Co-Digestion of Rice Straw Leachate and Domestic Waste Water for Biogas Production with Addition of Urea as Nitrogen Source

Abstract

This study investigates the methane production by anaerobic co-digestion of rice straw leachate (RSL) and domestic wastewater (WW). The experiment was conducted at a controlled mesophilic temperature of 38°C in Continuous Glass Reactor (CGR) for a period of approximately 12 weeks. The process performance was evaluated based on the efficiency of COD removal and methane production in relation to other parameters such as pH, (organic loading rate) OLR and alkalinity. This study confirmed that the rate of COD removal for co-digestion of WW and RSL achieved the stable condition at 89.33%, meanwhile the digestion of RSL with addition of urea was at 76.00%. The addition of urea into RSL, showed the synergistic effect in anaerobic digestion as the removal rate of COD increased from 61.33% to 76.00%. Meanwhile, methane production reached the highest value of 0.154 L/CH 4 at day 32 with the COD conversion ratio of 81.33%. SEM analysis showed a change in surface structure of the granules and it was confirmed by EDX analysis that there was some light metal crystallisation and salt agglomeration on the sludge granule surface. Index Terms-Anaerobic co-digestion, chemical oxygen demand, methane production, nitrogen and rice straw leachate. I. INTRODUCTION Rice is a vital source of food which can provide nutrients as well as calorie intake, and over half of the world's human population are depending on it as a main food source [1]. Rice straw as a by-product of rice production is one of the most abundant and renewable energy sources in the world. According to the data from Food and Agriculture Organization of the United Nations in year 2012, a total of 718 million tons of rice were produced which equates to approximately 969 million tons of rice straw available worldwide. According to the statistical data from the Department of Agriculture, Malaysia, the annual rice production of Malaysia in year 2010 is about 1.59 million tons with the generation of rice straw of approximately 0.88 million ton. The trend of global rice production is increasing in the last decade [2]. Hence, rice straw has becomes a relatively common agricultural waste and its biogas production potential has becomes a recent interest for numerous researchers. Rice straw is one of main agricultural Manuscript