Bioenergy recovery from methanogenic co-digestion of food waste and sewage sludge by a high-solid anaerobic membrane bioreactor (AnMBR): mass balance and energy potential

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.

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.Implication of Statement: The review paper provides information about the scenario of biogas in the world state-of-art and the biogas production from AD. Afterwards, 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.

A compound enzyme as an additive to a continuous anaerobic dynamic membrane bioreactor for enhanced lignocellulose removal from codigestion: Performance, membrane characteristics and microorganisms

To explore the enzyme-enhanced strategy of a continuous anaerobic dynamic membrane reactor (AnDMBR), the anaerobic codigestion system of food waste and corn straw was first operated stably, and then the best combination of compound enzymes (laccase, endo-β-1,4-glucanase, xylanase) was determined via a series of batch trials. The results showed that the methane yield (186.8 ± 19.9 mL/g VS) with enzyme addition was 12.2 % higher than that without enzyme addition. Furthermore, the removal rates of cellulose, hemicellulose and lignin increased by 31 %, 36 % and 78 %, respectively. In addition, dynamic membranes can form faster and more stably with enzyme addition. The addition of enzymes changed the structure of microbial communities while maintaining sufficient hydrolysis bacteria (Bacteroidetes), promoting the proliferation of Proteobacteria as a dominant strain and bringing stronger acetylation ability. In summary, the compound enzyme strengthening strategy successfully improved the methane production, dynamic membrane effect, and degradation rate of lignocellulose in AnDMBR.

Anaerobic acidification membrane bioreactor operating at acidic condition for treating concentrated municipal wastewater: Performance and implication

To address the low-carbon treatment requirements for municipal wastewater, a novel anaerobic acidification membrane bioreactor (AAMBR) was developed for recovering organic matter in terms of volatile fatty acids (VFAs). While the AAMBR successfully generated VFAs from municipal wastewater through forward osmosis (FO) membrane concentration, its operation was limited to a single pH value of 10.0. Here, performance of the AAMBR operating at acidic condition was evaluated and compared with that at alkaline condition. The findings revealed that the AAMBR with pH 5.0 efficiently transformed organic matter into acetic acid, propionic acid, and butyric acid, resulting in a VFAs yield of 0.48 g/g-CODfeed. In comparison with the AAMBR at pH 10.0, this study achieved a similar VFAs yield, a lower fouling tendency, a lower loss of nutrients and a lower controlling cost. In conclusion, this study demonstrated that a pH of 5.0 is optimal for the AAMBR treating municipal wastewater.

Incorporating saline microalgae biomass in anaerobic digester treating sewage sludge: Impact on performance and microbial populations

The aim of this study was to acclimate anaerobic prokaryotes to saline microalgae biomass. Semi-continuous experiments were conducted using two 1.5 L mesophilic reactors for 10 weeks, (hydraulic retention time of 21 days). The first reactor was solely fed with sewage sludge (control), while the second received a mixture of sewage sludge and microalgal biomass (80/20 %w/w) cultivated at 70 g·L-1 salinity. The in-reactor salinity reached after the acclimation phase was 14 g·L-1. Biomethane production was comparable between the control and acclimated reactors (205 ± 29 NmLMethane·gVolatileSolids-1). Salinity tolerance assessment of methanogenic archaea revealed that salinity causing 50% inhibition of methane production increased from 10 to 27 g·L-1 after acclimation. Microbial diversity analyses revealed notable changes in methanogenic archaea populations during co-digestion of saline microalgae biomass, particularly methylotrophic (+27%) and acetotrophic (-26%) methanogens. This study has highlighted the possibility of treating efficiently saline microalgae in co-digestion with sewage sludge in future industrial biogas plants.

