Rubbish to Electricity
When we put waste into a landfill, our microbial friends naturally start eating up the waste. As they consume the waste, they tend to produce methane as a by-product, similar to what happens in a cow’s stomach.
It is important to point out that this is a natural anaerobic process that occurs to anything organic we throw away, bury and allow to decompose, regardless of whether it is in a landfill or in your backyard.
Generally methane is contained within a landfill by the placement of a clay cap, a layer of clay that we place above the waste that contains the gasses within the landfill.
This ‘cap’ is not completely airtight and as the gas builds up under it, some of the landfill gasses escape into the air. This can cause unpleasant odours but more importantly, it also allows methane, a known greenhouse gas, to escape into the air.
Methane is about 100 times worse as a greenhouse gas than carbon dioxide. At the Southern Landfill, we recognise this is not ideal for the environment and our neighbours.
The Wellington City Council and its partners, Nova Gas, have installed gas wells to ’suck ‘ the gas through pipes and burn it in a generator to produce electricity, much like a petrol generator. The generation process does produce carbon dioxide but this is much better for the environment than releasing methane.
We currently have around 16 operating gas wells around the various stages of the landfill powering a 1 Megawatt generator that sends the power into the national electricity grid to power up houses heating and electric cars/buses.
As a landfill gets older, it produces less and less methane as the bugs eat all the waste. Over a period of 50 years, we expect landfills to produce only small amounts of gas and to ‘stabilise’. Because of this, over time it may become uneconomic to continue to suck the gas to produce electricity at the Southern Landfill.
When this occurs, the land can be repurposed for other uses but not housing. Most sports playing fields in Wellington are built on old landfills. With the appropriate infrastructure and a bit of work, these old landfills can be used as recreational areas for everyone to enjoy.