The pilot plant in Geiselbullach for the gamma irradiation of sewage sludge - design, operation experience and cost calculations

The pilot plant for sewage sludge irradiation in Geiselbullach near Munich has been in operation from July '73 to October '75 with a capacity of 30 m3 per day. Successful experiences during this period resulted in an increase of the installed radiation energy and in several improvements for the technique and the efficiency. From December 1975 on the plant has been operating with a daily capacity of 120 m3 of sludge per day. The experience with this plant brought several problems which caused interruptions of the continuous operation and that had to be solved with new measures. But although the facility at Geiselbullach is a pilot plant the availability was more than 350 days per year. Due to the simple design of the plant and of the fully automatic operation no special trained personal is necessary for the maintenance. Beside the effect of the hygienization the irradiation caused improved sedimentation properties of the sludge. Presently investigations are undertaken to prove better mechanical sludge dewatering properties. Cost calculations resulted in about DM 2.30 for operating expenses and DM 2.25 for capital costs per m3 of sludge for the fully charged plant. The capital costs will be less in commercial plants. The conditioning effect on the sludge by the irradiation means savings of about DM 1.00 per m3. The irradiation of sewage sludge proved to be possible at about equal costs compared to the wellknown heat treatment (pasteurization at 700C during 30 minutes.). Further investigations have to be done to overcome the contrary development of the plant capacity, limited by the decaying radiation energy and the normally rising sludge quantities of a sewage water treatment plant. (author)