Sludge digestion is a biological process, in which 50% of the organic material out of the sludge will be chemically broken down and converted in the assemblage of biogas. During the process the sludge water will be enriched with nitrogen, that releases from the sludge. That means the sludge is being cleared with the additional benefit that biogas appears. A Monostore tank is the perfect construction for an application like this.