Impact of ozone and biological filtration on water quality parameters in Arlington, Texas

The City of Arlington began experiencing atypical water quality problems beginning in 1999 after ozonation and biofiltration were added to the existing conventional treatment processes. These problems included high chloramine residual decay rates, system nitrification and elevated manganese levels in the finished water. This study reviewed literature, existing plant and system data and collected additional data to determine if modifications to the plant and system processes would resolve these water quality problems. Results demonstrated that chloramine stability is improved with increased free chlorine contact time at a pH near 8.3. Improved biofiltration by nurturing the biomass in the filters also improves chloramine stability as well as eliminating the breakthrough of manganese at the filters. Careful monitoring and minimizing water age in the distribution system can also reduce water quality issues.