Biogas Production from Modified Starch at the Anaerobic Digester

Abstract

Industrial wastewater from tapioca flour has long been a problem for the environment, due to the presence of high organic parameters of COD of 6,000–7,000 mg/L being recorded, in addition to an acidity with a pH of 4.0–4.5, suspended solids at a rate of 950 mg/L, and odors. This effluent can be a significant environmental problem if not managed properly according to environmental quality standards. Furthermore, this industry requires heat to dry tapioca flour and electricity to run the industrial processes. The tapioca starch factory of PT Tunas Jaya Lautan has a processing capacity of 200 tons/day of cassava, producing effluent at a rate of about 17,000 m³/day, which receives further treatment in six aerobic ponds. In this study, biogas production was obtained by modifying the existing treatment ponds into an anaerobic digester. Methanogens were taken from effluent treatment ponds and then cultivated in anaerobic conditions. Acclimatization was performed by converting the existing system into the anaerobic environment by covering aerobic ponds using high-density polyethylene (HDPE) plastic, 8-mm, half-shaped balloons. Acclimatization was conducted for 3 months, thus the bacteria were accustomed to the environmental conditions. A closed air recirculation system with R = 0.5 caused turbulence and blended perfectly with the existing effluents, further accelerating the acclimatization of anaerobic bacteria. In addition, a 35 °C operating temperature was maintained in the anaerobic digestion system, which was able to produce a biogas stream of 5.8 m³/min. The best biodigester production stream was 4.6 m³/min, which occurred in 35 °C conditions, with a flow recirculation (R = 0.5) and production of methane gas (CH₄) at levels of 42%. After passing through a purification unit, methane gas production increased to 73%. It was then ready to be used as an alternative fuel in the factory. This biogas product was utilized as the heat source for modified starch dryers, replacing diesel fuel.