Large pilot-scale submerged anaerobic membrane bioreactor for the treatment of municipal wastewater and biogas production at 25 °C

Combined inhibition of anaerobic digestion by sulfate, salinity, and ammonium: potential inhibitory factors in forward osmosis-concentrated municipal wastewater

This study investigated the combined and interactive effects of sulfate, salinity (NaCl), and ammonium on mesophilic anaerobic digestion using synthetic wastewater simulating concentrated municipal wastewater from the forward osmosis (FO) process. Batch anaerobic digestion experiments were conducted with varying concentrations of sulfate, NaCl, and ammonium. Complete sulfate reduction was observed in all test systems, regardless of the NaCl and ammonium concentration, indicating no significant inhibitory effect on sulfate-reducing bacteria (SRB). However, the increased toxicity of hydrogen sulfide produced by SRB under high concentrations of sulfate, NaCl, and ammonium inhibited methanogenic activity, resulting in reduced methane production. Despite this, methanogens, primarily Methanosarcina, tolerated low and moderate levels of sulfate, NaCl, and ammonium; thus, their coexistence with SRB (Desulfotomaculales) enabled efficient acetate utilization and methane production. The enhanced Methanosarcina activity was further confirmed through the antagonistic effects between NaCl and ammonium. No significant decrease in methane production was observed in the co-presence of 0.5 g/L sulfate, 10 g/L NaCl, and 1 g/L ammonium-nitrogen compared to the reference condition without the addition of these components. This study identified the inhibitory mechanisms resulting from sulfate, NaCl, and ammonium interactions, which may occur in FO-concentrated municipal wastewater. These findings offer insights for optimizing the FO process to maintain sulfate, NaCl, and ammonium concentrations below inhibitory levels, thereby ensuring efficient methane production.

Harvesting of dissolved methane from anaerobic effluents for enhanced nitrogen removal in mainstream wastewater

The presence of dissolved methane in anaerobic effluents from wastewater treatment plants (WWTPs) significantly contributes to methane emissions. To mitigate this issue, this study introduced the Self-breathing Biofilm Reactor (SbBfR), which achieved a 94 % retention rate of dissolved methane during the aeration stage. Counter-diffusion and co-diffusion systems were established to enhance microbial interactions for both dissolved methane oxidation and nitrogen removal. These systems varied based on alignment or opposition of substrates with externally supplied oxygen. Specifically, the counter-diffusion system isolated oxygen and methane, favoring denitrifying anaerobic methane oxidizing microorganisms, achieving nitrogen removal rate of 175 mg N/L/d with an efficiency of up to 88 %. The spatial distribution patterns of aerobic and anaerobic microbes within the biofilms were characterized using 16S rRNA gene amplicon sequencing combined with cryosection and qPCR analysis. This approach provides a promising solution for reducing dissolved methane emissions from WWTPs while simultaneously achieving efficient nitrogen removal, offering valuable insights for practical wastewater treatment applications.

The most important technologies and highlights for biogas production worldwide

Bioenergy or green fuel has been considered the fuel of the future for being a type of renewable energy that contributes to the preservation of the environment as it helps to reduce greenhouse gas emissions. In this way, biogas offers a potential alternative to fossil fuels from anaerobic digestion (AD) bioprocess, which allows the action of several microorganisms in the transformation of substrates into biogas and secondary bioproducts. Over the years, researchers have discussed that low yields in AD are associated with different factors such as type of wastewater, reactor configuration, substrate concentration, temperature, organic loading rates, and biomass concentration inside of the reactor. In this way, to better conduct the AD, studies point to the reactor configuration as one of the factors in the determination of high biogas production for a long period. Understanding and knowing the type of reactor and how the parameters such as biomass accumulation and immobilization, pH, or temperature occur in the system would provide information and can help to improve the bioenergy production in different systems. Moreover, research opportunities about different technologies are essential for the anaerobic digestion of many substrates and the stability of interest production. Thus, this type of scientific study gives a broad overview of the principal systems used in the AD process and information about the circular economy in the production of biogas in the world. Important considerations are highlighted.Implications: The review paper provides information about the scenario of biogas in the world state-of-art and the biogas production from AD. Afterward, an extensive analysis of different and principal types of reactors applied to the AD process, aimed at presenting an overview of the advantages and disadvantages of each configuration intending to gain new insights to improve traditional reactors or propose novel ones. This article enables us to have a perspective about the different technologies available and about new alternatives from an operational point of view for bioenergy from AD, not only in bench studies or pilot scale studies but also at an industrial level. Thus, this type of scientific study gives a broad overview of the principal systems used in the AD process and information about the circular economy in the production of biogas in the world.

CO2 removal from biogas improved stable treatment of low-alkalinity municipal wastewater using anaerobic membrane bioreactor

This study addressed a less-reported issue: the insufficient alkalinity encountered when anaerobic membrane bioreactors (AnMBRs) are used to treat municipal wastewater (MWW). In the present study, a 20-L AnMBR was initiated at an MWW treatment plant. During the initial startup, a continuous decrease in pH was observed. Through the analyses of the balance between HCO3-/CO2 in the biogas and alkalinity in the reactor, the cause of pH instability was determined to be that the alkalinity could not balance the acidity induced by the continuous dissolution of CO2 from biogas in the liquid phase. Therefore, this study employed the in-situ removal of CO2 from biogas using soda lime to reduce the CO2 partial pressure, thereby achieving stable control of the pH in the reactor. This study provides valuable experience and technical support for anaerobic processes for treating low-alkalinity MWW in the future applications.

Anaerobic treatment of nitrogenous industrial organic wastewater by carbon-neutral processes integrated with anaerobic digestion and partial nitritation/anammox: Critical review of current advances and future directions

Anaerobic digestion combined with partial nitritation/anammox technology holds promising potential for the carbon-neutral treatment of nitrogenous industrial organic wastewater, boasting remarkable advantages in effective removal of both organic matters and nitrogen, bio-energy recovery and carbon emission reduction. This study provides a concise overview of the development and advantages of anaerobic digestion combined with partial nitritation/anammox technology for treating nitrogenous industrial organic wastewater. The process excels in removing organic matter and nitrogen, recovering bio-energy, and reducing carbon emissions, compared to traditional physicochemical and biological methods. Case studies highlight its energy-saving and efficient attributes, especially for carbon-neutral nitrogen removal. Challenges for achieving stable operation in the future are discussed, and the study offers insights into the broader application of this integrated process in industrial wastewater treatment.

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

Use of reclaimed municipal wastewater in agriculture: Comparison of present practice versus an emerging paradigm of anaerobic membrane bioreactor treatment coupled with hydroponic controlled environment agriculture

Advancements in anaerobic membrane bioreactor (AnMBR) technology have opened up exciting possibilities for sustaining precise water quality control in wastewater treatment and reuse. This approach not only presents an opportunity for energy generation and recovery but also produces an effluent that can serve as a valuable nutrient source for crop cultivation in hydroponic controlled environment agriculture (CEA). In this perspective article, we undertake a comparative analysis of two approaches to municipal wastewater utilization in agriculture. The conventional method, rooted in established practices of conventional activated sludge (CAS) wastewater treatment for soil/land-based agriculture, is contrasted with a new paradigm that integrates AnMBR technology with hydroponic (soilless) CEA. This work encompasses various facets, including wastewater treatment efficiency, effluent quality, resource recovery, and sustainability metrics. By juxtaposing the established methodologies with this emerging synergistic model, this work aims to shed light on the transformative potential of the integration of AnMBR and hydroponic-CEA for enhanced agricultural sustainability and resource utilization.

