Effects of salinity build-up on biomass characteristics and trace organic chemical removal: implications on the development of high retention membrane bioreactors

Enhancing bioremediation potential of microalgae Chlorella vulgaris and Scenedesmus acutus by NaCl for pyrene degradation

Microalgae are increasingly recognized as promising organisms for bioremediation of organic pollutants. This study investigates the potential of enhancing the bioremediation efficiency of pyrene (PYR), a polycyclic aromatic hydrocarbon (PAH), through NaCl induced physiological and biochemical alterations in two microalgae species, Chlorella vulgaris and Scenedesmus acutus. Our findings reveal significant improvement in PYR removal when these microalgae were cultivated in the presence of 0.1% NaCl where PYR removal increased from 54 to 74% for C. vulgaris and from 26 to 75% for S. acutus. However, it was observed that NaCl induced stress had varying effects on the two species. While C. vulgaris exhibited increased PYR removal, it experienced reduced growth and biomass production, as well as lower photosynthetic efficiency when exposed to PYR and PYR + NaCl. In contrast, S. acutus displayed better growth and biomass accumulation under PYR + NaCl conditions, making it a more efficient candidate for enhancing PYR bioremediation in the presence of NaCl. In addition to assessing growth and biochemical content, we also investigated stress biomarkers, such as lipid peroxidation, polyphenol and proline contents. These findings suggest that S. acutus holds promise as an alternative microalgae species for PYR removal in the presence of NaCl, offering potential advantages in terms of bioremediation efficiency and ecological sustainability. This study highlights the importance of understanding the physiological and biochemical responses of microalgae to environmental stressors, which can be harnessed to optimize bioremediation strategies for the removal of organic pollutants like PYR.

An advanced treatment process for 3-high wastewater discharged from crude oil storage tanks

The wastewater discharged from crude oil storage tanks (WCOST) contains high concentrations of salt and metal iron ions, and high chemical oxygen demand (COD). It belongs to "3-high" wastewater, which is difficult for purification. In this study, WCOST treatments were comparatively investigated via an advanced pretreatment and the traditional coagulation-microfiltration (CMF) processes. After WCOST was purified through the conventional CMF process, fouling occurred in the microfiltration (MF) membrane, which is rather harmful to the following reverse osmosis (RO) membrane unit, and the effluent featured high COD and UV254 values. The analysis confirmed that the MF fouling was due to the oxidation of ferrous ions, and the high COD and UV254 values were mainly attributable to the organic compounds with small molecular sizes, including aromatic-like and fulvic-like compounds. After the pretreatment of the advanced process consisting of aeration, manganese sand filtration, and activated carbon adsorption in combination with CMF process, the removal efficiencies of organic matter and total iron ions reached 97.3% and 99.8%, respectively. All the water indexes of the effluent, after treatment by the advanced multi-unit process, meet well the corresponding standard. The advanced pretreatment process reported herein displayed a great potential for alleviating the MF membrane fouling and enhanced the lifetime of the RO membrane system in the 3-high WCOST treatment.

Evaluation of selenite reduction under salinity and sulfate stress in anaerobic membrane bioreactor

Current microbial reduction technologies have been proven to be suitable for decontaminating industrial wastewaters containing high concentrations of selenium (Se) oxyanions, however, their application is strictly limited by the elemental Se (Se0) accumulation in the system effluents. In this work, a continuous-flow anaerobic membrane bioreactor (AnMBR) was employed for the first time to treat synthetic wastewater containing 0.2 mM soluble selenite (SeO3 2-). The SeO3 2- removal efficiency by the AnMBR was approachable to 100% in most of the time, regardless of the fluctuation in influent salinity and sulfate (SO4 2-) stress. Se0 particles were always undetectable in the system effluents, owing to their interception by the surface micropores and adhering cake layer of membranes. High salt stress led to the aggravated membrane fouling and diminished content ratio of protein to polysaccharide in the cake layer-contained microbial products. The results of physicochemical characterization suggested that the sludge-attached Se0 particles presented either sphere- or rod-like morphology, hexagonal crystalline structure and were entrapped by the organic capping layer. According to the microbial community analysis, increasing influent salinity led to the diminished population of non-halotolerant Se-reducer (Acinetobacter) and increased abundance of halotolerant sulfate reducing bacteria (Desulfomicrobium). In the absence of Acinetobacter, the efficient SeO3 2- abatement performance of the system could still be maintained, as a result of the abiotic reaction between SeO3 2- and S2- generated by Desulfomicrobium, which then gave rise to the production of Se0 and S0.

Effect of salinity on removal performance of anaerobic membrane bioreactor treating azo dye wastewater

Membrane bioreactor (MBR) is an attractive option method for treating azo dye wastewater under extreme conditions. The present study assessed the effect of salinity on the performance of anaerobic MBR in treating azo dye wastewater. Increased salinity showed adverse effects on the decolorization efficiency and chemical oxygen demand (COD) removal efficiency. The decolorization efficiency decreased from 95.8% to 82.3% and 73.1% with a stepwise increasing of salinity from 0 to 3% and 5%, respectively. The COD removal efficiency decreased from 80.7% to 71.3% when the salinity increased from 0 to 3% and then decreased to 58.6% at 5% salinity. The volatile fatty acids (VFAs) concentration also increased as the salinity increased. Furthermore, increased salinity led to the elevated production of soluble microbial products (SMP) and extracellular polymeric substances (EPS), which can provide a protective barrier against harsh environments. More serious membrane fouling was observed as the SMP and EPS concentrations increased. The concentration of loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS), and the polysaccharide/protein (PS/PN) ratios in LB-EPS and TB-EPS all increased when the salinity was elevated. The production of SMP and EPS was caused by the generation of PS in response to the saline environment. Lactobacillus, Lactococcus, Anaerosporobacter, and Pectinatus were the dominant bacteria, and Lactobacillus and Lactococcus were the decolorization bacteria in the MBR. The lack of halophilic bacteria was the main reason for the decreased decolorization efficiency in the salinity environment.

