We have a problem with household waste in the UK. The stuff that gets collected at the kerbside. In 2017 we collected about 27 million tonnes of waste from our homes. We are getting better recycling, and just over 45% of it was separately collected as metals, plastics, glass, garden waste and food waste. That still leaves 14.6 million tonnes of residual waste to dispose of. All that stuff that goes in the black bags and black bins.
Burn it or bury it?
We burn it to recover the energy content or bury it in landfill. We even export solid waste to northern European countries for their energy from waste plants.
The problem is that energy from waste and landfill are the two least favoured options in the waste hierarchy. They generate little value and create significant problems.
If you landfill waste you have to be very careful the toxic materials created by the decomposition processes don’t escape from the site, contaminating groundwater and watercourses. The decomposition also generates methane, a potent greenhouse gas, that must be carefully managed. Just about the only value from landfilled waste is to use the methane to power generators to supply the electricity needs of the site.
Landfill sites are unpopular with their neighbours, and increasingly hard to find in densely populated countries. Governments in the developed world are working hard to reduce the amount of waste that goes to landfill.
Burning the waste and recovering the energy is a bit better than landfill, but only a bit better. Anything with an organic content like wood and paper, plastics or food waste can be burned. However, it’s about the lowest value use for waste. When I worked in the oleochemical industry turning natural oils and fats into chemical products, we sold any residues left from our processes for the heat energy they contained. We worked ferociously hard to make sure there was as little left over as possible as the value was so low compared to making a saleable product.
As well as being a low-value use of waste, incinerators can produce toxic gases unless properly controlled. Like any thermal power station, they release carbon dioxide, and the ash can be toxic and difficult to deal with.
It would be much better if we could find something useful and valuable to do with our nonrecyclable domestic waste. Fortunately, innovative companies are looking for ways to do exactly that.
Three approaches to getting value from waste
I recently visited the Rushlight Summer Showcase where clean technology companies exhibited their latest innovations and pitched their ideas to investors. It is always a fascinating day, and I spotted three different companies all working on the problem of how to generate value from domestic waste:
Rather than treating residual domestic waste as a problem requiring disposal, Fiberight see it as a mixed stream of raw materials with some commercially useful components that just need further separation. Their process removes larger items such as metals, electrical items and textiles from the waste stream. They pulp the rest, wash it and separate it into fibres, plastics and food waste. Enzymes can break the fibres into sugars for the chemical industry. Food waste goes to anaerobic digestion to produce biogas.
The flexibility of the process means that they can produce a range of commodities from black bag waste:
- Cellulose rich fibre
- Lignin rich fibre
- Biogas and energy
Fiberight have both demonstration plants for development and testing of the process, and the first full-scale plant in Maine which can process 180,000 tons of municipal solid waste p.a.
Green Fuels Research is a spin-off from the well-established biodiesel company Green Fuels Ltd. One area of focus is the production of sustainable aviation fuel, and they are partners in the EU project flexJET. The process being developed uses Thermo-Catalytic Reforming to convert a wide range of organic waste into a mix of aviation fuel, char and hydrogen. Char is a pure carbon residue that can be used as a fuel, a soil enhancer and for long-term carbon storage.
The process heats the waste in the absence of oxygen breaking down organic materials and driving off volatile compounds. The same basic process as used to make charcoal. Gases are separated out and vapours condensed into an energy-rich oil. They then upgrade the oil to a jet fuel using a standard petrochemical process – catalytic reforming.
flexJET will only use the organic fraction of waste, and so will need some separation if it is to use domestic waste directly.
Velocys is also targeting fuels but using a different chemistry. The waste is broken down at higher temperatures producing a mix of carbon monoxide and hydrogen known to chemists as synthesis gas (syngas). This mix of gases formed ‘town gas’ used for gas lighting, heating and cooking, but now we use ‘natural gas’ – methane. The main use of syngas these days is in the Fischer-Tropsch process. This sticks the individual carbon atoms in carbon monoxide together in long chains like popper beads from the 50s and 60s. And those long hydrocarbon chains make fuel and a range of other chemicals.
After demonstrating their technology using wood waste to produce diesel at a plant in Mississippi, they are now working on a project at Immingham in the UK to produce sustainable aviation fuel from household waste.
Three different companies, three different approaches to getting value from household waste. OK, Green Fuels Research and Velocys are producing a fuel which will ultimately burn, releasing carbon dioxide into the atmosphere. However, it diverts waste from landfill, avoids many of the problems of incineration, and recycles waste into liquid transport fuels which will continue to be needed for some time.