Abstract
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 (Pm)/g volatile solids added followed by SM in both A and B. This Pm 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.
Highlights
Anaerobic digestion has gained continuous attention in treating organic wastes such as cow manure, since it produces biogas, a renewable energy source and a digestate that can be used as organic fertilizer
At the second day of the digestion, the highest concentration of methane in produced biogas was obtained in the digesters without added waste milk (SM) in both A and B after which an increased methane concentration was observed in the digesters with 10% waste milk (SMWM10) in both A and B
The digesters added with 20% waste milk (SMWM20) and 30% waste milk (SMWM30) always produced the lower methane concentration than SM and SMWM10 despite the difference in slurry percentage
Summary
Anaerobic digestion has gained continuous attention in treating organic wastes such as cow manure, since it produces biogas, a renewable energy source and a digestate that can be used as organic fertilizer. The production of biogas through anaerobic digestion offers significant advantages over other forms of waste treatment, biogas plants are difficult to run with economically profitable results if the process is based only on livestock manure. In this regard, co-digestion strategies are of importance to enhance the methane production in agricultural biogas plants. For instance, in Denmark (Raven & Gregersen 2007) and Germany (Weiland 2006), the digestion of manure and organic waste is a well-established technological practice This process consists of combining several wastes with complementary characteristics in order to improve methane production. The co-digestion of cattle manure with municipal solid waste (Callaghan et al 1999; Hartmann & Ahring 2005), food wastes (Neves et al 2009), fruit and vegetable waste and chicken manure (Callaghan et al 2002) and so on, has been shown to enhance methane production
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