Thickening of sludges in a wastewater treatment plant with a hydrocyclone

Abstract

This paper describes the production of sewage sludge and the need for dewatering. Since drying is an energy-intensive process, mechanical dewatering prior to drying can minimize the energy needed to reduce the water content respectively total volume of sludge. The limit for mechanical dewatering, the so called bound-water content, is explained. Different thickening/dewatering devices are described. Some of these devices require the sludge to be chemically conditioned with polymers or other conditioners. In order to reduce the amount of conditioners needed, hydrocyclones for dewatering are examined. Hydrocyclones are not state of the art in the area of dewatering, but some existing literature confirms the possibility to dewater sludge with a hydrocyclone. The hydrocyclone's operation mode for this process is different than for the classification process. First tests in small-scale with water and Carolith particles showed that thickening is possible with a hydrocyclone. The particle concentration in the thickened flow can be adjusted with a mechanical device. This device is used to adjust the area for the hydrocyclone's underflow. For large-scale experiments, primary sludge and sewage sludge, with and without added polymer, are used to test the thickening ability of a hydrocyclone in a wastewater treatment plant. The experiments show that thickening in terms of increasing the dry matter content of sludge is possible with a hydrocyclone. Hence a hydrocyclone is a possible alternative to common thickening devices or could be used as a pre-dewatering device.