Blended Water Monitoring

Monitor for free chlorine when one of the blended source waters is a free chlorine treated water. The free chlorine value is used when the treated water is to be blended with a surface water which contains high levels of organic matter or contains ammonia. The chlorine will likely be consumed by the chlorine demand of the surface water, but can react with ammonia to form chloramines or with the organic matter to form disinfection byproducts.

Monitor for total chlorine when one of the blended source waters is a chlorine treated water. The chlorine will most likely be consumed by the chlorine demand of the blended water. Depending upon the ratio of the blended waters, the chlorine species and the chlorine concentration, ammonia and disinfection byproduct levels may be increased over the levels found when the individual source waters were tested separately.

Monitor for monochloramine when one of the blended source waters is a chloraminated treated water. The monochloramine will most likely be consumed by the chlorine demand of the surface water. As the monochloramine is consumed by reacting with the organic matter in the surface water, ammonia is generated and will increase the overall ammonia content of the combined source water.

Ammonia may be naturally occurring in the source water or may have formed if one of the blended waters was a chloraminated water. The salicylate ammonia method should be used to measure the ammonia when the combined waters have no total chlorine residual. The ammonia value is used in subsequent disinfection treatment processes.

Monitor the pH of the blended source waters to maintain the required pH range for the disinfectant being used.

Source waters should be tested to check for the tendency of the water to form trihalomethanes (THMs) disinfection byproducts when chlorine is used as a disinfectant. The THM Formation Potential test is a method used to determine the formation potential of a source water or a blending of source waters. Chlorine concentrations, pH levels and temperature conditions can be varied to characterize THM formation conditions. The formation potential test can be modified to use the specific conditions of your source water, to investigate the demand from alternative surface water sources and to study the impact of weather events or other seasonal occurrences on treatment processes.

If your water treatment process includes coagulation/flocculation to remove colloidal particles, you can use advanced monitoring and optimization tools available from Hach. The solids suspended in the water have negative charge and positively charged chemicals are added to neutralize the charge. Coagulation is the process of neutralization and growing a gelatinous mass to trap (or bridge) particles, thus forming a mass large enough to settle or be trapped in the filter. Settling prior to filtration is preferred, so the next step – flocculation – provides gentle stirring or agitation to encourage the larger particles formed with addition of coagulant to agglomerate into masses large enough to settle under gravity and be removed from solution prior to filtration. The entire process is called coagulation/flocculation/sedimentation and comprises the core of conventional water treatment prior to filtration.

Coagulation and flocculation are perhaps the most overlooked processes when installing instrumentation in a water treatment facility. This may be due to the fact that monitoring at these points is typically not a regulatory requirement. However, every step in the treatment process depends on preceding steps and those that follow to make the entire process function effectively. Measurement is critical at every step to optimize the process and control operational costs.

Nitrate is a regulated contaminant with 10 mg/L maximum contaminant level (MCL) often found in agricultural areas due to the use of fertilizers. Monitor your sources for nitrate because treatment is difficult and may require RO filtration.

Monitor your sources for nitrite as it may be present in the source and gets oxidized during treatment to produce nitrate.