The Reclamation Of The Saline Water Generated From Surface Water Desalination

The shortage of freshwater has seriously impeded the growing needs of industrialproduction and daily life of people. Nowadays, the desalination technologies,including thermo method, reverse osmosis method （RO）, electrodialysis method （ED）,etc, have become the primary methods in incresing freshwater supplies. Among them,ion exchange （IE） method embraces some significant advantages, including highrecovery ratio of water, low power consumption, low investment and maintenancecost and so on, and usually is considered as the first choice for the desalination ofwater whose TDS is smaller than1200mg/L. However, just the same as otherdesalination methods, the treatment of the saline water generated from surface waterdesalination is also a pressing problem of the day for IE besides its inherent problem,for an example, the treatment of waste acid and waste base after the regeneration ofion exchange resin.In this study, the bipolar membrane electrodialysis-based reclamation scheme forthe saline water was proposed. That is, the environmental pollution induced by thedirect dischargement of saline water can be effectively avoided. Simutaneously, thecorresponding acid and base used for the regeneration of ion exchange resin can beproduced from the saline water. Obviously, a closed loop can be formed. Azero-discharge desalination process can be expected.This work will focus on the following three topics. Firstly, bipolar membraneelectrodialysis （BMED） has serious requirements on water quality of feed solution,such as the contents of Ca²⁺, Mg²⁺, SiO₂, natural organic matter and so on. Therefore,an effective pretreatment scheme and the corresponding optimized operating condionsare need badly. Secondly, we investigated the effcts of some relevant factors,including membrane selection, current density, initial concentration of acid and base,product concentration, etc. on BMED performance, such as current efficiency andenergy consumption. At last, the economic evaluation on the reclamation scheme was conducted on the basis of the mentioned-above experiments for future possibleindustrialization and commercialization.The experimental results showed that the pretreatment scheme, so-called"soda-caustic soda-coagulation plus further treatment by ion exchange", caneffectively reduce the contents of objective ions and make the feed solution meet therequirements for BMED. In addition, we found that the membrane stack installed thedomestic membranes, including bipolar membranes, cation exchange membranes andanion exchange membranes has similar work performance to abroad products. Forexample, a current efficiency as much as72%was observed in our work. Obviously,the investment cost and maintenance cost can be reduced to a large extent. Tosomeone’s existing, the reclamation scheme proposed in this study has potential inbroad applications.