Soluble microbial products in membrane bioreactors in the presence of ZnO nanoparticles

Unveiling the spatiotemporal dynamics of membrane fouling: A focused review on dynamic fouling characterization techniques and future perspectives

Membrane technology has emerged as a crucial method for obtaining clean water from unconventional sources in the face of water scarcity. It finds wide applications in wastewater treatment, advanced treatment, and desalination of seawater and brackish water. However, membrane fouling poses a huge challenge that limits the development of membrane-based water treatment technologies. Characterizing the dynamics of membrane fouling is crucial for understanding its development, mechanisms, and effective mitigation. Instrumental techniques that enable in situ or real-time characterization of the dynamics of membrane fouling provide insights into the temporal and spatial evolution of fouling, which play a crucial role in understanding the fouling mechanism and the formulation of membrane control strategies. This review consolidates existing knowledge about the principal advanced instrumental analysis technologies employed to characterize the dynamics of membrane fouling, in terms of membrane structure, morphology, and intermolecular forces. Working principles, applications, and limitations of each technique are discussed, enabling researchers to select appropriate methods for their specific studies. Furthermore, prospects for the future development of dynamic characterization techniques for membrane fouling are discussed, underscoring the need for continued research and innovation in this field to overcome the challenges posed by membrane fouling.

Concurrent removal of carbon and nutrients in a one-stage dual internal circulation airlift A2O bioreactor from milk processing industrial wastewater: Process optimization, sludge characteristics and operating cost evaluation

In this work, a one-stage dual internal circulation airlift anaerobic/anoxic/aerobic (DCAL-A2O) bioreactor was continuously operated for concurrent removal of nutrients and organics from milk processing wastewater (MPW). Special configuration of the airlift A2O bioreactor created possibility of the formation of desired anaerobic, anoxic and aerobic zones in a single unit. The process functionality of the bioreactor was examined under three influential operating variables i.e. hydraulic retention time (HRT; 7-15 h), air flow rate (AFR; 1-3 L/min) and aerobic volume ratio (AVR; 0.324-0.464). The optimum region was identified at HRT of 13h, AFR of 2L/min and AVR of 0.437, leading to TCOD, TN and TP removal efficiency of 94.5 %, 59.6 %, and 62.2 %, respectively, and effluent turbidity of 8 NTU. The impact of feed biodegradability on the process performance of the bioreactor treating the MPW, soft drink wastewater (SDW) and soybean oil plant wastewater (SOW) was also assessed. From the results, the feed characteristics affected significantly the nutrients removal. Moreover, the feeding location played an effective role in the nutrient removal while treating the MPW at optimum operating conditions. In this study, the change in residual organic matters as soluble microbial products (SMP) was monitored at various operating conditions. In addition, the impact of SMP extracted from sludge, extracellular polymeric substances (EPS) comprising of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) was analyzed on sludge characteristics as bio-flocculation and settleability properties. According to the obtained data, the increase in operating variables led to the reduction in contents of effluent SMP, sludge SMP, LB-EPS, turbidity, and SVI, thereby, the enhancement in the sludge characteristics. Meanwhile, analysis of microbial communities verified the presence of various functional bacterial species. The cost operating evaluation confirmed the cost effectiveness of the airlift A2O bioreactor in reduction of energy consumption for the MPW treatment.

Impacts of draw solutes on the fate of tetracycline in an osmotic membrane bioreactor: Role of the combination between membrane fouling and microorganisms

Osmotic membrane bioreactors (OMBRs) are considered a suitable technology for treating wastewater containing tetracycline due to their high rejection and biodegradation efficiency. However, the impact of membrane fouling layer (i.e., chemical composition, microbial composition, and formation) on the filtration and biodegradation of tetracycline is still unclear. Herein, the effects of draw solute concentration and type on the formation of a membrane fouling layer for tetracycline filtration and its relationship with microbial activity were investigated. The results showed that over 99% of tetracycline was retained on the feed side by membrane rejection, and the fouling layer played an important role in tetracycline filtration. Specifically, membrane foulants resulted in a more hydrophilic membrane facilitating tetracycline filtration, while the tetracycline-degrading genera from the fouled membrane promoted tetracycline degradation. The structure equation model showed that tetracycline filtration dominated by electrostatic repulsion between tetracycline and the fouled membrane was more important than tetracycline degradation for tetracycline removal (path coefficient of 0.655 vs. 0.395). This study provided insights into the combined effect of membrane foulants and microorganisms on tetracycline removal.

Enhanced permeation performance of biofiltration-facilitated gravity-driven membrane (GDM) systems by in-situ application of UV and VUV: Comprehensive insights from thermodynamic and multi-omics perspectives

