Blog-Projects:

Warrnambool wastewater treatment plant was originally commissioned in 1996 and serves a mixed catchment with a significant industrial component in its influent.   It has four large intermittently aerated tanks, each of about 6,000kL capacity at bottom water level, and each was designed to operate on a cycle with 2-hours of aeration, followed by 1h for settlement and 1h for effluent decant.

For reasons not fully understood, the diffusers at this plant suffer from unusually high fouling rates leading to quite rapid increases in backpressure.   The original membranes were replaced in 2001, and have been regularly tested and dosed with formic acid vapour since then to keep backpressure rises somewhat in check.

In spite of regular acid dosing, a second membrane replacement became necessary in 2008, and this time EDI membranes were selected and supplied and installed under a contract awarded to Aer-Force.  This required delivery of about 17,000 membranes of the same 170mm dia size. The refurbishment work was expertly undertaken by Aer-Force’s local subcontractor, Critech.   In spite of the regular acid vapour dosing, large deposits of crystalline material were found to have accumulated not only in the diffuser bodies, but also within the distribution pipework which was accordingly flushed clean.

Although the EDI diffusers met all expectations, a third membrane replacement became necessary in 2017 and, in this case, the whole aeration system was redesigned by Wannon Water’s consultants to provide additional flexibility and capacity.  Aer-Force again won the diffuser replacement contract and supplied and installed about 17,000 whole 230mm dia diffusers on entirely new pipework, with Critech again our principal subcontractor.  The diffusers were again furnished and factory tested by EDI, and subsequent site testing by the consultancy Aqua-Audit confirmed a 35% gain in oxygen transfer capacity and efficiency as a result of the latest refurbishment.

The new diffuser installation is giving good service, and regular formic acid vapour dosing continues as before.

• Tom Lawson (September 2020)