Comparative study of high-performance mesophilic and thermophilic anaerobic membrane bioreactors in the co-digestion of sewage sludge and food waste: Methanogenic performance and energy recovery potential

To support smart cities in terms of waste management and bioenergy recovery, the co-digestion of sewage sludge (SeS) and food waste (FW) was conducted by the anaerobic membrane bioreactor (AnMBR) under mesophilic and thermophilic conditions in this study. The biogas production rate of the thermophilic AnMBR (ThAnMBR) at the SeS to FW ratio of 0:100, 75:25, 50:50 and 100:0 was 2.84 ± 0.21, 2.51 ± 0.26, 1.54 ± 0.26 and 1.31 ± 0.08 L-biogas/L/d, inconspicuous compared with that of the mesophilic AnMBR (MeAnMBR) at 3.00 ± 0.25, 2.46 ± 0.30, 1.63 ± 0.23 and 1.30 ± 0.17 L-biogas/L/d, respectively. The higher hydrolysis ratio and the poorer rejection efficiencies of the membrane under thermophilic conditions, resulting that the permeate COD, carbohydrate and protein of the ThAnMBR was higher than that of the MeAnMBR. The lost COD that might be converted into biogas was discharged with the permeate in the ThAnMBR, which was partly responsible for the inconspicuous methanogenic performance. Furthermore, the results of energy recovery potential assessment showed that the energy return on investment (EROI) of the MeAnMBR was 4.54, 3.81, 2.69 and 2.22 at the four SeS ratios, which was higher than that of the ThAnMBR at 3.29, 2.97, 2.02 and 1.80, respectively, indicating the advantage of the MeAnMBR over the ThAnMBR in energy recovery potential. The outcomes of this study will help to choose a more favorable temperature to co-digest SeS and FW to support the construction of smart cities.

Membrane-based technology in water and resources recovery from the perspective of water social circulation: A review

In this review, the application of membrane-based technology in water social circulation was summarized. Water social circulation encompassed the entire process from the acquirement to discharge of water from natural environment for human living and development. The focus of this review was primarily on the membrane-based technology in recovery of water and other valuable resources such as mineral ions, nitrogen and phosphorus. The main text was divided into four main sections according to water flow in the social circulation: drinking water treatment, agricultural utilization, industrial waste recycling, and urban wastewater reuse. In drinking water treatment, the acquirement of water resources was of the most importance. Pressure-driven membranes, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) were considered suitable in natural surface water treatment. Additionally, electrodialysis (ED) and membrane capacitive deionization (MCDI) were also effective in brackish water desalination. Agriculture required abundant water with relative low quality for irrigation. Therefore, the recovery of water from other stages of the social circulation has become a reasonable solution. Membrane bioreactor (MBR) was a typical technique attributed to low-toxicity effluent. In industrial waste reuse, the osmosis membranes (FO and PRO) were utilized due to the complex physical and chemical properties of industrial wastewater. Especially, membrane distillation (MD) might be promising when the wastewater was preheated. Resources recovery in urban wastewater was mainly divided into recovery of bioenergy (via anaerobic membrane bioreactors, AnMBR), nitrogen (utilizing MD and gas-permeable membrane), and phosphorus (through MBR with chemical precipitation). Furthermore, hybrid/integrated systems with membranes as the core component enhanced their performance and long-term working ability in utilization. Generally, concentrate management and energy consumption control might be the key areas for future advancements of membrane-based technology.

Enhanced digestion of sludge via co-digestion with food waste in a high-solid anaerobic membrane bioreactor: Performance evaluation and microbial response

A 15 L high-solid mesophilic AnMBR was operated for the digestion of food waste, primary sludge and excess sludge. The digestion performance was evaluated from the perspective of methane generation, permeate quality and organic reduction. Furthermore, the change in the microbial community was investigated by 16S rRNA gene analysis. The results showed that the introduction of sludge decreased the H2S levels in biogas compared with the mono-digestion of food waste and the co-digestion with food waste increased biogas and methane production compared with the mono-digestion of sludge. A substitution ratio of 25 % became a turning point of permeate composition and reaction rates. The energy recovery ratios of the mesophilic AnMBR were over 75 % based on stoichiometric analysis. In reaction kinetics analysis, hydrolysis as the first step of anaerobic digestion was found to be most influenced by the composition of the substrate. Finally, the microbial community structures were stable under tested conditions while the evolutionary relationships within the dominant phyla were observed. In the archaea community, Methanosaeta was the dominant methanogen regardless sludge ratio in the substrate.

