Design and development of biogas reactor ... 121 Indonesian Journal of Agriculture 2(2), 2009: 121-128 ABSTRACT Biogas technology has been introduced and developed for long time in Indonesia. However, its application as an alternative energy source is limited due to several constraints such as lack of technical expertise, misfunction of the reactor, non-user friendly design, manually handling, and highly investment for construction. A study was conducted to develop biogas reactor for farmer group scale. Reactor was designed with installed capacity of cattle dung from 10-12 heads or about 18 m 3 dung. Based on design calculation, digester was predicted to produce biogas up to 6 m 3 / day. Production of methane gas depended on C/N ratio, hydraulic retention time, pH, temperature, and toxicity of cattle dung used. Temperature of slurry inside digester was around 25-27 o C and pH 7.0-7.8. Reactor produced biogas containing methane of about 77%. Results showed that mantle lamp needed biogas of 0.23 m 3 / hour with pressure of 45 mm H 2 O and gas stove required biogas of 0.30 m 3 /hour with pressure of 75 mmH 2 O. Analysis of environmental impact indicated that COD of effluent decreased about 90% compared to fresh dung. Moreover, BOD/COD ratio was 0.37, less than that of normal waste water of 0.5. Effluent components (N, P and K contents) were not different to compost as a reference. [Keywords: renewable energy, biomass, cattle dung, biogas reactor] INTRODUCTION Fast population growth and industrial sector expansion cause increase in energy demand and decrease in environment quality. Although Indonesia is one of oil and gas producing countries, decrease in oil reserves and revocation of oil subsidy had increased oil price and decreased environment quality due to excessive utilization of fossil energy. Utilization of alternative renewable and environmentally-friendly energy resources, therefore, is required. Biogas is a renewable energy that has highly prospect to be developed. Biogas can be produced from wastes such as household wastewater; liquid wastes from chicken, cow, swine farming; and organic wastes from market and food industry. Installed capacity of biogas utilization is less than 1% of existed biogas potential (685 MW). Ruminants (dairy cattle, beef cattle, buffalo) with population of 13.68 million heads (in 2004) with population structure of calf, young, adults and average cattle dung of 12 kg/head/day, produce cattle dung of 164.16 million tons per day or equal to 8.2 million liters of kerosene/day (Syamsuddin and Iskandar 2005). The advantages of using biogas reactor system are reduce greenhouse gas effect, decrease unpleasant odor, prevent disease transmission, and produce heat, power (mechanic/electricity) and by-products such as solid and liquid fertilizers. Utilization of wastes as energy source will economically be competitive in line with increasing petroleum and inorganic fertilizer prices. Besides, this method is considered as environmentally-friendly and sustainable agricultural practices (United Nations 1984; Marchaim 1992). Biogas technology has been introduced in 1980, hence it is not a new innovation in Indonesia. However, its development was stagnant due to several constraints such as lack of technical expertise, misfunction of biogas reactor due to construction fault, non-user friendly design, manu- ally handling especially in enticing or expelling sludge from reactor, and highly investment for contruction. Therefore, indepth study technically and economically and new approaches for its development were highly required (Widodo and Nurhasanah 2004; Widodo et al. 2006). The study aimed to design and test biogas reactor for farmer group and analyzing its technical and economical development. MATERIALS AND METHODS Materials Biogas reactor was constructed from cement, pebble, brick, sand, and waterproof coating materials. The strength of the reactor is highly depended on material quality, DESIGN AND DEVELOPMENT OF BIOGAS REACTOR FOR FARMER GROUP SCALE Teguh Wikan Widodo, Ahmad Asari, Ana N., and Elita R. Indonesian Center for Agricultural Engineering Research and Development Situgadung, Legok, Tangerang, PO Box 2, Serpong 15310 Phone: (021) 5376787, 70936787, Facs: (021) 71695497, e-mail: cdam@cabi.net.id 1) Article in bahasa Indonesia has been published in Jurnal Enjiniring Pertanian Vol. IV No. 1, 2006, p. 41-52.