Oct. 24, 2002  15  US 2002/0153319 Al  [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 