How to deal with trash in pits - (Trash exclusion, Laws, Enforcement, Other...)


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  • FrancisdelosReyes
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  • I am a professor and environmental engineer at NC State University, USA. I am interested in wastewater treatment, WASH, microbial ecology.
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How to deal with trash in pits - (Trash exclusion, Laws, Enforcement, Other...)

Below is a summary of our new approach for dealing with trash/rubbish in pit latrines- LEAVE THEM BEHIND using active trash exclusion. We presented a new technology, called the Flex-X in Chennai at FSM4. We will describe the technology in a subsequent post

Options for dealing with trash during pit emptying
The main challenge in mechanized pit emptying is dealing with trash. Trash, such as large pieces of clothing, rope-type materials, bottles, shoes, etc., can clog any tube-based mechanical approach, if the material is bigger than the tube. Note that the tube is limited to around 10-12 cm in diameter, if it is to access through the squat holes or the pedestal. Trash clogs other human-powered machines such as the Gulper I and II.

There are several approaches to deal with trash in pit latrines. Most pit emptiers who use a machine either accept clogging as something that occurs, and try to minimize the downtime due to clogging. Others, such as those in Blantyre, Malawi, use a “fluidization” method, followed by manual “fishing” to remove the trash using manually operated hooks. This approach is messy and time consuming. “Fishing” can take hours, even half a day, while the subsequent pumping by vacuum pumps take just minutes (Chirwa, Personal communication). The trash in pit latrines is covered in faecal material, and comes in many forms and sizes, making manual removal unhygienic. A third approach is to “macerate” or somehow reduce the size of trash before they enter the hose or tube. To our knowledge, there has not been a single successful application of this technology in real pits. This is because high rotational speeds and a large amount of energy would be needed to chop up material such as cloth, or trash like jeans, shoes, or bottles. A fourth approach is to use screens to minimize clogging. Screens can increase the time between complete clogging, but will still need to be cleaned periodically.

The case for trash exclusion
Leaving the trash behind in the pit avoids all these issues. There is no clogging, no fishing, no fluidization needed (which requires addition of large amounts of water), and no messy trash outside the pit that needs to be handled and disposed. There is no need for additional energy for chopping or macerating trash.

What happens to the trash left behind? One option is to leave it there. This will decrease the subsequent working volume of the pit. Thus the homeowners will need more frequent pit emptying, which will increase their costs. The other option is for the homeowner to request removal of the trash left behind. Since the contract is for removal of faecal material, this additional service should also be additional cost to the homeowner. In both cases, the higher costs for dealing with trash will lead to the change in behavior that is needed- for users to stop using the pit latrine as a trash disposal system. It should be noted that the second option – subsequent removal of the trash that was left behind- will be likely a manual process, until a mechanical option is developed. The costs for removing the trash should be a function of the amount of trash in the pit, again directly incentivizing behavioural change.

Separating the trash from faecal material makes downstream treatment of faecal sludge easier. Current FS treatment technologies, such as anaerobic digestion, composting, fermentation, black soldier fly, vermicomposting, and supercritical water oxidation, all require the pre- removal of inorganics such as plastic, clothing, glass bottles, metals, etc. Technologies such as LaDePa would also benefit if trash were not present, as it would remove the need for the trash removal step that requires energy. If only faecal sludge needs to be treated, then needed steps, such as pathogen inactivation, become more economical and effective, as the volume of material to be treated is reduced. Other reuse options become more feasible. These include conversion technologies to energy or high-value materials (such as long-chain acids or biofuels). Note that the cost of removing trash is already included in the pit emptying step, and eliminated from the treatment step.

Separating the trash will lead to efficiencies in collection, since faecal sludge volumes would be lower. The separated trash can be collected separately and transported to a landfill or other trash management facility that is possibly in a different part of town. Alternatively, the trash can be disposed of in a trash pit within the homeowner’s property. In any case, the trash management system can be optimized to lower costs of dealing with trash.

The removal of only faecal material during pit emptying, and leaving the trash in the pit, is a new approach that has inherent advantages. It is realistic, solves many pit emptying problems, and makes downstream handling and treatment of faecal sludge and trash easier, more hygienic, and more cost-effective.
Francis de los Reyes III
Professor/TED Fellow
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