Highest Methane Yield Research Articles

Magnetite-mediating direct interspecies electron transfer is not pivotal role in directing electrons toward methane production from sulfate containing wastewater

Sulfate reduction can compete for electrons with methane production, thereby reducing methane production. Several factors, such as magnetite addition, carbon sources, and the chemical oxygen demand (COD)/SO42− ratio, can influence the direction of electron flow toward methanogenesis. However, their contributions to methane production remain unclear. In this study, the addition of magnetite significantly enhanced the maximum methane production rate (Rmax). The enrichment of Methanothrix and Methanobacterium in the conductive material groups indicated the establishment of a methanogenesis process through direct interspecies electron transfer (DIET). Although the DIET pathway enhanced Rmax in the conductive material groups, this increase did not translate into a higher methane yield in this study. The contribution of DIET pathway to methane yield was negligible compared with the effect of COD/SO42− ratio and carbon sources. The relative contribution of COD/SO42− ratio exceeded 40 % in directing electron flow.

Integration of biogas and liquid recirculation enhance methane production in high-solid anaerobic digestion of pig manure and rice husks

High-solid anaerobic digestion (HSAD) is a promising technology for treating livestock manure and agricultural waste; however, the wide application has been limited due to homogenization problems. This study established a novel HSAD system by integrating liquid and biogas recirculation (RBL), aiming to enhance the biogas conversion efficiency of high-solid substrates at low costs. Results showed that the highest methane yield was 357 mL/gVSadded in the novel HSAD system (RBL), 30.7 % and 251.7 % higher than those with only liquid recirculation (RL) or with no recirculation (RNo). Biogas recirculation helped enhance dissolution and degradation of organic matter, and prevented the VFAs accumulation, contributing to the enhanced methane production in the novel HSAD system. The net electric energy benefit of RBL was 301.2 kWh for treating 1-ton raw materials, suggesting the high economic feasibility of the novel HSAD system for the sustainable treatment of high-solid organic wastes.

Comparison of pyrolysis and anaerobic digestion processes for wheat straw biomass

Due to the growing interest in using biomass as a renewable energy source, this study presents a comparative analysis between two prominent biomass conversion technologies—anaerobic digestion and biomass pyrolysis—focused on wheat straw biomass. The objective of this study is to evaluate and compare the efficiency, energy output, and environmental impact. Anaerobic digestion was performed under mesophilic conditions (35 ± 0.5 °C) using the biochemical methanogenic potential (BMP) methodology. Pyrolysis was conducted through thermogravimetric analysis (TGA) to determine the thermal behaviour and kinetic parameters of the biomass. Biogas production led to better energetic results as high methane yields of over 11 mL CH₄ g⁻¹ VS were obtained. Additionally, the integration of both processes was considered by subjecting digestate from anaerobic digestion to pyrolysis process. Key findings demonstrate that the activation energy (Ea) for wheat straw ranged from 166.49 to 176.42 kJ·mol−1 across different kinetic methods, indicating its suitability for pyrolysis. In contrast, digestates exhibited significantly lower activation energies, with 1-week, 2-weeks, and 3-weeks digestates showing ranges of 53.27–60.79 kJ·mol−1, 38.69–46.86 kJ·mol−1, and 46.29–72.34 kJ·mol−1, respectively. These results suggest that anaerobic digestion not only produces biogas but also yields a byproduct with potential for efficient pyrolytic conversion suggesting opportunities for integrated waste management and renewable energy production systems.

