The object of this study is to feasibility assesment for co-digestion efficiency of food waste recycling wastewater(FWR) with thermal hydrolysis process dehydration cake (THP Sludge). As a result of THP pre-treatment experimental conditions to 160oC and 30 minutes, the solubility rate(conversion rate of TCOD to SCOD) of the THP sludge increased by 34%. And the bio-methane potential in the THP sludge increased by about 1.42 times from 0.230 to 0.328 m3 CH4/kg VS compared to the non-pre-treatment. The substrates of the co-digestion reactor were FWR and THP sludge at a 1:1 ratio. Whereas, only FWR was used as a substrate in the digestion reactor as a control group. The experimental conditions are 28.5 days of hydraulic retention time(HRT) and 3.5 kg VS/m3-day of organic loading rate(OLR). During the 120 days operation period, the co-digestion reactor was able to operate stably in terms of water quality and methane production, but the FWR digestion reactor deteriorated after 90 days, and methane production decreased to 0.233 m3 CH4/kg VS, which is 67% of normal condition. After 120 days of the experiment, organic loading rate(OLR) of co-digestion reactor was gradually increased to 4.5 kg VS/m3-day and operated for 80 days. Methane production during 80 days was evaluated to be good at the level of 0.349 m3 CH4/kg VS. As a result of evaluating the dehydration efficiency of the sludge before/after 150-180oC THP using a filter press, it was confirmed that the moisture content of the sludge treated before THP at 180oC was 75% and improved by 8% from 83-85% level. Therefore, it is expected that the co-digestion reactor of FWR and THP sludge will ensure stable treatment water quality and increase bio-methane production and reduction effect of dehydration sludge volume.

연구는 음식물 쓰레기를 음식물 소멸기에서 미생물에 의해 발효하여 유기물을 감량화하고, 음식물 발효시 발생되는 가스를 냉각기에서 기체와 수분으로 분리하여 기체는 반응기로 다시 보내고 수분은 응축하여 침지식 MF 중공사 분리막이 장착된 MBR 시스템에 적용하여 처리하는 시스템에 관한 연구이다. (주)바이오하이테크에서 제작한 음식물 소멸기와 수처리 장치에 침지식 MF 중공사 모듈을 설치하여 90일간 H연구소 직원식당에서 발생되는 음식물 쓰레기를 연속 투입하여 처리하였다. 음식물 소멸기 초기 Seeding를 위하여 수분조절제로 미강, 왕겨, 톱밥을 305 kg 투입하였고 음식물은 운전기간동안 1,648 kg투입하였고 응축폐수는 1,600 L 발생되었다. 음식물 소멸기 운전 종료 후 배출된 발효 부산물은 386 kg으로 감량율은 약 80%로 조사되었다. 침지식 MF 중공사 분리막 모듈을 응축폐수의 MBR 시스템에 적용하여 유기물 처리한 결과 제거율은 각각 BOD 99.9%, COD 97.5%, SS 98.6%, T-N 54.6%, T-P 34.7%였으며, 총대장균은 100%가 제거되었다.

In accordance with the 1996 London Protocol, the marine dumping of wastewater generated from food was totally banned from 2013. Therefore, establishing a food wastewater bio-gasification facility for stable and continuous food wastewater treatment is necessary. The biogas produced from the wastewater can be used as fuel for electricity generation or for heating in power plants and can be sold as gas in cities as well as fuel for vehicles after undergoing a refining process. Thus, the South Korean government is trying to expand the bio-gasification facility of wastewater generated from food. In this study, we try to obtain information about the public value of such an expansion. For this purpose, the household willingness to pay (WTP) for the expansion is determined by applying the contingent valuation (CV) approach. A total of 1,000 South Korean households were involved in the CV survey, which had questions with dichotomous choices. The mean yearly public value WTP for expansion is estimated at 2,564 KRW per household. If this WTP is extrapolated from the sample to the nation’s population, the expansion in the national value is worth 50.1 billion KRW per year. These results indicate that the expansion of food wastewater bio-gasification facility is supported by Korean households.

