technology waste

HERU: energy from waste at home

It wasn’t very long ago that the first domestic biogas unit went on the market in Britain. More common in other countries, it would allow households to generate cooking gas from food waste. But what about all the other rubbish the household generates?

Lots of ‘black bin’ waste is already used for generating power. It’s carted off and burned in an incinerator, or put through a gasification unit. What if you could miniaturise that process and do it at home? You’d cut out bin collections, waste processing, the emissions from transporting waste. People would benefit directly from the energy created, with no transmission losses.

That’s some of the logic behind the Home Energy Resources Unit, or HERU. This domestic pyrolysis unit has been developed by British inventor Nik Spencer, and it’s currently trialling in a couple of ordinary homes.

The HERU would be fitted in a kitchen or utility room, much like a washing machine or drier. You stick your waste in the top – anything except metal and glass. Don’t worry if it’s not full, it’s a hybrid and will top up from the gas mains if required. The machine then runs overnight, raising the temperature and removing oxygen until the material is effectively turned into charcoal. It is then burned to make hot water, with the emissions scrubbed before release. Come the morning, you have a hot shower and a teaspoon of ash that has already been swirled down the drain. Here’s a recent news piece that shows it in action:

There’s no doubt that the HERU is a clever idea. But how does it stack up environmentally?

In the video, we see the machine being crammed with ‘problem’ waste such as nappies or used coffee cups. Great – that’s waste not going to landfill. We also see fabrics and plastic milk bottles going in, which are recyclable. Less good presumably?

Or not – there’s no question that recycling is better than landfill, but it has a big carbon footprint of its own, especially since recyclate is often shipped across the world for processing. An independent lifecycle assessment showed that pyrolysing waste at home with a HERU generated a third of the emissions of mixed recycling collection. Since you’re replacing the natural gas that would normally be used to heat water, there’s a carbon saving there too. In theory, the average household would save 1.2 tonnes of CO2 a year.

According to the the inventor, if it was adopted by all 27 million households in Britain, it would result in “carbon savings of 32.4 million tonnes, equivalent to 8.8% of the UK’s total carbon output.” That’s a significant contribution, but what other consequences might follow?

Let’s imagine that they become as common as washing machines, and most households in Britain have one. Glass and metal recycling continues, but all plastic and paper is now in the machine – those recycling industries have been killed. With less recycled material on the market, there is increased pressure on virgin stocks – more timber for paper and card, more oil or gas for plastic. Perhaps food waste is going into the HERU too, reducing food waste to landfill, but also reducing material available for compost or biogas.

Universally applied, the HERU would be a better way of dealing with our waste problem, but it might remove the incentive to reduce waste in the first place. Our waste would disappear like magic, and it would be easy to forget that we were literally vaporising the earth’s resources in our kitchens. That’s definitely a downside.

Then again, it’s not likely that we’ll have one of these in every home. Not anytime soon. I suspect that the HERU will be picked up at the commercial level first. Waste is a more direct cost for businesses than it is for households, and the savings will be more obvious. The HERU could make a big difference, and while mine is a cautious welcome, I look forward to seeing how the technology develops.


  1. I don’t think it’s necessary that it would kill the recycling industries. Actually it could even increase them – if there was a shortage of waste paper and plastic then they have now become valuable commodities – worth enough for someone to buy them from you. If you were paid to recycle then instead of vaporising them you’d be incentivised to recycle instead of doing it out of civic duty and to solve a waste problem. As we all know people will change their behaviours significantly if they felt they had a monetary incentive. Just a thought

  2. This concept is interesting, but also flawed in so many ways. Burning rubbish in large municipal incinerators tends to produce toxic residue, often laden with heavy metals and carcinogens. Surely flushing these down the drain would be a terrible idea.
    The flue gasses from plastic incineration can also be carcinogenic and disruptive to the endocrine system. Effective scrubbing systems on municipal plants are extremely complex and expensive. The impact of these devices on local air quality is questionable.
    Lastly, while they would reduce the need for waste transport, the resources required to produce and maintain millions of highly complicated, privately owned micro incinerators would be huge.

    1. I have some questions about the emissions and waste, but it is very different from an incinerator. It uses pyrolysis, which has fewer emissions than incineration, and their breakthrough is that they achieve it at a much lower temperature. Metals won’t burn in a HERU, they’ll just come out very clean.

      The website says it’s all clean and safe, and obviously that will need to be fully verified before the product goes on the market.

    2. I also feel nervous about this as a household or small-industry technology. Throwing a varied mix in and hoping not to get harmful byproducts seems a tall order. I’m not sure that pyrolysis of such varied mixed feedstocks is inherently safer than incineration. I think it’s significant that incineration (which is supposed to break everything right down to very simple molecules through very high temperatures and plenty of reactive oxygen), has been so problematic even for municipal scale plants. How much less likely to ensure nothing untoward happens with thousands of far-less regulated (maintained?) small equipment installations? Lots more homework to be done on this, I feel…

  3. The two of us generate about a carrier bag’s (remember them?) worth of waste a week – almost all single use plastic that we cannot (yet) avoid – so hardly any weight in that bag. We have not found it all that hard to get to this point, so I would rather our knowledge and skills were shared than use one of these devices.

    1. We’re the same, and we’d need to burn the recycling, food and garden waste to make a decent quantity of hot water. I’d rather use the food and garden waste to make biogas, run the hot water off that and still have the compost left at the end.

      I suppose if you saved up larger things that would go to the tip, that might work. I had to dispose of an old sofa last year that was so wrecked we couldn’t give it away. I broke it down into its various materials, recycled what could be recycled and used the wood on the rocket stove. That would probably have kept us in hot water for a month. In fact, I could probably scrounge the streets of Luton and run our hot water entirely on fly-tipped furniture…

  4. Waste reduction, reuse and recycling are the way to go, not HERU.
    HERU gains a little energy but loses the material content. Recycling of simple materials and anaerobic digestion of food waste gains lots of energy and much more than used in collection and processing, especially with kerbside sort collections for food waste combined with separated dry materials.
    Recycling levels with kerbside sort are already high in some areas, notably all of Wales, with potential to still go higher.
    Waste avoidance, deposits, product durability and design for repair, circular economy, design for recycling and more all have great potential.
    Direct incentives forhouseholds to perform better are pay-as-you-throw for refuse disposal and less frequent refuse collections – three and four weekly refuse collections are starting to take off in UK with great results.
    How much would HERU cost for a household? Why invest?
    More can be better achieved by other routes. Don’t waste time on HERU!

  5. This would be a better idea if it made biogas at home and not charcoal.
    I compost in my garden but all of the biogas just drifts off into the air. It would be cool to cut my use of natural gas and release of methane into the environment.

  6. I was interested that in the bbc report which is used to advertise the heru on its website there is no reference to the fact that CO2 is an output of the system. No reference either to the fact the aqueous waste stream includes nitrate and chlorine which the water companies would presumably be expected to clean up as an externalised cost.

    1. Yes, the BBC report covers it as a new technology, and celebrates the innovation without asking too many questions about how it fits into the natural environment or existing waste systems.

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