Desalination of boron-containing wastewater at no boron transport

Abstract

In our present work, the preliminary electrodialytic desalination of wastewater containing 75 mg/L of boron and approximately 1.8 g/L TDS was investigated, as the first step in two-stage boron removal ED process. The wastewater in question originated from Tarnowskie Góry landfill chemicals storage. To avoid high boron ionization degree and high boron transport rate, the diluate was acidified with hydrochloric acid. To asses the influence of the process parameters on the desalination efficiency and boron transport rate, a set of experiments was designed. It was found that an increase in both pH and desalination degree results in enhanced boron transport and at high desalination degree, of ≈95%, the concentrate boron content may exceed the wastewater discharged to the public sever system limit of 1 mg B/L. Further research showed that the decrease in pH below the level of 3 results in addition of considerable amount of chloride that drastically increased electric charge demand and shortened desalination efficiency. Based on the conductivity, pH and pH-metric titration curve, the suitable condition for ED desalination at low boron transport rate pH value was found to be approximately 3. Additional experiments on boron removal at this pH level indicated that up to 99% desalination degree may be achieved at negligible boron transport rate (low enough to assure concentrate boron content less than 1 mg/L that is required by governmental regulations). The resulting deeply demineralized diluate may be then treated under alkaline conditions in the second step, when high boron transport rate as well as high electric current efficiency are suspected, without alkaline scaling risk.