Trihalomethane Reduction Using Ozonation

摘要

Ozonation can be used in potable water treatment as an effective means to remove sulfide without generation of treatment residuals. The results of the study also revealed that ozonation of Central Florida groundwater can reduce trihalomethane (THM) concentration by 10 to 15 parts per billion (ppb) with an ozone dosage of 1 ppm over that required for sulfide oxidation. Orange County Utilities (OCU), Orlando Florida is developing a new 27 MGD potable water supply facility in the County's Southern Water Service Area. That new facility is the Southern Regional Water Supply Facility (SRWSF). The raw water source for the SRWSF is the lower Floridan aquifer. The use of ozone at the proposed SRWSF is being recommended as an effective treatment process for sulfide removal. At the location of the proposed SRWSF previous water quality analysis of the raw water from the test production well revealed total organic carbon (TOC) levels ranging from 1.4 to 2.4 ppm. The disinfection by-product (DBP) formation potential for this water was not previously tested. The DBP formation rate for ozonated raw water needed to be considered so that further evaluation of this treatment process and the distribution system's compliance with Stage 1 and 2 DBP limits could be made. Specifically, the goal of this work was to determine what effect ozonation has on THM and haloacetic acid (HAA) formation. Pilot scale ozone testing was performed during the week of November 26, 2007. Water was drawn at a rate of 5 MGD from a well at the SRWSF. The well was pumped for approximately 12 hours prior to pilot scale testing. Raw water sulfide ranged from 2 to 3 ppm. Oxidation of sulfide was found at the rate of 2.9 mg ozone applied per mg sulfide, well within the expected ozone dosage range. Without ozone, THM and HAA levels reached as high as 80 ppb and 35 ppb, respectively. Controlling the ozone dose to 1 ppm above the sulfide ozone demand lowered THM concentration by 10 to 15 ppb; a HAA decrease was not seen, but HAA levels were low at no more than 35 ppb. Further increasing the ozone dose to greater than 1 ppm above the sulfide ozone demand, both THM and HAA concentration were seen to rise. However, under all ozone dosage rates THM and HAA concentrations remained below the regulatory limits for THMs and HAAS of 80 and 60 ppb, respectively.