Maximizing methane production from high solids anaerobic digestion of swine manure by investigating the loading rate and material flow

Industrial swine farming generates large amounts of swine manure ideally available for anaerobic digestion (AD) treatment. However, due to a potential bottleneck in mass transfer and the resulting suppression of microbial metabolism, it remains unclear whether high-performance AD can be achieved when treating high-solids swine manure. A continuous AD system was therefore investigated over 300 days to treat swine manure with a total solids (TS) content of up to 15% at consecutive hydraulic retention times (HRTs) of 60 and 30 days. The results obtained indicate that organic matter was hardly decomposed (only about 30–40%) with visible high viscosity at an HRT of 30 days, while an HRT of 60 days led to an increase of approximately 10% based on chemical oxygen demand (COD) removal efficiency and the methane yield was 0.30 L/g-VS. Carbohydrates were decomposed to the extent of about 50%, and proteins about 30%. The reactor maintained stability with volatile fatty acids (VFA) at around 600 mg/L and a total ammonium nitrogen (TAN) level of 2000–3000 mg/L. In conclusion, AD can be used to treat swine manure with feeding solids up to 15% when the HRT was 60 days or longer.