The liquid product that is left after biological treatment and separation of the active sludge is called effluent.  Since it is poor in phosphorus and nitrogen, it is used in Flanders as a potassium fertlizer.  

Effluent only contains 10-20% of the original phoshate in the untreated manure and less than 10% of the original nitrogen content. Soluble nutrients like potassium, sodium and chlorine are still present in the effluent.