Methane production from thermophilic co-digestion of dairy manure and waste milk obtained from therapeutically treated cows

Study of an enhanced dry anaerobic digestion of swine manure: Performance and microbial community property

Anaerobic digestion could treat organic wastes and recovery energy. Dry anaerobic digestion had advantages of low heating energy, small digester and less digestate, but its methane production was poor. In this study, an enhanced dry anaerobic digestion of swine manure (thermal treatment + dry anaerobic digestion) was proposed, and its feasibility was investigated via semi-continuous experiment. Results showed that methane production rates were 314.6, 416.0, 298.0 and 69.9 mL CH₄/g VS at solid retention time (SRT) of 41 d, 35 d, 29 d and 23 d. Volatile solids (VS) removal rate and methane production rate could reached 71.4% and 416.0 mL CH₄/g VS respectively at SRT of 35 d. Methane production rate of the enhanced dry anaerobic digestion was 390% higher than that of dry anaerobic digestion. Microbial study indicated that hydrogenotrophic methanogens predominated with the abundance of 90.2%, while acetoclastic methanogens were not detected. This process was feasible, and was of great practical importance.

Methane production from thermophilic co-digestion of dairy manure and waste milk obtained from therapeutically treated cows

Methane production from co‐digestion of dairy manure and waste milk, milk from cows treated with antibiotics for mastitis, was tested in a 2 × 4 factorial design. Four different waste milk percentages (w/w): 0% (SM), 10% (SMWM10), 20% (SMWM20) and 30% (SMWM30), were tested with two slurry percentages (w/w): 50% (A) and 25% (B) and the rest being manure at 55°C for 12 days in batch digesters. The results analyzed using a Gompertz model showed SMWM10 produced the highest methane production potential (P_m)/g volatile solids added followed by SM in both A and B. This P_m of SMWM10 in A and B was statistically non‐significant (P > 0.05). More than 96% of cefazolin‐resistant bacteria and 100% of multi‐drug‐resistant bacteria reductions were observed in all the treatments. Inclusion of waste milk at 10% in single stage digester enhances the methane production from dairy manure and could offer added benefit of waste milk treatment and disposal.