Performances of anaerobic and aerobic membrane bioreactors for the treatment of synthetic textile wastewater

Assessing greenhouse gas emissions from the printing and dyeing wastewater treatment and reuse system: Potential pathways towards carbon neutrality

The urgency of achieving carbon neutrality needs a reduction in greenhouse gas (GHG) emissions from the textile industry. Printing and dyeing wastewater (PDWW) plays a crucial role in the textile industry. The incomplete assessment of GHG emissions from PDWW impedes the attainment of carbon neutrality. Here, we firstly introduced a more standardized and systematic life-cycle GHG emission accounting method for printing and dyeing wastewater treatment and reuse system (PDWTRS) and proposed possible low-carbon pathways to achieve carbon neutrality. Utilizing case-specific operational data over 12 months, the study revealed that the PDWTRS generated 3.49 kg CO2eq/m3 or 1.58 kg CO2eq/kg CODrem in 2022. This exceeded the GHG intensity of municipal wastewater treatment (ranged from 0.58 to 1.14 kg CO2eq/m3). The primary contributor to GHG emissions was energy consumption (33 %), with the energy mix (sensitivity = 0.38) and consumption (sensitivity = 0.33) exerting the most significant impact on GHG emission intensity respectively. Employing prospective life cycle assessment (LCA), our study explored the potential of the anaerobic membrane bioreactor (AnMBR) to reduce emissions by 0.54 kg CO2eq/m3 and the solar-driven photocatalytic membrane reactor (PMR) to decrease by 0.20 kg CO2eq/m3 by 2050. Our projections suggested that the PDWTRS could achieve net-zero emissions before 2040 through an adoption of progressive transition to low-carbon management, with a GHG emission intensity of -0.10 kg CO2eq/m3 by 2050. Importantly, the study underscored the escalating significance of developing sustainable technologies for reclaimed water production amid water scarcity and climate change. The study may serve as a reminder of the critical role of PDWW treatment in carbon reduction within the textile industry and provides a roadmap for potential pathways towards carbon neutrality for PDWTRS.

Unveiling the influence of microaeration and sludge recirculation on enhancement of pharmaceutical removal and microbial community change of the novel anaerobic baffled biofilm - membrane bioreactor in treating building wastewater

This research aims to conduct a comparative investigation of the role played by microaeration and sludge recirculation in the novel anaerobic baffled biofilm-membrane bioreactor (AnBB-MBR) for enhancing pharmaceutical removal from building wastewater. Three AnBB-MBRs - R1: AnBB-MBR, R2: AnBB-MBR with microaeration and R3: AnBB-MBR with microaeration and sludge recirculation - were operated simultaneously to remove Ciprofloxacin (CIP), Caffeine (CAF), Sulfamethoxazole (SMX) and Diclofenac (DCF) from real building wastewater at the hydraulic retention time (HRT) of 30 h for 115 days. From the removal profiles of the targeted pharmaceuticals in the AnBB-MBRs, it was found that the fixed-film compartment (C1) could significantly reduce the targeted pharmaceuticals. The remaining pharmaceuticals were further removed with the microaeration compartment. R2 exhibited the utmost removal efficiency for CIP (78.0 %) and DCF (40.8 %), while SMX was removed most successfully by R3 (microaeration with sludge recirculation) at 91.3 %, followed by microaeration in R2 (88.5 %). For CAF, it was easily removed by all AnBB-MBR systems (>90 %). The removal mechanisms indicate that the microaeration in R2 facilitated the adsorption of CIP onto microaerobic biomass, while the enhanced biodegradation of CAF, SMX and DCF was confirmed by batch biotransformation kinetics and the adsorption isotherms of the targeted pharmaceuticals. The microbial groups involved in biodegradation of the targeted compounds under microaeration were identified as nitrogen removal microbials (Nitrosomonas, Nitrospira, Thiobacillus, and Denitratisoma) and methanotrophs (Methylosarcina, Methylocaldum, and Methylocystis). Overall, explication of the integration of AnBB-MBR with microaeration (R2) confirmed it as a prospective technology for pharmaceutical removal from building wastewater due to its energy-efficient approach characterized by minimal aeration supply.

Advances from conventional to biochar enhanced biotreatment of dyeing wastewater: A critical review

DW (Dyeing wastewater) contains a large amount of dye organic compounds. A considerable proportion of dye itself or its intermediate products generated during wastewater treatment process exhibits CMR (Carcinogenic/Mutagenic/Toxic to Reproduction) toxicity. Compared with physicochemical methods, biological treatment is advantageous in terms of operating costs and greenhouse gas emissions, and has become the indispensable mainstream technology for DW treatment. This article reviews the adsorption and degradation mechanisms of dye organic compounds in wastewater and analyzed different biological processes, ranging from traditional methods to processes enhanced by biochar (BC). For traditional biological processes, microbial characteristics and communities were discussed, as well as the removal efficiency of different bioreactors. BC has adsorption and redox electron mediated effects, and coupling with biological treatment can further enhance the process of biosorption and degradation. Although BC coupled biological treatment shows promising dye removal, further research is still needed to optimize the treatment process, especially in terms of technical and economic competitiveness.

Towards bio-utilization and energy recovery potential exploration of membrane foulant from membrane bioreactor by using microbial fuel cell-centered technology

The utilization of membrane foulant is expected to push forward the developments of membrane bioreactor (MBR). In this study, the combination of microbial fuel cell (MFC) with bio-electrochemical enhanced hydrolysis process was proposed, and three systems were conducted to utilize the membrane foulant and simultaneously harvest electricity. Polysaccharides (PS), proteins (PN) and humic acid (HA) concentration variations and the fluorescent compound changes in different chambers revealed the biodegradability of membrane foulant. Optimized HRT improved the hydrolysis of membrane foulant while allowing MFC to utilize the biodegradable components efficiently. MFC-MFC system had the highest voltage and satisfactory effluent quality at HRT of 1 d. Microbial community structure analysis indicated that Proteobacteria, Planctomycetes and Bacteroidetes were the majority phyla and network analysis further revealed that Proteobacteria played a key role in membrane foulant utilization. This study suggests that MFC hybrid systems has potential application for synchronous membrane foulant reuse and energy recovery.

