Numerical simulation of iodine speciation in relation to water disinfection aboard manned spacecraft I. Equilibria

Abstract

Elemental iodine (I₂) is currently used as the drinking water disinfectant aboard the Shuttle Orbiter and will also be incorporated into the water recovery and distribution system for the International Space Station Alpha. Controlled release of I₂ is achieved using the Microbial Check Valve (MCV), a flow‐through device containing an iodinated polymer which imparts a bacteriostatic residual concentration of ≍2mg/L to the aqueous stream. During regeneration of MCV canisters, I₂ concentrations of ≍300mg/L are used. Dissolved iodine undergoes a series of hydrolytic disproportionation and related reactions which result in the formation of an array of inorganic species including: I^‐, I₃ ^‐, HOI, OI^‐, IO₃ ^‐, HIO3, I₂OH^‐, I₂O^‐2, and H₂OI⁺. Numerical estimation of the steady‐state distribution of inorganic iodine containing species in pure water at 25°C has been achieved by simultaneous solution of the multiple equilibrium expressions as a function of pH. The results are reported herein.

Key words:

• Iodine
• aqueous
• speciation
• disinfection
• numerical simulation