Anaerobic degradation of pesticide wastewater: Improving sludge characteristics and reducing membrane fouling with combined tandem UASB+membrane system with high velocity settlers

In this pilot study, a combined tandem UASB+membrane reactor (R2) with high velocity settlers was proposed for the treatment of pesticide wastewater at different hydraulic retention times (HRT) and compared with a control reactor (R1). The average COD removal efficiencies of the R2 at HRTs of 96, 72, and 48 h were 83.7 %, 82.8 %, and 74.2 %, which are 14 %, 17 %, and 21 % higher than those of the R1, respectively. Throughout the operation, the biogas production of R2 was 33 %, 19 % and 28 % higher than that of R1 at the same stage, respectively, and the methane yield of R2 (0.19-0.26 L CH4/gCODremoved) was improved by 10-17 % compared to that of R1. Mean α values (VFA/ALK) of 0.13∼0.22 indicated that R2 did not undergo acidification. R2 reduced the extracellular polymers (EPS) content in the attached sludge by 56-62 % compared to R1. It also successfully delayed membrane fouling rate by 19-22 %. The results demonstrate that the R2 has a high treatment capacity, stability, and methane recovery, while also effectively reducing membrane fouling.

Anaerobic membrane bioreactors for municipal wastewater: Progress in resource and energy recovery improvement approaches

Anaerobic membrane bioreactor (AnMBR) offer promise in municipal wastewater treatment, with potential benefits including high-quality effluent, energy recovery, sludge reduction, and mitigating greenhouse gas emissions. However, AnMBR face hurdles like membrane fouling, low energy recovery, etc. In light of net-zero carbon target and circular economy strategy, this work sought to evaluate novel AnMBR configurations, focusing on performance, fouling mitigation, net-energy generation, and nutrients-enhancing integrated configurations, such as forward osmosis (FO), membrane distillation (MD), bioelectrochemical systems (BES), membrane photobioreactor (MPBR), and partial nitrification-anammox (PN/A). In addition, we highlight the essential role of AnMBR in advancing the circular economy and propose ideas for the water-energy-climate nexus. While AnMBR has made significant progress, challenges, such as fouling and cost-effectiveness persist. Overall, the use of novel configurations and energy recovery strategies can further improve the sustainability and efficiency of AnMBR systems, making them a promising technology for future sustainable municipal wastewater treatment.

Predictive modeling based on artificial neural networks for membrane fouling in a large pilot-scale anaerobic membrane bioreactor for treating real municipal wastewater

Membrane fouling is the primary obstacle to applying anaerobic membrane bioreactors (AnMBRs) in municipal wastewater treatment. This issue holds critical significance as efficient wastewater treatment serves as a cornerstone for achieving environmental sustainability. This study uses machine learning to predict membrane fouling, taking advantage of rapid computational and algorithmic advances. Based on the 525-day operation data of a large pilot-scale AnMBR for treating real municipal wastewater, regression prediction was realized using multilayer perceptron (MLP) and long short-term memory (LSTM) artificial neural networks under substantial variations in operating conditions. The models involved employing the organic loading rate, suspended solids concentration, protein concentration in extracellular polymeric substance (EPSp), polysaccharide concentration in EPS (EPSc), reactor temperature, and flux as input features, and transmembrane pressure as the prediction target output. Hyperparameter optimization enhanced the regression prediction accuracies, and the rationality and utility of the MLP model for predicting large-scale AnMBR membrane fouling were confirmed at global and local levels of interpretability analysis. This work not only provides a methodological advance but also underscores the importance of merging environmental engineering with computational advancements to address pressing environmental challenges.

Enhancing electricity-driven methanogenesis by assembling biotic-abiotic hybrid system in anaerobic membrane bioreactor

Biotic-abiotic hybrid systems are promising technologies to enhance methane production in anaerobic wastewater treatment. However, the dense structure of the extracellular polymeric substances (EPS) present in anaerobic granular sludge (AGS) poses challenges with respect to the implementation of hybrid systems and efficient interspecies electron transfer. In this study, the use of AGS with a Ni/Fe layered double hydroxide@activated carbon (Ni/Fe LDH@C-AGS) was investigated in an anaerobic membrane bioreactor (AnMBR). The hybrid system showed a significant increase of 82% in methane production. Further research revealed that Ni/Fe LDH@C regulated the dense structure of EPS, stimulated the production of cytochromes, and facilitated the decomposition of nonconductive substances. Surprisingly, the hybrid system also promoted resistance to membrane fouling and extended membrane life by 81%. This study provides insights into the operation of a biotic-abiotic hybrid system by regulating the dense structure of EPS ultimately resulting in an enhanced methane production.

Enhanced methanogenic degradation and membrane fouling associated with protein-EPS by extending sludge retention time in a high-solid anaerobic membrane bioreactor treating concentrated organic sludge

The improvement of organic sludge destruction efficiency and methanogenic performance is a key concern during anaerobic digestion toward maximum energy recovery. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was operated continuously for the treatment of organic sludge from Japanese small-scale collective wastewater treatment facility (Johkasou), and digestion efficiency was enhanced by the optimizing solid retention time (SRT). Degradation efficiency of the substrate improved from 36 % to 52 % and the biogas yield was enhanced from 0.37 to 0.51 L/g-VSfed when the SRT was extended from 30 to 60 d. The net energy yield of AnMBR at SRT 60 days was 9.83 kJ/g-VSfed, and the corresponding energy sufficiency ratio was 181 %, indicating that SRT extension could enhance substrate destruction with significant energy recovery potential. However, a long SRT is characterized by high mixed liquor total solids (MLTS), small particle size, high extracellular polymeric substances content, and poor filterability, which exert detrimental effects on membrane operation. Membrane fouling was effectively controlled by regulating the flux at a sustainable rate. The low fouling region and transition region of operating flux were determined as 0.21-4.6 L/m2/h (LMH) and 1.5-5.7 LMH, respectively, when MLTS was 25-50 g/L, and the main contributors to membrane fouling were high protein fractions and small sludge flocs. The current study proposes a promising method to promote digestion efficiency and provided adequate guidance for membrane operation at super-high MLTS by presenting practical engineering applications of AnMBRs in solid waste treatment.