Impact of salinity on anaerobic ceramic membrane bioreactor for textile wastewater treatment: Process performance, membrane fouling and machine learning models

Anaerobic membrane bioreactor (AnMBR) shows great potential for textile wastewater treatment, but high salinity in the influent may undermine its performance. This study evaluated the impact of salinity on the treatment performance of an upflow anaerobic sludge blanket (UASB) configured AnMBR using a flat sheet ceramic membrane. The salinity was stepwise increased (0, 5, 10 and 20 g/L) in four phases of the AnMBR operation. Results indicated that increased salinity jeopardized the COD removal efficiency of AnMBR from 92% to 73%, but had a marginal effect on dye removal efficacy (90-96%). Low salinity (5 g/L) boosted the biogas production whilst high salinity (>10 g/L) had a negative impact. Additionally, the increase of salinity resulted in the soluble microbial production (SMP) concentration soar and membrane fouling rate increase, peaking at a salinity of 10 g/L (Phase III) and recovering back to a lower level at a salinity of 20 g/L (Phase IV). This indicated a transition occurrence at a salinity of 10 g/L (Phase III). The microbial diversity analyses further suggested a transition from salinity-sensitive microbes (Aminiphilus, Caldatribacterium, Mesotoga, Methanobrevibacter, Methanobacterium, Methanosaeta) to salinity-tolerant microbes (Longilinea, Ignavibacterium, Rhodovarius, Bosea and Flexilinea). This transition can be associated with the increase SMP concentration and more severe membrane fouling in Phase III, which were mitigated after a new equilibrium was reached when the microbial consortium acclimatized to the high salinity. Finally, a machine learning model of the Adaboost algorithm was established to predict COD removal under different salinities. Importantly, this study revealed that AnMBR process performance and membrane operation can be maintained for high salinity textile wastewater treatment with a halophilic microbial community growth under high-salinity selection pressure.

Life cycle assessment of sequential microbial-based anaerobic-aerobic reactor technology developed onsite for treating textile effluent

Although biological treatment of textile effluent is a preferred option for industries avoiding toxic chemical sludge production and disposal, requirement of several extra pre-treatment units like neutralization, cooling systems or additives, results in higher operational cost. In the present study, a pilot scale sequential microbial-based anaerobic-aerobic reactor technology (SMAART) was developed and operated for the treatment of real textile effluent in the industrial premises in continuous mode for 180 d. The results showed an average ∼95% decolourization along with ∼92% reduction in the chemical oxygen demand establishing the resilience against fluctuations in the inlet parameters and climate conditions. Moreover, the pH of treated effluent was also reduced from alkaline range (∼11.05) to neutral range (∼7.76) along with turbidity reduction from ∼44.16 NTU to ∼0.14 NTU. A comparative life cycle assessment (LCA) of SMAART with the conventional activated sludge process (ASP) showed that ASP caused 41.5% more negative impacts on environment than SMAART. Besides, ASP had 46.15% more negative impact on human health, followed by 42.85% more negative impact on ecosystem quality as compared to SMAART. This was attributed to less electricity consumption, absence of pre-treatment units (cooling and neutralization) and less volume of sludge generation (∼50%) while using SMAART. Hence, integration of SMAART within the industrial effluent treatment plant is recommended to achieve a minimum waste discharge system in pursuit of sustainability.

Effects of solid retention time and exposure mode to electric current on Remazol Brilliant Violet removal in an electro-membrane bioreactor

The performance of an electrochemically assisted anoxic-oxic membrane bioreactor (A/O-eMBR) was assessed as an alternative for azo dye (Remazol Brilhant Violet (RBV)) removal from simulated textile wastewater. The A/O-eMBR was operated under three experimental conditions (runs I, II, and III), in which different solids retention time (SRT) (45 and 20 d) and exposure mode to electric current (6'ON/30'OFF and 6'ON/12'OFF) were assessed. The reactor exhibited excellent decolorization performance for all runs, with average dye removal efficiency ranging from 94.3 to 98.2%. Activity batch assays showed that the dye removal rate (DRR) decreased from 16.8 to 10.2 mg RBV L^-1 h^-1 when the SRT was reduced from 45 to 20 d, likely attributed to the lower biomass content under lower sludge age. At the electric current exposure mode of 6' ON/12'OFF, a more substantial decrease of DRR to 1.5 mg RBV L^-1 h^-1 was noticed, suggesting a possible inhibitory effect on dye removal via biodegradation. By reducing the SRT to 20 d, a worse mixed liquor filterability condition was observed, with a membrane fouling rate (MFR) of 0.979 kPa d^-1. In contrast, using the electric current exposure mode of 6'ON/12'OFF resulted in lower membrane fouling propensity, with an MFR of 0.333 kPa d^-1. A more attractive cost-benefit ratio for dye removal was obtained using the exposure mode of 6'ON/30'OFF, for which the energy demand was estimated at 21.9-22.6 kWh kg dye^-1 removed, almost two times lower than that observed for the mode of 6'ON/12'OFF.

Anaerobic Membrane Bioreactor (AnMBR) for the Removal of Dyes from Water and Wastewater: Progress, Challenges, and Future Perspectives

The presence of dyes in aquatic environments can have harmful effects on aquatic life, including inhibiting photosynthesis, decreasing dissolved oxygen levels, and altering the behavior and reproductive patterns of aquatic organisms. In the initial phase of this review study, our aim was to examine the categories and properties of dyes as well as the impact of their toxicity on aquatic environments. Azo, phthalocyanine, and xanthene are among the most frequently utilized dyes, almost 70–80% of used dyes, in industrial processes and have been identified as some of the most commonly occurring dyes in water bodies. Apart from that, the toxicity effects of dyes on aquatic ecosystems were discussed. Toxicity testing relies heavily on two key measures: the LC50 (half-lethal concentration) and EC50 (half-maximal effective concentration). In a recent study, microalgae exposed to Congo Red displayed a minimum EC50 of 4.8 mg/L, while fish exposed to Disperse Yellow 7 exhibited a minimum LC50 of 0.01 mg/L. Anaerobic membrane bioreactors (AnMBRs) are a promising method for removing dyes from water bodies. In the second stage of the study, the effectiveness of different AnMBRs in removing dyes was evaluated. Hybrid AnMBRs and AnMBRs with innovative designs have shown the capacity to eliminate dyes completely, reaching up to 100%. Proteobacteria, Firmicutes, and Bacteroidetes were found to be the dominant bacterial phyla in AnMBRs applied for dye treatment. However, fouling has been identified as a significant drawback of AnMBRs, and innovative designs and techniques are required to address this issue in the future.

