Chlorine needed to be removed from the mains water prior to the RO. This was previously done using sodium bisulfite. Occasionally this caused a process issue, as the dosing was done at a constant rate and if the chlorine levels dropped the residual SBS would go onto the process and cause premature fouling of downstream RO and EDI processes.
BHF were consulted to look into options for the use of UV to remove the chlorine in the mains water at ~4,500L/hr. As the process consisted of UF pre-treatment, UV was a good option, as it was well protected from particulate which would otherwise cause problems. The UV produces a constant dose of light between the wavelengths of 180-400nm, which produces a photochemical reaction that dissociates free chlorine to form hydrochloric acid. The peak wavelengths for dissociation of free chlorine sits in the range of 180-200nm, with wavelengths in the range of 245-365nm targeting chloramines.
The system needs no chemical additions, which reduces chemical costs, but most importantly reduces the premature fouling on the downstream processes that were previously caused by SBS dosing. Using UV in this process has the added advantage of high levels of UV disinfection (much higher than a standard UV system designed for disinfection which runs at lower rates).
The system consists of a single chamber 10 lamp UV system with variable control from 1.8-6.0kW to suit the flow and system conditions. Other features include a full 316L stainless steel chamber, UV intensity monitoring, and lamp fail alarms.
The system has been operational and has proven successful in removing chlorine from the process without the need for chemical additions or any other chlorine removal treatment.