Investigating the composting methods for enhancement of the fertilizing value of desiccated human faeces produced by the mobisan facility for agricultural application

Abstract

Agriculture in rural communities of South Africa is negatively affected by the poor quality of soils with low fertility. With limited financial resources, non-commercial farmers are not able to purchase chemical fertilizers or other products necessary for plant production. Alternatives such as composting of human excreta and animal manure have found favour in many regions of the world for improving soil fertility for sustainable crop production. Human faeces contain nutrients and have potential to be used as fertilizer in agriculture. Faeces should not be regarded as waste, but rather as a product that can be used for the provision of an affordable agricultural fertilizer. The MobiSan facility is a urine diversion toilet installed at Pooke se bos informal settlement, where the disposal of waste is difficult for number of reasons such as lack of space, inadequate infrastructure and no access roads. However, the lack of safe disposal of desiccated human faeces from MobiSan facility has created a detrimental effect within the settlement that lead to unwanted conditions. The alternative means of reducing the pollution loads within the settlement areas is to look at localized on-site treatment of composting methods that can treat desiccated human faeces from MobiSan facility to meet standards for agricultural applications. Faeces can be treated and stored under controlled process called composting to enhance the nutrients value for plant production. Without composting, human faeces usually have a low initial fertilizing value. Analysis of the studies done in Uganda showed an enhancement of the composted faeces-to-food waste from 78-litre reactors attained 19% N, 34% P and 28% K; and also E. coli and total coliforms were found lower than the detected value with high temperatures exceeding 50°C and pH (4.5-8.7). Given the initial low fertilizing value of human faeces, further treatment method is required to make it suitable for agricultural use. Several methods are used to enhance the fertilizing of human excreta, amongst these is the composting. In this line, three composting methods, namely Co-composting, Skyloo-composting and Bio-process composting were piloted with great importance in the settlement for reasons such as: Low O&M costs, Use of locally available materials, and no energy needed to treat human faeces…The application of the three composting methods could provide the community within the settlement with work opportunities and also improving soil fertility using locally-available fertilizers. The initial characteristics of desiccated human faeces from the MobiSan facility were determined by sampling and testing quality parameters namely pH, Oxygen, temperature, moisture content, Carbon, Nitrogen, Phosphorus, Potassium, Faecal coliform and E. coli. The initial results of desiccated human faeces from the MobiSan facility showed a low fertilizing value when compared to previous literature, with values of Nitrogen, Phosphorous and Potassium being respectively 4.7%, 3.4% and 1.5%, while those of E-Coli and Faecal coliform being 5.9x103cfu/g and 7.8x103cfu/g respectively. Results on the composted faeces using the Co-composting method were as follows: Nitrogen: 22.2%, Phosphorus: 25.4%, Potassium: 31.1%. Skyloo composting method results were found with Nitrogen: 16.2%, Phosphorus: 19.6%, Potassium: 15.2% and results obtained from Bio-process composting method were: Nitrogen: 25.3%, Phosphorus: 28.6%, Potassium: 33.2%. Results of the study showed that the three composting methods were suitable for treating human faeces from the MobiSan facility. Results indicate that the enhanced fertilizing value and reduction of pathogens in composting process could make the compost safe for agricultural application. Bio-process composting was found to be the most suitable method as it enhanced the fertilizing value of desiccated faeces to 83% N; 88% P and 95% K. The composting process also significantly reduced the concentration of E.coli and Faecal coliforms. Results of this study intended to address the issue for the disposal of desiccated human faeces from MobiSan by assessing the potential of composting in enhancing the fertilizing value of human faeces for agricultural application. Results provided also an understanding of the fertilizing value of human faeces and assisted subsistence farmers (small scale) with valuable knowledge of the fertilizing value of desiccated human faeces from Mobisan and the potential of composting in enhancing it for safe use in agriculture.