Antioch water plant halves a chemical dose, saving $18,000 a year

A membrane inspection at Antioch's water treatment plant turned into an $18,000-a-year saving, the city said in an account posted Aug. 25.

The plant sent its reverse osmosis membranes out for testing after the first season of running them. The results showed a high level of sodium bisulfite in the membranes, a sign the system was dosing far more of the chemical than it needed.

"It started when we sent the membranes out for an 'autopsy' to see what kind of buildup we had after our first season of running," said Brian Connelly, the city's acting senior water treatment plant operator, in a question-and-answer posted by the city.

Connelly's team got equipment to test and independently confirm the overdosing. They tried alternate injection locations on their own without solving it, then worked with Carollo Engineering on where to inject the chemical and what to change in the plant's SCADA control system.

The instrumentation crew handled the rest: updating SCADA, recalibrating the analyzers, and setting the system to adjust the chemical dose automatically against actual demand. Crews also changed the order in which the analyzers read the water.

The results, as the city described them:

• Chemical use down by about 50%, saving roughly $18,250 a year.
• Operators fill the chemical tank manually once a week instead of two or three times, about 100 hours of labor a year.
• Less handling of the chemical. "Less chemical handling means fewer chances for an accident or a spill, which keeps the crew a lot safer," Connelly said.

The city also said the change protects the membranes themselves, which are expensive to replace, and improves water quality.

The piece ran as part of the city's Antioch at Work series, which profiles staff work at city departments. The city did not publish a cost for the engineering help or a figure for what the membranes cost to replace.