Havelock WWTP uses biological larvicide to control midge flies

By Catherine Flannery

Midge flies, or chironomids (chironomidae), commonly occur in wastewater treatment plants and pond systems. Managing them can be challenging, but a local Ontario Clean Water Agency (OCWA) operations team used an innovative approach to control the midge fly population at the wastewater treatment plant (WWTP) in Havelock, Ontario.

The Havelock facility had been experiencing an issue with the flies in its sequential batch reactor process for some time. The red worm (larvae) that forms the midge loves the nutrient-rich conditions in a wastewater treatment plant and feeds off bacteria and sludge. The worms will eat mixed liquor (a combination of sludge and water removed from the clarifier) and once transformed into adults, they clog filters and building entrances.

“The midge flies also attract birds and spiders and are a general nuisance,” says Amber Coupland, OCWA senior operations manager at the Havelock WWTP.

The short life cycle of the midge fly means the population can grow quickly. Over a period of 10 days, eggs hatch into red worms and then pass through the pupa stage to become adult midge flies. With no aquatic life to feed on the midges, their life cycle runs uninterrupted, and they multiply fast.

If left alone, midge flies will cause poor settling and high total suspended solids, and disrupt the bacterial environment. The mixed liquor infested by red worms can see reduced solids, stringy or clumpy sludge, and poor nutrient removal.

Determined to tackle the midge fly issue at the Havelock WWTP, Brad Robinson, an operator/mechanic in OCWA’s Trent Valley Hub, began researching available methods of control. He soon identified AQUABAC xt, a highly effective biological larvicide for use against midge flies, as likely the best solution.

AQUABAC xt contains a species of bacteria called bacillus thuringiensis, an approved larvicide for controlling red worms and midge flies in wastewater treatment plants and waterways. It can be poured into either the aeration basin or secondary clarifiers, depending on where the red worm problem is. It also works extremely well in UV disinfection chambers, and it is safe for fish, birds, mammals, and other life forms.

In April 2021, Coupland and Robinson successfully applied to the Ministry of the Environment, Conservation and Parks for approval to conduct a trial of AQUABAC xt. The results were positive, with operations staff reporting reductions to the midge fly population at the Havelock WWTP.

“It didn’t take long for staff to see a difference,” says Coupland. “We are very happy with the effectiveness of the larvicide and how quickly it has reduced the midge fly population. The plant’s sand filtration system is running more smoothly and the air lift pumps require less cleaning.”

Based on the successful trial of AQUABAC xt, the product application has been added as part of the preventative maintenance for the Havelock WWTP. Reprinted with permission from OCWA.

Operator Brad Robinson.

Catherine Flannery is a Marketing and Community Outreach Specialist with OCWA. Email: ocwa@ocwa.com