This study evaluated the biochemical methane potential (BMP) of primary sludge, secondary sludge, and food waste in batch anaerobic mono-digestion tests, and investigated the effects of mixture ratio of those organic wastes on methane yield and production rate in batch anaerobic co-digestion tests, that were designed based on a simplex mixture design method. The BMP of primary sludge, secondary sludge and food waste were determined as 234.2, 172.7, and 379.1 mL CH4/g COD, respectively. The relationships between the mixing ratio of those organic wastes with methane yield and methane production rate were successfully expressed in special cubic models. Both methane yield and methane production rate were estimated as higher when the mixture ratio of food waste was higher. At a mixing ratio of 0.5 and 0.5 for primary sludge and food waste, the methane yield of 297.9 mL CH4/g COD was expected; this was 19.4% higher than that obtained at a mixing ratio of 0.3333, 0.3333 and 0.3333 for primary sludge, secondary sludge, and food waste (249.5 mL CH4/g COD). These findings could be useful when designing field-scale anaerobic digersters for mono- and co-digestion of sewage sludges and food waste.

Organic wastewater generated from polyester manufacturing processes was selected from H company to investigate the feasibility of anaerobic digestion that produces gases including methane. Bio Methane Potential (BMP) tests were conducted to measure the gas production and methane concentration for 7 process wastewater and 2 kinds of sludges from the H company. Also, along with monitoring pH and alkalinity during the anaerobic digestion process, the concentrations of COD and 1,4-dioxane were measured with 4 different operating conditions for N Emulsion (NE) and Ethylene Glycol (EG) wastewater. The BMP tests showed that 65% of methane was produced from NE and EG wastewater. This suggests that the organic wastewater from H company can be effectively treated by an anaerobic digester by which more than 90% of COD was removed.

가죽제품 제조 산업으로부터 발생되는 피혁폐기물의 양은 투입되는 원료 가죽의 약 50%를 차지하는 것으로 알려져 있다. 그러나 이들 피혁폐기물은 적절한 처리 방법이 개발되지 않아 대부분 매립이나 소각을 통해 처리되고 있다. 특히, 매립이나 소각을 통한 처리는 단가가 높아 관련 산업의 경제성을 악화시키고 고형폐기물의 친환경적 처리 관점에서 문제점이 제기되고 있는 실정이다. 최근 화석연료를 대체하기 위한 신규에너지원의 중요성이 높아짐에 따라, 폐기물을 이용한 에너지화에 많은 연구가 진행되고 있으며, 피혁폐기물은 주로 단백질과 지질로 구성되어 있는 특성으로 인해 혐기성소화를 통한 바이오가스 생산이 가능한 것으로 알려져 있다. 그러나 일반적으로 알려져 있는 혐기성소화 공정의 최적 C/N 비 (20-30)를 고려할 때, 피혁폐기물의 높은 C/N비 (약 35)는 공정의 제한요소가 될 수 있다. 본 연구에서는 피혁폐기물과 음폐수를 통합하여 혐기성소화를 실시함으로써 기질의 C/N 비 조절이 혐기성소화 효율에 미치는 영향을 관찰하였다. 기질의 C/N 비 조절을 통한 혐기성소화 효율의 변화는 BMP (Biochemical methane potential) test를 약 40일간 진행하였으며, 바이오가스 발생량을 비교하였다. 실험은 경기도 동두천시에 위치한 가죽제품 제조업체로부터 수거된 pelt scrap과 양주시에 위치한 음식물쓰레기 자원화시설에서 발생되는 음폐수를 각각 채취하여 사용하였다. 개별 기질의 C/N 비는 피혁폐기물이 34.1, 음폐수가 13.5로 확인되었으며, 이들의 무게에 따른 혼합비를 조절하여 통합 혐기성소화 기질의 C/N 비를 20, 25, 30으로 맞춰 실험을 진행하였다. 실험결과 기질을 통합하여 C/N 비를 조절한 소화 조건에서 개별 기질의 단독소화 조건보다 많은 바이오가스 생산량이 관찰되었으며, C/N 비 20에서 바이오가스 생산량이 높은 것으로 나타났다. 이는 통합 기질의 C/N 비 조절효과와 함께 피혁폐기물에 비해 생분해도가 높은 음폐수 함량이 기질의 C/N 비가 낮을수록 더 많이 포함되었기 때문으로 판단된다.