An overview of deploying membrane bioreactors in saline wastewater treatment from perspectives of microbial and treatment performance

The discharged saline wastewater has severely influenced the aquatic environment as the treatment performance of many wastewater treatment techniques is limited. In addition, the sources of saline wastewater are also plentiful from agricultural and various industrial fields such as food processing, tannery, pharmaceutical, etc. Although high salinity levels negatively impact the performance of both physicochemical and biological processes, membrane bioreactor (MBR) processes are considered as a potential technology to treat saline wastewater under different salinity levels depending on the adaption of the microbial community. Therefore, this study aims to systematically review the application of MBR widely used in the saline wastewater treatment from the perspectives of microbial structure and treatment efficiencies. At last, the concept of carbon dioxide capture and storage will be proposed for the MBR-treating saline wastewater technologies and considered toward the circular economy with the target of zero emission.

Enhanced anaerobic reduction of nitrobenzene at high salinity by betaine acting as osmoprotectant and regulator of metabolism

Anaerobic technology is extensively applied in the treatment of industrial organic wastewater, but high salinity always triggers microbial cell dehydration, causing the failure of the anaerobic process. In this work, betaine, one kind of compatible solutes which could balance the osmotic pressure of anaerobic biomass, was exogenously added for enhancing the anaerobic reduction of nitrobenzene (NB) at high salinity. Only 100 mg L^-1 betaine dosing could significantly promote the removal efficiency of NB within 35 h at 9% salinity (36.92 ± 4.02% without betaine and 72.94 ± 6.57% with betaine). The relieving effects on salt stress could be observed in the promotion of more extracellular polymeric substances (EPS) secretion with betaine addition. Additionally, the oxidation-reduction potential (ORP), as well as the electron transfer system (ETS) value, was increased with betaine addition, which was reflected in the improvement of system removal efficiency and enzyme activity. Microbial community analysis demonstrated that Bacillus and Clostridiisalibacter which were positively correlated with the stability of the anaerobic process were enriched with betaine addition at high salinity. Metagenomic analysis speculated that the encoding genes for salt tolerance (kdpB/oadA/betA/opuD/epsP/epsH) and NB degradation (nfsA/wrbA/ccdA/menC) obtained higher relative abundance with betaine addition under high salt environment, which might be the key to improving salt tolerance of anaerobic biomass. The long-term assessment demonstrated that exogenous addition betaine played an important role in maintaining the stability of the anaerobic system, which would be a potential strategy to achieve a high-efficiency anaerobic process under high salinity conditions.

Effects of Pressurized Aeration on the Biodegradation of Short-Chain Chlorinated Paraffins by Escherichia coli Strain 2

Short-chain chlorinated paraffins (SCCPs) were defined as persistent organic pollutants in 2017, and they can migrate and transform in the environment, accumulate in organisms, and amplify through the food chain. Although they pose a serious threat to environmental safety and human health, there are few papers on their removal. The current SCCP removal methods are expensive, require severe operating conditions, involve time-consuming biological treatment, and have poor removal specificities. Therefore, it is important to seek efficient methods to remove SCCPs. In this paper, a pressurized reactor was introduced, and the removal performance of SCCPs by Escherichia coli strain 2 was investigated. The results indicated that moderate pure oxygen pressurization promoted bacterial growth, but when it exceeded 0.15 MPa, the bacterial growth was severely inhibited. When the concentration of SCCPs was 20 mg/L, the removal rate of SCCPs was 85.61% under 0.15 MPa pure oxygen pressurization for 7 days, which was 25% higher than at atmospheric pressure (68.83%). In contrast, the removal rate was only 69.28% under 0.15 MPa air pressure. As the pressure continued to increase, the removal rate of SCCPs decreased significantly. The total amount of extracellular polymeric substances (EPS) increased significantly upon increasing the pressure, and the amount of tightly bound EPS (TB-EPS) was higher than that of loosely bound EPS (LB-EPS). The pressure mainly promoted the secretion of proteins in LB-EPS. Furthermore, an appropriate pure oxygen pressure of 0.15 MPa improved the dehydrogenase activity. The gas chromatography–mass spectrometry (GC–MS) results indicated that the degradation pathway possibly involved the cleavage of the C–Cl bond in SCCPs, which produced Cl⁻, followed by C–C bond breaking. This process degraded long-chain alkanes into short-chain alkanes. Moreover, the main degradation products detected were 2,4-dimethylheptane (C₉H₂₀), 2,5-dimethylheptane (C₉H₂₀), and 3,3-dimethylhexane (C₈H₁₈).

