Aqua Clear electrodialysis reversal (EDR) systems are used to treat and reuse wastewaters with high levels of TDS.
Applications include reuse of cooling tower blowdown, flue gas desulfurization wastewater, rinse waters, and brine concentrate from RO systems. Aqua Clear EDR systems further concentrate the brine into a smaller waste stream; thereby, reducing the cost of brine disposal while increasing the overall recovery of water within the plant.
An EDR stack consists of alternating layers of anion- and cation-selective membranes. This stack of cell-pairs is positioned between an anode and cathode which supply the voltage potential to the module. The membranes allow the ions to pass through with anion-selective membranes permeable only to anions and cation-selective membranes permeable only to cations.
Spacers placed between the alternating layers of anion- and cation-selective membranes create parallel channels for the permeate and concentrate to flow. By applying an electrical voltage potential difference between two electrodes, ions are removed from the feed water into the concentrate stream.
By periodically reversing the polarity of the electric current 3 to 4 times per hour, the direction of the ion flow is reversed. This reversal of polarity reduces the scaling and fouling of membranes.
EDR can operate at a higher recovery rate than a RO system. Since there is no osmotic pressure limitation, EDR can concentrate the brine up to 180,000 ppm TDS. EDR is also less susceptible to fouling and requires less pretreatment for TSS, TOC and silica. However, unlike RO, the percent salt passage for EDR varies with the TDS of the wastewater feed with rejection decreasing at higher TDS. An EDR permeate water quality of 1,500 ppm TDS is economical at high TDS.
