A New Optical Method for Measuring Suspended Solids in Pulp and Paper Mill Effluents

Abstract

A new optical method, the so-called TP-method, has been developed at the Swedish Forest Products Research Laboratory for measuring the amount of suspended solids. The great advantage of this method compared to other existing optical methods is that the result is independent of particle size. This is an important feature, since the characteristics of suspended solids from pulp and paper mills can vary significantly. The TP-method also provides a first order measure on the size distribution of the particles in the suspension. Furthermore, the TP-method is independent of the flow rate of the measuring medium and by compensation insensitive to variation in colour.The TP-method has been extensively tested in the laboratory and in mills with different kinds of production. The results show that the TP-method is well suited for quantitative measurement of suspended solids.Several years of experience with TP-instruments in different on-line positions is also very good. The instruments have shown to provide valuable and relevant information on both variations in concentration and variations in particle size distribution, with the result that it has been possible to indicate and to explain disturbances within the process - system. Several instruments have been used in an in-mill pollution control system, which was installed in a sulphate pulp mill in Sweden.