Primary and secondary effluents of three waste water treatment works were analyzed for the size distribution of particle mass, chemical oxygen demand (COD), and phosphorus. Fractionation of suspended solids was done by 0.1-8.0μm polycarbonate filters and 32-125μm sieves, respectively. Primary as well as secondary effluents exhibited characteristic differences in the size distribution curves. Particle size distributions in terms of particle mass could be represented by a power law function. Automatic measurement of particle size distribution by a laser scanning device (CIS-100) was evaluated. Especially low concentrated waste water suspensions proved to be susceptible to aggregation during analysis. Therefore repeated short time analysis of subsamples is recommended.

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