Evaluation of a sequential anaerobic-aerobic membrane bioreactor system for treatment of traditional and insensitive munitions constituents

New energetic formulations containing insensitive high explosives (IHE), such as 2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazole-5-one (NTO), and nitroguanidine (NQ) are being developed to provide safer munitions. The addition of IHE to munitions formulations results in complex wastewaters from explosives manufacturing, load and pour operations and demilitarization activities. New technologies are required to treat those wastewaters. The core objective of this research effort was to develop and optimize a dual anaerobic-aerobic membrane bioreactor (MBR) system for treatment of wastewater containing variable mixtures of traditional energetics, IHE, and anions. The combined system proved highly effective for treatment of traditional explosives (TNT, RDX, HMX), IHE (DNAN, NTO, NQ) and anions commonly used as military oxidants (ClO4-, NO3-). The anaerobic MBR, which was operated for more than 500 d, was observed to completely degrade mg L-1 concentrations of TNT, DNAN, ClO4- and NO3- under all operational conditions, including at the lowest hydraulic residence time (HRT) tested (2.2 d). The combined system generally resulted in complete treatment of mg L-1 concentrations of RDX and HMX to <20 μg L-1, with most of the degradation occurring in the anaerobic MBR and polishing in the aerobic system. No common daughter products of DNAN, TNT, RDX, or HMX were detected in the effluent. NTO was completely transformed in the anaerobic MBR, but residual 3-amino-1,2,4-triazole-5-one (ATO) was detected in system effluent. The ATO rapidly decomposed when bleach solution was added to the final effluent. NQ was initially recalcitrant in the system, but microbial populations eventually developed that could degrade >90% of the ∼10 mg L-1 NQ entering the anaerobic MBR, with the remainder degraded to <50 μg L-1 in the aerobic system. The dual MBR system proved to be capable of complete degradation of a wide mixture of munitions constituents and was resilient to changing influent composition.

Towards low energy-carbon footprint: Current versus potential P recovery paths in domestic wastewater treatment plants

With the unprecedented exhaustion of natural phosphorus (P) resource and the high eutrophication potential of the associated-P discharge, P recovery from the domestic wastewater is a promising way and has been putting on agenda of wastewater industry. To address the concern of P resource recovery in an environmentally sustainable way is indispensable especially in the carbon neutrality-oriented wastewater treatment plants (WWTPs). Therefore, this review aims to offer a critical view and a holistic analysis of different P removal/recovery process in current WWTPs and more P reclaim options with the focus on the energy consumption and greenhouse gas (GHG) emission. Unlike P mostly flowing out in the planned/semi-planned P removal/recovery process in current WWTPs, P could be maximumly sequestered via the A-2B- centered process, direct reuse of P-bearing permeate from anaerobic membrane bioreactor, nano-adsorption combined with anaerobic membrane and electrochemical P recovery process. The A-2B- centered process, in which the anaerobic fixed bed reactor was designated for COD capture for energy efficiency while P was enriched and recovered with further P crystallization treating, exhibited the lowest specific energy consumption and GHG emission on the basis of P mass recovered. P resource management in WWTPs tends to incorporate issues related to environmental protection, energy efficiency, GHG emission and socio-economic benefits. This review offers a holistic view with regard to the paradigm shift from "simple P removal" to "P reuse/recovery" and offers in-depth insights into the possible directions towards the P-recovery in the "water-energy-resource-GHG nexus" plant.

Influence of Solid Retention Time on Membrane Fouling and Biogas Recovery in Anerobic Membrane Bioreactor Treating Sugarcane Industry Wastewater in Sahelian Climate

Sugarcane industries produce wastewater loaded with various pollutants. For reuse of treated wastewater and valorization of biogas in a Sahelian climatic context, the performance of an anaerobic membrane bioreactor was studied for two solid retention times (40 days and infinity). The pilot was fed with real wastewater from a sugarcane operation with an organic load ranging from 15 to 22 gCOD/L/d for 353 days. The temperature in the reactor was maintained at 35 °C. Acclimatization was the first stage during which suspended solids (SS) and volatile suspended solids (VSS) evolved from 9 to 13 g/L and from 5 to 10 g/L respectively, with a VSS/SS ratio of about 80%. While operating the pilot at a solid retention time (SRT) of 40 days, the chemical oxygen demand (COD) removal efficiency reached 85%, and the (VSS)/(TSS) ratio was 94% in the reactor. At infinity solid retention time, these values were 96% and 80%, respectively. The 40-day solid retention time resulted in a change in transmembrane pressure (TMP) from 0.0812 to 2.18 bar, with a maximum methane production of 0.21 L/gCOD removed. These values are lower than those observed at an infinite solid retention time, at which the maximum methane production of 0.29 L/gCOD was achieved, with a corresponding transmembrane pressure variation of up to 3.1 bar. At a shorter solid retention time, the fouling seemed to decrease with biogas production. However, we note interesting retention rates of over 95% for turbidity.

Performance and economic evaluation of a pilot scale embedded ends-free membrane bioreactor (EEF-MBR)

In this work, an embedded ends-free membrane bioreactor (EEF-MBR) has been developed to overcome the fouling problem. The EEF-MBR unit has a novel configuration where a bed of granular activated carbon is placed in the bioreactor tank and fluidized by the aeration system. The performance of pilot-scale EEF-MBR was assessed based on flux and selectivity over 140 h. The permeate flux fluctuated between 2 and 10 L.m^-2.h^-1 under operating pressure of 0.07-0.2 bar when EEF-MBR was used to treat wastewater containing high organic matter. The COD removal efficiency was more than 99% after 1 h of operating time. Results from the pilot-scale performance were then used to design a large-scale EEF-MBR with 1200 m³.day^-1 capacity. Economic analysis showed that this new MBR configuration was cost-effective when the permeate flux was set at 10 L.m^-2.h^-1. The estimated additional cost for the large-scale wastewater treatment was about 0.25 US$.m^-3 with a payback period of 3 years. KEY POINTS: • Performance of new MBR configuration, EEF-MBR, was assessed in long term operation. • EEF-MBR shows high COD removal and relatively stable flux. • Cost estimation of large scale shows the cost effective EEF-MBR application.

The phosphorus harvest from low-temperature mainstream wastewater through iron phosphate crystallization in a pilot-scale partial nitritation/anammox reactor

The phosphorus harvest along nitrogen removal in the partial nitritation/anammox (PNA) reactor is promising for saving space and simplifying the management of mainstream wastewater treatment facilities. In this study, the phosphorus recovery from the low-temperature mainstream wastewater was explored through iron phosphate crystallization in a pilot-scale PNA reactor. With the COD-alleviated municipal wastewater as the influent, the ammonium concentration of about 50 mg/L and the phosphorus concentration ranged from 5.4 to 7.1 mg/L, under the temperature of 15 °C and the addition of external ferrous iron of 14 mg/L, the achieved nitrogen removal efficiency and the phosphorus removal efficiency were 37.6 % and 62.7 %, respectively. The good settleability of sludge indicated that the formed iron phosphate was well combined with the biomass. The quantitative analysis confirmed that the main iron phosphate in dry sludge was graftonite, and qualitative analysis confirmed that the equivalent of P₂O₅ content in the sludge was 5.8 %, which was suitable as fertilizer on agricultural land to realize the direct recycle of discharged phosphorus. In all, this study proposed a pioneering scheme to realize the nitrogen removal and phosphorus cycle in human society and given a meaningful reference for further research and application.

A Comprehensive Review on Wastewater Nitrogen Removal and Its Recovery Processes

Discharging large amounts of domestic and industrial wastewater drastically increases the reactive nitrogen content in aquatic ecosystems, which causes severe ecological stress and biodiversity loss. This paper reviews three common types of denitrification processes, including physical, chemical, and biological processes, and mainly focuses on the membrane technology for nitrogen recovery. The applicable conditions and effects of various treatment methods, as well as the advantages, disadvantages, and influencing factors of membrane technologies, are summarized. Finally, it is proposed that developing effective combinations of different treatment methods and researching new processes with high efficiency, economy, and energy savings, such as microbial fuel cells and anaerobic osmotic membrane bioreactors, are the research and development directions of wastewater treatment processes.

