Due to the strong associationof total suspended solids (TSS) with wastewater COD (Levine et al.,1985),primary treatment technologies could have a relevant impact on the performance of downstream biological processes (Bixio et al.,2000).Therefore,an efficient primary screening can result in significant energy cost savings to wastewater treatment plants (wwtps) operators (Rusten,2005),due to lower energy consumption in the biological treatment and an increase in energy recovery from the organic matter removed during the process (Mels,2001).In this study,Salsnes Filter (SF) fine mesh sieves were used as a primary treatment to characterize particles by size.The objective was to see if particles of certain sizes removed with SF would have any negative impact on downstream processes such as biological nitrogen removal.