Integrated membrane process for wastewater treatment from production of instant tea powders

Abstract This study investigated an integrated process to treat the wastewater from an instant tea powder factory. The wastewater was pretreated by combination of coagulation–flocculation. Polyaluminum ferric chloride (PAFC) was used as the coagulating agent. The optimum operating conditions with respect to contaminant removal were determined to be pH 5, 20 °C and 800 mg/L of PAFC, with polyacrylamide (PAM) as coagulant aid at a dosage of 20 mg/L. The discharged water from the coagulation–flocculation was treated with ceramic UF membranes. It was found that interactions between the molecules of PAFC and organic foulants reduced the membrane fouling and improved the removal efficiencies effectively. The permeate flux of UF membrane was almost three times higher than typical flux obtained without pretreatment. In the subsequent NF process, the removal efficiencies of turbidity, COD and TOC were all higher than 99.9%, and the TSS wasn't detected in the permeate. The effects of cleaning methods on permeate flux were also investigated. It was found out that 0.5 wt.% NaClO flushing produced the highest flux recovery ratio of 99% and showed good reproducibility. This study showed the feasibility of applying coagulation–flocculation, UF and NF in the treatment of instant tea powder factory wastewater.