Case Study

Dissolved Air Flotation Pretreatment Washes Away Waco's Foul T&O Problem

Source: Leopold -- A Xylem Brand

During the hot and dusty summers just a few years ago, many thirsty residents of Waco, TX, were reluctant to slake their thirst with the city’s water. That has changed since a dissolved air flotation (DAF) system entered service two years ago to purge the water utility‘s recurring taste and odor (T&O) problem. T&O remains an issue across much of the nation where water plants draw from lakes and other surface sources. It can be expensive to suppress with chemicals and even then often fails the ‘taste test’.

The water utility serving Waco has two plants and 67,492 connections along its 900 miles of mains. The city draws raw water from the 8465-acre Lake Waco whose watershed directly contributes nutrient loadings that further aggravated the strong T&O in the utility’s finished water.

There was some early debate over whether the mission for the 90-ft. deep Lake Waco impoundment should be merely a replacement for a 39,000-acre-ft. predecessor lake built in 1926 for drinking water or as a flood control structure. A convincing case could be made for both priorities since the region had endured both floods and severe drought. Many floods exceeded the retention of the old city lake and drought could sap its pool until tall weeds would emerge in the shallower areas. Lyndon B. Johnson exercised his political clout and made the project a federally-funded flood control facility that serves both missions, along with recreation uses.