Renewable energy powered membrane technology: Salt and inorganic contaminant removal by nanofiltration/reverse osmosis
Richards, Laura A.
Richards, Bryce S.
The objective of this study was to evaluate the effects of fluctuating energy and pH on retention of dissolved contaminants from real Australian groundwaters using a solar (photovoltaic) powered ultrafiltration – nanofiltration/reverse osmosis (UF-NF/RO) system. Four NF/RO membranes (BW30, ESPA4, NF90, and TFC-S) were used. Energy fluctuations affected pressure and flow. Solar irradiance levels impacted retention of fluoride, magnesium, nitrate, potassium, and sodium where convection/diffusion dominated retention. Retention of calcium, strontium, and uranium was very high and independent of solar irradiance, which was attributed to a combination of size and charge exclusion and for some solutes sorption and precipitation. Groundwater characteristics affected retention and the solutes were categorized into two groups according to retention as a function of pH: (1) pH independent retention (arsenic, calcium, chloride, nitrate, potassium, selenium, sodium, strontium, and sulfate); and (2) pH dependent retention (copper, magnesium, manganese, molybdenum, nickel, uranium, vanadium, and zinc). The retention of Group 1 solutes was typically high and attributed to steric effects. Group 2 solutes had dominant, insoluble species under certain conditions which led to deposition on the membrane surface (and thus varying apparent retention). The renewable energy membrane system removed a large number of groundwater solutes reliably over a range of real energy and pH conditions.