Anaerobic membrane bioreactor for carbon-neutral treatment of industrial wastewater containing N, N-dimethylformamide: Evaluation of electricity, bio-energy production and carbon emission

The feasibility of anaerobic membrane bioreactor (AnMBR) for the treatment of N, N-dimethylformamide (DMF)-containing wastewater was theoretically compared with the conventional activated sludge (CAS) process in this study. The electricity consumption and expenditure, bio-energy production and CO₂ emission were investigated using the operational results of a lab-scale AnMBR operated in a long-term operation. The AnMBR was capable of producing bio-methane from wastewater and generated 3.45 kWh/m³ of electricity as recovered bio-energy while the CAS just generated 1.17 kWh/m³ of electricity from the post-treatment of excessive sludge disposal. The large quantity of bio-methane recovered by the AnMBR can also be sold as sustainable bioresource for the use of household natural gas with a theoretical profit gain of 29,821 US$/year, while that of the CAS was unprofitable. The AnMBR was also demonstrated to significantly reduce the carbon emission by obtaining a theoretical negative CO₂ production of -2.34 kg CO₂/m³ with the recycle of bio-energy while that for the CAS was 4.50 kg CO₂/m³. The results of this study demonstrate that the AnMBR process has promising potential for the carbon-neutral treatment of high-strength DMF-containing wastewater in the future.

Recovery of methane dissolved in the effluent of a novel upflow anaerobic hybrid reactor (UAHB) submitted to temperature variation

Recent studies point out losses of 30-40% of the produced methane in the effluent of anaerobic reactors treating sewage, reducing the renewable energy potential and the environmental footprint. A novel bench-scale upflow anaerobic hybrid (UAHB) reactor combining a sludge blanket at the bottom and a filter media at the top, both with three-phase separators, was proposed to evaluate the recovery of dissolved methane. UAHB was operated with volumetric organic loading rate of 1.24 kg COD m^-3 d^-1 and hydraulic retention time of 8 h for 218 days to evaluate the influence of temperature (18°C, 23°C, and 28°C) in the methane dissolved in the effluent and collected from three-phase separators. Chemical oxygen demand (COD) and total suspended solids (TSS) removals efficiencies remained constant during the operation and equal to 90 and 95%, respectively, related to the activity of biomass retained in the filter media. Temperature increase influenced more the methane production in the sludge blanket rather than in the upper bed. The volume of recovered methane increased about 20% with the installation of the support media and the upper three-phase separator (3PHS). The loss of methane dissolved in the effluent was strongly influenced by the temperature, and higher with the decrease of this parameter. Non-statistically significant correlations were observed between the temperature and the methane production in the upper bed (p-value = 0.0943) and total (p-value = 0.0930). Thus, it can be concluded that the evaluated temperatures did not influence the global efficiency and the total methane yield of the UAHB reactor.

Material mass balance and elemental flow analysis in a submerged anaerobic membrane bioreactor for municipal wastewater treatment towards low-carbon operation and resource recovery

The anaerobic membrane bioreactor (AnMBR) has gained huge attention as a municipal wastewater (MWW) treatment process that combined high organics removal, a low sludge yield and bioenergy recovery. In this study, a 20 L AnMBR was set up and operated steadily for 70 days in temperate conditions with an HRT of 6 h and a flux of 12 LMH for the treatment of real MWW, focusing on the behavior of the major elements (C, N, P and S) from an elemental balance perspective. The results showed that the AnMBR achieved more than 85 % COD removal, a low sludge yield (0.081 gVSS/gCOD_removed) and high methane production (0.31 L-CH₄/gCOD_removed) close to the theoretical value. The elemental flow analysis revealed that the AnMBR converted 77 % of the influent COD to methane (57 % gaseous and 20 % dissolved) and 6 % of the COD for sludge production. In addition, the AnMBR converted 34 % of the total carbon to energy-generated carbon, and only 3 % was in the form of CO₂ in the biogas for further upgradation, which was in line with the concept of carbon neutrality. Since little nitrogen or phosphorus were removed, the permeate was nutrient-rich and further treatment to recover the nutrients would be required. This study illustrates the superior performance of the AnMBR for MWW treatment with a microscopic view of elemental behavior and provides a reference for implementing the mainstream AnMBR process in carbon-neutral wastewater treatment plants.

Two-stage anaerobic membrane bioreactor for co-treatment of food waste and kitchen wastewater for biogas production and nutrients recovery

Co-digestion of organic waste and wastewater is receiving increased attention as a plausible waste management approach toward energy recovery. However, traditional anaerobic processes for co-digestion are particularly susceptible to severe organic loading rates (OLRs) under long-term treatment. To enhance technological feasibility, this work presented a two-stage Anaerobic Membrane Bioreactor (2 S-AnMBR) composed of a hydrolysis reactor (HR) followed by an anaerobic membrane bioreactor (AnMBR) for long-term co-digestion of food waste and kitchen wastewater. The OLRs were expanded from 4.5, 5.6, and 6.9 kg COD m^-3 d^-1 to optimize biogas yield, nitrogen recovery, and membrane fouling at ambient temperatures of 25-32 °C. Results showed that specific methane production of UASB was 249 ± 7 L CH₄ kg^-1 COD_removed at the OLR of 6.9 kg TCOD m^-3 d^-1. Total Chemical Oxygen Demand (TCOD) loss by hydrolysis was 21.6% of the input TCOD load at the hydraulic retention time (HRT) of 2 days. However, low total volatile fatty acid concentrations were found in the AnMBR, indicating that a sufficiently high hydrolysis efficiency could be accomplished with a short HRT. Furthermore, using AnMBR structure consisting of an Upflow Anaerobic Sludge Blanket Reactor (UASB) followed by a side-stream ultrafiltration membrane alleviated cake membrane fouling. The wasted digestate from the AnMBR comprised 42-47% Total Kjeldahl Nitrogen (TKN) and 57-68% total phosphorous loading, making it suitable for use in soil amendments or fertilizers. Finally, the predominance of fine particles (D10 = 0.8 μm) in the ultrafiltration membrane housing (UFMH) could lead to a faster increase in trans-membrane pressure during the filtration process.

Long term operation performance and membrane fouling mechanisms of anaerobic membrane bioreactor treating waste activated sludge at high solid concentration and high flux

High solid anaerobic membrane bioreactor (HSAnMBR) is widely applied in biomass treatment and energy regeneration, while membrane operation performance and membrane fouling control remain critical issues. In this study, a HSAnMBR was utilized for waste activated sludge (WAS) treatment at organic loading rates of 3.69-3.72 gCOD/L·d and biogas yield was ranged in 0.38-0.39 L/gVS_fed with the COD conversion efficiency of 40 %. The membrane operated stably when the average flux was 9.6, 4.5 and 1.2 L/m²/h at mixed liquor total solid of 25, 30 and 40 g/L with a filtration: relaxation of 4:1, 1:1 and 1:2, respectively. The distinctive characteristics of membrane fouling at high solid condition were that the polysaccharides and proteins had high fouling propensity and were the main composition of the foulant layer. Furthermore, phosphorus and magnesium were the predominant causes of inorganic fouling. The minerals precipitated on the membrane and were embedded into membrane pores, contributing to cake layer formation and pore blocking. This research provided a comprehensive analysis of the membrane operation characterization and fouling mechanisms of HSAnMBR, which was expected to push forward HSAnMBR applications to WAS treatment.