Biofouling is a major challenge limiting the practical application of biofiltration-facilitated gravity-driven membrane (GDM) systems in drinking water treatment. In this study, ultraviolet irradiation, including ultraviolet (UV) and vacuum ultraviolet (VUV) irradiation, was used for in-situ purification of membrane tanks to control membrane biofouling. After using UV and VUV, the permeate flux increased significantly by 26.1% and 78.3%, respectively, which was mainly due to the decreased cake layer resistance (Rc). The permeability of the biofouling layer improved after UV and VUV application, as evidenced by the increased surface porosity and decreased thickness. The contents of loosely bound extracellular proteins (LB-PN) and tightly bound extracellular proteins (TB-PN) in the biofouling layer were reduced after UV and VUV irradiation. The decreased LB-PN and TB-PN improved the interfacial free energy between the fouling itself and between the fouling and the membrane, which contributed to the reduction of interfacial cohesion and adhesion, resulting in a looser and thinner biofouling layer and a cleaner membrane. The concentration of protein-like material in the membrane tank decreased after UV and VUV irradiation, significantly altering the bacterial community structure on the membrane surface (Mantel's r > 0.7, p < 0.05). The changes in the metabolic state were responsible for the differences in the LB-PN and TB-PN contents. The inhibition of "Alanine, aspartate and glutamate metabolism" and "Glycine, serine and threonine metabolism" reduced amino acid biosynthesis, which restricted the secretion of LB-PN and TB-PN. Critical genera in the Proteobacteria phylum, such as Hirschia, Rhodobacter, Nordella, Candidatus_Berkiella, and Limnohabitans, were involved in metabolite transformation. Overall, the in-situ application of UV and VUV can be an effective alternative strategy to mitigate membrane biofouling, which would facilitate the practical application of biofiltration-facilitated GDM systems in drinking water treatment.

Acute impact of salinity and C/N ratio on the formation and properties of soluble microbial products from activated sludge

The present study investigated the shock of NaCl and C/N ratio on properties of soluble microbial products (SMPs), focusing on their sized fractions. The results indicated that the NaCl stress increased the content of biopolymers, humic substances, building blocks, and LMW substances in SMPs, while the addition of 40 g NaCl L^-1 significantly changed their relative abundance in SMPs. The acute impact of both N-rich and N-deficient conditions accelerated the secretion of SMPs, but the characteristics of LMW substances differed. Meanwhile, the bio-utilization of SMPs has been enhanced with the increase of NaCl dosage but decreased with the increase of the C/N ratio. The mass balance of sized fractions in SMPs + EPS could be set up when NaCl dosage <10 g/L and C/N ratio >5, which indicates the hydrolysis of sized fractions in EPS mainly compensated for their increase/reduction in SMPs. Besides, the results of the toxic assessment indicated that the oxidative damage caused by the NaCl shock was an important factor affecting the property of SMPs, and the abnormal expression of DNA transcription cannot be neglected for bacteria metabolisms with the change of C/N ratio.

Impacts of metal stress on extracellular microbial products, and potential for selective metal recovery

Harnessing microbial capabilities for metal recovery from secondary waste sources is an eco-friendly and sustainable approach for the management of metal-containing wastes. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are the two main groups of extracellular compounds produced by microorganisms in response to metal stress that are of great importance for remediation and recovery of metals. These include various high-, and low, molecular weight components, which serve various functional and structural roles. These compounds often contain functional groups with metal binding potential that can attenuate metal stress by sequestering metal ions, making them less bioavailable. Microorganisms can regulate the content and composition of EPS and SMP in response to metal stress in order to increase the compounds specificity and capacity for metal binding. Thus, EPS and SMP represent ideal candidates for developing technologies for selective metal recovery from complex wastes. To discover highly metal-sorptive compounds with specific metal binding affinity for metal recovery applications, it is necessary to investigate the metal binding affinity of these compounds, especially under metal stressed conditions. In this review we critically reviewed microbial EPS and SMP production as a response to metal stress with a particular emphasis on the metal binding properties of these compounds and their role in altering metal bioavailability. Furthermore, for the first time, we compiled the available data on potential application of these compounds for selective metal recovery from waste streams.

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes

Soluble microbial products (SMPs), dissolved organic matter excreted by activated sludge, can interact with antibiotics in wastewater and natural water bodies. Interactions between SMPs and antibiotics can influence antibiotic migration, transformation, and toxicity but the mechanisms involved in such interactions are not fully understood. In this study, integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic, trimethoprim (TMP), which has a low biodegradation rate and has been detected in wastewater. The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances (based on the total dissolved organic carbon concentration) so would have contained sites that could interact with TMP. A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed (R²>0.99), indicating that the fluorescence enhancement between SMP and TMP occurred. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl, carbonyl, and hydroxyl groups were the main functional groups involved in the interactions. The electrostatic and π-π interactions were discovered by the UV-vis spectra and ¹H nuclear magnetic resonance spectra. Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory, and the results confirmed the conclusions drawn from the ¹H nuclear magnetic resonance spectra. The results help characterize SMP-TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Co-existence effect of copper oxide nanoparticles and ciprofloxacin on simultaneous nitrification, endogenous denitrification, and phosphorus removal by aerobic granular sludge

Nanoparticles and antibiotics are toxic to humans and ecosystems, and they inevitably coexist in the wastewater treatment plants. Hence, the co-existence effects and stress mechanism of copper (II) oxide nanoparticles (CuO NPs) and ciprofloxacin (CIP) on simultaneous nitrification, endogenous denitrification and phosphorus removal (SNEDPR) by aerobic granular sludge (AGS) were investigated here. The co-existence stress of 5 mg/L CuO NPs and 5 mg/L CIP resulted in the synergistic inhibitory effect on nutrient removal. Transformation inhibition mechanisms of carbon (C), nitrogen (N) and phosphorus (P) with CuO NPs and CIP addition were time-dependent. Furthermore, the long-term stress mainly inhibited PO₄^3--P removal by inhibiting phosphorus release process, while short-term stress mainly inhibited phosphorus uptake process. The synergistic inhibitory effect of CuO NPs and CIP may be due to the changes of physicochemical characteristics under the co-existence of CuO NPs and CIP. This further altered the sludge characteristics, microbial community structure and functional metabolic pathways under the long-term stress. Resistance genes analysis exhibited that the co-existence stress of CuO NPs and CIP induced the amplification of qnrA (2.38 folds), qnrB (4.70 folds) and intI1 (3.41 folds) compared with the control group.