The Advancement in Membrane Bioreactor (MBR) Technology toward Sustainable Industrial Wastewater Management

The advancement in water treatment technology has revolutionized the progress of membrane bioreactor (MBR) technology in the modern era. The large space requirement, low efficiency, and high cost of the traditional activated sludge process have given the necessary space for the MBR system to come into action. The conventional activated sludge (CAS) process and tertiary filtration can be replaced by immersed and side-stream MBR. This article outlines the historical advancement of the MBR process in the treatment of industrial and municipal wastewaters. The structural features and design parameters of MBR, e.g., membrane surface properties, permeate flux, retention time, pH, alkalinity, temperature, cleaning frequency, etc., highly influence the efficiency of the MBR process. The submerged MBR can handle lower permeate flux (requires less power), whereas the side-stream MBR can handle higher permeate flux (requires more power). However, MBR has some operational issues with conventional water treatment technologies. The quality of sludge, equipment requirements, and fouling are major drawbacks of the MBR process. This review paper also deals with the approach to address these constraints. However, given the energy limitations, climatic changes, and resource depletion, conventional wastewater treatment systems face significant obstacles. When compared with CAS, MBR has better permeate quality, simpler operational management, and a reduced footprint requirement. Thus, for sustainable water treatment, MBR can be an efficient tool.

Performance of sulfur-based autotrophic denitrification process for nitrate removal from permeate of an MBR treating textile wastewater and concentrate of a real scale reverse osmosis process

Textile is one of the industrial sectors generating the highest amount of wastewater with various polluting substances. Lately, water reuse in textile industries, especially, with the reverse osmosis (RO) process following membrane bioreactor (MBR) treatment has been applied more commonly. In this study, an autotrophic sulfur-based denitrifying column performance was evaluated, for the first time, for nitrate reduction from permeate of a lab-scale MBR receiving real textile wastewater and from the concentrate stream of a real scale-RO plant used for recovering water from textile wastewater. Nitrate concentration in the MBR effluent and RO concentrate averaged 35 ± 3 and 12 ± 2 mg-N/L, respectively. With the sulfur-based column bioreactor, quite high (≥90%) denitrification performances were attained both for MBR effluent and RO concentrate up to nitrate loadings of 0.432 and 0.12 g-N/(L.d), respectively. COD present in wastewater was not utilized in the column bioreactor, which illustrates no or minimal contribution of heterotrophic denitrification. Alkalinity concentration in the wastewater was enough to buffer the acid formation during autotrophic denitrification. Sulfate was generated accompanied by nitrate reduction and sulfide was formed at low nitrate loadings. In the batch tests, the denitrification rates for the MBR effluent and RO concentrate were 0.31 and 0.28 g-N/(g-VSS.d), respectively, which were relatively higher than the ones observed for the synthetic nitrate-contaminated groundwater. Autotrophic sulfur-based denitrification is a promising and robust process alternative even for textile RO concentrate with high concentrations of salinity, non-biodegradable COD, and color.

Impact of textile dyes on health and ecosystem: a review of structure, causes, and potential solutions

The rapid growth of population and industrialization have intensified the problem of water pollution globally. To meet the challenge of industrialization, the use of synthetic dyes in the textile industry, dyeing and printing industry, tannery and paint industry, paper and pulp industry, cosmetic and food industry, dye manufacturing industry, and pharmaceutical industry has increased exponentially. Among these industries, the textile industry is prominent for the water pollution due to the hefty consumption of water and discharge of coloring materials in the effluent. The discharge of this effluent into the aquatic reservoir affects its biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), and pH. The release of the effluents without any remedial treatment will generate a gigantic peril to the aquatic ecosystem and human health. The ecological-friendly treatment of the dye-containing wastewater to minimize the detrimental effect on human health and the environment is the need of the hour. The purpose of this review is to evaluate the catastrophic effects of textile dyes on human health and the environment. This review provides a comprehensive insight into the dyes and chemicals used in the textile industry, focusing on the typical treatment processes for their removal from industrial wastewaters, including chemical, biological, physical, and hybrid techniques.

Impact of temperature and biomass augmentation on biosulfur-driven autotrophic denitrification in membrane bioreactors treating real nitrate-contaminated groundwater

Nitrate (NO₃^-) contamination of groundwater is a major health concern worldwide as it can lead to serious illnesses such as methemoglobinemia and cancer. Autotrophic denitrification is a smart approach for treating groundwater, being typically organic-deficient. Lately, biogenic sulfur (S⁰_bio) has emerged as a sustainable, free, and high-efficiency substrate to fuel membrane bioreactors (MBRs) treating contaminated groundwater. However, the effects of moderate temperature and biomass concentration on the performance and fouling of the S⁰_bio-fed MBR were not investigated previously. This study shows that biomass levels of ~1 g MLVSS/L limit membrane fouling but also denitrification efficiency. Biomass augmentation up to 3 g MLVSS/L enhanced denitrification but worsened fouling due to increase of extracellular polymeric substance (EPS) levels in the bulk liquid. Temperature decrease from 30 °C to 20 °C halved denitrification efficiency, which could be partially recovered through bioaugmentation. The mechanisms affected by temperature decrease, practical applications, and future research needs were discussed.

Cake layer reformation rates on self forming dynamic membranes and performance comparison with microfiltration membranes

Dynamic membranes (DMs) keep on attracting attention progressively as an alternative to conventional membranes because they can be operated with relatively higher fluxes and lower fouling rates. However, there are many factors affecting the performance of DMs, such as DM pore size, structure, and operating conditions. In this study, mainly focused on the investigation of cake formation rates both in initial formation and reformation rates after physical/chemical cleaning. In this context, it has been evaluated the performances of DMs with different pore sizes (171 μm, 90 μm, and 30 μm) and different structures under the same conditions and compared their performances with microfiltration (MF) membranes (0.45 μm and 0.22 μm) in a single reactor. In the study, the effects of different fluxes (15-, 20-, 25 L/m²·h (LMH), SAD_m (1-, 0.8-, 0.5 m³-air /m²·h) and F/M (0.095, 0.125, 0.19 g-COD/g-MLSS·day) conditions on the treatment and filtration performance of DMs were investigated. High COD (>95%) and turbidity (<10 NTU) removals were obtained in this study. In particular, the 30 μm DM (0.65 ± 0.47 NTU) produced quite close effluent turbidity compared to MFs (0.12 ± 0.05 NTU). Low SAD_m and high F/M values resulted in increased effluent COD concentrations and turbidity values. By decreasing the SAD_m, the cake formation rate and the fouling rate increased, which showed that there is a definite relationship between the cake formation rates and the fouling rates. Additionally, considering all the results, the most stable operation was obtained in the 30 μm DM, although it has been occurred the least fouling in the 90 μm membrane in the study. This study, focused on cake reformation rates, attempts to show that DMs can be used as an alternative to MBRs. Especially, when taking into account the results of the reformation rate of 30 μm DM (6.09 NTU/h) and other high filterability features.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

