Oct. 24, 2002  11  US 2002/0153319 Al  [0123]  Operational results of the pilot test unit may also be  better appreciated by reference to  FIGS. 5, 6, 7,  and  8. FIG.  5  illustrates the relationship between the axial differential  pressure (!i.P) versus time, in pounds per square inch, for the  reverse osmosis membrane employed in the pilot reverse  osmosis test equipment. The differential pressure shown has  not been corrected for changes in feedwater flowrate. In  comparison to conventional RO, the pilot test results show  that a stable normalized permeate flow rate, a stable silica  rejection rate, and a stable differential pressure have been  achieved. This indicates that fouling/scaling have been  essentially eliminated in my new process.  FIG. 6  shows the  normalized permeate flow, in liters per minute, versus time  over a six month period, for the reverse osmosis membrane  employed in the pilot reverse osmosis test equipment.  [0124]  FIG.  7 illustrates the silica concentration in the  reverse osmosis reject stream over a six month period in  pilot reverse osmosis test equipment.  FIG. 8  illustrates the  rejection percentage of silica, versus time over a six month  period, for the reverse osmosis membrane employed in pilot  reverse osmosis test equipment. This silica rejection is based  on an arithmetical mean silica concentration in the pilot RO  unit.  [0125]  After each shutdown of pilot plant operation due to  a ten percent (10%) or more decline in normalized permeate  flow, the membranes were inspected and cleaned.  An impor› tant finding was that cleaning can be simply and effectively  accomplished by commodity membrane cleaning chemicals,  such as hydrochloric acid solutions, tetrasodium  EDTA,  and  sodium hydroxide. Expensive proprietary chemical cleaning  agents were not required.  An RO  membrane operated with  feedwater pretreatment in the manner set forth herein was  proven to be completely restored to a flux of essentially one  hundred percent  (100%) of startup performance values.  Substantially all of the cleaning was accomplished with the  acidic first step of the cleaning process, thus indicating that  calcium carbonate, magnesium hydroxide, magnesium sili› cate, and the like, were the predominant scaling species.  Importantly, this revealed that neither silica scaling or bio› fouling were major concerns under the specified process  conditions. The enhanced runnability, or increased system  availability, with minimal scaling and virtually non-existent  bio-fouling, is clearly another important benefit of my novel  RO operational method.  [0126]  Biological fouling of thin film composite mem› branes has heretofore tended to be a common problem, and,  with certain specific feedwater sources, has been virtually  insurmountable. Although it was anticipated that control of  biological fouling would be improved due to operation at  relatively high  pH  levels, the degree of is biological fouling  control actually achieved far exceeded expectations, with  bacteria levels being virtually non-detectable during autopsy  of RO membrane elements. This means that instead of  accumulating living and dead bacteria against the membrane  surface, as is common in conventional RO systems, in my  unique method, incoming bacteria are killed and dissolved  away from the membrane surface. Thus, this method of RO  pretreatment and operation may become useful for treating  problematic water sources. This is effective because high pH  solutions cause disinfection by cell lysing or rupture of the  cell wall. This is a quite potent and quick acting method of  anti-bacterial activity, when compared, for example, with  chlorination which acts by the much slower method of  diffusion through the cell wall to cause death by inactivation  of the microorganism’s enzymes. Also in contrast to chlorine  sanitized systems, at the high pH operation preferred in the  present method, viruses and endotoxins (lipopolysaccharide  fragments derived from cell walls of Gram-negative bacte› ria) are effectively destroyed by lysis, thus enabling the  present method to be employable for the production of  pyrogen free or sterile water. In essence, the present method,  when operated at a pH in excess of about 10, provides  sanitization (3 log reduction in bacteria and destruction of  vegetative matter), and may also prove to essentially provide  true sterilization (12 log reduction in bacteria and the  elimination of biofilm and spores) of the process equipment,  as test results showed a zero  (0) bacteria count in the  permeate. Also, it should be noted that the increased  pH  of  permeate in this method of operation enables similar, helpful  results in the post RO treatment equipment. Such a method  of operation should be of particular benefit in the production  of high purity water for pharmaceutical applications, where  the requirements for United States Pharmacopeia 23 ("USP  23") standards, as supplemented, must ultimately be met by  the final product water. In this regard, the avoidance of use  of raw water polymers, antiscalants, and other proprietary  chemicals in  RO  pretreatment, as described herein with  respect to a preferred embodiment, can eliminate undesir› able additives to pharmaceutical grade water, and reduce  costs by reducing the necessary tests on  RO  product water.  More concisely, the selection of a pH for RO operating  conditions which does not support bacteria growth, and  carrying out of hardness and alkalinity removal to a level  which avoid use of additives, is a superior method for  production of high purity water.  [0127]  A further benefit of high pH operation is with  respect increased protection of membranes, particular the  thin film composite types, which have limited tolerance for  oxidizing agents at neutral, near neutral, and moderate  alkaline pH’s (up to roughly pH 9). When chlorine is added  to  RO  feedwater,  gaseous chlorine (Cl$_{2}$ )  or sodium  hypochlorite (NaOCl) are typically utilized. Because of  membrane sensitivity to free chlorine, in conventional RO  systems, it is normally removed by sulfite (SO$_{3}$ --)  injection.  However, above.pH 9, and particularly above pH 10, the  effect of chlorine and other similar oxidants on thin film  composite membranes is significantly reduced. This is  because the concentration of the non-ionized species (such  as HOCl, known as hypochlorous acid) is decreased dra› matically, since such acids are relatively weak. Conse› quently, in my HERO(tm) high pH reverse osmosis process,  typically operating at a pH of  10 or higher, chlorine removal  is not generally necessary, thus reducing system complexity  and costs. This may be especially beneficial for those  systems which utilize a municipal water source as the  feedwater to the water treatment plant.  [0128]  Enhanced membrane life is also another benefit of  my novel membrane operation process. In membrane opera› tions, and in particular with respect to  RO  operations, longer  membrane element life may be expected, primarily because  scaling and biofouling are avoided, and thus, exposure to  harsh cleaning chemicals (for instance, acid chemicals and  surfactants) is reduced dramatically.  [0129]  RO membranes are taken out of service when the  rejection of critical species, for example silica, boron, or  TOC, falls below an acceptable limit. For silica, this usually 