Optimization of membrane filtration and cleaning strategy in a high solid thermophilic AnMBR treating food waste

Anaerobic membrane bioreactor is advantageous over traditional processes for food waste treatment, i.e. short retention time, high loading rate, and particulate clean permeate. However, establishing a sustainable membrane filtration is a long-standing challenge because of its high viscosity and solids concentration characteristics. Therefore, this study investigated the changes in the membrane permeability before and after the cleaning during a 130-day thermophilic anaerobic experiment. Results show that the AnMBR system could maintain high stability even under a short HRT of 10 days and OLR of 9.0 kg-COD/(m3·d) with low volatile fatty acid of 50 mg/L. The membrane filtration deteriorates with the concurrence of a sharp increase of viscosity when the volatile solids reached 23 g/L. A critical flux was achieved at 5.5 L/(m2·h) under optimized operation conditions, membrane filtration/relaxing ratio with less than 4:1 at a hydraulic retention time of 15 d. Membrane fouling can be removed by soaking the membrane in NaClO (1 g/L, 15 h) and citric acid (2 g/L, 2 h). Conclusively, this work provides insight to establish the operation strategy for a thermophilic AnMBR treating food waste.

Evaluation of anaerobic membrane bioreactor treating dairy processing wastewater: Elemental flow, bioenergy production and reduction of CO2 emission

The management of dairy processing wastewater (DPW) must address water pollution while delivering renewable energy and recovering resources. A high-rate anaerobic membrane bioreactor (AnMBR) was investigated for treating DPW, and the system was evaluated in terms of elemental flow, nutrient recovery, energy balance, and reduction of CO2 emission. The AnMBR system was superior in terms of both methanogenic performance and efficiency of bioenergy recovery in the DPW treatment, with a high net energy potential of 51.4-53.2 kWh/m3. The theoretical economic values of the digestate (13.8 $/m3) and permeate (4.1 $/m3) were assessed according to nutrient transformation and price of mineral fertilizer. The total CO2 emission equivalent in the AnMBR was 44.7 kg CO2-eq/m3, with a significant reduction of 54.1 kg CO2-eq/m3 compared to the conventional process. The application of the AnMBR in the DPW treatment is a promising approach for the development of carbon neutrality and a circular economy.

Treatment of fresh leachate by anaerobic membrane bioreactor: On-site investigation, long-term performance and response of microbial community

This study proposed fresh leachate treatment with anaerobic membrane bioreactor (AnMBR) based on the on-site investigation of the characteristics of fresh leachate. Temperature-related profiles of fresh leachate properties, like chemical oxygen demand (COD), were observed. In addition, AnMBR achieved a high COD removal of 98% with a maximum organic loading rate (OLR) of 19.27 kg-COD/m3/d at the shortest hydraulic retention time (HRT) of 1.5 d. The microbial analysis implied that the abundant protein and carbohydrate degraders (e.g., Thermovirga and Petrimonas) as well as syntrophic bacteria, such as Syntrophomonas, ensured the effective adaptation of AnMBR to the reduced HRTs. However, an excessive OLR at 36.55 kg-COD/m3/d at HRT of 1 d resulted in a sharp decrease in key microbes, such as archaea (from 37% to 15%), finally leading to the deterioration of AnMBR. This study provides scientific guidance for treating fresh leachate by AnMBR and its full-scale application for high-strength wastewater.