Optimization of two-stage thermophilic anaerobic digestion of dairy wastewater: Effect of carrier material on process performance and microbial community

Although two-stage anaerobic digestion (TSAD) is not a novel process, information of the process stability, microbial community and effective operating conditions is limited and often contradictory. In this work, the influence of different carrier materials (polyurethane foam, carbon felt, Raschig rings and a combination of carbon felt and Raschig rings) on the performance of the thermophilic TSAD of dairy wastewater was studied. The organic loading rate (OLR) in the acidogenic reactor (RH) was gradually increased from 13.74 to 32.56 g COD/(L d), and from 0.64 to 11.46 g COD/(L d) in the methanogenic reactors by correspondingly reducing the hydraulic retention time (HRT). The highest hydrogen production rate of 1280.3 mL/(L·d) and hydrogen yield of 93.2 mL/g COD were achieved at OLR of 13.74 g COD/(L·d), but hydrogen production stopped at higher OLR. The main soluble metabolites in RH were butyrate and lactate, and the microbial community was dominated by Streptococcus, Thermoanaerobacterium, Veillonellales-Selenomonadales and Pseudomonas. The highest methane production rate (2674 mL/(L·d) at HRT of 0.5 days) was observed in the reactor with polyurethane foam, while the highest methane yield (305.5 mL/g COD at HRT of 1.5 days) was obtained in a reactor containing carbon felt. Spirochaetaceae, Desulfomicrobium, Anaerolineaceae, Candidatus Caldatribacterium and Cloacimonadaceae W5 were linked to these materials and explained the highest methanogenic performance.

High rate methanogenesis and nitrogenous component transformation in the high-solids anaerobic digestion of chicken manure enhanced by biogas recirculation ammonia stripping

High-solids anaerobic digestion is a promising technology for treating animal manure. However, the high nitrogen content in chicken manure leads to severe ammonia inhibition, thereby hindering the application of this technology for chicken manure. This study operated a high-solid anaerobic system feeding the reactor with 20 % total solids (TS) chicken manure for 650 days to investigate whether the anaerobic metabolic performance could be enhanced by adopting biogas recirculation ammonia stripping. The results show that, with ammonia stripping, the total ammonia nitrogen (TAN) was reduced from 8.2 to 3.0 g/L. The methanogenic activity was enhanced 1.3 – 2.9 fold. This led to a low level of volatile fatty acids (VFA, 0.6 g/L) and a high methane yield of 0.3 L/g-volatile solids (VS). Protein decomposition was facilitated under stripping conditions and correlated with a higher abundance of protein decomposition bacteria and enhanced methane production. The dynamics of ammonium formation and removal were illustrated for different stripping conditions. The ability to maintain low ammonium and the carbon and nitrogen balance was also verified. The proven effectiveness observed in this long continuous experiment may provide a foundation for further demonstrating the high-solids anaerobic digestion of chicken manure.

Cascading valorization of defatted rice bran for lactic acid fermentation and biogas production

This study investigated the integrated valorization of defatted rice bran (DRB) by converting it into lactic acid (LA) and subsequently utilizing the residues from LA production for biomethane generation through anaerobic digestion (AD). Processing 480 kg of DRB resulted in the production of 70 L of pure LA and generated significant waste streams, primarily consisting of 572 kg of decanted hydrolysate pellet (Pellet DEC) and 220 kg of microfiltration retentate (Retentate MF). Exceptionally high methane yields of 374‒434 LN kgVS-1 were observed for residues from LA fermentation in biochemical methane potential tests, indicating their high potential for biogas production. During long-term semi-continuous AD, varying organic loading rates (OLRs) from 0.5‒2.5 kgVS m-3 d⁻¹ demonstrated feedstock- and OLR-dependent methane production. Reactor failure at higher OLRs was attributed to the accumulation of total ammoniacal nitrogen (TAN). The co-digestion of Pellet DEC and Retentate MF proved to be more resilient, with OLRs up to 2 kgVS m-3 d-1, mitigating TAN inhibition. Methane yields, ranging from 265‒334 LN kgVS-1 before reaching inhibitory OLR levels, were higher than those found in the literature. Process integration has emerged as a promising approach because the biogas generated from residues could effectively offset the energy demands of LA production. Supported by life cycle assessment, the integrated processes showed a 67% lower environmental impact at the midpoint and a 71% lower environmental impact at the endpoint, along with an 80% reduction in energy costs compared to the standalone LA production. Results proved a significant enhancement of the sustainability and economic viability of this integrated biorefinery approach.

