Particle related fractionation and characterisation of municipal wastewater A.F. van Nieuwenhuijzen*, J.H.J.M. van der Graaf*, M.J. Kampschreur** and A.R. Mels*** * Delft University of Technology, Faculty of Civil Engineering, Section Sanitary Engineering/Witteveen+Bos Consulting Engineers – P.O. Box 233 – 7400 AE Deventer – The Netherlands (E-mail: a.vnieuwenhuijzen@witbo.nl) ** Witteveen+Bos Consulting Engineers – P.O. Box 233 – 7400 AE Deventer – The Netherlands *** Lettinga Associates Foundation LeAF/Wageningen UR – P.O. Box 500 – 6700 AM Wageningen – The Netherlands (E-mail: adriaan.mels@wur.nl) Abstract Several studies show that a more detailed characterisation of the particulate matter in municipal wastewater gives a better understanding and prediction of removal efficiencies of physical-chemical treatment techniques and the application of optimal chemical dosages. Such a characterisation should include the distribution of contaminants over various particle sizes. This article describes a method and results of experimental and full-scale investigations, conducted to determine how contaminants in wastewater are distributed over different particle sizes. For this purpose, particle size fractionations of wastewater influents originating from more than thirteen WWTP were carried out. One of these fractionations (WWTP Venray) is shown and interpreted in this article. First, the wastewaters were fractionated into 5 to 6 particle fractions (45, 5.0, 1.0/1.2, 0.45 and 0.1 μm) after which the fractions were analyzed for various water quality parameters like organic components, nutrients, salts, solids and turbidity. Based on the results the effects of removal of the different size fractions on design of the biological treatment and energy balance of a wastewater treatment plant can be assessed. The method also indicates whether a certain wastewater is efficiently treatable with physical-chemical pre-treatment methods. It is concluded wastewater fractionation on particle size is very useful, but that wastewater characteristics and particle size distributions should not be generalised, but have to be interpreted as indications for a certain average wastewater composition. To give more insight into the distribution of contaminants over particle size and the particle removal potential, a specific wastewater fractionation has to be carried out per WWTP. Keywords Fractionation; micro particles; particle removal; particle size distribution; wastewater treatment Introduction Since a major part of the organic material and the nutrients in municipal wastewater is relat- ed to particulate material, advanced particle removal by physical-chemical pre-treatment, results in a lower pollutants load to subsequent treatment steps. In this way the total treat- ment system can be designed smaller and operated in a more energy efficient way (Ødegaard, 1998; Nieuwenhuijzen, van et al., 1998; Mels et al., 1999). Traditionally, the choice of treatment methods is mainly based on the effluent standards as well as on practical experience with the various techniques by engineering companies and water- boards. Especially the choice of adding pre-treatment steps, mainly primary sedimentation tank, preceding activated sludge systems was not, in general, based on technical knowledge and wastewater characteristics, but was made according to traditional practice and on plant size. The applicability and efficiency of specific particle removal techniques is closely relat- ed to the particle size distribution in the water medium. Especially the distribution of con- taminants over particle size is of interest. These data are wastewater specific and can differ per country or even per region due to differences in climatic circumstances, landscape and consuming habits. For example, it is stated that contaminants in wastewaters in the Water Science and Technology Vol 50 No 12 pp 125–132 © IWA Publishing 2004 125 Downloaded from https://iwaponline.com/wst/article-pdf/50/12/125/419404/125.pdf by guest on 23 May 2020