Selection of Suitable Additives for Composting Toilet

Abstract

Abstract Selection of Suitable Additives for Composting Toilet 퇴비화 변소에 적합한 첨가물의 선택

Nguyen Danh Tien Dept. of Civil and Environmental Engineering College of Engineering Seoul National University

This research presented the effects of mixing human feces with differing additives on improvement performance of composting, considering the efficiency of enhancement on decomposition of organic matter, reduction of nitrogen loss and pathogen bacteria removal. Three selected types of additives were available in Korea including sawdust, rice husk and rice husk charcoal used for mixing with human manure with ratio 1 : 2 (by human feces/additives, v/v). In addition, optimization of mixing ratio between human feces with rice husk charcoal for better improvement in composting performance was estimated also. Raw materials characteristics and changes of compost properties during process were measured being moisture content, pH, organic matter content, total nitrogen content, NH4 ?N and Escherichia coli (E. coli) concentration. Decomposition rate of organic matter in the composting buckets of both feces ? sawdust (F-S) and feces ? rice husk (F-RH) were obtained at 13.4% and 18.6%, respectively while it was much higher in the composting bucket of feces ? rice husk charcoal (F-RHC) being 32%. Total nitrogen content rose overtime of composting period in F-RHC bucket from 1.9% to 2.25%. However, in cases of F-S and F-RH, it reduced during first two weeks of process. In term of pathogen bacteria, E. coli concentration was rapidly reduced after first week of composting period in three cases. Interestingly, E. coli was not detected in F-RHC case after 5 weeks whilst F-RH and F-S cases were not completely inactivated E. coli after two months. These results therefore demonstrated the efficacy of using rice husk charcoal to enhance decomposition of organic matter, reduction of nitrogen loss and removal pathogen bacteria. For optimization of composting, the mixing ratio of human feces with rice husk charcoal was also investigated. Mixtures with increasing amounts of rice husk charcoal at different ratio being 1:0.3

1:0.5

1:1

1:2

1:3 (by human feces / rice husk charcoal, v/v) were incubated in a laboratory scale reactor under aerobic conditions at 25°C for 30 days. The decomposition rate of organic matter evolution shows highest value at the mixing ratio of 1:1 being 33% and the lowest at mixing ratio of 1:3 (10.6%). The losses of total nitrogen mass was reduced when amount of rice husk charcoal increasing. However, the total nitrogen mass loss rate was similar in three mixing ratio of 1:1, 1:2 and 1:3 being 15.9%, 15.5% and 15.2%, respectively. Therefore, moderate amounts of rice husk charcoal with mixing ratio of 1:1 would be the best compromise.

Keywords: Composting toilet

pathogen bacteria

organic matter decomposition

rice husk charcoal

nitrogen loss

Student number: 2013-23858