Chemical and thermal properties of VIP latrine sludge

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 NH3-N/g dry mass; TKN – 39 mg N/g dry mass; pH – 8.03; orthophosphate – 0.06 mg PO4/g dry mass; thermal conductivity – 0.55 W/m K; calorific value – 14 kJ/g dry mass; heat capacity – 2.4x103 kJ/kg K. On average, 87% of pit content is faecal sludge; the remainder consists of wastes such as paper, plastics and textiles.Keywords: faecal sludge, VIP latrines, chemical properties, thermal propertie

Faecal sludge simulants to aid the development of desludging technologies

This paper presents a review of currently available data from the literature on the undrained shear strength, bulk density, stickiness and debris content of faecal sludge. Those data have been used to develop two different simulants that replicate the full range of shear strengths and densities reported for faecal sludge. Comprehensive specifications are also presented for the debris or solid waste found in latrines to more closely replicate the challenge of pumping faecal sludge. Finally, a design guide has been produced to capture these results and support quantitative performance testing of desludging pumps. The simulants have already been used as part of the Bill & Melinda Gates Foundation's Faecal Sludge Omni-Ingestor project and by Water for People's SaniHub in developing improved desludging pumps. The wider use of these simulants could accelerate the development of pit emptying technologies and help standardize the quantitative evaluation of their performance.The development of the simulants presented here was funded by the Bill & Melinda Gates Foundation under the Faecal Sludge Omni-Ingestor project.This is the author accepted manuscript. The final version is available from IWA Publishing via http://dx.doi.org/10.2166/washdev.2015.01

Characterisation of wastes towards sustainable landfilling by some physical and mechanical properties with an emphasis on solid particles compressibility

The EU landfill directive requires the amount of wastes going to landfills to be reduced significantly in compliance with the sustainable waste management principles. However, the disposal has been and will continue to play a significant role, and the overall aim is an improved design and operation of the landfill sites, and reduction of their negative environmental impact towards sustainable landfilling. Waste has been recognised by other researchers as the primary structural element in landfills; therefore for better understanding of its behaviour, the physical and engineering properties of its components must be well known. The main aspect of this research was focused on investigation of particle compressibility and its effect on the overall compressibility and settlement of the waste body. A methodology to measure particle compressibility in saturated conditions at various stress levels was developed, using synthetic deformable materials and mechanically-biologically treated (MBT) waste. MBT waste sample with particle size reduced to 9 mm showed a response to loading similar to soils, hence soil mechanics principles will be applicable. Simultaneously, a categorisation of different types of pre-treated wastes was carried out by some of their physical and geometrical properties. The results were interconnected into a newly developed waste classification system, which allowed an assessment and comparison of their geomechanical and flow properties, and predict to some extent their future behaviour in landfills. About a third of the MBT samples by mass comprised a matrix (fine material of <5 mm) into which the larger particles were embedded. The large 2D elements (mainly presented by plastics, glass and metal foils) will play an important role for stability and flow transportation, taking about 25% by mass. On one hand, they will have a reinforcing effect but on the other, they will modify, divert, or impede the flow paths in the waste which may result in reduced permeability or preferential flows. Highly compressible synthetic materials were also used to simulate the deformable materials in landfills (such as hollow 3D elements). They tend to embed into each other and form a horizontal highly dense structure which reduces significantly or completely the volume of voids. In large scale, this will lead to modified or blocked the flow paths and hence reduce the flow rates and impede the flushing of contaminants in landfills. Compressible particles reach their maximum compressibility at certain stress thresholds and progressively change their shape from 3D compressible to 2D incompressible. At the end of the study, a simplified phase relationship model was suggested, considering changes in the solid phase due to both particle compressibility and decomposition. The applicability of the conventional effective stress theory on highly compressible materials was questioned as well

Drying of faecal sludge from VIP latrines through a medium infrared radiation process

In order to treat faecal sludge from ventilated improved pit (VIP) latrines, eThekwini Municipality (Durban, South Africa) developed an infrared dryer, ‘LaDePa’ (Latrine Dehydration Pasteurization). Parameters that influence its operation were investigated using a laboratory-scale replica of the full-scale machine. For this, faecal sludge collected from VIP latrines was pelletized and dried under different operating conditions. Drying curves were obtained by plotting medium wave infrared intensity (MIR), height of emitters above the belt, air flowrate and pellet diameter against the residence time. These curves were then used to determine the drying rate and energy consumption. The results show that the drying rate increased while the energy consumption decreased by increasing the power of the MIR emitters and decreasing the size of the pellets. For example, the drying time to get a moisture content of 0.8 g water/g dry solid was shortened from 27 to 6 min while the energy consumption for this reduced from 1.5 to 0.8 kWh after increasing the MIR power from 1.5 to 3.3 kW. Similar drying curves were obtained by varying the distance between the pellets and MIR emitters, and adjusting intensity of the MIR radiation to obtain the same temperature in the drying zone. It was also observed that higher airflow rates enhanced mass transfer rates, but led to a cooling effect. No effect on the drying rate was observed after pre-drying the sludge or adding sawdust. The study shows that for the process to be efficient, the MIR intensity should be high enough for fast drying to occur (T ≥ 150°C), but without causing thermal degradation (T ≤ 220°C). The height of emitter above the belt and the pellet size should be as small as possible (8 mm); airflow rate should be optimised to maximize the mass transfer rate and minimize the cooling effect

‘LaDePa’ process for the drying and pasteurization of faecal sludge from VIP latrines using infrared radiation

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. Keywords: Faecal sludge, Rheology, Extrusion, Drying, Infrared, Pasteurization, Reus

A pilot-scale microwave technology for sludge sanitization and drying

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