days by three parallel positioned ovens of such a pyrolysis unit initially the first oven is charged and ignited after three days the pyrolysis in this first oven is completed and the ash combustion phase begins while in the second oven the pyrolysis is started after 5 or 6 days the third oven is ignited for the pyrolysis while the first oven is then in the cooling down phase and the ash combustion phase begins in the second oven this cycle can be continued so that waste may be processed without interruption the substantial advantage of such a way of processing is that on the one hand continued operation may be performed on a semi continuous basis while on the other hand also various types of waste may be processed in charges so that the destination and further treatment or recycling of the ash may also be chosen the treatment of the gases by means of the central gas washing column may proceed continuously in the above description the invention has been described with reference to more or less specific examples of a pyrolysis oven and a universal combustion system with two combustion units each of which has three such pyrolysis ovens however it will be obvious that modifications are possible without deviating from the scope of the invention thus for example within the framework of the required conditions and demands the ovens may be modified with respect to shape and with respect to positioning while also other provisions may be made for a universal combustion system more combustion units than the two described in the example may additional be used thus for example four of such systems may be centrally connected with a gas washing system an efficient positioning is for.