Open access publications in the SLU publication database

Abstract

This thesis examines simple, cheap, environmentally friendly and resource efficient technologies for the treatment of source-separated human faeces and urine to enable safe recycling of their plant nutrients for plant production in developing countries. Composting of faeces-to-food waste (F:FW) in wet weight mix ratios of 1:0, 3:1 and 1:1 was studied in 78 L reactors insulated by 25 mm styrofoam; and of F:FW in wet volume/weight ratios of 1:0, 1:1 and 1:3 in 216 L reactors insulated by 75 mm styrofoam. At both scales, composting without insulation produced temperatures that differed from the ambient by ≤15 °C. A sanitised compost product was produced when the temperature was maintained above sanitising levels (>50 °C) for a sufficiently long time (at least 2 weeks). High moisture levels (>60%) led to low pH (<6), which impeded composting and the attainment of sanitising temperatures. Incineration of well prepared source-separated faeces with ash as cover material produced high temperatures (800-1000 °C). This process decreased the organic matter, total N and plant-available P by 70->90%. Mass decrease was 15-36% due to high ash content of the incoming material. Incinerating faeces/ash mixtures with DM<90% resulted in a strong smell that lessened when DM was higher. The ash produced by incineration can be used as cover material for faeces during toilet use, which is advantageous in urban areas of developing countries where access to ash is limited. In urine treatment, a breakpoint concentration of ammonia was found at approximately 40 mM NH3 (e.g. 2.1 g NH3-N L-1 and pH 8.9 at 24 °C), below which all studied organisms, except Salmonella Typhimurium (S. Typhimurium), persisted considerably longer irrespective of treatment temperature, showing that urine dilution rate is highly important for pathogen inactivation. The time to no detection in urine stored in the sun (Uganda; mean temperature±amplitude 24±7.5 °C, NH4-N of 4±1.5 mg L-1 and pH 9) for E. coli, Salmonella and Ascaris suum was 11 hours, 14 hours and 40 days respectively. Under similar conditions, Enterococcus spp. reached non-detection levels in 50 days, while the phages studied persisted considerably longer. The t90 for MS2, Φx 174 and S. Typhimurium 28B was 8.2, 37 and 55 days respectively. Fluctuating temperatures in combination with ammonia were shown to inactivate pathogens in urine faster than the same average steady temperature.