Quorum quenching strategy for biofouling control in membrane photobioreactor

This study aims to reduce membrane fouling in membrane photobioreactor (MPBR) through the quorum quenching (QQ) strategy. For this purpose, the QQ beads (immobilized Rhodococcus sp. BH4) were added to the MPBR, and antifouling ability was evaluated in consideration of the changes in transmembrane pressure (TMP), extracellular polymeric substance (EPS), microbial community, and cake layer morphology on the membrane surface. The results showed that the TMP of control MPBR (MPBR-C) reached 818 mbar and 912 mbar on the operation hours of 35 and 170, while the TMP of experimental MPBR (MPBR-QQ) was only 448 mbar and 676 mbar, respectively. The QQ strategy effectively reduced the EPS content in MPBR. The microscopic observations indicated that the QQ diminished the cake layer formation and pore-blocking on the membrane surface. Comparisons of 16S and 18S gene communities revealed minor differences between bacterial and eukaryotic species in MPBRs at phylum and class levels.

Membrane bioreactors for hospital wastewater treatment: recent advancements in membranes and processes

Discharged hospital wastewater contains various pathogenic microorganisms, antibiotic groups, toxic organic compounds, radioactive elements, and ionic pollutants. These contaminants harm the environment and human health causing the spread of disease. Thus, effective treatment of hospital wastewater is an urgent task for sustainable development. Membranes, with controllable porous and nonporous structures, have been rapidly developed for molecular separations. In particular, membrane bioreactor (MBR) technology demonstrated high removal efficiency toward organic compounds and low waste sludge production. To further enhance the separation efficiency and achieve material recovery from hospital waste streams, novel concepts of MBRs and their applications are rapidly evolved through hybridizing novel membranes (non hydrophilic ultrafiltration/microfiltration) into the MBR units (hybrid MBRs) or the MBR as a pretreatment step and integrating other membrane processes as subsequent secondary purification step (integrated MBR-membrane systems). However, there is a lack of reviews on the latest advancement in MBR technologies for hospital wastewater treatment, and analysis on its major challenges and future trends. This review started with an overview of main pollutants in common hospital waste-water, followed by an understanding on the key performance indicators/criteria in MBR membranes (i.e., solute selectivity) and processes (e.g., fouling). Then, an in-depth analysis was provided into the recent development of hybrid MBR and integrated MBR-membrane system concepts, and applications correlated with wastewater sources, with a particular focus on hospital wastewaters. It is anticipated that this review will shed light on the knowledge gaps in the field, highlighting the potential contribution of hybrid MBRs and integrated MBR-membrane systems toward global epidemic prevention.

Resource recovery from industrial effluents through the cultivation of microalgae: A review

Industrial effluents such as pharmaceutical residues, pesticides, dyes, and metal processes holds abundant value-added products (VAPs), where its recovery has become essential. The purpose of such recovery is for sustainable treatment, which is an approach that considers the economic, social, and environmental aspects. Microalgae with its potential in the recovery process from effluents, can reduce energy usage of waste management strategies and regenerate nutrients such as carbon, phosphorus, and nitrogen. Microalgae cultures offer the use of inorganic materials by microalgae for their growth and the help of bacteria to produce biomass, thus, resulting in the absence of secondary emissions due to its ability to eliminate volatile organic compounds. Moreover, recovered bioactive compounds are transformed into bioethanol, bio-fertilizers, biopolymer, health supplements and animal feed. Therefore, it is significant to focus on an economical and efficient utilization of microalgae in recovering nutrients that can be further used in various commercial applications.

β-cyclodextrin-containing polymer based on renewable cellulose resources for effective removal of ionic and non-ionic toxic organic pollutants from water

A novel, bio-derived cyclodextrin-based trifunctional adsorbent has been successfully synthesized for efficient, rapid and simultaneous removal of a broad-spectrum of toxic ionic (anionic and cationic dyes) and non-ionic organic pollutants from water. The composition, morphology and the presence of functional groups in the obtained sorption material were characterized by elemental analysis, XRD, SEM, and FTIR spectroscopy. The adsorption results were represented by cationic dye (crystal violet, CV) and endocrine disrupting compound (bisphenol A, BPA) as an adsorbate. The sorption processes of the model pollutants were studied with both kinetic and equilibrium models. The results showed that the sorption was rapid (less than 1 min) and the time evolution could be fitted using a pseudo-second order model. According to Langmuir isotherm model, the maximum adsorption capacities were found at 113.64 and 43.10 mg g^-1 for BPA and CV, respectively. The adsorption ability of β-CDPs was kept nearly on the same level after five regeneration cycles. Furthermore, almost complete removal of the pollutants was observed during the treatment of real effluents samples thus the bio-derived, cheap and reusable BAN-EPI-CDP has a promising potential for practical applications.

Treatment of landfill leachate using single-stage anoxic moving bed biofilm reactor and aerobic membrane reactor

Landfill leachate (LFL) is one of the most serious environmental problems due to the high concentrations of toxic and hazardous matters. Although several physical, chemical, methods have been tested, biological processes and single or multiple-stage combinations of them have been receiving more attention due to their cost-effective and environmentally-friendly manner. The present work recommended coupling of conventional single-stage A/O with moving bed biofilm reactor and membrane bioreactor (AnoxMBBR/AeMBR) for LFL treatment. The system performance was evaluated for 233 d under varying nitrate concentrations (100-1000 mgNO₃^--N/L), sludge retention time (SRT) (30-90 d), and HRT (24-48 h) in AnoxMBBR, and constant SRT (infinite) and HRT (48 h) in the AeMBR. The best system performances were observed at 1000 mgNO₃^--N/L concentration, SRT of 90 d and HRT of 48 h, and the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and nitrate‑nitrogen (NO₃^-N) were 74.2%, 99.7%, and 89.1%, respectively. Besides, the AeMBR was achieved above 99% NH₄⁺-N removal and not adversely affected by varying operation conditions of AnoxMBBR. A slight increase in selected phthalic acid ester (PAE) concentrations (diethyl phthalate (DEP), di (2-Ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP)) was detected in the AnoxMBR, and complete PAEs removal was attained in the AeMBR. Mg, Al, Si, Na, Fe was detected by SEM-EDX analyses in both biofilm of AnoxMBBR and the cake layers of AeMBR. Nitrobacter and Nitratireductor which showed a relatively high abundance played an important role in the removal of NH₄⁺-N and COD in LFL. The results confirmed that the proposed sequence is efficient for COD removal, nitrogen removal, and PAEs being an acceptable treatment for landfill leachates.