우리나라는 런던협약 이행을 위하여 2012년부터 하수슬러지의 해양투기를 금지하고, 매립용 복토재, 발전소 보조연료, 바이오가스 생산 원료 등 하수슬러지를 다양한 재활용 물질로써 활용하기 위한 방법을 모색하여왔다. 이중 수열탄화(Hydrothermal carbonization)방법은 닫힌계에서 180℃~250℃온도조건과 이때 생성되는 반응기내 압력으로 운영되는 기술로, 기존 건조기술대비 에너지소비가 적은 연료화 기술이나 수열탄화 공정이후 다량으로 발생하는 탈리액의 처리가 필요하다. 이처럼 수열탄화 공정이후 고액분리된 액체생성물을 효과적으로 처리·활용하고자 본 연구는 하수슬러지 수열탄화 액체생성물의 단독 혐기소화 및 음폐수와의 혼합소화실험을 통하여 바이오가스 생산추이를 비롯한 혐기소화 특성변화를 관찰하였다. 실험은 유효용적 5L 규모의 혐기성소화조를 이용하였고, 35℃ 항온조건을 유지하기 위하여 water jacket형태로 반응기를 구성하였으며, 반응기 내부 균질화를 위하여 80rpm속도로 기계적 교반을 진행하였다. 유기물부하율(OLR)은 1g VS/L-day로 운영후 1.5g VS/L-day까지 증대시켰다. 실험 결과, OLR 1g VS/L-day 조건에서 하수슬러지 수열탄화 액체생성물의 경우 0.17L/g COD의 메탄전환율을 보였고, 음폐수혼합액의 경우 메탄전환율은 0.30L/g COD로 수열탄화 액체생성물 단독소화일 때 보다 높은 값을 보였다. OLR 1.5g VS/L-day 조건에서는 수열탄화액 액체생성물 단독처리시 OLR 1g VS/L-day 조건보다 메탄전환율이 크게 감소하는 경향을 보였고, 음폐수 혼합액은 OLR 1g VS/L-day 조건과 유사한 메탄전환율을 나타냈다.

Biological nitrogen removal is generally accomplished by aerobic nitrification coupled with anoxic denitrification. Many commercial wastewater treatment plants (WWTPs) use external carbon source, such as methanol, to support heterotrophic denitrification process. Using organic wastes as an alternative to commercial carbon sources could thus be beneficial by saving the expense as well as reducing the environmental footprint. Here we report a full-scale (treating 2300 m3 wastewater/d) WWTP that previously utilized a butanediol-based organic waste as the sole external carbon source, which diversified the carbon sources by using a second organic waste generated from food waste recycling. Process parameters were extensively monitored for seven months at all biological unit processes, the aerobic and anoxic tanks, as well as the recirculation flow. Bacterial community structures were analyzed at anoxic tank using next-generation sequencing. The WWTP showed a stable nitrogen-removing performance over the seven months period. The estimated COD/N utilization ratio for food waste-recycling wastewater (FRW) was near 30. The bacterial populations significantly shifted during the operation. Lactobacillaceae and Prevotellaceae were the major bacterial families in the FRW, whereas the denitrification tank was populated by many families including Saprospiraceae, Nannocystaceae, Chitinophagaceae, Eubacteriaceae, and Rhodocyclaceae. Detailed discussion of the results will be presented at the conference.

현재 국내에서 발생하는 음폐수의 해양투기 금지와 음식물류 폐기물의 에너지화 정책에 따라 유기성 폐기물의 혐기소화를 통한 바이오가스화 시설이 지속적으로 설치 및 운영되고 있다. 그동안 많은 연구와 운영 경험을 통해 유기성 폐기물의 바이오가스화 공정은 점차적으로 안정화되어 가고 있는 가운데, 해당 시설에서 발생하는 혐기소화여액에 대한 적정 처리가 전체 시설의 경제성에 큰 영향을 미치고 있다. 해외, 특히 유럽에서는 유기성 폐기물의 혐기소화여액을 대부분 퇴비 또는 비료로 활용하고 있으나 국내에서는 경작 면적 및 시비 시기 등에 대한 제약으로 인해 해외의 경우처럼 혐기소화여액을 퇴비 및 비료로 활용하는데 한계를 가지고 있다. 이에 대다수의 국내 음식물류 폐기물 바이오가스화 시설에서는 혐기소화여액을 별도의 폐수처리 후 하수처리장에 연계 처리하고 있으며, 고형물인 탈수케익은 일부 퇴비원료로 생산하고 있으나 이에 대한 수요 및 구매 매력도가 떨어져 무상공급 또는 유상처리하고 있는 실정이다. 이에 따라 탈수케익을 퇴비원료로 생산하는 대신 매립 또는 소각 처리로 전환하는 시설도 늘어나고 있다. 또한, 음식물류 폐기물의 혐기소화여액은 높은 질소 농도로 인해 하수처리장 연계수질에 따라 단순 응집침전부터 다단 고도처리까지 적용하여 처리하고 있어, 본 과제에서는 국내 음식물류 폐기물 바이오가스화 시설을 직접 방문 조사하여 각 시설의 폐수처리공정 성능 및 애로사항 파악을 통해 주요 연계수질 기준에 따른 최적 폐수처리공정 선정 Guideline을 도출하고자 하였다.

