Anaerobic digestion of pig and dairy manure under photo-dark fermentation condition

Anaerobic digestion (AD) with livestock manure is a promising way for biogas production. This work presents the influence of photo-dark fermentation on biogas production of pig manure (PM) and dairy manure (DM). All sets were conducted with temperature 35 ± 2 °C and total solid concentrations 8%: PM1 and DM1 in transparent reactor under sunlight for photo-dark fermentation, and PM2 and DM2 in non-transparent reactor for dark fermentation. DM2 had the best cumulative biogas production (CBP) of 15,447.5 mL, followed by PM1 (15,020 mL) with stable pH and low total ammonium nitrogen (TAN) concentration (1384.99 mg/L), and DM1 and PM2. The CBP of DM2 was 5.77 times as much as PM2. The relationship between CBP and four factors including volatile fatty acid (VFA), TAN, total alkalinity and pH was analyzed. pH gained the maximum determination coefficient with the CBP among all sets and total alkalinity showed negative correlation with CBP of PM1 and DM1.