I was recently given the opportunity to visit EnviroWaste’s Hampton Downs Landfill. The 80-hectare site that will take waste from Auckland until 2030. This is one of the largest landfills in the Southern hemisphere, with room to expand if required. The site was chosen because it is a natural valley with groundwater actually rising rather than seeping away from the through the ground. This means that the natural groundwater can be analysed as pure before leaving the site.
There is very little rubbish to see, because modern landfills work off a tipping platform, backfilling as they go, onto a prepared multi-layered mat like surface. Leachate is a soup of liquid and suspended solids that have seeped out of the landfill. All Leachate is collected and treated on-site, via a reverse osmosis system, where the permeate is recovered as useable water for the landfill site.
Once the waste is deposited on the tip face, it is compacted to produce a stable base. When this stable base reaches a required height, it is capped with a combination of clay and topsoil. In this way after the completion of the landfill, the land may return to usable farmland.
Spaced at about a 40-meter radius, are steel pipes that extend down into the landfill. Inside these steel pipes are gas wells from which landfill gas is extracted. Landfill gas is created by anaerobic bacteria that break down the organic content of the waste, disposed of at the landfill. The main component of landfill gas is methane. This gas is a major contributor to global warming, consequently, none can be allowed to escape from the landfill.
Draped across the landscape are large plastic pipes that connect to these steel pipes and take all the gas to a central point. Imagine these wells as a giant vacuum cleaner sucking up all the gas, and then you are not far off what is happening. This suction is so strong that it actually sucks in a bit of air from above the surface of the landfill. In this way, the landfill operator by monitoring the oxygen content knows that no gas is escaping from the landfill.
The landfill gas is cooled to remove condensable materials. Cooler gas has more energy because it expands more on combustion – the gas is then fed into one of seven gas engines. Each state of the art engine produces 1 megawatt of electricity 24 hours a day. At any given time five to six engines are in operation with more to come as the gas field increases.
This landfill gas field produces about 35 to 40,000 megawatts of baseload power per year and will do so for many years. Electricity will still be generated long after the landfill is closed. 35,000 megawatts is enough energy to power 23,000 electric cars each traveling 15,000kms per year. A Car produces about two tons of co2 per year so you could say about 46000 tons of co2 could be saved by going electric.
Clearly, in the future, everything from cars to perhaps ships and airplanes may need to be powered by electricity. Electric cars alone will require a 30% increase in power production. It is obvious that renewable electricity will be the clean energy currency of the future and that landfills that use methane capture to provide baseload electricity will have a positive part to play.