Waste Wednesday

BRISTOL BIORESOURCES AND RENEWABLE ENERGY PARK INTERVIEW

We stepped out of the office and into the BFWRF to speak with Tom Phelps, food waste treatment plant manager, to learn more about the daily activities that take place at this exciting hub!

  1. Can you explain what happens to our food once it has been brought to the BFWRF?

    Although it is quite complex, there are four main steps:

    1. Delivery and de-packaging

      This all happens within the main building. We use a shredder, mixing tanks and a hammer mill to remove the packaging, most of which is plastic. This packaging waste is about 4% of what comes in and it is used as fuel to generate electricity at another site nearby.

    2. Hydrolysis and pasteurisation.

      A series of tanks allow the ‘soup’ of de-packaged food waste to start breaking down naturally (hydrolyse to acids) for a few days and then it is heated to 70°C to kill any potentially harmful bacteria.
      This pasteurisation step holds the hot slurry for an hour before recovering some heat and pumping it to the digester.

    3. Anaerobic digestion (AD) to make biogas

      An ancient form of bacteria called archaea, which only live without oxygen, break down the soup slurry. This gives off biogas, which is mostly methane. The biogas bubbles off and is collected to make renewable energy. The process takes about 3 weeks in large tanks.

      Some biogas is used in Combined Heat and Power (CHP) engines to generate electricity and some goes to be purified to enter the gas grid and replace fossil fuels.

    4. Dewatering digestate to send to farms

      The digestate which leaves the digesters as a weak liquid is thickened up in a centrifuge to make a fibrous fertiliser material, very like compost.
      Farmers find this solid ‘cake’ material great for replacing artificial nitrate and phosphate fertilisers and to improve soil structure.

  2. What does a typical day look like for you and your team?

    The morning shift start at 6am. We take process samples and check the equipment, ready for the first deliveries. The busiest time for deliveries is around mid-day.
    The operators drive a loading shovel to put the food waste into the shredder and keep the pile of food waste tidy ready for each delivery. The team also looks after all the pumps and pipes and do some of the maintenance and cleaning each day. There is paperwork to do to ensure the right sorts of waste are being processed.
    The team carry on processing until after 11pm on the second shift and have a good clean up before checking the facility and locking up overnight. The pasteurisers and digester feed processes are automated, and this carries on running all night but sometimes pump jams or other alarms mean that an operator needs to come in and restart the system.

  3. What are some of the obstacles that you face at the BFWRF?

    Some large lumps of metal end up getting stuck in the shredder and need unjamming. Also,  glass and eggshell cause the pumps to wear out and can block the pipes.

  4. Are there certain times of year that are busier for you than others?

    Pumpkin season at the start of November is busy, but the busiest time is after Christmas when there is loads more food waste.

  5. What is your favourite part of the job?

    We all enjoy having a chat with the drivers and the friendly banter which makes it a cheerful place to work.

  6. Can you give us an update on the work being done to trial the breakdown of compostable plastics in our anaerobic digestor?

    We have found big differences between the types of bio-plastic and compostable plastic. If the material is hard it will get removed at the start of processing, but some more fibrous materials like boxes made from sugarcane waste called bagasse can also make biogas.
    The green compostable bags aren’t really designed for AD so we have to remove them, but if any fragments get through, they will break down in the fields.

  7. Do you have any tips to help businesses and individuals reduce their food waste?

    I would always encourage people to just buy what they need to avoid throwing good food away. Remember best before dates are only a guide and food is usually wholesome long after those dates.
    Make pumpkin soup and roast chunks of pumpkin rather than just carving for Halloween. We also encourage business customers to try to give food to food bank charities by keeping surplus good food separated from unavoidable waste caused by spoilage or mould.

  8. Give us one last fun fact!

    Eggshells don’t make biogas, so you’re better off washing, crushing and putting them in old washing powder boxes to use to discourage slugs or snails from eating your new plants.
    Food waste is powerful, and yours can be too. Whether you’re a business or individual, have a look at our website to learn how GENeco can help you utilise this underused resource, or give one of our friendly team a call on 01225 524560.

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