AWWA WQTC57019

The Upper Trinity Regional Water District is planning for a new plant in the metropolitan Dallas area. The raw water source for the new facility will be Chapman Lake. Conventional treatment with ozonation was evaluated to address water quality challenges, which included episodic occurrences of objectionable taste and odors, variable turbidity with spikes up to 200 NTU, and occasionally elevated concentrations of iron and manganese. Ozone demand of the raw water was high (in the range of 6 to 15 mg/L) and therefore, ozone disinfection of the raw water was found to be cost prohibitive. Ozonation of settled water (at the optimum alum dose for turbidity removal) had much lower ozone demands (2 to 5 mg/L). Formation of BDOC during ozonation for 1-log Cryptosporidium inactivation was substantial, and biologically active filters with an extended empty bed contact time (ie. greater than 10 minutes) may be required to produce a biologically stable effluent. Bromate formation during ozonation of the settled water was low to moderate. In subsequent testing, the percent removal of 2-MIB and geosmin were found to be essentially constant for a given ozone dose. It was concluded that during episodes of elevated T&O, higher ozone dosages or an advanced oxidation process, such as peroxone (ozone plus hydrogen peroxide) would be required to provide an aesthetically acceptable water. Includes 3 references, tables, figures.