Effect of thermal and thermo-alkaline pretreatment on cattle paunch anaerobic digestion

The present study evaluates the effect of thermal and thermo-alkaline pretreatment in terms of kinetic and methane yields on paunch anaerobic digestion. A first attempt of pretreatment consisted in mixing different quantities of calcium hydroxide (ranging from 0% to 8%TS) to a sample of cattle paunch, which was preliminary diluted to 5%TS in order to be pumpable. Samples were incubated at different temperatures (20, 37 and 70°C) for 24 hours, and then the substrates were used for a BMP test. Likewise, catalysed steam-explosion was also assessed for anaerobic digestion performance. Calcium hydroxide was used as catalyst (ranging from 0% to 2%TS) also in this case and contact time was fixed to 15 minutes. Temperatures were set to 150, 180 and 200°C. A kinetic improvement was observed in both BMP tests, but to a different extent. Steam-explosion practically halved the digestion length. No significant effect was visible on methane yields for both pretreatments, which may indicate that the pretreatments tried were only able to shorten the hydrolysis. Further research is needed to understand whether is the cation, which is unsuitable for the breaking down the interlinkages of hemicellulose and lignin or is the type of substrate, which is strongly recalcitrant to biodegradation.