Effects of pharmaceuticals on membrane bioreactor: Review on membrane fouling mechanisms and fouling control strategies

Pharmaceuticals have become contaminants of emerging concern due to their toxicity towards aquatic life and pseudo persistent nature in the environment. Membrane bioreactor (MBR) is one such technology that has the potential to act as a barrier against the release of pharmaceuticals into the environment. Fouling is the deposition of the constituents of the mixed liquor on the membrane surface and it limit the world-wide applicability of MBRs. To remove foulant layer, aggressive chemicals and extra cost consideration in terms of energy are required. Extracellular polymeric substances (EPS) and soluble microbial products (SMP) are recognized as principal foulants. Presence of pharmaceuticals has been found to increase the fouling in MBRs. Fouling aggravates in proportion to the concentration of pharmaceuticals. Pharmaceuticals exert chemical stress in microbes, hence forcing them to secrete more EPS/SMP. Pharmaceuticals alter the composition of the foulants and affect microbial metabolism, thereby inflicting direct/indirect effects on fouling. Pharmaceuticals have been found to increase or decrease the size of sludge flocs, however the exact mechanism that govern the floc size change is yet to be understood. Different techniques such as coupling advanced oxidation processes with MBR, adding activated carbon, bioaugmenting MBR with quorum quenching strains have shown to reduce fouling in MBRs treating pharmaceutical wastewater. These fouling mitigation techniques work on reducing the EPS/SMP concentration, thereby alleviating fouling. The present review provides a comprehensive understanding of the effects induced by pharmaceuticals in the activated sludge characteristics and identifying the fouling mechanism. Furthermore, significant knowledge gaps and recent advances in fouling mitigation strategies are discussed. This review has also made an effort to highlight the positive aspect of the foulant layer in retaining pharmaceuticals and antibiotic resistance genes, thereby suggesting a possible delicate trade-off between the flux decline and enhanced removal of pharmaceuticals.

Anaerobic membrane bioreactors (AnMBRs) for municipal wastewater treatment- potential benefits, constraints, and future perspectives: An updated review

The application of Anaerobic Membrane Bioreactors (AnMBRs) for municipal wastewater treatment has been made sufficiently sustainable for practical implementations. The potential benefits are significant as AnMBRs effectively remove a broad range of contaminants from wastewater for water reuse, degrade organics in wastewater to yield methane-rich biogas for resultant energy production, and concentrate nutrients for subsequent recovery for fertilizer production. However, there still exist some concerns requiring vigilant considerations to make AnMBRs economically and technically viable. This review paper briefly describes process fundamentals and the basic AnMBR configurations and highlights six major factors which obstruct the way to AnMBRs installations affecting their performance for municipal wastewater treatment: (i) organic strength, (ii) membrane fouling, (iii) salinity build-up, (iv) inhibitory substances, (v) temperature, and (vi) membrane stability. This review also covers the energy utilization and energy potential in AnMBRs aiming energy neutrality or positivity of the systems which entails the requirement to further determine the economics of AnMBRs. The implications and related discussions have also been made on future perspectives of the concurrent challenges being faced in AnMBRs operation.

Strategies to enhance micropollutant removal from wastewater by membrane bioreactors: Recent advances and future perspectives

Membrane bioreactor (MBR) has been widely implemented to advance wastewater treatment and reuse. Nevertheless, conventional MBRs with porous microfiltration or ultrafiltration membranes are not designed for the removal of micropollutants, which ubiquitously occur in wastewater at trace concentrations, but potentially exert detrimental impacts to the ecosystem. Several effective strategies have been applied to improve MBR performance for micropollutant removal, particularly the hydrophilic and recalcitrant compounds. These strategies mainly include the optimization of operational conditions, employment of high-retention membranes to replace porous ones, addition of functional materials into bioreactor, and integration of effluent purification processes. In particular, effluent purification by advanced oxidation processes (AOPs) and high-retention membranes can complement MBR to secure almost complete removal of micropollutants. Nevertheless, further research is still necessary to evaluate the technical and economic feasibility of these strategies, especially for long-term treatment performance, to screen the suitable techniques for industrial MBR applications.

Enhancing the water flux and biological treatment in bilateral influent submerged FOMBR via applying the strategy of intermittent discharging salt

The forward osmotic membrane bioreactor (FOMBR) is an emerging innovative technology with broad application prospects in the field of wastewater treatment. Its application is severely limited by concentration polarization, salinity accumulation, and evident water flux decline. Gradual salinity accumulation to a maximum conductivity of 19.7 mS cm^-1 under continuous flow operation suppressed the activities of sludge and biodegradation efficiencies. The employment of the regulation of intermittent supernatant discharge was first investigated to alleviate inhibition caused via accumulated salinity in the bioreactor, and bilateral influent was examined with respect to the performance of the FOMBR. The preferable condition to be applied was FO orientation mode (i.e. active layer facing feed) with spacers added to the surface. Given the decreased salt concentration with 2 L of the supernatant removed per day, the water flux declined more slowly and sludge activities were recovered. When compared to the performance without discharging supernatant, the strategy of controlling salinity could improve the removal efficiencies of NH₄⁺-N, PO₄^3--P, and total organic carbon (TOC) by 15.1, 14.3, and 2.3%, respectively. Additionally, the sludge in the intermittent supernatant discharge bioreactor exhibited better sludge property, larger sludge particle size, and recovered sludge activities with the mixed liquid suspended solids (MLSS) stable at around 4.90 g L^-1. Therefore, regulation of intermittent salt discharge and controlling the salinity concentration in bioreactor can be employed as an effective method to deal with concentration polarization and salinity accumulation in the FOMBR.

