP, and CBZ is comprised of both adsorption and degradation. In general, the main removal mechanism for the emerging contaminants was initially adsorption, however it transitions to degradation as the adsorption capacity is saturated. The stabilized degradation for EE2 and NP in the SBR, was 16.09 μg/g and 20.05 μg/g, respectively. There was limited degradation of CBZ during the anaerobic phase. Both the Langmuir and Freundlich adsorption isotherms fit the data well and constants for the equations are calculated. The constants for the Langmuir Isotherm are found to be (X/m)_max = 36.23, b = 0.0019 for EE2 and (X/m)_max = 44.25, b = 0.0004 for CBZ. None of the tested compounds were found to be detrimental to the performance of the aerobic granules, and high macronutrient removal efficiency was maintained. The granule sludge bed and particle size were not negatively affected by EE2 and NP, however, carbamazepine appeared to interfere with the mechanism of granule formation resulting in a decrease in particle size during the experiment.

Enhanced degradation of bisphenol A and ibuprofen by an up-flow microbial fuel cell-coupled constructed wetland and analysis of bacterial community structure

This study aims to demonstrate that an up-flow microbial fuel cell-coupled constructed wetland (UCW-MFC) can effectively treat synthetic wastewater that contains a high concentration of pharmaceutical and personal care products (PPCPs, 10 mg L^-1 level), such as ibuprofen (IBP) and bisphenol A (BPA). A significant decline in chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) removal was observed when BPA was added, which indicated that BPA was more toxic to bacteria. The closed circuit operation of UCW-MFC performed better than the open circuit mode for COD and NH₄⁺-N removal. Similarly, the removal rates of IBP and BPA were increased by 9.3% and 18%, respectively, compared with the open circuit mode. The majority of PPCPs were removed from the bottom and anode layer, which accounted for 63.2-78.7% of the total removal. The main degradation products were identified. The removal rates of IBP and BPA decreased by 14.6% and 23.7% due to a reduction in the hydraulic detention times (HRTs) from 16 h to 4 h, respectively. Electricity generation performance, including voltage and maximum power density, initially increased and then declined with a decrease in the HRT. Additionally, both the current circuit operation mode and the HRT have an impact on the bacterial community diversity of the anode according to the results of high-throughput sequencing. The possible bacterial groups involved in PPCP degradation were identified. In summary, UCW-MFC is suitable for enabling the simultaneous removal of IBP and BPA and successful electricity production.

Fate of pharmaceuticals during membrane bioreactor treatment: Status and perspectives

Pharmaceuticals in surface waters and wastewater treatment plants (WWTPs) as emerging pollutants have become a major concern. In comparison with other wastewater treatments, removal of pharmaceuticals in MBR has received much attention. This review presents the source and occurrence of pharmaceuticals in WWTPs influents. Experimental studies related to the removal of pharmaceuticals during MBR treatment, key affecting factors (including the different stages of MBR process configuration and the process parameters), and the underlying mechanisms proposed to explain the biodegradation and adsorption behaviors, have been comprehensively discussed. Several transformation products of pharmaceuticals are also reviewed in this paper. Furthermore, further research is needed to gain more information about the multiple influence factors of the pharmaceuticals elimination, appropriate methods for promoting pharmaceuticals elimination, more essential removal pathways, effect of pharmaceuticals on membrane fouling, and the detection and analysis of transformation products.

Toxicity assessment of pharmaceutical compounds on mixed culture from activated sludge using respirometric technique: The role of microbial community structure