Nanomaterials in membrane bioreactors: Recent progresses, challenges, and potentials

The use of nanomaterials (NMs) in the fabrication and modification of membranes as well as the coupling of nanomaterial-based processes with membrane processes have been attracted many researchers today. The NMs due to a wide range of types, different chemistry, the possibility of various kinds of functionality, different properties like antibacterial activity, hydrophilicity, and large surface area were applied to enhance the membrane properties. In the membrane bioreactors (MBRs) as a highly successful process of membrane technology in wastewater treatment, the NMs have been applied for improving the efficiency of MBR process. This review assessed the application of NMs both as the modifiers of membrane and as the effective part of hybrid techniques with MBR system for wastewater treatment. The efficiency of NMs blended membranes in the MBR process has been reviewed in terms of antifouling and antibacterial improvement and removal performance of the pollutants. Novel kinds of NMs were recognized and discussed based on their properties and advantages. The NMs-based photocatalytic and electrochemical processes integrated with MBR were reviewed with their benefits and drawbacks. In addition, the effect of the presence of mobilized NPs in the sludge on MBR performance was surveyed. As a result of this review, it can be concluded that nanomaterials generally improve MBR performance. The high flux and antifouling properties can be obtained by adding nanomaterials with hydrophilic and antibacterial properties to the membrane, and further studies are required for photocatalytic NMs applications. In addition, this review shows that the low amounts of NMs in the membrane structure could have an effective influence on the MBR process. Besides, since many studies in the literature are carried out at the laboratory scale, it is thought that pilot and real-scale studies should be carried out to obtain more reliable data.

From Himba indigenous knowledge to engineered Fe2O3 UV-blocking green nanocosmetics

This contribution reports on the physical properties of the natural Namibian red Ochre used by the Himba Community in a form of a formulation, so called Otjize as a skin protective and beauty cream. The morphological and crystallographic studies of this red ochre validated its nano-scaled dominating phase of rhombohedral α-Fe₂O₃ nanocrystals with an additional hydrolized oxide component in a form of γ-FeOOH. The optical investigations showed that such a red ochre exhibits an exceptional UV filtration and a significant IR reflectivity substantiating its effectiveness as an effective UV-blocking & solar heat IR reflector in support of the low skin cancer rate within the Namibian Himba community. In addition, such nanocrystals exhibited a non-negligible antibacterial response against E. Coli & S. Aurus. This study seems confirming the effectiveness of the indigenous Otjize as an effective skin UV protection cream with a sound antimicrobial efficacy against e-Coli & S-Aurus.

Influence mechanism of filling ratio on solid-phase denitrification with polycaprolactone as biofilm carrier

In this study, three up-flow fixed-bed bioreactors were constructed with three different filling ratios (filling volume/effective volume: 30%, 60% and 90%) of polycaprolactone (PCL). Above 98% of nitrate removal efficiency was achieved with low accumulations of nitrite and ammonium for each filling ratio. Low filling ratio of PCL had extensive folds and pores that favored the attachment and growth of microorganisms; however, excessive biomass restrained nitrate specific reduction rate (NaSRR). The most dominant genera were Comamonas (0.80-57.64%), Stenotrophomonas (2.59-54.39%), Acidovorax (7.32-23.55%), Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium (0.30-19.74%) and Thermomonas (0.12-14.58%). Nitrate reductase (EC 1.7.99.4), nitrite reductase (EC 1.7.2.1) and nitric oxide reductase (EC 1.7.2.5) predicted by PICRUSt2 were abundant in high influent nitrate load (NaL). According to the analysis of carbon balance model, the utilization rate (η) of PCL showed a highly positive correlation with influent NaL, indicating reducing filling ratio or HRT might be an effective measure to save cost for nitrate removal.

Recent Advances in the Rejection of Endocrine-Disrupting Compounds from Water Using Membrane and Membrane Bioreactor Technologies: A Review

Water is a critical resource necessary for life to be sustained, and its availability should be secured, appropriated, and easily obtainable. The continual detection of endocrine-disrupting chemicals (EDCs) (ng/L or µg/L) in water and wastewater has attracted critical concerns among the regulatory authorities and general public, due to its associated public health, ecological risks, and a threat to global water quality. Presently, there is a lack of stringent discharge standards regulating the emerging multiclass contaminants to obviate its possible undesirable impacts. The conventional treatment processes have reportedly ineffectual in eliminating the persistent EDCs pollutants, necessitating the researchers to develop alternative treatment methods. Occurrences of the EDCs and the attributed effects on humans and the environment are adequately reviewed. It indicated that comprehensive information on the recent advances in the rejection of EDCs via a novel membrane and membrane bioreactor (MBR) treatment techniques are still lacking. This paper critically studies and reports on recent advances in the membrane and MBR treatment methods for removing EDCs, fouling challenges, and its mitigation strategies. The removal mechanisms and the operating factors influencing the EDCs remediation were also examined. Membranes and MBR approaches have proven successful and viable to eliminate various EDCs contaminants.

