Purification of real car wash wastewater with complex coagulation/flocculation methods using polyaluminum chloride, polyelectrolyte, clay mineral and cationic surfactant

Abstract

In the present study, real car wash wastewater was purified by different coagulation/flocculation methods. As coagulant, polyaluminum chloride ('BOPAC'), conventional iron(III) chloride, iron(III) sulfate, and aluminum(III) chloride were used, while as flocculant non-ionic and anionic polyelectrolytes were investigated. The effects of added clay mineral (Na-bentonite) and cationic surfactant (hexadecyltrimethyl ammonium bromide - 'HTABr') were also investigated. The use of BOPAC was significantly more effective than conventional coagulants. Extra addition of clay mineral was also beneficial in relation to both the sediment volume and sedimentation speed, while polyelectrolyte addition enhanced further the sedimentation. Moreover, the simultaneous addition of HTABr significantly enhanced the color removal efficiency due to the successful in-situ generation of organophilic bentonite. In summary, the application of 100 mg L-1 Na-bentonite with 20 mg L-1 Al3+ (from BOPAC) and 0.5 mg L-1 anionic polyelectrolyte resulted in the efficient reduction of the turbidity (4-6 NTU), the COD (158 mg L-1) and the extractable oil content (4 mg L-1) with efficiencies of 98%, 59%, and 85%, respectively. By applying organophilic bentonite in high concentration (500 mg L-1) with identical concentrations of BOPAC and anionic polyelectrolyte, significant color removal (5 times lower absorbance at γ = 400 nm) and 27% lower sediment volume were achieved.