A faecal sludge simulant to enable septic sanitation innovation by mimicking the filterable solids and viscosity of septage

Process flow diagram showing that the Radford and Fenner (RF) simulant is designed for pit latrine sludge and is made of topsoil, Kaolin, and water. Modifications to the manufacturing process were made, leading to the modified-RF simulant. Next, all the RF simulant ingredients, sodium alginate, and synthetic urine were analysed for their total suspended solids (TSS) and total dissolved solids (TDS) content. After analysis, the topsoil was removed from the recipe. Next, all the remaining ingredients were analysed for their viscosity in water. Finally, the final simulant recipe was built and led to the simulant mimicking TSS with an absolute error of 1.11%, TDS with an absolute error of 0.35%, and viscosity with an absolute error of 1.54 cP. Septic tanks are an integral part of decentralized sanitation infrastructure in the Global South. Septage is a type of faecal sludge found in septic tanks, but unlike sludge found in drier containment types, septage has a lower solids content and viscosity. This has implications for the technology used to pump, characterize, and treat it. Faecal sludge simulants have played a critical role in the technology development and verification process for other sanitation containments, such as pit latrines. They can mimic key properties of sludge in a controllable manner while being pathogen free. However, no existing simulants can mimic septage. We developed a septage simulant made of kaolin, sodium alginate, urea, sodium chloride, and water that enables sanitation innovators to create suspensions designed to mimic the total suspended solids, total dissolved solids, and viscosities found in real septage with an absolute accuracy of 1.11%, 0.35%, and 2.84 centipoise (cP), respectively. This simulant recipe can be used to create innovations designed for septic tank–based communities, so that everyone can have access to a functional sanitation service chain.