A comparative study of some novel "green" and traditional antiscalants efficiency for the reverse osmotic Black Sea water desalination

Abstract

a b s t r a c tDesalination of seawater and brackish water by reverse osmosis to produce potable and process water has been widely used. But the precipitation of low soluble salts is one of the major problems in RO plants operation. Several well-known techniques are used to protect membranes and antiscalant dosing is one of the most widespread. A wide range of reliable and efficient inhibitors have been developed but the trend of the last decade is creation environmentally friendly ("green") chemicals: phosphorus-free and biodegradable. A relative ability of industrial samples of four phosphorus-free polymers (polyaspartate (PASP); polyepoxysuccinate (PESA); polyacrylic acid sodium salt (PAAS); copolymer of maleic and acrylic acid (MA/AA)) and of three phosphonates (aminotris (methylenephosphonic acid), ATMP; phosphonobutane-1,2,4-tricarboxylic acid, PBTC; and AMINAT) to inhibit carbonate membrane fouling in the simulated Black Sea water under reverse osmosis (RO) conditions for the dosages ranging from 1 to 25 ppm is tested. The following ranking ATMP > HEDP > PESA (400 ÷ 1500 Da) ~ PASP (1000 ÷ 5000 Da) > PAAS (3000-5000 Da) ~ MA-AA is found. A comparison of this ranking with that one performed following the NACE Standard TM0374-2007 under static conditions confirmed results provided by NACE Protocol.

Use of a Fluorescent Antiscalant to Investigate Scaling of Reverse Osmosis Membranes

“…Antiscalant doses are prescribed depending on the hardness of the source water. However, as was shown in a number of studies by the authors [22], the dose of an antiscalant has almost no effect on its performance in a certain range of hardness values. This is due to the fact that the nucleation of crystals occurs at high values of supersaturation in the "stagnant zones" of membrane devices, where supersaturation is achieved by increasing the concentrations of either ions contained in water or antiscalants or both.…”

“…Experiments of the first and second sets were performed using a single BLN 1812 membrane element. As shown earlier [22], comparative tests to determine the scaling rates should be carried out on the same element, since membrane surfaces in different membrane devices may have a different number of "stagnant zones" and, accordingly, the deposition rates in different devices will differ despite their identical operating conditions. The amount of the antiscalant Aminat-K in water was monitored by measuring the concentration of the ion…”

“…In experimental studies on testing the performance of antiscalants, the method of introducing seed crystals into a supersaturated solution held sway for a long time [1][2][3][4][5][6][7]. As was shown earlier [22], the patterns of crystal growth and antiscalant sorption on the surface of crystals under conditions of low supersaturation do not correspond to the actual conditions for the nucleation of crystals and scale formation on the membrane surface. However, the studies by numerous adherents of this method [1][2][3][4][5][6][7][8] made it possible to reveal the dependences of the crystal growth rates on the supersaturation of the solution and the laws of adsorption of antiscalants on crystal surfaces.…”

“…Naturally, an increase in the antiscalant dose led to an increase in the amount of adsorbed antiscalant and a decrease in the rate of crystal growth. The same applies to the conclusions about the patterns of adsorption of antiscalants on seed crystals in experiments in a closed volume [22][23][24][25][26][27]. A number of researchers are currently using the concept of induction period (the time of nucleation of crystals of a visible size in the presence of an antiscalant at high values of supersaturation) to evaluate the effectiveness of antiscalants [24].…”

“…A number of works [22,24] have been devoted to the study of stagnant zones and the conditions for scale formation in them. Based on the results of these studies, the following ideas about scaling were formulated:…”