Large volumes of sludge are produced from onsite sanitation systems in densely populated areas (e.g. slums and emergency settlements) and wastewater treatment facilities that contain high amounts of pathogens. There is a need for technological options which can effectively treat the rapidly accumulating sludge under these conditions. This study explored a pilot-scale microwave (MW) based reactor as a possible alternative for rapid sludge treatment. The reactor performance was examined by conducting a series of batch tests using centrifuged waste activated sludge (C-WAS), non-centrifuged waste activated sludge (WAS), faecal sludge (FS), and septic tank sludge (SS). Four kilograms of each sludge type were subjected to MW treatment at a power of 3.4 kW for various time durations ranging from 30 to 240 min. During the treatment the temperature change, bacteria inactivation (E. coli, coliforms, Staphylococcus aureus, and enterococcus faecalis) and sludge weight/volume reduction were measured. Calorific values (CV) of the dried sludge and the nutrient content (total nitrogen (TN) and total phosphorus (TP)) in both the dried sludge and the condensate were also determined. It was found that MW treatment was successful to achieve a complete bacterial inactivation and a sludge weight/volume reduction above 60%. Besides, the dried sludge and condensate had high energy (≥ 16 MJ/kg) and nutrient contents (solids; TN ≥ 28 mg/g TS and TP ≥ 15 mg/g TS; condensate TN ≥ 49 mg/L TS and TP ≥ 0.2 mg/L), having the potential to be used as biofuel, soil conditioner, fertilizer, etc. The MW reactor can be applied for the rapid treatment of sludge in areas such as slums and emergency settlements.

This work aims at characterizing the rheological properties of faecal sludge from Ventilated Improved Pit (VIP) latrines and their implication on pit emptying. Faecal sludge was sampled from 3 pit latrines located in the eThekwini Municipality (Durban, South Africa). Samples were taken at different positions within the pit. For each of the samples, measurements in the rheometer in triplicates were performed in order to determine their rheological properties, and their moisture and ash content were measured also in triplicates. Experiments in the rheometer were performed for samples for which its moisture content was modified. In order to better understand the influence of water addition into the pit. During pit emptying, calculations were carried out from the experimental data, based in the criteria set in the Omni-Ingestor initiative, carried out by the Bill & Melinda Gates Foundation.Faecal sludge exhibited a shear thinning behaviour, i.e. a decrease in viscosity with increasing shear rate, and presented a yield stress comprised between 500 to 1000 Pa. This needs to be surpassed in order to overcome the elastic resistance of the sludge to flow. Similar viscosities were found for the samples from the different pits, irrespective of the position within the pit, except for the sample from the bottom of one of the pits for which it was not possible to induce a flow. This sample had a considerably lower moisture content (67% wet basis) compared to the other samples (around 80% wet basis), probably due to a higher biodegradation as it was the most aged sludge in the pit.According to the experimental results and calculations, the pumping requirements during pit emptying will decrease drastically by increasing the moisture content of the sludge. The addition of water into the pit would then facilitate the pit emptying operation by reducing the head and power required for pumping. However, this practice would require employing considerable amounts of water and handling higher volumes of sludge, which would lead to longer pit emptying times and increase the difficulty of the operation. For example, increasing the moisture content of the sludge from 75 to 90% will reduce the head and power of the pump by a factor 100, but will triplicate the amount of water in the sludge and, consequently, the time for pit emptying. Therefore, a compromise has to be made between increasing the pumping feasibility and adding water to the pit.

This study investigated the chemical and thermal properties of faecal sludge from 10 dry VIP latrines in Bester's Camp in the eThekwini Municipality, Durban, South Africa. Faecal sludge samples were selected at different depths and from the front and back sections of 10 VIP latrines during a manual emptying process. The samples were analysed for: moisture content; volatile solids; chemical oxygen demand; ammonia; total Kjeldahl nitrogen; pH; orthophosphate; thermal conductivity; calorific value and heat capacity. These properties will facilitate the design of faecal sludge emptying and treatment equipment. A manual sorting of the pit contents was carried out to determine the categories and amounts of household waste present. There was a significant difference in the moisture, volatile solids, chemical oxygen demand, ammonia, total Kjeldahl nitrogen and orthophosphate content of the faecal sludge between the front and back sections of the pit. There was minimal change in the thermal properties within the pit. The median values through the pit of each property analysed were: moisture content -0.81 g water/g wet mass; volatile solids -1.5 g VS/g ash; COD -1.7 g COD/g ash; ammonia nitrogen -10 mg NH 3 -N/g dry mass; TKN -39 mg N/g dry mass; pH -8.03; orthophosphate -0.06 mg PO 4 /g dry mass; thermal conductivity -0.55 W/m K; calorific value -14 kJ/g dry mass; heat capacity -2.4x10 3 kJ/kg K. On average, 87% of pit content is faecal sludge; the remainder consists of wastes such as paper, plastics and textiles.

This paper studies a faecal sludge treatment process, LaDePa (Latrine Dehydration and Pasteurization), which includes: (i) the characterization of the rheological and plastic behaviour of faecal sludge in the feeding section; (ii) the study of the drying and pasteurization performance of the process using a laboratory-scale prototype; and (iii) an evaluation of the processed faecal sludge for reuse in agriculture or as a biofuel.Experiments conducted using a rheometer show that the faecal sludge exhibits shear thinning behaviour, i.e. viscosity decrease with shear rate increase. Plasticity tests in a cone penetrometer showed that the faecal sludge has a more liquid than plastic behaviour, which may affect extrusion quality, unless a plasticizer is added, as sawdust in this study.The extent of drying and pasteurization of the samples was determined based on moisture content and the presence of viable Ascaris eggs respectively. As the intensity of infrared radiation was increased, drying was faster and more efficient in terms of energy consumption. However, the pellets were thermally degraded at temperatures above 200 °C. After processing in the LaDePa, Ascaris eggs were deactivated or severely damaged so that they would be not able to develop.The last part of the study was conducted by determining the content of nutrients (C, N, P, K) and calorific value. The results showed that the processed pellets have suitable characteristics for reuse in agriculture and as a biofuel: similar nutrient content to manure and compost, and similar calorific value to wood. Drying did not affect the nutrient content and calorific value of the dry bone of faecal sludge.

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