Progress in osmotic membrane bioreactors research: Contaminant removal, microbial community and bioenergy production in wastewater

Renewable energy, water conservation, and environmental protection are the most important challenges today. Osmotic membrane bioreactor (OMBR) is an innovative process showing superior performance in bioenergy production, eliminating contaminants, and low fouling tendency. However, salinity build-up is the main drawback of this process. Identifying the microbial community can improve the process in bioenergy production and contaminant treatment. This review aims to study the recent progress and challenges of OMBRs in contaminant removal, microbial communities and bioenergy production. OMBRs are widely reported to remove over 80% of total organic carbon, PO₄^3-, NH₄⁺ and emerging contaminants from wastewater. The most important microbial phyla for both hydrogen and methane production in OMBR are Firmicutes, Proteobacteria and Bacteroidetes. Firmicutes' dominance in anaerobic processes is considerably increased from usually 20% at the beginning to 80% under stable condition. Overall, OMBR process has great potential to be applied for simultaneous bioenergy production and wastewater treatment.

Optimization of Operating Conditions for Electrochemical Decolorization of Methylene Blue with Ti/α-PbO2/β-PbO2 Composite Electrode

α-PbO2 was introduced into the intermediate layer of an electrode to prevent the separation of the electrodeposited layer and maintain oxidizing power. The resulting Ti/α-PbO2/β-PbO2 composite electrode was applied to the electrochemical decolorization of methylene blue (MB) and the operating conditions for MB decolorization with the Ti/α-PbO2/β-PbO2 electrode were optimized. The morphology, structure, composition, and electrochemical performance of Ti/α-PbO2 and Ti/α-PbO2/β-PbO2 anode were evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The optimum operating parameters for the electrochemical decolorization of MB at Ti/α-PbO2/β-PbO2 composites were as follows: Na2SO4 electrolyte 0.05 g L−1, initial concentration of MB 9 mg L−1, cell voltage 20 V, current density 0.05–0.10 A cm−2, and pH 6.0. MB dye could be completely decolorized with Ti/α-PbO2/β-PbO2 for the treatment time of less than one hour, and the dye decolorization efficiency with Ti/α-PbO2/β-PbO2 was about 5 times better, compared with those obtained with Ti/α-PbO2.

Core nitrogen cycle of biofoulant in full-scale anoxic & oxic biofilm-membrane bioreactors treating textile wastewater

Core nitrogen cycle within biofoulant in full-scale anoxic & oxic biofilm-membrane bioreactor (bMBR) treating textile wastewater was investigated. Wastewater filtered through membrane with biofoulant had elevated NH₄⁺-N and NO₂^--N concentrations corresponding to decreased NO₃^--N concentrations. Nevertheless, total nitrogen concentrations did not change significantly, indicating negligible nitrogen removal activities within biofoulant. Metagenomic analysis revealed a lack of genes, such as AmoCAB and Hao in biofoulant, indicating absence of nitrification or anammox populations. However, genes encoding complete pathway for dissimilatory nitrate reduction to ammonium (DNRA) were discovered in 15 species that also carry genes encoding both nitrate reductase and nitrite reductase. No specie contained all genes for complete denitrification pathway. High temperature, high C:N ratio, and anoxic conditions of textile wastewater could favorite microbes growth with DNRA pathway over those with canonical denitrification pathway. High dissolved oxygen concentrations could effectively inhibit DNRA to minimize ammonia concentration in the effluent.

Variation and comparison of biotoxicity during typical biological treatment of dyeing wastewater

In present study, dyeing wastewater samples were collected from three typical dyeing wastewater treatment plants in Wujiang, Shengze and Shanghai, China. Physicochemical properties and biotoxicity indicators (luminescent bacteria acute toxicity and umu genotoxicity) were tested and the relationships among them were analyzed. The results revealed that two biotoxicity indicators varied significantly among different treatment units of three plants. After treatment by plant A, luminescent bacteria acute toxicity of dyeing wastewater reduced effectively, while umu genotoxicity increased significantly. Two biotoxicity indicators exhibited decrease and increase trends during the treatment processes of plant B and plant C, respectively. Correlation analysis indicated that there was little correlation among biotoxicity indicators and physicochemical properties, meanwhile two kinds of biotoxicity indicators were relatively independent. Therefore, it was recommended that comprehensive evaluation of dyeing wastewater toxicity needs the combination of various biotoxicity indicators, and the relationship among biotoxicity indicators and physicochemical properties of dyeing wastewater should be established individually. The results of this study would offer a general understanding and evaluation of biotoxicity during actual dyeing wastewater treatment processes and provide database for toxicity reduction and management of dyeing wastewater.

Self-forming dynamic membrane bioreactor for textile industry wastewater treatment

The robustness of anaerobic dynamic membrane bioreactor (AnDMBR) for synthetic textile wastewater treatment was investigated. Textile wastewater may contain high concentrations of NaCl and sulfate, hence their impact on the AnDMBR performance was investigated in detail. A dynamic membrane was formed on a 20-μm pore sized nylon support layer at a constant flux of around 8 LMH. In the absence of sulfate addition, total and filtered (soluble) COD averaged 96 ± 49 mg/L (91% removal) and 75 ± 35 mg/L (93% removal), respectively. Sulfate addition increased total COD in the permeate to 222 ± 68 mg/L (79% removal). Average SS concentration was lower than 30 mg/L in the permeate although its concentration in the bioreactor reached 10 g/L. Throughout the AnDMBR operation dye removal averaged >97%. Sludge filterability, which was assessed by specific resistance to filtration, supernatant filtration, capillary suction time and viscosity, decreased after sulfate addition. Organic and inorganic matters in the dynamic layer were characterized by SEM-EDS and FTIR analyses.

Performance evaluation of conventional membrane bioreactor and moving bed membrane bioreactor for synthetic textile wastewater treatment

In this study, conventional membrane bioreactor (MBR) and moving bed-membrane bioreactor (MB-MBR) processes were compared in synthetic textile wastewater treatment. For this purpose, the bioreactors were operated as a conventional MBR, an MB-MBR with a biocarrier filling ratio of 20 % and an MB-MBR with a biocarrier filling ratio of 10 %, respectively. In the conventional MBR operation, 93.1 % chemical oxygen demand (COD) and 87.1 % color (Reactive Red 390) removal efficiencies were obtained. In both MB-MBR operations, almost equal COD and color removal efficiencies were found as 98.5 % and 89.5 %, respectively. Moreover, offline physical and chemical membrane cleaning processes were applied every other day and every 15 days throughout the conventional MBR operation, respectively, while no physical or chemical membrane cleaning was required during both MB-MBR operations. Furthermore, lower polysaccharide concentrations of extracellular polymeric substances (EPS) and floc sizes of sludge and higher zeta potential of sludge were determined in MB-MBR. Considering the obtained results, it may be stated that the MB-MBR process is an attractive treatment technology for reducing membrane fouling propensity for treatment of textile wastewater.

