Enhancement of Anaerobic Digestion of Cow Manure Through Inoculation Under Mesophilic Conditions

A wide range of techniques are currently used to improve the performance of the anaerobic digestion (AD) process, including co-digestion, inoculation, and addition of various accelerants. In the current study, ruminant intestinal waste inoculum effect on AD of cow manure was investigated. It was hypothesized that methanogens present in intestinal waste will enhance anaerobic digestion, which will result in increased biogas production. Five different cow manure/intestinal waste ratios (1:0, 9:1, 7:3, 1:1, 0:1) on wet weight basis were introduced in AD systems at mesophilic environment (37 °C) to find the best combination of cow manure and intestinal waste. Among tested cow manure/intestinal waste ratios, 9:1, 7:3, and 1:1 demonstrated a good synergistic effect and yielded higher cumulative biogas yields than cow manure and ruminant intestinal waste alone. The cow manure/intestinal waste (9:1) had the maximum cumulative biogas yield (239 ± 5.0 mL/g VS), chemical oxygen demand (COD) removal rate (40 ± 0.56%), volatile solid (VS) removal rate (27 ± 1%), and total solid (TS) removal rate (24 ± 0.52%). In the current study, nutrients’ status (nitrogen, N; phosphorus, P; and potassium, K) of digestate was determined while most of the previous studies are only on biogas production. A 9:1 ratio of cow manure to intestinal waste was found to be the best with a cumulative NPK of 4.53%. The inoculation technique using intestinal waste can be an effective means of increasing the efficiency of biodegradable waste.