1 APPLICATION OF ZINC OXIDE TO STIMULATE BIOGAS YIELD RELEBOHILE MOKETE AND OSAMA ELJAMAL* Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Science, Kyushu University 6-1 Kasuga-koen, Kasuga-shi, Fukuoka 816-8580, Japan * E-mail: osama-eljamal@kyudai.jp ABSTRACT The objective of this research was to study the outcome of applying ZnO (1g/L) to the Thickened Waste Activated Sludge (TWAS) to produce methane gas. The results implied that the 1g/L ZnO improved the biogas hence methane gas generation as opposed to the control due to the ability of ZnO to dissolve into Zn 2+ thus adsorbing the H2S and reducing its toxicity. The Volatile Fatty Acids (VFAs) slightly reduced the pH to acid state but their concentration decreased during their stepwise conversion to methane gas. KEYWORDS Zinc Oxide; Biogas; Methane; Anaerobic digestion; Wastewater. 1. INTRODUCTION To date, the Wastewater (WW) Treatment plants are commonly used as a countermeasure for the WW generated from various sources. 1 In particular, the raw material of Waste Activated Sludge (WAS) is one of the used sources of Organic Matter (OM) whereby the microorganisms degrade the OM into the biogas through Anaerobic digestion (AD) process. 1-2 Due to the challenges of high energy consumption and low economic efficiency when considering other approaches of improving AD process, which is naturally slow, there is a need to stimulate the biogas production using other effective methods. 3 The nanoparticles have been widely applied to enhance AD [3]. Accordingly, ZnO has very excellent adsorbent properties and its monocrystallinity help to improve the reactivity. 4 The main objective of this research was to study the outcome of applying ZnO (1g/L) to the Thickened Waste Activated Sludge (TWAS) so as to produce methane gas. 2. MATERIALS AND METHODS 2.1 Materials TWAS (Mikasagawa Purification Centre, Japan), Zinc Oxide (Junsei Chemical Co., Japan), Sodium hydroxide (> 93%, Wako Co., Japan), hydrochloric acid (35–37%, Wako Co., Japan). 2.2 Batch Experiments Two batches of control and 1g/L ZnO (Sg-ZnO) were prepared and the general conditions of batch experiments are shown in Table 1. Table 1: General batch experiments conditions. TWAS Volume (ml) pH Temperature ( o C) ZnO dose (g/L) Shaking 150 7±2 38 1 Physical Methane content was analyzed by Gas Chromatograph whereas the biogas content was analyzed by the gas displacement method. 3. RESULTS AND DISCUSSIONS The accumulative biogas and methane generation results are indicated on Fig. 1 and 2 respectively. Fig.l: Accumulative biogas generation. As seen from the accumulative biogas curve, the biogas generation began from the first day and the control had the slightly higher biogas values in the first 4 days after which the Sg-ZnO generated more biogas than the control. However, towards the last day, the biogas volumes of 655ml and 647.1ml in the Sg-ZnO and control respectively were almost alike. The trend of methane gas generation (Fig. 2) corresponds to that of the biogas but there is a slight difference towards the end of the reaction whereby the accumulative methane gas volume from Sg-ZnO is distinctively greater than that of the control with the corresponding values of 601.24ml and 572.41ml (Fig. 2). It can be seen from Fig. 3 that the relevant pH for both batches changed from neutral to acidic then towards the neutral state again at the end of the experiment where both Sg-ZnO and the control