Hydrogen and methane production from food wastes by anaerobic fermentation using mixed microbial cultures

Hydrogen (H2) and methane (CH4) production from food waste and cheese processing wastewater via anaerobic fermentation were conducted using mixed microbial cultures under mesophilic conditions. Batch H2 fermentation studies from the food waste showed that a H2 yield of 5.8 mM/g-VS-fed was achieved at food to microorganism ratio (F/M) of 1.0, while H2 fermentation from the cheese processing wastewater showed that a H2 yield of 8 and 10 mM/g-COD fed, respectively, at the F/M of 1.0 and 1.5. Butyric, acetic, propionic, and valeric acids were the major volatile fatty acids produced in the fermentation process of both substrates.; The continuous H2 fermentation of the cheese whey wastewater was studied using a completely mixed reactor. The pH of the reactor was controlled in a range of 4.0 to 5.0 by adding alkalinity. The maximum H2 yield was between 2.0 and 2.3 mM/g-COD-fed for loading rates tested when the HRT of the H2 reactor was 24 hrs. It was found that CH4 was present in the biogas at various levels even at a low pH. The biogas production and H2 content of the biogas for each loading rate varied largely over time, but continuous H2 production was achieved for two to three weeks at each loading rate. Based on bacterial analysis on selected samples from the reactors fed with cheese whey wastewater, more than 50% of the bacteria detected were lactobacillus and about 5% of the isolates were Clostridia when the reactor was able to produce a good amount of H2. When the reactor did not produce a good amount of H2, there was about three fold lower number of Lactobacillus than when the reactor had good H2.; The H2 reactor effluent was treated with an anaerobic sequencing batch reactor (ASBR). At the loading rate of 0.54 to 2.15 g-COD/L/d, a CH 4 yield of 0.253 to 0.304 L/g-COD-fed was obtained. For a steady-state operation of the ASBR, it was necessary to add Ca(OH)2 in the substrate in order to keep a desired pH level (around 7.0) to ensure healthy growth of methanogens. The highest COD and VFA removals achieved in the ASBR were 94% and 98% at 0.54 g-COD/L/d, respectively.