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Odour management is key to anaerobic digestion plants

For the anaerobic digestion (AD) sector to flourish, two key principles need to be addressed. First, the Government needs to enforce the diversion of food waste from landfill and incineration. Second, existing AD facilities must be designed with the best available technology and to the best operational standards. Biffa is running Europe’s largest food waste processing AD facility. Its energy deal with Sainsbury’s Cannock store allows the retailer to be powered by its own food waste using an electricity cable direct from the AD plant in Poplars.

This project brought the plant under the national spotlight and cemented its status as one of the UK’s most influential green ventures. When the company took over the facility from its building and commissioning contractors, it was falling well short of its contractual requirements for odour control. The biofilters designed and built to treat odorous air from the plant were not fit for purpose, and created a focal point of dissension from residents and the regional Environment Agency (EA) team. As any operator of a waste facility will know, protecting neighbours from unwanted environmental effects is a crucial part of fostering acceptance and respon­sible long-term engagement with local residents and businesses. In the Poplars case, residents – some of whom lived just 200m from the plant – were disappointed about the level and frequency of odour escaping from the plant. Biffa was thereby obligated to develop a robust and bespoke solution for long-term community harmony. With board-level commitment from Biffa to invest in an exemplar facility, we had the in-house skills to make it happen.

The EA had no template or pre­defined standards for an odour management plan for AD, so it took the company’s in-house engineering team to come up with the solution. Poplar AD 1 They researched across other industries to establish best prac­tice in technologies and manage­ment procedures, gradually drafting the odour management plan step-by-step. Sampling and testing each possible source of odour, and then benchmarking against best available technologies, the team finally engineered a robust odour man­agement system for the Poplars site. Biffa invested in a novel vortex scrubber system which uses a combination of speed, turbulence and moisture to separate volatile organics (odorous compounds) from the air stream.

The removal rate of the vortex scrubber is far superior to that of a conventional scrubber: its installation made a significant and lasting improve­ment. Pre-treated air from the vortex scrubber was then passed to the main odour control treatment plant, providing a double barrier to odour escape. While this pro­vides an effective abatement solu­tion, further works were needed to ensure robust 24/7 operations.
Once the new scrubber was installed, addressing any remain­ing odour followed the law of diminishing returns. The team introduced systems, procedures and equipment to tackle the challenge. There was no single cure, so the final plan included aspects of training, housekeeping, instru­mentation, controls, maintenance and system management. Despite the years of challenging problems,
Biffa has addressed the issues head on, investing a further £4m in process improvements at Poplars. This demonstrates the value that the company places on this flagship facility. The conditions and checks set out in the detailed odour management plan ensure that the plant operates to the highest possible standards and achieves mini-mal impact on the local environ­ment. The Poplars team is now proud to have received zero compliance assessment reports from the EA in the past 12 months, as well as a dramatic fall in odour complaints.

 Poplar AD 2 Taking three years and 15 drafts, the odour management plan was finally approved by the EA in March 2015. The improvement has elevated Poplars AD to a ‘best in class’ status with the EA. It is a UK first for such a facility and sets an example for others in the industry to follow. Lisa Pinney, EA area manager for West Midlands, said: “Biffa has made significant investment at the Poplars site. Through 2014, the AD plant has operated not only in line with its permit but also best practice for the industry, which shows what can be achieved when we work together well.” The Poplars management plan is now being used as a template for Biffa’s mechanical biological treatment facility in West Sussex, and is publicly available on the EA website for other AD developers and operators to learn from. Following this experience, the EA is now requiring that any pro­posed AD facilities have an approved odour management plan before being granted a licence to operate. This will further help the industry to raise its standards and prove that, as a green solution for society, AD is here to stay and will only improve.
The UK generates 14.8 million tonnes of food waste each year, yet many AD facilities are struggling to access this feedstock. Without more Government support for food waste collections, we run the risk of plants failing, financially and operationally. So Biffa is working hard to convince the Gov­ernment that separate food waste collections from homes and businesses is the right way to go. We would encourage operators to review their odour manage­ment systems and procedures, and to learn from what has been, at times, a challenging process. Despite separate food waste col­lections being unsupported by the main political parties, the Green Investment Bank’s recent report Smarter, Greener Cities:

Ten Ways to Modernise and Improve UK Urban Infrastructure highlights AD as ready to be “rolled-out immediately and at scale across the country”. Tackling the technology weak spots will pay dividends, particu­larly issues of odour release in urban settings. The EA is right to insist that odour management plans are approved as a prerequi­site to new AD developments. If AD is to fulfil its potential as the poster child for low-carbon Britain, we all need to play our part in protecting its reputation and delivering excellence.

Dr John Casey is Energy Division managing director at Biffa Economies of scale made it possible Compared with most AD facilities in Europe, Poplars is a giant. It treats 120,000 tonnes of food waste each year and generates 6.5MW of renewable energy, enough to power 15,000 homes.

The scale of Poplars has made Biffa’s investments possible, and it is important that the company helps the industry to follow in its footsteps.

Controlling sources of odour In order of priority:

1 Eliminating or reducing the source of the odour
2 Disrupting the transmission pathway to site boundary 3 Actively capturing and treating the odour, or increasing dilution and dispersion.


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