Performance of an Innovative Low-Cost Recycled Filling (LCRF) in Anaerobic Treatment of Dairy Effluent-A Pilot-Scale Study

The rapid growth in dairy production leads to increasing outputs of high-load effluent, necessitating new methods of treating such waste. Anaerobic processes have been increasingly popular but are hamstrung by limited nutrient removal efficiency. The aim of the present study was to investigate whether low-cost recycled filling (LCRF) improves the anaerobic treatment of dairy effluent. The addition of LCRF was found to increase both COD removal (86.1 ± 2.6%-92.8 ± 1.6%) and P_tot. removal (22.1 ± 3.5% to 36.9 ± 4.6%) from the wastewater. The LCRF ensured near-neutral pH and stabilized the structure of the anaerobic microbe community (including Archaea) across all pollutant loads tested. This translated to efficient biogas production and high methane content in the LCRF reactors, peaking at 0.35 ± 0.01 m³/kg COD_removed and 68.2 ± 0.6% (respectively) in the best-performing variant.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Performance evaluation of a full-scale upflow anaerobic sludge blanket reactor coupled with trickling filters for municipal wastewater treatment in a developing country

Poor wastewater management remains a critical health and environmental challenge in most developing countries in Sub-Saharan Africa due to the lack of adequate infrastructure for collection and treatment. This study evaluated the performance and methane production of a full-scale upflow anaerobic sludge blanket (UASB) reactor of capacity 18000 m3/d, with post-treatment unit: trickling filters followed by final settling tanks for municipal wastewater treatment in Ghana. Data was collected on operational conditions and physicochemical parameters of wastewater (influent and effluent) over a period of 35 weeks in 2021 (from January to August). The influent biochemical oxygen demand to chemical oxygen demand (BOD:COD) ratio was 0.58 ± 0.16, indicating the presence of highly biodegradable compounds in the sewage. Operational conditions for the UASB reactors were observed to be within the optimal range for anaerobic systems, with an applied organic loading rate of 1.30 ± 0.79 kgCOD/m3/d. Generally, Plant performance was satisfactory with carbon removal at 93% for COD and 98% for BOD. Biogas yield was 0.2 m3/kgCOD removed, culminating in an average biogas production rate of 831.6 ± 292.7 m3/d. Average methane composition was 64.7 ± 11.9% of the biogas output, whilst an estimated 35% of the methane generated remained dissolved in the UASB effluent. The UASB reactor presents an efficient technology that can be implemented in developing countries for effective and sustainable wastewater management.

Applications of submerged and staged membrane systems for pollutant removal from effluents and mechanism studies - a review

Membrane based filtration is one of the promising technologies for rehabilitation of wastewater streams for reuse and recycle. Many advancements have emerged with the use of novel materials and innovative integrated technologies. The present investigation focuses on the treatment methods based on submerged and stages systems of membranes for water purification. Ceramic, polymeric and mixed matrix type of membranes fabricated for specific type of effluents, their modification methods for accelerating the rejection efficiency, permeability, durability, stability and antifouling properties are detailed in this review. Graphene oxide is the most considered membrane material for adsorption purposes as it exhibits larger surface area, abundant functional groups contain oxygen and has good supply of ligands which is responsible in metal adsorption as it enhances electrostatic interaction by bonding metal ions with graphene oxide nanosheets. Energy derivation in terms of biogas production was also reported in some integrated methods. In many cases, embedded nanomaterial matrices yielded maximum efficiencies in both the submerged and staged operations. However, submerged type of membranes are reported more than the staged type due to simpler configuration with relatively lesser equipment, operational and maintenance issues. In treatment of a low strength wastewater, aluminum oxide based membrane in fluidized bed assembly was reported to yield promising results with reduced power requirement.

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.

Enhanced organic degradation and biogas production of domestic wastewater at psychrophilic temperature through submerged granular anaerobic membrane bioreactor for energy-positive treatment

This study deals with the conversion of organic matter into methane at ambient temperature, during anaerobic digestion of domestic wastewater combined with a submerged ultrafiltration membrane with no gas-sparging. A one-stage submerged granular anaerobic membrane bioreactor (G-AnMBR) and a control anaerobic digester (UASB type) were operated during four months, after 500 days of biomass acclimatization to psychrophilic and low loading rate conditions. Membrane barrier led to the retention of biomass, suspended solids and dissolved and colloidal organic matter which greatly enhanced total COD (tCOD) removal (92.3%) and COD to methane conversion (84.7% of tCOD converted into dissolved and gaseous CH4). G-AnMBR overcame the usual long start-up period and led to a higher sludge heterogeneity, without altering the granular biomass activity. The feasibility of the G-AnMBR without gas-sparging was also assessed and the net positive energy balance was estimated around + 0.58 kWh.m^-3.

Pilot plant demonstration of temperature impacts on the methanogenic performance and membrane fouling control of the anaerobic membrane bioreactor in treating real municipal wastewater

A 5,000-L anaerobic membrane bioreactor (AnMBR) fed with actual municipal wastewater was employed to study the impact of temperature drops on methanogenic performance and membrane fouling. With temperature dropped from 25 °C to 15 °C, the methane yield decreased from 0.244 to 0.205 NL-CH₄/g-COD_removal and the dissolved methane increased from 29% to 43%, resulted in the methanogenic performance reduced by 25%. The membrane rejection offset the deteriorated anaerobic digestion at low temperatures and ensured the stable COD removal efficiency of 84.5%-90.0%. The synergistic effects of the increased microbial products and viscosity and the residual inorganic foulants aggravated the membrane fouling at lower temperatures. As the organic fouling was easily removed by NaClO, the inorganics related to the elements of S, Ca and Fe were the stubborn membrane foulants and required the enhanced acid membrane cleaning. These findings obtained under the quasi-practical condition are expected to promote the practical applications of mainstream AnMBR.

A review on anaerobic membrane bioreactors for enhanced valorization of urban organic wastes: Achievements, limitations, energy balance and future perspectives

Sustainable urban development is threatened by an impending energy crisis and large amounts of organic wastes generated from the municipal sector among others. Conventional waste management methods involve greenhouse gas (GHG) emission and limited resource recovery, thus necessitating advanced techniques to convert such wastes into bioenergy, bio-fertilizers and valuable-added products. Research and application experiences from different scale applications indicate that the anaerobic membrane bioreactor (AnMBR) process is a kind of high-rate anaerobic digester for urban organic wastes valorization including food waste and waste sludge, while the research status is still insufficiently summarized. Through compiling recent achievements and literature, this review will focus on the following aspects, including AnMBR treatment performance and membrane fouling, technical limitations, energy balance and techno-economic assessment as well as future perspectives. AnMBR can enhance organic wastes treatment via complete retention of functional microbes and suspended solids, and timely separation of products and potential inhibitory substances, thus improving digestion efficiency in terms of increased organics degradation rates, biogas production and process robustness at a low footprint. When handling high-solid organic wastes, membrane fouling and mass transfer issues can be the challenges limiting AnMBR applications to a wet-type digestion, thus countermeasures are required to pursue extended implementations. A conceptual framework is proposed by taking various organic wastes disposal and final productions (permeate, biogas and biosolids) utilization into consideration, which will contribute to the development of AnMBR-based waste-to-resource facilities towards sustainable waste management and more economic-environmental benefits output.