Characteristics and mechanism of anammox granular sludge with different granule size in high load and low rising velocity sewage treatment

An integrated investigation to structural, activity and microbial diversity of anammox granular sludge (AnGS) in a wastewater treatment system with high ammonia nitrogen load was performed and aimed to establish the relationship between granular size and performance. With the increase in granule size, the main component of extracellular polymeric substances (EPS) changed from slime EPS to tightly-bound EPS, while the organic component remained the same, and the specific anammox activity increased. However, the results of qPCR and high-throughput sequencing showed that for granules with sizes inferior than 4.75 mm, the abundance of ammonia-oxidizing bacteria (AnAOB) increased as the size increased, and the copies of AnAOB decreased when the granule size increased above 4.75 mm, and the community complexity increased. According to the correlation analysis results, AnAOB first accumulated and then optimized the flora structure to improve efficiency and 2.8 mm to 4.75 mm was the optimal size of AnGS.

Sodium azide inhibition of microbial activities and impact on sludge floc destabilization

Absence of sludge deflocculation under prolonged (24 h or longer) conditions with dissolved oxygen (DO) less than 0.5 mg L⁻¹ was recently reported. The reduced aerobic microbial activity, was speculated, had been compensated by the activity of other bacterial (i.e. facultative) communities. To assess such a compensation mechanism and to better evaluate impact of overall microbial activity on the flocculation process, SBR sludge samples were inhibited by using sodium azide under various DO conditions. Sludge deflocculated only in the presence of sodium azide, regardless of DO conditions. This was linked to sodium azide's inhibitory effects on the microbes as indicated by the reduced ammonium and DOC removals. Extracellular potassium level in the mixed liquor of azide spiked samples also indicated simultaneous cell lysis. Fluorescence excitation emission matrix (FEEM) analysis of the extracted bound EPS and fluorescence quenching based interaction studies indicated sodium azide had interacted with the EPS components, and especially with the bound EPS proteins. The impact of such interactions on reduced floc stability needs consideration. This study confirmed the importance of overall microbial activity in the biological flocculation process and the role of bacterial communities, other than the aerobes, in mitigating deflocculation under low DO conditions.

Box-Behnken response surface approach to identify factors affecting membrane fouling in a hybrid membrane bioreactor treating domestic sewage

The effect of hydraulic retention time (HRT) and sludge retention time (SRT) on extracellular polymer substrate (EPS) content and resistance of a hybrid membrane bioreactor (HMBR) treating domestic sewage was analyzed by Box-Behnken response surface methodology. The quadratic response surface model demonstrated significant effects of both HRT and SRT on EPS content (both P value < 0.05), SRT on membrane resistance (P value = 0.0119), and their interaction was significant (P value = 0.0273) for EPS but not membrane resistance (P value = 0.0609). Model optimization indicates that the optimal conditions for the HMBR to control membrane fouling were an HRT of 10 h and SRT of 30 days. Under these optimal conditions, both the EPS content and the predicted membrane resistance closely matched the actual average value with the error about 8%. Thus, the feasibility of applying response surface methodology to an HMBR for treating domestic sewage was demonstrated. According to the detection result of the three-dimensional fluorescence (excitation-emission matrix), humic acid-like and fulvic acid-like substances gain much higher levels in the suspended carriers than those in the membrane and sludge, suggesting that these are key components of the membrane pollutants. Graphical abstract .

Physicochemical and Biological Effects on Activated Sludge Performance and Activity Recovery of Damaged Sludge by Exposure to CeO2 Nanoparticles in Sequencing Batch Reactors

Recently, the growing release of CeO₂ nanoparticles (CeO₂ NPs) into sewage systems has attracted great concern. Several studies have extensively explored CeO₂ NPs' potential adverse impacts on wastewater treatment plants; however, the impaired activated sludge recovery potentials have seldom been addressed to date. To explore the physicochemical and biological effects on the activated sludge performance and activity recovery of damaged sludge by exposure to CeO₂ NPs in sequencing batch reactors (SBRs), four reactors and multiple indicators including water quality, key enzymes, microbial metabolites, the microbial community structure and toxicity were used. Results showed that 10-week exposure to higher CeO₂ NP concentration (1, 10 mg/L) resulted in a sharp decrease in nitrogen and phosphorus removal efficiencies, which were consistent with the tendencies of key enzymes. Meanwhile, CeO₂ NPs at concentrations of 0.1, 1, and 10 mg/L decreased the secretion of tightly bound extracellular polymeric substances to 0.13%, 3.14%, and 28.60%, respectively, compared to the control. In addition, two-week recovery period assays revealed that the functional bacteria Proteobacteria, Nitrospirae and Planctomycetes recovered slightly at the phyla level, as analyzed through high-throughput sequencing, which was consistent with the small amount of improvement of the effluent performance of the system. This reflected the small possibility of the activity recovery of damaged sludge.

Nitrogen removal in a combined aerobic granular sludge and solid-phase biological denitrification system: System evaluation and community structure

In the present study, the feasibility of treating high ammonia wastewater was evaluated in a combination of aerobic granular sludge nitrification reactor (AGS-SBR) and poly(butylene succinate) solid denitrification reactor (PBS-SBR). After 90 days operation, the effluent NH₄⁺-N and total nitrogen (TN) removal efficiencies were high of 99.6% and 99.7%, respectively. According to typical cycle, N₂O emission rate in AGS nitrification process was much higher than PBS denitrification process. It was found from EEM-PARAFAC that the fluorescence intensity scores (protein-like and humic like substances) of soluble microbial products (SMP) in AGS-SBR were the significant higher than in PBS-SBR. Microbial community analysis showed that Thauera was main genus in AGS-SBR and Hydrogenophaga Simplicispira and Thiomonas were dominant genus in PBS-SBR. The obtained result implied that the combined technology is feasible to remove nitrogen compounds from wastewater to meet the stringent emission standards.

