Age of Potable Water Impacts on DBP’s and Disinfection Residuals

Two Basic Strategies Keep Your Water Young Strategy –Manage residence time in the system Preserve Your Water Quality Strategy –Manage water properties to extend the storage life

Water Ageing Factors System Demands –Water conservation programs –Water rates –Seasonal fluctuations System Storage –Reservoir capacity –Pipeline capacity –Local demands

Manage System Demands Water Conservation Programs –Often required by situations beyond your control. These could be: Supply shortage Funding requirements Political –Evaluate the down side –Strike a balance

Manage System Demands Water rates –Higher rates = Lower usage –Evaluate the down side of rate increase Seasonal rate structure –Strike a balance

Manage System Demands

Manage Reservoir Storage Set Seasonal Operating Levels –Maintain minimum levels in winter Fire capacity Average use Manage Fill and Drain Cycles –Fluctuate Levels –Manage fill rates

Manage Reservoir Storage –Higher fill rates promote mixing –Mixing reduces dead storage –Down side is higher demand charge for power utility –Pump during low consumption times of the day –Consider you reservoir design

Manage Reservoir Storage Mixing systems Solar Bee Tideflex

Manage Pipeline Storage Fire flow normally determines the pipe size Reduce dead ends Monitor and actively manage the system –Mainline flows –Disinfectant levels –Flush as necessary –Use EPS model –Identify and manage problem areas

Manage Pipeline Storage Identify and Manage Problem Areas –Dead ends –Stagnate loops –Pressure zone breaks –Long transmission lines –Pipe condition Age Material Lining

Extend Useful Pipe Life Goals Protect customers from acute illness –Maintain disinfection residual levels –Prevent microbiological contamination Protect customers from chronic illness –Inhibit disinfection by product formation –Nitrification Maintain aesthetic quality –Taste & Odor –Color

Manage pH Bulk Water Disinfection Lower pHHigher pH Biofilm Disinfection Corrosion BioFilm Stability Disinfectant Decay Rate Persistent Combine Chlorine residuals DBP formation Nitrification

Manage pH

Chlorine Break point and pH

Manage DBP’s Remove precursor materials –TOC removal –Color –UV 254 abs –Source water Minimum Chlorine Levels –Microbes –Distribution system

Manage DBP’s TOC Removal –Enhanced Coagulation –Absorption PAC GAC –Reduce Chlorine Demand

Manage Disinfectant Demand

Manage DBP’s Reduce Disinfectant Aeration Inhibit Formation –Ozone –Oxygen

Laramie’s Experience Starting Conditions –Raw Water TTHMFP 350 – 500 ppb –Distribution THM ppb –Chlorine level 0.7- ND –pH not managed –Coagulation not enhanced –Pressure zone flow not managed Current Conditions –Raw Water TTHMFP unknown new source –Distribution THM ppb –Chlorine Level –pH managed at 7.6 –Enhanced coagulation –Active pressure zone flow management

Laramie’s Treatment Strategies Remove precursor material Inhibit formation Monitor removal by –Color removal –Chlorine demand –TOC removal –Chlorine decay rate Monitor inhibition by –UV 254 abs

Chlorine Decay Rate Place sample in a series of non reacting glass bottles Analyze residual over time Plot Ln(Ct/Co) Should be a straight line. Slope of the line is the decay rate.

Laramie’s Distribution Strategies Minimize residence time Remove precursors –Reservoir operating levels –Eliminate dead ends –Redesign Low Level reservoir inlet –Color removal –Chlorine demand –TOC removal –Chlorine decay rate –Pressure zone circulation –Take advantage of large irrigation flows –Flush where necessary –Identify and correct problem areas

Laramie’s Distribution Strategies Stabilize Bio-Film Extend usable water age –Manage pH –Maintain alkalinity –Manage corrosion –Maintain consistent chlorine residuals –Maintain consistent TOC removal –Lower chlorine decay rate –Promote circulation and mixing –Identify problem areas

Distribution System Modeling Long term process requires many iterations Requires regular maintenance Calibrate using systematic field measurements –SCADA –Grab