Characterisation of faecal material waste from rural schools’ onsite sanitation systems for its safe disposal and optimal valorisation.

Abstract

Poor sanitation facilities in South African rural schools are barricading youth from their education, due to an unsafe learning environment. Inadequate sanitation facilities in South African rural schools not only pose severe health risks but also hinder progress towards achieving the 4th and 6th Sustainable Development Goals (SDGs). This study aims to assess the optimal valorisation of faecal material derived from rural school sanitation systems, including ventilated improved pit latrines (VIPs), mobile toilets (MTs), and septic tanks (STs) in Durban, South Africa. Faecal material, defined as the combination of solid waste, urine, and other gastrointestinal excretions, underwent a thorough analysis of its physico-chemical, thermal, thermodynamic, and mechanical properties. Analytical tests for characterizing faecal material were conducted in line with standard methods utilized by the WASH R&D Centre and the Methods for Faecal Sludge Analysis by Velkushanova et al. (2021). The findings were used to formulate decision matrices for determining the most efficient treatment and emptying strategies based on the characteristics of the faecal material. Notably, all containment systems exhibited comparable energy and nutrient potential suitable for the production of fuels and fertilizers, respectively.Particularly, fresh faeces from MTs exhibited the highest solids concentration (~18% TS), organic fraction (~78.37%) Volatile Solids, and calorific value (23.24 MJ/kg dry solids). The opposite was observed for VIPs (~45.47% VS, ~8.5% TS) with a calorific value of (18.4 MJ/kg dry solids). MTs illustrated the highest mean nutrient composition and improved treatability - a lower shear yield stress at the same solid’s concentration to the more degraded faecal sludge from VIPs and STs. This inadvertently improved flowability and reduced the pump head requirement for emptying technologies and treatment processes.. Ultimately faeces from MTs were considered to have high strength. VIPs demonstrated the highest TSS, TDS and lowest SVI at 3,6 g/L, 1422 mg/L and 75 ml/g respectively. Together faecal material from all On Site Sanitation systems, exhibited a water activity of ~1, suggesting good dewaterability potential, with results signifying the moisture in the sludge is unbound, so less difficult to remove. Particle size for school toilets ranged between 0,7- 2046,7 μm 0,6 -1202,3 μm and 0,7-1492,5 μm for VIPs, MTs, and STs, respectively. Thermal conductivity for each OSS (MTs, VIPs, STs) represented a narrow range for faecal sludge and faeces ranging between 0,48-0,59 (W/K/m), which were in close approximation to the thermal conductivity of water. Overall, this study guides engineers and regulators in establishing safe, equitable and sustainable rural school sanitation systems, by promoting resource recovery options such as biochar, fertilizers, and biogas. High strength faecal material from MTs offered the greatest potential for resource recovery, however, requires multiple treatment stages to ensure safe environmental discharge standards are met. They also act as a temporary containment solution, with limited maintenance and negative user perception. The large presence of trash, high TS% and denser faecal material within MTs rendered it most applicable to manual emptying methods (MAPET and manual diaphragm). Consequently, the preferable direction for advancing rural school sanitation, is the adoption of water-borne systems where possible. A transition towards these systems will minimize the spread of diseases associated with non-flush systems (MTs and VIPs). Additionally, it will enhance the overall comfort of female students using school toilets, subsequently reducing the fatalities that have occurred from children drowning in pit latrines. Water-borne sanitation systems, such as STs better facilitate the use mechanical emptying methods, providing a wider array of mechanical emptying options. Furthermore, STs demonstrated viable treatment options owing to its better stabilized waste, like composting and vermicomposting. Moreover, progressive options for areas with no water access, include, contained-based sanitation or re-invented toilets such as composting toilets. This will allow for faeces to be valorised relatively fresh, obtaining direct resource recovery, for high quality end-use products like biogas, and biochar for a fuel source.