Browsing by Author "Naidoo, Pareshin."

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Development and testing of a faecal sludge greenhouse solar dryer.
(2023) Naidoo, Pareshin.; Stringel, Santiago Septien.; McGregor, Craig.
Faecal sludge poses a significant global challenge, contributing to pollution and disease transmission if not managed appropriately. Thermal drying presents a viable treatment method, reducing sludge mass and eliminating pathogens. However, the high energy requirements associated with conventionally powered methods of thermal drying raise operating costs, and to address this issue, solar drying was evaluated as an efficient and sustainable alternative for this process. This project aims to develop and test a solar thermal drying system for the treatment of faecal sludge, measure its performance characteristics, and identify areas of improvement and optimization. This project presents an adaptation of a greenhouse-type solar dryer developed by the WASH R&D Centre at the University of KwaZulu-Natal for the treatment of faecal sludge. Greenhouse solar dryers utilise solar thermal energy and ventilation to dry a product. This dryer consists of seven subsystems: an enclosure, absorber wall, ventilation and circulation system, sludge mixing system, drainage system, drying tray, and testing instrumentation. Polymethyl methacrylate and aluminium were used in the construction of the enclosure, which measures 2 × 1.5 × 2 m (length × width × height). A ventilation and circulation system were installed in the greenhouse to remove moisture from the dryer and to improve moisture evaporation by enhancing external mass transfer at high air velocities. A rake system was designed to mix sludge and promote homogenous drying. The sludge was placed in a suspended grid where it could be dried from the top and bottom. A temperature and humidity control system was developed to record both the humidity and temperature at seven different areas in the dryer. The dryer was tested in Durban during the winter season of 2022 using feedstock consisting of water, wet soil, and synthetic sludge as a proxy of real faecal sludge, at UKZN, Howard College campus on the roof of the Chemical Engineering building. Temperatures higher than 40 °C were recorded inside the dryer with ambient outside temperatures lower than 30 °C were recorded, leading to relative humidity lower than 40 %. Functionality tests were conducted to ensure the various subsystems were operating correctly, after which, the system was tested with feedstock. During the water tests, 7 small crucibles filled with water were used in the greenhouse dryer to determine how well water evaporated. Adjustments of both the ventilation and circulation fan speeds were made to determine the best airflow rates for the drying of water. Lower fan speeds proved more effective for water evaporation so the lowest fan speed combinations, ventilation speed 1 (V1) and circulation speed 1 (C1) were used in the wet soil tests and synthetic sludge. Tests with soil and sludge were conducted at these speeds. A large reduction of the moisture content of wet soil was observed during a single day from around 70 % moisture content to less than 20 % in the space of 5 hours. Synthetic sludge was made and tested during the winter season. Synthetic sludge has very similar properties and texture to faecal sludge and therefore is an effective feedstock for measuring the dryer's performance. A 10 kg sample of synthetic sludge was tested in the greenhouse solar dryer between the dates of 05-08-2022 and 08-08-2022. Synthetic sludge with an 80 % moisture content was reduced to 6.5 % over 4 days. Drying times ranged from 5 to 6 hours a day, with an overall drying rate of 0.36 kg/h on average, a specific energy consumption (SEC) of approximately 655 kWh/t and an overall dryer efficiency of 9.6 %. A second test was conducted on the dates of 14-08-2022 and 15-08-2022. Better weather conditions on the second test enabled the dryer to dry 80 % moisture content sludge to 12 % in 2 days. The overall dryer efficiency of approximately 18 % and average SEC of 363 kWh/t were calculated over the two days of testing. The greenhouse solar dryer research and testing indicated that solar thermal dryers can potentially address the drying and disposal of faecal sludge, a matter that is a major problem in developing countries. Further steps to conclude the study include tests with real faecal. sludge, improvement and optimization of the system, and the development of a techno-economic analysis.