AWWA WQTC60730

According to the Stage 1 Disinfection Byproduct Rule (DBP), utilitiesmust comply with a trihalomethane (THM) maximum contaminant level (MCL) of 0.080mg/L and a haloacetic acids (HAA) MCL of 0.060 mg/L. The formation of THMs andHAAs are impacted by total organic carbon, bromide, pH, temperature,chlorine dose, and contact time. As the elevation of Lake Mead continuesto decrease due to drought, these water quality parameters will result inchanges more conducive to forming THMs and HAAs potentially near theMCL. The current regulations coupled with water quality changes haveprompted the Southern Nevada Water Authority (SNWA) to investigatevarious strategies to reduce THM and HAA concentrations. Bench scaleexperiments were performed to identify ways to optimize the currenttreatment plant performance without a major capital improvement.Results showed ozonation reduced THM concentrations 4-7% at a 1.0-logCryptosporidium inactivation, and 7-17% at a 2.0-log Cryptosporidiuminactivation. Biological filtration did not provide any substantial THM (<5%) or HAA (<10%) reduction. Rechlorination results lowered THMconcentration by 10-15% when a 1.8 mg/L free chlorine residual wasrechlorinated with 0.7 mg/L Cl2 after 48 hours, compared to an initial freechlorine residual of 2.5 mg/L. A temperature increase from 16.7°C to23.7°C increased the chlorine decay rate 30-40% and increased THMformation by 30%. These bench scale results provide SNWA alternativesto continue compliance with the Stage 1 DBP Rule and proposed Stage 2DBP rule without requiring a major capital improvement. Includes table, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

10

File Size:

1 file , 340 KB