Anaerobic Digestion

Firstly, we need to know about food waste that goes to landfill and food waste that can be composted.

Half of local Councils, including Leeds, do not collect food waste separately from home owners. The food waste, fruit, vegetable, fish, meat goes into the black bin and is taken away for Incineration, or in the past went into landfill.  In landfill, the waste is covered by soil and other rubbish and oxygen cannot get into the tip. Anaerobic bacteria (they can survive without oxygen) begin to work on the waste food and produce methane gas, which eventually escapes into the atmosphere.

Methane gas is 20 x more polluting than CO2 and No2, the other greenhouse gases.  Therefore, if all gases escaping into the earth’s atmosphere were replaced by methane, the earth would heat up 20 x more quickly and cause global warming to  greatly accelerate.

Methane gas is the same as the gas we use for our gas hobs and central heating boilers. In some tips it can be captured, cleaned to remove other gases and then pumped into the gas grid.

By collecting food waste separately from home-owners, it can be taken to an Anaerobic Digestor. This is a sealed vessel which can accept food waste, animal waste and other organic matter. The sealed container means that the Methane gas can be collected safely, cleaned to remove gases other than Methane and then methane can be pumped into the gas grid or used to fire large boilers which produce steam -> turbines-> electricity -> Electricity grid.

By collecting food waste separately, the waste in the black bin is not contaminated with food and is therefore cleaner and more likely to be recyclable rather than going for Incineration.

Where home owners have the facility/space to make a compost heap, any fruit and vegetable peelings can be added to the heap, along with greenery from the garden, cardboard and newspaper. However, food waste such as meat and fish scraps must not go on a compost heap. The temperature of the compost doesn’t get high enough to kill pathogens and the protein waste attracts vermin. A compost heap works in the presence of oxygen loving bacteria, earthworms, slugs and insects etc.

Leeds City Council is looking into collecting household food waste within the next year or so. All councils must collect food waste by 2024.

There are many AD systems within Yorkshire and many farms have AD systems to deal with animal waste. Some farm facilities are used to produce methane-> electricity from crops such as maize.

Ingrid McLaughlin                                  February 2020

1 Comment

  1. Adrian on February 17, 2020 at 9:45 PM

    If you want to know more about home composting, we’ve written a blog about it here

    Lesson is, look after a home compost, and over time it will work out, just have patience 🙂

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