The Malabar Biomethane Injection Project is an Australian-first biogas-to-grid trial; converting wastewater into renewable biomethane and blending it with Sydney’s existing gas networks. Not only will the five-year pilot will put gas directly into the supply network, it will also help industries across New South Wales meet their net zero emissions targets. Here, we look at the $16 million project, and breakdown the equipment and technology powering the process.

Partnering with Jemena, and with support from the Australian Renewable Energy Agency (ARENA), the project will generate zero-carbon emissions and high- quality biomethane gas from the wastewater treatment process and inject it into the gas grid for heating, cooking and hot water.

Biomethane production began in 2022, and it is expected to enhance New South Wales’ energy resilience and contribute to the establishment of a sustainable green gas market in Australia. The Malabar Biomethane project is expected to offset 5,000t of carbon, and up to 11,000t if fully scaled.

From 2022, approximately 95,000GJ of biomethane is expected to be generated each year through the Malabar project, enough to meet the gas demand of 6,300 homes.

What is biomethane?

Biomethane is produced from biological waste via a process called anaerobic digestion – similar to composting but instead conducted in an oxygen-free environment – this creates biogas, which is then purified in a process that removes excess materials including carbon dioxide, hydrogen sulphide and water.

The resulting product is a low-cost net zero alternative to carbon-intensive natural gas and can be used to supplement Australia’s existing gas distribution network. Anaerobic digestion occurs in wastewater treatment plants to break down waste products, producing methane that can be captured and refined into a sustainable and green bioenergy source.

Many wastewater treatment plants use this process to provide an alternative power source. However, upgrading these existing systems for biomethane production could offer broader solutions in everyday applications.

The Malabar Biomethane Injection Project

Jemena constructed the Malabar Biomethane Injection Project, which was installed at Sydney Water’s Malabar Wastewater Treatment Plant, with Zinfra engaged for project management, engineering, procurement and construction.

Previously, the biogas from the wastewater treatment plant was used to power cogeneration engines that produce electricity to reduce the overall energy of the plant, with some excess biogas being flared.

In the future, at least 95,000GJ will go to the new biomethane production, with the rest used for onsite operational use. The Malabar Biomethane Injection Project will redirect raw biogas into a biogas upgrader system and convert it into biomethane – turning waste into clean, green energy.

The biogas upgrading system is easily integrated into a biogas plant, providing a refined and efficient method of gas cleaning that can recover up to 99.5 per cent of methane. The biomethane is refined to Australian standards before ultimately ending up in the gas grid as a green gas alternative.

Complementing the existing biogas electricity generators, this project will enhance Malabar Wastewater Treatment Facility’s performance as a clean and renewable bioenergy producer, creating more energy than is needed to run the entire facility.

Procuring the equipment

Zinfra engaged Brisbane-based company Eneraque to deliver the upgrader package, who in turn contracted Dutch biomethane specialist Bright Biomethane to provide the major equipment. The electrical components of the equipment were converted to meet Australian standards.

The Australian-first biomethane upgrader was sized for 1100Nm3/hr of biogas to the inlet prior to separating the CO2 and CH4 with a patented three-stage membrane system.

How does biogas upgrading work?

Biogas upgrading is the process to remove impurities and moisture from raw biogas to transform it into high-quality biomethane that meets the stringent gas specification requirements stipulated by the grid infrastructure provider. This purified gas is then blended into the gas grid network.

Membrane separation – the process being used at Malabar – is one technology available to produce renewable natural gas. It consists of a number of stages and equipment.

Pretreatment – After biogas has been produced by the anaerobic digesters it enters the upgrading plant where it is cooled and dehumidified, before Volatile Organic Compounds (VOCs) and Hydrogen Sulfide (H2S) are removed through the use of activated carbon filters. During this stage, the extracted heat can be reused for other purposes.

Compression – The pre-treated biogas is then compressed to the required pressure for the final upgrading process.

Upgrading process and control – The upgrading process usually consists of a two or three stage membrane system, whereby CO2 and biomethane are separated into concentrated gas streams for final processing. Biomethane is then purified to meet network quality standards and CO2 is reprocessed for maximum biomethane recovery. Depending on the application, CO2 can be recovered for industrial users. Biogas can be both compressed into the front of the membrane system to roughly 200psi and pulled out the back end with a vacuum pump to enhance performance.

