Treatment and Characterization of Biological Sludges from the Pulp and Paper Industry

Abstract

A research project on characterization and treatment of sludges from the pulp and paper industry was initiated at the Technical Research Centre of Finland (VTT) at the beginning of 1986. The research is included in a research programme on non-waste technology. The aim of the work is to develop optimal treatment processes for pulp and paper mill sludges. The first experimental phase, currently underway, is focused on investigations of various ways of releasing bound water from the sludge, with particular emphasis on developing correlations between measurable sludge properties and dewatering behaviour. Activated sludges of different origin have been subjected to various chemical, thermal and enzymatic treatments. The effects of these conditioning treatments on the properties of the sludges have been characterized by different analytical methods, for example, by measuring changes in the specific resistance to filtration, the amount of water bound in different ways, the particle size distribution, and the chemical composition of the sludges. Results of these experiments are discussed. The interpretation of the effects of the treatment methods studied was hampered by deviating properties of sludges. A treatment effective for one sludge under certain conditions did not have a similar effect on the dewatering properties of some other sludge. Thermal treatment of sludges proved to be the most effective method for breaking water binding, although the most influential factor could not be identified. Ultrasonic treatment had a clear effect on the particle size distribution and settling of the sludges, but not on dewaterability, and proved to be closely related to the sludge concerned. The enzymes tested had no significant effect on the dewatering characteristics of the sludges. The results obtained so far will be used for designing an optimal sludge treatment process in future work.