The disposal of food waste has raised environmental concerns. The use of food waste disposers can be a convenient measure to manage household organic wastes. This device can be introduced to resolve the inconvenience of separating food wastes and implement the policy for converting food wastes into resources. However, the use of disposer has been prohibited in Korea unless the total solid recovery rate is greater than 80% (by dry wt.). Therefore, it is important to separate solid portions from disposer wastewater as much as possible to meet the standard. The objective of this study is to examine the control factors such as sieve size of screen, coagulation, RPM of centrifuge on solid-liquid separation. The result revealed that the use of sieve less than or equal to 0.3 mm could meet the total solid recovery rate of 80% (by dry wt.). Also, the coagulation filtrate recirculation using a coagulant, PAC, improved the solid recovery rate of 11.0% (by dry wt.) in using the sieve of 0.6 mm. This led to the total solid recovery rate of 79.3% (by dry wt.). Although RPM variation of centrifuge hardly influences the total solid recovery rate, when the separated solid residue is processed to compost or feedstock it is good because of low moisture content.

According to the elementary analysis on organic wastes, the C/N ratio, a major condition for anaerobic digestion, is 5.40 to 9.23, except for food waste leachate (FWL). Defined by Tchobanoglous’ mathematical biogas prediction model, methane gas and biogas productions increased, depending on the mixing rate of FWL. Furthermore, anaerobic digestion both wastewater sludge and food waste leachate based on the right mixing ratio, increases methane gas productions compared to digesting wastewater sludge alone. In other words, co-anaerobic digestion is more likely to realize biogasification than single anaerobic digestion. We mix food waste leachate and wastewater sludge from the dairy and beer manufacturing industry by the proportion of 1 : 9, 3 : 7 and 5 : 5. It turns out that they produced 118, 175 and 223 CH4 mL/g VS in the dairy manufacturing and 176, 233 and 263 CH4 mL/g VS in beer manufacturing of methane gas. The result suggests that as the mixing rate of food waste leachate rises, the methane gas productions increases as well. And more methane gas is made when co-digesting wastewater sludge and food waste leachate based on the mixing ratio, rather than digesting only wastewater sludge alone. Modified Gompertz and Exponential Model describe the BMP test results that show how methane gas are produced from organic waste. According to the test, higher the mixing rate of food waste leachate is, higher the methane gas productions is. The mixing ratio of food waste leachate that produces the largest volume of methane gas is 1 : 9 for the dairy industries and 3 : 7 for brewery. Modified Gompertz model and Exponential model describe the test results very well. The correlation values (R2) that show how the results of model prediction and experiment are close is 0.920 to 0.996.

The objectives of this study were to evaluate biogas production and changes of CH4 contents by trace elements solution dosing to improve the operation efficiency of anaerobic digestion. The solution with trace elements was manufactured by Co, Mo, Ni, and Fe, and the trace elements dosages were gradually increased from reactor R1 to R4. Operation was performed as four modes and organic loading rate was increased from R1 to R4. As a result, digestion efficiency of R2 or R3 was higher than R1 without trace elements solution. Also, it showed that biogas production and CH4 contents of R3 were high compared with R2. However, R4 had a negative effect on the efficiency of anaerobic digestion due to the additional dosing of unnecessary trace elements. Moreover, from the results compared with anaerobic digestion conditions on effect of each trace element, it showed that experiment with the mixture of Co, Ni, Mo, and Fe was the highest digestion efficiency and individual trace element showed high digestion efficiency in the order of Fe, Co, Mo, and Ni. In conclusion, the additional dosing of optimum trace elements is essential to enhance the efficiency of anaerobic digestion.

