This week I continued to explore the acceptability and suitability of evapotranspirative fields for water drainage from the waste. Although overflow and contamination during the monsoon season is a concern, we believe it can be tackled by ensuring quick drainage of the topsoil layers to ensure the capillarity action from bottom to the top. We are now working on consolidating our finding and recommendations into a comprehensive report. Our discussion with Tim this week also threw some light on the lessons we were learning through the process of trying to find solutions to sanitation. We noticed that our approach was to find one cure-all solution that would take care of hygiene, safe disposal as well as a profitable waste recovery model, rather than an adequate alternative to open defecation. Although overwhelming, this resulted in the uncovering of all the possible bottlenecks to the technologies we researched, but also in our gaining a deeper understanding of the many layers of the sanitation problem.
This week we were able to meet with Tim Burke and discuss our current design options and attempt to hammer out some of the problems we’ve encountered so far. One design we spent a considerable amount of time on was the biogas reactor. As has been mentioned in previous posts, one of the challenges we’ve faced is what to do with the sludge produced in the biogas generation process. We had been largely operating on a model with a single holding tank, whether baffled or unbaffled. Tim suggested that we consider a two-tank system. As far as construction is concerned, the design would be similar to the septic tanks currently being constructed by the program. Because of the similarity to the existing design, the cost of construction would probably be comparable. The primary difference would be that the first tank would generate biogas and the second tank would hold the sludge to increase the residence time. Like a traditional septic tank, it would have to be emptied periodically. We also further examined the toilet design in an attempt to reduce the amount of water entering the digester with the solids. However, we haven’t yet been successful at coming up with a method that siphons off a portion of the water (~25%) that is also compatible with the local toilet design.
This week we focused on putting together all the information we have learned over the past weeks and figuring out whether there was some best solution or at least top contender for us to recommend. We also returned to the design of the toilet itself rather than the water treatment issue. Our discussion with Tim was extremely helpful in that it reminded us of our goals, and that maybe our goals were far too large. We had been hoping to find both a solution that would give people a concrete product from the waste, in order to help incentivize them to adopt the toilets, and also were requiring it to be completely safe and remove all pathogens. However, Tim reminded us that our solution simply had to be a reasonable improvement on the current situation, and that a magical cure-all may not exist. Therefore we started to look back at our information and progress in a new light. So far, we have a tentative design for the biogas toilet, and our main issue is how to get rid of some but not all of the water, since the ratio will still be somewhat off. We have been able to basically eliminate composting, as it is a solution that often sounds good at first glance and in practice usually doesn’t work. Finally, we have not yet eliminated biochar, but we still need to look into whether it is energy efficient and whether it is even useful for the soil.
For week 8, the EPC team had focused on determining the exact content of the recommendations that would be made in the final report. This included deciding on the types of waste management methodologies that could be usefully utilized on the field, and therefore the best-practice implementations of these methodologies.
In the group’s opinion, composting still seems to present problems with pathogen extermination and a reduced efficacy of deactivation that can be achieved with human waste. Therefore, it is unlikely that composting can be the most effective solution at the scales that Parishudh would work on.
Similarly, biogas also presents interesting challenges in balancing the ratio of solid and liquid content. Another challenge was to make enough biogas so that the entire system could be net income-positive. However, we have realized that the end-goal of profitability may not be as crucial as imagined, and iterative improvements should first deal with the proper treatment of the waste rather than simply concentrate on income generation. To this effect, we have moved on to not only look at biogas plants with renewed interest, but also to another potential application in biochar.
This week has been very productive in terms of model and design of the toilet, specifically the biogas plant. We have currently been able to model the biogas plant onto a 3D modeling program and subsequently show our design to Tim Burke. Burke was able to give some feedback on the biogas, having built some himself. However, he had not built any for human waste processing. We also created 3D models for the leachate/evaporation system that we were designing, and also showed it to him. His feedback was most helpful.
He was most enthusiastic about the biogas plant, since in the case that it was a “failure” (in the wsense that it wouldn’t produce biogas) it would act as a waste processing system and as a two pit septic tank. Although we really would like the biogas to work, it is a reasonable argument.
Our future goal for the biogas is to begin to try to optimize how it would function. We would need to optimize the content input, as well as create the awareness level so that they are able to understand what goes into the biogas plant. Obviously, on a elemental level, we know the basic compositions of what should be input into the biogas plant, however, we need to put this into layman’s terms so that they know what ratio of what stuff should be put into the biogas plant.