Massive cover delivers valuable biogas benefits

Harvest valuable biogas from anaerobic digestion with a gas collection cover.

Custom designed for tanks and lagoons of all sizes, Evoqua’s Geomembrane Technologies brand covers collect methane gas from wastewater treatment. The covers are gas-tight to contain odour and protect biogas from contamination.

In waste-to-energy projects, the collected biogas can be used as a renewable fuel to generate process heat or electricity, helping offset energy costs. The covers are safe to walk on, allowing operators to sample tank or lagoon contents and perform maintenance.

For safe biogas handling, the gas collection cover is best operated by Evoqua’s Geomembrane Technologies​ brand biogas control system, which regulates biogas flow from under the cover.

Applications:

• Collect biogas to be converted into green energy.
• Control odours.
• Provide thermal insulation.
• Lower operating costs.
• Allow access for sampling and maintenance.

Features and benefits:

• ​​Built to withstand tough conditions and operate in any climate.
• Fabricated using strong, long-lasting materials to resist tears, punctures, chemicals and UV rays.
• Built-in systems for drainage of rainwater and snowmelt.
• Insulated versions provide additional buoyancy.
• Help maintain consistent temperatures throughout anaerobic digestion.
• Installation and maintenance can be done without disrupting plant operation.
• Hatches and ports can be provided for simple access to mixers and other equipment.
• Advanced controls can be incorporated for biogas storage to optimise utilisation in engines or boilers.

Client

Melbourne Water is a water wholesaler in Victoria, Australia, and is ranked among the top-performing Australian and international water utilities. Melbourne Water delivers over 430 billion litres of safe drinking water and treats over 300 billion litres of sewage from across Melbourne.

The Western Treatment Plant (WTP) in Werribee (Melbourne, Victoria) is a world leader in technical and environmental innovation. The site treats half of Melbourne’s population’s wastewater, is one of Australia’s most important wetlands for water birds and is listed under the international Ramsar Convention.

Challenge

Melbourne Water’s WTP has been harnessing the value from biogas for more than 25 years. Floating lagoon covers collect methane-rich biogas from the site’s primary treatment lagoons for renewable energy conversion and odour management. Collecting the biogas for conversion to green energy is a huge benefit for the environment by eliminating the emission of methane, a notorious greenhouse gas, and reducing the demand for power from other sources. An added benefit of the lagoon covers for the plant staff and surrounding community of the facility is the management of odour produced from the treatment process.

In early 2015, Melbourne Water identified the need to replace the biogas cover of the 25 W lagoon system as it was coming to the end of its service life. The replacement cover was to stand up to the harsh and rugged environment and provide operational efficiencies from the original system.

​Solution

John Holland-KBR Joint Venture​ engaged ​Evoqua’s Geomembrane Technologies to design, fabricate and install the replacement cover for the 25 W anaerobic lagoon and associated biogas piping headworks. The gas collection cover measures 171 m x 450 m or 7.6 hectares (19 acres) with 500 m of large diameter pipework.

The new cover has an eastern and western section connected by a dual arched central panel referred to as the “bowtie”. Each section of the cover operates independently. The independent operation allows for maintenance and cleaning of various segments to take place while other segments remain in service managing odour and collecting biogas.

The unique design was required to allow Melbourne Water to remove sections to pump the accumulation of sludge and floating materials that collects under the cover. The eastern section of the cover accepts the influent and consists of four segments. Each segment can be removed and replaced to facilitate debris, sludge removal and ongoing maintenance. The cover includes access and inspection ports for sludge management while the cover remains in place.

The biogas pipework included two headers for the eastern and western sections. Each cover segment has dual connections with isolation valves. Instrumentation was installed to provide pressure readings to a PLC system for biogas flow control, while condensate and vent systems are vital components of the pipework to provide reliable delivery of biogas.

Results

The economic, environmental and social benefits of the replacement cover are evident. The cover collects over 60,000 m³ of biogas per day worth over AU$3,500,000 per year, and contributes to generating over 40% of the site’s electricity requirements for treatment processes. The site’s greenhouse gas emissions are substantially reduced and odours are minimised.

Melbourne Water and​ Evoqua’s Geomembrane Technologies have a longstanding relationship. Nearly two decades ago, Evoqua supplied two covers and a biogas handling system to the WTP, and ​has been involved in various upgrade and maintenance projects at the plant since. ​Evoqua’s Geomembrane Technologies is proud to work with forward-thinking, environmentally responsible companies such as Melbourne Water.

Originally published by Geomembrane Technologies, an Evoqua brand.

Originally published here.