Your question is not clear. What do you mean by maintaining the quality of the biogas slurry? Do you mean the inorganic content of the biogas slurry, do you mean the nitrogen content of the biogas slurry, do you mean the organic concentration, do you mean other physical and chemical parameters?

In order to answer your question, I recommend rephrasing it so that it is clear what you need to know.

It would also be useful to indicate whether you are referring to the treatment of biogas slurries on a full scale or on a laboratory scale.

Bets regards

Vit