Biogas production through anaerobic digestion (AD) of organic wastes has gained increased popularity as it can solve the security of energy supply and provide environmental benefits over fossil fuels. However, the true economic potential of AD is often compromised due to the low CH4 content (50-60%) in biogas by presence of CO2 (40-50%), which reduces the calorific value of biogas and efficiency in the transportation as well as storage. Thus CO2 removal, so called biogas upgrading, could allow producing CH4-rich biogas. To date, the most commonly employed biogas upgrading techniques have been physico-chemical process. However, the costs of the all methods are high since those need either high pressure or addition of chemicals. In addition, during process of biogas upgrading, small amounts of CH4 losses will increase GHG emissions and decrease net energy gain. To circumvent these disadvantages and use milder treatments with minimal chemical and energy input, biological biogas upgrading has gained increased popularity by utilization of hydrogenotrophic methanogens which can bind CO2 with H2 and convert to CH4. Recently, a number of different biological
biogas upgrading methods have been developed. Among them, the trickling filter bed reactor (TFBR) system has gained increased popularity as it can promote the conversion of methane by injecting a substrate into a media that has large specific surface area, thereby increasing the reaction area of H2 and CO2 to increase the mass transfer coefficient. From below TFBR is divided into sludge layer, media layer and sludge trickling layer, and sludge is circulated from top to bottom, and gaseous substrate circulates from bottom to top and reacts in large area of media. Because TFBR can be operated with a relatively small volume compared to AD, it
is economical and can be easily applied to existing infrastructure and processes. AD effluent which is injected into TFBR mostly consists of hardly decomposable material, which has been reported to be removed by supplying a small amount of voltage. In addition to the biogas upgrading, treatment of digested effluent is
another issue. It still includes a high level of chemical oxygen demand (COD) of 4500 ± 500 mg/L which can be further converted to methane by post-treatment process. Therefore, in this study, the TFBR was applied for both biogas upgrading and post-treatment of digested sludge. This study consisted of: (1) run 1, which is a
microorganism enrichment by attaching to media, (2) run 2, which evaluates treatment efficiency of TFBR by simultaneously injecting effluent and biogas, and (3) run 3, which is a voltage supply step. In the basic experiments for the optimum operation, specific methanogenic activity (SMA) test reached 0.0134
L-CH4/g-vs·d and 0.0207 L-CH4/g-vs·d at AD and TFBR, which indicate that the hydrogenotrophic methanogen was enriched in theTFBR. In run 2, the total amount of AD effluent and biogas was divided into two reactors and injected. As a result. methane conversion rate and total methane production were 76.5 ± 6.8% and 3,035 ± 40 mL with COD removal efficiency of 1002 ± 40 mg/L. In the run 3, the pall ring was separated into two layers, the upper and lower layers, and the voltage of 0.6 V in the reactor was supplied to oxidation, reduction layer. The removed COD was 1691 ± 44 mg/L, and 691 mg/L was more removed than run2. Methane production was 3,340 ± 48 mL, 305 mL more than run 2. Through these results, TBFR can stably remove COD and improve methane production and maximize the effect through voltage supply. Therefore, TBFR would significantly contribute to allowing the biogas upgrading together with post-treatment of digested effluent.