Micropollutants of emerging concern such as pharmaceuticals can significantly affect the performance of secondary biological processes in wastewater treatment plants. The present study is aimed to evaluate the toxicity and inhibition of three pharmaceutical compounds (caffeine, sulfamethoxazole and carbamazepine) on two cultures of microbial consortia enriched from wastewater aerobic activated sludge. One of them was acclimated to pharmaceuticals and the other was non-acclimated as control bioassay. The toxic and inhibitory effects on these cultures were assessed by respirometric tests through the oxygen uptake rate as an indicator of their capacity to degrade a readily available carbon source. Higher values of toxicity and inhibition of pharmaceutical compounds were observed for the control culture as compared to the acclimated one. Sulfamethoxazole and carbamazepine exhibited higher toxicity and inhibition effects than caffeine in both acclimated and control cultures. The microbial diversity of the two cultures was also studied. The composition of microbial community of acclimated and control cultures, was determined by targeting the 16S ribosomal RNA gene. It was observed that Proteobacteria was the most abundant phylum, with Gammaproteobacteria dominating both cultures. Control culture was dominated by Gammaproteobacteria and mostly by the genera Pseudomonas and Sodalis, which belong to common families present in wastewater. Results suggested that the acclimated culture to the three pharmaceuticals was mostly comprised of the extremely multiresistant genera Escherichia-Shigella (38%) of Gammaproteobacteria, resulting to higher resistance as compared to the control culture (Escherichia-Shigella, 7%). Finally, the microbial structure of the microorganisms present in a real bioreactor, which was initially seeded with the acclimated culture and fed in a continuous mode with the selected pharmaceuticals, was also analyzed. The continuous loading of pharmaceuticals in the bioreactor affected its microbial diversity, leading to the dominance of Betaproteobacteria and to the resistant genus Rhizobium of Alphaproteobacteria.

Treatment of tapioca processing wastewater in a sequencing batch reactor: Mechanism of granule formation and performance

The formation of aerobic granular sludge was carried out in a sequencing batch reactor (SBR) for tapioca processing wastewater treatment. The effect of organic loading rates (OLRs) in the range of 2.5-10.0 kg COD m^-3 day^-1 on the granulation was investigated. The size and settleability of the aerobic granular sludge increased with increasing OLR from 2.5 to 7.5 kg COD m^-3 day^-1. The mature granules had an average size of 2.5 mm and good settleability with the sludge volume index (SVI) lower than 50 mL g^-1. The granules had a layered structure consisting of anoxic sludge core with nematodes and an outer aerobic layer surrounded by stalked ciliates. Removal efficiencies of chemical oxygen demand (COD) and NH₄⁺-N reached 90.0%-93.0% and 86.6%-92.5%, respectively. Simultaneous nitrification and denitrification at the OLR of 7.5 kg COD m^-3 day^-1 resulted in the improvement of total nitrogen (TN) removal efficiency to 66.1%.

Sewage Sludge Microbial Structures and Relations to Their Sources, Treatments, and Chemical Attributes

Sewage sludges generation and their disposal have become one of the greatest challenges of the 21st century. They have great microbial diversity that may impact wastewater treatment plant (WWTP) efficiency and soil quality whether used as fertilizers. Therefore, this research aimed to characterize microbial community diversity and structure of 19 sewage sludges from São Paulo, Brazil, as well as to draw their relations to sludge sources [domestic and mixed (domestic+industrial)], biological treatments (redox conditions and liming), and chemical attributes, using molecular biology as a tool. All sludges revealed high bacterial diversity, but their sources and redox operating conditions as well as liming did not consistently affect bacterial community structures. Proteobacteria was the dominant phylum followed by Bacteroidetes and Firmicutes; whereas Clostridium was the dominant genus followed by Treponema, Propionibacterium, Syntrophus, and Desulfobulbus. The sludge samples could be clustered into six groups (C1 to C6) according their microbial structure similarities. Very high pH (≥11.9) was the main sludge attribute segregating C6, that presented very distinct microbial structure from the others. Its most dominant genera were Propionibacterium > > Comamonas > Brevundimonas > Methylobacterium ∼Stenotrophomonas ∼Cloacibacterium. The other clusters' dominant genera were Clostridium > > Treponema > Desulfobulbus ∼Syntrophus. Moreover, high Fe and S were important modulators of microbial structure in certain sludges undertaking anaerobic treatment and having relatively low N-Kj, B, and P contents (C5). However, high N-Kj, B, P, and low Fe and Al contents were typical of domestic, unlimed, and aerobically treated sludges (C1). In general, heavy metals had little impact on microbial community structure of the sludges. However, our sludges shared a common core of 77 bacteria, mostly Clostridium, Treponema, Syntrophus, and Comamonas. They should dictate microbial functioning within WWTPs, except by SS12 and SS13.