Impact of sandwich-type composite anodic membrane on membrane fouling and methane recovery from sewage sludge and food waste via electrochemical anaerobic membrane bioreactor

Membrane fouling presents a big challenge for the real-world implementation of anaerobic membrane bioreactors (AnMBRs) in digesting high-solid biowastes. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) with a novel sandwich-type composite anodic membrane was designed and constructed for controlling membrane fouling whilst improving the energy recovery. The results showed that EC-AnMBR produced a higher methane yield of 358.5 ± 74.8 mL/d, rising by 12.8% compared to the AnMBR without applied voltage. Integration of composite anodic membrane induced a stable membrane flux and low transmembrane pressure through forming an anodic biofilm while total coliforms removal reached 97.9%. The microbial community analysis further provided compelling evidence that EC-AnMBR enriched the relative abundance of hydrolyzing (Chryseobacterium 2.6%) bacteria and methane-producing (Methanobacterium 32.8%) archaea. These findings offered new insights into anti-biofouling performance and provided significant implications for municipal organic waste treatment and energy recovery in the new EC-AnMBR.

Characteristics of Biogas Production and Synergistic Effect of Primary Sludge and Food Waste Co-Digestion

Co-digestion implementation in wastewater treatment plants enhances biogas yield, so this research investigated the optimal ratio of biodegradable waste and sewage sludge. The increase in biogas production was investigated through batch tests using basic BMP equipment, while synergistic effects were evaluated by chemical oxygen demand (COD) balance. Analyses were performed in four volume basis ratios (3/1, 1/1, 1/3, 1/0) of primary sludge and food waste with added low food waste: 3.375%, 4.675%, and 5.35%, respectively. The best proportion was found to be 1/3 with the maximum biogas production (618.7 mL/g VS added) and the organic removal of 52.8% COD elimination. The highest enhancement rate was observed among co-digs 3/1 and 1/1 (105.72 mL/g VS). A positive correlation between biogas yield and COD removal is noticed while microbial flux required an optimal pH, value of 8 significantly decreased daily production rate. COD reductions further supported the synergistic impact; specifically, an additional 7.1%, 12.8%, and 17% of COD were converted into biogas during the co-digestions 1, 2, and 3, respectively. Three mathematical models were applied to estimate the kinetic parameters and check the accuracy of the experiment. The first-order model with a hydrolysis rate of 0.23-0.27 indicated rapidly biodegradable co-/substrates, modified Gompertz confirmed immediate commencement of co-digs through zero lag phase, while the Cone model had the best fit of over 99% for all trials. Finally, the study points out that the COD method based on linear dependence can be used for developing relatively accurate model for biogas potential estimation in anaerobic digestors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12155-023-10620-8.

Bioengineering of biowaste to recover bioproducts and bioenergy: A circular economy approach towards sustainable zero-waste environment

The inevitable need for waste valorisation and management has revolutionized the way in which the waste is visualised as a potential biorefinery for various product development rather than offensive trash. Biowaste has emerged as a potential feedstock to produce several value-added products. Bioenergy generation is one of the potential applications originating from the valorisation of biowaste. Bioenergy production requires analysis and optimization of various parameters such as biowaste composition and conversion potential to develop innovative and sustainable technologies for most effective utilization of biowaste with enhanced bioenergy production. In this context, feedstocks, such as food, agriculture, beverage, and municipal solid waste act as promising resources to produce renewable energy. Similarly, the concept of microbial fuel cells employing biowaste has clearly gained research focus in the past few decades. Despite of these potential benefits, the area of bioenergy generation still is in infancy and requires more interdisciplinary research to be sustainable alternatives. This review is aimed at analysing the bioconversion potential of biowaste to renewable energy. The possibility of valorising underutilized biowaste substrates is elaborately presented. In addition, the application and efficiency of microbial fuel cells in utilizing biowaste are described in detail taking into consideration of its great scope. Furthermore, the review addresses the significance bioreactor development for energy production along with major challenges and future prospects in bioenergy production. Based on this review it can be concluded that bioenergy production utilizing biowaste can clearly open new avenues in the field of waste valorisation and energy research. Systematic and strategic developments considering the techno economic feasibilities of this excellent energy generation process will make them a true sustainable alternative for conventional energy sources.