Brewery spent grain valorization through fermentation: Targeting biohydrogen, carboxylic acids and methane production

This study investigated three different fermentation approaches to explore the potential for producing biohydrogen, carboxylic acids, and methane from hydrolysates of thermally dilute acid pretreated brewer's spent grains (BSG). Initially, the research focused on maximizing the volumetric hydrogen production rate (HPR) in the continuous dark fermentation (DF) of BSG hydrolysates by varying the hydraulic retention time (HRT). The highest HPR reported to date of 5.9 NL/L-d was achieved at 6 h HRT, with a Clostridium-dominated microbial community. The effect of the operational pH (4, 5, 6, and 7) on the continuous acidogenic fermentation was then investigated. A peak carboxylic acid concentration of 17.3 g CODequiv./L was recorded at pH 6, with an associated volumetric productivity of 900.5 ± 13.1 mg CODequiv./L-h and a degree of acidification of 68.3 %. Lactic acid bacteria such as Limosilactobacillus and Lactobacillus were dominant at pH 4–5, while Weissella, Enterococcus, and Lachnoclostridium appeared at pH 6 and 7. Finally, this study evaluated the biochemical methane potential of the DF broth and the unfermented hydrolysates and found high methane yields of 659 and 517 NmL CH4/g-VSadded, respectively, both within one week. Overall, the results showed that pretreated BSG can be a low-cost feedstock for the production of bioenergy and valuable bio-based chemicals in a circular economy.

Comprehensive assessment of cow manure hydrothermal treatment products for land application and energy recovery

In this study, cow manure was hydrothermally treated in a 2-litre reactor for 1 h at temperatures between 100 °C and 260 °C. Both the raw manure and the solid and liquid products of the hydrothermal treatment were characterized to understand the fate of the inorganic elements and to assess the suitability of the products for land applications and energy recovery. Satisfactory elemental balances were obtained for the organic and most inorganic elements and indicated that most inorganic elements were incorporated into the solids with lower solubility, with the exception of potassium and sodium, which were mostly solubilized in the process water; calcium and chlorine were also solubilized to a lesser extent in the process water. Elemental composition and surface functional groups showed that hydrochar produced within the hydrothermal carbonization range (180–260 °C) seemed better suited for utilization as a soil amendment than raw cow manure. The potential for energy recovery lies in the anaerobic digestion of the process water, from which higher methane yields can be obtained than from raw cow manure. Lower temperatures in hydrothermal carbonization are considered a compromise for the safe land applications of cow manure, energy recovery from the process water, and enhanced dewaterability. These findings can help to eliminate bottlenecks in the upscaling of cow manure hydrothermal treatment and promote the circular bio-economy.

Enhancing methane production from corn straw via illumination-assisted Fe3O4/g-C3N4 nanocomposite in anaerobic digestion

This study proposes a novel anaerobic digestion (AD) strategy combining recyclable photoactivated nanomaterials with illumination to enhance electronic transfer for anaerobic microorganisms. Results showed that 7000 Lux illumination increased methane production yield and rate. Incorporating Fe3O4 into graphite carbon nitride (g-C3N4) created a recyclable Fe3O4/g-C3N4 (FG) nanocomposite with improved light absorption, conductivity, redox properties, and methane promotion. The highest methane yield from corn straw was achieved with 7000 Lux and 1.5 g/L FG nanocomposite, 22.6% higher than the dark control. The AD system exhibited increased adenosine triphosphate content, improved redox performance, reduced electron transfer resistance, and higher photocurrent intensity. These improvements bolstered the microorganisms and key genes involved in hydrolysis and acidification, which in turn optimized the acetoclastic pathway. Furthermore, this strategy promoted microorganisms associated with direct interspecies electron transfer, fostering a favorable environment for methanogenic activities, paving the way for future anaerobic reactor developments.

