Conditioning, Thickening, and Dewatering of Mechanically Disintegrated Excess Sludge

Abstract

The influence of mechanical disintegration of excess sewage sludge on the performance of centrifugal dewatering and filtration was investigated. Examining different methods of mechanical cell disintegration, the best results were obtained using a high-pressure homogenizer. As a result of disintegration the dry solids content of the dewatered sludge increases when applying centrifugal forces. In the case of unconditioned sludge separated by using a beaker centrifuge this can be explained by the large portion of organic components that can be found in the centrate, whereas a high degree of the inorganic components can be found in the sediment. By adding conditioning agents the organic components are flocculated while the disruption of the particle structure leads to an increase in conditioner-demand. A dual conditioning using ferric salts and polymer led to the lowest dosage and the best dewatering results. Thickening results (using a decanter) are improved for disintegrated sludge that may be caused by a different floc structure. Sludge flocs created from smaller sludge particles and a higher amount of flocculation agent lead to better thickening properties. Dewatering results (using a membrane plate and frame filter) were deteriorated due to the disintegration. Improved dewatering results obtained in a high-pressure filter press show a potential improvement by disintegration, but not for commercially available dewatering equipment. In industrial application disintegration shows some positive effect on thickening of excess sludge, while the dewatering results are deteriorated. The disintegration of cells presents an opportunity to reduce the waste solid, but there are still challenges to achieve effective dewatering with existing industrial technologies.