Abstract

A coagulation–flocculation process was used to treat water-based printing ink wastewater with aluminum sulphate {Al₂(SO₄)₃} as coagulant and with Praestol as flocculant. To minimize turbidity and sludge volume index (SVI), the experiments were carried out using jar tests and response surface methodology (RSM) was applied to optimize this process. A central composite design, which is the standard design of RSM, was used to evaluate the effects and interactions of three factors, that is, coagulant dosage, flocculant dosage and pH on the treatment efficiency. The optimal conditions obtained from the desirable response, chemical oxygen demand (COD) removal, were coagulant dosage of 8250 mgl^-1, flocculant dosage of 80 mgl^-1 and pH 7.25, respectively. The RSM was demonstrated as an appropriate approach for the optimization of the coagulation–flocculation process by confirmation experiments.

Key words: Printing ink industry effluent, chemical oxygen demand (COD) removal, response surface methodology, coagulation-flocculation process.

Abbreviation

Abbreviations: RSM, Response surface methodology; COD, chemical oxygen demand; TSS, total suspended solid; VS, volatile solid; TS, total solid; BOD, biological oxygen demand; CCD, central composite design.