Effect of electrochemical pretreatment on the control of scaling and fouling caused by circulating cooling water on heat exchanger and side-stream reverse osmosis membrane

Abstract

An environment-friendly electrochemical pretreatment process was used to purify the circulating cooling water (Including salts extraction and organics removal), and the effect of electrochemical pretreatment on scale inhibition and reverse osmosis (RO) was explored. Results showed that the electrochemical pretreatment exhibits a good softening ability for different types of water with hardness from 100 to 500 mg/L (Calculated by CaCO3). Considering the treatment efficiency and energy consumption, 5 V and 7 V were suitable for softening treatment of low hardness water and high hardness water respectively (with 300 mg/L hardness as the limit). After electrochemical pretreatment, CaCO3 scale on heater surface can be effectively inhibited and the maximum scale inhibition rate can reach 73.9% at 7 V. Meanwhile, the CaCO3 scale is loose after electrochemical pretreatment, accompanied by the transformation of crystalline phase from calcite to aragonite. The long-term RO membrane flux experiment shows that the pure inorganic salt solution has the least contribution to RO membrane fouling, followed by the pure organic solution. Notably, when inorganic salt ions coexist with organic matters in water, a complex structure of gel network can be formed, which causes serious pollution to RO membrane and sharp decrease of the specific flux (J/J0). Interestingly, RO membrane fouling can be effectively controlled after electrochemical pretreatment even for actual circulating water. This work provides a simple strategy for the development and application of electrochemical technology in softening and RO membrane fouling control.