Comparative progressive composting, evaluation and profiling of minerals and heavy metals in human solid waste collected by green toilet system, cow dung, poultry droppings, and goat waste composts

The value of human excreta, a resource that is available in all societies is underestimated in present agriculture. In parts of South East Asia, the use of human excreta as fertilizer in agriculture is a common practice benefiting production. The excreta contain chemical elements that circulate in biogeochemical cycles necessary in plant nutrition. This study aimed to progressively detect, quantify, and profile minerals (micro, macro and heavy metals) levels in human solid waste from Green Toilet System and compare with cow dung, poultry droppings, and goat waste composts at different stages of composting for a time duration of six months (183 days). Green Toilet System, developed by LIXIL destined solid and liquid human wastes to different collection points with negligible or zero interaction. Micro (Mn, Cu, Zn, and Fe), macro nutrients (Ca, K, P, N, and Mg) and heavy metals (Pb, Cd and Cr) analysis was done after every 21 days. Individual means were compared and separated using Duncan’s multiple range test with a significant level at p<0.05. There were significant differences between the means recorded for micro/macronutrients, and heavy metals between all composts analyzed. Micronutrients levels increased with increase in composting time. Lead and chromium reached an optimal level of 28.000±0.000mg/Kg and 35.000±0.000mg/Kg on days 168 and 105 respectively. The findings showed that composts contained different profiles of macro- and micronutrients that may contribute to soil enrichment and have agronomic value. Green Toilet System for collection of human solid waste and progressive composting of cow dung, poultry droppings, and goat waste can be used to determine optimal levels of micro/ macronutrients and heavy metals at different composting stages. In conclusion, human solid waste compost should be considered for use when the levels of micro/macronutrients are optimal and heavy metal levels are minimal after composting.