Combination of H2SO4-acidification and temperature-decrease for eco-friendly storage of pig slurry.

Owing to the economic benefit and efficiency, H2SO4-acidification is often applied for reducing CH4 emissions during storage of pig slurry (PS). However, it encounters with several problems related with safety and the concomitant H2S emissions. To reduce the required amount of H2SO4, in this study, the storage at low temperature (20-35 °C) was applied to the mild-acidified PS (pH 6.5 and 7.0). 55.1 kg CO2 eq./ton PS of CH4 was emitted from the control (non-acidified at 35 °C), which was reduced to 14.4-40.2 kg CO2 eq./ton PS at 20-30 °C. Temperature-decrease led to the increase of the abundance of methanogens (Methanobrevibacter and Methanolobus) that can grow at low temperature and the drop of specific methanogenic activity value. To achieve 70 % CH4 reduction, 1.6 kg H2SO4/ton PS was needed in PS acidification, which was decreased to 0.5 kg H2SO4/ton PS by decreasing temperature from 35 °C to 25 °C. CH4 production potential of the PS stored at 35 °C-pH 6.5 and 25 °C-pH 7.0 was increased by 21-33 % compared to the control. The GHG reduction of 33.6-41.9 kg CO2 eq./ton PS and the profit of 6.6 USD/ton PS could be attained by applying acidification or combined storage, indicating that the temperature-decrease can be effectively combined with H2SO4-acidification.

Effects of pig slurry acidification on methane emissions during storage and subsequent biogas production.

In addition to undesirable odorous gases, substantial amounts of greenhouse gases (GHG), particularly methane (CH4), are generated during the storage of livestock manure. To reduce the CH4 emissions, first, pig slurry (PS) was stored for 40 d at 30 °C after adjusting the pH at 5.0-7.0 using H2SO4 solution. In the control (non-acidified PS), 3.7 kg CO2 eq./ton PS of CH4 emissions was detected, which was reduced to 1.8, 0.9, 0.4, 0.2, and 0.1 kg CO2 eq./ton PS at pH 7.0, 6.5, 6.0, 5.5, and 5.0, respectively. Methanosarcina was found to be the dominant genus (67% of the total archaeal sequence) in the control, whose dominance was reduced as storage pH decreased. The results of ribonucleic acid analysis and specific methanogenic activity test further confirmed the inhibition of indigenous methanogens by acidification. Later, the biochemical CH4 potential of stored PS was tested. Compared to the control (10.6 L CH4/L PS), the acidified PS showed higher CH4 yields of 12.7-14.6 L CH4/L PS, presumably by keeping degradable organic matters in PS under acidic condition. Among different acidification pHs tested, the maximum amount of GHG reduction was achieved at pH 6.0 by reducing CH4 emission to +0.4 kg CO2 eq./ton PS during storage while increasing biogas production potential equivalent to 48.3 kWh/ton PS (-22.5 kg CO2 eq./ton PS), resulting in a further reduction of (-)9.6 kg CO2 eq./ton PS compared to the control.

Biohydrogen production from food waste: Current status, limitations, and future perspectives.

Among the various biological routes for H2 production, dark fermentation is considered the most practically applicable owing to its capability to degrade organic wastes and high H2 production rate. Food waste (FW) has high carbohydrate content and easily hydrolysable in nature, exhibiting higher H2 production potential than that of other organic wastes. In this review article, first, the current status of H2 production from FW by dark fermentation and the strategies applied for enhanced performance are briefly summarized. Then, the technical and economic limitations of dark fermentation of FW are thoroughly discussed. Economic assessment revealed that the economic feasibility of H2 production from FW by dark fermentation is questionable. Current efforts to further increase H2 yield and waste removal efficiency are also introduced. Finally, future perspectives along with possible routes converting dark fermentation effluent to valuable fuels and chemicals are discussed.