Two-Staged Wet Anaerobic Digestion of Landfill Leachate and Organic Waste: The Effect of Organic Waste Type on Biogas Production

In this study, five different experiments were conducted over a period of 170 days to produce biogas by using a variety of mixtures of organic materials and landfill leachate. The aim of this study is to develop a more robust two-stage biogas plant that can accept a wide spectrum of waste products and continue to function without any malfunction. The facility has 5m3 total digester volume, with a maintained digester temperature of 36±0.1 °C. Biogas production of up to 523L CH4/(kgVS) with an organic load rate (OLR) of 3.93 kgVS /(m3 d) was observed by using refectory waste, spoiled prebiotic yogurt additive, decomposed milk and landfill leachate mixtures in different variations and ratios. Keywords— two-stage biogas production, refectory waste, prebiotic yogurt, milk, landfill leachate Introduction (HEADING 1) Each year, millions of tons of industrial, agricultural and refectory organic wastes (food wastes) have been systematically disposed of in landfills. Landfilling of organic waste in a non-systematic way leads to soil and water pollution on a large scale. Additionally, the resulting gas by-products contribute to air pollution and global warming [1-4]. In order to diminish this type of environmental damage, anaerobic digestion can be used to dispose of organic waste. Almost any form of organic waste can be used in anaerobic digestion to produce a mixture of methane and carbon dioxide gas. This “biogas” is a clean combustible gas which can be put to many different applications, such as cooking, heating, or electrical generation [5]. A two-stage system with landfill leachate has been explored in an experimental study [6] and also through simulation [7]. In another experimental study [8], it was shown that it is possible to produce biogas from landfill leachate. Two-stage systems have been proven to be advantageous due to their short start-up period, system stability, optimized microbial conditions, shorter HRT, stable gas production, and smaller requisite reactor volume [9-16]. As a result of these advantages, widespread future construction of industrial scale two-stage biogas production systems is expected [17,18]. I. OPERATION OF THE TWO-STAGED BIOGAS PRODUCTION FACILITY Due to the fact that the acetogen process in the first digester occurs much more rapidly than the methane formation process in the second digester, the optimized volumes of the digesters were built to be 1.2 m and 3.8 m, respectively. In a two-stage R&D biogas production facility, a mixing unit, grinder, two digesters, and a fertilizer storage tank are connected as shown in Fig. 1. Organic materials are manually loaded into the mixing unit, where they are mixed with an appropriate volume of landfill leachate. The mixture is then ground to slurry with an approximate particle size of 5mm before being moved to the first digester. In the first digester, the feedstock will undergo hydrolysis and acidification to produce VFA, an integral component for the bacterial reaction that occurs in the second digester. Once the methane production process in the second digester has finished and the methane has been captured, the remaining mixture is transferred to a fertilizer storage tank. Figure I. Schematic diagram of experimental two-staged set-up II. EXPERIMENTAL STUDY The study has been conducted for 170 days, using the continuous feeding method detailed in Table 1. TABLE I. EXPERIMENTAL PROCEDURES Experi ment No Experimental Plan Duration (days) Organic Feed I 1-35 Cow, chicken manure and paunch manure with landfill leachate (start-up for 2 digester) II 19-35 Refectory waste, paunch manure and landfill leachate (start-up for 1 digester) III 36-65 Refectory waste and landfill leachate IV 66-125 Refectory waste, spoiled prebiotic yogurt additive, decomposed milk and landfill leachate V 126-170 Spoiled prebiotic yogurt additive, decomposed milk and landfill leachate The first two experiments were used to prime the cultures in each of the digesters; the hydraulic retention time (HRT) of International Scientific Journal Journal of Environmental Science http://environment.scientific-journal.com/