Biogas Production from Anaerobic Co-digestion of Cow Manure, Residual Edible Oil with Two Qualities of Waste Activated Sludge

The quality of waste activated sludge produced in urban wastewater treatment systems varies according to the efficiency of the operation of treatment units along the content of microflora and organic carbon. However, these represent a biogas-energy alternative through anaerobic co-digestion, contributing to reducing the environmental impacts caused by their inadequate disposal. Biogas production by the Two-stage production method in batch digesters was evaluated by two qualities of waste activated sludge (SLB50 y SLB90) and with a mixture of two co-substrates: cattle manure (CEV50 y CEV90) and residual edible oil with mixing, pH and temperature control. Bacteria in good quality sludge (SLB90) showed a faster adaptation of 2 days than those in low quality (SLB50) with 25 days lag phase. The highest CH4 production was for SLB90 (303.99cm3 d-1) compared to SLB50 (4.33 cm3 d-1); while cow manure sludge mixture (CEV90) contributed to increasing production of CH4 (42 422.8 cm3 d-1) compared to CEV50 (12 881.45 cm3 CH4 d-1), while in residual edible oil mixture they were 767.32 cm3 d-1 and 211.42 cm3 d-1 for CAV90 y CAV50, respectively. The addition of sludge co-substrates improves the nutrient balance, C/N rate and micro flora diversity; consequently methane production improves too; this methodology could be integrated into concepts of Circular economy.