What type, and how much of solids, organics, nutrients and pathogens are included in faecal sludge in your city? This is a very important question to ask for a selection of collection technologies and the design and operation of treatment plants. In this module, we introduce such relevant characterization parameters. Following this module, you'll be able to explain the importance of characterization, select relevant characterization parameters, and choose existing resources for characterization. Characterization of sludge can be qualitative, for example, by monitoring the sludge color that is discharged at a treatment plant. The color is different from brown or black, as shown in this video, which could indicate an industrial contamination. Such qualitative characterization is important for treatment operation but does not replace quantitative characterization. It is always required for the design, operation, and monitoring of treatment plants. Missing or unreliable information on characteristics commonly leads to poor performance or complete failure of collection and treatment services. Let's consider, for example, this settling-thickening tank: one technology for solid-liquid separation that is discussed in a separate module. Among others, a settling-thickening tank is designed based on an amount of solid that requires treatment. On the one hand, underestimating a solid's concentration in the design process will likely overload the technology during operation and result in poor effluent characteristics that can affect subsequent treatment technologies, and ultimately, the discharge concentrations. On the other hand, overestimating solid concentrations will lead to the construction of tanks that are too big which wastes financial resources, and also influences its operation. Quantitative sludge characterization requires laboratories with equipment and technicians, as shown at a treatment plant here, in Dakar in Senegal. As these laboratories and their operation incur costs, characterization parameters should be carefully selected to answer one, or several, specific questions. These questions could be, for example: What is an appropriate collection technology? What are design parameters for treatment technologies? Or does the effluent from a treatment plant meet legal discharge limits? To answer these questions, it is helpful to group characterization parameters that are relevant for collection and treatment. Parameters that are relevant for resource recovery, for example, compost, are discussed in another module. For the selection of sludge collection technologies it is important to know whether the sludge can be pumped. Therefore, solid parameters such as total solids, total suspended solids, and viscosity are important. In addition, it is important to know the amount of solid waste as it can clog and damage collection equipment. Characterization parameters that are relevant for different treatment technologies can be grouped according to their treatment objectives. For technologies designed for solid-liquid separation, solid parameters such as total solids, also called TS, and total suspended solids are important. Total solids are, for example, important for the dimensioning of drying beds and other solid-liquid separation technology, shown here at a faecal sludge treatment plant, close to Bangalore, in India. Other important parameters for solid-liquid separation technologies include the sludge volume index, a metric to estimate solid and liquid separation of faecal sludge, the amount of solid waste, oil and grease and grit and sand. Removal of grit and sand and solid waste is often the first treatment step following discharge, as shown here at a treatment plant in Kampala in Uganda. For technologies designed for sludge stabilization total volatile solids, also called TVS, the chemical oxygen demand, also called COD, and the biochemical oxygen demand, also called BOD, are important parameters. The BOD and COD are, for example, important for the design of waste stabilization ponds that can be used for treatment of effluents from solid-liquid separation technologies, such as settling-thickening tanks, or drying beds. The ratio of BOD and COD, and TVS and TS, can also be used as an indicator for the relative biodegradability of organics and faecal sludge that affects biological treatment processes. For technologies designed for nutrient management, ammonium, nitrate, nitrite, and phosphate are important parameters. Pathogen inactivation is ultimately the most important objective in faecal sludge treatment. Instead of measuring individual pathogens, indicator organisms are used to provide a measure of pathogen concentrations and inactivation during treatment. Examples of indicator organisms are viable helminth eggs, and E-coli. Helminth eggs are commonly used as an indicator for pathogens in the solids. For example, in dried sludge, or a compost, as shown here in these pictures, at a faecal sludge treatment plant in San Jose in Costa Rica. In contrast, E-coli are important for the liquid fraction, for example, from settling-thickening technologies, drying beds, or the effluent from a faecal sludge treatment plant. Other important general characterization parameters include the pH, the temperature, and the electric conductivity. In reality, a combination of these parameters is selected for design, operation, and monitoring of different treatment technologies, and an entire treatment plant. This could be during research, or to collect characteristics for treatment design. In this picture, one of my colleagues is collecting faecal sludge samples for a characterization study in Kampala. All during operation of a treatment plant, as for this treatment plant in Kampala, where samples may be collected at in flow, before and after treatment technologies, such as the settling-thickening tanks and drying beds. To assess their performance only effluent from treatment to assess the effluent characteristics meet discharge limits. You might be overwhelmed by the number of characterization parameters presented here. For implementation of characterization in your city, you can find more information on sample collection, preparation, protocols, and considerations for quality assurance and control In these Sandec reports that can be downloaded for free from our website. Standard operating procedures are also available from the website of the Pollution Research Group at the University of KwaZulu-Natal in Durban, South Africa. In this module, we introduced you to characterization parameters that are important for collection, design, operation and monitoring of treatment plants. These parameters are measures of solids, organics, nutrients and pathogens in faecal sludge. We hope that you explore the additional material provided and find it helpful for faecal sludge characterization in your city.