Assessment of Microbial Community Structure and Function in Serially Passaged Wastewater Electro-Bioreactor Sludge: An Approach to Enhance Sludge Settleability

Several studies have been carried out to understand bulking phenomena and the importance of environmental factors on sludge settling characteristics. The main objective of this study was to carry out functional characterization of microbial community structure of wastewater electro-bioreactor sludge as it undergoes serial passaging in the presence or absence of a current density over 15 days. Illumina MiSeq sequencing and QIIME were used to assess sludge microbial community shifts over time. (α) and (β) diversity analysis were conducted to assess the microbial diversity in electro-bioreactors. A phylogeny-based weighted UniFrac distance analysis was used to compare between bacterial communities while BIO-ENV trend and Spearman’s rank correlation analysis were performed to investigate how reactor operational parameters correlated with bacterial community diversity. Results showed that the removal efficiency of soluble chemical oxygen demand (sCOD) ranged from 91–97%, while phosphorous (PO₄³⁻-P) removal was approximately 99%. Phylogenetic analysis revealed stark differences in the development of sludge microbial communities in the control and treatment reactor. There was no mention of any studies aimed at characterizing functional microbial communities under electric field and the results communicated here are the first, to our knowledge, that address this gap in the literature.

Variation of antibiotics in sludge pretreatment and anaerobic digestion processes: Degradation and solid-liquid distribution

Degradation and solid-liquid distribution of antibiotics in three sludge pretreatments (ultrasonic, alkaline and thermal hydrolysis pretreatment) and subsequent anaerobic digestion processes were investigated. The contamination of fluoroquinolones (FQs) was most serious in the raw sludge, while sulfonamides (SAs) were negligible. Obvious solubilization of antibiotics was observed after sludge pretreatments. The intracellular antibiotics were released after thermal hydrolysis pretreatment, meanwhile tetracyclines (TCs) were thermally decomposed. Compared to TCs and macrolides (MLs), FQs were hardly degraded in anaerobic digestion with removal efficiencies lower than 42.02%, and the residual FQs were mostly adsorbed on the digested sludge. The limiting step for FQs reduction was the biodegradation, rather than desorption of adsorbed antibiotics. Addition of pretreatments had no obvious effect on the degradation and distribution of antibiotics in the anaerobic digested sludge, except that the thermal hydrolysis enhanced the migration of antibiotics to the liquid phase.

Improvement of sulfamethoxazole (SMX) elimination and inhibition of formations of hydroxylamine-SMX and N4-acetyl-SMX by membrane bioreactor systems

Sulfamethoxazole (SMX) has frequently been detected in aquatic environments. In natural environment, not only individual microorganism but also microbial consortia are involved in some biotransformation of pollutants. The competition for space under consortia causing cell-cell contact inhibition changes the cellular behaviors. Herein, the membrane bioreactor system (MBRS) was applied to improve SMX elimination thorough exchanging the cell-free broths (CFB). The removal efficiency of SMX was increased by more than 24% whether under the pure culture of A. faecalis or under the co-culture of A. faecalis and P. denitrificans with MBRS. Meanwhile, MBRS significantly inhibited the formation of HA-SMX, and Ac-SMX from parent compound. Additionally, the cellular growth under MBRS was obviously enhanced, indicating that the increases in the cellular growth under MBRS are possibly related to the decreases in the levels of HA-SMX and Ac-SMX compared to that without MBRS. The intracellular NADH/NAD⁺ ratios of A. faecalis under MBRS were increased whether thorough itself-recycle of CFB or exchanging CFB between the pure cultures of A. faecalis and P. denitrificans, suggesting that the enhancement in the bioremoval efficiencies of SMX under MBRS by A. faecalis is likely related to the increases in the NADH/NAD⁺ ratio. Taken together, the regulation of cell-to-cell communication is preferable strategy to improve the bioremoval efficiency of SMX.