Performance evaluation and energy potential analysis of anaerobic membrane bioreactor (AnMBR) in the treatment of simulated milk wastewater

An anaerobic membrane bioreactor (AnMBR) was employed as primary treatment unit for anaerobic treatment of simulated wastewater to produce high effluent quality. A lab scale hollow fiber membrane was used to scrutinize the performance of AnMBR as a potential treatment system for simulated milk wastewater and analyze its energy recovery potential. The 15 L bioreactor was operated continuously at mesophilic conditions (35 °C) with a pH constant of 7.0. The membrane flux was in the range of 9.6-12.6 L/m². h. The different organic loading rates (OLRs) of 1.61, 3.28, 5.01, and 8.38 g-COD/L/d, of simulated milk wastewater, were fed to the reactor and the biogas production rate was analyzed, respectively. The results revealed that the COD removal efficiencies of 99.54 ± 0.001% were achieved at the OLR of 5.01 gCOD/L/d. The highest methane yield was found to be at OLR of 1.61 gCOD/L/d at HRT of 30 d with the value of 0.33 ± 0.01 L-CH₄/gCOD. Moreover, based on the analysis of energy balance in the AnMBR system, it was found that energy is positive at all the given HRTs. The net energy production (NEP) ranged from 2.594 to 3.268 kJ/gCOD, with a maximum NEP value of 3.268 kJ/gCOD at HRT 10 d HRT. Bioenergy recovery with the maximum energy ratio, of 4.237, was achieved with an HRT of 5 d. The study suggests a sizable energy saving with the anaerobic membrane process.

Volatile Fatty Acids (VFA) Production and Recovery from Chicken Manure Using a High-Solid Anaerobic Membrane Bioreactor (AnMBR)

Acidogenic fermentation of chicken manure (CM) for production and recovery of volatile fatty acids (VFA) is an interesting biological waste-to-value approach compared to benchmark organic waste management strategies. Considering the wide range of high value applications of VFA, a semi-continuous immersed anaerobic membrane bioreactor (AnMBR) was applied to boost VFA productivity and yield, while reducing downstream processing stages assisting the recovery of VFA. In this regard, the effect of parameters such as pH and organic loading rates (OLR) on the overall bioconversion and filtration performance was investigated. Thermal-shocked CM was applied both as inoculum and substrate. A very high VFA yield (0.90 g-VFA/g-VS) was obtained in the treatment with no pH control (~8.2) at an OLR of 2 g-VS/(L·d), presenting 24% higher yield compared to that of the controlled pH. Batch assays further demonstrated the enhanced hydrolysis and acidogenesis activities at weak alkaline conditions. A long-term (78 days) fermentation and filtration was successfully performed, where stable membrane filtration performance was experienced for about 50 days under high-solid (suspended solid of 37-45 g/L) and high flux (20 L/(m²·h)) conditions. Results suggest that AnMBR of CM is a feasible and promising process for VFA production and recovery.

Seasonal and annual energy efficiency of mainstream anaerobic membrane bioreactor (AnMBR) in temperate climates: Assessment in onsite pilot plant and estimation in scaled-up plant

The seasonal and annual energy efficiency of mainstream anaerobic membrane bioreactor (AnMBR) was first assessed in an onsite pilot plant (15 m³/d) and then estimated in a scaled-up plant (10,000 m³/d) in temperate climates (15-25 °C). It was found that the annual net electricity demand was 0.100 and 0.090 kWh/m³, and the annual net energy (electricity + heat) demand was -0.158 and -0.309 kWh/m³ under the dissolved methane recovery condition and the non-recovery condition, respectively, demonstrated that the application of mainstream AnMBR in temperate climates is electricity saving and energy positive. The energy efficiency of the AnMBR decreased with temperature drop due to the reduction of methane production, and the increase in biogas sparging to mitigate membrane fouling. Since approximately 26.7%-39.7% of input COD remained in sludge, attention should be paid to recovering this potential energy to improve the overall energy performance of the mainstream AnMBR plants in future.

