The City of Houston, Texas has been aware of the implications that current and pending regulatory standards would have on the operation of their four surface water treatment facilities. In particular, the City has closely monitored changes in regulations related to enhanced coagulation, total organic carbon (TOC) removal, and disinfection by-products (DBP) reduction. The City has, and continues, to conduct extensive bench, pilot, and plant scale tests to determine how these regulatory changes would impact the operation of their surface water facilities.
The TOC content of the source and finished water is the common attribute that significantly impacts each of the regulations of interest. TOC is perhaps the one water quality parameter that could impact the financial bottom line of a utility most. In most cases, a fully automated surface treatment facility still measures TOC by collecting
periodic grab samples for laboratory analysis. Making treatment decisions based on periodic TOC grab samples is comparable to flying a commercial airliner without instrumentation.
In a collaborative effort between the Water Quality Laboratory and the Operations Group at the City’s East Water Purification Complex (EWPC), an evaluation of on-line TOC equipment has been completed. After nearly a year of plant scale evaluation, the recommendation is being made that on-line TOC analyzers be purchased to enhance facility operations. During the trial, the instrument was used to monitor plant performance and to evaluate alternate coagulants and coagulant aids. The most interesting results of the study related to how poorly the operators responded to changing raw water parameters when given daily grab sample results and how much better they were able to respond when allowed to utilize the on-line analyzer. The on-line TOC analyzer allowed the operators to track real time water quality changes and therefore respond much quicker than would be possible if grab samples were being used. Because the City of Houston has two raw water sources that are dramatically different (alkalinity, pH, turbidity, TOC concentration, and TOC composition), blends of the two raw water sources present special treatment challenges, especially related to coagulation efficiency and TOC removal.