Carbamazepine and Diclofenac Removal Double Treatment: Oxidation and Adsorption

In the present research, the effect of two hybrid treatments, ozone followed by powdered activated carbon (PAC) or PAC followed by ozone (O₃), was studied for the removal of two drugs present in water: diclofenac and carbamazepine. In the study, two initial concentrations of each of the contaminants, 0.7 mg L^-1 and 1.8 mg L^-1, were used. Different doses of PAC between 4-20 mg L^-1 were studied as variables, as well as different doses of O₃ between 0.056-0.280 mg L^-1. The evolution of the concentration of each contaminant over time was evaluated. From the results obtained, it was concluded that the combined treatment with ozone followed by PAC reduces between 50% and 75% the time required to achieve 90% removal of diclofenac when compared with the time required when only activated carbon was used. In the case of carbamazepine, the time required was 97% less. For carbamazepine, to achieve reduction percentages of up to 90%, O₃ treatment followed by PAC acted faster than PAC followed by O₃. In the case of diclofenac, PAC treatment followed by O₃ was faster to reach concentrations of up to 90%. However, to reach yields below 80%, O₃ treatment followed by PAC was more efficient.

Effect of salinity on removal performance in hydrolysis acidification reactors treating textile wastewater

Hydrolysis acidification (HA) is a classical method for synthetic textile wastewater treatment. However, the salinity effect on the functional mechanism of the microorganisms carrying out HA has rarely been researched. In the present study, the salinity effect on the dye removal efficiency was investigated, and the soluble microbial products (SMP), extracellular polymeric substances (EPS), and microbial community were analyzed at different salinities. The dye and COD removal rates in the HA reactor decreased with increasing salinity. Volatile fatty acids (VFAs) accumulated. The remarkable increases in SMP and EPS were found at high salinity, mainly because more polysaccharides were synthesized than protein. In addition, sequencing analysis showed that high salinity altered the microbial community structure, and Lactococcus, Raoultella and Enterococcus were the decolorizing bacteria at high salinity. This work will improve the understanding of the influence of salinity on the removal efficiency and microbial community during HA.

Customized thin and loose cake layer to mitigate membrane fouling in an electro-assisted anaerobic forward osmosis membrane bioreactor (AnOMEBR)

Anaerobic forward osmosis membrane bioreactor (AnOMBR) is a potential wastewater treatment technology, due to its low energy consumption and high effluent quality. However, membrane fouling is still a considerable problem which causes dwindling of water flux and shortening the membrane lifetime. In this study, electro-assisted anaerobic forward osmosis membrane bioreactor (AnOMEBR) was developed to treat wastewater and mitigate membrane fouling, in which the conductive FO membrane was used both as the separation unit and cathode. The formation, development and alleviation of membrane fouling in AnOMEBR were investigated. The results showed that the soluble microbial products (SMP) content and the proteins/polysaccharides (PN/PS) value in AnOMEBR were 26% and 15% lower than that in AnOMBR, respectively. The absolute value of Zeta of sludge mixture in AnOMEBR was 1.2 times that of the AnOMBR. The increase in the interaction between the membrane surface and the negatively charged foulants could inhibit the adsorption of foulants on membrane surface in the initial stage of membrane fouling. The strong interaction among foulants further affected the composition, structure and thickness of the cake layer on the FO membrane surface. AnOMEBR with a shorter hydraulic retention time, a higher organic loading rate and a lower osmotic pressure difference, could still obtain a lower flux decline rate of 0.063 LMH/h, which was 35.7% lower than AnOMBR. The wastewater treatment capacity of AnOMEBR was nearly 1.5 times that of the AnOMBR. This work provides an efficient strategy for mitigating membrane fouling and improving wastewater treatment capacity.

Pressure retarded osmosis coupled with activated sludge process for wastewater treatment: Performance and fouling behaviors

A novel hybrid technology integrating pressure retarded osmosis with activated sludge process (denoted as PRO-MBR) was proposed in this study for wastewater treatment. Here, performance and fouling behaviors of PRO-MBR were investigated. Excellent contaminants removal and power production were simultaneously achieved in the PRO-MBR. A significant drop of water flux in the PRO-MBR was mainly due to the severe fouling of the support layer in forward osmosis (FO) membrane including internal fouling and external fouling. Although the external fouling was identified to be the major type of fouling, the internal fouling dominated the overall decline of water flux. In addition, organic foulants and biofoulants were the dominant foulants for the external fouling while inorganic foulants were equal to organic foulants and biofoulants for the internal fouling. According to the variations of water flux in the PRO-MBR, the development of support layer fouling was divided into three stages.

Membrane fouling mitigation in different biofilm membrane bioreactors with pre-anoxic tanks for treating mariculture wastewater

