INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 3, ISSUE 11, NOVEMBER 2014 ISSN 2277-8616 165 IJSTR©2014 www.ijstr.org Thermal And Chemical Pre-Treatments Of Cow Dung And Poultry Litter Enhance Biogas Production In Batch Fermentation Animut Assefa, Meseret C. Egigu, Ameha Kebede Abstract: Low degradability of substrates is one of the factors that hinder the production of biogas. With the aim of maximizing biogas yields from cow dung (CD) and poultry litter (PL), a series of experiments were carried out under mesophilic conditions at 38 ºC using batch digester operating for 21 days hydraulic retention time (HRT). Temperature pre-treatment at 60 and 80 ºC and chemical pre-treatment with NaOH (0.45 g, 1.35 g and 2.25 g) were applied as a pre-treatment. Cumulative biogas production and VS reduction from anaerobic digestion of 80 ºC pre-treated substrate was 46.3% and 26.1% higher than the control, respectively. However, thermal pre-treatment at 60 and 80 ºC did not show statistically significant difference in biogas production. Biogas yields of substrates that received 0.45 g, 1.35 g, and 2.25 g of NaOH increased biogas production by 0.03%, 21% and 56% over that of the control, respectively. Overall results indicated that the biogas yield and VS and TS reduction can be enhanced through thermal and chemical pre- treatments prior to anaerobic digestion. Keywords: Anaerobic digestion, biogas, chemical pre-treatment, temperature pr- treatment, total solids, volatile solids ———————————————————— 1. INTRODUCTION As far as fuel is concerned, the rural population in developing countries including Ethiopia heavily depend on biomass mainly in the form of fire wood. It accounts for about 94.7% of the total energy supply [1]. The dependence on fossil fuel and forest resources as primary energy source has led to global climate change, environmental degradation and human health problems. Therefore, environmentally friendly renewable energy source is a key to curb these problems. Biogas, which consists mainly of methane is one of such alternative renewable energy source produced through anaerobic digestion of organic matter by various specialized groups of bacteria in several successive steps [2]. Biogas technology represents one of a number of village-scale technologies that offer the technical possibility of obtaining energy from organic wastes. Apart from energy, this technology offers many opportunities. In Ethiopia for example, households with at least four cattle and access to water can install a biogas plant, which then help them reduce the daily work load, mainly of women that spend collecting fire wood for energy source [3]. As a clean energy source it reduces air pollution, while the digested residue (effluent) is serving as organic fertilizer [4]. The National Biogas Program (NBP) of Ethiopia, which aimed to establish 14000 biogas plants between 2008 and 2012 in different parts of the country, utilizes manure (cow dung) as the feedstock for biogas production [3]. However, the efficient use of this technology is limited by the low degradability of manure, which is only in the range of 30– 43% [5]. Biogas yield, however, can be improved by increasing the rate of hydrolysis of lignocellulose through different mechanisms [6]. For example, pretreatment of organic substrates (corn stover) with NaOH results in more biogas yield than untreated substrate [7, 8]. Thermal pre- treatment commonly between 60 and 180 ºC has also been evaluated to help biogas production [9]. Thermal pre- treatments, which are considered as low temperature treatments (below 100 ºC) were found to enhance biogas production [10, 9]. Cow dung is not the only source of biogas. Ethiopia ranks first in cattle from Africa. Apart from cattle husbandry, farmers also raise considerable number of poultry with their wastes not used for biogas production. Some studies have shown that mixing different substrates in some proportions will result in more biogas production than sole digestion. This study was therefore conducted with the objectives of (i) identifying the optimum mix ratio of cow dung and poultry manure yielding high amount of biogas and (ii) to evaluate the effects of thermal and chemical pre-treatments on biogas yield of the optimum substrate mix. 2. MATERIALS AND METHODS 2.1. Substrates Collection and Preparation Two types of lignocellulosic biomass, cow dung (CD) and poultry manure (PM) obtained from Haramaya University animal farm were used in this study. The two substrates were mixed in a 4:1 ratio of CD: PM. This mix ratio was selected as optimal substrate (OS) due to its high biogas yielding nature based on preliminary identification of the optimum mix ratio to yield biogas [14]. Fresh rumen fluid used as a starter of anaerobic digestion was obtained from the nearby slaughterhouse at Haramaya University. The fluid was filtered through a cloth of 0.5 mm sieve diameter to separate solid content from slurry and starved for a week _____________________  Animut Assefa; M.Sc. student in the Department of Biology, Haramaya University, Ethiopia  Meseret C.Egigu: Corresponding author, Assistant professor in the Department of Biology, Haramaya University, Ethiopia. Email: swamy12in@yahoo.co.in  Ameha Kebede: Associate Professor in the Department of Biology, Haramaya University, Ethiopia.