Anaerobically treated food wastewater still contains high concentration of organic carbon and nitrogen. Consequently,subsequent treatments are needed to meet the effluent criteria of wastewater. Injection of treated food wastewater into awaste landfill body could be one alternative for its subsequent treatment. In this study, preliminary experiments wereconducted to inject treated food wastewater into waste landfill body. Firstly, Biochemical Methane Potential (BMP) testwas conducted to evaluate the methane generation potential of the injected food wastewater. Secondly, anaerobicallytreated food wastewater showed clogging problem during the initial stage of laboratory scale lysimeter injectionexperiment. Accordingly, pretreatments were needed, and we experimented the change of viscosity of the wastewater afterchemical injection (1N acid or base solution) or aeration of wastewater. From the results, BMP for the treated foodwastewater showed 373.8mL CH4/g VS, which was 53% of untreated food wastewater’s. Practically feasible solution toreduce the viscosity of treated food wastewater was 1 day aeration before injection into the waste landfill body.

In this study, waste landfill site was used as a bioreactor landfill for the treatment of anaerobically digested foodwastewater, and a basic study on waste landfill injection of anaerobically digested food wastewater was conducted. To studythe effect of different operating condition on the quality of lysimeter leachate, 3 lysimeters were operated at differentcondition (i.e., Lys 1=no recirculation, Lys 2=leachate recirculation, Lys 3=leachate recirculation after one day aeration),and the results of leachate quality were as followings. pH Level of leachate became similar to the digested food wastewaterafter 63 days of operation(equivalent to the 11.2% of bed volume) and Cl- concentration of leachate was higher than injectedfood wastewater during whole 6 months of operation period. Leachate COD showed stable values after 70 days of operation,and reduction rate of COD concentration after 6 months was 86%, 89, and 90% for Lys 1, Lys 2, and Lys 3, respectively.The reduction rates of TKN concentration were 19, 28, and 65% for Lys 1, Lys 2, and Lys 3. Lys 3 showed the mosteffective TKN reduction. Leachate recirculation after one day aeration resulted effective reduction of cumulative COD andTKN mass, which were 61% and 40% respectively, compared to the no recirculation case.

Batch cultivations were performed to evaluate the influences of the initial pH condition on mesophilic and thermophilic acidogenic fermentation with food waste recycling wastewater. In both conditions of mesophilic and thermophilic fermentation, TVFAs production rates were maximized at the initial pH 7 condition as 0.15 and 0.23 g TVFAs/L·hr, respectively. And pH was also maintained stably between 6 and 7 during 72hr acidogenic cultivation at both conditions. However, predominant VFA components were different according to reaction temperature conditions. In mesophilic condition, propionic acid which has low conversion efficiency to methane was accumulated up to 1,348 mg/L while acetic and butyric acid were predominant in thermophilic condition. Therefore, thermophilic acidogenic fermentation was superior for the effective VFAs production than mesophilic condition. From the DGGE analysis, the band patterns were different according to the initial pH conditions but the correlations of the each band were increased in similar pH conditions. These results mean that microbial communities were certainly affected by the initial pH condition. Consequently, the adjustment of the initial pH to neutral region and thermophilic operation are needed to enhance acidogenic fermentation of food waste recycling wastewater.

This study was conducted to evaluate the treatment efficiency including reaction kinetics and hydraulic characteristics of food processing wastewater by using an ejector-type aeration system (ETAS) in activated sludge process. The oxygen transfer efficiency in ETAS can be changed in accordance with the depth of reactor. However, the optimum air velocity was found less than 1.82 m/hr at a superficial liquid velocity of 634 m/hr. The ETAS process showed higher organic material removal efficiency than that of the existing activated sludge process under hydraulic detention time ranged from 6 to 12 hours. This process, which can maintain MLVSS highly, is able to have high organic material removal efficiency at short HRT and deal with variable organic material loading.