Injection/blending – Once the biogas has passed through the membrane system, THT is injected to give it the characteristic gas smell to allow it to be safely and easily detected. Different technologies are available for this step, with absorption and pump systems traditionally used, but new technologies that incorporate solenoid valve injection can also be used. It is then blended with natural gas within the gas network.

Biomethane injection into the network

For the Malabar project, once the biomethane has been processed it will be injected into Jemena’s existing gas distribution network, specifically its Eastern Gas Pipeline between Victoria and New South Wales. The product will be transferred from the Malabar facility to Jemena’s compressor stations, which pressurise the biomethane to be consistent with national and local standards.

The main function of these stations is to propel the medium forwards by boosting pressure and keeping natural gas moving through the network. Compressor stations are usually centrifugal compressors powered by turbines, electric motors or reciprocating compressors.

Natural gas compressor systems contain monitoring and backup measures to ensure safety and reliability. Heat is generated when gas is compressed, with every 100psi increase in pressure creating a seven to eight degree increase in natural gas temperature.

As a result compressor stations need to have safety measures in place to cool the gas to a manageable temperature before the gas is sent out into the pipeline again. The project will supply biomethane to these stations, where it will be blended into the natural gas network for distribution to commercial and residential customers.

Anaerobic digestion

Before the biogas enters the biogas upgrading system, the waste that will become biogas goes through anaerobic digestion, a process through which bacteria break down organic matter – such as animal manure, wastewater biosolids, and food wastes – in the absence of oxygen.

Anaerobic digestion is driven by positive displacement pumps such as progressive cavity or peristaltic, which enables the movement of raw waste materials – including agricultural, food, and municipal waste – from large hoppers through to the primary anaerobic digesters.

Positive displacement pumps excel in transferring fluids with higher viscosity, such as waste materials, a role unsuited to centrifugal pumps as they are less efficient in maintaining flow rates for thicker fluids.

In biogas production, a grinder can be integrated into some progressive cavity systems to break down biomass into a slurry mixture for more efficient transportation and processing. The slurried biomass is then transferred to the anaerobic digester silo, consisting of layered rubber membranes that expand and contract to accommodate the resulting biogas product.

Other pumps can be used for various applications in anaerobic digestion including:

  • Submersible centrifugal pumps for general flow duties in sumps and chambers, site surface water drainage, slurry pumping, etc
  • Chemical dosing pumps where precisely times flow is required for the dosing of a liquid
  • Chopper pumps
  • Slurry pumps
  • Screw pumps
  • Lobe pumps

The Malabar Wastewater Treatment Plant currently hosts extensive anaerobic digestion facilities for the production of biogas, which is used for power generation and water heating, with excess materials combusted via onsite waste gas burners.

Building business in biogas

Jemena’s General Manager Renewable Gas, Peter Harcus, said biomethane has the potential to play a huge role in meeting Australia’s net zero emissions targets. “This project will start to allow Sydney households to keep using gas, while also reducing their carbon footprint,” Mr Harcus said.

“For our commercial and industrial customers – whose manufacturing processes are difficult to decarbonise – this project will help enable them to maintain their operations, keep people in jobs, and help to decarbonise their supply chain.” According to ARENA’s Bioenergy Roadmap, by 2030 the bioenergy sector will not only enhance Australia’s fuel security but also contribute to around $10 billion in GDP per annum, create 26,200 new jobs, reduce emissions by about nine per cent and divert an extra six per cent of waste from landfill.



Malabar’s next steps

The Malabar Wastewater Treatment Plant will be the first participant in the five-year pilot, which seeks to establish the groundwork for a green gas certification scheme. Delivered as a partnership between Jemena, GreenPower and Energy Networks Australia, the project will provide customers with a way to purchase verified and accredited zero emission gas.

The gas certification scheme was announced following ARENA’s $16 million investment in the Malabar project. Jemena’s Executive General Manager, Shaun Reardon, said such a scheme could improve investments in renewable gas alternatives, including biomethane and hydrogen.

“We are driving the call for a national certification scheme because our customers have told us they want certainty in their ability to purchase verified and accredited zero emission gas just as is currently the case for renewable electricity,” Mr Reardon said. “This is an important first step towards a Renewable Gas Target, which Jemena is calling for to achieve net zero emissions in Australia by 2050.”

Though biomethane production is by now well underway at Malabar, much remains to be seen in whether such processes can be reliably and sustainably implemented at-scale. But no matter the result, the Malabar project and resulting certification scheme will be instrumental in shaping the future of Australian gas supply.

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