Impact of Adding Cow Dung with Different Ratios on Anaerobic Co-Digestion of Waste Food for Biogas Production

Kitchen wastes and animals’ manure are accumulated annually with a large quantity which represent a human health problems and lead to environment degradation. One of the effective techniques for processing these wastes is by producing biogas using anaerobic co-digestion of kitchen wastes and animals’ manure. The production of biogas as a sustainable source of energy can be significantly enhanced by adding cow dung as inoculum for anaerobic co-digestion of the substrates. In the municipal regions where the present study is carried out, there is a scarcity of animal’s manure. Therefore, it is necessary to determine the minimal effective ratios of cow dung in substrate mixture to enhance the biogas yield for household utilizations. An experimental investigation to evaluate the effect of adding cow dung as a substrate on biogas productivity from anaerobic co-digestion of food waste and used food oils was presented in this study. Five bench-scale digesters of 1Litre capacity with five substrates samples placed in controllable temperature water bath were used to conduct the co-digestion of the substrate’s mixtures at mesophilic conditions (35 ±1ᴼC) during digestion time of 35days. The results revealed that, maximum daily gas productivity was 84.5, 85.8, 87, 88.2 and 91.6 ml/day for cow dung mixing ratios of 4, 8, 12, 16 and 20% respectively. The production of biogas began after 4 days of starting the digestion and the best digestion time was 25 days for the five mixing samples. The maximum daily and cumulative biogas yield were 91.6 ml/day and 2914 ml respectively by mixing sample five of relatively higher dung ratio 20%. Concentration of CH4 in the produced biogas was in range of 57 – 63 %, and the maximum daily production of CH4 was 48, 51, 52, 55 and 58 ml/day by the samples with dung ratios 4, 8, 12, 16 and 20% respectively. It can be concluded that, adding cow dung with mixing ratio in range of 4–20% could improve the yield and quality of the biogas. The enhancement in cumulative biogas and CH4 produced from the mixing sample five of relatively higher dung ratio 20 % were 9.7 % and 27.9 % respectively compared to the mixing sample one with relatively lower dung ratio.