The performance of sludge blanket clarifier against conventional settler under high water turbidity conditions Moharram Fouad* and Shaban Hassan Public Works Dept., Faculty of Engineering, Mansoura University, Mansoura, Egypt *Corresponding author. E-mail: m123f12317@yahoo.com Abstract The performance of a sludge blanket clarifier was evaluated and compared to conventional settlers under high levels of turbidity and algae in the field and experimentally. Field data of sludge blanket and conventional clarifier operation were observed simultaneously for the treatment of highly turbid water. In addition, a comparison was carried out on turbidity removal efficiency, algae removal, and sludge accumulation pattern. Finally, these sys- tems were simulated in the laboratory and operated to treat turbid water with high levels of turbidity and algae up to 80 NTU and 10 9 cells/l respectively. Field data confirmed that the sludge blanket clarifier equipped with upper sludge cones has a high removal efficiency of turbidity and algae, ease of use and has insignificant sludge accumulation compared to the conventional settler. Further, laboratory experiments have confirmed that sludge blanket clarifier is also very effective for the treatment of high algae concentrations up to 10 9 cells/l, with a short retention time, compared to a conventional settler, which was not effective under these conditions. Key words: cones, settler, sludge blanket, treatment, water INTRODUCTION Usually, preliminary disinfection by ozone, chlorine dioxide, or chlorine improves the removal of small concentrations of algae in conventional sedimentation tanks (Plummer & Edzwald 2002). How- ever, high concentrations of algae causes many problems and increases the consumption of disinfectants in treatment plants (Gerde et al. 2014). Further, a high concentration of algae cause many other problems such as color, odor, taste and toxic compounds, as well as reducing the effi- ciency of water treatment and increasing the clogging of filters (Chen et al. 1998; Teixeira & Rosa 2006; Henderson et al. 2008). In regions with a hot climate, algae removal by sedimentation is not easy (Tumsri & Chavalparit 2011). Although high temperatures increases the efficiency of sedimentation for most particles due to the decrease in fluid viscosity, it has a negative effect on the removal efficiency of algal cells (Ma & Liu 2002). At high temperatures, most algae cells swell and release large quantities of gases that reduce the coagulation of these cells. Conversely, at low temperatures, better algal removal is achieved as production of gases due to algae photosynthesis is decreased, but low temperatures decrease the efficiency of the sediment particles due to a decrease in fluid viscosity (Wu et al. 2007). Therefore, algae removal is improved at temperatures of 10°C and below, but removal of solids is improved only at temperatures of 20°C and above (Al-Layla et al. 1974; Wells & LaLiberte 1998; Mkpenie et al. 2007; Goula et al. 2008). Although algae and clay colloids are the same size, ranging from 0.001 to 1.0 microns, the density of algae (1.2 g/cm 3 ) is generally lower than that of clay (2.6 g/cm 3 )(Han & Kim 2001). Compared to clay colloids, algae consumes a large amount of alum (Al-Layla et al. 1974). Further, the presence of algae © IWA Publishing 2018 Water Practice & Technology Vol 13 No 3 642 doi: 10.2166/wpt.2018.079 Downloaded from http://iwaponline.com/wpt/article-pdf/13/3/642/479632/wpt0130642.pdf by guest on 16 June 2021