Health and safety aspects of the use of products from urine-diversion toilets

Abstract

The use of human excreta as a fertilizer has been used to a very limited extent. Human excreta has been distributed throughout the environment as a result of faulty sanitation system design, improper use and/or the total absence of any sanitation system. Human excreta contain nutrients in the form of nitrogen (N), phosphorus (P) and potassium (K). Agricultural use of sludge may be an alternative to conventional fertilizers provided that the risk to public health is considered. The application of biosolids to agricultural fields however poses an environmental and health risk since sludge may contain toxic chemicals, pollutant organic compounds and pathogenic parasitic microorganisms of faecal origin. If urine and faeces were separated the risks could potentially be minimized and both of these fractions could possibly be disinfected and utilized. Dehydrated faeces (humanure), urine, soil, irrigation water and crop samples were analysed for the total coliform, faecal coliform, faecal Streptococci, Salmonella spp, Aspergillus spp and helminth eggs. Moisture content and pH of each sample were also determined. Survival studies of microorganisms in dehydrated faeces using different treatments (ash; NaOH and pasteurization) were performed. Human urine both sterile and non-sterile was stored at 15oC, 20oC and 30oC for 50 d to estimate the effect of different storage conditions on the survival of pathogens. Four agricultural plots were prepared for treatment, two for spinach and two for carrot crops. Dehydrated faeces contained total coliform, faecal coliform, Faecal Streptococci and Salmonella spp. Treatment with NaOH and ash reduced the number of pathogens in dehydrated faeces, but not to safe levels. The number of helminth eggs was higher in dehydrated faeces (humanure) than in the soil and crops. Few helminth eggs survived pasteurization at 60oC for 30 min, 70oC for 20 min and 90oC for 5 min. Pathogens survived after storage of human urine at 15oC and 20oC for 50 d. Most of the pathogens (total coliform, faecal coliform, Salmonella spp and Aspergillus spp) were reduced at 30oC. 62.8% of helminth eggs found in humanure were Ascaris eggs and 82% ofAscaris eggs found were viable. Application of humanure to soil resulted in the contamination of soil and crops. However the viability of helminth eggs in crops was very low. No bacteria survived pasteurization at 70oC for 20 min and 90oC for 5 min. Therefore heat treatment at 70oC for 20 min and 90oC for 5 min was the most effective disinfection method for the bacteria. The results showed that Ascaris spp, Toxocara spp, Trichuris spp, Enterobius vermicularis, Hymnologies diminutionsand Taenia spp were present in soil, carrots, and spinach samples when humanure was applied to soil as a fertilizer. Pathogenic and parasitic microorganisms present in humanure represented a high risk of infection.