Biogas production, waste stabilization efficiency, and hygienization potential of a mesophilic anaerobic plug flow reactor processing swine manure and corn stover

Advanced biofuel production, policy and technological implementation of nano-additives for sustainable environmental management - A critical review

This review article critically evaluates the significance of adopting advanced biofuel production techniques that employ lignocellulosic materials, waste biomass, and cutting-edge technology, to achieve sustainable environmental stewardship. Through the analysis of conducted research and development initiatives, the study highlights the potential of these techniques in addressing the challenges of feedstock supply and environmental impact and implementation policies that have historically plagued the conventional biofuel industry. The integration of state-of-the-art technologies, such as nanotechnology, pre-treatments and enzymatic processes, has shown considerable promise in enhancing the productivity, quality, and environmental performance of biofuel production. These developments have improved conversion methods, feedstock efficiency, and reduced environmental impacts. They aid in creating a greener and sustainable future by encouraging the adoption of sustainable feedstocks, mitigating greenhouse gas emissions, and accelerating the shift to cleaner energy sources. To realize the full potential of these techniques, continued collaboration between academia, industry representatives, and policymakers remains essential.

Impact of mesophilic anaerobic digestion and post-treatment of digestates on the transfer of conjugative antimicrobial resistance plasmids

Manure is a major source of antimicrobial-resistant bacteria and resistance genes carried by mobile genetic elements such as plasmids. In France, the number of on-farm biogas plants has increased significantly in recent years. Our study investigated the impact of mesophilic anaerobic digestion (AD) and the post-treatment of digestates on the fate of conjugative plasmids, along with their potential transfer of antimicrobial resistance. Samples of raw manure, digestates and post-treated digestates were collected from three on-farm biogas plants. Conjugative plasmids were captured using the Escherichia coli CV601 recipient strain and media supplemented with rifampicin and kanamycin - to which the recipient strain is resistant - and tetracycline, sulfamethoxazole, gentamicin, trimethoprim, amoxicillin, cefotaxime, ciprofloxacin or colistin. Putative transconjugants were identified and characterised by disc diffusion and whole genome sequencing. The results showed that the antimicrobial resistance genes transferred from the different matrices conferred resistance to tetracyclines, sulphonamides, trimethoprim, and/or streptomycin. Transconjugants were obtained from raw manure samples but not from digestates or post-digestates, suggesting that mesophilic AD processes may produce fewer conjugative plasmids potentially able to be transferred to Enterobacterales.

Dry Anaerobic Digestion of the Organic Fraction of Municipal Solid Waste: Biogas Production Optimization by Reducing Ammonia Inhibition

The aim of this work is to optimize biogas production from thermophilic dry anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) by comparing various operational strategies to reduce ammonia inhibition. A pilot-scale plug flow reactor (PFR) operated semi-continuously for 170 days. Three scenarios with different feedstock, namely solely OFMSW, OFMSW supplemented with structural material, and OFMSW altered to have an optimal carbon-to-nitrogen (C/N) ratio, were tested. Specific biogas production (SGP), specific methane production (SMP), the biogas production rate (GPR), and bioenergy recovery were evaluated to assess the process performance. In addition, process stability was monitored to highlight process problems, and digestate was characterized for utilization as fertilizer. The OFMSW and the structural material revealed an unbalanced content of C and N. The ammonia concentration decreased when the optimal C/N ratio was tested and was reduced by 72% if compared with feeding solely OFMSW. In such conditions, optimal biogas production was obtained, operating with an organic loading rate (OLR) equal to 12.7 gVS/(L d). In particular, the SGP result was 361.27 ± 30.52 NLbiogas/kgVS, the GPR was 5.11 NLbiogas/(Lr d), and the potential energy recovery was 8.21 ± 0.9 MJ/kgVS. Nevertheless, the digestate showed an accumulation of heavy metals and low aerobic stability.

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.

Biogas production from high solids digestion of Pennisetum purpureum x Pennisetum typhoideum: Suitable conditions and microbial communities

Effects of organic loading rates (OLRs), temperatures and effluent recirculation rates on biogas production from Giant Juncao Grass (GJG) using pilot-scale semi-continuously fed CSTRs were investigated. Thermophilic reactors could be stably operated at OLR up to 5.0 kg VS m^-3 d^-1, while damaged process stability was detected in mesophilic reactors at OLR of 4.0 kg VS m^-3 d^-1. Higher effluent recirculation rate (3:1) helped lessen negative effects of system being over-loaded, especially for mesophilic reactors. Microbial community analysis revealed that temperatures had the highest effect on bacterial community structure. Firmicutes were the dominant bacterial phyla found under high temperatures, while majority of archaea in all reactors belonged to the phylum Bathyarchaeota. Changes of microbial communities could partly explain system performance under different operating conditions. This study was the first to show GJG as a superior biogas feedstock to other energy crops thanks to its higher methane yields per planting area.