Biogas potential of organosolv pretreated wheat straw as mono and co-substrate: substrate synergy and microbial dynamics

Anaerobic digestion (AD) technology can potentially address the gap between energy demand and supply playing a crucial role in the production of sustainable energy from utilization of biogenic waste materials as feedstock. The biogas production from anaerobic digestion is primarily influenced by the chemical compositions and biodegradability of the feedstock. Organosolv-steam explosion offers a constructive approach as a promising pretreatment method for the fractionation of lignocellulosic biomasses delivering high cellulose content.This study showed how synergetic co-digestion serves to overcome the challenges of mono-digestion's low efficiency. Particularly, the study evaluated the digestibility of organosolv-steam pretreated wheat straw (WSOSOL) in mono as well as co-digesting substrate with cheese whey (CW) and brewery spent grains (BSG). The highest methane yield was attained with co-digestion of WSOSOL + CW (338 mL/gVS) representing an enhanced biogas output of 1–1.15 times greater than its mono digestion. An ammonium production was favored under co-digestion strategy accounting for 921 mg/L from WSOSOL + BSG. Metagenomic study was conducted to determine the predominant bacteria and archaea, as well as its variations in their populations and their functional contributions during the AD process. The Firmicutes have been identified as playing a significant role in the hydrolysis process and the initial stages of AD. An enrichment of the most prevalent archaea genera enriched were Methanobacterium, Methanothrix, and Methanosarsina. Reactors digesting simpler substrate CW followed the acetoclastic, while digesting more complex substrates like BSG and WSOSOL followed the hydrogenotrophic pathway for biomethane production. To regulate the process for an enhanced AD process to maximize CH4, a comprehensive understanding of microbial communities is beneficial.

Anaerobic co-digestion of cow manure and microalgae to increase biogas production: A sustainable bioenergy source

The biogas production from microalgae has gained attention due to fast depleting of fossil fuels and oil reserves. This study evaluated the anaerobic co-digestion of microalgae in various concentrations with cow manure to enhance biogas production. The biogas production of each experiment was measured using the water displacement method. The results indicated that the addition of microalgae significantly enhanced biogas production. Particularly, high methane yield of Anabaena sp. 50 %, Chlorella sp. 50 %, control was 345 ± 2.88 mL CH4/g VS, 297.96 ± 0.49 mL CH4/g VS, 138.32 ± 0.50 CH4/g VS respectively. The slurry produced by 50 % Anabaena sp. biogas plant exhibited the greatest level of seed germination. The current study demonstrated that Sorgham bicolor had the highest seed germination rate (94.2 %) root and shoot length of all crops. Therefore, it is possible to employ Anabaena sp. (50 %) and Chlorella sp. (50 %) in the rapid production of biogas. Moreover, agricultural output would be increased by using biogas slurry.

Sodium disilicate pretreatment enhancing methane production from anaerobic digestion of waste activated sludge

Improving the efficiency of digestion is a major focus of waste activated sludge (WAS) anaerobic digestion (AD) research. This study investigates the viability and mechanism of sodium disilicate (SD) in enhancing the digestive efficacy of WAS. Batch AD experiments for the sludges pretreated by varied amounts of SD were carried out, and the results revealed that a dosage of 90 mmol/L resulted in the highest methane yield (247.9 mL/g·VS), marking a 90.0 % increase compared to the raw sludge. Mechanistic investigations highlighted that SD pretreatment facilitated EPS degradation, cell lysis, and modulation of interfacial interaction energy, ultimately enhancing sludge disintegration and methane generation. Microbial community analysis unveiled an enrichment of crucial functional microorganisms associated with hydrolysis, acidification, and methanation. The heightened presence of acetotrophic and hydrogenotrophic methanogens significantly boosted methane production. Furthermore, metagenomic analysis corroborated that the SD pretreatment stimulated amino acid metabolism, energy metabolism (specifically ABC transporter proteins), and carbohydrate metabolism, thereby enhancing methanogenic activity through increased microbial metabolic activities and upregulated key enzyme expression. This research underscores the potential of SD-assisted pretreatment strategies in augmenting WAS digestion, introducing supplementary pretreatment avenues for optimizing anaerobic biotechnology.

