Influence of food waste addition over microbial communities in an Anaerobic Membrane Bioreactor plant treating urban wastewater

Co-digestion and co-treatment of sewage and organic waste in mainstream anaerobic reactors: operational insights and future perspectives

The global shift towards sustainable waste management has led to an intensified exploration of co-digestion and co-treatment of sewage and organic waste using anaerobic reactors. This review advocates for an integrated approach where organic waste is treated along with the sewage stream, as a promising solution to collect, treat, and dispose of organic waste, thereby reducing the environmental and economic burden on municipalities. Various efforts, ranging from laboratory to full-scale studies, have been undertaken to assess the feasibility and impacts of co-digestion or co-management of sewage and organic waste, using technologies such as up-flow anaerobic sludge blankets or anaerobic membrane bioreactors. However, there has been no consensus on a standardized definition of co-digestion, nor a comprehensive understanding of its impacts. In this paper, we present a comprehensive review of the state-of-the-art in liquid anaerobic co-digestion systems, which typically operate at 1.1% total solids. The research aims to investigate how the integration of organic waste into mainstream anaerobic-based sewage treatment plants has the potential to enhance the sustainability of both sewage and organic waste management. In addition, utilizing the surplus capacity of existing anaerobic reactors leads to significant increases in methane production ranging from 190 to 388% (v/v). However, it should be noted that certain challenges may arise, such as the necessity for the development of tailored strategies and regulatory frameworks to enhance co-digestion practices and address the inherent challenges.

Utilization strategy for algal bloom waste through co-digestion with kitchen waste: Comprehensive kinetic and metagenomic analysis

Anaerobic co-digestion (AcoD) with kitchen waste (KW) is an alternative utilization strategy for algal bloom waste (AW). However, the kinetic characteristic and metabolic pathway during this process need to be explored further. This study conducted a comprehensive kinetic and metagenomic analysis for AcoD of AW and KW. A maximum co-digestion performance index (CPI) of 1.13 was achieved under the 12% AW addition. Co-digestion improved the total volatile fatty acids generation and the organic matter transformation efficiency. Kinetic analysis showed that the Superimposed model fit optimally (R2Adj = 0.9988-0.9995). The improvement of the kinetic process by co-digestion was mainly reflected in the increase of the methane production from slowly biodegradable components. Co-digestion enriched the cellulolytic bacterium Clostridium and the hydrogenotrophic methanogenic archaea Methanobacterium. Furthermore, for metagenome analysis, the abundance of key genes concerned in cellulose and lipid hydrolysis, pyruvate and methane metabolism were both increased in co-digestion process. This study provided a feasible process for the utilization of AW produced seasonally and a deeper understanding of the AcoD synergistic mechanism from kinetic and metagenomic perspectives.

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.

Prospecting cellulose fibre-reinforced composite membranes for sustainable remediation and mitigation of emerging contaminants

Many environmental pollutants caused by uncontrolled urbanization and rapid industrial growth have provoked serious concerns worldwide. These pollutants, including toxic metals, dyes, pharmaceuticals, pesticides, volatile organic compounds, and petroleum hydrocarbons, unenviably compromise the water quality and manifest a severe menace to aquatic entities and human beings. Therefore, it is of utmost importance to acquaint bio-nanocomposites with the capability to remove and decontaminate this extensive range of emerging pollutants. Recently, considerable emphasis has been devoted to developing low-cost novel materials obtained from natural resources accompanied by minimal toxicity to the environment. One such component is cellulose, naturally the most abundant organic polymer found in nature. Given bio-renewable sources, natural abundance, and impressive nanofibril arrangement, cellulose-reinforced composites are widely engineered and utilized for multiple applications, such as wastewater decontamination, energy storage devices, drug delivery systems, paper and pulp industries, construction industries, and adhesives, etc. Environmental remediation prospective is among the fascinating application of these cellulose-reinforced composites. This review discusses the structural attributes of cellulose, types of cellulose fibrils-based nano-biocomposites, preparatory techniques, and the potential of cellulose-based composites to remediate a diverse array of organic and inorganic pollutants in wastewater.

