첨가제를 활용한 인분의 지렁이분퇴비화 개선방안

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 건설환경공학부, 2020. 8. Mooyoung Han.소변분리건조화장실(Urine-diverting dry toilets)은 사람의 배설물관리를 위한 지속가능한 위생시스템 중 하나이다. UDDT에서는 대변과 소변을 따로 분리하여 처리한다. 현재, UDDTs는 냄새 조절, 대소변처리, 영양소 손실과 관련된 여러 문제에 직면해 있다. 그중 대변처리는 우선관심사가 되고 있다. 인분에는 식물성장에 유용한 영양성분이 많이 포함되어 있기 때문에 천연비료로도 알려져 있다. 높은 영양성분이외에도 다량의 병원균들이 있기 때문에 이에 노출되면 질병의 원인이 된다. 따라서 인분을 토양에 비료로 사용하기 위해선 세계보건기구 (WHO) 2006년 가이드라인에 명시된 대장균의 최대 허용치 (< 3 log10 cfu/g 건량)을 충족하여 처리해야 한다. 유기폐기물을 분해하는 지속가능한 방법으로는 지렁이분 퇴비화가 있다. 지렁이분 퇴비화는 지렁이를 사용하여 유기폐기물의 유기물질을 토양 개량제로 전환시키는 것을 의미한다. 마찬가지로, 인분에는 다량의 유기물질을 포함하고 있기 때문에 이 공정을 적용시킬 수 있다. 그러나 퇴비화 시간(처리 시간)이 길기 때문에 대규모로 인분을 분해하는 지렁이분 퇴비화공정의 적용에 걸림돌이 된다. 따라서 본 연구에서 톱밥을 지렁이분 퇴비화 공정을 개선하기 위해 처리 시간을 단축하는 촉매로 사용하였다. 본 연구는 (1) UDDT에서 분리되는 인분에 대한 처리 방법으로서 지렁이분 퇴비화의 타당성, (2) 지렁이분 퇴비화에 대한 톱밥의 효과, (3) 톱밥 유무에 따른 인분의 지렁이분 퇴비화 중 질소 형태의 변화, 그리고 (4) 톱밥 첨가의 적정량(optimization)을 평가하기 위한 것이다. 목표 (1), (2) 및 (3)를 달성하기 위해 4가지 각기 다른 지렁이 서식 상자를 설계하였는데, 이는 대변만을 포함하는 대조 서식상자(F), 톱밥 없이 대변과 지렁이를 포함하는 서식상자(FV), 지렁이 없이 대변과 톱밥을 포함하는 서식상자(FA), 대변, 톱밥, 지렁이를 포함하는 서식상자 (FAV) 이다. 목표(4)을 달성하기 위해 대변 대 톱밥의 세 가지 비율, 즉 1 : 0.5, 1 : 1, 1 : 2가 고려되었다. pH는 FA와 FAV에서 처음 2주 동안 급격히 증가(최대 8.88 - 8.9)한 후 105일까지 서서히 감속하여 pH가 6.79 - 6.87 범위로 유지되는 것이 관찰되었다. 대조적으로, FV에서는 pH의 점진적인 감소만 관찰되었다(8 ~ 7.25). FAV에서 가장 짧은 인분 처리 시간(90일)이 관찰됐으며 75일 이후 휘발성 고형분(VS)이 전체 고형분(TS)의 약 45%로 안정화됐다. 또한 대장균 개체수(2.73 log10 cfu/g건조량)는 90일 이후 WHO 가이드라인 기준을 만족하였다. 지렁이가 없는 다른 서식상자는 105일의 치료 후에도 VS(TS의 62.02~80.05%)와 대장균군(4.42~6.57 log10 cfu/g건중량)의 수치가 다소 높게 측정되었다. 그러나 VS와 대장균 개체수가 감소했음에도 불구하고, 인분의 대변을 지렁이분 퇴비화 과정에서 상당한 질소 손실이 관찰되었다. 총 용존 질소(TDN) 손실은 FAV에서 45일 후 약 85%인 반면, FV에서는 105일 후 TDN의 44%가 손실되었다. 또한, 질소 형태는 지렁이분 퇴비화 과정에서 암모늄이 암모니아, 질산염, 질소 가스 순의 형태로 바뀌었으며, 이는 NH4+/NO3-의 변화로 나타낼 수 있다. FAV에서 최종 생산물의 NH4+/NO3-비율은 75일 이후 0.22~0.02 범위인 것으로 관찰되었고, FV에서는 퇴비화 105일 후 8.75였다. 지렁이분 퇴비화에서 대변 대 톱밥 비율(1:0.5, 1:1, 1:2)을 최적화한 결과 휘발성 고형분(VS)과 대장균군 감소가 톱밥 함량과는 무관한 것으로 나타났다. VS 감소량은 약 41.56 – 45.57%였으며 대장균 감소량은 4.1 log – 4.5 log에서 모든 비율을 고려했다. 마찬가지로, 모든 고려 비율(52% – 71%)에서 바이오매스 증가의 유의미한 차이는 관찰되지 않았다. 따라서 인체 대변의 지렁이분 퇴비화에 대변과 톱밥의 비율(1:0.5)을 권장하여 퇴비화를 위한 지렁이분 퇴비화 서식상자의 부피를 최소화할 수 있었다. 결론적으로, 이 연구를 통해 지렁이분 퇴비화가 분리된 인분을 처리하는 더 나은 대안으로 제안하는 바이다. 또한 서식상자의 처리 시간과 부피를 줄이기 위해 인분의 지렁이분 퇴비화에 톱밥을 첨가하는 것이 권장될 수 있다.Urine-diverting dry toilets (UDDTs) is one of the sustainable sanitation systems for human excreta management. In UDDTs, feces and urine are collected and treated separately. Currently, UDDTs are facing many problems relating to odor control, feces and urine treatment, and nutrient loss. Among these problems, feces treatment could be highlighted as the primary concern. Human feces are considered as natural fertilizer due to the large quantity of nutrients contained within feces which is useful for plants growth. Besides the high nutrient levels, high levels of pathogens were also observed in feces, which can cause diseases if exposed. Thus, before the application of human feces to soil as a fertilizer, it has to be treated to meet the maximum allowable limit of E. coli stipulated in the guideline of