Feasibility of an Optical Sensor to Monitor Toilet Pretreat Quality

Processing urine is a critical function on the International Space Station (ISS). It provides a sizeable portion of the water used on ISS stored in the Potable Water Bus (PWB). Yet processing of urine is a sensitive undertaking. The urine must be collected, stabilized, and stored to inhibit molecular breakdown, organic growth, or solid precipitation. The stabilization process mixes a strong acid with the urine which must be carefully balanced to achieve the desired urine stabilization, but also to minimize the corrosive properties of the mixture at higher acid concentrations. A precise method for mixing and monitoring the urine pretreat acid in real time is vital to protecting waste processing hardware and maintaining water recollection capabilities on ISS. This paper discusses the data, testing, and analysis around using an optical sensor for measuring fluid transmittivity in order monitor the pretreat quality being mixed with crew urine.