This study evaluates the potential of Rice Straw Leachate (RSL) to generate biogas and investigate its biodegradability by determining the differences between the theoretical yield and the actual one at its increasing organic loading rate. Seven litre working volume of Up-Flow Anaerobic Sludge Blanket (UASB) reactor is employed under mesophilic condition at temperature of 38 for approximately 17 consecutive weeks. The process performance was evaluated based on the efficiency of COD removal and Specific Methane Production (SMP) in relation to the other parameters such as pH, Organic Loading Rate (OLR), Total Ammonia Nitrogen (TAN) and alkalinity ratio. The OLR were varied at 0.43, 0.55, 0.9 and 1.55g COD/L/d with average COD removal of 79%, 81.2%, 76.1%, and 75.8% respectively. The stability of anaerobic digestion of RSL in UASB was found maintained at an increasing OLR with indicator of pH, TAN and IA/PA ratio that always maintain in the range of 6.5-6.8, below 200mg/L and 0.3 respectively. Meanwhile, the optimum average SMP and COD removal efficiency were 0.18L CH 4 g -1 COD rem and 81.2% respectively, at applied OLR of 0.55g COD/L/d. This study also revealed a relatively high deviation of SMP from its theoretical value, indicating its low degradability and the limitation of nutrient factors present in RSL.

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

This study aims to investigate the potential methane yield by mono-anaerobic digestion of rice straw washwater (RSWW) and pineapple waste extract (PWE) as well as the codigestion of both RSWW and PWE at a ratio of 50:50 (v/v). The experiment was conducted at a controlled mesophilic temperature of 37 °C in Upflow Anaerobic Sludge Blanket (UASB) reactor for a period of approximately 55 days. The process performances were 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 ratio. This study confirmed that the rate of COD removal for RSWW, PWE, and RSWW:PWE (50:50) were achieved the stable condition at 81, 89, and 86% respectively. The alkalinity ratio value and pH throughout the experimental period remained below 0.30 and kept in the range of 6.5-7.0 indicated the stable and good environment existed for anaerobic digestion within the UASB reactor. This study implies that the co-digestion of RSWW:PWE found to improve the efficiency of COD removal and production of methane during the mono-digestion of RSWW from 81 to 86% and 0.093 to 0.13 LCH4/g CODrem by the increment of 6.2 and 40%, respectively.