A toilet system based on hydrothermal carbonization

We are developing a toilet system that converts faecal material to an aqueous suspension of carbonised material that is safe to handle, and readily separated from the remaining liquid. It will also extract useful salts from the liquid. The system is aim to be the new generation universally appealing toilet and it will be of particular and urgent interest to areas where no (or very crude) sanitation exists. The system is designed to be self-sufficient in terms of energy input and to scale for a number of users in the range a few tens to a thousand or more. In parallel with our engineering development we are designing the system to provide users with a positive and comfortable experience. Hydrothermal carbonisation (HTC) has received attention recently as a way to convert biomass - including sewerage - into coal like material. It involves heating the start material in water at high temperatures and pressures. Depending on the conditions used the process can produce hydrocarbon gases or liquids or coal like particles. Most HTC work involving sewerage treatment is currently aimed at replacing established large-scale treatment plants i.e. for places with well-developed sewerage services. Our system, using HTC, is aimed at bringing the process at a decentralized household ( including combination of households) level so that the new generation toilet become accessible to all and particularly to those areas where none currently exists. Using HTC for toilets on continuous basis for such a small scale is the key innovation of our proposed system. We will describe our work to characterise the energetics of the HTC process in order to optimise the process in terms of total energy input and how we have used this information to develop a continuous system based on a plug flow reactor. The material produced by the system can be easily separated from the remaining liquid and used to generate heat and power (via a generator including solar) in order to maintain the process. The solids are safe to handle, and look, feel and smell much like coffee grounds. In situations where electrical (or renewable energy like solar) power is available the solid material can be used either as a fuel for heating and cooking, as a soil conditioner and possibly for carbon capture. We will discuss the possibility of including other waste material (food, sanitary waste etc.) into the system. In order to minimize the amount of water required to flush material away from the toilet bowl and to help maintain high sanitary standards we have been investigating anti-fouling coatings for the system. We will describe the results of studies of a nano-coating based on a responsive polymer that significantly enhances the rate at which water flushes away material that adheres to the toilet surface.