On Monday night we had our bi-monthly discussion meeting, where a topic is presented by a group member or special guest, before moving into a group discussion on the topic. This month’s topic was anaerobic digestion.

The meeting started with a presentation from Karine and John about what anaerobic digestion is and how it works. They explained that food matter is collected from houses and, after sorting and screening, is put into a large fermenter. The food is digested without air, hence the name anaerobic, using lots of bacteria to break down the food matter, in a similar way to how our stomachs work.

It can then be made to produce gas, or with a press can be made into liquid or solid fertiliser. If it is kept as a gas, it can be fed into the gas network, used to generate electricity on site to be fed into the electricity grid, or used as a fuel for cars. The anaerobic digester in Cannock, for example, generates electricity on-site which it feeds into the grid.

Nationally, anaerobic digestion currently produces 1.3TWh and if the right financial incentives were in place this could rise to 11TWh, it could also produce around 10% of UK gas demand, which is around the same amount as Shale Gas. 

The technology is being developed to make it possible to create digesters that are smaller, more viable and cheaper. Large scale digesters cost millions of pounds, but new technologies could make small digesters at a cost of £350,000 possible.

The discussion moved onto another technology called Pyrolysis. This uses heat and gas to turn waste matter into gas and bio-char, the latter of which can be used as charcoal. John and Karine visited a pyrolysis plant being built by Aston University, which should be operational by the New Year.

We then discussed the obvious problem with producing energy from waste, in that if we are successful in reducing waste we then have less fuel, which lessens the incentive to reduce our waste. However, it was also pointed out that we are so far from a position where we have so little waste that anaerobic digestion would be untenable. Therefore at present using this process as a means to generate fuel would still be viable during a transitional period.

However, we would also have to be careful that only waste matter is used in anaerobic digestion, and that crops are not grown specifically for this process, so that we don’t end up with a similar situation as bio-fuel.

The discussion was less sure about pyrolysis’ claims that it can remove more carbon than the process produces, through putting the carbon in the ground in the form of the bio-char produced, but there did seem to be a feeling that it was less harmful than incineration for disposing of waste that there is no other way of disposing of, such as inorganic composite materials.

While obviously the ideal would be for these to be designed out of the system, before we get to that stage we need to know what to do with the waste. John Newson suggested that we take a trip to the pyrolysis plant when it is operational and ask some of our questions about the technology.

The discussion concluded around the topic of waste collection and waste in Birmingham. The council have received money from central government for a roll-out of wheelie bins, and are working out their plans for this. This, alongside the upcoming Green Commission report on waste and the council’s post-2018 waste review scrutiny in January, means it is a perfect time to engage with the topic and influence our local decision makers.