Alkimos Wastewater Treatment Plant, Perth, Australia

Alkimos Wastewater Treatment Plant (WWTP) is located in Alkimos, which is approximately 42km north-west of the Perth Central Business District (CBD), Western Australia. The plant was constructed as part of the Alkimos Wastewater Treatment Scheme, which officially opened in April 2011.

Built over a period of three years, the $366m scheme also included an ocean disposal outlet, the extension of a main sewer to facilitate the transfer of wastewater to the new plant and major excavation for the new WWTP.

The initial daily capacity of the plant is to treat and dispose up to 20 million litres of wastewater. The capacity would eventually be expanded to treat 160 million litres of wastewater daily. The plant will ultimately benefit an estimated 800,000 people.

Purpose of the Alkimos project

It is estimated that Perth's north-west corridor from Mindarie northwards will have a population of 150,000 by 2030, which will ultimately reach 800,000. Alkimos, the upcoming suburb, will be the heart of this new community. Because a water and wastewater infrastructure is essential for the growth and development of a new region, it was decided by the government to provide a new WWTP to serve Alkimos.

The Alkimos plant was built as part of a long-term plan to provide Perth metropolitan area with a series of wastewater treatment plants from north to south.

Alkimos background

"The initial daily capacity of the Alkimos plant is 20 million litres of wastewater."

The need for a WWTP to serve the planned residential growth in Perth's north-west corridor was identified in 1970.

Alkimos Lot 101 was selected as the preferred site for the new WWTP by Water Corporation, the principal supplier of water, wastewater and drainage services throughout the state of Western Australia.

Land acquisition on this site was finalised in 1987. Alkimos Wastewater Treatment Works Coordinating Committee was established in February 2004.

In 2007, the Environmental Protection Authority formally assessed the proposal of the construction of the WWTP.

In December 2006, an alliance was formed between the Water Corporation and the private sector for the design and construction of the Alkimos Wastewater Treatment Scheme.

Construction of the Alkimos project

Construction of the Quinns Main Sewer began in February 2008. After a delay of over a year, construction work on the excavation and ocean outfall pipeline began in March 2008.

Design work for the new WWTP began in mid-December 2008 and its construction started in February 2009. The plant became operational in November 2010. Site work involved excavation of around two million cubic metres of sand and limestone.

Wastewater treatment process

A system of gravity sewers delivers the wastewater to the plant. The wastewater is treated by the activated sludge process. Because of low solids and nitrogen levels, the treated wastewater is suitable for further treatment for recycling or discharge to the ocean.

Alkimos WWTP does not apply primary treatment before the activated sludge process. As a result, the plant produces fewer odours.

Odour control

The Alkimos plant has an approved buffer zone of 600m. A high level of emission control will be maintained in order to reduce the impact of odour on the surroundings. In order to collect, treat and vent odorous gases, the plant is installed with a 50 metre tall stack.

Key players on the Alkimos project

The project was undertaken by Alkimos Water Alliance, which comprises Water Corporation and a joint venture of Brookfield Multiplex, Macmahon Contractors and Zublin Australia.

"Construction of the Quinns Main Sewer began in February 2008."

DHV was subcontracted to provide the design of the treatment process and deliver key equipment. D+Z Constructions carried out construction on all the concrete structures and facilities. The plant was designed by GHD. Humes supplied approximately 1,450m of 1,950mm and 1,200mm AKS HDPE lined class 4 and 6 pipes and specials. These pipes were manufactured at Humes' Welshpool Plant in Perth.

Z├╝blin Australia supplied approximately 6,200m of 2,000mm AKS HDPE lined jacking pipe. These pipes were manufactured in Thailand.