Lamella Clarification and Biofiltration

9 This study investigates the occurrence of all priority substances (n = 41) listed in the 10 Water Framework Directive and additional substances (n = 47) in raw sewage, as well as the 11 removal performance of lamella clarification and biofiltration techniques. Once the efficiency 12 of both types of techniques has been assessed for typical wastewater parameters, the 13 differences in each technique's ability to remove pollutants becomes obvious; nevertheless, 14 pollutant removal in quantitative terms still depends on the physico-chemical properties of the 15 compounds used and operating conditions within the selected facility. For lamella 16 clarification, the removal of organic chemicals was found to be primarily correlated with their 17 sorption potential and, hence, strongly dependent upon log Kow of the compound under study. 18 Compounds with a strong hydrophobic character (log Kow > 4.5) are removed to a significant 19 extent (approx. 85%), while hydrophilic compounds (log Kow < 3.5) are poorly removed (< 20 20%). For biofiltration, the removal of chemicals appears to be compound-dependent, 21 although this outcome involves several mechanisms, namely: i) physical filtration of total 22 suspended solids, ii) volatilisation, iii) adsorption on biomass, and iv) biotransformation of 23 substances. Even if the complex processes within a biofilter system do not yield an accurate 24 prediction of pollutant removal, two groups of chemicals can still be clearly identified: i) 25 hydrophobic or volatile compounds, for which moderate to high removal rates are observed 26 (from 50% to over 80%); and ii) hydrophilic, non-volatile and refractory compounds for 27 which a low removal rate would be expected (< 20%). 28