Effluent pretreatment by iron coagulation applying various dose pH combinations for optimum particle separation

Wastewater reuse often requires particle destabilization and removal to pro tect water transport systems and membranes from clogging. Flocculation proc ess of activated sludge effluent applying ferric chloride is examined and c omparison with alum (aluminium sulfate) application is made in this work. O ptimum flocculation conditions are determined based on the removal efficien cy of different particle size groups and on turbidity as a function of coag ulant dosage and pH. Results show that the best removal for ferric chloride coagulant occurs at pH 4-5 and dosage of 20-30 mgl(-1). Sealed water total particle count (TPC) of particle size greater than or equal to 2 mu m was reduced by more than 99%, while turbidity removal reached 86%. Zeta potenti al measurements and visual observations indicate domination of adsorption a nd charge neutralization mechanisms. Best removal with alum occurred at pH 6-7 while dosing 30 mgl(-1) and higher. Destabilization mechanism of adsorp tion and sweep coagulation is proposed. Generally alum performed somewhat b etter than iron for turbidity removal and worse for TPC removal, CMD (count mean diameter) is proposed for particle removal index: the higher the TPC removal, the lower the CMD. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.