• Energy Research

Anaerobic ethanol oxidation relies on syntrophic interactions among functional microorganisms to become thermodynamically feasible. Different operational modes (sequencing batch reactors, SBRs, and continuous flow reactors, CFRs) and solids retention times (SRT, 25 days and 10 days) were employed in four ethanol-fed reactors, named as SBR25d, SBR10d, CFR25d, and CFR10d, respectively. System performance, syntrophic relationships, microbial communities, and metabolic pathways were examined. During the long-term operation, 2002.7 ± 56.0 mg COD/L acetate was accumulated in CFR10d due to the washout of acetotrophic methanogens. Microorganisms with high half-saturation constants were enriched in reactors of 25-day SRT. Moreover, ethanol oxidizing bacteria and acetotrophic methanogens with high half-saturation constants could be acclimated in SBRs. In SBRs, Syner-01 and Methanothrix dominated, and the low SRT of 10 days increased the relative abundance of Geobacter to 38.0%. In CFRs, the low SRT of 10 days resulted in an increase of Desulfovibrio among syntrophic bacteria, and CFR10d could be employed in enriching hydrogenotrophic methanogens like Methanobrevibacter.

Abstract In this study, the environmental impacts of pig manure direct land application and anaerobic digestion (mono- and co-digestion) for biomethane production followed by digestate land application were evaluated by life cycle assessment, with a focus on the dynamic land application of digestate in terms of the nutrient profiles, soil nutrient status and environmental regulations. Ireland was used as a case study where co-digestion of manure with grass silage is viable, and an Irish emission inventory was established. The results indicate that pig manure and grass silage co-digestion performs best in 9 of the 11 impact categories assessed. Compared with direct land application, mono-digestion of pig manure decreases direct greenhouse gas emissions by 48% (190 tonne CO2e). Co-digestion with grass silage increases the total energy recovery by 226% (1592 MWh) than mono-digestion. The nitrogen available for plants in digestate (41.8%) is a little lower than that in raw pig manure (43.2%) due to the higher ammonia emissions after anaerobic degradation. The environmental impacts of the three pig manure management methods are greatly affected by soil nutrient conditions and regional environmental regulations, which determine the organic fertilizer application rates and consequently the required land areas and transport distances. In this case study, the land application area for digestate is determined by phosphorus acceptance of soils rather than nitrogen or potassium. This study provides practical insights to farmers, the gas industry, and policy makers to conduct effective organic fertilizer application, select optimal AD plant location, and maximize environmental benefits.

Biogas is a promising and robust renewable energy that holds potential as clean energy in the context of the current climatic emergency. Biogas has the immense advantage of coupling waste management and clean energy production. In other words, it is not only a renewable energy source, but also a central tool in recycling a vast range of waste products from the agroindustry. Despite its potential, the process is microbiologically complex and is usually carried out in both industrial and pilot laboratories, utilizing a variety of reactors and systems. In this work, we present a very simple, Do It Yourself (DIY) biogas fermenter that we have designed, operated, and characterized. We propose this technology as both an inexpensive proxy for biogas reactors in academic and private laboratories and as an effective dissemination tool to foster the knowledge and potential of biogas as a key technology to contribute to the development of a global bioeconomy.