Redvale Landfill - Waste to Energy

The Redvale Landfill - not the most glamorous of site visits but truly fascinating. 

50% of Auckland’s waste arrives here, that is up to 325 trucks of waste per day.

Consented in 1993 for 30 years to hold 20 million cubic metres of waste, a 5 year extension (2028) was granted as the site was not projected to be full. This is due to the efficient running of the facility and products going elsewhere for recycling. Not just a landfill, Redvale is a resource management “waste to energy” site which generates electricity and heat from these resources which would otherwise be thrown away or dispersed into the air.  Redvale accepts approx. 2,500-5,000m3/day of non-hazardous (USEPA) waste. It also has a separate section for processing asbestos removed from old buildings, etc. The site will have cost $120m in total by the time it winds up.

There will be a 30-year aftercare policy as the methane gas created from decomposing organic material will continue to be captured and used to generate electricity. In NZ, Redvale rates as the 9th largest commercially extracted gas field in the country and has perfect green credentials. Waste Management is owned by the Beijing Capital Group, which supports the site as their flagship in new technologies and advanced sustainability. Although owned by BCG, Waste Management has its own NZ management team.

The Redvale site of around 82 hectares is located in an old lime quarry off the Dairy Flat Highway with the clay substrate (mudstone) offering good geology for its low permeability. The leachate of the site also desirably sits lower than the surrounding water table so cannot leak out. The landfill, contained within its impermeable shell of mudstone combined with other substrates, means leachate cannot escape into either deep or shallow groundwater. Rainwater is managed to largely runoff the clay cap and is collected in a series of perimeter ponds.

50% of Auckland’s waste arrives here, up to 325 trucks per day. The circular route through the facility allows for a quick turn-around and all trucks go back out onto the main road via a wheel washing station, so no clay residue is taken offsite.  Only a small area of the landfill is exposed at any one time, so the landfill process is filled with waste, rolled and compacted, and finally covered with 1 metre depth of clay and then 20-30 cm of top soil. Thus finished, it is then grassed as another area is opened up. Vacuumed pipes remain in place, collecting the potential energy (gases) and can be managed by a specialist maintenance crew. The only visual reminder is occasional hose-like pipes extending above the grassy knoll.

Once the finished area is grassed, shrubs and small trees can be planted, and sheep can graze. The area cannot be built upon, nor can large trees be planted on the knolls as the risk of trees blowing over could pull off the clay cap. An area of 100 ha has been set aside for planting trees. It is planned that parts of the site could become a recreational area, with wetlands and ponds.  The bird life we saw was extensive around the water areas.  We all commented on how serene the site was and how clean and healthy the pond water appeared to be.

As soon as waste has been deposited, large bulldozers and compactors run over the area crushing and compacting the fill.  Every night the exposed waste area is covered with soil to reduce smell, blow-away and bird activity.  Odour cannons drift a mild bleach solution over the area to further reduce any problems for their close neighbours, and litter fences further reduce escaping waste. Every morning, the previous day’s daily cover is peeled back to re-expose the working edge of the landfill ready for the new day’s waste

Most people expect landfills to smell, but at Redvale the landfill gas, which is 60% methane, generated by the rotting down of the organic waste, is channelled and vacuum sucked into gas lines which is then burned to generate electricity – with (short-cycle carbon GHG) CO2 as a by-product. Some of this is sent next door to the largest aubergine glasshouse in NZ.  This neighbour also heats its glasshouses from piped Redvale hot water.  

Redvale sells its electricity to the grid – but only after they first use their own electricity produced from the 14 container-sized generators on site! Production of 80 GW per annum is only 1% of the potential output of Huntly but is very worthwhile, powering approx. 14,000 houses and making it Auckland’s largest generator of green electricity.

WM is moving towards electrifying their truck fleet, as each diesel truck consumes 135 litres of diesel per day – due to the stop start nature of a collection truck’s day. An EV truck is very efficient and the EV trucks they do have often come back to base only half empty – there is of course on site EV charging – powered by waste!

WM also own the brand ‘Living Earth’ which takes household organic waste in Auckland and Christchurch to turn into compost.  This is what their website says:-

“For over 20 years we've crafted our amazing compost and helped recycle well over a million tonnes of New Zealand’s organic waste! That's a lot of great gardens, healthy crops and exciting city green areas that Living Earth has helped to grow. Waste Management, NZ's largest waste recovery company, is proud to own Living Earth, NZ's largest organic waste to composting operation, as part of its commitment to efficient waste processing in NZ.”

 


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