According to a news report by WRAP (link updated – apologies), the UK composting industry generated over £165 million last year by processing over 4.5 million tonnes of organic waste. 88% of this originated from local authorities as part of municipal waste collections (household, schools, churches etc.).
An increasing amount (currently 36%) of the compost produced is fully certified to BSI PAS 100 (the national specification for quality compost). This means that composters can generate even greater income as they can charge for processing the organic and food waste in the first place and can then sell the end product for agricultural use.
In-vessel composting, where the waste is treated “in vessels” (who could have guessed?) to enable it to reach higher temperatures, also allows for the composting of meat, fish and oil scraps so it’s a complete system for a wide range of organic waste.
All in all things look pretty rosy for composting companies, especially as businesses start to think about their own organic waste and composting firms begin to work with collection companies (or set up their own collections) to provide collections for local businesses. However, all may not be as perfect as it seems in the world of organic waste recycling as it seems some stiff competition may be on the horizon in the form of another way to deal with organic waste which generates energy and a viable compost: anaerobic digestion.
Anaerobic digestion (AD) facilities take advantage of the highly flammable methane gas (aka biogas) produced by decomposing matter (aka biomass) when it breaks down in the absence of oxygen (i.e. anaerobically) to generate energy (aka clean electricity). As you might expect from a large sealed container full of waste matter AD plants don’t just produce gas. You are also left with a digestate and waste water, both of which require further treatment before being used or disposed of into the environment. This could be a disadvantage compared to the relatively straightforward composting method.
Both systems have pros and cons but both ultimately divert food waste from landfill so get the thumbs up from us. However there is a note of caution: burning methane does release CO2. So unless you capture and store the CO2 produced from burning methane you arguably don’t solve the whole problem. In-vessel and other forms of composting don’t produce methane because the decomposition occurs aerobically (in the presence of oxygen) and the only by-product is a relatively small amount of CO2 (certainly compared with burning methane). However, just to complicate matters further, the life-cycle of methane means that it breaks down within 12 years in the atmosphere. Therefore, although it is more effective as a greenhouse gas (some 25 times more effective than CO2) it is only effective over a much shorter period. CO2 stays in the atmosphere for hundreds of years so is potentially more of a concern. Either way, CO2 is the gas getting all the headlines so a recycling company won’t want to contribute to CO2 emissions if it can be avoided.
Overall the science behind the two processes seems to just about favour AD over in-vessel composting in terms of some key factors: speed, quality of end product and associated benefits of the biogas (provided it is used to generate electricity and not released into the atmosphere). However the jury is still out about which benefits the environment most.
Time will tell which system is adopted by businesses. There is certainly room for both processes as they arguably fill different niches in terms of the end product. A farmer wants a ready soil improver, which composting provides. An industrial estate would probably prefer clean electricity, so would go down the AD route. Ultimately, it’s horses for courses.