In the UK, ten million tonnes of food are wasted every year, with around 70 per cent of that coming from our homes[i].
Clearly the greatest effort should be made to reduce the level of surplus food discarded in the first place. However, when food needs to be thrown-away, we all know that it can be collected and effectively handled and disposed of through composting and anaerobic digestion. Yet much of it still ends up in landfill where it decomposes and gives off methane, a potent greenhouse gas, contributing to climate change.
Food waste recycling collection
In April 2015 East Lothian Council made major changes to the way that rubbish is managed from homes across the county. That saw weekly food collections introduced, with a switch to fortnightly refuse collections. The changes also saw the introduction of new bins, boxes and kitchen caddies for food waste. The kitchen caddies hold seven litres and can be filled indoors before being transferred to an outdoor caddy for collection.
Initially when the service was rolled out, biodegradable liners were provided, designed to break down with their contents. However, there were issues with some of the bags decomposing while still in the residents’ caddies. The Council considered increasing the thickness of the bags, but this would have caused issues at the processing facility being used at the time, as they were concerned about thicker liners not breaking down fully and leaving a visible fraction of liner in the end composting product.
Switch from compostable liners to AD-friendly
The processing facility used at the time had a combined in-vessel composting and anaerobic digestion (AD) process that allowed them to take material contained in both plastic and biodegradable liners.
With this in mind, the Council decided to switch to using AD-friendly liners, provided by Cromwell Polythene, which supplies products for the capture and containment of materials for recycling. The bags the Council now use were designed with both the treatment and recovery process in mind, as well as trying to balance the practical use of the liners for households using the collection system.
The food waste processing facility that the Council now uses is Earnside Energy, which also offers both anaerobic digestion and in-vessel composting. When the food waste arrives at its anaerobic digestion plant, it carries out a pre-treatment process whereby the food waste is cleanly separated from any packaging. The dry packaging is suitable for use within with refuse derived fuel (RDF) and solid recovered fuel (SRF) processes, thereby avoiding landfill entirely.
The food is then processed into a liquid and fed into large tanks in the absence of oxygen. This liquid food undergoes a natural biological process over the next thirty days where it breaks down into methane and carbon dioxide gases. The methane is then used as a fuel to feed the combined heat and power (CHP) engine that generates heat and electricity. The heat is used as part of the anaerobic digestion process and the electricity is exported to the grid, for use by homes and businesses across the country.
Anaerobic digestion also generates large volumes of liquid digestate which is stored in tanks on site. This liquor is used by local farmers as a fertiliser. This digestate is BSI PAS-110 accredited for quality anaerobic digestate, and approved by Quality Meat Scotland (QMS) for use in growing crops on arable land. This means anaerobic digestion has twin carbon benefits, both reducing reliance on fossil fuels and avoiding the use of synthetic fertilisers in agriculture.
In-house management of the waste by the Council at a waste transfer station also resulted in less seepage from the plastic bags during handling, which increased cleaning and hygiene standards.
Positive changes
Around 250 tonnages of food waste is collected by East Lothian Council each month and it is one of their most successful services, thanks to the hard work of the management team and staff on the ground as well as local residents who are separating out their waste materials for recycling.
James Lee, managing director of Cromwell Polythene said “We’re pleased to work with East Lothian Council and help them adapt to changing requirements. As food waste collections become ever more popular, we recognise the need to provide councils and waste management companies with alternatives to compostable bags, which can be conveniently removed with debagging equipment at the front end of AD plants. Both compostable and AD are an option for recycling of food waste, but the right product needs to be used for the right recycling process and make it as straightforward as possible for the householder to recycle.”
[i] Love Food Hate Waste statistics from its website
Opinions expressed in thIS blog belong to the author and not necessarily to LARAC