Looking for lipases and lipolytic organisms in low-temperature anaerobic reactors treating domestic wastewater

Poor lipid degradation limits low-temperature anaerobic treatment of domestic wastewater even when psychrophiles are used. We combined metagenomics and metaproteomics to find lipolytic bacteria and their potential, and actual, cold-adapted extracellular lipases in anaerobic membrane bioreactors treating domestic wastewater at 4 and 15 °C. Of the 40 recovered putative lipolytic metagenome-assembled genomes (MAGs), only three (Chlorobium, Desulfobacter, and Mycolicibacterium) were common and abundant (relative abundance ≥ 1%) in all reactors. Notably, some MAGs that represented aerobic autotrophs contained lipases. Therefore, we hypothesised that the lipases we found are not always associated with exogenous lipid degradation and can have other roles such as polyhydroxyalkanoates (PHA) accumulation/degradation and interference with the outer membranes of other bacteria. Metaproteomics did not provide sufficient proteome coverage for relatively lower abundant proteins such as lipases though the expression of fadL genes, long-chain fatty acid transporters, was confirmed for four genera (Dechloromonas, Azoarcus, Aeromonas and Sulfurimonas), none of which were recovered as putative lipolytic MAGs. Metaproteomics also confirmed the presence of 15 relatively abundant (≥ 1%) genera in all reactors, of which at least 6 can potentially accumulate lipid/polyhydroxyalkanoates. For most putative lipolytic MAGs, there was no statistically significant correlation between the read abundance and reactor conditions such as temperature, phase (biofilm and bulk liquid), and feed type (treated by ultraviolet light or not). Results obtained by metagenomics and metaproteomics did not confirm each other and extracellular lipases and lipolytic bacteria were not easily identifiable in the anaerobic membrane reactors used in this study. Further work is required to identify the true lipid degraders in these systems.

Unveiling the characterization and development of prokaryotic community during the start-up and long-term operation of a pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater

The anaerobic membrane bioreactor (AnMBR) is a promising sustainable process and technology for the treatment of municipal wastewater from the perspective of carbon neutrality. In this study, a large pilot-scale AnMBR was constructed and the microbial community development of the anaerobic digested sludge in the AnMBR was determined during the treatment of municipal wastewater. The AnMBR system was conducted for 217 days during a long-term operation with the feed of real municipal wastewater. The characterization and dynamics of the microorganisms revealed that a stable prokaryotic community was gradually achieved. In the community of methane-producing archaea (or methanogens), the acetotrophic methanogen Methanosaeta was significantly enriched at an ambient temperature of 25 °C with an overwhelming relative abundance in the entire community. The abundance of Methanosaeta was even higher than the most abundant bacterial phyla Chloroflexi, Firmicutes, Proteobacteria and Bacteroidetes. This phenomenon is quite different from that found in other typical anaerobic systems. The massive enrichment of methanogens is the key to maintaining stable methane production in the treatment of municipal wastewater by the AnMBR. The interspecies cooperation of major functional bacterial groups including protein/carbohydrate/cellulose-degrading (genera Anaerovorax, Aminomonas, Levilinea, Flexilinea and Ruminococcus etc.), sulfate-reducing (Desulfovibrio and Desulfomicrobium etc.) and syntrophic (Syntrophorhabdus and Syntrophus etc.) bacteria with acetotrophic and hydrogenotrophic archaea enhances the stability of reactor operation and help to acclimate the entire prokaryotic community to the characteristics of real municipal wastewater.

Bioremediation of industrial effluents: A synergistic approach

Industrial wastewater consists of inorganic and organic toxic pollutants that pose a threat to environmental sustainability. The organic pollutants are a menace to the environment and life forms than the inorganic substances and pose teratogenic, mutagenic, carcinogenic, and other serious detrimental effects on the living entities, moreover, they have a gene-altering effect on aquatic life forms and affect the soil fertility and quality. Removal of varying effluents having recalcitrant contaminants with conventional treatment technologies is strenuous. In contrast to physical and chemical methods, biological treatment methods are environmentally friendly, versatile, efficient, and technically feasible with low operational costs and energy footprints. Biological treatment is a secondary wastewater treatment system that utilizes the metabolic activities of microorganisms to oxidize or reduce inorganic and organic compounds and transform them into dense biomass, which later can be removed by the sedimentation process. Biological treatment in bioreactors is an ex situ method of bioremediation and provides the benefits of continuous monitoring under controlled parameters. This paper attempts to provide a review of bioremediation technologies discussing most concerning widespread bioreactors and advances used for different industrial effluents with their comparative merits and limitations.

Use of spray nozzles to recover dissolved methane from an Upflow Anaerobic Sludge Blanket (UASB) reactor effluent

Methane is a powerful greenhouse gas and a source of energy. Recovering this gas means lower greenhouse gas emission and potential reduction of energetic costs. The lack of full-scale results, the use of different methodologies to detect dissolved methane (d-CH₄) and the fact that no process to remove d-CH₄ from anaerobic effluents is energetically or economically viable at full-scale urged a different approach to the problem. To avoid methodological interference and facilitate comparison of results the Standard Test Method number D8028-17 published by ASTM International can be used to determine d-CH₄. The use of real anaerobic reactor effluent also helps results to be compared. In this study, 80 samples from a full-scale anaerobic reactor showed an average concentration of dissolved methane of 14.9 mg·L^-1, meaning an emission of 229 kg of CO₂ eq·h^-1 and an average of 113.5 kW wasted. Using spray nozzles, an alternative to the methods being researched, the average methane recovery was 11.5 mg·L^-1 of CH₄, an efficiency of 81.6%, meaning 177 kg of CO₂ eq·h^-1 emissions avoided and 87.9 kW of recoverable energy.

Virus removal during sewage treatment by anaerobic membrane bioreactor (AnMBR): The role of membrane fouling

Anaerobic membrane bioreactor (AnMBR) is a low-energy and promising solution for sewage treatment. During the treatment, the fouled membrane of AnMBR is recognized as an important barrier against pathogenic viruses. Here, the role of membrane fouling of an AnMBR at room temperature in the virus removal was investigated using MS2 bacteriophage as a virus surrogate. Results revealed that the virus removal efficiency of AnMBR was in the range of 0.2 to 3.6 logs, gradually increasing with the course of AnMBR operation. Virus removal efficiency was found to be significantly correlated with transmembrane pressure (R²=0.92, p<0.01), especially in the rapid fouling stage, indicating that membrane fouling was the key factor in the virus removal. The proportion of virus decreased from 52.03% to 15.04% in the membrane foulants when membrane fouling was aggravating rapidly, yet increased from 0.74% to 21.52% in the mixed liquor. Meanwhile, the permeate flux dramatically dropped. These imply that the primary rejection mechanism of virus by membrane in the slow fouling stage is the virus adsorption onto membrane, while the sieving effect is the main reason in the rapid fouling stage. Ex-situ virus rejection test unveiled that the cake layer was the main contributor to the overall virus rejection, while the greatest resistance-specific virus rejection was provided by the organic pore blocking. This paper provides operation strategies to balance enhanced virus removal and high permeate flux by regulating the membrane fouling process.

