Modified ADEPT를 이용한 하수슬러지-음식물폐수의 병합 혐기소화

Abstract

2012년부터 슬러지의 해양투기가 전면 금지됨에 따라 폐수의 처리과정에서 발생하는 슬러지는 전량 육상에서 처리해야 한다. 최근에는 다양한 슬러지의 처리 및 저감 방법이 연구되고 있으며 그 중 한 가지가 혐기성 소화를 이용한 슬러지의 처리이다. 하지만 하수슬러지 중 폐활성 슬러지의 경우 난분해성 유기물의 농도가 높고, 처리시간이 많이 소요되는 단점이 있어 혐기성 처리에 단독적으로 적용하기에는 다소 무리가 있다. 또한 음식물폐수의 경우 단백질, 탄수화물, 지방산 등 다양한 유기물로 구성이 되어 있으나 높은 염분으로 인하여 생물학적 처리 시 분해 효율을 떨어뜨리는 동시에 반응기 내부에 메탄생성 반응을 억제하여 단독 혐기소화 시 많은 문제가 따를 수 있다. 따라서 본 연구에서는 이와 같은 단점을 극복하기 위하여 생물학적 처리가 용이하고 유기물의 농도가 높은 음식물폐수와의 병합처리가 고려되었으며 공정의 효율적인 운영을 위해서 두 폐수의 적절한 혼합비율을 도출하고자 하였다. 본 연구에서 사용되는 ADEPT(Anaerobic Digestion Elutriated Phased Treatment) 공정은 기존의 2상 혐기성 소화방식에 비해 짧은 HRT(Hydraulic Retention Time)에서도 높은 농도의 고형물 제거가 가능하다. 하지만 ADEPT공정의 경우 산형성 반응조에서 세정된 슬러지의 농축이 발생되며, 대부분 난분해성 고형 물질로 처리 없이 폐기 시켜야 하는 문제점이 있다. 따라서 이러한 농축 슬러지 처리를 위해 가용화조를 이용하여 기존에 폐기되었던 농축슬러지를 전처리하는 Modified-ADEPT 공정을 실시하였다. Modified-ADEPT 공정은 전처리하는 과정을 거친 난분해성 물질이 분해성 물질로 전환 됨 으로써 잔존 슬러지 발생 문제점을 보완하고, 분해성 물질의 증가를 통해 혐기성 소화 효율의 극대화 및 바이오 가스 생산량을 증대 시킬 수 있다는 장점이 있다. 따라서 본 연구에서는 ADEPT공정과 Modified-ADEPT 공정을 비교⋅분석함으로써 그에 대한 효율을 평가하고자 하였다. 최적의 혼합비율을 찾기 위한 BMP test 결과 음식물폐수의 비율이 높을수록 효율이 낮아져, 높은 하수슬러지의 비율 하에 안정적인 혐기성 처리가 가능하다고 판단하여 이를 바탕으로 하수슬러지와 음식물폐수의 혼합비율이 4:1을 최적의 혼합비율로 선정하였다. 또한 ADEPT와 Modified-ADEPT 공정을 비교한 결과 Modified-ADEPT 공정은 ADEPT 공정에 비하여 유기물 제거율 TCOD 25%, VS 33%, 고형물 제거율 TSS 18%, VSS 24%의 효율이 증가하였고, 제거된 유기물당 발생하는 메탄가스도 약 11% 더 발생하는 것으로 나타났으며 발생 슬러지는 약 60%가 감소하는 효율을 보였다.| The sludge from wastewater treatment process must be treated on national land (Korea) since the ocean dumping has been forbidden in 2012. Recently, various approaches for sludge treatment and reduction were studied and anaerobic digestion is one of them. However, treatment of waste sludge using an independent anaerobic digestion is untoward due to high strength of hardly degradable organics and very long time for treatment. Furthermore, the independent anaerobic digestion can be followed by many problems such as low efficiency for biological degradation and inhibition for methane generation in the reactor due to high strength salts when treating food wastewater which even contains various organics such as carbohydrates and fatty acids. Accordingly, in order to overcome these shortcomings, the co-anaerobic digestion using food wastewater and waste sludge was estimated in this study. The purpose of this study is to determine the appropriate mixing ratio between two wastewaters for effective operation. The ADEPT (Anaerobic Digestion Elutriated Phased Treatment) process in this study is capable of removal of high concentration solids in shorter HRT (Hydraulic Retention Time) when comparing with the existing two phase anaerobic digestion processes. However, this process causes concentration of elutriated sludge in fermentation reactor and wastes a majority of hardly degradable solids without treatment. Accordingly, the Modified-ADEPT which pretreats waste sludge using solubilization was carried out for treating the concentrated sludge. The Modified-ADEPT process could make up for the problem of remaining sludge generation by converting hardly degradable matters to degradable mattes and maximize the efficiency of anaerobic digestion and increase the biogas generation by increasing degradable mattes. This study estimated the efficiencies of ADEPT and Modified-ADEPT after comparison and analysis. In the result of BMP test, it was estimated that the stable treatment was feasible under the high ratio of waste sludge since the efficiency was decreased at high ratio of food wastewater. On the basis of this result, the optimal mixing ratio between waste sludge and food wastewater was determined as 4:1. In the result by comparison between ADEPT and Modified-ADEPT, the removal efficiencies of the Modified-ADEPT for TCOD, VS, TSS and VSS were increased 25, 33, 18 and 24 %, respectively, when comparing with the ADEPT. In addition, the methane gas generation per removed organics was increased about 11 % and the sludge generation was decreased about 60 %.; The sludge from wastewater treatment process must be treated on national land (Korea) since the ocean dumping has been forbidden in 2012. Recently, various approaches for sludge treatment and reduction were studied and anaerobic digestion is one of them. However, treatment of waste sludge using an independent anaerobic digestion is untoward due to high strength of hardly degradable organics and very long time for treatment. Furthermore, the independent anaerobic digestion can be followed by many problems such as low efficiency for biological degradation and inhibition for methane generation in the reactor due to high strength salts when treating food wastewater which even contains various organics such as carbohydrates and fatty acids. Accordingly, in order to overcome these shortcomings, the co-anaerobic digestion using food wastewater and waste sludge was estimated in this study. The purpose of this study is to determine the appropriate mixing ratio between two wastewaters for effective operation. The ADEPT (Anaerobic Digestion Elutriated Phased Treatment) process in this study is capable of removal of high concentration solids in shorter HRT (Hydraulic Retention Time) when comparing with the existing two phase anaerobic digestion processes. However, this process causes concentration of elutriated sludge in fermentation reactor and wastes a majority of hardly degradable solids without treatment. Accordingly, the Modified-ADEPT which pretreats waste sludge using solubilization was carried out for treating the concentrated sludge. The Modified-ADEPT process could make up for the problem of remaining sludge generation by converting hardly degradable matters to degradable mattes and maximize the efficiency of anaerobic digestion and increase the biogas generation by increasing degradable mattes. This study estimated the efficiencies of ADEPT and Modified-ADEPT after comparison and analysis. In the result of BMP test, it was estimated that the stable treatment was feasible under the high ratio of waste sludge since the efficiency was decreased at high ratio of food wastewater. On the basis of this result, the optimal mixing ratio between waste sludge and food wastewater was determined as 4:1. In the result by comparison between ADEPT and Modified-ADEPT, the removal efficiencies of the Modified-ADEPT for TCOD, VS, TSS and VSS were increased 25, 33, 18 and 24 %, respectively, when comparing with the ADEPT. In addition, the methane gas generation per removed organics was increased about 11 % and the sludge generation was decreased about 60 %.