Abstract
Drying is one of the treatment techniques used for the dual purpose of safe disposal and energy recovery of faecal sludge (FS). Limited data are available regarding the FS drying process. In this paper the drying properties of FS were investigated using samples from ventilated improved pit (VIP) latrines and urine diversion dry toilets (UDDT) and an anaerobic baffle reactor (ABR) from a decentralized wastewater treatment systems. Moisture content, total solids content, volatile solids content, water activity, coupled thermogravimetry & differential thermal analysis (TGA-DTA) and calorific value tests were used to characterize FS drying. Drying kinetics and water activity measured at different moisture content during drying (100 °C) were similar for the samples from different on-site sanitation facilities. Experimental heat of drying results revealed that FS requires two to three times that of the latent heat of vaporization of water for drying. Drying temperature was more significant than the sludge source in determining the final volatile solids content of the dried samples. This was reinforced by the dynamic TGA that showed considerable thermal degradation (2–11% dry solid mass) near 200 °C. Below 200 C, the calorific value of the dried samples exhibited no significant difference. The average calorific values of VIP, UDDT and ABR samples at 100 °C were 14.78, 15.70, 17.26 MJ/kg dry solid, respectively. This suggests that the fuel value of FS from the aforementioned sanitation facilities will not be significantly affected by drying temperature below 200 °C. Based on this study, the most suitable temperature for drying of FS for a solid fuel application was found to be 150 °C.
| Original language | English |
|---|---|
| Article number | 110267 |
| Number of pages | 8 |
| Journal | Journal of Environmental Management |
| Volume | 261 |
| Early online date | 2 Mar 2020 |
| DOIs | |
| Publication status | Published - 1 May 2020 |
Funding
This work is based upon research supported by Bill & Melinda Gates Foundation through “Thermal Drying” project research grant, OPP1164143. The support of the foundation is acknowledged. The authors kindly thank eThekwini Water and Sanitation staff members for their collaboration and permission to access the faecal sludge from the municipal pit latrines and facilitating the sampling procedure. The authors would also thank the laboratory staff at Pollution Research Group (PRG) at University of KwaZulu-Natal.
Keywords
- calorific value
- drying
- faecal sludge
- heat of drying
- temperature
- valorisation