Deciphering the evolution characteristics of extracellular microbial products from autotrophic and mixotrophic anammox consortia in response to nitrogen loading variations

Extracellular microbial products (EMP) in biological wastewater treatment systems vary with operational conditions and in turn indicate the metabolic status of functional bacteria. In this study, the response of EMP from autotrophic and mixotrophic anammox consortia (AAC and MAC) to the variation of total nitrogen loading rates (TNLR) were investigated as well as their correlations with the community evolution. The variation of TNLR showed a significantly negative correlation with the production of bound microbial products (BMP) but a significantly positive correlation with the production of soluble microbial products (SMP). The presence of organic matters with COD/TN ratio of 0.15 limited the abundance of anammox bacteria in MAC at the full-load phase and suppressed their proliferation at the restart phase. Due to the improved abundance of carbohydrate metabolism genes, MAC with lower abundance of anammox bacteria produced lower soluble polysaccharides than AMC at the full-load phase. Furthermore, four components (C1-4) were identified on the excitation-emission matrix fluorescence spectra of SMP using parallel factor analysis. C1 exhibited a relative higher proportion at the full-load phase, whereas C4 was generated only at the light-load phase or empty-load phase. At the restart phase, C2 and C3 appeared simultaneously and accounted for a high proportion. The information of four components also suggested the metabolic status of AC as revealed by the specific anammox activity, which therefore provided a novel complementary but direct approach for monitoring the operation status of anammox bioreactors.

Applications of membrane bioreactors for water reclamation: Micropollutant removal, mechanisms and perspectives

Membrane bioreactors (MBRs) have attracted attention in water reclamation as a result of the recent technical advances and cost reduction in membranes. However, the increasing occurrence of micropollutants in wastewaters has posed new challenges. Therefore, we reviewed the current state of research to identify the outstanding needs in this field. In general, the fate of micropollutants in MBRs relates to sorption, biodegradation and membrane separation processes. Hydrophobic, nonionized micropollutants are favorable in sorption, and the biological degradation shows higher efficiency at relatively long SRTs (30-40 days) and HRTs (20-30 h), as a result of co-metabolism, metabolism and/or ion trapping. Although the membrane rejection rates for micropollutants are generally minor, final water quality can be improved via combination with other technologies. This review highlights the challenges and perspectives that should be addressed to facilitate the extended use of MBRs for the removal of micropollutants in water reclamation.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

Over the years, different types of alternative technologies have been developed and used for palm oil mill effluent (POME) treatment. Specifically, membrane bioreactor (MBR) has been employed to relegate pollutants contained in POME under different operating conditions, and the technology was found to be promising. The major challenge impeding the wider application of this technology is membrane fouling, which usually attracts high operating energy and running cost. In this regard, novel methods of mitigating membrane fouling through the treatment processes have been developed. Therefore, this review article specifically focuses on the recent treatment processes of POME using MBR, with particular emphasis on innovative processes conditions such as aerobic, anaerobic, and hybrid processing as well as their performance in relation to fouling minimization. Furthermore, the effects of sonication and thermophilic and mesophilic conditions on membrane blockage were critically reviewed. The types of foulants and fouling mechanism as influenced by different operating conditions were also analyzed censoriously.

Microbial responses to transient shock loads of quaternary ammonium compounds with different length of alkyl chain in a membrane bioreactor

Extensive applications of quaternary ammonium compounds (QACs) in household and industrial products inevitably lead to their release into wastewaters; however, little attention has been paid to the acute effects on activated sludge. In this work, we investigated the responses of microorganisms in a membrane bioreactor (MBR) to transient shock loads of QACs with different alkyl chain length and their impacts on MBR performance. Results showed that QACs affected microbial viability and caused damage to key enzymes (e.g., ammonium monooxygenase and nitrite oxidoreductase), inhibiting organic matter degradation and nitrogen removal. The presence of QACs also caused negative influences on dehydrogenase activity, catalase and superoxide dismutase, thus increasing the production of reactive oxygen species. Moreover, QACs with longer alkyl chains and/or benzyl groups bonded to the nitrogen atom could induce a more severe damage to cell integrity and microbial viability. The interaction with QACs also induced the release of organic matters and the changes of adhesion properties of microbial products, resulting in aggravated membrane fouling in MBRs. Our results demonstrate the acute negative effects of QACs on activated sludge, and special attention should be paid to the performance of biological wastewater treatment processes subject to the shock loads of QAC-bearing industrial streams.

