Just how does covering a slurry pit help with emissions? Unless the methane is taken off as in a digester surely it’s still there waiting to enter the atmosphere at some point.
The rate of loss of methane from a slurry store will depend on the temperature more than anything else. The bugs that produce it perform best at cow body temperature, and produce very little at winter temperatures.
Ammonia is a different story, it is split between ammonia (which readily evaporates) and ammonium ions (which stay in the slurry). The higher the pH, the greater proportion as ammonia, and the same with temperature. As ammonia is lost from solution, more ammonium will be converted into ammonia, but the lower the proportion as ammonia the slower that will be.
Note that the y axis of the graph is a log scale, so going from pH 8 to pH 5.5 is a thousand fold reduction.
I think the best way to reduce ammonia losses is to reduce pH with sulphuric acid (cheaper than buying sulphur as Double Top or ammonium sulphate), rather than covering lagoons. I am part way through developing a system for our AD digestate.
the methane is the product of digesting slurry. As far as i know, and i am not an 'expert', no methane comes from an open slurry store.
In fact, little ammonia evaporates until spread. There is a study on spreading which found - the runnier the slurry being spread, the less the ammonia evaporates.
Trying to get my head round this.
What is gained, in terms of emissions, by putting a cover on your slurry store ?