In-situ biogas upgrading with H2 addition in an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge

Biological in-situ biogas upgrading is a promising approach for sustainable energy-powered technologies. This method increases the CH₄ content in biogas via hydrogenotrophic methanogenesis with an external H₂ supply. In this study, an anaerobic membrane bioreactor (AnMBR) was employed for in-situ biogas upgrading. The AnMBR was operated in semi-batch mode using waste activated sludge as the substrate. Pulsed H₂ addition into the reactor and biogas recirculation effectively increased the CH₄ content in the biogas. The addition of 4 equivalents of H₂ relative to CO₂ did not lead to appreciable biogas upgrading, although the acetate concentration increased significantly. When 11 equivalents of H₂ were introduced, the biogas was successfully upgraded, and the CH₄ content increased to 92%. The CH₄ yield and CH₄ production rate were 0.31 L/g-VS_input and 0.086 L/L/d, respectively. In this phase of the process, H₂ addition increased the acetate concentration and the pH because of CO₂ depletion. Compared with a continuously-stirred tank reactor, the AnMBR system attained higher CH₄ content, even without the addition of H₂. The longer solid retention time (100 d) in the AnMBR led to greater degradation of volatile solids. Severe membrane fouling was not observed, and the transmembrane pressure remained stable under 10 kPa for 117 d of continuous filtration without cleaning of the membrane. The AnMBR could be a promising reactor configuration to achieve in-situ biogas upgrading during sludge digestion.

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.

Primary and A-sludge treatment by anaerobic membrane bioreactors in view of energy-positive wastewater treatment plants

Energy-rich sludge can be obtained from primary clarifiers preceding biological reactors. Alternatively, the incoming wastewater can be sent to a very-high-loaded activated sludge system, i.e., a so-called A-stage. However, the effects of applying an A-stage instead of a primary clarifier, on the subsequent sludge digestion for long-term operation is still unknown. In this study, biogas production and permeate quality, and filterability characteristics were investigated in a lab-scale anaerobic membrane bioreactor for primary sludge and A-stage sludge (A-sludge) treatment. A higher specific methane yield was obtained from digestion of A-sludge compared to primary sludge. Similarly, specific methanogenic activity was higher when the anaerobic membrane bioreactor was fed with A-sludge compared to primary sludge. Plant-wide mass balance analysis indicated that about 35% of the organic matter in wastewater was recovered as methane by including an A-stage, compared to about 20% with a primary clarifier.

Enhanced methane production coupled with livestock wastewater treatment using anaerobic membrane bioreactor: Performance and membrane filtration properties

The present study introduced a new method for enhanced biomethane production and pollution control of swine wastewater (SW) using anaerobic membrane bioreactor (AnMBR). Results confirmed 35 °C as the optimum temperature for enhanced anaerobic digestion which resulted in relatively higher methane production rate and potential. In AnMBR system, robust pollutants removal and conversion rate were achieved under various hydraulic retention time (HRT) ranging from 20 to 10 days, while the highest methane yield (0.24 L/g-COD_removed) and microbial activity (6.65 mg-COD/g-VSS·h) were recorded at HRT of 15 days. Reduction of HRT to 10 days resulted in serious membrane fouling due to accumulation of extracellularpolymericsubstances(EPS) and cake layer on the membrane. However, cake layer as the dominant membrane foulant could be effectively removed through periodic physical backwash to recover the membrane permeability. Overall, the suggested AnMBR is a promising technology to enhance SW treatment and energy recovery.

Enhanced degradation and biogas production of waste activated sludge by a high-solid anaerobic membrane bioreactor together with in pipe thermal pretreatment process

An integrated system combining in pipe thermal pretreatment with a high-solid anaerobic membrane bioreactor (AnMBR) was developed to promote the anaerobic digestion of waste activated sludge (WAS). Two different pretreatment methods investigated were the venturi nozzle treatment (VNT) and steam injector treatment (SIT), both at a low temperature of 70 °C. The biogas production after pretreatment was 23.5-30.5% higher than that of untreated WAS, and the VS based biogas yield was 0.46-0.47 L/g-VS when HRT was 15 days. The membrane operated smoothly when the average flux was 9.6 and 4.5 L/m²/h under an MLTS of 25 and 30 g/L, respectively. The calculations of the mass balance indicated that 44-45% COD was converted to methane with pretreatment and only 1% remained in the permeate. That is, high energy recovery and organic matter removal efficiency were achieved for the treatment of WAS using the high-solid AnMBR with in pipe thermal pretreatment.