Influence of elevated Zn (II) on Anammox system: Microbial variation and zinc tolerance

Nitrogen removal by anaerobic ammonium oxidation (Anammox) has attracted increasing attention in nowadays. An Anammox biofilter was subjected to a continuous loading of elevated Zn (II). The influence of Zn (II) on the nitrogen removal, microbial community and biofilm property was investigated in the condition of 23-26 °C and 3.5 h HRT. The nitrogen removal greatly decreased to 0.054 from the initial 0.502 kg m^-3 d^-1, with the Zn (II) addition. Anaerobic ammonia-oxidizing bacteria (AAOB) had self-adaption to Zn (II) in 1-10 mg L^-1 and was significantly enhanced after long-term acclimatization, while the suppression threshold was 20 mg L^-1. Soluble microbial products (SMP) increased correspondingly with Zn (II), while extracellular polymeric substance (EPS) climbed up initially and then decreased. Anammox biofilm performed the highest zinc adsorption as 158.27 mg g^-1 SS in biofilm. High Zn (II) improved the microbial diversity and lowered the Candidatus Kuenenia abuandance to 1.38% from 20.89%.

Production of soluble microbial products in aerobic granular sludge system under the stress of toxic 4-chlorophenol

The purpose of this study was to evaluate the effect of toxic 4-chlorophenol (4-CP) on the production of soluble microbial products (SMP) in an aerobic granular sludge system. Compared with the control experiment, [Formula: see text] removal efficiency generally reduced by 37.90% after the exposure of 4-CP of 10 mg L^-1, indicating that 4-CP had a toxic effect on the performance of biological nitrification. Meanwhile, the contents of polysaccharides and proteins (PN) of SMP increased from 31.0 ± 0.32 and 0.8 ± 0.12 mg L^-1 to 39.0 ± 0.56 and 61.70 ± 0.78 mg L^-1, respectively. Specific oxygen uptake rate (SOUR) showed that the values of (SOUR)_H, [Formula: see text]and [Formula: see text] reduced by 27%, 48% and 41% in the presence of 4-CP. The characteristic and chemical components of SMP were assessed by using three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra, two-dimensional correlation spectroscopy (2D-COS), scanning electron microscope and Fourier transform infrared spectroscopy . 3D-EEM implied that SMP were mainly composed of tryptophan PN-like, aromatic PN-like and humic acid-like substances after 4-CP exposure. Synchronous fluorescence spectra coupled with 2D-COS suggested that SMP samples changed in the following sequences: PN-like substances > humic acid-like substances in the absence of 4-CP, and shorter wavelength > longer wavelength in PN-like substances in the presence of 4-CP.

Response of anaerobic membrane bioreactor to the presence of nano-Bi2WO6: reactor performance, supernatant characteristics, and microbial community

Considering the increasing incorporation of manufactured nano-material into consumer products, there is a concern about its potential impacts in biological wastewater treatment. In this study, the response of anaerobic sludge to the presence of Bi₂WO₆ nano-particles (NPs) was investigated in the anaerobic membrane bioreactor (AnMBR). As the concentration of Bi₂WO₆ in the reactor was controlled around 1 mg/L, there was no significant difference in effluent water quality or bacterial activities before and after NP exposure, partially due to the microbial-induced NP aggregation and stable complex formation. However, with the increasing dosage of Bi₂WO₆ from 5 to 40 mg/L, great influences on the AnMBR performance were observed, including the reduction of COD removal efficiency, inhibition of the mechanization step, increased production of soluble microbial products, and enhanced secretion of extracellular polymer substrates. Additional investigation with high-throughput sequencing was conducted, clearly demonstrating that Bi₂WO₆ NPs induced changes in the bacterial community.

Spectroscopic descriptors for dynamic changes of soluble microbial products from activated sludge at different biomass growth phases under prolonged starvation

In this study, the spectroscopic indices of soluble microbial products (SMP) were explored using absorption and fluorescence spectroscopy to identify different distinctive biomass growth phases (i.e., exponential phase, pseudo-endogenous phase, and endogenous phase) and to describe the microbial activity of activated sludge in a batch type bioreactor under prolonged starvation. The optical descriptors, including UV absorption at 254 nm (UVA254), spectral slope, absorbance slope index (ASI), biological index (BIX), humification index (HIX), and the ratio of tryptophan-like to humic-like components (C1/C2), were examined to describe the dynamic changes in SMP. These indices were mostly associated with dissolved organic carbon (DOC) of SMPs and specific oxygen uptake rate (SOUR). Among those, ASI was the most strongly correlated with the SOUR data for the pseudo-endogenous and the endogenous periods. Although the three microbial phases were well discriminated using the spectral slope, BIX, and the C1/C2 ratio, the C1/C2 ratio can be suggested as the most preferable indicator as it can also trace the changes of the relative abundance of proteins to humic-like substances in SMPs. The suggested spectroscopic descriptors were reasonably explained by the general trends of decreased large-sized biopolymer fractions (e.g., proteins) and increased humic substrates (HS) with starvation time, which were detected by size exclusion chromatography. This study provides a novel insight into the strong potential of using optical descriptors to easily probe microbial status in biological treatment systems.

Influence of Surface Functional Groups on Deposition and Release of TiO2 Nanoparticles

A clear understanding of the factors governing the deposition and release behaviors of engineered nanoparticles (NPs), such as TiO₂ NPs, is necessary for predicting their transport and fate in both natural and engineered aquatic environments. In this study, impacts of specific chemistries on TiO₂ NP deposition, as a function of TiO₂ NP concentration and ionic strength/valence, were investigated using self-assembled monolayers (SAMs) with five different ending chemical functionalities (-CH₃, -OH, -COOH, -NH₂, and -CONH₂). The fastest deposition and maximum deposition mass were observed on -NH₂, followed by -COOH, -CONH₂, -CH₃, and -OH, showing that contact angle and zeta potential of surfaces were not good indicators for predicting the deposition. Specific interactions, for instance, between -COOH and -CONH₂ and TiO₂, significantly affected their deposition. Deposition rate increased linearly with TiO₂ NP concentration; however, specific deposition rate was dependent on the type of SAMs. The increase of monovalent (Na⁺) and divalent (Ca²⁺) led to different changes in deposition rates for the SAMs due to different functionalities. Results also showed that favorable SAM (e.g., -NH₂) had lowered release of NPs compared to unfavorable surface (e.g., -OH). The obtained deposition and release behaviors will support more accurate prediction of the environmental fate of nanoparticles.

