DEVELOPING A HORIZONTAL IN-LINE DIFFUSED AERATION SYSTEM FOR REMOVING TRIHALOMETHANES FROM WATER DISTRIBUTION MAINS

This study collected removal data for four EPA regulated trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane, and bromoform) for a pilot scale horizontal in-line diffused aeration (HILDA) system under various design and operational variables. Design variables included water flow rate, air to water (A:W) ratio, reactor length, pressure, trihalomethane (THM) speciation and mixer type. A HILDA system that could remove THMs from a pressurized piping system was developed and an air-water mixing expression was used to model the treatment performance when using Komax static in-line mixers in the system. The models can be used to predict the mixing intensity needed to achieve a certain total THM removal in the system. Models for total THM removal were created for A:W ratios of 5:1, 10:1, and 20:1, with an influent THM speciation of approximately 70% chloroform and 10% each of the other three species, and at a temperature and pressure reasonably close to 20 °C and 40 PSI, respectively. Models were also developed for each THM species, allowing for the prediction of the needed mixing intensity even if the influent speciation varies. Once a value of mixing intensity is predicted, an air-water mixer configuration can be determined. Adding turbulence is required in order to reach saturation THM removals especially at lower flow rates. Turbulence can be created by increasing the flow rate, increasing the A:W ratio, increasing the mixing length, decreasing the reactor diameter, or adding a static mixer into the system. When using Komax static in-line mixers to facilitate air-water mixing, significant variables included air flow rate, water flow rate, and length, which had contributions to THM removal of 81.0%, 12.7%, and 3.3%, respectively, with a 3% contribution from error. When comparing systems at 25 PSI and 40 PSI for a 10:1 A:W ratio, pressure was found to have little contribution to the overall % removals of THMs