This study compared the membrane fouling mitigation in two novel types of biofilm membrane bioreactor coupled with a pre-anoxic tank (BF-AO-MBR)-namely a fixed biofilm membrane bioreactor (FB-MBR) with fiber bundle bio-carriers and a moving-bed biofilm membrane bioreactor (MB-MBR) with suspended bio-carriers-relative to an anoxic/oxic MBR (AO-MBR), at salinities ranging from zero to 60 g/L. The results showed that the FB-MBR mitigated membrane fouling to a greater degree than the MB-MBR and AO-MBR. During operation, the FB-MBR exhibited the lowest fouling development, with three membrane filtration cycles, while the AO-MBR and MB-MBR had 22 and nine cycles, respectively. The key fouling factor in all reactors was cake layer resistance (R_C), which contributed to 89.61, 62.20, and 83.17% of the total fouling resistance (R_T) in AO-MBR, FB-MBR and MB-MBR, respectively. Additionally, in the FB-MBR, the pore blocking resistance (30.07%) was also an important cause of fouling. Fiber bundle bio-carriers and suspended bio-carriers reduced the R_T by 37.68% and 21.24% (mainly the R_C) compared to that of AO-MBR. Furthermore, FB-MBR and MB-MBR caused a decrease of suspended biomass (80.14 and 15.90%, respectively), and the latter exhibited a higher sludge particle size than AO-MBR, possibly resulting in the cake layer decline. The studied BF-AO-MBRs further alleviated the fouling propensity by reducing the amount of soluble microbial product (SMP) and extracellular polymeric substances (EPS) under all salinity levels, especially the FB-MBR. Among the protein components, the amounts of tryptophan protein-like substance and aromatic protein-like substance were significantly lower in the FB-MBR compared to the AO-MBR and MB-MBR. Additionally, at 60 g/L salinity, the structure of the microbial community in the FB-MBR had a lower abundance of Bacteroidetes and more biomacromolecule degraders, which may have contributed to the moderation of membrane fouling.

A Survey of the Presence of Pharmaceutical Residues in Wastewaters. Evaluation of Their Removal using Conventional and Natural Treatment Procedures

To encourage the reutilization of treated wastewaters as an adaptation strategy to climate change it is necessary to demonstrate their quality. If this is ensured, reclaimed waters could be a valuable resource that produces very little environmental impact and risks to human health. However, wastewaters are one of the main sources of emerging pollutants that are discharged in the environment. For this, it is essential to assess the presence of these pollutants, especially pharmaceutical compounds, in treated wastewaters. Moreover, the different treatment processes must be evaluated in order to know if conventional and natural treatment technologies are efficient in the removal of these types of compounds. This is an important consideration if the treated wastewaters are used in agricultural activities. Owing to the complexity of wastewater matrixes and the low concentrations of pharmaceutical residues in these types of samples, it is necessary to use sensitive analytical methodologies. In this study, the presence of 11 pharmaceutical compounds were assessed in three different wastewater treatment plants (WWTPs) in Gran Canaria (Spain). Two of these WWTPs use conventional purification technologies and they are located in densely populated areas, while the other studied WWTP is based in constructed wetlands which purify the wastewaters of a rural area. The sampling was performed monthly for two years. A solid phase extraction (SPE) coupled to ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) method was applied for the analysis of the samples, and the 11 pharmaceuticals were detected in all the studied WWTPs. The concentrations were variable and ranged from ng·L^-1 in some compounds like diclofenac or carbamazepine to µg·L^-1 in common pharmaceutical compounds such as caffeine, naproxen or ibuprofen. In addition, removal efficiencies in both conventional and natural purification systems were evaluated. Similar removal efficiencies were obtained using different purifying treatments, especially for some pharmaceutical families as stimulants or anti-inflammatories. Other compounds like carbamazepine showed a recalcitrant behavior. Secondary treatments presented similar removal efficiencies in both conventional and natural wastewater treatment plants, but conventional treatments showed slightly higher elimination ratios. Regarding tertiary system, the treatment with highest removal efficiencies was reverse osmosis in comparison with microfiltration and electrodialysis reversal.

Understanding the mechanisms of trace organic contaminant removal by high retention membrane bioreactors: a critical review

High retention membrane bioreactors (HR-MBR) combine a high retention membrane separation process such as membrane distillation, forward osmosis, or nanofiltration with a conventional activated sludge (CAS) process. Depending on the physicochemical properties of the trace organic contaminants (TrOCs) as well as the selected high retention membrane process, HR-MBR can achieve effective removal (80-99%) of a broad spectrum of TrOCs. An in-depth assessment of the available literature on HR-MBR performance suggests that compared to CAS and conventional MBRs (using micro- or ultra-filtration membrane), aqueous phase removal of TrOCs in HR-MBR is significantly better. Conceptually, longer retention time may significantly improve TrOC biodegradation, but there are insufficient data in the literature to evaluate the extent of TrOC biodegradation improvement by HR-MBR. The accumulation of hardly biodegradable TrOCs within the bioreactor of an HR-MBR system may complicate further treatment and beneficial reuse of sludge. In addition to TrOCs, accumulation of salts gradually increases the salinity in bioreactor and can adversely affect microbial activities. Strategies to mitigate these limitations are discussed. A qualitative framework is proposed to predict the contribution of the different key mechanisms of TrOC removal (i.e., membrane retention, biodegradation, and sorption) in HR-MBR.

Elimination of Micropollutants in Activated Sludge Reactors with a Special Focus on the Effect of Biomass Concentration

This study aimed to investigate the effects of sludge retention time (SRT), hydraulic retention time (HRT), and biomass concentration (CTSS) in activated sludge systems on removal of various micropollutants (MPs), covering a wide spectrum of biodegradability. The influence of biomass concentration on the classical pseudo-first-order rate constant was verified. Results showed that the removal rate constants were affected by both the HRT and SRT. The enhancement of the SRT increased the removal of all the MPs except for two macrolide antibiotics. Application of a higher HRT also improved MP removal, as was expected from the measured removal rate constants. More interesting, our results indicated that, logically, the increase of biomass concentration (expressed as total suspended solids CTSS) from 3 to 5 gTSS L−1 significantly enhanced the removal rate of the highly and moderately degradable compounds. Conversely, a further increase to 8 gTSS L−1 produced only an unexpected moderate effect, showing that the rate was not proportional to biomass concentration, contrary to what is generally postulated. Therefore, the use of classical kinetic models is questionable, since they do not cover the entire range of boundary conditions in activated sludge systems. This work opens new research paths and suggests potential improvements to processes.

