Psychrophilic Reactor Research Articles

Microbial adaptation and response to high ammonia concentrations and precipitates during anaerobic digestion under psychrophilic and mesophilic conditions

This study explored microbial adaptation to high ammonia concentrations (<1000 mg/L to 4000 mg/L) during anaerobic digestion (AD) under psychrophilic and mesophilic conditions, the latter of which yielded precipitates facilitating investigation of microbial response. The experimental setup was performed at bench-scale using microbial consortia from four different operating anaerobic digesters treating different organic wastes (WW-wastewater sludge, MN-manure, FW- food waste and CO-co-digestion (FW & MN)). Adaptation experiments were conducted with semi-continuous flow mode to resemble large-scale operation. Metagenome and 16S RNA analysis were performed for the first time in a psychrophilic reactor during an ammonia acclimation process. These analyses were also performed in mesophilic reactor exposed to precipitates and high ammonia levels. Diversity reduced when adaptation occurred successfully from 1.1 to 4 g/L of total ammonia nitrogen (TAN) under psychrophilic conditions, while the microbial community became more diverse under mesophilic conditions with ammonia inhibition. We report for the first time Methanocorposculum as a robust hydrogenotrophic methanogen at high ammoniacal concentrations under psychrophilic conditions. Additionally, Methanosarcina was present in low and high ammoniacal concentrations in mesophilic conditions, but there was a shift in species dominance. Methanosarcina barkeri stands out as a more resilient methanogen compared to Methanosarcina mazei, which initially dominated at <1.1 g/L TAN. We also explored the effects of sudden precipitates on methanogenic communities and methane production when they occurred under mesophilic conditions in two reactors. Methane production declined by more than 50% when precipitates occurred and was accompanied by pH reduction and VFA accumulation. Diversity data corroborated that methanogens were severely reduced. These two reactors were not able to recover with 50 days of added operation, demonstrating potential for long-term negative impacts of precipitate formation on AD performance stemming from negative impact to methanogenic communities.

Impacts of different operational temperatures and organic loads in anaerobic co-digestion of food waste and sewage sludge on the fate of SARS-CoV-2

The impacts of different operational temperatures, and organic load (OL) on the fate of SARS-CoV-2 during the anaerobic co-digestion of food waste (FW) and sewage sludge (SS) was evaluated. The lab-scaled batch reactors (i.e. R1-R7) were performed under psychrophilic, mesophilic, and thermophilic conditions and the OL of systems was 1.5, 3.5, 6 gVS/L. The performance parameters showed that at higher OL the stability of systems failed and low biogas was produced. In contrast, increasing of operational temperature of systems induced more biogas generation due to the increment of metabolic activity of bacteria. Therefore, R1-R7 achieved biogas yield of 202.5, 249, 187, 260, 246, 163, and 300 mL/gVS respectively. Both SARS-CoV-2 genes i.e. ORF1ab, and N genes were detected in the effluent of psychrophilic reactors i.e. R1, and R2, with a total concentration of 46 × 103, and 11 × 103 copies/L respectively. In R3, no viral genes were observed, when the VFAs was accumulated up to 2000 mg/L and caused a pH drop to 5.6. At the mesophilic condition, the viral concentration was significantly declined, and no viral genes were observed at an OL of 3.5 gVS/L. Furthermore, the synergistic effect of temperature and accumulation of intermediate metabolites provided a sever condition for SARS-CoV-2 survival at an operational temperature and OL of 50 °C, and 1.5 gVS/L respectively.

Two-stage psychrophilic anaerobic digestion of food waste: Comparison to conventional single-stage mesophilic process

Food waste collected exclusively from University restaurant was tested under anaerobic digestion (AD) conditions to determine its biomethane generation potential. The digestion characteristics of food waste were evaluated in BMP tests and in a conventional single-stage mesophilic CST Reactor. The suitability of psychrophilic two-stage AD to convert food waste was investigated by using a novel two-stage psychrophilic semi-continuous reactor, consisted of a vertically-oriented cylindrical reactor and a coaxially incorporated vertical tube able to spatially separate acidification from methanogenesis. Food waste presented significant methane generation performance under mesophilic conditions. Relatively high amounts of H2S released during process evolution did not have a significant effect on biogas production. For psychrophilic two-stage AD, H2S generated during start-up provoked reactor’s instability only for a few days. The system was stable and operated at steady-state conditions over the course of the main AD. Higher amount of biogas was produced by the two-stage psychrophilic reactor (0.800 m3 kgVS−1) than the mesophilic single-stage system (0.751 m3 kgVS−1). However, the average methane quantities generated by the two systems were remarkably similar (0.444 and 0.440 m3 kgVS−1). Psychrophilic process was more efficient in utilizing higher proportions of volatile organics contained in substrate for methane generation than mesophilic operation. The low-temperature two-stage reactor was more energy-efficient than the mesophilic CSTR for digestion of food waste. Two-stage anaerobic digestion system operating under psychrophilic conditions might be an economically feasible option for efficiently digesting food waste.

Anaerobic Digestion of Laminaria digitata: The Effect of Temperature on Biogas Production and Composition

Seaweed biomass has emerged as an alternative for the production of renewable fuels such as biogas from anaerobic digestion (AD). In relation to the biogas production rate, digester temperature setting is one of the most critical factors for an economically viable digester operation, especially in temperate countries like Ireland, as most annual temperatures are below the mesophilic range. In this study, the effect of digester temperature on biogas and methane production efficiency during the AD of Laminaria digitata was evaluated. 120 ml batch reactors were incubated at 20, 35 and 45 °C for 54 days to determine a temperature profile for the AD process. Reactors incubated at 35 °C produced the highest biogas and methane yields (336 ml biogas/g VS and 184 ml methane/g VS). Thermophilic reactors (45 °C) produced 30 % less biogas and 23.3 % less methane, followed by psychrophilic reactors (20 °C) which produced 41 % less biogas and 39.7 % less methane. A drop in pH in the mesophilic and thermophilic reactors was identified as an inhibitory factor during the first days of digestion. Psychrophilic reactors were better able to withstand the observed changes. Mesophilic temperatures will be used in further studies to examine scaling up of the process.