Method for improving reverse osmosis recovery of high silica water

Abstract

The present invention is a semi-batch, multi-stage reverse osmosis process for the treatment of silica-containing water with the aim of achieving 90% and higher recovery without the need for chemically enhanced pretreatment.

Description

Technical Field

[0001] The present invention relates to a reverse osmosis method for treating water, and more particularly, to a reverse osmosis method for treating water having a high concentration of silica. Background Art

[0002] Conventional reverse osmosis (RO) systems are used to treat water with relatively high silica concentrations. The recovery rates typically achieved by treating water with significant concentrations of silica through conventional RO systems are limited. The recovery rates can be improved by using methods to remove silica through pretreatment. For example, it is known to remove silica using chemical precipitation before treatment in an RO system. Another pretreatment approach requires chemical addition to the water, which is designed to increase the pH of the water, which in turn increases the solubility of silica, which tends to reduce the tendency of RO membrane scaling. In addition, it is common practice to inject antiscalants into the RO feed water, and in particular antiscalants specifically for silica, to achieve 150%-250% silica saturation in the RO concentrate. These chemical addition and pretreatment methods have disadvantages. These and other pretreatment methods are costly to implement and maintain, particularly because they require chemical additions. In addition, for example, with chemical precipitation, sludge is produced, and solid-liquid separation methods need to be combined to remove the sludge, and the sludge also needs to be properly treated. The ability of antiscalants to inhibit silica scale formation is limited. In addition, when using silica-specific antiscalants, other scales and foulants (such as calcium carbonate, magnesium, iron and aluminum) need to be carefully controlled via robust pretreatment and / or chemical adjustments, as their presence in excessive concentrations can inhibit the effectiveness of the silica-specific antiscalants. The methods or processes described below achieve much higher silica concentrations in the RO concentrate than can be achieved using conventional RO with antiscalants, and do not require the use of robust and chemically enhanced pretreatments (such as chemical softening or chemical precipitation).

[0003] Therefore, the problem is to develop an RO system and method that achieves relatively high recoveries when treating water having high concentrations of silica without the need for chemical precipitation or other methods requiring chemically intensive pretreatment. Summary of the invention

[0004] In one embodiment, the present invention is a semi-batch multi-stage reverse osmosis (RO) process for treating water containing silica, with the goal of achieving recoveries of 90% and higher without necessarily requiring the addition of chemicals.

[0005] In one embodiment, the present invention requires a multi-stage reverse osmosis method, the method comprising a reverse osmosis unit that produces a permeate and a concentrate. The concentrate including silica is mixed with water containing silica to form an RO feed, which is continuously introduced into and passed through the RO unit. During this first stage, the silica concentration of the feed will increase. Once the silica concentration of the feed reaches a selected level or set point, such as close to saturation or at saturation, the method switches from the first stage to the second stage. In the second stage, the feed of concentrate and water or a portion thereof is guided through a silica adsorption unit located upstream of the RO unit. As the feed flows through the silica adsorption unit, silica is adsorbed on the medium in the silica adsorption unit. During the second stage, the silica concentration in the feed remains approximately constant close to saturation, but preferably just below saturation. Continue the second stage until a second set point or threshold is achieved. In one embodiment, the second set point is based on the method to achieve a selected recovery, such as a recovery of 90% or more. Once the second set point or threshold is reached, the method switches from the second stage to the third purification stage. In this third purification stage, the concentrate discharged from the RO unit is purified from the process.

[0006] A second embodiment is also described in which the water to be treated is supersaturated, saturated or nearly saturated with silica. Here, the first production stage entails directing the RO feed or a portion thereof through a silica adsorption unit, which reduces the silica concentration of the RO feed before reaching the RO unit. In the second stage, all or most of the RO feed bypasses the silica adsorption unit, and the silica concentration of the concentrate is increased to supersaturation. Thereafter, the process switches to a third purification stage in which the concentrate is purified from the RO system.

[0007] Other objects and advantages of the present invention will become apparent and obvious through a study of the following description and accompanying drawings which are intended to illustrate the present invention only. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a schematic diagram depicting the first production stage of the multi-stage reverse osmosis process of the present invention.

