Lower Molonglo Water Quality Control Centre - an engineering marvel

Ray Hezkial, General Manager Project Delivery, Operations and Maintenance 

The Lower Molonglo Water Quality Control Centre was constructed in 1978 but it marked the end of a very long and at times hotly debated process to work out what would provide the best sewage treatment option for Canberra.

Initial debate in the 1920s put forth many different options for sewage treatment and disposal. At the Federal Capital Advisory Committee on 28 January 1924, an extensive scheme for disposal into the Weston Creek area was agreed to. This resulted in the construction of the Weston Creek Sewage Treatment Works. The plant came into operation in 1927.

Additions were made to the plant in 1939 and 1948 to cope with additional population and upgrade treatment processes. In its final form, the plant was using primary and secondary sedimentation, high and low rate trickling filters, sludge digestion and some activated sludge.

Through the 50s, 60s and early 70s, other sewage treatment works were constructed across Canberra. In the early 1960’s treatment works were established at Fyshwick to consolidate a vast range of smaller treatment systems in the area, a treatment plant at Belconnen was constructed too to support the growth in that area and even temporary works were established for the first residents in the Tuggeranong Valley in the early 1970’s.

However, the main treatment plant remained at Weston Creek. In the late 1960s neighbours of the plant in the Woden- Weston Creek area were about complaining about the odour and at Government House in Yarralumla too. To combat this, several refinements were made to the plant and sludge drying beds were abandoned.

Rumour has it that when Prince Phillip visited Canberra in the late 1960s he was so confronted by the sewage smells coming from Weston Creek that he wrote letters of complaint.

Whether this was the trigger or not, planning for the next step in Canberra’s sewage treatment story commenced soon after.

In 1967, the National Capital Development Commission and the Department of Works were engaging in in-house studies to determine the best way forward. The National Capital Development Commission engaged Camp, Dresser and McKee, a firm of leading hydraulic consulting engineers from the USA to review the existing system and future expansion, from which they were asked to prepare a metropolitan sewerage strategy plan.

These consultants, working closely with National Capital Development Commission and the Department of Works engineers recommended that the individual treatment plants in across Canberra be phased out and one large plant be constructed well downstream, capable of staged development to cope with all expected expansion of Canberra, and to treat wastewater to a high standard that minimised biological growth. These consultants forecast the need to reduce nutrients, nitrogen and phosphorus, to very low figures. At the time, considerable concern had been expressed around the world for the need to maintain the quality of the environment. Algal blooms were continuing to appear in the Murrumbidgee and Burrinjuck Dam, and reports from senior engineers visiting other countries, all led to acceptance of the consultants’ recommendations.

These recommendations were supported by the findings of both the National Capital Development Commission and Department of Works’ specialists and American consultant, David Caldwell was selected to design the plant.

The consultants proposed a physical, chemical and biological plant, and a new set of rules for inland wastewater treatment which were fairly contentious and even criticised at the time they were introduced. Caldwell’s design included nitrogen and phosphorus removal which hadn’t been strong features in other plant designs at that stage, it also included particularly unique features such as the disinfection of effluent with chlorine and the incineration of sludge to make an ash product.

The plant was built between 1974 and 1978 and led by Department of Works engineer Donald Stockdill, whose 20-year involvement in the planning, design and construction of the plant led to the road being named after him and we are honoured to be joined by members of this family here today.

The plant cost $50 million dollars. To rebuild a similar plant today would cost around $600 million dollars.

Water leaving this plant enters the Molonglo River and soon flows into the Murrumbidgee River. As we are part of the Murray-Darling Basin river system, which ultimately discharges into the ocean south of Adelaide, minimising environmental impact remains the priority for all work undertaken here at Lower Molonglo.

The plant was designed to service up to a population of 400,000 people and could be extended to serve up to a million people. The plant currently treats 80 to 90 million litres of sewage every day to a quality that is often better than the quality of the water in the river in to which it discharges.

The treatment plant removes an average of 1 million litres of sludge, and creates 16 tonnes of ash every day which is beneficially used for soil conditioning.

Lower Molonglo remains the largest inland wastewater treatment facility in Australia. The plant operates 24/7 and our operators, engineers and maintenance teams are some of the most dedicated and skilled in the country. I’d particularly like to the note the dedication of some of our past and present team members who are with us here today who share between them over 100 years of operational knowledge of this amazing plant. Thank you for all the unseen hard work and your daily contributions in seamlessly keeping this plant and indeed all of our assets operating for the benefit of our community.