Relationship between centrifugation and drying of sludge and the organic halogens

This work is focused on determination of adsorbable organic halogens (AOX) concentration in the digested sludge from the sewage treatment plant and the losses of this component during dewatering and drying of sludge. Drying of the sludge from wastewater treatment plant is not extended too much in Czech Republic. In this work,the AOX are monitored,because AOX is one of the limits restraining use of the sludge on an agricultural land. Another reason is technological demand for using the sludge in cement processing,because chlorine in AOX can cause decrease in a heat transfer effect in a cement kiln. It is clear from the results that both centrifuged and dried sludge from the sewage treatment plant Brno fulfilled limits for using sludge on agriculture land. They can also be composted,in case they meet other requirements. If not,it is a possibility of co-incineration in cement kiln. In such case,limit for total chlorine including the AOX is required too. This limit was not exceeded. Another aim was to calculate a mass balance of AOX during the centrifugation and drying processes. It was found out,that after centrifugation the main part of AOX remained in the centrifuged sludge (96.4%). The rest was drawn-off with reject water. 60 % of AOX in the reject water were dissolved compounds. A similar situation occurred during the drying process. More than 99 % of AOX was bound in the dried sludge. The air and vaporised water contained such quantity of AOX,which corresponded with the amount of the dust in the air and the amount of particles of sludge in vaporised water.