How West London rose to the odour challenge

When West London Composting first opened its doors in 2004, controlling odours became one of its biggest challenges and before long, the firm faced an hostile local community. To make matters worse, rumours began spreading around the neighbourhood that West London Composting (WLC) – or “the landfill on the hill” as it was referred to by some residents – was merely a ghastly waste site treating all sorts of unmentionable rubbish.

For WLC, it soon became evident that a major problem was one of perception. Perhaps even more frustrating was, in its early days of operation, complaints by residents were invariably levied each Tuesday – the day the local authority collected garden material in the same area. Talk to WLC and they still recall a particular instance when, on investigating a complaint within 20 minutes of it being lodged, it was discovered that the council had been emptying gullies in the very road from where the protest had stemmed. Needless to say the neighbourhood automatically blamed any unpleasant smells on WLC.

Distinctive smells

Nevertheless, odours, good and bad, are a result of the activity of bacteria. Composting emits a whole range of volatile organic compounds (VOCs) – and it is the range and level of these which give rise to odour. During anaerobic composting for example, where waste rots without available oxygen, substances such as acetone, ammonia, ethanol and methyl sulphides can be produced – distinctive and, if concentrated, extremely unpleasant odours.

Such offensive odours are legally categorised as a statutory nuisance under the Environmental Protection Act 1990. With the best will in the world, even exemplar composting sites will, at some point, face patches and pockets of anaerobic composting due to biological waste brought in for processing that is wet, degraded and unsorted.

As soon as it became apparent to WLC that the site was accountable for producing some odours, it joined forces with The Composting Company (TCCL) for additional assistance. Having already been involved in the original design and construction of WLC’s facility, TCCL was an obvious choice to help WLC investigate into from where odours were arising.

To do this, TCCL commissioned the Applied Environmental Research Centre (AERC) a leading environmental consultancy specialising in such problems, to undertake a complete odour survey of WLC’s site to include a process audit of the plant, review of previous odour complaint records, the identification of any odour sources associated with the composting process and assessment of their potential impact.

Fingerprinting points to the source

Using its unique ‘fingerprinting’ technique, AERC was able to identify that the specific source of the problem stemmed from WLC’s windrow pad and screening/storage area. While it confirmed the company’s in-vessel composting area was well managed, scarcely contributing towards the production of any smells even, AERC highlighted that improved management of material on leaving a vessel was necessary.

In the first instance, to help control odours, TCCL installed Danish-developed New Era Compost Biosa at the Harefield-based site in June 2006. To date, not one validated complaint has been received. Now successfully in use at other UK sites, Biosa is an unique mix of organic herbs, plants and living micro-organisms, sprayed on to newly shredded compost.

Encouragingly, the Biosa story does not end with the elimination of odour. Today’s users are witnessing material reaching stability up to 25% more quickly and product is being screened twice as fast, thus significantly increasing income and reducing costs.

What’s more, ongoing Biosa trials are demonstrating that home composters keen to encourage microbial activity for an enhanced end product need simply spray 125ml of the solution onto their compost after each new deposit, turning each batch with a fork. Tests into the use of the product as a bin freshener are now underway with further announcements by TCCL expected imminently.

However, Biosa used in isolation at large composting facilities is not a miracle cure. First rate site practice is, of course, imperative. Therefore in a bid to help composters of all sizes improve current processes, TCCL set out to develop a set of stringent site management procedures to help composters manage day-to-day operations as efficiently and effectively as possible.

“Adhering to the correct procedures means, for example, a site not accepting and processing more material each day than it can physically cope with,” points out Chris Field, managing director of TCCL. “Stockpiling is a definite no-no and simply creates a definite source of odour.”

Consider influence of pre-processing

Field is also convinced that the way in which material is pre-processed has the biggest impact on the entire composting process. “Blending and homogenising material rather than simply shredding is of paramount importance. After all brought in waste will change daily, and from load to load, and the way in which it is shredded must reflect this.”

Take WLC as an example of good practice. Here, 99% of the feedstock is kerbside-collected and does not contain civic amenity site material – known for its courser, more woody material necessary for blending. As the firm is dedicated to manufacturing a product rather than on managing waste, it utilises techniques and procedures different from a site accepting say, civic amenity green and separately collected kitchen material. Therefore, what happens at the front end will have significant impact on the quality of the final compost, and as a result WLC’s processes include particular attention to blending as opposed to shredding alone.

Field continues: “If you create a dense mass containing nitrogen-rich grass in the spring say, you are guaranteed to end up with a smelling anaerobic pile. There is no textbook method for pre-processing feedstock, instead it has to be flexible and based on individual circumstances and material.”

As with all SVS licensed sites, a stringent vehicle washing down procedure is imperative. A build-up of odours is preventable if water does not become trapped behind walls and sit in any crevices – washing the shredder daily avoids the build-up of material on and beneath the machine. Clean and maintained aeration pipes helps keep material placed in a vessel aerobic. Other pitfalls to avoid include the careful management and containment of waste water on the in-vessel composting and maturation pads. A constant movement of this water will help avoid the build up of odours.

As with any quality control protocol or SVS licence, monitoring is important. Take TCCL’s procedure at WLC. Monitoring for oxygen is not placed solely on the in-vessel part of the process, but on the maturation windrows too. Turning is carried out only when there is a demand, rather than on a blanket weekly basis. This ensures each windrow is turned on its own merit rather than merely for the sake of it.

The Composting Company

www.thecomposting.co.uk