Effect of nano-ZnO on biogas generation from simulated landfills

Extensive use of nanomaterials in commercial consumer products and industrial applications eventually leads to their release to the waste streams and the environment. Nano-ZnO is one of the most widely-used nanomaterials (NMs) due to its unique properties. It is also known to impact biological processes adversely. In this study, the effect of nano-ZnO on biogas generation from sanitary landfills was investigated. Two conventional and two bioreactor landfills were operated using real MSW samples at mesophilic temperature (35°C) for a period of about 1year. 100mg nano-ZnO/kg of dry waste was added to the simulated landfill reactors. Daily gas production, gas composition and leachate Zn concentrations were regularly monitored. A model describing the fate of the nano-ZnO was also developed. The results obtained indicated that as much as 99% of the nano-ZnO was retained within the waste matrix for both reactor operation modes. Waste stabilization was faster in simulated landfill bioreactors with and without the addition of nano-ZnO. Moreover, the presence of the nano-ZnO within the waste led to a decrease in biogas production of about 15%, suggesting that the nano-ZnO might have some inhibitory effects on waste stabilization. This reduction can have potentially significant implications on waste stabilization and the use of biogas from landfills as a renewable energy source.

Effects of ZnO nanoparticle exposure on wastewater treatment and soluble microbial products (SMPs) in an anoxic-aerobic membrane bioreactor

The effect of zinc oxide nanoparticles (ZnO NPs) on the performance of an anoxic-aerobic submerged membrane bioreactor (MBR), and the characterization of the soluble microbial products (SMPs) produced in the presence of ZnO NPs was evaluated. Continuous operation over 144 days showed that ZnO NPs at concentrations of 10 and 50 mg/L exerted a negative impact on chemical oxygen demand (COD) and nitrogen removal, although ZnO NPs were efficiently removed in the MBR (>92%). 10 and 50 mg/L ZnO NPs decreased COD removal substantially from 93.1± 0.6% to 90.1± 0.8% (<0.05) and 86.3± 2.3% (<0.05), respectively. Similarly, with 10 and 50 mg L ZnO NPs, the decreased in NH₄N removal was 8.1% and 21.1%, respectively. Exposure to 1, 10 and 50 mg/L ZnO NPs increased SMP concentrations by 12.8%, 42.4% and 51.5%, respecti. High performance size exclusion chromatograph (HP-SEC) analysis revealed that the presence of ZnO NPs caused a significant increase in high-molecular weight (MW) (583 kDa) SMPs at 1 and 10 mg/L ZnO NP concentration. A substantial decrease in the concentration of high-MW compounds in the MBR effluent was observed at the end of the experiment. Excitation emission matrix (EEM) fluorescence contours revealed that SMPs were dominated by amino acid-, tryptophan protein-, polyaromatic-, and polycarboxylate-type substances. The presence of ZnO NPs enhanced the production of amino acid-like (7.5-25.1%) and tryptophan protein-like compounds (31.7-38.1%), compared to the control (6.0-20.2% for amino acid-like compounds; and 28.5-36.7% for tryptophan protein-like compounds). In contrast, the fulvic and humic acid-like compounds decreased with exposure to ZnO NPs. This work may help better understanding the effect of nanoparticle exposure on wastewater treatment performance and SMP characteristics.

Characterization and biodegradability of sludge from a high rate A-stage contact tank and B-stage membrane bioreactor of a pilot-scale AB system treating municipal wastewaters

In light of global warming mitigation efforts, increasing sludge disposal costs, and need for reduction in the carbon footprint of wastewater treatment plants, innovation in treatment technology has been tailored towards energy self-sufficiency. The AB process is a promising technology for achieving maximal energy recovery from wastewaters with minimum energy expenditure and therefore inherently reducing excess sludge production. Characterization of this novel sludge and its comparison with the more conventional B-stage sludge are necessary for a deeper understanding of AB treatment process design. This paper presents a case study of a pilot-scale AB system treating municipal wastewaters as well as a bio- (biochemical methane potential and adenosine tri-phosphate analysis) and physico-chemical properties (chemical oxygen demand, sludge volume index, dewaterability, calorific value, zeta potential and particle size distribution) comparison of the organic-rich A-stage against the B-stage activated sludge. Compared to the B-sludge, the A-sludge yielded 1.4 to 4.9 times more methane throughout the 62-week operation.

