Ti Tree Bioenergy: Clean Energy From An Old Coal Mine
At first glance Ti Tree Bioenergy’s site looks like a regular, but very tidy, landfill. It’s a big hole in the ground that is being filled up with household, industrial and other suitable waste. But that’s about where the similarity ends.
With a regular landfill, waste is compacted and covered each day to help keep rainwater out. As a result, it can take hundreds of years for waste to break down. In contrast, the Ti Tree Bioenergy site is managed as a bioreactor, to produce biogas that is burnt to generate electricity. This requires a different approach.
As the Ti Tree’s manager Bo-Eric Holmkvist explains, “We provide optimal conditions for microorganisms to degrade waste. A key factor is maintaining a moisture content of between 35% and 45% by weight which is managed by recirculating leachate and controlling the waste stream.” That means rejecting large volumes of high moisture content materials, and other things that would upset the bugs such as salt. Other than that, nature takes over and the waste is stabilised within a five to ten year timeframe. This also results is more rapid production of biogas. Once decomposition is complete, the residue is considered inert in terms of environmental impact and settlement.
While some traditional landfills have been retrofitted to allow for biogas capture, much better and quicker results are likely to be obtained from a dedicated bioreactor. “A bioreactor is more like an anaerobic digester than a traditional landfill,” says Bo-Eric. “However anaerobic digesters can only cater for organic input streams, rather than the mixed waste stream that we can handle.”
Ti Tree's bioreactor is quite different to your regular landfill.
Bo-Eric sees Ti Tree Bioenergy as a waste disposal facility and electricity generator in equal measure, so perhaps it’s fitting that it is a joint venture between international environmental solutions company Veolia, and JJ Richards, an Australian, family-owned waste management business.
Ti Tree currently has a generation capacity of 3MW, with the majority of its electricity exported to the grid. Only a very small amount is used to power the site. With the bugs beavering away 24/7, the rate of gas production is fairly constant, so in contrast to wind and solar power, Ti Tree Bioenergy provides clean, renewable base load electricity generation. However, in common with other renewable energy sources, what happens with the Renewable Energy Target (RET) will have an impact on the facility. It may enjoy twin revenue streams from waste disposal and the sale of electricity, but it is a more complex site to run than a conventional landfill, and in a competitive waste market schemes such as the RET do assist its financial viability.
Old coal and a big hole
Ti Tree is about more than just waste disposal and power generation. It owes its existence to a 36 million cubic metre hole left behind by coal mining, and over time the site will be restored to the bushland state that existed prior to mining. Forty hectares have already been planted with spotted gum and red gum to create the basis of a sustainable hardwood plantation.
How long will it take to fill up that big hole and complete site rehabilitation? “Based on current inputs and legislation it will take about 90 years to completely fill the available void,” says Bo-Eric.
That opens up an interesting prospect. With the days of coal mining (hopefully) numbered, Ti Tree Bioenergy might be setting the example as to how other coal mines can redeem themselves.
All images: supplied