Health Risk Assessment of Compost-Amended Soils

Abstract

Application of improperly treated compost from composting toilet is one of the causes of bacterial contamination in the field, crops, food and water. The study characterized the die-off represented by kinetic inactivation rate coefficient, k (h-1) of Enterococcus in clay and sandy loam soils, determined the effect of temperature, compost-to-soil ratio and soil type on the inactivation rates of Enterococcus and evaluated the health risk associated with the amendment of compost from composting toilet in real conditions using local climatic data. The soils were amended with compost to soil ratios of 1:10, 1:25, 1:50 and 1:100 held at different temperatures (30°C, 40°C and 50°C). Inactivation of Enterococcus (pathogenic bacteria) in the soil with high temperature under different compost application rates was tried in the laboratory test and the Quantitative Microbial Health Risk evaluated. The study results indicated the inactivation rates of Enterococcus in clay soils as 0.015 - 0.027 h-1, 0.246 - 0.322 h-1, 0.397 - 0.571 h-1 whilst sandy loam soils recorded 0.056 - 0.130 h-1, 0.348 - 0.447 h-1 and 0.475 - 0.630 h-1 for 30°C, 40°C and 50°C respectively. Inactivation rates of Enterococcus in soils amended with compost from the composting toilet depended on temperature and soil type but not on the compost-to-soil ratios and compost from the composting toilet amended to the soils is safe for use in six (6) days.