[0009] Figure 2 is a schematic diagram depicting the second production stage of the multi-stage reverse osmosis process of the present invention.

[0010] Figure 3 is a schematic diagram depicting the third purification stage of the multi-stage reverse osmosis process of the present invention.

[0011] Figure 4 is an example graph illustrating how the recovery of a multi-stage RO process varies over several stages.

[0012] Figure 5is a schematic diagram of the first production stage of the second process, which is designed to process water that is saturated, supersaturated or nearly saturated with silica.

[0013] Figure 6 is a schematic diagram of the second production stage of the method.

[0014] Figure 7 is a schematic diagram of the third concentrate purification stage of the process.

[0015] Figure 8 is an example diagram illustrating how the recovery of the second multi-stage RO process varies over several stages.

[0016] Figure 1-3 5-7 schematically illustrate the three stages of two different RO methods described below. The schematic diagrams include solid lines and dashed lines. In each figure, the solid line represents the active part of the method, while the dashed line represents the inactive part of the method. DETAILED DESCRIPTION

[0017] Referring further to the drawings, there is shown a reverse osmosis (RO) system, generally designated by the numeral 10, which is designed to perform the semi-batch multi-stage RO process described below. The multi-stage reverse osmosis process differs from the conventional steady-state reverse osmosis process in that the process includes several different stages. Before discussing the RO process, it is helpful to briefly review the components of the RO system 10. Figure 1-8, the RO system 10 includes an RO container array 12, which is sometimes referred to as an RO unit. The RO unit 12 produces permeate and concentrate. Extending from the RO unit 12 is a permeate line 14, which includes an automatic permeate control valve 14A, which can be an automatic regulating control valve or an automatic on / off valve. At certain stages of the RO process, it is beneficial to recirculate permeate or part of the permeate. This is especially true during the purification stage of the method. In order to accommodate permeate recycling, a permeate recycling line 38 is provided, which can include an automatic valve or an orifice plate. In many cases, an orifice plate is preferred because it can be designed to prevent permeate recycling during the production stage, but allow permeate recycling during the purification stage. Also extending from the RO unit 12 is a concentrate line 16 including a pump 16A. The concentrate line 16 is operably connected to a purification line 18 including a purification control valve 18A. The concentrate purification valve 18A is preferably a regulating flow control valve that can be partially opened to maintain a concentrate flow rate set point. In addition, the concentrate line 16 is operably connected to a concentrate recirculation line 20. A raw water inlet line 22 directs water to be treated into the RO system 10. A filter unit 24 is optionally included in the raw water inlet line 22. The filter unit 24 is not necessary in many applications of the present invention. An RO booster pump 26 is disposed in the raw water inlet line 22 and, as will be understood from the following discussion, is operable to drive the RO feed (a mixture of concentrate and raw water) through the RO unit 12 and various components located between the booster pump and the RO unit. Downstream of the RO booster pump 26 is a feed line 28. The concentrate recirculation line 20 merges with the feed line 28 downstream of the booster pump 26.

[0018] The feed line 28 is operably connected to a through line 30, which includes a regulating flow control valve 30A and a buffer tank 32. Arranged in parallel relationship with the buffer tank 32 are two (or more) silica adsorption units 34 and 36, which themselves are also arranged in parallel relationship. During certain stages of the process, the feed lines 34A and 36A operate to direct the RO feed to either of the silica adsorption tanks 34, 36. Each silica adsorption unit 34, 36 includes a media that effectively adsorbs dissolved silica in the feed as the feed passes through the silica adsorption unit and contacts the media therein. Various types of media are known to adsorb silica. For example, metal oxide adsorbents such as activated alumina, goethite, or hematite can be used to remove dissolved silica in ionic form from solution.

