Evaluating the dewaterability of waste activated sludge via iron dosing and forward osmosis membrane filtration

Abstract

The activated sludge process has been widely applied in the wastewater treatment for the past 100 years because of its high efficiency. The water content in waste activated sludge (WAS) accounts for over 90% [1], which leads to higher operating costs for disposal and transportation of sludge. However, to-date, the efficiency of the sludge dewateribility remains as a major challenge and progressive research are currently been conducted.To remove the water from WAS, several feasible methods are used in the majority of wastewater treatment plants, which can be categorized as: thickening, stabilization, dewatering, conditioning and disposal [2]. In this study, chemical conditioning by combination of ferrous and ferric ions and forward osmosis (FO) membrane filtration are chosen to increase the sludge dewatering performance due to their advantages of cost-effective and simple operating procedure. Based on the experimental results, both ferrous and ferric ions can enhance the sludge dewaterabilty. However, ferric is verified to be more efficient than ferrous. This is due to the higher charge density of ferric and better bridging properties that provides stronger flocculation for water removal. In addition, Forward osmosis process is not a promising technique for enhancing anaerobic digested (AD) sludge dewaterability. The digestion would break the cell into small substances, which leads to a deteriorative membrane fouling. Although applying iron conditioning and FO process together increases the rejection percentage of nutrients, the water flux performance is still unsatisfactory because of the serious membrane fouling.ii Acknowledge Firstly, I would like to express my gratitude to Dr. Liu Ye, my supervisor always provided me many precious suggestions and helped me in many ways during the whole thesis process. I am so thankful that I can work with her to finish this interesting topic.