Development of trash exclusion for mechanized pit latrine emptying

Abstract

Nearly 1.8 billion people use pit latrines for basic sanitation, and approximately 600 million kg of feces and 2.1 billion kg of urine are deposited in pit latrines every day. Due to lack of access to mechanized emptying services, or challenges such as the presence of trash in pits, most latrines are emptied by hand. Alternatively, “fishing” (removal of trash using manual tools) is used prior to mechanical emptying. Both approaches are time consuming and expose workers to pathogens. To develop a safer method of emptying pit latrines, we explored mechanized trash exclusion, allowing the removal of fecal sludge in the presence of trash. Three exclusion mechanisms: screening, deflecting, and clearing, were investigated. The effects of varying design features, such as the diameter of screen holes, length of screen pipe, auger characteristics, level of negative pressure (vacuum setting), and rotational speeds, were evaluated in pits with varying solids concentrations. Continuous prototyping and testing showed that a combination of the screening and clearing mechanisms was most efficient in excluding trash in wet pits (less than 12% solids) and allowed a maximum flow rate of between 3 to 4.5 L s⁻¹. The resulting product, called the Flexcrevator + Excluder, is a vacuum system that excludes trash and was field-tested in pit latrines in Kisumu, Kenya. While there are remaining challenges for the current design such as pumping thick fecal sludge and dealing with fibrous material encountered in the field, trash exclusion can provide an efficient and safe emptying solution for a wide range of pit latrines.