Nitrogen removal by a Hydroxyapatite-enhanced Micro-granule type One-stage partial Nitritation/anammox process following anaerobic membrane bioreactor treating municipal wastewater

Nitrogen removal from wastewater by the partial nitritation/anammox (PNA) technology is promising from both economic and environmental perspectives. However, this technology has not been popularized in the mainstream because of low biomass retention and the growth of the nitrite oxidizing bacteria. In this study, a one-stage PNA process with hydroxyapatite (HAP)-enhanced granules was used to treat effluent from a mainstream anaerobic membrane bioreactor. The HAP-enhanced reactor allowed an enriched high biomass of 6.9 ± 0.2 g/L at a low hydraulic retention time of 2 h. A nitrogen removal efficiency of 80 ± 6.0 %, a nitrogen removal rate of 0.36 ± 0.05 kg/m³/d and a COD removal efficiency of 54 ± 15 % were achieved stably, leading to a low total nitrogen concentration of 8.5 ± 2.7 mg/L and a low COD concentration of 19.7 ± 5.9 mg/L in the effluent. Anammox bacteria of Candidatus Kuenenia stuttgartiensis and ammonium oxidizing bacteria of Nitrosomonas were found to be the two most predominant bacteria.

In-situ monitoring of membrane fouling migration and compression mechanism with improved ultraviolet technique in membrane bioreactors

An improved UV spectrum in-situ monitoring system was applied to explore the membrane fouling behavior in membrane bioreactors (MBRs). The changes in absorbance curve illustrated that the formation of a stubborn fouling layer includes the migration and compression of membrane surface foulants. The initial flux negatively correlates with the migration degree (unevenness) of membrane fouling, while fiber length is positively correlated. In further experiments, ultrasonic thickness measurement excludes fouling layer compression caused by spatial collapse under external force. Moisture content measurement tests demonstrated that the moisture content changed from 52% to 31% after fouling layer compression, which confirmed that the fouling layer compression is mainly caused by the "high pressure dehydration effect". Finally, a membrane backwashing strategy based on fouling layer compression theory indicated that the backwashing process should be carried out at a stage where the accumulation of membrane fouling is constant but the fouling layer is not compressed.

Microstructure and granulation cycle mechanisms of anammox-HAP coupled granule in the anammox EGSB reactor

The formation of anammox-hydroxyapatite (HAP) coupled granules has been shown to be an approach to efficient nitrogen removal and phosphorus recovery in the anammox EGSB reactor. However, the granulation cycle mechanism of anammox-HAP coupled granules for sustainable regeneration and growth is still not well understood. In this study, the microstructure, chemical composition and microbial structure of a total of six different-sized granules, from 0.25 mm to 2.8 mm, was determined. An SEM-EDS analysis indicated that the small granules (<0.5 mm) were composed of poly-pellet clusters with anammox biofilms attached to the HAP cores, and the large granules (>0.5 mm) consisted of a three-layer structure: a surface anammox biofilm layer, a middle connection layer, and a HAP mineral inner core. The analysis of elemental composition and microbial structure suggested homogenous granular characteristics regardless of granule size. The dominant microorganisms were anammox bacteria of Candidatus Kuenenia stuttgartiensis and heterotrophic denitrifying bacteria. Based on these results, a granulation cycle mechanism for anammox-HAP coupled granules was proposed for the first time. The growth of the small granules with the simultaneous enlargement of anammox biofilms and HAP cores results in the formation of large granules. Large granules regenerate new small granules in a two-step procedure. The first step is the separation of embryo HAP crystals from the mother core via heterogeneous growth, and the second step is the separation of the biofilms due to biodegradation and shear stress.

The first pilot-scale demonstration of the partial nitritation/anammox-hydroxyapatite process to treat the effluent of the anaerobic membrane bioreactor fed with the actual municipal wastewater

Recently, it was reported that for synthetic low-strength wastewater, the excellent nitrogen removal rate (NRR) accompanied with phosphorus removal could be achieved through the partial nitritation/anammox (PNA)-hydroxyapatite (HAP) process. Thus, this research further investigated the performance of the pilot-scale PNA-HAP process treating the effluent of an anaerobic membrane bioreactor (AnMBR) fed with the actual municipal wastewater. The results showed that with the hydraulic retention time of 4.0 h, the influent ammonium concentration ranging from 36.0 to 41.0 mg/L, and the BOD₅ ranging from 6.3 to 12.7 mg/L, the average NRR and the nitrogen removal efficiency was 0.13 kg/m³/d and 63.38%, respectively. The specific activity test of sludge confirmed that the PNA process was the main nitrogen metabolism pathway. The effluent nitrate and the BOD₅ were almost zero, indicating the existence of denitrification activity in reactor. Given that the oxygenation condition, the heterotrophic organic matter oxidization activity also occurred in reactor. The sludge analysis confirmed the phosphate formation in sludge. Thus, in the reactor, four kinds of biological activities and chemical crystallization occurred harmoniously in sludge. From the mixed liquid volatile suspended solid of 2.4 g/L and the low distribution range of granule size, it was obvious that the sludge had a high dispersity. Based on the well settling ability of sludge during the operation, it was inferred that there was a close bond between biomass and HAP in sludge, which was helpful to enhance the settleability of sludge granule. Besides, the phosphorus-containing sludge was suitable as the fertilizer. In all, this study demonstrated that the PNA-HAP process is an ideal alternative treating the effluent of the AnMBR process in the municipal wastewater treatment.

Optimizing anaerobic technology by using electrochemistry and membrane module for treating pesticide wastewater: Chemical oxygen demand components and fractions distribution, membrane fouling, effluent toxicity and economic analysis

Optimization in performance and membrane fouling of an electrochemical anaerobic membrane bioreactor (R1) for treating pesticide wastewater was investigated and compared with a conventional anaerobic membrane bioreactor (R2). The maximum COD removal efficiency of R2 was 80.1%, 80.0%, 67.4%, 61.1% with HRT of 96, 72, 48 and 24 h, which of R1 was enhanced to 84.7%, 84.3%, 82.0% and 66.3%. These results demonstrated that the optimum HRT of R1 was shortened to 48 h, which of R2 required 72 h. R1 reduced the contents of particulate and colloidal COD, and the fraction of COD converted to sludge was 5.0-8.2% lower than that of R2. The fouling rate was 0.99-1.44 kPa/d and reduced by 31.0%-38.5% compared with R2. Detoxification was enhanced by 7.8-47.7% with the assistance of bio-electrochemistry. Ultimately, ensuring similar performance, R1 achieved a 65.6% improvement in environmental benefit, a 26.3% and 38.9% reduction in unit capital and operating costs.

