1 March 2017
Doing Good with Waste
Too often, the words “sustainable living” and “landfill” are diametrically opposed. However, as New Zealand’s population ticks over 4.7 million, the humble and often derided landfill provides critical infrastructure to support the great lifestyle we enjoy within our communities.
The number of landfills in New Zealand has reduced markedly over the last 20 years. Back in 1995 there were 327 local landfills and today there are less than 50. Landfills perform an important role for New Zealand by providing an environmentally secure means for the disposal of residual waste.
There is a growing appreciation that waste is a resource and more materials are being recovered from the waste stream than ever before, with science and technology being used to recapture the value from these discarded materials. Furthermore, recent legislation (Waste Minimisation Act 2008, Climate Change Response Act 2002 and the Emissions Trading Scheme) provide additional drivers for greater waste minimisation and protection of the environment.
Waste volumes are linked to population and economic growth. When there is high GDP, waste generation typically outgrows waste recovery operations (hence, there needs to be an emphasis on not producing waste in the first place). Consequently, there is a continuing role for landfill disposal of residuals in our society. Landfills are no longer considered to be part of the linear disposal model but now are part of the circular model where wastes are stored long term until economic to be recovered. Landfill mining of historically disposed resources is now a growing trend across the world and recovery of landfill gas and its conversion to power is a common practice.
At EnviroWaste we believe in protecting the environment and minimising the use of non-renewable resources. We are actively involved in building circular solutions with our clients. Together with Foodstuffs, we are proud to have jointly won the 2016 WasteMinz Excellence Award for Best Project or Initiative in the Commercial or Public Sector. The initiative is the Foodstuffs waste minimisation programme designed to divert 80 to 90 percent of their stores’ waste materials away from landfill and into ten recycling streams. The programme is currently operated at approximately 100 stores nationwide. In the year to 30 June 2016 more than 23,500 tonnes of waste materials were repurposed and recycled.
Even with all the good work being done, there is still residual waste arising from today’s communities, commercial businesses and industries. It is regarded as residual waste because it is unable to be treated, recycled or recovered cost effectively (or energy efficiently). Its complexity, heterogeneity and randomness (both in quality and quantity) challenge the cost effective processing of this stream. As residual wastes arrive at the transfer station and/or landfill, any materials that are easily and cost effectively removed are recovered. What is left is disposed to landfill for long term storage. The challenge is to recover whatever is useful during this storage period.
Landfills have successfully managed the secure storage of residual solid waste in an environmentally responsible and cost effective manner for many years. There has been considerable technological advancement in landfill engineering and operation over the past decade. EnviroWaste believes landfills provide the optimal solution for the secure storage of residual waste for most locations within New Zealand and will continue to do so for the foreseeable future. There is unlikely to be a ‘one-size-suits-all’ technological silver bullet that outperforms the flexibility and cost effectiveness of an engineered landfill facility.
EnviroWaste owns and operates a number of highly engineered landfill facilities. Each of these facilities has been designed, consented, constructed and is operated to provide a high degree of environmental protection along with providing social and economic benefits to the communities they serve.
One increasingly important benefit from the landfill storage of residual waste, is the generation of landfill methane gas from the anaerobic biodegradation of its organic waste components. This methane can then be utilised for energy, either as a liquid or gaseous fuel, combusted to generate electricity or used as a raw material in chemical manufacture.
In today’s modern landfill, this gas is managed to ensure safety and to protect the environment. The gas is extracted from the landfill under vacuum via a reticulation network and used to generate electricity. Any extracted gas not used is flared. The production of gas within landfills typically increases as refuse is placed and then peaks as it decomposes. This is followed by a slow decline over subsequent years. The commercial lifetime of a landfill gas field is typically 10 to 20 years from closure.
Back in 1989, EnviroWaste (its predecessors and partners) installed and operated the first landfill gas to electricity (LFGTE) systems at the Rosedale and Greenmount landfills in Auckland. Both of these landfills are now closed. At their peak, the combined generation from these sites was approximately nine megawatts (MW), which was sufficient electricity to power approximately 7,200 homes per year. The electricity was generated by burning landfill methane gas in Waukesha VHP 7100 series, 12-cylinder gas engines. Today, the gas generation from these closed landfills has reduced considerably as both facilities ceased receiving waste in the mid 2000’s. Ten years later in 2016, the Greenmount LFGTE facility continues to generate approximately 1 MW, equivalent to the electrical demand of approximately 800 households. Now, at the end of its lifecycle, having played a critical role in residual waste management in South Auckland since 1980 and after 11 years as a cleanfill, the spectacular 54-hectare site has been returned to the local Council and will be developed into a public park. As demand for housing grows in Auckland and we see an increase in high-density housing, the park will provide greenspace with walking and cycling tracks for thousands of residents.
At our Hampton Downs Landfill facility (called “Hampton PARRC” for ‘Power and Resource Recovery Centre’) we have a very new and modern landfill gas to energy installation, which consists of a gas processing plant and seven specialist biogas engines. Each containerised engine generates approximately 1 MW of electricity and together the seven engines are capable of generating approximately 7 MW, which is sufficient to meet the electricity demand from approximately 5,600 households per year.
As the volume of residual waste stored at Hampton PARRC increases, the quantity of landfill gas will increase and more gas engines or additional landfill gas processing technology will be required to beneficially reuse the gas e.g. landfill gas to vehicle fuel.
At Hampton PARRC, landfill gas is extracted from the landfill using a complex system of gas wells and connecting pipework reticulated to the gas processing plant, via a series of blowers which draw the gas from the landfill under vacuum. This negative pressure on the landfill helps mitigate fugitive landfill gas emissions and odour. Before the landfill gas can be fed to the engines, it needs to be dried to remove any moisture, filtered, compressed, reheated and any silica contaminants removed.
The processed landfill gas is fed to the engines to generate electricity. The generation is equivalent to baseload as it is generally produced 24 hours per day, seven days per week, unlike other forms of renewable energy such as solar and wind. The 11kV electricity produced is transmitted under the Waikato River using the Counties Power Network to the Bombay grid exit point, where it enters the national grid network for distribution. The electricity is sold under a term contract at wholesale rates via an electricity retailer.
Hampton PARRC is at the forefront of where we see the future. A landfill site, which is a regional residual waste processing and storage site.
Hampton PARRC precinct is a large rural site of 350 Ha, appropriately consented with a buffer distance from neighbours of more than a kilometre. Already at Hampton PARRC we have the landfill gas to energy business, a greenwaste to high quality compost business using in-vessel GORE technology and a reverse osmosis leachate treatment plant that can recover up to 300,000 litres per day of high purity water. We also have a large worm farm, with approximately 12 million worms, to compost food waste. In the future we hope to build the country’s first regional (Auckland, Waikato and Bay of Plenty) food waste anaerobic digestion plant.
It’s easy to demonise waste, but it is also important that we approach waste as a resource that with continued innovation, can have significant environmental and economic benefits to New Zealand.
Pictured below: Gas engines at Hampton PARRC