WHO, 2006 (< 3 log10 cfu/g dry weight). One sustainable method of decomposing organic wastes is vermicomposting. Vermicomposting could be defined as the use of earthworms and microorganisms in converting organic matter in organic wastes to soil conditioner. Similarly, since human feces contain a substantial amount of organic matter, this process could be applied to human feces. However, higher composting time (treatment time) has created a barrier in the adaptation of vermicomposting process for decomposition of human feces in large scale. Thus, in this study, sawdust was considered as a catalyst to reduce the treatment time to improve the vermicomposting process. This study was aimed at evaluating (1) the feasibility of vermicomposting as a treatment method for source-separated human feces from UDDTs, (2) the effect of sawdust on vermicomposting of the feces to reduce treatment time, (3) observation of the changes in nitrogen forms during vermicomposting of human feces with and without sawdust, and (4) optimizing the addition of sawdust in the process. To achieve the target (1), (2) and (3), four reactors consisting bedding material were designed; blank (F) containing the feces only, one containing the feces and earthworm without sawdust (FV), one containing feces and sawdust without earthworm (FA), and another containing feces, sawdust and earthworm (FAV). Three ratios of feces to sawdust; 1 : 0.5, 1 : 1, and 1 : 2 were considered in reaching target (4). pH was observed to increase rapidly (up to 8.88 - 8.9) in first two weeks in FA and FAV, then decease slowly until 105th day until pH was in the range of 6.79 - 6.87. Contrastingly, only a marginal reduction of pH was observed (from 8 to 7.25) in FV. The shortest treatment time of human feces in was observed in FAV (90 days), with volatile solids (VS) stabilized around 45% of total solids (TS) after 75th day. Further, E. coli population (2.73 log10 cfu/g dry weight) was below the WHO guideline after 90th day. Other reactors without earthworms showed higher amount of VS (62.02 – 80.05 % of TS) and E. coli population (4.42 – 6.57 log10 cfu/g dry weight) even after 105 days of treatment. However, despite the reduction of VS and E. coli population, a significant nitrogen loss was observed during vermicomposting of human feces. Total dissolved nitrogen (TDN) loss was about 85% after 45 days in FAV, while, 44% of TDN was lost after 105th day in FV. In addition, nitrogen forms have changed from ammonium to ammonia, nitrate and nitrogen gas form during vermicomposting which is indicated by the changes in NH4+/NO3-. The NH4+/NO3- ratio in final product in FAV was observed to be in the range of 0.22 – 0.02 after 75 days while, the ratio in FV was 8.75 after 105 days of treatment. The optimization of feces to sawdust ratio (1:0.5, 1:1 and 1:2) in vermicomposting showed that the reduction of volatile solids (VS) and E. coli population are independent from the sawdust content. VS reduction was about 41.56 – 45.57 % and E. coli reduction ranged from 4.1 log – 4.5 log under all ratios considered. Similarly, no