The invention relates to a method for decomposing biogenic material, wherein a percolator is charged with biogenic material, a percolation liquid is separated by sieving and re-sprayed again onto the biogenic material, excess percolation liquid is pumped into a buffer from where it is transported into a biogas reactor and fermented to form biogas. The method is characterized in that the purified percolation liquid is transferred as waste water to a storage buffer container from where it can be retransferred to the percolator.