In future, it will be necessary to incinerate an increasing proportion of the sludge produced by public wastewater treatment. In this context, equipment for more effective dewatering of sewage sludge is required. A hydraulic press system (Bucher HP) which has been used to date in the food industry could represent an alternative to the sludge dewatering systems currently used. The basic suitability of this press system was demonstrated in comprehensive industrial-scale trials at the Glarnerland STP (Switzerland). Dry solids contents of up to 43% were measured in the pressed sludge. Currently, the optimization of individual process parameters is being investigated in a pilot plant at the Schwelm STP operated by Wupperverband (Germany).
This paper presents the results of full-scale WWTP sludge dewatering trials, using a Bucher de-juicing press model HP2500 (Bohler et al., 2002). Besides digested sludge from the WWTP also sludge from another 4 WWTPs were dewatered. The investigations show that with the tested hydraulic system dry solids (DS) contents of 32-39% (with a throughput of approximately 5 m(3) h(-1)) could be reached. By prolonging the final compression step DS contents of up to 43.5% could be achieved. Dewatering trials with primary sludge resulted in an average DS content of 37%. The dosage of coagulant aids, the particle size distribution and the volatile suspended solids (VSS) have a big influence on the dewatering results. An economic efficiency calculation is presented with direct comparison to a centrifuge in use on the WWTP. Return of investment is expected to be achieved within 3.1 years.
The radiation-induced attenuation of pure silica core fibers measured at 0.85 μm has been reduced by treating the soot preforms in various oxidizing atmospheres; the most effective of the treatments used in this study was SOCl 2 . Fibers treated in SOCl 2 or Cl 2 also have low OH contents. The radiation-induced loss of the treated fibers has been found to follow the square root of the drawing-induced absorption band height at 0.63μm.
