Effect of storage time on the properties of faeces

Abstract

Background: This short-term study was carried out in 2013 at the Pollution Research Group at the University of KwaZulu-Natal (Durban, South Africa) as an asisgnemnt of a final year Chemical engineering student project. It focussed on the effect of storage time on the properties of fresh human faeces, more particularly moisture content, thermal conductivity, volatile solids and chemical oxygen demand (COD). These properties are important as they are often used in the design of drying or thermal treatment technologies for faeces. A storage period of one week was hypothesised at room ambient temperature. Methods: The samples were tested for chemical properties using standard operational procedures developed at the Pollution Research Group with parameters such as totals solids, moisture content, suspended solids, volatile solids, COD and thermal conductivity. Results: The thermal conductivity on average was 0.44 W/m.K. The moisture content was observed to decrease by 16%, from 77% to 61%.  Thermal conductivity was plotted over the range of moisture contents to observe any trends, varying from 0.074 W/m.K to 0.61 W/m.K for dry faeces and water respectively. The use of a composition weighted average model fitted the data well and was found to be within 95% of the confidence interval of the best fit line. Conclusions: The effect of storage time was found to be negligible on COD and thermal conductivity however moisture content decreased as days progressed and the volatile solids increased with an increase in storage time. Examining the relationship between thermal conductivity and moisture content, it was found that thermal conductivity increase with an increase in moisture content.