"Food waste-wastewater-energy/resource" nexus: Integrating food waste management with wastewater treatment towards urban sustainability

Sustainable food waste management is a global issue with high priority for improving food security and conserving natural resources and ecosystems. Diverting food waste from the solid waste stream to the wastewater stream is a promising way for food waste source separation, collection, treatment, and disposal. Given the advances in wastewater treatment, this integrated system has great potential for the concurrent recovery of water, resource, and energy. To this end, many efforts from lab-scale to full-scale studies have been devoted to evaluating the feasibility and associated impacts on both solid waste and wastewater systems. This paper summarizes the current status of food waste diversion from the aspects of principle and application. The impacts of food waste diversion on solid waste treatment, sewer system, wastewater treatment, and environmental benefits have been comprehensively reviewed and analysed. In the context of the critical review, this paper further identified the challenges of food waste diversion in unified definitions of the field, sewer network assessment, emerging wastewater treatment technologies, scale-up studies, and policy drivers. Perspectives on the contribution of food waste diversion to a food waste management hierarchy were discussed for initiating the nexus of "food waste-wastewater-energy/resource". We conclude that food waste diversion could facilitate sustainable urban development, but the area-specific factors (e.g., household practices, water resource, sewerage system condition, and treatment techniques) require adequate evaluations to determine the implementation. The outcomes of this study could contribute to the practice and policy-making of food waste management towards urban sustainability.

Acclimatization of anaerobic sludge with cow manure and realization of high-rate food waste digestion for biogas production

Long-term acclimatization of anaerobic sludge was conducted by operating a mesophilic continuously stirred anaerobic reactor (CSTR) with continuous feeding of food wastes (FW) and cow manure (CM). During the long-term acclimatization, continued increase of enzyme activity was revealed, while the microbial structure tended stable as shown by the Shannon index and microbial community. By biomethane potential analysis, the acclimated sludge had a methane yield about 13 times higher than the initial anaerobic sludge. The acclimated sludge was subsequently used for FW digestion with stepwise organic loading rate increase without CM addition. The functional phyla of Bacteroidetes and Proteobacteria, which originated from CM but not very abundant, were significantly enriched not only during sludge acclimatization with CM addition but also in the process of FW digestion without CM addition. A microbe coexistence network was proposed to support an explanation of the metabolic pathways of FW digestion using the acclimated sludge.

Identification and characterization of core sludge and biofilm microbiota in anaerobic membrane bioreactors

An analysis of sludge (i.e., 63 samples) and biofilm (i.e., 79 samples) sampled from 13 anaerobic membrane bioreactors (AnMBR) was conducted. Predominant microbial community identification and multivariate analysis indicate that these reactors showed different microbial community structure, but these differences had no impact on the overall AnMBR performance. Instead, core microbial genera which occurred in ≥90% of sludge (20 genera) and biofilm (12 genera) samples could potentially account for the AnMBR performance. A further calculation on net growth rate (NGR) of core genera in sludge suggested distribution into two main groups (i.e., I: low relative abundance and NGR, II: high relative abundance or high NGR). Consistent positive correlations between bacterial genera were observed among those that exhibited either high relative abundance or high NGR. The anaerobic microbial consortium in both sludge and biofilm were largely affected by stochastic dispersal and migration processes (i.e., neutral assembly). However, Acinetobacter spp. and Methanobacterium spp. occurred consistently in higher frequency in the biofilm but in lower occurrence frequency in the AnMBR permeate. Findings from this study suggest first, specific core microorganisms exist in the sludge regardless of the operating conditions of the AnMBRs, and second, prevention of biofoulant layer on anaerobic membranes can be devised by minimizing attachment of microbes on surfaces in a non-selective manner.

Linking process performances and core microbial community structures in anaerobic membrane bioreactor with rotatory disk (ARMBR) system fed with high-strength food waste recycling wastewater

This study first evaluated the process performances and microbial community structures of anaerobic rotary membrane bioreactor (ARMBR) fed with food waste recycling wastewater (FRW). Three identical ARMBRs were operated under different organic loading rate (OLR) conditions (1.5, 3.0, and 6.0 kg COD m^-3 d^-1) after the same start-up periods. The start-up performances and archaeal community structures differed among the ARMBRs, probably due to the sudden OLR shock. After the start-up, bio-methane was stably produced until the end of the operational period, with all of the ARMBRs showing >95% COD removal efficiency. Methanosaeta spp. was the predominant methanogen; diverse hydrogenotrophic methanogens co-existed. Bacteroidetes-like bacteria and Candidatus Cloacamonas acted as major fermentative bacteria producing acetate or hydrogen for the growth of methanogens. The results suggest that our ARMBR system can be a promising option to manage high-strength organic wastewater such as FRW.

