Anaerobic co-digestion of waste fruits and vegetables and swine manure in a pilot-scale bioreactor

Anaerobic digestion (AD) of mixtures of different substrates is a new trend in biogas production. It gives possibilities to stimulate the AD of materials not easily susceptible to this process by mixing them with other substances which are easier degradable or to improve the content of compounds, C/N ratio and thus the process stability. In this study, swine manure (SM) and a specific mixture of waste fruits and vegetables (WFV) were used as single substrates and in a mixture at various ratios. The mixture of WFV was with a constant ratio of 40% waste potatoes (WP), 20% waste tomatoes (WT), 20% waste cucumbers (WC) and 20% waste apples (WA). The results showed that the increase of the WFV in the inlet organics mixture led to an increase of the specific daily biogas flow rate at a slight decrease of methane and small increase of the carbon dioxide content in the biogas obtained. The optimal mix ratio for co-digestion of SM and WFV maximizing the biogas and the methane yields obtained from a unit of biodegraded organics was found to be SM:WFV = 70:30. Under this conditions, the biogas and methane yields from a unit of degraded organics reached 1.090 m(3)/kgVS.day and 0.65 m(3)/kgVS.day, respectively. The co-digestion of SM and WFV not only improved the stability of the anaerobic process, but also led to a higher methane production.