Bioaugmentation protocols involving Methanobrevibacter thaueri and Pecoramyces ruminantium for investigating lignocellulose degradation and methane production from alfalfa stalks

Two protocols involving batch cultures were used to investigate the bioaugmentation of methane production by Pecoramyces ruminantium, and Methanobrevibacter thaueri. Protocol I examined the effect of altering the proportion of the microbial constituents in inoculum on alfalfa stalk fermentations and showed a 25 % improvement in dry matter loss in cultures where the inoculum contained just 30 % of co-culture and 70 % of fungal monoculture. Protocol II involved consecutive cultures and alternating inoculations. This protocol resulted in 17–22 mL/g DM methane production with co-cultures a 30 % increase in methane relative to the fungal monoculture. Both protocols indicate that the co-culture rapidly dominated and was more resilient than the monoculture. Synergistic interaction between fungus and methanogen, promoted more efficient lignocellulose degradation and higher methane yield. This study highlighted the potential of microbial co-cultures for enhancing methane production from lignocellulosic biomass, offering a promising bioaugmentation strategy for improving biogas yields and waste valorization.

Methanomethylovorans are the dominant dimethylsulfide-degrading methanogens in gravel and sandy river sediment microcosms

BackgroundRivers and streams are important components of the global carbon cycle and methane budget. However, our understanding of the microbial diversity and the metabolic pathways underpinning methylotrophic methane production in river sediments is limited. Dimethylsulfide is an important methylated compound, found in freshwater sediments. Yet, the magnitude of DMS-dependent methanogenesis nor the methanogens carrying out this process in river sediments have been explored before. This study addressed this knowledge gap in DMS-dependent methanogenesis in gravel and sandy river sediments.ResultsSignificant methane production via DMS degradation was found in all sediment microcosms. Sandy, less permeable river sediments had higher methane yields (83 and 92%) than gravel, permeable sediments (40 and 48%). There was no significant difference between the methanogen diversity in DMS-amended gravel and sandy sediment microcosms, which Methanomethylovorans dominated. Metagenomics data analysis also showed the dominance of Methanomethylovorans and Methanosarcina. DMS-specific methyltransferase genes (mts) were found in very low relative abundances whilst the methanol-, trimethylamine- and dimethylamine-specific methyltransferase genes (mtaA, mttB and mtbB) had the highest relative abundances, suggesting their involvement in DMS-dependent methanogenesis.ConclusionsThis is the first study demonstrating a significant potential for DMS-dependent methanogenesis in river sediments with contrasting geologies. Methanomethylovorans were the dominant methylotrophic methanogen in all river sediment microcosms. Methyltransferases specific to methylotrophic substrates other than DMS are likely key enzymes in DMS-dependent methanogenesis, highlighting their versatility and importance in the methane cycle in freshwater sediments, which would warrant further study.

Biochar alleviates inhibition effects of humic acid on anaerobic digestion: Insights to performances and mechanisms

To recover methane from waste activated sludge through anaerobic digestion (AD) is one promising alternative to achieve carbon neutrality for wastewater treatment plants. However, humic acids (HAs) are one of the major compositions in waste activated sludge, and their accumulation performs inhibition effects on AD. This study investigated the potentials of biochar (BC) in alleviating inhibition effects of HAs on AD. Results showed that although the accumulated HAs reduced methane yield by 9.37% compared to control, the highest methane yield, 132.6 mL CH4/g VSS, was obtained after adding BC, which was 45.9% higher than that in HA group. Mechanism analysis showed that BC promoted the activities of hydrolase such as protease and α-glucosidase, which were 69.7% and 29.7% higher than those in HA group, respectively. The conversion of short-chain fatty acids was accelerated. In addition, the evolutions of electroactive microorganisms like Clostridium_sensu_stricto_13 and Methanosaeta were consistent with the activitiies of electron transfer and the contents of cytochrome c. Furthermore, parts of HAs rather than all of them were adsorbed by BC, and the remaining free HAs and BC formed synergistic effects on methanogenesis, then both CO2 reduction and acetoclastic methanogenesis pathways were improved. The findings may provide some solutions to alleviate inhibition effects of HAs on AD.

