How the Food Waste Composting scheme started

In December 2007, Furniture Now! approached Transition Town Lewes (TTL) to explore whether there were any projects that might be conducted in partnership. Representatives of TTL Waste Group, met with the Director to sift through some ideas and it soon became clear that both parties had an interest in looking at a food waste composting solution that could be run economically in Lewes.

At this time, East Sussex County Council, was beginning discussions internally and with French partners SMEDAR about the possibility of working up another proposal for an INTERREG project. The cross border project would focus on reducing business waste, education and training of professional waste officers, the promotion of domestic green waste composting and also the trialling of a facility to compost food waste from the main office building (County Hall) in Lewes housing 1,000 staff.

A chance encounter at County Hall brought both groups together and a project was quickly worked up. There would be a pilot phase when the in-vessel system would be installed, Furniture Now! would employ two members of staff to collect the food waste generated in the offices and feed it into the machine and these operatives would collect the compost product at the other end.

Finally, in November 2009 the composter has been installed and the pilot phase is going ahead. After the pilot, the substantial amount of spare space in the machine will be opened up to the commercial sector for a fee.

Technology and Permitting

Installing apparatus to compost a controlled waste is not an easy task. Not only is the plant expensive but it is subject to a rigorous permitting regime due to the potentially hazardous nature of the material that is being put into the machine. Cooked waste quickly turns into a bio-hazard and the addition of animal by-products such as meat and fish makes it absolutely imperative that whatever leaves the machine is free of salmonella or any other dangerous bacteria or virus.

A tendering process was conducted and a Rocket A900 manufactured by Accelerated Compost Ltd was chosen as the best solution for the volumes of waste to be composted and the reliability of the product. The technical specifications for the A900 Rocket Food Compostor can be viewed here.

Further information will be published on this website in time. However, in short, the material passes down the machine over a period of about two weeks. It will be above 60 degrees C for at least 96 hours, almost exclusively driven by the heat generated from the decomposition process, which ensures the destruction of salmonella and other pathogens.

The movement of these relatively small amounts of food waste requires an exemption to the waste management regime overseen by the Environment Agency on behalf of the government. Additionally, the state vet is involved as the composting of food waste comes under the Animal By-products Regulations (ABPR). During the pilot phase, every batch of material exiting the machine will be sampled and sent away to a laboratory to check that there is no salmonella content in the decomposed product. It is only when the all clear is given that the machine may be opened up to commercial usage. This will take some months. In the meantime, the correct microbial culture needs to be developed inside the machine. Therefore, the initial material leaving the machine (less the sample) will be fed back into the process to bulk it out and recycle the “good microbes”. It is likely that the first bags of product will not be as thoroughly composted as required, therefore this also ensures the compost is re-processed until clean.

Operational Procedure

FN! has employed two compost operatives, Max Brownrig and Ken Gurr, to collect the waste and run the machine. 

Compost caddies have been issued to every office in County Hall and to the canteen. Food waste is placed into these caddies and collected on a daily basis, the full caddies being replaced with clean ones for the next day's waste. The food waste is then taken to the Rocket and mixed with the same volume again of partially rotted woodchip. This gives the compost the correct nitrogen/ carbon mix and is an ideal environment for the microbes to thrive. In the first instance, compost from a garden compost heap is also added to boost the microbial content and help the culture establish.

The Rocket is top loaded at the dirty end, which is separated by a physical barrier from the clean end to ensure no cross contamination. A good mix is required so one caddy of food waste is followed by one of woodchip and then one of compost.

The Rocket is a sealed vessel. The outer casing houses an inner cylinder mounted on a slight slope so any water material exiting the food waste as it decomposes is gathered at the dirty end in a white leachate bottle and can be disposed of to drainage. A damp composting environment can lead to putrification, an anaerobic process that will destroy the bacterial culture and smell terrible as well as producing a bio-hazard as opposed to a compost product. 

Internally, the composter has a number of blades mounted on a spindle. The first blades are angled to push the compost away from the opening moving the material forwards over a 24 hour period and leaving space for the next batch. The following blades are not angled, relying on displacement from the new bulk of food waste to push the material through the machine. This increases the residency time to an acceptable level and ensures the material is in-vessel long enough to be composted. The machine needs to be fed daily where at all possible and works most efficiently when fed seven days a week to capacity.

Two days in		First batch

There are four electronic temperature probes in the machine attached to a data logger. It is imperative that the material is above 60 degrees C for 96 hours during its transit down the vessel. To ensure this is the case, the permitting regime requires that two of the probes must read more than 60 deg in the apparatus. The data is stored on flash memory chips and is downloadable to a laptop. It can be used to check the Rocket is working properly and is submitted to the state vet's laboratory with the sample from each batch. The Rocket is also supplied with an internal heat blanket and thermostat to ensure the temperature does not dip. 

Once the material has proceeded through the machine it drops into a bag at the clean end of the machine. This material mounts up and as much as a whole bag will be produced daily when the machine is operating at full capacity. The product is not yet compost that can be applied to land. The woodchip has decomposed significantly in the machine but can be sieved out for re-use. Eventually it will decompose entirely.

The composted material is then taken through the school and placed into maturation bins, one pictured. The material then absorbs bacterial and fungal spores from the air and rots down even further. Once it has matured for two months it is ready to be applied to land providing the state vet has passed the machine off as safe. The product, though clean, is still classed as waste and cannot be exported or sold until it has passed yet another regime, the PAS100 quality regime applied to all commercial compost producers.

Once the Rocket has been successfully permitted and appropriate planning permission has been granted, catering waste will be imported to the site. It is expected the waste will be more challenging than the cooked waste that is currently being collected at County Hall and will contain a higher content of cooked and raw meat products. This material will need to go through a macerator/ de-waterer before being added to the Rocket but providing the particle size is small enough and dry enough and well mixed with other materials, there is no reason why it should not compost just as effectively as a banana skin. 

Further updates and technical information will be made available on this website in the near future including a short video with interviews with the composting operatives.

Rik Child