PARTICLE REMOVAL IN DIFFERENT FILTRATION SYSTEMS FOR TERTIARY WASTE-WATER TREATMENT - A COMPARISON

In seven wastewater installations in the area of Zurich, Switzerland, four different filtration systems for tertiary wastewater treatment (d eep bed, cloth drum, continuous up-flow and cell filters) were investi gated with special attention to particle size distributions in the in- and outflow of the flocculation and the filtration step. Flocculation and filter performance was characterised by the shift of particle numb er curves. For each filter, particle number, surface and volume remova l as a function of particle size was determined and revealed to be an excellent tool to evaluate the filter plants under practical condition s. The number removal efficiency for small particles in the colloidal size range proved to be the most sensitive parameter and could be rela ted to operating parameters such as flocculant dose and filtration rat e. The results of the particle analysis were compared to quality param eters related to small particles such as micro-organism and heavy meta l concentrations. A good agreement between the removal of small size p articles (< 8 mu m) and bacteria counts as well as copper was found in the different filter systems. The filters were finally classified acc ording to their particle removal performance. (C) 1997 IAWQ. Published by Elsevier Science Ltd.