Mineralization of dichloromethane using solar-oxidation and activated TiO2: Pilot scale study

Abstract

The oxidation of gaseous dichloromethane (DCM) by advanced oxidation technology, advanced solar oxidation technology, biological treatment, and the combination of solar advanced oxidation technology and biological treatment were investigated in a pilot study. The effects of the inlet concentration of DCM, flow rate, and relative humidity on the percentage DCM removal were recorded. Photolysis and photocatalytic oxidation using TiO2 does not result in the complete removal of DCM, while ozone, ozone/solar-hν and TiO2/ozone/solar-hν can completely remove DCM from the gas stream. Combined photocatalytic oxidation processes enhance the process efficiency and reduce both ozone demand and the energy requirements needed to completely remove DCM. Through a combination of processes, ozone, solar photons, and hydroxyl radicals oxidize DCM, generating byproducts that are water soluble and more biodegradable than the original DCM, providing the possibility for it to be combined with subsequent biological treatment. The decomposition of DCM was affected by the inlet flow rate, gas relative humidity, and gas flow rate with high percentage DCM removal achieved at low flow rate, DCM initial concentration up to 200 mg/m3, and humidity around 40%. The kinetics of DCM oxidation in different processes were successfully modeled to pseudo-first order or second-order kinetics. The kinetic analysis showed that the choice of oxidation process greatly affected the kinetic constants of DCM conversion, and RH 40% could cause faster oxidation. The results support the use of solar oxidation, not only for the mineralization of DCM, but also as a pretreatment before biodegradation.