Two-Phase Improves Performance of Anaerobic Membrane Bioreactor Treatment of Food Waste at High Organic Loading Rates

Anaerobic membrane bioreactors (AnMBRs) are in use at the full-scale for energy recovery from food waste (FW). In this study, the potential for two-phase (acid/gas) AnMBR treatment of FW was investigated as a strategy to increase microbial diversity, thereby improving performance. Two bench-scale AnMBRs were operated in single-phase (SP) and two-phase (TP) mode across incremental increases in organic loading rate (OLR) from 2.5 to 15 g total chemical oxygen demand (COD) L·d^-1. The TP acid-phase (TP-AP) enriched total VFAs by 3-fold compared to influent FW and harbored a distinct microbial community enriched in fermenters that thrived in the low pH environment. The TP methane phase (TP-MP) showed increased methane production and resilience relative to SP as OLR increased from 3.5 to 10 g COD L·d^-1. SP showed signs of inhibition (i.e., rapid decrease in methane production per OLR) at 10 g COD L·d^-1, whereas both systems were inhibited at 15 g COD L·d^-1. At 10 g COD L·d^-1, where the highest difference in performance was observed (20.3% increase in methane production), activity of syntrophic bacteria in TP-MP was double that of SP. Our results indicate that AnMBRs in TP mode could effectively treat FW at OLRs up to 10 g COD·L day^-1 by improving hydrolysis rates, microbial diversity, and syntroph activity, and enriching resistant communities to high OLRs relative to AnMBRs in SP mode.

Improved anaerobic co-digestion of food waste and domestic wastewater by copper supplementation - Microbial community change and enhanced effluent quality

Anaerobic co-digesters are biorefineries for energy recovery from food waste and domestic wastewater via methane production. Nonetheless, the performance of this technology was not always satisfied due to the long chain fatty acids (LCFAs) generation from food waste. Micronutrient supplementation is an effective strategy that could be applied during the anaerobic (co-)digestion to further enhance the digestion efficiency while treating food waste. In this study, supplementing copper (as CuSO₄ and CuCl₂) at 10, 30, and 50 mg/L Cu²⁺ was selected to further enhance the methane production of anaerobic co-digester while treating food waste and domestic wastewater. Overall, with the supplementation of copper, the chemical oxygen demand (COD) removal efficiency was over 90%, while higher methane yields (0.260-0.325 L CH₄/g COD _removed) were obtained compared to the control without supplementation (0.175 L CH₄/g COD _removed). For the cumulative methane yield, the highest increment of 94.1% was obtained when 10 mg/L of Cu²⁺ were added. The results showed copper as a cofactor of many microbial enzymes and coenzymes involved in the methane production further improved both methane production and COD removal efficiency. Meanwhile, the microbial community analysis verified the copper supplementation significantly changed the bacterial communities but with the limited effect on the diversity of archaea. Furthermore, since the anaerobic co-digester was not that much efficient on the nutrients removal, the effluent from the upflow anaerobic sludge blanket (UASB) reactor was further treated by the anaerobic/anoxic/oxic (A²O) rector and the resulting effluent reached the satisfying quality in terms of COD, total nitrogen (TN), and NH₃-N removal, meeting the regional effluent discharge limits.

Characterization of microbial community and main functional groups of prokaryotes in thermophilic anaerobic co-digestion of food waste and paper waste

The thermophilic anaerobic co-digestion of food waste and paper waste was successfully operated with a 0% to 70% fraction of paper waste. The variation of functional microbial community was investigated by 16S rRNA gene analysis. The results indicated that the hydrolyzing bacterial community changed from carbohydrate/protein-degrading bacteria to cellulose-degrading bacteria when the paper waste ratio was higher than 50%. Significant changes in the taxon responsible for cellulose degradation were found depending on the paper waste fraction. Cellulose-degrading bacteria outcompeted lactic acid bacteria in the degradation of monosaccharide, resulting in a decline in the proportion of lactic acid bacteria and the absence of an accumulation of lactic acid. At high paper waste ratios, because the cellulose-degrading bacteria, such as Defluviitoga tunisiensis, were more likely to degrade monosaccharides directly to acetate and hydrogen rather than to propionate and butyrate, the abundance of syntrophs was reduced. The variation of those bacteria with high H₂-producing ability significantly influenced the proportion of hydrogenotrophic archaea. The change in the microbial community as the paper waste fraction increased was illustrated with regard to anaerobic degradation steps.

A review on anaerobic membrane bioreactors (AnMBRs) focused on modelling and control aspects

The use of anaerobic membrane bioreactor technology (AnMBR) is rapidly expanding. However, depending on the application, AnMBR design and operation is not fully mature, and needs further research to optimize process efficiency and enhance applicability. This paper reviews state-of-the-art of AnMBR focusing on modelling and control aspects. Quantitative environmental and economic evaluation has demonstrated substantial advantages in application of AnMBR to domestic wastewater treatment, but detailed modelling is less mature. While anaerobic process modelling is generally mature, more work is needed on integrated models which include coupling between membrane performance (including fouling) and the biological process. This should include microbial factors, which are important to generation of specific foulants such as soluble and particulate inert organics. Mature and well-established control tools, including better feedback control strategies are also required for both the process, and for fouling control.