Assessing the removal of organic micropollutants by a novel baffled osmotic membrane bioreactor-microfiltration hybrid system

A novel approach was employed to study removal of organic micropollutants (OMPs) in a baffled osmotic membrane bioreactor-microfiltration (OMBR-MF) hybrid system under oxicanoxic conditions. The performance of OMBR-MF system was examined employing three different draw solutes (DS), and three model OMPs. The highest forward osmosis (FO) membrane rejection was attained with atenolol (100%) due to its higher molar mass and positive charge. With inorganic DS caffeine (94-100%) revealed highest removal followed by atenolol (89-96%) and atrazine (16-40%) respectively. All three OMPs exhibited higher removal with organic DS as compared to inorganic DS. Significant anoxic removal was observed for atrazine under very different redox conditions with extended anoxic cycle time. This can be linked with possible development of different microbial consortia responsible for diverse enzymes secretion. Overall, the OMBR-MF process showed effective removal of total organic carbon (98%) and nutrients (phosphate 97% and total nitrogen 85%), respectively.

Salinity build-up in osmotic membrane bioreactors: Causes, impacts, and potential cures

Osmotic membrane bioreactor (OMBR), which integrates forward osmosis (FO) with biological treatment, has been developed to advance wastewater treatment and reuse. OMBR is superior to conventional MBR, particularly in terms of higher effluent quality, lower membrane fouling propensity, and higher membrane fouling reversibility. Nevertheless, advancement and future deployment of OMBR are hindered by salinity build-up in the bioreactor (e.g., up to 50 mS/cm indicated by the mixed liquor conductivity), due to high salt rejection of the FO membrane and reverse diffusion of the draw solution. This review comprehensively elucidates the relative significance of these two mechanisms towards salinity build-up and its associated effects in OMBR operation. Recently proposed strategies to mitigate salinity build-up in OMBR are evaluated and compared to highlight their potential in practical applications. In addition, the complementarity of system optimization and modification to effectively manage salinity build-up are recommended for sustainable OMBR development.

Greenhouse gases from membrane bioreactors: Mathematical modelling, sensitivity and uncertainty analysis

In this study a new mathematical model to quantify greenhouse gas emissions (namely, carbon dioxide and nitrous oxide) from membrane bioreactors (MBRs) is presented. The model has been adopted to predict the key processes of a pilot plant with pre-denitrification MBR scheme, filled with domestic and saline wastewater. The model was calibrated by adopting an advanced protocol based on an extensive dataset. In terms of nitrous oxide, the results show that an important role is played by the half saturation coefficients related to nitrogen removal processes and the model factors affecting the oxygen transfer rate in the aerobic and MBR tanks. Uncertainty analysis showed that for the gaseous model outputs 88-93% of the measured data lays inside the confidence bands showing an accurate model prediction.

Dominance of candidate Saccharibacteria in a membrane bioreactor treating medium age landfill leachate: Effects of organic load on microbial communities, hydrolytic potential and extracellular polymeric substances

A membrane bioreactor (MBR), accomplishing high nitrogen removal efficiencies, was evaluated under various landfill leachate concentrations (50, 75 and 100% v/v). Proteinous and carbohydrate extracellular polymeric substances (EPS) and soluble microbial product (SMP) were strongly correlated (p<0.01) with organic load, salinity and NH₄⁺-N. Exceptionally high β-glucosidase activities (6700-10,100Ug^-1) were determined during MBR operation with 50% v/v leachate, as a result of the low organic carbon availability that extendedly induced β-glucosidases to breakdown the least biodegradable organic fraction. Illumina sequencing revealed that candidate Saccharibacteria were dominant, independently of the leachate concentration applied, whereas other microbiota (21.2% of total reads) disappeared when undiluted leachate was used. Fungal taxa shifted from a Saccharomyces- to a newly-described Cryptomycota-based community with increasing leachate concentration. Indeed, this is the first report on the dominance of candidate Saccharibacteria and on the examination of their metabolic behavior in a bioreactor treating real wastewater.

Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal

This study systematically compares the performance of osmotic membrane bioreactor - reverse osmosis (OMBR-RO) and conventional membrane bioreactor - reverse osmosis (MBR-RO) for advanced wastewater treatment and water reuse. Both systems achieved effective removal of bulk organic matter and nutrients, and almost complete removal of all 31 trace organic contaminants investigated. They both could produce high quality water suitable for recycling applications. During OMBR-RO operation, salinity build-up in the bioreactor reduced the water flux and negatively impacted the system biological treatment by altering biomass characteristics and microbial community structure. In addition, the elevated salinity also increased soluble microbial products and extracellular polymeric substances in the mixed liquor, which induced fouling of the forward osmosis (FO) membrane. Nevertheless, microbial analysis indicated that salinity stress resulted in the development of halotolerant bacteria, consequently sustaining biodegradation in the OMBR system. By contrast, biological performance was relatively stable throughout conventional MBR-RO operation. Compared to conventional MBR-RO, the FO process effectively prevented foulants from permeating into the draw solution, thereby significantly reducing fouling of the downstream RO membrane in OMBR-RO operation. Accumulation of organic matter, including humic- and protein-like substances, as well as inorganic salts in the MBR effluent resulted in severe RO membrane fouling in conventional MBR-RO operation.