Synergism of floated paperboard sludge cake /sewage sludge for maximizing biomethane yield and biochar recovery from digestate: A step towards circular economy

Anaerobic digestion of floated paperboard sludge (PS) cake suffers from volatile fatty acids (VFAs) accumulation, nutrient unbalanced condition, and generation of digestate with a risk of secondary pollution. To overcome these drawbacks, sewage sludge (SS) was added to PS cake for biogas recovery improvement under a co-digestion process followed by the thermal treatment of solid fraction of digestate for biochar production. Batch experimental assays were conducted at different SS:PS mixing ratios of 70:30, 50:50, 30:70, and 20:80 (w/w), and their anaerobic co-digestion performances were compared to the mono-digestion systems at 35 ± 0.2 °C for 45 days. The highest methane yield (MY) of 241.68 ± 14.81 mL/g CODremoved was obtained at the optimum SS:PS ratio of 50:50 (w/w). This experimental condition was accompanied by protein, carbohydrate, and VFA conversion efficiencies of 47.3 ± 3.2%, 46.8 ± 3.2%, and 56.3 ± 3.8%, respectively. The synergistic effect of SS and PS cake encouraged the dominance of Bacteroidota (23.19%), Proteobacteria (49.65%), Patescibacteria (8.12%), and Acidovorax (12.60%) responsible for hydrolyzing the complex organic compounds and converting the VFAs into biomethane. Further, the solid fraction of digestate was subjected to thermal treatment at a temperature of 500 °C for 2.0 h, under an oxygen-limited condition. The obtained biochar had a yield of 0.48 g/g dry digestate, and its oxygen-to-carbon (O/C), carbon-to-nitrogen (C/N), and carbon-to-phosphorous (C/P) ratios were 0.55, 10.23, and 16.42, respectively. A combined anaerobic co-digestion/pyrolysis system (capacity 50 m3/d) was designed based on the COD mass balance experimental data and biogenic CO2 market price of 22 USD/ton. This project could earn profits from biogas (12,565 USD/yr), biochar (6641 USD/yr), carbon credit (8014 USD/yr), and COD shadow price (6932 USD/yr). The proposed project could maintain a payback period of 6.60 yr. However, further studies are required to determine the associated life cycle cost model that is useful to validate the batch experiment assumptions.

Enhanced thermophilic high-solids anaerobic digestion of organic fraction of municipal solid waste with spatial separation from conductive materials in a single reactor volume

Despite benefits such as lower water and working volume requirements, thermophilic high solids anaerobic digestion (THSAD) often fails due to the rapid build-up of volatile fatty acids (VFAs) and the associated drop in pH. Use of conductive materials (CM) can promote THSAD through stimulation of direct interspecies electron transfer (DIET), while the need for their constant dosing due to poor separation from effluent impairs economic feasibility. This study used an approach of spatially separating magnetite and granular activated carbon (GAC) from the organic fraction of municipal solid waste (OFMSW) in a single reactor for THSAD. GAC and magnetite addition could both mitigate the severe inhibition of methanogenesis after VFAs build-up to ∼28–30 g/L, while negligible methane production was observed in the control group. The highest methane yield (286 mL CH4/g volatile solids (VS)) was achieved in magnetite-added reactors, while the highest maximum CH4 production rates (26.38 mL CH4/g VS/d) and lowest lag-phase (2.83 days) were obtained in GAC-added reactors. The enrichment of GAC and magnetite biofilms with various syntrophic and potentially electroactive microbial groups (Ruminiclostridium 1, Clostridia MBA03, Defluviitoga, Lentimicrobiaceae) in different relative abundances indicates the existence of specific preferences of these groups for the nature of CM. According to predicted basic metabolic functions, CM can enhance cellular processes and signals, lipid transport and metabolism, and methane metabolism, resulting in improved methane production. Rearrangement of metabolic pathways, formation of pili-like structures, enrichment of biofilms with electroactive groups and a significant improvement in THSAD performance was attributed to the enhancement of the DIET pathway. Promising results obtained in this work due to the spatial separation of the bulk OFMSW and CM can be useful for modeling larger-scale THSAD systems with better recovery of CM and cost-effectiveness.