Integration of aerobic granular sludge and membrane bioreactors for wastewater treatment

Environmental deterioration together with the need for water reuse and the increasingly restrictive legislation of water quality standards have led to a demand for compact, efficient and less energy consuming technologies for wastewater treatment. Aerobic granular sludge and membrane bioreactors (MBRs) are two technologies with several advantages, such as small footprint, high-microbial density and activity, ability to operate at high organic- and nitrogen-loading rates, and tolerance to toxicity. However, they also have some disadvantages. The aerobic granular sludge process generally requires post-treatment in order to fulfill effluent standards and MBRs suffer from fouling of the membranes. Integrating the two technologies could be a way of combining the advantages and addressing the main problems associated with both processes. The use of membranes to separate the aerobic granules from the treated water would ensure high-quality effluents suitable for reuse. Moreover, the use of granular sludge in MBRs has been shown to reduce fouling. Several recent studies have shown that the aerobic granular membrane bioreactor (AGMBR) is a promising hybrid process with many attractive features. However, major challenges that have to be addressed include how to achieve granulation and maintain granular stability during continuous operation of reactors. This paper aims to review the current state of research on AGMBR technology while drawing attention to relevant findings and highlight current limitations.

Bacterial community dynamics within an aerobic granular sludge reactor treating wastewater loaded with pharmaceuticals

Pharmaceuticals are micropollutants often present in wastewater treatment systems. In this study, the potential impact of such micropollutants on the bacterial population within aerobic granular sludge (AGS) bioreactor was investigated. The AGS bacterial community structure and composition were accessed combining DGGE fingerprinting and barcoded pyrosequencing analysis. Both revealed the existence of a dynamic bacterial community, independently of the pharmaceuticals presence. The AGS microbiome at both phylum and class levels varied over time and, after stopping pharmaceuticals feeding, the bacterial community did not return to its initial composition. Nevertheless, most of the assigned OTUs were present throughout the different operational phases. This core microbiome, represented by over 72% of the total sequences in each phase, probably played an important role in biological removal processes, avoiding their failure during the disturbance period. Quantitative-PCR revealed that pharmaceuticals load led to gradual changes on the abundance of ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB) and polyphosphate-accumulating organisms (PAO) but their persistence during that phase demonstrated the resilience of such bacterial groups. AGS microbiome changed over time but a core community was maintained, probably ensuring the accomplishment of the main biological removal processes.

Effect of residual H2O2 from advanced oxidation processes on subsequent biological water treatment: A laboratory batch study

H₂O₂ residuals from advanced oxidation processes (AOPs) may have critical impacts on the microbial ecology and performance of subsequent biological treatment processes, but little is known. The objective of this study was to evaluate how H₂O₂ residuals influence sand systems with an emphasis on dissolved organic carbon (DOC) removal, microbial activity change and bacterial community evolution. The results from laboratory batch studies showed that 0.25 mg/L H₂O₂ lowered DOC removal by 10% while higher H₂O₂ concentrations at 3 and 5 mg/L promoted DOC removal by 8% and 28%. A H₂O₂ dosage of 0.25 mg/L did not impact microbial activity (as measured by ATP) while high H₂O₂ dosages, 1, 3 and 5 mg/L, resulted in reduced microbial activity of 23%, 37% and 37% respectively. Therefore, DOC removal was promoted by the increase of H₂O₂ dosage while microbial activity was reduced. The pyrosequencing results illustrated that bacterial communities were dominated by Proteobacteria. The presence of H₂O₂ showed clear influence on the diversity and composition of bacterial communities, which became more diverse under 0.25 mg/L H₂O₂ but conversely less diverse when the dosage increased to 5 mg/L H₂O₂. Anaerobic bacteria were found to be most sensitive to H₂O₂ as their growth in batch reactors was limited by both 0.25 and 5 mg/L H₂O₂ (17-88% reduction). In conclusion, special attention should be given to effects of AOPs residuals on microbial ecology before introducing AOPs as a pre-treatment to biological (sand) processes. Additionally, the guideline on the maximum allowable H₂O₂ concentration should be properly evaluated.