[0019] Continue to refer Figure 1-3, feed lines 34A and 36A are operated to deliver feed from feed line 28 to respective silica adsorption units 34 and 36. Also note the effluent lines 34B and 36B extending from the silica adsorption units. In order to control the flow of feed through the silica adsorption units 34 and 36 during certain stages of the RO process, feed lines 34A and 36A include automatic valves 34C and 36C, which may be automatic regulating control valves or automatic on / off valves. In the exemplary process shown and described, it is contemplated that during the multi-stage process, only one silica adsorption unit will be online at any one time, while the other silica adsorption unit will be undergoing regeneration or will be in a standby ready mode after regeneration.

[0020] Figure 1-3 The method shown and described below can be used to treat water containing silica in which the silica concentration varies within a significant range. However, the method is particularly suitable for treating water with a moderate concentration of dissolved silica, i.e., a silica concentration below saturation. Typically, the silica concentration of the water to be treated is in the approximate range of 20-45 mg / L, but may be higher. In the first production stage of the method, the concentrate produced by the RO unit 12 is recycled and mixed with raw water to form a feed, and the feed is directed through a pipeline 30 and enters the RO unit 12 through a water buffer tank 32, and the RO unit 12 produces a permeate directed out of the pipeline 14 and the previously mentioned concentrate. In the first stage, valves 30A and 14A are opened. All other valves are closed. Therefore, in the first stage, the entire RO feed bypasses the silica adsorption unit 34 or 36. In the first stage, as the number of turns increases, the concentration of silica in the feed also increases. The term "turn" is used for semi-batch RO systems, such as the present invention, which do not operate in a continuous steady-state mode. A loop is one trip of the recirculated concentrate through the RO unit 12. The process is designed to continue in the first stage until the concentration of silica in the concentrate reaches a selected level. One of the principles of the process is to run the first stage until the number of loops produces a silica concentration in the concentrate that enables the silica adsorption unit 34 or 36 to operate at optimal or near optimal efficiency. Typically, this occurs when the concentrate becomes saturated or nearly saturated with silica. Depending on temperature, pH, water chemistry, and other variables, in one example, this may occur when the silica concentration in the concentrate reaches about 100 mg / L.

[0021] As will be appreciated by those skilled in the art, it is difficult to measure silica concentration online. However, it will also be appreciated by those skilled in the art that there are many indirect ways to determine or estimate the concentration of dissolved silica in the concentrate. For example, the triggering set point can be based on the conductivity of the concentrate because there is a relationship between silica concentration and conductivity. The conductivity of the concentrate can be continuously measured and monitored via an online conductivity instrument operably connected to a programmable logic controller (PLC). In addition, the RO system recovery can be used as a set point basis. Typically, there is a relationship or correlation between the system recovery and the silica concentration of the concentrate. By monitoring and measuring various flow rates in the RO system, the recovery can be determined via the PLC. In addition, the set point in the present method can be based on a timer setting. In the entire method described herein, one approach to triggering a phase change is to establish the phase change on the basis of all three approaches - concentrate conductivity, RO system recovery, timer setting - and to initiate the phase change when the first event or the first set point occurs.

[0022] Figure 1-3 One concept underlying the process shown in is to run the process in the first stage until the point where the silica concentration of the concentrate begins to approach saturation. Once the silica concentration in the feed approaches saturation or a reasonable degree of supersaturation allowed by the addition of antiscalants, it is no longer advisable or prudent to run the process in the first stage due to the risks associated with RO membrane fouling. At this point in the process, recoveries of approximately 75% or in the range of 60-75% are expected. See Figure 4 The letter "A" in the middle. However, the multipurpose method aims to achieve significantly higher recoveries, on the order of 90% or more. Figure 4 . It is at this point in the process that the process switches from the first production stage to the second production stage. As discussed below, in the second stage, one silica adsorption unit 34 or 36 is online and functions to remove silica from the RO feed while permeate production continues. Furthermore, once the silica adsorption unit 34 or 36 is online, the process is controlled throughout the second stage so that the silica concentration of the concentrate remains approximately constant and close to saturation, preferably just below saturation.