Process optimization and filtration performance of an anaerobic dynamic membrane bioreactor treating textile wastewaters

The study aimed at investigating the performance of anaerobic dynamic MBR (AnDMBR) for the treatment of synthetic textile wastewater. A laboratory scale anaerobic bioreactor was operated to test nylon mesh support materials with different pore sizes (20 μm, 53 μm and 100 μm). The performances of the AnDMBR were evaluated with a stimulated wastewater containing 1,000 mg.L^-1 COD and 100 mg.L^-1 dye (Remazol Brilliant Violet 5R). To develop an effective dynamic cake layer on the support material, different operational strategies, i.e. high flux, continuous and intermittently biogas recycle were studied for process optimization and increase the filtration performances. Initially, the bioreactor was operated under continuous biogas recycle. Under this operation strategy, the cake layer was not formed, then intermittent biogas recycle was applied to improve the development of dynamic layer. Effluent SS decreased below 20 mg-SS.L^-1 for all the tested different pore sized supports after the development of the cake layer. Almost complete color (>99%) and high COD removal efficiencies (95-97%) were observed. For all the three supports, the bioreactor was operated at fluxes of 5-15 L.(m².h)^-1 (LMH), which was quite high compared to conventional AnMBRs equipped with micro/ultra-filtration membranes. In order to better understand the formation and its structure, detailed cake layer characterization analyses were conducted with scanning electron microscopy (SEM), SEM coupled Energy Dispersive X-ray Spectroscopy (EDS) and inductively coupled plasma-optical emission spectrometer (ICP). Provided the formation of the cake layer, the comparable flux and removal performances with AnMBRs for all three tested support materials were possible.

Anaerobic membrane bioreactors for treatment of emerging contaminants: A review

Emerging contaminants (ECs) are synthetic organic chemicals that released into the environment, which pose a serious threat to the ecosystem and human health. Due to the high costs of physicochemical methods and the possibility of secondary pollution, and conventional biological treatment techniques are not efficient to remove ECs. Thus, there is a need to develop novel technologies to treat ECs. Anaerobic digestion (AD) is reported to degrade most ECs. Anaerobic membrane bioreactor (AnMBR) is an upgraded AD technology that has high system stability and microbial community abundance. The biogas production and EC biodegradation efficiency in the AnMBR system are markedly higher than those in the traditional AD system. In recent years, AnMBR is widely used to remove environmental ECs. This review analyzes the feasibility and challenges of AnMBR in the treatment of ECs and provides useful insights for improving the performance and efficiency of AnMBR to treat ECs.

Chemical Characterization of Specific Micropollutants from Textile Industry Effluents in Fez City, Morocco

Textile industry is one of the most polluting industries in the world. It has a high importance in terms of its environment impact, since it consumes a considerably large amount of water and produces highly polluted discharge water. In this work, characterization of toxic organic compounds is proposed. Based on gas chromatography coupled to mass spectrometry (GC/MS) screening analysis, organic micropollutant diversity of textile effluents from a local textile processing factory was investigated. In the present work, physicochemical characterization of the studied textile effluents showed considerably high values of principal pollution parameters above the prescribed discharge water limits. Heavy metals like zinc (Zn), copper (Cu), iron (Fe), nickel (Ni), cadmium (Cd), chromium (Cr), and lead (Pb) were found to be present within the permissible limits. The results of GC/MS revealed the presence of various organic compounds belonging to a wide range of chemical classes. Main groups of chemical compounds detected in these effluents were aromatic carboxylic acids, alkanes, aromatic amines, phthalates, aliphatic carboxylic acids, and linear aliphatic alcohols. The results of this study allowed significant contributions to the chemical characterization of textile industry contaminants and identification of indicators that can be considered an important tool for assessment of the potential impact of textile activities to the contamination of aquatic environment and health hazard.

Green synthesis of a magnetic β-cyclodextrin polymer for rapid removal of organic micro-pollutants and heavy metals from dyeing wastewater

Adsorption is one of the most preferred techniques in the advanced treatment of dyeing wastewater. Magnetic porous materials with good adsorption performance, excellent reusability, and a green synthesis route are highly desirable adsorbents in commerce. In this study, we synthesized a magnetic β-cyclodextrin polymer (MNP-CM-CDP) containing many macro- and ultramicropores in aqueous phase. CO₂ adsorption-desorption isotherms and a dye adsorption method provided Langmuir specific surface areas for the MNP-CM-CDP of 114.4 m² g^-1 and 153 m² g^-1, respectively. Model pollutants (BPA, MB, BO₂, RhB, Cr(III), Pb(II), Zn(II), and Cu(II)) were rapidly and efficiently removed from the aqueous solution by the MNP-CM-CDP. In addition, the polymer could be easily separated from the solution under an external magnetic field. The adsorption of the contaminants was dependent on pH, while the effects of ionic strength and humic acid were slight in the concentration range studied. The polymer could be easily regenerated at room temperature and retained good adsorption performance. Moreover, the MNP-CM-CDP showed good feasibility for the removal of pollutants from actual dyeing wastewater samples.

Inhibiting effect of textile wastewater on the activity of sludge from the biological treatment process of the activated sludge plant

Textile industry represents an important source of toxic substances rejected in environment. Indeed, effluent of these industries contains dyes and chemicals. They are rejected in environment without any treatment. The aim of this work is to evaluate ecotoxicological effect of industrial textile effluents on the sludge harvested from activated sludge treatment plant of Marrakech city (Morocco). For this, we are interested in determining the inhibition condition that corresponds to 50% decrease of bacterial activity in sludge. Obtained results showed that inhibition percentage of bacterial activity depends narrowly on contact time and on added effluent volume, until a limit concentration where there is no degradation of substratum. In fact, substratum degradation speed shows about 65 times decrease when 80% (v/v) of textile wastewater is added, in comparison with the controlled one. Consequently the inhibition constant (Ki) that corresponds to 50% of bacterial inhibition activity is estimated to 0.65 mg l^-1 of dye. These studies confirm a real ecotoxicological risk of these effluents. Therefore, a treatment is mandatory before their rejection in environment.

