The design process for the Sanergy EcoSan Toilet began with an intense brainstorming session at the MIT Sloan Entrepreneurship Center throughout the month of June with revisions continuing well into the team’s time in Kenya.
Sanergy’s design goals were generally to create a toilet that was both economical and socially sustainable; and specifically for the pilot to 1) create a low-cost building solution under US$500, 2) design an efficient system for the ease of construction, and 3) provide a low-maintenance system for ease of operations. It was essential that the units be highly cost effective in order to make personal ownership attainable to entrepreneurs, yet not at the expense of its ability to attract and retain paying customers over its life cycle.
In order to reach the largest population of users possible the model needed to be sustainable, scalable, and financially viable. Cost-saving techniques drove the team to consider using a building technique not yet used in Kenya called ferrocement. The structural components of the toilet were constructed of precast cement panels reinforced with chicken wire; just 1.5 inches thick, the unit mass was greatly reduced from that of a typical mortar and brick construction. Adorned with readily available bush-pole and corregated sheet roofing and doors, then finished with off-the-shelf collection containers and squat pan the design was economical to produce and maintain.
The precast process helped to control quality and cost of the panels. (Look for a post coming soon about the mold-making process.) Casting at a central location helped to ensure proper curing and limits material waste by using trained labor. After scale-up there would be significant benefits to buying material in bulk; including, economies of scale and flexibility to ride-out price hikes. Not fully developed in the pilot, the unit was designed to be a flexible, modular design that could be grouped to share walls and foundation posts, further saving on material.
Easy assembly: Precast panels, interlocking joints, one day assembly, limit skilled labor
Fast and easy assembly reduced the construction cost and time. It was essential to getting the business up and running as quickly as possible. Precast panels made for a fast assembly and reduced the need for skilled labor on-site. Because the units were fabricated off-site, the pieces were brought in and assembled for use in one day.
The design aimed to preempt elements of construction and maintenance into the cast forms. The corner panels were designed to receive the wall panels, which was received by the monolithic floor plate and roof ring which locked the whole assembly together without using fittings. Tongue and groove connections relieved the need for on-site mortar and resolved concerns of using typical screw connections which would likely have exposed the chicken wire to water penetration and compromised the structure.
Using a the panel system reduced the area required for construction; only a 3 foot by 5 foot clear area, with no need for formwork or material storage, spaces that had been written-off in the past for being too small were reconsidered. Also, rather than the deep pits commonly associated with latrines in the settlements, the Sanergy EcoSan Toilet used shallow foundation tubes which eliminated the need for deep digging and stable soil.
Precast concrete combined the benefits of high durability with low maintenance. Because all of the sealants and hardeners were integrated into the floor surface it requires little to no maintenance. Many design considerations were taken into account to promote perceived cleanliness. Plasticizer, water-proofer, and fiber reinforcement added in the mix the panels were cast with interlocking joinery so they were ready-to-use straight from the mold, without any further plaster, paint, or mortar required. Filleted corners along the low-wall of the floor plate and in the L-shaped corner panels helped to eliminate crevices that would normally collect dirt. A slope was molded into the floor surface to promote wash water flowed toward the drainage hole in the floor.
Kenya proved to be full of unforeseen challenges which required the team to remain adaptive. During the construction of the pilot some additional reinforcement was added on-site due to time constraints on mold edits and cast curing. Also paint and plaster was added because of discoloration in the panels due to casting conditions. These conditional and aesthetic issues will be worked out in the future to further reduce the cost of construction from the pilot model. Until then the team will continue to monitor the maintenance procedures of the pilots and train local youth groups on operations.