Integrated anaerobic and algal bioreactors: A promising conceptual alternative approach for conventional sewage treatment

Conventional sewage treatment applying activated sludge processes is energy-intensive and requires great financial input, hampering widespread implementation. The introduction of anaerobic membrane bioreactors (AnMBR) followed by an algal reactor growing species of commercial interest, may present an alternative, contributing to the envisaged resource recovery at sewage treatment plants. AnMBRs can be applied for organic matter removal with energy self-sufficiency, provided that effective membrane fouling management is applied. Haematococcus pluvialis, an algal species with commercial value, can be selected for ammonium and phosphate removal. Theoretical analysis showed that good pollutant removal, positive financial output, as well as a significant reduction in the amount of hazardous activated sludge can be achieved by applying the proposed process, showing interesting advantages over current sewage treatment processes. Microbial contamination to H. pluvialis is a challenge, and technologies for preventing the contamination during continuous sewage treatment need to be applied.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

Chemical oxygen demand and nitrogen transformation in a large pilot-scale plant with a combined submerged anaerobic membrane bioreactor and one-stage partial nitritation-anammox for treating mainstream wastewater at 25 °C

A novel municipal wastewater treatment process towards energy neutrality and reduced carbon emissions was established by combining a submerged anaerobic membrane bioreactor (SAnMBR) with a one-stage partial nitritation-anammox (PN/A), and was demonstrated at pilot-scale at 25 °C. The overall COD and BOD₅ removal efficiencies were 95.1% and 96.4%, respectively, with 20.3 mg L^-1 COD and 5.2 mg L^-1 BOD₅ remaining in the final effluent. The total nitrogen (TN) removal efficiency was 81.7%, resulting 7.3 mg L^-1 TN was discharged from the system. The biogas yield was 0.222 NL g^-1 COD _removed with a methane content range of 78-81%. Approximately 90% of influent COD was removed in the SAnMBR, and 70% of influent nitrogen was removed in the PN/A. The denitrification which occurred in the PN/A enhanced overall COD and nitrogen removal. The successful operation of this pilot-scale plant indicates the SAnMBR-PN/A process is suitable for treating real municipal wastewater.

Physico-chemical and biological treatment strategies for converting municipal wastewater and its residue to resources

An increase in urbanization and industrialization has not only contributed to an improvement in the lifestyle of people, but it has also contributed to a surge in the generation of wastewater. To date, conventional physico-chemical and biological treatment methods are widely used for the treatment of wastewater. However, the efficient operation of these systems require substantial operation and maintenance costs, and the application of novel technologies for the treatment and disposal of sludge/residues. This review paper focuses on the application of different treatment options such as chemical, catalyst-based, thermochemical and biological processes for wastewater or sludge treatment and membrane-based technologies (i.e. pressure-driven and non-pressure driven) for the separation of the recovered products from wastewater and its residues. As evident from the literature, a wide variety of treatment and resource recovery options are possible, both from wastewater and its residues; however, the lack of planning and selecting the most appropriate design (treatment train) to scale up from pilot to the field scale has limited its practical application. The economic feasibility of the selected technologies was critically analyzed and the future research prospects of resource recovery from wastewater have been outlined in this review.

Evaluation of bio-energy recovery from the anaerobic treatment of municipal wastewater by a pilot-scale submerged anaerobic membrane bioreactor (AnMBR) at ambient temperature

The potential of bio-energy recovery from real municipal wastewater was investigated using a one-stage pilot-scale submerged anaerobic membrane bioreactor (AnMBR) for a range of HRTs from 24 h to 6 h at ambient temperature around 25 °C. This pilot-scale AnMBR demonstrated a high COD removal efficiency of over 90% during an operation of 217 days for municipal wastewater treatment. The energy balance of the AnMBR was calculated from both theoretical and practical aspects. The theoretical net energy potential was calculated as 0.174 kWh/m³ by applying operational data to empirical equations, obtaining a bio-energy recovery efficiency of 69.4%. The practical net energy potential was estimated as -0.014 kWh/m³ using the powers of engines applied in a full-scale wastewater treatment plant. This is considerably lower than that of the conventional activated sludge process. These results are evidence of the potential of the AnMBR and feasibility in the treatment of municipal wastewater treatment.

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.

Important effects of temperature on treating real municipal wastewater by a submerged anaerobic membrane bioreactor: Removal efficiency, biogas, and microbial community

A submerged anaerobic membrane bioreactor (SAnMBR) was used in the treatment of real municipal wastewater at operation temperatures ranging from 15 °C to 25 °C and hydraulic retention time (HRT) of 6 h. The treatment process was evaluated in terms of organic removal efficiency, biogas production, sludge growth and membrane filtration. During long-term operation, the SAnMBR achieved chemical oxygen demand removal efficiencies of about 90% with a low sludge yield (0.12-0.19 g-VSS/g-COD_rem) at 20-25 °C. Approximately 1.82-2.27 kWh/d of electric energy was generated during the wastewater treatment process at 20-25 °C, 0.67 kWh/d was generated at 15 °C. The microbial community analysis results showed that microbial community was dominated by aceticlastic methanogens, coupled by hydrogenotrophic methanogens and a very small quantity of methylotrophic methanogens. It was also shown that the stabilization of the microbial community could be attributed to the carbohydrate-protein degrading bacteria and the carbohydrate degrading bacteria.

Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance

Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) was varied from 20–90 days. This was achieved at a constant membrane flux, maintained by adjusting transmembrane pressure (TMP) in the range 1.8–9.8 kPa. Membrane fouling was assessed based on the required TMP, with mixed liquors characterised using capillary suction time, frozen image centrifugation and quantification of extracellular polymeric substances (EPS). SRT had a significant effect on these parameters: fouling was least at an SRT of 30 days and highest at 60 days, with some reduction as this extended to 90 days. Operation at SRT < 30 days showed no further benefits. Although operation at a short SRT was optimal for membrane performance it led to lower specific methane productivity, higher biomass yields and higher effluent COD. Short SRT may also have accelerated the loss of essential trace elements, leading to reduced performance under these conditions. A COD-based mass balance was conducted, including both biomass and methane dissolved in the effluent.

Sludge yield and degradation of suspended solids by a large pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater at 25 °C

Sludge yield and suspended solid are important factors concerned in the anaerobic treatment of municipal wastewater. In this study, a large pilot-scale anaerobic membrane bioreactor (AnMBR) was constructed for effectively treating real municipal wastewater at an ambient temperature of 25 °C. The sludge yield and the degradation of influent suspended solids were evaluated during the long-term operation of the AnMBR. This reactor with 5.0 m³ effective volume is the largest one-stage submerged AnMBR that has ever been used to treat municipal wastewater. During the long-term operation of 217 days, this AnMBR obtained excellent COD and BOD₅ removal efficiency over 90%. Stable biogas production was also successfully obtained from treating municipal wastewater. The sludge yield of the AnMBR was approximately 0.19-0.26 g MLSS g^-1 COD removed for the treatment of real municipal wastewater. The shortest SRT of the AnMBR was calculated as 29 days for an HRT of 6 h at an empirical MLSS of 10 g L^-1. While the influent suspended solid (SS) contained in the municipal wastewater was completely removed by the AnMBR, only 57%-66% of the influent SS was degraded. The rest of influent SS was directly converted to MLSS instead of being degraded. The AnMBR maintained a stable membrane filtration using a hollow-fiber membrane with a total area of 72 m², realizing a flux of 2.75-17.83 LMH, and the mean transmembrane pressure (TMP) was 0.9-23.5 kPa. An online chemical backwash cleaning system helped to lower the TMP timely using sodium hypochlorite and citric acid when the TMP increased rapidly and reached the rated limit of membrane. This is the first report on demonstrating the successful operation and detailed performance of a large pilot-scale AnMBR applied to the treatment of real municipal wastewater.