[0152] With feedwater relatively high in barium content, RO system recovery can be limited by barium sulfate precipitation potential at the reject end. The HERO system eliminates this concern altogether, since barium is quanti› tatively removed prior to the RO. The same outcome is also applicable for RO systems limited (in recovery) by stron› tium sulfate, calcium sulfate, calcium fluoride, and other sparingly soluble calcium, magnesium, iron, and aluminum salts. 

[0153] Of course, the final limit in RO recovery, repre› sented by osmotic pressure of the RO reject, will still control the maximum feasible recovery achievable with a specific feedwater, but this limit is not usually reached at recoveries less than 99 percent with most feedwaters. 

[0154] (C) Biological Fouling is Essentially Eliminated 

[0155] Most commonly occurring microbial species are completely lysed (physically destroyed) at the high operat› ing pH. In fact, even virus, spores, and endotoxins are either destroyed or rendered incapable of reproduction/prolifera› tion at very high pH levels. Saponification of lipids (fat) is expected to play a role in the process as well since fatty acids and their corresponding glycerides will form soluble "soaps" at the high operating pH. 

[0156] In one location where long-term tests were carried out, biofouling was conspicuous by its absence during the test of the HERO technology. This pilot RO system exhib› ited very stable operating performance in terms of normal› ized permeate flow and system pressure drop throughout the test period. Further confirmation of the absence of biofoul› ing was obtained during autopsy of RO elements at regular intervals. A stage wise program to test and autopsy the FILMTEC FT30 based elements was conducted over a 15 month period. The data showed higher salt rejection than the initial Quality Assurance values under standard test condi› tions. Also, the membrane surface was clean and free of any evidence of biofouling. 

[0157] This characteristic of the new process can be of significant benefit for sites with known biofouling problems or for the treatment of bio-contaminated/bio-active waste› water. It can also be very effective for systems with higher› than-ambient temperature RO operation. 

[0158] (D) Particulate Fouling is Substantially Reduced 

[0159] It has been known (and practiced) for almost 30 years that softening of RO feedwater destabilizes colloidal solids present in the feedwater and significantly reduces the associated fouling problems. Mandatory softening require› ment as pretreatment for hollow fine fiber RO elements in the late 1960s and early 1970s attests to this strategy. In addition, zeta potential is generally reduced between a surface and foulant particles at high pH, thus reducing the likelihood of adhesion. This property is accentuated by the fact that most naturally occurring particles (including bac› teria) exhibit negative surface charges. While side-by-side zeta potential determination is yet to be carried out, the new process is expected to significantly reduce, if not eliminate, particulate fouling problems. The reduction of zeta potential further reduces the possibility of particle adhesion to the slightly negatively charged membrane surface. The in-situ formation of surfactants from bacterial lipids, if present, will further help in reducing particle adhesion to the membrane surface. 

[0160] This unique characteristic of the new process can be of significant value in the design of an RO system, particularly in the potential to reduce capital cost and operating complexity of treating UPW. In addition to the ability to accept a certain level of particulate foulants, the new process may also minimize the need for multimedia filtration, coagulant/floucculant addition, Diatomaceous Earth filtration, etc., as pretreatment to is the RO system. 

[0161] (E) Significantly Reduction in Chemical Usage 

[0162] Dechlorination, either by chemical addition or by activated carbon, may very well be unnecessary as well since the level of free (undissociated) hypochlorous acid (HOCL) is extremely low at the very high operating pH. 

[0163] (F) Elimination of Scale Inhibitor Use 

[0164] Use of antiscalants or scale inhibitors, while not harmful or incompatible with the new process, can be completely eliminated, as proven by an 18-month test at a semiconductor manufacturing facility. 

[0165] (G) High Flux Rates 

[0166] Given the reduced thickness of the concentration polarization layer, as well as the elimination of biofouling and the reduction of particulate adhesion to the membrane surface, it is not surprising that an RO system utilizing the new process can operate at higher flux compared to con› ventional operation. Compared to a normal design flux of 15 gfd (gallons per square foot per day), the HERO brand RO system is designed in excess of 15 gfd, and is preferably designed at about 20 gfd, and more preferably up to about 25 gfd, and, where feasible, in excess of 25 gfd. 

[0167] (H) Higher Product Purity 

[0168] In addition to reduced capital cost for the RO system, the quality of the RO permeate is improved signifi› cantly due to the higher design flux. For example, at 25 gfd, the RO permeate will contain 40 percent lower dissolved solids compared to a 15 gfd design basis. The higher pH operation, in combination with the high product flux, pro› vides the result that the salt flux (which is concentration dependent, rather than pressure dependent) is significantly reduced. The RO system can be expected to be about 20 percent less expensive due to this factor alone ( or more than 20 percent less expensive), all other parameters being equal. 

[0169] (I) Reject Usable as Scrubber Makeup 

[0170] The reject from the HERO brand RO system, with high pH, low carbonate alkalinity, and virtually no hardness, can be used as makeup to acidic gas scrubbers. Due to concerns about potential silica precipitation if the pH is lowered significantly in the scrubber, the RO reject should be used on a once-through basis, and thus not be evaporation rate limited. 

[0171] Process Chemistry 

[0172] As discussed earlier, very high reject pH is one factors which characterize operation of the HERO brand RO system. Extremely high rejection of the weakly ionized anions such as TOC, silica, boron, etc., can be correlated to such characteristics. The following example, based on silica, can be used to explore this relationship. 

[0173] In naturally occurring waters and at near-neutral pH range (6-8), silica is primarily present as orthosilicic acid 

