Effects of different ratios of pig manure and straw on solid acidogenic fermentation

In this study, the effect on solid acidogenic fermentation of different proportion with pig manure and straw under the condition of biogas slurry returning were investigated. For this purpose, five sets of anaerobic batch reactor experiments were performed using straw and the mixtures of pig manure and straw in five different ratios (80% pig manure, 20% straw; 66.7% pig manure, 33.3% straw; 50% pig manure, 50% straw; 25% pig manure, 75%straw; 100% straw). The results showed that increasing the proportion of pig manure done well for controlling pH value, but the higher concentration of ammonia nitrogen appeared simultaneously. Returning of biogas slurry could avoid cumulating of VFAs effectively. Acetic acid which was dominant in fermentation products of different raw material ratios experiments accounted for 80.8%, 81.8%, 77.1%, 78.3% and 73.8% respectively of total output VFAs. Propionic acid concentrations in five reactors were less than 1.6 g/L, and accounted for 4.8%, 2.8%, 7.2%, 6.5% and 8.4% of total VFAs produced respectively. Comprehensive analysis showed that 2:1 ratio of pig manure to straw was better for acidogenic fermentation than other treatments.