The concept of waste is manmade – it doesn’t exist in nature. Explain that to consumers, however, who send more than 20 million tonnes of waste a year to Australian landfills. The key waste stream is municipal solid waste, the stuff we pack into our red bins and that is turned out by the commercial and industrial sectors. Don’t think of it as rubbish, however, because municipal solid waste has a good amount of energy that can be recovered and turned into heat, electricity or into second-generation, combustible fuels (such as methanol, methane, synthetic fuels, ethanol and even hydrogen).

Waste to energy (WtE) or its synonym energy from waste (EfW) is not new. In fact, it was worth over $35 billion globally in 2019.

It has been estimated that WtE could provide up to 2% of Australia’s electricity needs. While that doesn’t seem like much, the key here is that these plants can be dispatchable and are also located close to load. This scenario has the advantage of providing local baseload during peak usage times. One also can imagine battery storage playing a role in providing additional peak load capacity in tandem with these plants.

Some reports refer to these WtE projects as generating renewable energy, and this is only partly true.

Converting biogenic resources, previously destined for landfill, to heat or electricity can be defined as renewable energy. Biogenic resources are materials that come from living things (that is, paper, cardboard, wood, cloth and food from both animals and plants).

Let’s call the balance of landfill-destined resources that are non-renewable – such as plastics – non-biogenic resources. We will come back to these shortly.

Are WtE facilities good investments?

Waste to energy solves two problems: what to do with our waste and how to provide dispatchable and partly renewable energy. 

There has been a rapid growth in WtE projects under development both globally and now in Australia, and they are not small. In Kwinana, Western Australia, a $700 million plant under construction will process 400,000 tonnes of waste a year and generate 36MW. A quick tally of ongoing projects around the country shows they will process over 1.6 million tonnes of waste a year and generate around 130MW of electricity, a useful amount – but we must look at the cost benefit to understand its value.

On a cost-per-Watt basis, the Kwinana project (pictured) will come in at about $20/Watt installed. The solar benchmark is 20 times cheaper at around a $1/Watt.

Still, there are other benefits that build a bridge to the WtE business case. The site reduces the amount of landfill required; in this case, about 25% of Perth’s post-recycling rubbish will be diverted from landfill. At a current landfill levy of $70 per tonne, the project will provide a benefit of $28 million a year in avoided landfill costs over its planned 25-year life.

Electricity sales would be additional and depending on how the offtake is structured it may add a supplemental income stream. There also is potential upside from new energy services that will evolve, such as demand response and ancillary services, either directly or complemented with energy storage.

Resource availability is key

The key to the longevity and viability of WtE facilities is the availability of resources of suitable quality and volume at a price that supports the business model. Electricity offtake agreements round out the key elements that make these projects work.

Let’s consider the energy content of biogenic and non-biogenic resources; plastics have a high energy content relative to biogenic waste sources but the vast majority of plastics are made from fossil fuels, so the energy produced is fossil fuel-derived energy.

If the objective is to produce energy, then high-energy feedstocks are a really good idea. The problem is that using energy for waste is not its highest usage as defined by the waste hierarchy.

Clearly, avoidance, reuse and recycling are all preferable to energy from waste. On the waste hierarchy the highest use of the resource is the desired outcome. More recently, thought leaders believe we must refine how we think about the resources we squander as waste.

Thinking in terms of resources, not waste

There is no concept of waste in nature – everything is a nutrient for another process. This principle underpins the concept of a circular economy, a key driver of reductions in the waste streams that power WtE projects.

Let’s look at the fuel resource and its long-term security for WtE projects: our waste production increases with population growth, which is a “good” sign. This means there is more available waste. The makeup of the waste is likely to change over time due to pressures to increase the amount of waste that is recycled, as this is a better use of the resource. 

Plastics can contain seven times the energy of biogenic waste, which comes from living things. This means the more plastics you remove from the waste stream, the less energy is available to generate electricity – leading to a quick drop off.

I contend that the ongoing march to reduce plastic waste streams means their role in WtE has a limited life. But there is an alternative to ensure WtE plays its part in the future global energy mix.

As we attack food waste across Australia in the name of the circular economy, this will potentially remove WtE feedstock as well. The technologies around engineered wood – that take lower value wood streams – is likely to mean less WtE feedstock from the C&I waste stream in particular.

It appears that our march to sustainability undermines the viability of municipal WtE projects at a macro level and in the medium term.

If the circular economy is going to cut into WtE projects in the medium term, what are we left with? We will need a more suitable feedstock volume, but we firstly need to look at another pathway to a sustainable energy future.

Better value from biomass

Is the right path for biogenic waste the current thermal treatment paths used in municipal WtE projects, globally and soon in Australia? Or is it liquid/gaseous fuels as a second emerging path?

The complete oxidation of waste in the majority of WtE plants globally robs us of other value streams from biomass. Biomass is abundant and wasted in huge quantities. One third of all food globally is wasted, according to the Food and Agriculture Organization. This also ignores the vast amounts of agricultural residues available. These residues can replace the reduction in resources due to circular economy-related initiatives.

What if there were a clear third way? Is there a way to solve the waste and energy problem and at the same time repair environmental damage to our ecosystems among other benefits?

One such pathway recognises the need to provide a way of restoring our soil and ecosystem health. That process is called pyrolysis and the product is biochar, which is charcoal from biomass.

Biochar is a carbon-rich product that has a huge number of applications: a soil-restoring additive that improves the health and productivity of the soil; an animal feed supplement that reduces methane emissions and improves health, and; a sequestration resource the locks up heavy metals and other pollutants.

Biochar, when used in soils, also captures and stores carbon for potentially thousands of years. Biochar does this very cost effectively and simply – more simply, I would argue, than liquefying CO2 and “landfilling” it at huge complexity and cost.

The pyrolysis process produces heat that can be converted to electricity, as in the current WtE projects. This electricity is also renewable and dispatchable bioenergy.

The role that WtE can play in the energy grid may help balance variable renewable energy and could have a significant input in the energy mix of the future.

We also have the opportunity to take the resources we can get from different pathways to propel WtE to a new level of economic, environmental and social benefits.

Shaun Scallan is head of products at Capricorn Power.