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.

Phosphorus Recovery by Adsorption from the Membrane Permeate of an Anaerobic Membrane Bioreactor Digesting Waste-Activated Sludge

The recovery of phosphorus (P) from waste activated sludge (WAS) is a promising approach for sustainable resource management. During the anaerobic digestion of WAS, orthophosphate is released, and this P species is favorable for adsorption recovery. In the present study, an anerobic membrane bioreactor (AnMBR) with a P-adsorption column was developed to generate biogas from WAS and to recover P from membrane permeate simultaneously. The effects of the hydraulic retention time (HRT) and solid retention time (SRT) of the AnMBR on P solubilization were investigated. As a result, the maximum P solubilization was 21% when the HRT and SRT were 45 days and 100 days, respectively. Orthophosphate in the membrane permeate was adsorbed and recovered using a mesoporous material called zirconium sulfate–surfactant micelle mesostructure (ZS) in the column. The adsorbed P could be desorbed from the ZS with a NaOH solution, and P was recovered as a concentrated solution by a factor of 25. When the HRT was 19 days, the biogas yield and biogas production rate were 0.26 L/g-VSinput and 0.123 L/L/d, respectively. The average methane content in the biogas was 80%. The developed membrane-based process may be effective for resource recovery from WAS.

Recovery of Household Waste by Generation of Biogas as Energy and Compost as Bio-Fertilizer—A Review

Nowadays, organic waste and especially household waste represents a significant global issue due to population growth. The anaerobic digestion (AD) process is an essential operation contributing powerfully to the valorization of organic waste including food waste in terms of renewable energy generation (biogas) and the rich-nutrient residue that can be utilized as bio-fertilizer. Thus, this process (AD) allows for good recovery of household waste by generating biogas and compost. However, the AD operation has been affected by several key factors. In this paper, we aim to involve different critical parameters influencing the AD process, including temperature, pH, organic loading rate (OLR), carbon to nitrogen ratio (C/N), and total solid content (TS(%)). Further, the paper highlights the inhibition caused by the excessive accumulation of volatile fatty acids (VFAs) and ammoniac, which exhibits the positive effects of co-digestion, pretreatment methods, and mixing techniques for maintaining process stability and enhancing biogas production. We analyze some current mathematical models explored in the literature, such as distinct generic, non-structural, combined, and kinetic first-order models. Finally, the study discusses challenges, provides some possible solutions, and a future perspective that promises to be a highly useful resource for researchers working in the field of household waste recovery for the generation of biogas.

Anaerobic co-digestion of textile dyeing sludge: Digestion efficiency and heavy metal stability

Anaerobic co-digestion (AcoD) has become an important mean for the stabilization and recycling of textile dyeing sludge (TDS). Using the soybean okara byproduct (SOB) as a co-digestion substrate, the effects on AcoD performance and heavy metal stability were studied. The results indicated that the optimal mixing ratio was 1:1 (calculated by total sloid). Under this condition, the SCOD removal efficiency was 64% (that of TDS alone and SOB alone were 47% and 48%, respectively) and the cumulative methane production field was 503 L CH₄/kg VS (that of TDS alone and SOB alone were 435 L CH₄/kg VS and 408 L CH₄/kg VS, respectively). At the same time, the addition of SOB could also enhance the stability of heavy metals (Zn, Cu, Cr and Ni) in TDS. Remarkably, that could increase the steady state content nickel from 47.98% to 57.21%, while anaerobic digestion of TDS caused no increase but a decrease (only 42.13%). According to the risk assessment code analyses, the AcoD of TDS by SOB can significantly reduce the ecotoxicity risk caused by Ni, Zn and Cr.