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MWH's Applied Research Department (ARD) and SFPUC developed a bench-scale protocolwith the overall objectives of screening the effects of utilizing ClOsub2/sub on the HHA supply(Moccasin Reservoir) not only on disinfection performance, but also on finished water quality,formation of DBPs (chlorite and chlorate), and potential operational issues, such as maintaining atarget chlorine residual. To address the study objectives, an unfiltered water sample was collected from the Moccasinlocation and utilized to conduct bench-scale testing, according to a protocol that identified thefollowing three major tasks. Task 1 consisted of monitoring ClOsub2/sub demand and decay kinetics over a 48-hour period afterthe addition of a specific ClOsub2/sub dose (t=0). During this task ClOsub2/sub residuals, chlorite,chlorate, apparent color and UVsub254/sub (unfiltered) levels were monitored to identify anysignificant trends. At t=5.5 hours, the sample was pH adjusted to 9.2 using lime addition tosimulate the process occurring to the source water at the Rock River location. The effect oflime addition on ClOsub2/sub kinetics was also addressed.Task 2 focused on determining the stoichiometric amount of a quenching agent required toeliminate any residual ClOsub2/sub at t=16 hr (simulation of Tesla Portal location where sodiumhypochlorite is added). The quenching agent initially utilized was calcium thiosulfate(CaSsub2/subOsub3/sub) and the required quenching dose was established via titration following a proceduresimilar to that described in the Standard Methods (Method 4500-CI B. Iodometric Method)(APHA et al., 1998). This method also allowed estimating ClOsub2/sub residual present in thesample.Subsequently, a comparative evaluation of quenching kinetics was performed utilizingsodium sulfite (Nasub2/subSOsub3/sub). Since the kinetics of the reaction of ClOsub2/sub and Nasub2/subSOsub3/sub wereexpected to be slower than that with CaSsub2/subOsub3/sub, the system was monitored for 8 hours after theaddition of Nasub2SOsub3/sub. Residual ClOsub2/sub, chlorite, and chlorate formation were monitored duringthis period.Task 3 investigated the effects of utilizing extended ClOsub2/sub oxidation (and further quenchingwith CaSsub2/subOsub3/sub) on post-treatment chlorine demand and decay. At t=16 hours (i.e., 16 hoursafter ClOsub2/sub addition), a sample was quenched with a 10% excess of the CaSsub2/subOsub3/sub quenchingdose established in Task 2. This sample was then dosed with sodium hypochlorite (NaOCl)and the decay was subsequently monitored for 8 hours. The effect of ClOsub2/sub treatment on finalchlorine demand is of particular interest, as literature on the utilization of ClOsub2/sub followed bychlorine have reported mixed results. While some studies report a synergy in terms ofreduced formation of chlorinated DBPs and no significant reduction in disinfectioncapabilities from this combined process (Narkis et al., 1995), other studies report reduceddisinfection ability, particularly for Cryptosporidium control (Corona-Vasquez et al., 2002). Includes 11 references, table, figures.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 11File Size: 1 file , 420 KB