Dairy products have the biggest impact in our diet, are anaerobic digesters the answer?

I’ve been particularly struck by the fact that dairy products make up 25% of average purchases from supermarkets and are 50% of our food carbon emissions.

I’ve been thinking about whether digesters placed on dairy farms would make a difference? The basic premise would be that when cows are indoors (during milking, calving and indoors during winter) the manure is fed into an anaerobic digester and methane is captured and then used to power heating or to provide electricity.

I wonder if you did this at scale what impact it would make. Has anyone thought about this or have any examples to share?

I didn’t realise dairy made up such a large amount of purchases. Is this by weight, value or number? And is the disproportionate carbon footprint compared to meat just becuase we consume more of it?

AD is sometimes used by wastewater treatment works to treat the ‘sludge’ from sewage but it requires scale to be commercially viable due to throughput and the gas cleaning kit required. I’m not sure how prevalent farm slurry digestion is but some farmers just store slurry before using it directly on land, to replace fertiliser. Maybe the NFU or similar organisation keeps stats on it?

Looking at where dairy carbon emissions actually come from, the report in the link below has got some useful stats and stories on the carbon footprint of milk production (highlights below). I imagine cheese production increases this due to the additional processing.

The three major sources of GHG emissions were: • Carbon dioxide emissions – derived from inputs of fertiliser, lime, herbicides, pesticides, fuel, electricity, straw/bedding and animal feed (26% of the average carbon footprint was due to concentrated feed use)

• Nitrous oxide – derived from fertiliser application, animal and organic manure management, sewage sludge (if applied), other crop residues and atmospheric deposition

• Methane – arising from enteric fermentation in the rumen (40% of carbon footprint) and, to a lesser extent, emissions from manure management.

It is by weight, which is incredible right?! I was amazed when I did the vegetarian vrs vegan analysis as part of the carbon footprint that only about 15% reduction in food carbon footprint can be attributed to meat, and it is because of quantities. Diary per weight is more damaging than chicken and pork. This has led me to we’re I’ve got regarding dairy.

Really useful report- thanks. So we can only do something about 40% of dairy footprint in not changing feedstock etc. Your figures also point to the fact that actually the best thing you could do around dairy is get dairy from pasture fed beef…