Performance of a pilot-scale reverse osmosis process for water recovery from biologically-treated textile wastewater

Textile industry generates a high volume of wastewater containing various type of pollutants. Although high color and chemical oxygen demand (COD) removals are achieved with the combination of biological and chemical treatment processes, reverse osmosis (RO) process is generally needed for water recovery due to high conductivity of the textile wastewater. In this study, a pilot scale RO process containing one spiral wound membrane element was operated under three different operational modes, i.e. concentrated, complete recycle and continuous, to collect more information for the prediction of a real-scale RO process performance. It was claimed that complete recycle mode of operation enabled mimicking the operational conditions exerted on the first membrane, whereas continuous mode of operation created conditions very similar to the ones exerted on the last membrane element in a real scale RO process train. In the concentrated and continuous mode of operation, water recovery and flux were around 70% and 19 L/m²/h (LMH). Permeate produced in the RO process can be safely reused in the dyeing process as the feed and permeate conductivities were around 5500 μS/cm and 150 μS/cm, respectively, at 70% water recovery. However, color concentration in the concentrate exceeded the discharge limits and would need further treatment. The RO performance was accurately predicted by ROSA simulations.

Treatment of synthetic wastewater and cheese whey by the anaerobic dynamic membrane bioreactor

The aim of this study was to develop a laboratory-scale anaerobic dynamic membrane bioreactor (AnDMBR) for the treatment of high-strength synthetic and real cheese whey wastewater. We determined the appropriate pore size for a convenient type of support material (nylon mesh) to optimize cake layer formation. The performance of the AnDMBRs was measured in terms of chemical oxygen demand (COD) and solids removal efficiencies. During high-strength synthetic wastewater treatment, the 70-μm pore size AnDMBR achieved COD removal efficiencies of 78% and 96% with COD loading rates of 4.03 and 2.34 kg m^-3 day^-1, respectively, while the 10-μm pore size AnDMBR achieved 66% and 92% COD removal efficiencies at COD loading rates of 5.02 and 3.16 kg m^-3 day^-1. The 10 μm pore size AnDMBR was operated in two periods: first period and second period (before and after physical cleaning) during high-strength synthetic wastewater treatment. The 10-μm pore size AnDMBR removed 83% and 88% of suspended solids during period 1 and period 2, respectively. Furthermore, using a pore size of 10 μm retained 72% of solids (973 mg L^-1) in the reactor outlet. The 10-μm pore size AnDMBR performed better than the 70-μm pore size AnDMBR in terms of cake layer formation. The 10-μm pore size AnDMBR was used to treat real cheese whey wastewater, resulting in COD removal efficiencies ranging from 59% (4.32 kg m^-3 day^-1) to 97% (5.22 kg m^-3 day^-1). In addition, 85% of suspended solids were removed from real cheese whey wastewater after treatment. The results show that dynamic membrane technology using a pore size of 10 μm can be used to treat real industrial wastewater.

Evaluation of advanced oxidation processes (AOPs) integrated membrane bioreactor (MBR) for the real textile wastewater treatment

A novel submerged membrane bioreactor integrated with ozonation and photocatalysis has been developed to treat the real textile wastewater and study the fouling behaviour. This study evaluates the performance efficiency in pilot-scale for the three reactors such as membrane bioreactor, ozonised membrane bioreactor and further clubbed with photocatalysis. The membrane filtration consists of polyvinilidine difluoride hollow fibre membrane module having pore size 0.1 μm. Tungsten oxide, a visible photocatalyst was made into spongy alginate beads and used in photocatalytic reactor. The photocatalyst dose has been optimised as 500 mg/L. About 10% membrane filterability ratio has been achieved by integrating ozone with MBR with the maximal ozone dosage of 5 g/h. It showed better removal efficiency in colour and chemical oxygen demand of 94% and 93% respectively. The biodegradability efficiency also was enhanced from 0.2 to 0.4 with optimised ozone dosage (5 g/h). The study on reversible and irreversible fouling has been done to understand the fouling nature. The important analysis such as microbial community and scanning electron microscopy analysis were done to study the biofouling and extent of fouling after filtration. The treatability studies implemented for textile wastewater showed that integrated MBR systems are suitable in meeting the discharge norms prescribed by the Indian statutory body in terms of chemical oxygen demand, colour and total suspended solids.

Halogenated organics generated during online chemical cleaning of MBR: An emerging threat to water supply and public health

The global wastewater treatment capacity of MBR has been constantly growing due to the strong needs in water reuse/cycle and restrictive availability of land. Recent research revealed generation of a variety of halogenated organics during online chemical cleaning of MBR with sodium hypochlorite (NaClO) which has been commonly practiced for fouling control and permeability recovery of MBR. These exogenous halogenated organics may likely migrate into natural water bodies and soils through the discharge of MBR permeate, while they tend to bioaccumulate in aquatic food chains (e.g. aquatic animals and plants), leading to a dangerous concentration level for human health. It should be realized that the potent environmental and public health risks associated with produced halogenated organics in MBR permeate have not yet been aware and assessed in consideration of the entire water life cycles. Therefore, this article attempts to express serious concern on, while raising scientific and public awareness on this emerging issue.

Newly Designed Hydrolysis Acidification Flat-Sheet Ceramic Membrane Bioreactor for Treating High-Strength Dyeing Wastewater

Cost-effective treatment of dyeing wastewater remains a challenge. In this study, a newly designed hydrolysis acidification flat-sheet ceramic membrane bioreactor (HA-CMBR) was used in treating high-strength dyeing wastewater. The start-up phase of the HA-CMBR was accomplished in 29 days by using cultivated seed sludge. Chemical oxygen demand (COD) removal rate reached about 62% with influent COD of 7800 mg/L and an organic loading rate of 7.80 kg-COD/(m³·d). Chromaticity removal exceeded 99%. The results show that the HA-CMBR has good removal performance in treating dyeing wastewater. The HA-CMBR could run with low energy consumption at trans-membrane pressure (TMP) <10 kPa due to the good water permeability of the flat-sheet ceramic membrane. New strains with 92%⁻96% similarity to Alkalibaculum bacchi, Pseudomonas sp., Desulfovibrio sp., and Halothiobacillaceae were identified in the HA-CMBR. Microbial population analysis indicated that Desulfovibrio sp., Deltaproteobacteria, Halothiobacillaceae, Alkalibaculum sp., Pseudomonas sp., Desulfomicrobium sp., and Chlorobaculum sp. dominated in the HA-CMBR.