Effect of bioflocculation on fouling-related biofoulants in a membrane bioreactor during saline wastewater treatments

A membrane bioreactor (MBR) was operated in two modes; with and without the inoculation of marine Arthrobacter cells, to investigate the effect of bioflocculation on membrane biofouling during saline wastewater treatments. The MBR-Arthrobacter system showed a higher resistance to membrane fouling than the normal MBR system. Lower concentrations of the fouling-related components and higher removal efficiencies of COD and NH₃-N were observed in the MBR-Arthrobacter system. The bioflocculation of Arthrobacter preferred to settle down the humic acid-like, fulvic acid-like and aromatic proteins components (larger biomolecules) rather than the soluble microbial by-product-like components (smaller biomolecules).

Effects of pressurized aeration on organic degradation efficiency and bacterial community structure of activated sludge treating saline wastewater

This study was aimed to investigate the effect of moderate pressure on organic matter removal efficiency and microbial population of activated sludge treating saline wastewater. The activated sludge was cultivated with a gradual increase of salt concentrations under gage pressure of 0.3MPa for 71days. Microbial diversities of activated sludge sampled in different stages of domestication were investigated by Illumina sequencing technology. Results showed that pressurized aeration could improve the treatment efficiency and the dehydrogenase activity (DHA) of activated sludge, especially at high salinity (35, 50gNaClL^-1). Bacterial richness and community diversity of activated sludge in the pressurized reactor were significantly higher than those in the control reactor. Microbial population structures were quite different between the two reactors. More species originating from fresh wastewater biological treatment process would survive and remain in pressurized activated sludge.

Behaviour of fouling-related components in an enhanced membrane bioreactor using marine activated sludge

This paper presents an experimental study on behaviour of fouling-related components during saline wastewater treatments in an enhanced mesoporous membrane bioreactor (MBR) system integrated with a biological contact oxidation reactor (BCOR). By monitoring the transmembrane pressure, the MBR system without BCOR assistance was observed to get membrane fouling easier during saline wastewater treatments. Typically, the concentration of total EPS gradually increased in the MBR system over the operation time, while no significant change in its concentration was observed in the BCOR-MBR system. The concentration of total SMP in the MBR system reached high levels earlier than the BCOR-MBR system, causing a significant membrane fouling. Besides, unlike a simple MBR system, the BCOR-MBR system produced more soluble microbial by-product-like components (simple) instead of fulvic acid-like or humic acid-like components (complex) during the saline wastewater treatments, resulting in higher resistance to a membrane fouling.

Effect of different salinity adaptation on the performance and microbial community in a sequencing batch reactor

The performance and microbial community profiles in a sequencing batch reactor (SBR) treating saline wastewater were studied over 300days from 0wt% to 3.0wt% salinity. The experimental results indicated that the activated sludge had high sensitivity to salinity variations in terms of pollutants removal and sedimentation. At 2.0wt% salinity, the system retained a good performance, and 95% removal rate of chemical oxygen demand (COD), biochemical oxygen demand (BOD), NH4(+)-N and total phosphorus (TP) could be achieved. Operation before addition salinity revealed the optimal performance and the most microbial diversity indicated by 16S rRNA gene clone library. Sequence analyses illustrated that Candidate_division_TM7 (TM7) was predominant at 2.0 wt% salinity; however, Actinobacteria was more abundant at 3.0wt% salinity.

Effects of salinity build-up on the performance of an anaerobic membrane bioreactor regarding basic water quality parameters and removal of trace organic contaminants

The effects of elevated inorganic salt concentration on anaerobic membrane bioreactor (AnMBR) treatment regarding basic biological performance and trace organic contaminant (TrOC) removal were investigated. A set of 33 TrOCs were selected to represent pharmaceuticals, steroids, and pesticides in municipal wastewater. Results show potential adverse effects of increase in the bioreactor salinity to 15g/L (as NaCl) on the performance of AnMBR with respect to chemical oxygen demand removal, biogas production, and the removal of most hydrophilic TrOCs. Furthermore, a decrease in biomass production was observed as salinity in the bioreactor increased. The removal of most hydrophobic TrOCs was high and was not significantly affected by salinity build-up in the bioreactor. The accumulation of a few persistent TrOCs in the sludge phase was observed, but such accumulation did not vary significantly as salinity in the bioreactor increased.

Biofouling behavior and performance of forward osmosis membranes with bioinspired surface modification in osmotic membrane bioreactor

Forward osmosis (FO) has received considerable interest for water and energy related applications in recent years. Biofouling behavior and performance of cellulose triacetate (CTA) forward osmosis membranes with bioinspired surface modification via polydopamine (PD) coating and poly (ethylene glycol) (PEG) grafting (PD-g-PEG) in a submerged osmotic membrane bioreactor (OMBR) were investigated in this work. The modified membranes exhibited lower flux decline than the pristine one in OMBR, confirming that the bioinspired surface modification improved the antifouling ability of the CTA FO membrane. The result showed that the decline of membrane flux related to the increase of the salinity and MLSS concentration of the mixed liquid. It was concluded that the antifouling ability of modified membranes ascribed to the change of surface morphology in addition to the improvement of membrane hydrophilicity. The bioinspired surface modifications might improve the anti-adhesion for the biopolymers and biocake.