significant difference in the increase of biomass was observed in all ratios considered (52% – 71%). Thus, the ratio (1:0.5) of feces and sawdust could be recommended in vermicomposting of human feces to minimize volume of vermicomposting reactor for the treatment. Overall, the results of this study suggest that vermicomposting is a better alternative for treating source-separated human feces. Addition of sawdust to human feces can be recommended in vermicomposting of human feces to reduce the treatment time and volume of reactor.CHAPTER 1. INTRODUCTION 1 1.1 Current global sanitation situation 1 1.2 Urine-diverting dry toilets (UDDTs) 3 1.3 Treatment objectives of human feces 4 1.4 Current challenges of human feces treatment 5 1.5 Vermicomposting as a sustainable technology for treatment of source-separated human feces 7 1.5.1 What is vermicomposting? 7 1.5.2 Human feces 8 1.5.3 Earthworm 9 1.5.4 Additives (bulking agent) 12 1.5.5 Microorganisms 13 1.5.6 Bedding material 14 1.5.7. Reactor 14 1.5.8 Product 15 1.6 Review of research issues 15 1.7 Objective of the study 16 1.8 Dissertation structure 17 Reference 19 CHAPTER 2. INVESTIGATE THE EFFECT OF VERMICOMPOSTING FOR HUMAN FECES TREATMENT 25 2.1 Objectives 25 2.2 Material and methods 25 2.2.1 Raw substrates, earthworm, sawdust and bedding material 25 2.2.2. Reactors 27 2.2.3 Experimental setup 28 2.2.4 Physico-chemical analysis 29 2.2.5 E. coli analysis 30 2.2.6 Statistical analysis 30 2.3 Results and discussion 31 2.3.1 pH variation during vermicomposting 31 2.3.2 Evaluation of the effect of vermicomposting of human feces to reduce treatment time 32 2.3.3 Evaluation of the changes of nitrogen forms during vermicomposting of human feces 35 2.4 Summary 38 References 39 CHAPTER 3. INVESTIGATE THE EFFECT OF SAWDUST ON HUMAN FECES TREATMENT BY VERMICOMPOSTING 44 3.1 Objectives 44 3.2 Material and methods 44 3.2.1 Experimental setup 44 3.3 Results and discussion 45 3.3.1 pH variation during vermicomposting 45 3.3.2. Evaluation of the effect of adding sawdust on vermicomposting of human feces to reduce treatment time 46 3.3.3 Evaluation of the impact of adding sawdust on the changes of nitrogen forms during vermicomposting of human feces 49 3.4 Summary 52 References 53 CHAPTER 4. THE OPTIMIZATION MIXING RATIO OF HUMAN FECES WITH SAWDUST IN VERMICOMPOSTING PROCESS 57 4.1 Objectives 57 4.2 Experiment setup 57 4.3 Physical analysis 58 4.4 E. coli analysis 58 4.5 Biomass analysis 58 4.6 Results and discussion 59 4.6.1 The effect of different ratio on treatment time of vermicomposting 59 4.6.2 The effect of different ratio on biomass and amount of earthworm 61 4.7 Summary 63 References 64 CHAPTER 5. CONCLUSIONS AND RECOMMENDATIONS 66 5.1 Conclusions 66 5.2 Recommendation for further study 69 5.2.1 Larger-scale experiments 69 5.2.2 Size of organic additives 70 5.2.3 Microbial additives 70 5.2.4 Earthworm density and growth rates 70 5.2.5 Carbon to nitrogen (C/N) ratio 70 5.2.6 Vermicompost quality 71 5.2.7 Continuous-flow vermicomposting 71Maste

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