The best it yet to come for anaerobic digestion

Written by: Nigel Lee | Published:
Nigel Lee is general manager at Amur

For once, food waste is a hot topic. Wonky veg is on the menu and retailers are pledging to reduce food waste all the way from farm to fork.

This is great news for climate change – after all, food waste is responsible for 8% of the world’s greenhouse gases (according to the World Biogas Association’s Global Food Waste Management report).

However, with so much of the talk based around reduction and redistribution, we also need to ensure that unavoidable food waste is utilised to its full potential. This means sending food waste to an anaerobic digestion (AD) plant that is run effectively enough to produce a reasonable gas yield.

Over the past year, the industry has been hearing about food waste from a range of sources. First, the government’s consultation on food waste highlighted the need for greater reduction and redistribution.

Following this came the announcement of the latest Circular Economy Package with binding recycling targets for EU member states.


More recently, the Global Food Waste Management report made the case for AD by showing that not only could global warming see a reduction of 0.5oC by 2050, but digestate from the anaerobic digestion process could also be used to improve food security by adding nutrients to the 52% of agricultural land that is degraded globally.

As part of AB Agri, Amur is keenly aware of the importance of food waste reduction. The key for us is to make the most of every resource passing through the doors – from raw ingredient resources to food waste sourced from external businesses and blended to feed our AD plant.

AD clearly has a part to play in producing clean renewable gas, improving soil quality and tackling air quality through renewable transport fuel, yet there is a tendency for those producing or handling food waste to dispatch the waste to AD without following up on whether the plant is performing well or whether material is generating the expected gas yield.

For a waste AD plant, failure to produce gas at business plan target levels is clearly highly detrimental, but currently this is also compounded by gate fees that are unrealistically low. Therefore operating below par will have a far greater impact on income.

While many food waste plants struggle to source suitable feedstock – the Anaerobic Digestion and Biogas Association reports that ADs typically run at 80% capacity – others are limited by lack of specialist knowledge that would help them to make the most of their technology.

Access to greater volumes of feedstock makes a significant difference, although operators need to avoid the common misconception that more food waste means more gas. One of the most common scenarios encountered by Amur’s AD services team is a tendency to over-feed, when what the plant really needs is to balance one type of feedstock with a small amount of another.

This is not always easy. Operators often have to take what they can find, which results in regular changes in diet. AD is all about maintaining good biology, and good biology relies on consistency. This means sticking to one type of feedstock or, where that is not possible, giving bacteria time to adapt.

Of the 10 million tonnes of food waste produced each year, just 2.5 million tonnes are processed through AD. Waste management firms can deliver greater volumes by encouraging separate collections and also by building relationships with businesses that are able to source the right type of feedstock to suit a particular plant.

At Amur we have taken the process a step further, blending incoming feedstock to make an AD ‘soup’ that meets the same specification each time and comes with a guaranteed gas yield.

Reporting across the industry could also improve. Typically, food waste producers receive a bare ‘tonnage recycled’ figure for their material; instead, including feedback on methane levels and gas yields helps to position food waste as a genuine resource and also makes producers – and operators – reflect on performance.

For smaller plants that do not have access to in-house expertise, biological support can be pulled in to cover everything from the balancing of feedstocks for improved performance or testing of feedstocks for gas yields and inhibition, to advice on additives.

The key to optimum performance is to find a partner that will look for patterns over time and work to anticipate changes before major problems occur.

Waste managers and food waste producers also need to play their part by driving separate collections and calling for greater insight into plant performance.

If we want AD to step up and play a full role in renewable energy generation, we need greater transparency and an industry-wide commitment to an AD sector that fulfils its potential.

Nigel Lee is general manager at Amur


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