[0023] In one example, the entire RO feed is routed through one of the silica adsorption units 34 or 36. Valves 34C and 14A are opened, while all remaining valves are closed. Figure 2. In another example, only a portion of the RO feed is routed through one of the silica adsorption units, while another portion of the feed is directed through line 30 into and through the water buffer tank 32. In this case, valves 30A, 34C and 14A are open, while the remaining valves are closed. In either case, the adsorption medium in the silica adsorption unit is not fully loaded or exhausted, and thus the silica adsorption unit is effective in removing silica from the RO feed at the beginning of the second stage. The effectiveness of the adsorption medium is not necessarily associated with the duration of the second stage, or even with the three stages of the process. It is expected that the effectiveness of the adsorption medium may span multiple cycles of the multi-stage process, (a cycle is a complete cycle of the first, second and third stages of the process), perhaps several days, before regeneration is required. This may be of great significance because regeneration of the adsorption medium in the silica adsorption unit 34 or 36 may last significantly longer than the time required to go through one cycle of the multi-stage process.

[0024] As described above, in the second stage, the process is controlled so that the silica concentration of the concentrate remains approximately constant, and the parameters of the process are set to ensure that the silica concentration is controlled so that the RO membrane can operate effectively and withstand the silica concentration in the concentrate. This may mean that the feed directed through the silica adsorption unit and the feed directed through the buffer tank 32 are monitored and balanced to control the silica concentration of the concentrate leaving the RO unit 12 to be just below saturation. In the event that it is desired to divide the feed to the RO unit 12 between one silica adsorption unit 34 or 36 and the through line 30 (including the buffer tank 32), it should be understood that the silica adsorption unit will cause head loss. In order to address this problem and solve it, some device in the form of an adjustable valve or some mechanical resistance can be incorporated so that the feed flow rate through the pipeline 30 and the silica adsorption unit 34 or 36 can be controlled. For example, the valve 30A in the pipeline 30 can be a regulating flow control valve, which is controlled to prevent the feed from taking the path of least resistance, in this case, the path will be through the water buffer tank 32. Therefore, the control valve 30A is controlled so that the flow rate of the RO feed through the silica adsorbent tank 34 or 36 is not insufficient.

[0025] Preferably, sufficient flow monitoring instrumentation is implemented to ensure that the desired flow through each unit is maintained. In this case, the flow rate instrumentation will automatically control the positioning of the flow control valve 30A via a programmable logic controller to make the valve fully open, fully closed or partially open.

[0026] During the second stage, the recovery of the RO process continues to increase relative to the recovery achieved in the first stage. Figure 4However, ultimately the method will achieve a maximum recovery greater than 75%, and in many cases, about 90% or even higher. Figure 4 ' point in the process. When this occurs, the process switches from the second production stage to the third purification stage. The triggering set point event can be the same as discussed above with respect to the switch from the first production stage to the second production stage. Thus, set points based on system recovery, concentrate conductivity, timer settings, and high feed pressure can be used here, provided that when the first event or set point is reached, the actual triggering event occurs.

[0027] In the third purification stage, one of the silica adsorption units 34 or 36 can be online or offline. If offline, valves 18A and 30A are opened, and valves 14A, 34C and 36C are closed. If online, valve 34C or 36C is opened. Whether one of the silica adsorption units 34 or 36 is online or offline depends on the raw water silica concentration entering. That is, the chemical properties of the raw water will determine how much feed is directed through the silica adsorption unit 34 or 36, and how much RO feed will be directed through the pipeline 30 and the buffer tank 32. Again, this can be controlled by adjusting the control valve 30A in the pipeline 30. During the third purification stage, various purification sources or combinations of sources can be used to purify the concentrate from the RO system. These purification sources include influent water (raw water influent), permeate recirculation through pipeline 38, or added dilution water. At a certain moment, the third purification stage is completed. The completion of the third purification stage can be based on the purification volume, the conductivity of the concentrate, or the timer setting as a group, and when the first event or the first set point is met, a trigger event occurs.

