Small Water Distribution System Operations and Disinfection By Product Fate

Abstract

The Stage-2 Disinfectant and Disinfection By-Product (D/DBP) regulations force water utilities to be more concerned with their finished and distributed water quality. Compliance requires changes to their current operational strategy, which affect the formation of DBPs over time. This study quantifies changes in DBP formation and chlorine decay kinetics under different operational conditions and pipe materials found at many small-scale water utilities. A physical model (Pipe Loop) of a distribution system was used to evaluate the change in water quality from conditions such as having a high chlorine dosage entering the distribution system, using a chlorine booster system in the distribution system, and operation of clearwells/storage tanks. The High Chlorine Run (HC) is least favorable option with approximately 64% and 30% higher TTHMs than Normal Run (NR) and Chlorine Booster Run (CB), respectively. High Chlorine conditions also minimize the wall effects. The location of Boosters should always be after the storage systems to avoid extra contact time that can produce approximately 23% -78% higher TTHMs. The following trends are discovered from the data analysis: Chlorine residual HC > CB > NR and TTHM NR > CB > HC.

A Review on Formation and Decay Kinetics of Trihalomethanes in Water of Different Qualities

“…Moreover, it was found by Chowdhury et al that THMs concentrations can increase significantly within the consumer pipe plumbing system and hot water tanks beyond the WDS. Poleneni and Poleneni and Innis found that booster chlorination should be practiced after utility storage tanks as practicing booster chlorination at the utility storage tanks increases TTHM significantly. Management of THM levels in drinking WDSs has not been easy due to the reasons mentioned earlier in this article.…”

“…High chlorine dose reduces the risk of the deterioration of the biological quality of drinking water, however, it increases the risk of THMs concentration exceeding the permissible limits at the consumers’ tap, especially at the WDS extremities. Poleneni and Poleneni and Innis investigated chlorine residual and THM formation in small WDSs under different operational conditions of normal chlorine dosing, booster dosing, and high chlorine dosing. It was found out that the high chlorine dosing maintained chlorine residual concentration in the WDS, however, it elevated TTHM concentration significantly.…”

Enhanced Flocculation Using Drinking Water Treatment Plant Sedimentation Residual Solids

“…As observed in Missouri, in many small-scale utilities the floc formed is usually too small or light in weight for it to settle down and travels beyond the final clarification step into the filtration stage resulting in more frequent back wash cycles [9]. This also allows for higher concentrations of TOC to react with chlorine, forming higher concentrations of DBPs even before the finished water leaves the system [10,11]. Factors such as detention time in first and second stage basins in the 2-stage water treatment process, floc thickness (robust floc is denser and will settle out easily), raw water quality and coagulant type, and concentration used can dictate how efficient the treatment process is in removing TOC.…”

Small Water Distribution System Disinfection by-Product Control: Water Quality Management Using Storage Systems

“…The adverse effect of increased contact time and chlorine dosage on TTHM formation in the distribution system is explained in detail in our previous research [16], [20]. Therefore, storage time before the dilution process takes effect and contact time in the tank play an important role in water quality management in storage tanks.…”

“…When operated under proper mixing and filling conditions, the clearwell can provide better water quality in terms of TTHM formation and chlorine residual without additional chlorine. The change in TTHM formation and chlorine decay kinetics between a high chlorine dosage scenario and usage of chlorine boosters scenario is explained in detail in our previous research [16], [20].…”