Auckland’s new food waste collection - a boost for renewable gas

Image by Freepik

Auckland has become a trailblazer in its contribution to renewable gas. And it’s doing it by collecting separated food waste, to convert into gas, with energy partner Ecogas.

Did you know that 22% of landfill rubbish is made up of food waste? When it goes straight to landfill it produces greenhouse gases like CO2 and methane. Some of this is captured but the rest goes into the atmosphere, and the nutrients remaining in the food waste are lost and unused.

Collecting and processing this food waste into other forms of energy and useful products prevents this from happening.

After a successful trial project, Auckland Council has begun a rollout of food waste collection and processing for the whole city. Starting in April this year, Aucklanders will be provided with 23 litre bins for their food waste. The aim is to collect around 70,000 tonnes of waste each year – waste that would previously have gone to the landfill.

The bins containing organic material like tea bags, paper towels, fruit and vegetable skins, bread, dairy products and coffee grounds are collected weekly and taken to a pre-processing plant in Papakura for sorting.

Sorted matter is then trucked south to the central North Island’s rural township of Reporoa to Ecogas Organics Processing Facility. The plant opened in October 2022 and is New Zealand’s first large-scale anaerobic digestion facility. This is where the transformation of food waste into energy happens.

The pre-sorted food waste is loaded into large hoppers before being screened for metals and plastic waste. The resulting chunky brown “soup” is piped into one of four large digestion tanks. Next, bacteria break the soup down in a natural process called anaerobic digestion where micro-organisms produce methane, CO2 and liquid fertiliser.

Some of the methane is used to generate electricity to power the facility making it fully self-sufficient. Once New Zealand’s first biogas to pipeline project is completed, in collaboration with FirstGas Group, the leftover methane will be pumped into the country’s natural gas pipeline which is only 400m from the Reporoa site. A tomato greenhouse uses the CO2 as an atmospheric fertiliser for the tomatoes. The liquid fertiliser produced is pasteurised and spread over nearby farms as a local substitute for the imported fertilisers that are usually used.

Janet Carson, Chief Executive GasNZ says, “The rollout of Auckland’s new food waste collection and processing is encouraging for those of us who have been pushing for biogas to be a larger part of the energy mix in New Zealand.”

“When we look at what’s happening in Auckland and Reporoa along with the recent decision to make compulsory kerbside collection and separation of food waste by 2030, we see further opportunities for the renewable gas market across many communities and rohe (regions).”