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.
Highlights
World Health Organisation (WHO) has reported an estimated 4.2 billion people globally lacked safely managed sanitation facilities in 2017 (WHO, 2019)
Final moisture content ventilated improved pit (VIP), urine diversion dry toilets (UDDT) and anaerobic baffle reactor (ABR) samples were dried in an oven for 24 h at 50, 100, 150 and 200 C to evaluate the effect of drying temperature
The results discussed in this paper provide insights on faecal sludge (FS) drying and provide information that could be applied to improve drying technolo gies
Summary
World Health Organisation (WHO) has reported an estimated 4.2 billion people globally lacked safely managed sanitation facilities in 2017 (WHO, 2019). Since 2011, transformative sanitation technologies that function without connection to external water source, energy or sewer systems have appeared. One of the generation technologies that came through the RTTC is the Nano-Membrane Toilet. This toilet uses a membrane to remove the water from human waste and leaves solids that can be utilized as fuel or fertilizer (Hanak et al, 2016; Onabanjo et al, 2016). The system uses the steam power generated by burning the dried sludge. Most of these systems involve drying and efficient resource recovery
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