If I asked you how many fish were in this lake could you tell me? Even more complicated, what if I asked you how many of each type of species there were? It's pretty difficult since you can't even see them. This is a similar problem that faces us with the quantification of fecal sludge. Following this module, you should understand the importance of reasonably accurate estimations for quantities of fecal sludge on a city wide scale. Be able to explain the difference between produced, accumulated emptied, dumped, or discharged fecal sludge and explain methods that could be used to estimate quantities of fecal sludge. To understand why quantification is important let's go back to our engineering design approach where to select and design technologies we first need to know treatment objectives so we know what we are designing for and then we need to know what is coming into the treatment plant so we can appropriately size them. So quantification is very important for the management and treatment of fecal sludge. But how can we do this? For waste water it's relatively straight forward to make assumptions as it is typically know how many household connections there are to a sewer and average per capita water usage. But for fecal sludge they are typically not records of the existing situation, and so we do not know how many on-site sanitation systems there even are or how many different types of containment technologies like septic tanks, cesspits, lined or unlined pit latrines how many people are using them, how frequently they are emptied and other factors such as usage patterns that affect characteristics. We need to think about how to start making good estimations now for the design of infrastructure, but also consider what type of actions need to be put in place so that in the future we can even more accurately assess the management need. Starting with the current situation let's first think about the different places in the service chain where fecal sludge could be quantified. Number one is the amount of excreta that's produced which is not fecal sludge but can be readily estimated based on the literature. Number two is the amount of fecal sludge that's produced So what is going into containment along with excreta like cleansing material or flush water and can also be estimated if you know enough about types of containment and water usage patterns in the city. Number three is the amount of fecal sludge that actually accumulates in containment technologies. For the development of the fecal sludge management on a city wide scale, number three is the number we want to know, but it is too difficult to calculate because it is a rate equation that varies depending on lots of different factors, such as inflow and infiltration rates of biological degradation which are also affected by temperature, moisture, Ph redox potential, etc. Number four is fecal sludge that is emptied but not collected. So for example when people break a containment and let it drain directly out into the environment. This is very difficultly to estimate but mostly we just want to eradicate it. Number five is the amount of fecal sludge that is collected but not delivered to treatment. This could be manual or mechanical emptiers. Reasonable estimations can be made if dumping is concentrated in a few areas or if the current number and operating capacity of trucks and emptiers in a city is known. And number six is what we want to see. Fecal sludge that is collected and delivered to a treatment plant or legal discharge location. This should be very easy to estimate based on operating records. The reason why number three is so important is that it tells us the full magnitude of the problem so we can develop sustainable management. For example, if a treatment plant design is based on volume estimates for the current demand for example current emptying practices in a community what is going to happen when a treatment plant opens? The current demand will immediately increase because now there is a legal and convenient option for the disposal of fecal sludge. As it's frequently been observed, this means as soon as the treatment plant opens, it will already be over capacity. This is why it is important to evaluate the current demand but also the future demand, which is based on the total fecal sludge accumulation. So if we cannot precisely calculate rates of fecal sludge accumulation in containment technologies, how could we estimate them with the current lack of records? One way could be to survey a select representation of the city wide distribution during emptying operations. You could ask the household questions like when did they last have their containment emptied how often do they have it emptied how many people use it, what is the containment volume was it full, was it fully emptied? You could simultaneously ask the emptying service provider if they fully empty the containment if their truck is full or barrels with the manual emptier the truck volume and emptying practices like did they add water while emptying and how much. Based on the possible answers with the emptying frequency you can then estimate accumulation rates. Depending on the infrastructure in your city or community estimates like this will be easier or more complicated. For example if a community is all on septic tanks built at a similar time with a similar design with regularly scheduled emptying and equitable water usage then sludge accumulation could also be estimated based on factors such as influent COD and hydraulic retention time. Or in a small town with similarly sized pit latrines and usage habits, like whether or not there's household water estimates will also be more similar. Other difficulties with estimating future demand for fecal sludge management include rapid urbanization and rapidly growing cities commuting populations, meaning many cities actually double in size during the day with people who come in for work and another important consideration that people frequently do not consider is non-household sources of fecal sludge from commercial enterprises like restaurants, hotels, public toilets toilets for employees of factories, the commuting population depending on the context this could easily be half of all the fecal sludge that is delivered to treatment. What can be done to improve estimations of quantities in the future? The implementation of data management. For example, instituting a GPS database of all existing on-site technologies and maintaining GPS-based records of how often and the volumes when they are emptied. And one more very important point. Quantities of fecal sludge can not be considered without simultaneously considering the characteristics because as we know, fecal sludge is highly variable. This is especially important when designing treatment plants as on a mass balance basis, the concentrations can have as much to do with loading of treatment plants as volumes do. Setting up a sampling plan for fully understanding city-wide characteristics can be just as or even much more complicated than quantification. Some of our unpublished research indicates that one way to do this could be through designing sampling plans based on spatially available demographic data. So stay tuned for further results. In summary, in this module you've learned about the importance of estimating quantities of fecal sludge for designing sustainable management options. The differences between produced, accumulated, emptied, dumped and/or discharged fecal sludge and possible approaches that could be used for estimating quantities of fecal sludge. Thanks for joining, see you next time!
