Perth Voice Interactive

WITH midges on the rise at Maylands Lakes again, all eyes were on Bayswater council’s latest attempt to quell their numbers at this week’s council meeting.

The council recently asked for treatment ideas from industry, and has narrowed down the responses from four companies that will be invited to tender for the works, though following concerns about the process, deputy mayor Elli Petersen-Pik successfully moved for an open tender process.

Engineered Solutions has proposed a centrifuge separation system similar to those used in algae farms and a floatation system that uses micro bubbles to attach to impurities in the water and bring them to the surface.

NewGround and Osmoflo have proposed ultrafiltration with with coagulation, which would leave the council having to chemically clean filters and deal with the effluent.

Water Rentals has a mix of dissolved air flotation to remove solids from the water and activated carbon filters for microparticles, with the equipment rented to Bayswater.

But a report to the council notes that it won’t be cheap; of the options on the table, mechanical mixing and aeration comes in at around $500,000, while ultrafiltration and sludge dewatering could set the council back $3 million. Then there’s $1.5m annually to rent pumps and filters.

Consultants Plexus Water, who’ve been engaged to advise the council on managing the lakes, also noted that whatever method the council chooses, it won’t fix the design problems with the lakes that have led to algal blooms and midge plagues.

Blooms

“Whatever solution is selected, it will need to be operated indefinitely to prevent the problems reoccurring,” Plexus said.

“Making significant changes to nutrient inputs and flows in the lakes, is beyond the scope of this assessment, however, will be necessary to change the causes.”

Friends of Maylands Lakes chair Kevin Hamersley said the group was strongly in support of going out to tender, but queried whether the council’s expression of interest was detailed enough to have attracted the most suitable company.

“I’ve received a copy of an email from a water treatment business that states they did not apply to the EOI because it lacked the required detail,” Mr Hamersley said.

He asked the council to make sure it got industry input to ensure critical water flow requirements were included in the tender document, receiving assurance from the City’s infrastructure manager Luke Botica.

Mr Botica said the EOI was deliberately broad, so the feedback from industry was expected, but when the official tender document was prepared, it would have more specific requirements.

He said the community will be able to learn more at a community briefing session on September 5.

The latest data from the council shows that at Lake Brearley, midge numbers have skyrocketed in August, with the count rising from less than 1000 at the beginning of the month to 7560 Monday just gone.

by STEVE GRANT