This seems effective and green.

[damduck-egg]

Correct. Comes from trying to complete and send the post by a low bed site light before the missus says "you are on that dam Internet" again.

G.Harman

[harry]

This one runs on cowshit.

[news]

The ones that I know of get most of their biogas production from maize silage or sugar beet, one makes use of whey from a cheese making operation. These high energy inputs are what keeps the biogas generation stable. The slurry contains the methanogenic bugs from the cows' rumens that produce the methane and CO2 from the "volatile solids" in the feedstock. The thing is volatile solids is the food value in a crop, so much of these are used up in normal digestion, hence the crops grown especially are used.

I worked at a food waste plant that wet composted commercial waste (still fit for human consumption), which would once have gone for pig swill, the heat from the process pasteurised the waste which was then spread on land. Subsequently the plant has been sold and changed to anaerobic digestion for producing electricity, in engines and generators the heat from which keeps the digester at blood temperature, but in addition to the food waste it contracts local farmers to grow 200 acres of maize for silage.

As well as the gate fee for the food waste I think the plant depends of the FIT.

Digestate is still stored and then spread on the land, often the solids are separated out for later application and the liquid is used to irrigate all the time the soil is warm enough for the plants to make use of it.

AJH

[Roger Hayter]

Nitrogen containing fertiliser is a large scale industrial product, so there must still be appropriate times and places when it can be used. Even if ecologists are still not keen on it.