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

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. © 2014 Elsevier B.V. All rights reserved.

In this study, the combinations of coagulation–membrane treatments were applied to the instant tea powder factory wastewater. The results highlighted by this work have shown that coagulation was an excellent pre-treatment which can increase the permeate flux. The optimum results were obtained in terms of COD removal (77.3%) and turbidity reduction (99.8%) for coupling coagulation–flocculation and UF. However, a few low molecular weight organic matters that contributed to the remaining COD were still dissolved in the wastewater which could be removed by a subsequent NF process. The removal of turbidity, COD and the TOC was all over 99.9%, and the total suspended solids were not detected in the water. The characterization of sewerage after NF meets China standard (integrated wastewater discharge standard GB 8978-1996). The optimum parameter of coagulation is at the dosage of 800 mg/L, pH 5 and 20 °C, and under those conditions, the permeate flux of wastewater of ceramic membrane showed great improvement. 0.5 wt.% NaClO was found to be the most effective cleaning agent. Furthermore, this work represents the first successful application of coagulation–flocculation, UF and NF in the treatment of instant tea powder factory wastewater. Acknowledgments The financial support comes from the National Natural Science Foundation of China (no. 21276124), the Key Projects in the National Science & Technology Pillar Program (no. 2011BAE07B09-3), and the Jiangsu Province Industrial Supporting Project (no. BE2012399).