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The current study examines the impact of using solar energy, specifically the use of a solar greenhouse to surround the digester and a second inner greenhouse to heat the digester inlet (System A), by simulation and validation for warming biogas digester. The simulation study compares the heat balances of System A and System B, which had no heating resource. Both systems were assumed to be located in Xianyang, Shaanxi province, northwest China. The simulation and modeling were undertaken using EPBSS, OpenStudio, and SketchUp. The simulation had the following results: in System A, the monthly average temperature of the process during the winter was maintained high enough (≥9.8 °C) to support biogas production for the whole year, in contrary to System B, which had a temperature of <8 °C for 5 months of the year. The results also show that System A could only be viable in regions where the average temperature during the winter is above −5 °C. The validation study was conducted on an actual digester with the same model and location as System A, and the results were within the range of results from simulation results (≤0.34 °C observed difference). Consequently, this model could be used for predicting the geographic locations where System A’s design could be used. Economic analysis of System A showed that the installation of the two greenhouses could increase revenue from biogas by US$1,290 per year, which could cover the costs of the greenhouses within 14 months of operation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conductive NPs potential to improve AD performance was critically discussed. • Impact of different NPs and sizes on AD biogas quantity and quality are elucidated. • The interactions of AD microorganisms and DIET with the aid of NPs were reviewed. • The role of NPs in biochemical pathways direction and metabolites utilization are covered. Anaerobic digestion (AD) is a biochemical process that converts waste organic matter into energy-rich biogas with methane as the main component. Addition of electric electro-conductive, such as that nanoparticles (NP), has been shown to improve biogas generation. Interspecies electron transfer and direct interspecies electron transfer (DIET) using conductive materials is one of the mechanisms responsible for observed increases in CH 4. This article discusses the effect of the type and size of electro-conductive NPs on improving microbial degradation within AD systems, as well as the effect of electro-conductive NPs on microbial community shifts and syntrophic metabolism. Limitations and future perspectives of using NPs in an AD system is also discussed. [ABSTRACT FROM AUTHOR]

Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value. [ABSTRACT FROM AUTHOR]

[Display omitted] • FNA pretreatment can significantly improve the solubilization of organic waste. • pH change within the system can adversely impact the FNA pretreatment performance. • Effective FNA concentration may decrease due to NO 2 – consumption by denitrifiers. • FNA-pretreated organic waste does not always show a higher biogas production in AD. • FNA at 1.0–5.2 mg FNA-N/L effectively controlled H 2 S-odor in the organic wastes. This work investigated the effectiveness of free nitrous acid (FNA) in enhancing organic waste solubilization to improve biogas production in anaerobic digestion (AD). The results indicated that FNA pretreatment can enhance soluble organic content and control H 2 S odor in tested organic wastes, including food waste, sewage sludge, and their combination. However, a significant decrease (>50 %) in FNA concentration was found in the reactors, possibly due to denitrifier-driven NO 2 – consumption. Biochemical methane potential (BMP) tests showed a 25 ± 8 % enhancement in CH 4 production in the reactors fed with mixed substrate pretreated with 2.9 mg FNA-N/L. However, the presence of NO 2 – (325.6–2368.0 mg N/L) in some BMP reactors, due to carryover from FNA pretreatment, adversely affected CH 4 production (>55 %) and prolonged lag time (>4.2 times). These findings are valuable for researchers and practitioners in waste management, offering insights for implementing FNA pretreatment to enhance the biodegradability of organic wastes in AD. [ABSTRACT FROM AUTHOR]