Impact of tannery wastes on anaerobic co-digestion: enhancing biogas production and process efficiency

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry.Graphical

Iron Recycle-Driven Organic Capture and Sidestream Anaerobic Membrane Bioreactor for Revolutionizing Bioenergy Generation in Municipal Wastewater Treatment.

The practicality of intensifying organic matter capture for bioenergy recovery to achieve energy-neutral municipal wastewater treatment is hindered by the lack of sustainable methods. This study developed innovative processes integrating iron recycle-driven organic capture with a sidestream anaerobic membrane bioreactor (AnMBR). Iron-assisted chemically enhanced primary treatment achieved elemental redirection with 75.2% of chemical oxygen demand (COD), 20.2% of nitrogen, and 97.4% of phosphorus captured into the sidestream process as iron-enhanced primary sludge (Fe-PS). A stable and efficient biomethanation of Fe-PS was obtained in AnMBR with a high methane yield of 224 mL/g COD. Consequently, 64.1% of the COD in Fe-PS and 48.2% of the COD in municipal wastewater were converted into bioenergy. The acidification of anaerobically digested sludge at pH = 2 achieved a high iron release efficiency of 96.1% and a sludge reduction of 29.3% in total suspended solids. Ultimately, 87.4% of iron was recycled for coagulant reuse, resulting in a theoretical 70% reduction in chemical costs. The novel system evaluation exhibited a 75.2% improvement in bioenergy recovery and an 83.3% enhancement in net energy compared to the conventional system (primary sedimentation and anaerobic digestion). This self-reliant and novel process can be applied in municipal wastewater treatment to advance energy neutrality at a lower cost.

Evaluating the Environmental Impacts of Pretreatment and Nanoparticles in Solid-State Anaerobic Digestion Using Life Cycle Assessment

The yield of green energy from solid-state anaerobic co-digestion (SSAD) has recently been enhanced by incorporating innovative pretreatment methods and nanoparticles. However, the environmental consequences of employing new processes have not been fully examined. In this study, the environmental impacts of three high-methane-yielding scenarios including SSAD of corn stover blended with dairy manure (DM) denoted as (SYM1), calcium hydroxide-pretreated corn stover (CpCS) blended with DM (SYM2), and the CpCS blended with DM and nanoparticles (SYM3) were assessed and compared the baselines of solid-state and semi-solid-state anaerobic digestion using a life cycle assessment (LCA) approach. The approach investigated the best management practices that would result in high methane yield and low environmental impact. Results of the life cycle assessment indicate the inclusion of calcium hydroxide and nanoparticle has minimal negative environmental impact. There was an environmental gain in GWP when corn stover was co-digestion with DM (SYM1) relative to DM mono-digestions (baselines) and the carbon footprint of SYM1 was less by more than 85% compared to SYM2 and SYM3. However, the large volume of untreated corn stover harnessed for SYM1 scenario resulted in over 75% fossil fuel depletion compared to the other scenarios. The surplus methane from the SYM3 (at least twofold of other scenarios and baselines) in conjunction with being the least with the environmental implication makes the scenario the most attractive option for on-farm practice capable of harnessing the growing organic waste volume. These outcomes can guide trade-off between pretreatment and nanoparticle application to reduce solid-state anaerobic digestion’s negative environmental impact.