Sanergy recently piloted a prototype mobile waste transfer system (mWTS) in Nairobi’s urban slums to figure out an easily deployable waste-management solution for emergency response scenarios. The challenges of waste collection in urban slums are similar to those faced by responders in rapid-onset emergency situations, so the conditions are ideal for testing the efficiency and scalability of waste transfer solutions.
After developing alpha and beta prototypes in 2015, we launched a five-week pilot of the beta prototype earlier this year in Nairobi’s Mukuru slum. With an area of about 3 square kilometers, Mukuru is home to 500,000 people. Throughout the pilot, the testing team collected detailed data on time and resource requirements for each step of the collection and transfer process, to determine the feasibility of applying this solution in emergency scenarios. We are still analyzing the data from the pilot, but we already have a few early learnings to share…
1. Weight limits are tricky to determine
The mWTS has the volume to hold up to 300 liters of solid waste and up to 100 liters of liquid waste. However, the amount of waste at each toilet varies very widely and often unpredictably on a daily, weekly, and monthly basis. Allowing for a volume buffer based on this variability means that maximum efficiency will be difficult to reach without over-filling the mWTS. Because the density of urine is greater than that of solid waste, fluctuations in liquid/solid ratios may cause the mWTS to fill beyond the weight capacity of available transport and lifting methods.
2. Urine is difficult to manage in a mechanized way
The corrosiveness of the urine had a more significant impact on the mWTS than we had anticipated. The liquid waste we collected corroded the metal fittings of the containers and left deposits that impeded the proper functioning of the valves. In addition, there is a tendency for the cover material used for our solid waste to enter into the urine stream, which can cause further clogging. Plastic valves would prevent corrosion, but hard deposits and particles in the urine pose a difficult challenge that can be mitigated by minimizing the number of moving parts in the system. Finally, the urine bladder in the mWTS was designed to accommodate different ratios of solid/liquid waste collected, which turned out to be an unnecessary accommodation in our context.
3. The mWTS process was easy to learn
During the pilot, our collection teams found the mWTS easier to use than our usual method of waste collection. Since most of the neighborhoods we serve have narrow paths that are difficult to navigate with cars or trucks, our normal method of waste collection has two-man teams taking hand carts, loaded with empty cartridges, from the collection centers to each toilet on a particular route, removing the solid and liquid cartridges from each container, and replacing them with empty ones. Once their collection route is complete, the team returns to the collection center with a handcart of full waste cartridges. These cartridges are then emptied into larger containers, which are trucked to our processing site.
Each day, the teams would set off from the collection centers with the empty mWTS. At each toilet, they would empty each toilet’s cartridges into the mWTS and return the empty cartridges to the toilet. When they finished their collection route, the teams would return to the collection center, where the mWTS would be loaded directly onto a truck and taken to our processing center. The clear benefit here is that although it is a new technology, the use is so similar to the current processes that it is intuitive for our collections team and could easily be implemented at a large scale. The comparative advantage of the mWTS over the current processes is that it minimizes the number of times the waste is transferred between containers: once the waste is out of the toilet, there is zero exposure until it is being treated.
4. We could better accommodate weight variations
The final takeaway was around ensuring a workable weight balance in the prototype. In the handcarts we use, it’s easy to properly balance the load for easy transport, since the cartridges can be placed anywhere on an open platform. With the current mWTS design, on the other hand, the weight balance is determined by the ratio of solid waste to liquid waste, which changes daily and especially toilet to toilet. In order to address this, future designs could redistribute waste containment within the mWTS or use adjustable axles to better accommodate weight variations.
Based on our preliminary learnings, we believe the mWTS could be deployed on most of Sanergy’s current collection routes in urban informal settlements. The impact of using the mWTS for our routes depends on the toilets: In areas with a large number of low-usage toilets, we could collect from many more toilets with one mWTS than with a handcart, while in areas with high-usage toilets, the human resources needed for collection would remain about the same as Sanergy’s current system.
The main benefit of deploying the mWTS on collection routes is in reducing the downstream re-consolidation, transportation, and management steps currently required to properly handle our cartridges. The only areas where the mWTS wouldn’t work as well are those where the distance between toilets is too great to access efficiently on foot, which are currently served by trucks.
Our trials indicate that the mWTS would also be a workable solution for the safe and efficient transport of waste from emergency areas. Our beta prototype is flexible enough to use in a variety of disaster scenarios and logistics networks. It would feasibly work across commonly available transportation methods (handcarts, pickup trucks, and flat-bed trucks) and a variety of collection schedules (daily or weekly).
We are grateful to GOAL, The Humanitarian Innovation Fund, and elhra for their support in helping us develop new solutions to tackle this critical issue for at-risk populations.
Sanergy, March 2016
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