[0028] Figure 4 is a graphical depiction of a number of process variables and how they may change during the first and second stages of the process described above. It shows the recovery of the process through the first and second stages, the silica saturation (expressed as a percentage) for the first two stages, and the concentration of total dissolved solids in the concentrate in both stages, with these variables plotted against the duration of the cycle. During the first stage, silica saturation reached almost 100%, while the recovery achieved was 75%. However, once the process entered the second stage, the recovery increased to about 90%, while silica saturation remained close to 100%.

[0029] Figure 1-3 The multi-stage RO process shown and discussed above is particularly suitable for applications where the silica concentration of the raw water is below saturation. However, there are applications where the silica concentration of the raw water or influent is supersaturated, saturated, or near saturation. As used herein, the term "near saturation" means that the silica concentration is less than 100% saturation but greater than 75% saturation. For example, Figure 5-7The methods shown and described below may be used to process concentrate from another RO system, in which case the RO concentrate to be processed is supersaturated, saturated or nearly saturated with silica.

[0030] Figure 5 The first production stage of an RO process for treating an influent that is supersaturated, saturated or nearly saturated with silica is schematically shown. In this case, the silica adsorbent tank 34 is online. Therefore, valves 34C and 14A are open. Valves 36C and 18A are closed. Due to the high silica concentration in the influent, it is expected that during the first production stage, all or at least most of the RO feed will be directed through the silica adsorption unit 34. In the case where all RO feed is directed through the silica adsorption unit 34, the regulating control valve 30A is closed. In this first production stage, the process is controlled so that the total silica concentration in the RO system remains approximately constant and is at a silica concentration level that enables the silica adsorption unit 34 to operate at optimal efficiency. Therefore, as long as the silica adsorption unit 34 operates at optimal efficiency, most of the RO feed is directed through the silica adsorption unit to reduce the silica concentration of the RO feed before it reaches the RO unit 12. However, due to the specific chemical properties of the influent, it may be desirable to direct some of the RO feed through line 30 and directly into the RO unit 12. In this case, the RO feed can be divided into a first RO feed stream directed through the silica adsorption unit 34 and a second RO feed stream directed through the buffer tank 32. In this case, the regulating valve 30A is opened and controlled to balance the flow of the RO feed through the buffer tank 32 and the silica adsorption unit 34 so that the silica adsorption unit 34 is generally operated within the optimal efficiency range. Throughout the first production stage, the regulating valve 30A is controlled to maintain this balanced approach, that is, to control the overall silica concentration to be approximately constant while maintaining the efficiency of the silica adsorption unit 34 within the optimal range.

[0031] In some cases, the set point for ending the first production phase can be based on a determined recovery of the RO system. Also in some cases, the first set point can be based on a concentrate conductivity measurement or a timer setting. As discussed previously, all three of these possibilities can be grouped and trigger a phase transition at the first occurrence of any of the three. In this first production phase, one can expect a system recovery of 50-75%. To achieve a higher recovery of about 90-95%, the process is switched from the first production phase to the second production phase.

[0032] Figure 6 The second production stage is schematically shown. Here, the silica adsorption unit 34 is off-line. Therefore, valves 34C and 18A are closed, while the regulating valve 30A and the permeate flow control valve 14A are opened. Figure 8 As shown, during the second production phase, the concentration of silica in the concentrate increased over time, and the system recovery also increased. Figure 8 A second set point or threshold is employed for the purpose of terminating the second production phase. The second set point may be based on the silica concentration or conductivity of the concentrate, system recovery, high feed pressure, or a timer setting, or a combination of any of these. Typically, the process is designed to achieve a recovery of 90% or more, and when this occurs, it is expected that the silica concentration of the concentrate may be as high as, for example, 400% saturation, or possibly higher. See Figure 8 Once this set point is reached, the process will switch from the second production stage to the third concentrate purification stage.

[0033] Figure 7 The third stage of the process, i.e., the concentrate purification stage, is schematically shown. In this stage, the silica adsorption unit 34 can be online or offline. If offline, the regulating flow control valve 30A is opened so that the purge flows through the valve and through the water buffer tank 32 to the RO unit 12. If online, the regulating control valve 30A can be closed or adjusted to appropriately control the ratio of the purge passing through the silica adsorbent tank 34 and the water buffer tank 32. In all cases during the third stage, valve 14A is closed and valve 18A is open.

