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But what about the smell? Myth-busting anaerobic digestion in food processing

Paul Giles

02 May 19

food and bev

The days of ‘greenwashing’ and outsourcing sustainability are over, with consumers increasingly holding the companies they buy from - including large-scale UK retailers and food companies - accountable for their environmental impact.

As a result of pressure to meet stringent environmental expectations and a shift in corporate culture towards responsible resource efficiency, an increasing number of major retail and food companies are implementing ambitious renewable energy targets and standards.

These standards will apply to entire supply chains, meaning that over the next five years, food processors and manufacturers will need to quickly adapt in order to retain and attract business.

When your biggest customer releases an environmental policy stating that they will be a business powered by renewable energy by 2025, will you still be able to supply them?

As daunting as this may seem, particularly for small-to-medium sized companies, it should be understood that there are cost-efficient and straight-forward options in the renewable energy market that not only meet or exceed environmental standards, but provide unexpected benefits.

One of the most logical solutions for food and drink processors is on-site anaerobic digestion. This involves the treatment of industrial by-products and wastewater to generate on-site power or enriched bio-gas sold to the grid. Anaerobic digestion also produces biosolids or ‘sludge’ which can be sold to seed new anaerobic systems or as agricultural soil conditioner.

However, at the same time we have seen a stagnation in the number of onsite anaerobic treatment plants.

Innovation in anaerobic digestion has come an exceptionally long way in recent years, yet several misconceptions still remain from a time of badly-designed reactors and early experimental technology.

Firstly, one lingering misunderstanding is that anaerobic digestion plants are smelly. This is no longer the case as modern sealed reactors are designed to contain odours.

Another mistaken belief is that anaerobic digestion systems are difficult and costly to operate. Through innovation and expert design, on-site plants have become straight-forward to operate and maintain.

Furthermore, the outsourcing of operational support is becoming increasingly common. Anaerobic digestion technology is becoming autonomous and many companies choose externally-run technical support to manage their anaerobic digestion facilities rather than hiring specialist operations staff to work full-time on-site. Some systems even offer remote monitoring and control of plants, meaning that there is no need for 24/7 onsite cover.

An additional concern is the scale and size of anaerobic digestion facilities, as multi-stage systems with complex and bulky equipment chains were common in the past. Modern hydrolysis systems - such as Anglian Water’s HpH Technology - have been streamlined, with fewer tanks needed than older anaerobic digestion facilities. Additionally, anaerobic membrane bioreactors – which filter and separate sludge to release biogas – have consolidated what used to be several processes into one.

On a related note, it is often assumed that anaerobic digestion only suits larger food processing factories, but improved and streamlined technology means that is increasingly cost-effective for small-to-medium sized companies to install on-site facilities.  

It is true that incentives and funding for anaerobic digestion have been inadequate, and Alpheus Environmental recently called for this to be addressed. For example, Feed-in Tariffs closed in March 2019 and Renewables Obligation closed in 2017, while the Renewable Heat Incentive programme will close in March 2021.

Anaerobic digestion in food and drink processing is growing 8 times slower than the agricultural sector, and in part this is due to most renewable energy incentives targeting agricultural projects rather than food processing.

In addition to improving incentives and funding for food and drink processers, Alpheus has suggested that a new green energy and circular economy product marking be considered for manufacturers who invest in on-site renewable energy production. Given increased consumer interest in supply chain sustainability, this could be one measure to reward and incentivise those who invest in an on-site anaerobic digestion system.

Regardless of inadequate funding and incentives, rising electricity costs mean that anaerobic digestion is becoming an increasingly cost-effective option. Powering facilities through ‘free’ energy generated on-site is evolving not only as an environmentally-sound option but a fiscally sensible decision.

Another significant cost to producers is wastewater treatment. The common measure for pollution in your wastewater is COD (Chemical Oxygen Demand) and is the largest influencer in your wastewater treatment bill. Treated through an anaerobic reactor, approximately 1 tonne of COD produces 320m3 of bio-methane which in turn produces 1100 kWhr of electricity that can be utilised on your site.

This is a saving in both wastewater treatment and electricity costs, and these savings are available without the help of the government. There are also continued innovations in the areas of biogas generation that will see these savings improve for new and existing systems.

Anaerobic digestion has come a long way in recent years. Gone are the odorous, bulky and complex systems of the past. Innovation in design, operations and maintenance has made anaerobic digestion an increasingly simple and cost-effective option for food processing companies to meet rising environmental expectations and cut costs in electricity and wastewater treatment.


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