This is an F diagram. It is called that because there 6 important "F" words covered in the diagram. They are feces, fingers, flies, fields, food and fluids. Do you know what these 6 F words have to do with treatment objectives? You'll learn about that in this module. Following this module you'll be able to name different treatment objectives, relate health and environmental impacts to these treatment objectives and understand that there are different levels of appropriate treatment depending on end-use of treatment products. The F diagram depicts fecal oral routes of contamination which is what we need to prevent to ensure public health. Fluids, if excreta contaminates drinking water, fields, if excreta contaminates food crops, flies, as flies are vector. They are attracted to both feces and food resulting in cross contamination and fingers; not adequately washing your hands before touching food or eating. Our number 1 goal in Sanitary Engineering and Fecal Sludge Management is always the protection of public health. Protection of environmental health is also very important and as shown in the F diagram, these first 2 goals are often very closely linked together. If excreta is contaminating the urban environment, then it is a public health risk. A third goal that is important to meet whenever possible is resource recovery from treatment products which is also tied closely to the first 2 objectives. Resource recovery is covered in more detail in other modules. If it's not possible, then safe disposal is a requirement to ensure the first 2 goals. To achieve these goals during treatment processes we focus on 4 main treatment objectives: The first one is de-watering. Fecal sludge is typically over 90% water so de-watering to seperate the liquid and solids is very important. De-watering is the removal of more easily separated water like wringing out this dripping wet towel whereas drying is the further removal of water that is bound with the solids; like then hanging the towel on a laundry line. De-watering is important because water is heavy and expensive to transport. Prior to effluent discharge into the environment, solids and liquids need to be seperated to ensure adequate treatment can take place for public and environmental health and de-watering is typically required for resource recovery. Also important is stabilization. Stabilization is the process of readily degradable organic matter being converted as a result of biodegradation to more stable complex molecules. Here we see that happening in composting with heat being released during the active decomposition phase. This is important for treatment as readily degradable organic matter consumes significant amounts of oxygen during degradation. For example, the classic Streeter-Phelps equation illustrates what happens if waste water is discharged to a river with high concentrations of BOD resulting in the dissolved oxygen in the river being consumed which can gradually be recovered with time or distance travelled in the river until readily degradable organic matter has been consumed and there was no longer an oxygen demand. Why do we care about oxygen demand? Because aquatic organisms need dissolved oxygen to live. Stabilization also results in nutrient stabilization and odor reduction. Also important is nutrient management. Fecal sludge contains nutrients which can be beneficial if harnessed for resource recovery but if not managed properly, result in environmental contamination. Environmental impacts from nutrients include eutrophication and algal blooms in surface waters and contamination of drinking water. In pathogen reduction, to revisit what we learned from the F diagram fecal sludge contains large amounts of micro-organisms mainly resulting from feces. These micro-organisms can be pathogenic and exposure to untreated fecal sludge constitutes a significant health risk to humans either through direct contact or indirect exposure. The transmission cycle of pathogens can be interrupted by putting barriers in place to block transmission pathways and prevent cycle completion. The appropriate level of treatment will depend on the resource recovery or disposal option. For example, drying fecal sludge to use it as a fuel in combustion, our number 1 objective is to de-water to increase fuel potential and in this case pathogen reduction is not so important as the sludge will be incinerated. Whereas on the other hand if treatment products are to be used as soil conditioners in agriculture then pathogen reduction is an extremely important treatment objective. The first barrier for beneficial use is provided by the level of pathogen reduction achieved through the treatment of fecal sludge. A selection of further post-treatment barriers may include restriction of use on crops that are eaten raw, withholding periods between application and harvest to allow pathogen die off, drip or sub-surface irrigation methods, restricting worker and public access during application and use of personal protective equipment and safe food preparation methods such as thorough cooking, washing or peeling. When considering risk of infection, all potential exposure groups should be accounted for which can be broadly categorized as workers and their families, surrounding communities and product consumers. For more information on a multi-barrier risk based approach to ensure adequate protection of public health I recommend the WHO guidelines for safe use of waste-water, excreta and grey-water in agriculture and aquaculture. The Sanitation Safety Planning Manual and the Sanitation Safety Planning Module in Sandec's Mooc on sanitation systems. Monitoring to ensure treatment objectives have been met is an important part of ongoing operations and maintenance. In summary, in this module you learned about treatment objectives of de-watering, stabilization, nutrient managment and pathogen reduction. Why they are all important for the protection of human and environmental health and that appropriate levels of treatment will depend on the intended end-use. Thanks for joining. See you next time.