혐기성소화 공정은 기본적으로 가수분해단계(Hydrolysis), 산생성 단계(Acidogenesis), 메탄생성단계(Methanogenesis) 총 3단계로 구분지울 수 있으며, 메탄생성단계에서 아세트산(Acetic acid)과 수소 등의 유기물이 메탄으로 전환되면서 혐기발효의 안정화가 이루어진다. 유기성 폐기물의 혐기성 소화는 유기성 폐기물을 기질로 하여 가수분해와 산발효 및 메탄발효 과정을 통하여 메탄으로 생성된다. 혐기 발효 시 유기산과 pH 변화는 혐기발효의 중요한 영향인자 중 하나이며, 혐기 발효의 안정성을 판단할 수 있는 지표가 된다. 본 연구에서는 보편적으로 사용되는 단상 혐기 발효조를 이용하여 투입되는 유기물(VS)농도, 원료배합(돈분 중 분 성분이 30%, 뇨 성분이 70%) 등 운전조건의 변화에 따라 유기성 폐기물의 혐기성 발효가 진행되는 과정을 분석하였으며, 발효 과정 중 생성되는 아세트산, 프로피온산, 부틸산 등 총 9종류의 유기산 분석과 이에 따른 바이오가스 생산량과 메탄발생량을 분석하였다. 혐기성 발효조는 호기성 산화열을 이용하여 혐기성 소화조를 간접적으로 가온하였으며, 중온 혐기성 소화를 진행하였다. 음식물류 폐기물과 돈분뇨 혼합비에 따라 CASE 1, CASE 2, CASE 3로 분류하였으며, CASE 1의 비율은 음식물류 폐기물 8kg과 돈분뇨 20L, CASE 2 음식물류 폐기물 10kg과 돈분뇨 20L, CASE 3는 음식물류 폐기물 8kg과 물 20L의 조건으로 실험을 진행하였다. 본 실험에서 혐기성 소화조의 pH는 평균 8.17로 나타내어 안정적인 혐기 소화 효율을 나타내었다. 혐기성 소화조의 온도는 평균적으로 38℃로 중온소화가 가능한 것으로 확인되었다. 혐기성 발효 과정 중 생성된 유기산의 농도는 33.67∼1,452.81mg/L로 분석되었다. 일반적으로 혐기발효시 안정적인 VFA의 농도는 500mg/L 이하이며, 운전기간 동안 전체 유기산 농도는 432.86mg/L로 분석되어 안정적인 혐기 발효가 진행되었다고 판단하였다. 바이오가스 발생량의 경우 CASE 1에서 0.29~0.31㎥/day로 나타났으며, CASE 2는 0.325㎥/day로 나타났다. 본 연구를 통하여 혐기 발효시 발생되는 유기산 농도와 pH 변화에 따라 유기성 폐기물의 혐기 발효 시 안정성을 판단한 결과 운전기간 동안 혐기발효는 안정적으로 이루어 졌다고 판단되었다.

Anaerobic mesophilic batch tests of food waste and food waste leachate collected from food waste treatment facility were carried out to evaluate their ultimate biodegradability and two distinctive decay rate coefficients (k1 and k2) with their corresponding degradable substrate fractions (S1 and S2), respectively. Each 3 liter batch reactor was operated for more than 60 days at substrate to inoculum ratio (S/I) of 0.5 as an initial total volatile solids (TVS) mass basis. Result of Ultimate biodegradability of 74 ~ 83% for food waste and 85 ~ 90% for food waste leachate were obtained respectively. The readily biodegradable fraction of 85 ~ 93% (S1) of food waste Biodegradable Volatile Solids (BVS, So) degraded within the initial 15 days with a range of of 0.151 ~ 0.168 day−1, whereas the rest slowly biodegradable fraction (S2) of BVS degraded for more than 53 days with the long term batch decay rate coefficients of 0.009 ~ 0.010 day−1. For the food waste leachate, the readily biodegradable portion (S1) appeared to be 92 ~ 94% of BVS (So), which degrades with of 0.172 ~ 0.206 day−1 for an initial 15 days. Its corresponding long term batch decay rate coefficients were 0.005 ~ 0.009 day−1. It is recommended that the hydraulic retention times of mesophilic anaerobic digesters be 16 days for the food waste and 15 days for the food waste leachate, respectively. However a safety factor should be considered when designing a full scale plant.

