Combined coagulation/ceramic membrane ultrafiltration system for reclamation of degreasing washing water

Currently, there is growing emphasis on wastewater reclamation and reuse around the world. In this study, a combined coagulation/ceramic membrane ultrafiltration system was used to treat degreasing washing water under high pH/alkalinity conditions containing surfactants, organic matter and other materials resulting from rinsing processes in the plating industry. Coagulant exists as sol or gel species that was not suitable for complexation with smaller surfactants and organic matter under high pH/alkalinity conditions. A pH neutralization process was introduced to improve the removal efficiency of the coagulant prior to coagulation. An optimal coagulant (ferric chloride), optimal coagulation pH 5, and optimal coagulant dosage (700 mg Fe/L) were proposed as a result of coagulation tests. Under slightly acidic conditions, species distribution of ferric chloride consisted of monomers and medium polymers that were favorable for the formation of surfactant–coagulant or organic matter–coagulant complexes. In coagulation/ultrafiltration tests, filtration with in-line coagulation enhanced flux and also reduced resistance caused by internal pore blocking. This phenomenon is due to the rapid formation of a cake layer on the ceramic membrane and this cake layer lessens the adsorption of small foulants in feed water on the membrane. Moreover, filtration with in-line coagulation provided water quality similar to that of filtration of the supernatant. It is concluded that filtration with ferric chloride and in-line coagulation are valuable processes for treating degreasing washing water with reduced capital costs by excluding the need for flocculation and sedimentation zones in a water treatment plant.