Impact of selected non-steroidal anti-inflammatory pharmaceuticals on microbial community assembly and activity in sequencing batch reactors

This study covers three widely detected non-steroidal anti-inflammatory pharmaceuticals (NSAIDs), diclofenac (DCF), ibuprofen (IBP) and naproxen (NPX), as NSAIDs pollutants. The objective is to evaluate the impact of NSAIDs at their environmental concentrations on microbial community assembly and activity. The exposure experiments were conducted under three conditions (5 μg L^-1 DCF, 5 μg L^-1 DCF+5 μg L^-1 IBP and 5 μg L^-1 DCF+5 μg L^-1 IBP+ 5 μg L^-1 NPX) in sequencing batch reactors (SBRs) for 130 days. Removals of COD and NH₄⁺-N were not affected but total nitrogen (TN) removal decreased. IBP and NPX had the high removal efficiencies (79.96% to 85.64%), whereas DCF was more persistent (57.24% to 64.12%). In addition, the decreased removals of TN remained the same under the three conditions (p > 0.05). The results of oxidizing enzyme activities, live cell percentages and extracellular polymeric substances (EPS) indicated that NSAIDs damaged the cell walls or microorganisms and the mixtures of the three NSAIDs increased the toxicity. The increased Shannon-Wiener diversity index suggested that bacterial diversity was increased with the addition of selected NSAIDs. Bacterial ribosomal RNA small subunit (16S) gene sequencing results indicated that Actinobacteria and Bacteroidetes were enriched, while Micropruina and Nakamurella decreased with the addition of NSAIDs. The enrichment of Actinobacteria and Bacteroidetes indicated that both of them might have the ability to degrade NSAIDs and thereby could adapt well with the presence of NSAIDs.

Aerobic Granular Sludge

Aerobic Granular Sludge (AGS) has been successfully applied for carbon, nitrogen and phosphorous removal from wastewaters, in a single tank, reducing the space and energy requirements. This is especially beneficial for, often space restricted, industrial facilities. Moreover, AGS holds a promise for the toxic pollutants removal, due to its layered and compact structure and the bacteria embedding in a protective extracellular polymeric matrix. These outstanding features contribute to AGS tolerance to toxicity and stability. Strategies available to deal with toxic compounds, namely granulation with effluents containing toxics and bioaugmentation, are addressed here. Different applications for the toxics/micropollutants removal through biosorption and/or biodegradation are presented, illustrating the technology versatility. The anthropogenic substances effects on system performance and bacterial populations established within AGS are also addressed. Combination of contaminants removal to allow water discharge, and simultaneous valuable products recovery are presented as final remark.

Seasonal variations in fate and removal of trace organic chemical contaminants while operating a full-scale membrane bioreactor

Trace organic chemical (TrOC) contaminants are of concern for finished water from water recycling schemes because of their potential adverse environmental and public health effects. Understanding the impacts of seasonal variations on fate and removal of TrOCs is important for proper operation, risk assessment and management of treatment systems for water recycling such as membrane bioreactors (MBRs). Accordingly, this study investigated the fate and removal of a wide range of TrOCs through a full-scale MBR plant during summer and winter seasons. TrOCs included 12 steroidal hormones, 3 xeno-estrogens, 2 pesticides and 23 pharmaceuticals and personal care products. Seasonal differences in the mechanisms responsible for removing some of the TrOCs were evident. In particular the contribution of biotransformation and biomass adsorption to the overall removal of estrone, bisphenol A, 17β-estradiol and triclosan were consistently different between the two seasons. Substantially higher percentage removal via biotransformation was observed during the summer sampling period, which compensated for a reduction in removal attributed to biomass adsorption. The opposite was observed during winter, where the contribution of biotransformation to the overall removal of these TrOCs had decreased, which was offset by an improvement in biomass adsorption. The exact mechanisms responsible for this shift are unknown, however are likely to be temperature related as warmer temperatures can lower sorption efficiency, yet enhance biotransformation of these TrOCs.