Putting Waste Nutrients to Good Use: A Novel N/P/K Fertilizer and Soil Conditioner from Pyrolyzed Urban Latrine Waste.

We have attempted to create a novel N/P/K fertilizer and soil conditioner from a biochar made from human solid waste (HSW) and human urine. Thermal treatment of HSW through pyrolysis assures adequate sanitization while preserving carbon (C) and ash nutrients, such as phosphorous (P) and potassium (K) in the form of pyrolyzed biomass, or biochar. HSW biochar also captures nutrients from urine, serving as a slow-release reservior for plant-essential macro- and micronutrients.

HSW biochar was produced from latrine waste collected in an informal settlement in Nairobi, Kenya and combined with urine  A chemical characterization of human waste biochar produced at 500C revealed P and K content of 2% and 2.5%, respectively. The high C content of HSW biochar, 64%, and the proliferation of aromatic carbon compounds within the biochar matrix contribute to persistance in the soil environment. Additionally, the high pH of HSW biochar in water, 10, confers a liming capability in acidic soils. Human urine contains 12,000 ppm plant-available nitrogen (N) in the form of urea and ammonium (NH4). However, its high alkalinity, pH 9.5, facilitates ammonia (NH3) volitalization. HSW biochar may serve as a carrier of nitrogen originating from urine through either adsorption or precipitation mechanisms, resulting in a unique N/P/K-enriched, alkaline, organic-C amendment. 

Current research efforts are aimed at establishing the N- loading capacity and mechanism from urine onto biochar. We are investigating both adsorption of ammonium (NH4) and NH4 precipitation with biochar-P. Additionally, incubation trials are being carried out to determine C and N mineralization rates of HSW biochar. The nutrient uptake and N-use efficiency of HSW biochar was also tested with maize in four different soils from Western Kenya against compost produced from human waste and commecial urea. Effects of the biochar fertilizer on soil chemical and physical properties was also assessed, namely pH, P availability, and N cycling.