Ceramic Membranes in Removing Boron from Processed Geothermal Waters

Abstract

The main objective of this work was to investigate the removal of boron from processed geothermal waters (i.e., after energy production) in lab-scale tests using ceramic ultrafiltration membranes. The impacts of membrane operating pressure, feed water pH and temperature and membrane pore size on boron rejections were determined. Three different single-channel tubular ceramic membrane modules with average pore sizes of 4 nm, 10 nm and 1 kD were tested. Fine-UF ceramic membrane with 4 nm pore size provided higher boron and salt rejections than the other two tested membranes. Increasing pH from 8.8 to 10.5 did not enhance boron rejections. Operating pressure around 8 bar was found to be optimum in terms of flux values and boron and salt rejections for the 4 nm pore-sized membrane. The results indicated that ceramic ultrafiltration membranes can only partially (around 25-30%) remove boron from geothermal waters. Once much lower pore-sized nanofiltration or brackish water reverse osmosis type ceramic membranes are available, they may be used for the desalination of processed geothermal waters since ceramic membranes are resistant to extreme conditions. Ceramic fine-UF membranes can also be used as a pre-treatment stage prior to polymeric brackish water reverse osmosis processes in desalination of geothermal waters.