Anaerobic Digestion (AD) is a natural process where micro-organisms break down organic waste such as food scraps in a sealed system, without oxygen. This produces valuable resources in the form of energy (heat, gas and used to generate electricity) and digestate.

Digestate is a nutrient rich substance which is used as fertiliser that actively regenerates soil health and replenishes carbon. The fertiliser, Fertify, is an alternative to synthetic, imported fertilisers.

For more information visit fertify.co.nz.

Composting and Anaerobic Digestion (AD) are great complementary tools for different jobs. Most importantly, they both keep waste out of landfills. Both composting and AD preserve nutrients contained in the original feedstock and recycle them back into the soil.

Composting is best suited for primarily drier and bulky greenwaste and plant materials.

Organic waste that is full of fats, oils or protein is better processed through anaerobic digestion. Food waste is typically high in water content, which is processed well using AD.

Organic waste, such as the following can be processed in an anaerobic digester:

• Inedible food

• Meal leftovers

• Meat scraps, bones & fish

• Eggs & Shellfish (including shells)

• Fruit and Veggie scraps

• Pasta & bread

• Coffee Grounds & tea bags

• Paper towels

• Green garden waste (grass clippings, flowers etc)

The AD plant cannot process with following items:

• Food packaging, including most compostable packaging. This is removed during the pre-treatment processes.

• Woody garden waste

• Nappies

• Pet waste

Currently compostable packaging is difficult to identify from its non-compostable counterparts and so unfortunately ends up being removed as a contaminant.

Ideally, we would have no packaging in the waste we process. However that is not always possible. Our focus is on stopping food waste entering our landfills so we have processes in place to remove packaging.

Where we can, we remove large packaging (plastic, cardboard) and recycle it.

All of the smaller plastics, metal or other packaging are extracted from the waste by machines, baled and sent to landfill at present.

We are working on solutions that will allow us to recycle the different types of packaging.

Anaerobic Digestion results in two products: energy (gas, heat and generating electricity) and digestate.

Liquid digestate is used as fertiliser on local farmland while the biogas is used to heat nearby glasshouses, used to generate electricity to power our plant and converted to a renewable substitute to natural gas.

For Christchurch Organics Processing Facility we have designed a bespoke solution which will process the more woody and fibrous materials into biofuel (e.g. wood chips) that can be used as a replacement for fossil fuels such as coal.

For more information on the Christchurch Organics Processing Facility, click here.

Ecogas sites are self-sufficient in energy, producing enough to power the plant. The facilities produce minimal emissions due to the capture of gas during the anaerobic digestion process.

Where possible, Ecogas use backhaul loads (where trucks would otherwise returned emtpy) to transport organic waste. This minimises transport emissions and reduces additional vehicles on our roads.

Anaerobic digestion produces biogas which when combusted in boilers or engines, is turned into carbon dioxide. As the biogas is biogenic (from recent plant growth as opposed to a fossilised source such as coal), this CO2 is considered neutral from a greenhouse gas (GHG) perspective.

Digestate replaces synthetic fertilisers on farms, reducing reliance on imported materials with a high carbon footprint.

Overall, anaerobic digestion and biofuel production has a net positive impact on the environment, by diverting organics from landfill and providing renewable, alternative energy sources. Organics that end up in our landfills produce greenhouse gas emissions as they breakdown.

Anaerobic digestion of food waste produces a liquid residue called digestate which can be applied to land as a nutrient rich fertiliser. Synthetic fertilisers are manufactured using energy intensive processes that rely on fossil fuels.

Biofertilisers such as anaerobic digestate can help to displace the demand for synthetic fertilisers by providing nutrients from organic waste streams in fertiliser form. Digestate consequently reduces our reliance on fossil fuels, the need to transport these fertilisers worldwide, and all the emissions incurred from this supply chain.

Additionally, the digestate produced by Ecogas, Fertify™, has a high carbon content which is valued in regenerative farming practices for promoting healthy soils.