Results of reviews on bio-gas production and policy trends in the European Union (EU) are as follows. In the EU,Germany leads in bio-gas production with 29 TWh of energy produced through energy crops as of 2013. This could beachieved through renewable energy laws and increases in feed in tariff (FIT) schemes in Germany. In the EU, bio-gashas been verified to play an important role and contribute to greenhouse gas reduction. However, it is necessary to providea measure to improve sustainability criteria and decrease the consumer's share of expenses. If bio-gas is produced usingorganic wastes instead of energy crops, this problem can be solved. If the bio-gas production policies in the EU are appliedin South Korea, bio-gas market will be promoted and greenhouse gas emission can be reduced in the future.

Efforts were made to identify the optimum operational condition of Semi-continuously Fed and Mixed Reactor(SCFMR) to treat the dairy cow manure and saw dust mixture. Step-wise increase in organic loading rates (OLRs) and decrease in hydraulic retention times (HRTs) were utilized until the biogas volume became significantly decreased in SCFMR at mesophilic temperature (35℃). The optimum operating condition of the SCFMR fed with TS 15% dairy cow manure and saw dust mixture was found to be at HRTs of 30 days and its corresponding OLRs of 4.27 kgVS/m³-day. The optimum ranges of biogas and methane production rates were 1.47 volume of biogas per volume of reactor per day(v/v-d) and 1.14 v/v-d, respectively. This result was due to the high alkalinity concentration of SCFMR fed with the original substrate, dairy cow manure and saw dust mixture whose alkalinity was more than 10,000 mg/L as CaCO3. The parameters for the reactor stability, the ratios of volatile acids and alkalinity concentrations (V/A) and the ratio of propionic acid and acetic acid concentrations (P/A) appeared to be 0.07-0.09 and 0.38-0.43, respectively, that were greatly stable in operation. The Total Volatile Solids(TVS) removal efficiency based on the biogas production was 45.2% at the optimum HRTs. Free ammonia toxicity was not experienced at above 160 mg/L due to the acclimation of high concentration of ammonia by the high reactor TS content above 9.0%.

Efforts were made to identify the optimum operational condition of Semi-continuously Fed and Mixed Reactor (SCFMR) to treat the dairy cow manure and saw dust mixture. Step-wise increase in organic loading rates (OLRs) and decrease in hydraulic retention times (HRTs) were utilized until the biogas volume became significantly decreased in SCFMR at mesophilic temperature (35oC). The optimum operating condition of the SCFMR fed with TS 15% dairy cow manure and saw dust mixture was found to be at HRTs of 30 ~ 35 days and its corresponding OLRs of 3.5 ~ 4.3 kgVS/ m3-day. The optimum ranges of biogas and methane production rates were 1.36 ~ 1.47 volume of biogas per volume of reactor per day (v/v-d) and 1.0 ~ 1.14 v/v-d, respectively. This result was due to the high alkalinity concentration of SCFMR fed with the original substrate, dairy cow manure and saw dust mixture whose alkalinity was more than 10,000 mg/L as CaCO3. The parameters for the reactor stability, the ratios of volatile acids and alkalinity concentrations (V/A) and the ratio of propionic acid and acetic acid concentrations (P/A) appeared to be 0.07 ~ 0.09 and 0.38 ~ 0.43, respectively, that were greatly stable in operation. The Total Volatile Solids (TVS) removal efficiency based on the biogas production was 39 ~ 45% at the optimum HRTs. Free ammonia toxicity was not experienced at above 160mg/L due to the acclimation of high concentration of ammonia by the high reactor TS content above 9.0%.