One development that DRACE medioambientehas tested with successful results is the application of power systems to excess sludge.  High intensity ultrasound results in cellular lysis of the sludge which would take a week with mesophylic digestion.  The main advantage is the increased elimination of volatile matter, that implies a reduction of the amount of the sludge produced, a larger production of biogas and greater dryness in dehydration.  It is also the most efficient system used to expand existing plants as it makes it possible to increase the treated flow without building new digesters.