Laboratory Design Process to Increase Dessication

Faecal sludge desiccation is a function of the operating temperature and ventilation of the system. Ventilation is assumed to occur due to an intermittent convection current that is induced through the system’s plenum (“black chimney”) which is heated by the sun. There is potential for composting to occur within the system’s raised pit. The heat from the composting pile will contribute to the evaporation (and volume reduction). It also induces a convection current contributing to ventilation potentially reducing odours. Before these factors are tested in a complete parametric study, a preliminary assessment of passive desiccation rates is needed to determine the baseline rates that can be achieved.NEW_LINENEW_LINEThe goal of reducing the faecal volume by 75% has cost saving implications but the challenge is to keep the cost of installation, operation and maintenance down.NEW_LINEThe potential of the Aerosan latrine has been demonstrated through initial field trials and empirical evidence of faecal sludge desiccation, further optimisation of the system’s design is warranted. Desiccation rates of faecal sludge under different operational conditions (temperature, humidity, ventilation rates) need to be determined. The characterisation of this variable will allow for a more rational design. This project seeks to address this issue through a collaborative effort between the University of Victoria (UVic), University of Swansea and Aerosan.NEW_LINENEW_LINEThe overall goal of this research project is to conduct a lab and field-based determination of fresh faecal sludge desiccation rates in varied conditions to optimise the design of the enhanced passive ventilation. The approach is iterative in which data from literature and field observations (SO1) will feed initial laboratory experiments on desiccation rates (SO2 &; SO3). These will be scaled up and used to optimise the latrine design (SO4).NEW_LINENEW_LINEField testing will determine initial experimental parameters by closely monitoring the passive ventilation that is achieved and the sludge volume reductions that are attainable. Performance of the ventilation within the system will be monitored with airflow measurements coupled with temperature and other environmental operating conditions (humidity, prevailing wind direction/velocity). These measurements will be made with dataloging instruments (hotwire anemometers and temperature probes) based on field methodologies developed for pit latrine ventilation evaluations Ryan &; Mara (1983). Sludge volume reductions will be determined through lasers to measure differences in sludge level height through time, as utilized in pit latrine sludge level determinations Bakare et al. (2015). Such measurements will be compared to user frequency as well as the vault emptying frequency.NEW_LINENEW_LINEAn experimental reduced-scale latrine drying chamber will be fabricated (SO2). This bench-scale chamber will allow for a parametric study of desiccation rates (SO3) of triplicate samples subject to a variety of relevant simulated operating conditions (ranges to be identified by the activity SO1), temperature, relative humidity, and ventilation rates. Each of those will be tested at different levels. A subset of the total possible combinations will selected for testing using a partial factorial experimental design, to be generated using the rsm package in R (Lenth 2010, R Development Team 2016). Such combinations will be tested in a randomized sequence, the tests will be replicated in selected discrete runs of tests performed in different sequences.NEW_LINENEW_LINETemperature is controlled in a temperature programmable incubator. Relative humidity is controlled by passing compressed air through solutions of different water dilutions of glycol. Firstly, desiccation rates under “static” (no ventilation) drying conditions will serve as a baseline “control” for comparison. Subsequently, ventilation rates will vary so as to determine a range of “dynamic” conditions representative of field conditions as well as maximum theoretically attainable passive ventilation rates through design configurations. These parameters will be monitored with data-logging instrumentation. Faecal loading rates will initially be tested under a “single” loading regime in which the desiccation of a single sample is followed over a 5-day period. These trials will be followed by “live” loading experiments in which fresh faecal matter will be added to the setup, simulating multiple latrine users. This will provide a highly resolved dataset that will allow for the interpretation of results with statistical robustness.NEW_LINENEW_LINEDesiccation rates will be calculated based on closely monitoring moisture content, total solids, and total volatile solids of samples being subject to treatment in. Such parameters will be measured using protocols validated by other studies on faecal sludge characterisation (Bourgault et al 2017; Gold et al. 2017). Airflow will be measured and other parameters of relevance will also be closely followed (pH, COD, NH3). These experiments will also serve to study the fate of microbial indicators (bacteria, viruses) during selected desiccation experiments to determine any other potential advantages of an augmented drying rate by passive ventilation.NEW_LINENEW_LINESelect experiments from SO3 will be scaled up (SO4) to verify scaling up effects to predict performance efficiencies of full-scale latrines. Results from bench-scale and scaled-up trials will be modelled in collaboration with Swansea University (UK) using discrete element analysis and computational fluid dynamics modelling to increase understanding of airflow within the system and how it can be designed to maximise desiccation. Once the model is set up and accurately predicts controlled models, then a number of scenarios will be run to optimise designs and conditions. This will inform field tests which will also serve to verify the models and confirm their usefulness.NEW_LINENEW_LINEThe output of the project will provide us with design parameters further supporting the development of a training manual and module to train humanitarian aid agencies in the construction of the toilet system for difficult to serve areas (high water tables, floodplains).NEW_LINENEW_LINEAerosan has arranged with the University of Malawi to construct and test the system in Malawi using local materials. Once we have the results from UVic and Swansea, our builder will spend time in Malawi training local tradespeople and students, who will carry out subsequent testing.NEW_LINENEW_LINEDr Dorea, the principal researcher has moved from the University of Laval (Quebec) to the University of Victoria (BC).