A Fluorescence Approach to Assess the Production of Soluble Microbial Products from Aerobic Granular Sludge Under the Stress of 2,4-Dichlorophenol

In this study, a fluorescence approach was used to evaluate the production of soluble microbial products (SMP) in aerobic granular sludge system under the stress of 2,4-dichlorophenol (2,4-DCP). A combined use of three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM), Parallel factor analysis (PARAFAC), synchronous fluorescence and two-dimensional correlation spectroscopy (2D-COS) were explored to respect the SMP formation in the exposure of different doses of 2,4-DCP. Data implied that the presence of 2,4-DCP had an obvious inhibition on biological nitrogen removal. According to EEM-PARAFAC, two fluorescent components were derived and represented to the presence of fulvic-like substances and humic-like substances in Component 1 and protein-like substances in Component 2. It was found from synchronous fluorescence that protein-like peak presented slightly higher intensity than that of fulvic-like peak. 2D-COS further revealed that fluorescence change took place sequentially in the following order: protein-like fraction > fulvic-like fraction. The obtained results could provide a potential application of fluorescence spectra in the released SMP assessment in the exposure of toxic compound during wastewater treatment.

Identification of recalcitrant compounds in a pilot-scale AB system: An adsorption (A) stage followed by a biological (B) stage to treat municipal wastewater

This manuscript presents a comparison of the A-stage and B-stage sludges in terms of anaerobic biodegradability and low molecular weight compounds present in the supernatant using Gas Chromatography-Mass Spectrometry (GC-MS). The GC-MS analysis of A-stage and B-stage supernatants identified respectively 43 and 19 organic compounds consisting mainly of aromatics (27.9% and 21%), alcohols (25.6% and 15%) and acids (30.2% and 15%). The methane potential was found to be 349±1 mL CH4/g VS and 238±12 mL CH4/g VS, respectively. After anaerobic digestion of these sludges, a greater proportion of aromatics (42% and 58%) and a lower proportion of acids (10% and 10%) and alcohols (16% and 10%) was observed.

"Protein" Measurement in Biological Wastewater Treatment Systems: A Critical Evaluation

Five commercially available assay kits were tested on the same protein sample with the addition of 17 different types of interfering substances typically found in the biological wastewater treatment, and a comparison of the use of these assays with 22 different protein and peptide samples is also presented. It was shown that a wide variety of substances can interfere dramatically with these assays; the metachromatic response was also clearly influenced by different proteinaceous material. Measurement of the "protein" content in the effluent of an anaerobic membrane bioreactor was then carried out using these assay methods. Quantitative results of the "protein" concentration in the different effluent samples, with or without spiked additions of Bovine Serum Albumin (BSA), showed considerable disagreement. We concluded that the "protein" measured in wastewater samples using standard colorimetric assays often shows false positive results and has little correlation to their real value. A new analytical method needs to be developed in order to gain greater insight into the biological transformations occurring in anaerobic digestion, and how soluble microbial products (SMPs) are produced.

The impact of zinc oxide nanoparticles on phosphorus removal and the microbial community in activated sludge in an SBR

10 and 20 mg L⁻¹ ZnO NPs damaged the integrity of cell membranes and the microbial community and affected phosphorus removal.

Effects of ZnO nanoparticles on wastewater treatment and their removal behavior in a membrane bioreactor

Long-term effects of ZnO nanoparticles on the system performance of an MBR were investigated together with their removal behavior in the system. Continuous operation over 242days showed that ZnO NPs at both 1.0 and 10.0mg/L caused moderate deterioration in the removal of COD, nitrogen and phosphorus. Denitrification was affected upon the exposure but recovered subsequently. Although no significant acute effect on ammonia-oxidization was observed, permanent inhibition occurred after long-term exposure. Nitrite-oxidization was not affected even with 10.0mg/L ZnO NPs. Significant changes were observed in activated sludge properties which resulted in severe membrane fouling. Although ZnO NPs caused changes in the bacteria community structure, the diversity however remain unchanged. ZnO NPs was removed effectively in the MBR (>98%) with biosorption being a major removal mechanism. Membrane filtration also played an important role (20% of the total removal) especially at high ZnO NPs concentrations (around 10.0mg/L).

The impact of zinc oxide nanoparticles on nitrification and the bacterial community in activated sludge in an SBR

20 and 50 mg L⁻¹ of ZnO NPs affect transformation of NH₄⁺–N to NO₂⁻–N and NO₂⁻–N to NO₃⁻–N.

Analytical methods for soluble microbial products (SMP) and extracellular polymers (ECP) in wastewater treatment systems: a review

Effluents from biological processes contain a wide range of complex organic compounds, including soluble microbial products (SMP) and extracellular polymers (ECP), released during bacteria metabolism in mixed culture in bioreactors. It is important to clearly identify the primary components of SMPs and ECPs in order to understand the fundamental mechanisms of biological activity that create these compounds, and how to reduce these compounds in the effluent. In addition, these compounds constitute the main foulants in membrane bioreactors which are being used more widely around the world. A review on the extraction of ECP, characterization, and identification of SMPs and ECPs is presented, and we summarize up-to-date pretreatments and analytical methods for SMPs. Most researchers have focused more on the overall properties of SMPs and ECPs such as their concentrations, molecular weight distribution, aromaticity, hydrophobic and hydrophilic properties, biodegradability, and toxicity characteristics. Many studies on the identification of effluent SMPs show that most of these compounds were not present in the influent, such as humic acids, polysaccharides, proteins, nucleic acids, organic acids, amino acids, exocellular enzymes, structural components of cells and products of energy metabolism. A few groups of researchers have been working on the identification of compounds in SMPs using advanced analytical techniques such as GC-MS, LC-IT-TOF-MS and MALDI-TOF-MS. However, there is still considerably more work needed to be done analytically to fully understand the chemical characteristics of SMPs and ECPs.