Removal of Turbidity from Travertine Processing Wastewaters by Coagulants, Flocculants and Natural Materials

Abstract

The sedimentation behaviour of travertine-processing wastewater containing a high concentration of suspended solids was investigated using different coagulation and flocculation methods. In batch experiments, four types of coagulants [FeC13, Al2(SO4)3, PACl, NaAlO2], six types of flocculants (40% MMW–40% HMW cationic, 30% MMW, 40% MMW, 40% HMW anionic and nonionic) and three types of natural materials (NMs) (sepiolite, zeolite, and pumice) were used to treat wastewater with an initial turbidity of 570–880 NTU. The optimum process conditions (dosage, mixing time/speed, sedimentation time, and pH) were investigated for each. Sedimentation performance was assessed by the effluent turbidity (T eff) values of the treated water. The best performances obtained were 99.3% (T eff = 4 NTU), 99.1% (T eff = 8 NTU), and 97.8% (T eff = 18 NTU) with 40% HMW anionic-cationic flocculants, zeolite, and FeCl3, respectively. Sludge properties, including sludge settling velocity (mm/min), sludge density (g/cm3), suspended solids (SS) content (mg/L), and sludge solids (%) were determined and compared under optimized conditions. The type of additive significantly affected performance. Travertine processing wastewater flocculation with polymeric materials and NMs, especially zeolite, was more favourable than coagulants in terms of both turbidity removal and sludge quality. Since zeolite is a NM, additional studies on using and recycling of the generated sludge as an industrial feedstock would be worthwhile.