Energy and greenhouse gas life cycle assessment and cost analysis of aerobic and anaerobic membrane bioreactor systems: Influence of scale, population density, climate, and methane recovery

This study calculated the energy and greenhouse gas life cycle and cost profiles of transitional aerobic membrane bioreactors (AeMBR) and anaerobic membrane bioreactors (AnMBR). Membrane bioreactors (MBR) represent a promising technology for decentralized wastewater treatment and can produce recycled water to displace potable water. Energy recovery is possible with methane generated from AnMBRs. Scenarios for these technologies were investigated for different scale systems serving various population densities under a number of climate conditions with multiple methane recovery options. When incorporating the displacement of drinking water, AeMBRs started to realize net energy benefits at the 1 million gallons per day (MGD) scale and mesophilic AnMBRs at the 5 MGD scale. For all scales, the psychrophilic AnMBR resulted in net energy benefits. This study provides insights into key performance characteristics needed before an informed decision can be made for a community to transition towards the adoption of MBR technologies.

Analysis of the best available techniques for wastewaters from a denim manufacturing textile mill

The present study was undertaken as the first plant scale application and evaluation of Best Available Techniques (BAT) within the context of the Integrated Pollution Prevention and Control/Industrial Emissions Directive to a textile mill in Turkey. A "best practice example" was developed for the textile sector; and within this context, BAT requirements for one of the World's leading denim manufacturing textile mills were determined. In order to achieve a sustainable wastewater management; firstly, a detailed wastewater characterization study was conducted and the possible candidate wastewaters to be reused within the mill were identified. A wastewater management strategy was adopted to investigate the possible reuse opportunities for the dyeing and finishing process wastewaters along with the composite mill effluent. In line with this strategy, production processes were analysed in depth in accordance with the BAT Reference Document not only to treat the generated wastewaters for their possible reuse, but also to reduce the amount of water consumed and wastewater generated. As a result, several applicable BAT options and strategies were determined such as reuse of dyeing wastewaters after treatment, recovery of caustic from alkaline finishing wastewaters, reuse of biologically treated composite mill effluent after membrane processes, minimization of wash water consumption in the water softening plant, reuse of concentrate stream from reverse osmosis plant, reducing water consumption by adoption of counter-current washing in the dyeing and finishing processes. The adoption of the selected in-process BAT options for the minimization of water use provided a 30% reduction in the total specific water consumption of the mill. The treatability studies adopted for both segregated and composite wastewaters indicated that nanofiltration is satisfactory in meeting the reuse criteria for all the wastewater streams considered.

Rapid establishment of phenol- and quinoline-degrading consortia driven by the scoured cake layer in an anaerobic baffled ceramic membrane bioreactor

Although toxic and refractory organics, such as phenol and quinoline, are decomposed by anaerobic bacteria, the establishment of specific degrading consortia is a relatively slow process. An anaerobic membrane bioreactor allows for complete biomass retention that can aid the establishment of phenol- and quinoline-degrading consortia. In this study, the anaerobic digestion of phenol (500 mg L^-1) and quinoline (50 mg L^-1) was investigated using an anaerobic baffled ceramic membrane bioreactor (ABCMBR). The results showed that, within 30 days, 99% of phenol, 98% of quinoline and 88% of chemical oxygen demand (COD) were removed. The substrate utilisation rates of the cake layer for phenol and quinoline, and specific methanogenic activity of the cake layer, were 7.58 mg phenol g^-1 mixed liquor volatile suspended solids (MLVSS) day^-1, 8.23 mg quinoline g^-1 MLVSS day^-1 and 0.55 g COD_CH4 g^-1 MLVSS day^-1, respectively. The contribution of the cake layer to the removals of phenol and quinoline was extremely underestimated because the uncounted scoured cake layer was disregarded. Syntrophus was the key population for phenol and quinoline degradation, and it was more abundant in the cake layer than in the bulk sludge. The highly active scattered cake layer sped up the establishment of phenol- and quinoline-degrading consortia in the ABCMBR.

Acute Responses of Microorganisms from Membrane Bioreactors in the Presence of NaOCl: Protective Mechanisms of Extracellular Polymeric Substances

Extracellular polymeric substances (EPS) are key foulants in membrane bioreactors (MBRs). However, their positive functions of protecting microorganisms from environmental stresses, e.g., during in situ hypochlorite chemical cleaning of membranes, have not been adequately elucidated. In this work, we investigated the response of microorganisms in an MBR to various dosages of NaOCl, with a particular emphasis on the mechanistic roles of EPS. Results showed that functional groups in EPS such as the hydroxyl and amino groups were attacked by NaOCl, causing the oxidation of polysaccharides, denaturation of amino acids, damage to protein secondary structure, and transformation of tryptophan protein-like substances to condensed aromatic ring substances. The presence of EPS alleviated the negative impacts on catalase and superoxide dismutase, which in turn reduced the concentration of reactive oxygen species (ROS) in microbial cells. The direct extracellular reaction and the mitigated intracellular oxidative responses facilitated the maintenance of microbial metabolism, as indicated by the quantity of adenosine triphosphate and the activity of dehydrogenase. The reaction with NaOCl also led to the changes of cell integrity and adhesion properties of EPS, which promoted the release of organic matter into bulk solution. Our results systematically demonstrate the protective roles of EPS and the underlying mechanisms in resisting the environmental stress caused by NaOCl, which provides important implications for in situ chemical cleaning in MBRs.

Simultaneous photocatalytic and microbial degradation of dye-containing wastewater by a novel g-C3N4-P25/photosynthetic bacteria composite

Azo dyes are very resistant to light-induced fading and biodegradation. Existing advanced oxidative pre-treatment methods based on the generation of non-selective radicals cannot efficiently remove these dyes from wastewater streams, and post-treatment oxidative dye removal is problematic because it may leave many byproducts with unknown toxicity profiles in the outgoing water, or cause expensive complete mineralization. These problems could potentially be overcome by combining photocatalysis and biodegradation. A novel visible-light-responsive hybrid dye removal agent featuring both photocatalysts (g-C₃N₄-P₂₅) and photosynthetic bacteria encapsulated in calcium alginate beads was prepared by self-assembly. This system achieved a removal efficiency of 94% for the dye reactive brilliant red X-3b and also reduced the COD of synthetic wastewater samples by 84.7%, successfully decolorized synthetic dye-contaminated wastewater and reduced its COD, demonstrating the advantages of combining photocatalysis and biocatalysis for wastewater purification. The composite apparently degrades X-3b by initially converting the dye into aniline and phenol derivatives whose aryl moieties are then attacked by free radicals to form alkyl derivatives, preventing the accumulation of aromatic hydrocarbons that might suppress microbial activity. These alkyl intermediates are finally degraded by the photosynthetic bacteria.