Characterisation of trickling filter effluent by particle size distribution and high performance size exclusion chromatography

Wastewater treatment objectives are still typically defined in terms of nonspecific parameters such as biochemical oxygen demand and total suspended solids. However, wastewaters are a heterogeneous mixture of materials with a wide range of particle size and molecular weight, and most processes involved in treatment (sedimentation, mass transfer, adsorption, diffusion, biochemical reactions, filtration) are effected by particle dimension. This study deals with the evolution of the particular and dissolved content of synthetic sewage during treatment. The experimental system consisted of a pilot-scale low-rate trickling filter, with and without secondary settlement, followed by crossflow microfiltration (CFMF). In terms of particle size distribution (PSD), results show a shift towards larger particle sizes through biological filtration, most of which can then be removed by settlement. Some fine particles remain and these can be removed by CFMF with a 0.1 μm pore size membrane. High performance size exclusion chromatography (HPSEC) was used to study the evolution of the dissolved fraction of wastewater through treatment. Both PSD and HPSEC are shown to be valuable tools to assess the performance of wastewater treatment processes.