Transforming the infectious septage into biogas by co-digestion process

Abstract

As population growth rapidly increases, energy consumption becomes higher while natural resources have been continuously reduced. As a result of the population increasing, also the waste is increased. For example, infectious septage (the sludge accumulated in the septic tank and contained of essential nutrients) that is usually mismanaged. To address these problems, the researcher aimed to determine the ratio (v/v) between septage and wastewater generated from Golden Dried Longan production (LW) that provided the maximum methane yield by using of the Modified Biochemical Methane Potential (BMP) test. Three different waste mixtures (septage+LW) with the COD:TKN ratios of 100:1.1, 100:2.5, and 100:5 are tested. The experimental results presented that the ultimate specific methane yield of the COD:TKN ratio of 100:5 rendered the highest value (143 mlCH4/gVSadded). The Temperature-phased Anaerobic Digestion (TPAD) system was then tested for co-digesting waste mixture to produce biogas and organic fertilizer. The TPAD system was consisted of a 30 L-thermophilic (55˚C) and a 10 L-mesophilic (35˚C) reactors. The Organic Loading Rate (OLR) was started from 0.5/1.0 kg VS/m3-d (OLR of thermophilic/mesophilic reactor) and sequentially increased to 1.7/2.0, 1.5/3.0, and 4.5/5.0 kg VS/m3-d, respectively. Biogas volume and specific methane yield at OLR of 1.5/3.0 kg VS/m3-d were 1,659 ml/day and 22.2 mlCH4/gVSadded, while 3,628 ml/day and 13.4 mlCH4/gVSadded were obtained at OLR of 4.5/5.0 kg VS/m3-d. The volatile solids removal at OLR1.4/3.0 was 27.4% while 47.8% was detected at OLR4.5/5.0. The pathogen removal efficiency of TPAD system was over 90% throughout the experimental period.