Sequential batch membrane bio-reactor for wastewater treatment: The effect of increased salinity

In this work, a sequential batch membrane bioreactor pilot plant is investigated to analyze the effect of a gradual increase in salinity on carbon and nutrient removal, membrane fouling and biomass kinetic parameters. The salinity was increased by 2gNaClL(-1) per week up to 10gNaClL(-1). The total COD removal efficiency was quite high (93%) throughout the experiment. A gradual biomass acclimation to the salinity level was observed during the experiment, highlighting the good recovery capabilities of the system. Nitrification was also influenced by the increase in salinity, with a slight decrease in nitrification efficiency (the lowest value was obtained at 10gNaClL(-1) due to lower nitrifier activity). Irreversible cake deposition was the predominant fouling mechanism observed during the experiment. Respirometric tests exhibited a stress effect due to salinity, with a reduction in the respiration rates observed (from 8.85mgO2L(-1)h(-1) to 4mgO2L(-1)h(-1)).

Composition and aggregation of extracellular polymeric substances (EPS) in hyperhaline and municipal wastewater treatment plants

As important constituents of activated sludge flocs, extracellular polymeric substances (EPS) play significant roles in pollutants adsorption, the formation and maintenance of microbial aggregates, and the protection of microbes from external environmental stresses. In this work, EPS in activated sludge from a municipal wastewater treatment plant (M-WWTP) with anaerobic/anoxic/oxic (A(2)/O) process and a hyperhaline wastewater treatment plant (H-WWTP) with anaerobic/oxic (A/O) process were extracted by ultrasound method. The proteins and polysaccharides contents in EPS were determined by using a modified Lowry method and anthrone colorimetry respectively to analyze the detail differences in two types of WWTPs. Fourier transform-infrared spectroscopy and three-dimensional excitation-emission matrix fluorescence spectroscopy demonstrated proteins and polysaccharides were the dominant components of the two types of EPS, and the aromatic protein-like substances accounted for a larger proportion in EPS proteins. The results of the aggregation test indicated that EPS were good for the sludge aggregation, and the EPS in oxic sludge were more beneficial to sludge aggregation than that in anoxic sludge. Anoxic sludge EPS in H-WWTP showed a negligible effect on sludge aggregation. Comparative study on EPS of different tanks in the M-WWTP and H-WWTP was valuable for understanding the characteristics of EPS isolated from two typical wastewater treatment processes.

Effects of salinity build-up on the performance and bacterial community structure of a membrane bioreactor

This study investigated the effects of salinity increase on bacterial community structure in a membrane bioreactor (MBR) for wastewater treatment. The influent salt loading was increased gradually to simulate salinity build-up in the bioreactor during the operation of a high retention-membrane bioreactor (HR-MBR). Bacterial community diversity and structure were analyzed using 454 pyrosequencing of 16S rRNA genes of MBR mixed liquor samples. Results show that salinity increase reduced biological performance but did not affect microbial diversity in the bioreactor. Unweighted UniFrac and taxonomic analyses were conducted to relate the reduced biological performance to the change of bacterial community structure. In response to the elevated salinity condition, the succession of halophobic bacteria by halotolerant/halophilic microbes occurred and thereby the biological performance of MBR was recovered. These results suggest that salinity build-up during HR-MBR operation could be managed by allowing for the proliferation of halotolerant/halophilic bacteria.

Correlation between microbial community structure and biofouling as determined by analysis of microbial community dynamics

Three lab-scale membrane bioreactors (MBRs) were continuously operated to treat saline wastewater under 0%, 0.75% and 1.5% NaCl stress. 0.75% and 1.5% NaCl reduced the COD and NH4(+)-N removal at the beginning, while the removal efficiencies could be recovered along with the operation of MBRs. Also, the polysaccharide in extracellular polymeric substances (EPS) and soluble microbial products (SMP) played an important role in the membrane fouling. Illumina sequencing of 16S rRNA gene showed that the increasing level of salinity reduced the diversity of the microbial community, and a higher salinity stimulated the growth of Bacteroidetes. At genus level, Flavobacterium, Aequorivita, Gelidibacter, Microbacterium, and Algoriphagus increased with the increase of salinity, which are shown to be highly salt tolerant. The strength of salinity or the duration of salinity could stimulate the microorganisms with similar functions, and the changes of polysaccharide in EPS and SMP were closely related to the membrane fouling rate as well as correlated with some saline-resistance genera.

Modeling full-scale osmotic membrane bioreactor systems with high sludge retention and low salt concentration factor for wastewater reclamation

A full-scale model was developed to find optimal design parameters for osmotic membrane bioreactor (OMBR) and reverse osmosis (RO) hybrid system for wastewater reclamation. The model simulates salt accumulation, draw solution dilution and water flux in OMBR with sludge concentrator for high retention and low salt concentration factor. The full-scale OMBR simulation results reveal that flat-sheet module with spacers exhibits slightly higher flux than hollow-fiber; forward osmosis (FO) membrane with high water permeability, low salt permeability, and low resistance to salt diffusion shows high water flux; an optimal water recovery around 50% ensures high flux and no adverse effect on microbial activity; and FO membrane cost decreases and RO energy consumption and product water concentration increases at higher DS flow rates and concentrations. The simulated FO water flux and RO energy consumption ranges from 3.03 to 13.76LMH and 0.35 to 1.39kWh/m(3), respectively.