[0034] At the beginning of the concentrate purification stage, the concentrate in the system has a high silica concentration (up to 400% saturation). To purify the concentrate, a variety of purification sources can be used. First, the permeate produced by the RO unit 12 can be recycled to the front of the process via line 38, where the permeate works to purify the concentrate in the system. In addition, dilution water can be fed into the system at a point just upstream of the RO booster pump 26. See Figure 7 . Finally, feed water from other sources may be introduced into line 22 for the purpose of purifying or assisting in purifying the concentrate. For example, the potential dilution water may be feed water or pre-treated feed water from the main RO system from which the present method processes the concentrate. One or more of these sources may be used. It is advantageous to use permeate or dilution water to purify the concentrate from the system. This causes the silica concentration in the concentrate to drop to below saturation. After 2-3 cycles, this has a flushing and cleaning effect on the RO system so that the induction time can be utilized in subsequent cycles. Whether the silica adsorption unit 34 is online or offline depends on the silica concentration of the incoming feed water. That is, the feed water chemistry will determine the proportion of feed water that is directed through the silica adsorption unit 34 relative to the feed water that is directed through the water buffer tank 32.

[0035] Figure 5-7One advantage of the process shown is that it enables RO recoveries of about 90% or more even when the silica concentration of the second and third stage concentrates approaches 400% saturation. Figure 8 . Note that in the first stage, the silica concentration of the concentrate is maintained at about 100% saturation. This typically produces a 75% recovery. However, after switching from the first stage to the second production stage ( Figure 6 ), over time, the silica concentration in the concentrate increases and may approach 400% saturation. At the same time, the system recovery rate increases from 75% to 90%. See Figure 8 . For conventional RO processes, the expected recovery cannot exceed 75% when the RO concentrate is supersaturated or saturated with silica, as is the case in the second and third stages of the above process. An obvious problem in RO systems and processes is the risk of RO membrane scaling. The process mitigates RO membrane scaling. This is because the silica concentration of the purifier (whether RO permeate, dilution water or other feed water) is unsaturated, which enables the process to destroy chemicals that tend to cause scaling and take advantage of the silica induction time. That is, it takes a certain amount of time for supersaturated silica to precipitate and scale the RO membrane, and if the silica concentration is diluted to an unsaturated concentration before the induction time, the silica will not scale the RO membrane.

[0036] Of course, without departing from the scope and essential features of the present invention, the present invention may be implemented in other specific ways different from those described herein. Therefore, the present embodiment disclosed herein should be interpreted as illustrative in all aspects, rather than restrictive, and all changes within the meaning and equivalent scope of the appended claims should be included therein.

Claims

1. A multi-stage method for treating water containing silica in a reverse osmosis (RO) system, the system comprising a silica adsorption unit and an RO unit producing a permeate and a concentrate, the method comprising: In the first production phase: mixing concentrate from the RO unit with water to be treated to form an RO feed, and directing the RO feed through the RO unit to produce a permeate; continuing to direct the RO feed through the RO unit until the silica concentration in the concentrate reaches a set point, at which time the process is switched from the first production stage to the second production stage; In the second production phase: reducing the concentration of silica in the concentrate by directing at least a portion of the RO feed through a silica adsorption unit containing a media that adsorbs silica from the RO feed as the RO feed passes through the silica adsorption unit; directing the silica-depleted RO feed through the RO unit after passing the RO feed through the silica adsorption unit and continuing to produce permeate; continuing the second production stage of the process until a production threshold set point is reached, at which time the process is switched from the second production stage to a third concentrate purification stage; and In the third concentrate purification stage: Purify concentrate from RO systems.

2. The process according to claim 1, wherein during the second production stage, a portion of the RO feed bypasses the silica adsorption unit and is combined upstream of the RO unit with a portion of the RO feed leaving the silica adsorption unit.

3. The method of claim 1 , wherein during the second production stage, the silica concentration of the concentrate is maintained substantially constant and close to but below saturation in order to induce an efficient silica adsorption process in the silica adsorption unit.

