Good gas: How organic waste will help cut greenhouse gas emissions

Recovering landfill gas for conversion to power isn’t new. But as New Zealand rebalances energy sources to meet its obligations under the Paris Agreement, gas from green sources, rather than fossil fuels, will contribute more to the country’s energy requirements.  

Gas that flames from the hob on your stove top is likely to have different origins over the coming years. More of the 4.7 billion cubic metres of natural gas New Zealand burns through each year will be ‘green’ – meaning it won’t come from fossil fuels. One day those flames might even burn hydrogen.

Change is being driven by local legislation, including the Waste Minimisation Act 2008, Climate Change Response Act 2002, and the Emissions Trading Scheme, as well as the country’s commitment to the Paris Accord – a global agreement on climate change, under which New Zealand is to reduce greenhouse gas emissions by 30 per cent below 2005 levels, by 2030.

New Zealand landfills will play a role in reducing greenhouse gas emissions - even as their number dwindle. Back in 1995, there were 327 local landfills - today there are less than 50, demonstrating the efficiency of modern approaches to waste management.

Today, the recovery of ‘green’ methane from landfill gas and its conversion to green electricity plays an important role in strengthening the regional electricity supply network. Methane, as natural gas, is also used as a gaseous fuel, and in chemical manufacture.

As such, landfills and other facilities that generate green methane from the anaerobic biodegradation of organic materials, are likely to play a bigger role in our energy future.

Gas recovery

Back in 1989, EnviroNZ (and its predecessors and partners) installed and operated the first landfill gas to electricity (LFGTE) systems at the Rosedale and Greenmount landfills in Auckland. Both landfills are now closed, but at their peak, they generated a combined total of approximately nine megawatts – enough electricity to power around 7,200 homes per year.

Now, at the end of its lifecycle, having played a critical role in residual waste management in South Auckland, and after a further 11 years as a clean-fill, the 54-hectare site at Greenmount is set to be returned to the local council and developed into a public park. 

Just as Greenmount’s days are over, many of New Zealand’s now closed landfills are past their days of peak gas production, winding up and then down over a commercial lifetime of 30 to 40 years.

Landfill gas today

EnviroWaste’s Hampton Downs Landfill facility, called Hampton PARRC (Power and Resource Recovery Centre) operates a modern landfill gas to energy installation, comprising a gas processing plant and seven containerised biogas engines, each of which generates approximately one megawatt of electricity. The potential total of seven megawatts is enough to meet the electricity demands of approximately 5,600 households per year.

Residual waste stored at Hampton PARRC produces gas for future recovery. But harvesting landfill gas is no walk in the park, requiring complex systems of gas wells and connecting pipework to a gas processing plant, where a series of blowers draw gas under vacuum from the landfill. That’s just the start. Landfill gas must be dried, reheated and processed to remove contaminants, before being fed to the biogas engines. 

Electricity generated by Hampton PARRC’s biogas engines is distributed under the Waikato River into the Counties Power network and the national grid for distribution and sale. 

Methane (CH4) provides the building blocks for a Hydrogen (H2)-powered future

While New Zealand’s prolific burning of natural gas is less taxing on carbon emissions than other fossil fuels, carbon dioxide is released to the atmosphere when gas is combusted – which is why landfill methane and other ‘green’ methane sources are important contributors to our future decarbonised energy network.

These sources can be cleaned up to make a renewable natural gas, which can be injected into the natural gas network to offset the use of fossil fuels. They can also be used to produce green hydrogen, which in the future could replace fossil fuel natural gas in our homes, and the liquid fuels in our transport system.

Experts put the cost of meeting New Zealand’s first commitment under the Paris Agreement at $14 billion to $36 billion between 2021 and 2030 – a move likely to remove about 220 million tons of carbon from our economy.

Landfill gas has a role to play, offering a readily available renewable energy source to replace fossil fuels and reduce carbon emissions.

Pictured below: Containerised biogas engines at Hampton PARRC

Gas Engines Hampton Downs

By Chris Lobb, General Manager Special Projects, EnviroWaste