Factorial experimental design to enhance methane production of dairy wastes co-digestion

Factorial design was used to investigate the parameters involved in co-digestion mixture of dairy wastes (from a Moroccan dairy industry) in order to improve methane production of this mixture. Indeed, evaluation of methane yield as a function of three parameters (pH, inoculum and organic load) showed the correlation between the experimental and statistical data in terms of pH 8 and inoculum 1 (constituted by sludge diluted in 1 L of basal medium of methanogenic bacteria, in addition to formic acid (5 mL L−1), propionic acid (5 mL L−1), lactic acid (5 mL L−1) and micro-nutrient (10 mL L−1)) as optimum parameters. However, a discrepancy was detected about organic load. The interaction between parameters had a positive effect on methane yield because it led to produce experimentally a maximum methane using the higher load (3.44 g VS). These results allow selecting the parameters for the improvement of methane production. Furthermore, the validity of the fitting model to describe and improve the efficiency of dairy wastes co-digestion was investigated. In addition, an abatement of 89% of volatile solids was observed and the mineral solids was increased from 4 to 7.2 g L−1, which is important of digestat value as fertilizer.