4. The method according to claim 1, wherein during the third purification stage at least a portion of the water to be treated is directed through a silica adsorption unit before reaching the RO unit.

5. The method of claim 1, wherein during the third purification stage, an RO unit produces a permeate, and at least a portion of the permeate produced by the RO unit is recycled to a point upstream of the RO unit.

6. The method of claim 1, wherein by reducing the silica concentration of the RO feed in the second production stage, the overall recovery of the RO system is increased.

7. The process of claim 1 , wherein during the second production stage, the RO feed is divided into a first and a second portion, wherein the first portion of the RO feed is directed through a silica adsorption unit and the second portion of the RO feed is directed through a bypass line that bypasses the silica adsorption unit; and wherein the first and second portions of the RO feed are combined upstream of the RO unit.

8. The method of claim 1 , wherein the method is conducted without removing the silica by chemical precipitation or other means, or without increasing the solubility of the silica in the concentrate by raising the pH of the concentrate to 9.5 or higher.

9. The method of claim 1, wherein the RO system comprises first and second silica adsorption units, wherein the first silica adsorption unit is in operation and the second silica adsorption unit is offline and undergoing media regeneration or in a ready standby state.

10. The method of claim 1, wherein the third concentrate purification stage comprises purifying concentrate from the RO system by directing water to be treated, dilution water, or permeate recycle, or a combination thereof, through the RO system.

11. The method of claim 1 , wherein the set point is based on system recovery rate, concentrate conductivity, a timer setting, or feed water pressure.

12. A multi-stage method for treating water supersaturated, saturated or nearly saturated with silica in an RO system comprising a silica adsorption unit and an RO unit producing a permeate and a concentrate, the method comprising: In the first production phase: mixing the concentrate from the RO unit with water supersaturated, saturated or nearly saturated with silica to form the RO feed; reducing the silica concentration in the RO feed prior to reaching the RO unit by directing at least a portion of the RO feed through a silica adsorption unit located upstream of the RO unit, the silica adsorption unit comprising a media that adsorbs silica from the RO feed as the RO feed passes through the silica adsorption unit; continuing the first production phase until a first set point is reached; switching the process from said first production phase to a second production phase once a first set point is reached; in a second production stage: bypassing the silica adsorption unit with a majority of the RO feed and directing the majority of the RO feed through the RO unit to produce a permeate and a concentrate; continuing to direct a majority of the RO feed through the RO unit and causing the concentrate produced by the RO unit to become supersaturated with silica; switching the method from the second production stage to the concentrate purification stage when a second set point is reached; During the concentrate purification stage: Purify supersaturated concentrate from RO systems.

13. The method of claim 12, wherein the concentrate purification stage comprises purifying supersaturated concentrate from the RO system by directing water to be treated, dilution water, or permeate recycle, or a combination thereof, through the RO system.

14. The method of claim 12, wherein in the first production stage, the silica concentration of the concentrate is maintained close to saturation.

15. The method of claim 12, wherein the silica concentration of the concentrate is maintained at about 80-150% saturation during the first production stage.

16. The method of claim 12, wherein the first and second set points are based on recovery rate of the RO system, conductivity of the concentrate, a timer setting, or feed water pressure.

17. The method of claim 12, wherein during the concentrate purification stage, all or substantially all of the RO feed bypasses the silica adsorption unit and is directed directly to the RO unit.

18. The method of claim 12, wherein during the concentrate purification stage, the RO feed is split into first and second portions, the first portion being directed through the silica adsorption unit, and the second portion bypassing the silica adsorption unit and being combined with the effluent from the silica adsorption unit before being directed into the RO unit.

19. The method of claim 12, wherein during the concentrate purification stage, the RO unit produces a permeate, and at least a portion of the permeate produced by the RO unit is recycled to a point upstream of the RO unit.

20. The method of claim 12, wherein the method is carried out without removing the silica by chemical precipitation or other means, or without increasing the solubility of the silica in the concentrate by raising the pH of the concentrate to 9.5 or higher.

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