Our Water Purification Blog

Basic Design of High Purity Water Systems

Process and Water High Purity Water Systems contain three core groups of equipment. These groups of equipment are typically categorized as pretreatment, primary purification and distribution systems.

Pretreatment System

The three major water treatment components of standard pretreatment systems used in Process and Water High Purity Water Systems are sediment filters, activated carbon filters and water softeners.

Sediment Filters

Sediment filters remove dirt, suspended solids and other particulates and generally lowers the turbidity of the feedwater supplied to the high purity water system.

Sediment filters in most small high purity water systems are standard cartridge filter housings with 5-micron cartridge filters. Most medium to large systems utilize multi-media backwashing filters.

Activated Carbon Filters

Activated carbon filters remove chlorine and reduce organic contaminants. The removal of chlorine protects the reverse osmosis (RO) membranes and ion exchange (IX) resins downstream in the high purity water system. The reduction of organic contaminants contributes to lower total organic carbon (TOC) levels in the water produced by high purity water systems.

The activated carbon filters in most small high purity water systems are standard cartridge filter housings with granular activated carbon (GAC) cartridge filters or carbon block cartridge filters. Most medium to large systems utilize exchange tanks filled with activated carbon or backwashing filters filled with activated carbon.

Water Softeners

Water softeners remove minerals and other scale forming ions along with dissolved metals like iron and manganese. The removal of minerals and metals prevents fouling and scale formation on the RO membranes, resulting in maximum RO membrane life.

Water softeners of appropriate size are generally used in high purity water systems. As an alternative, anti-scalant chemicals can be fed into the feedwater using metering pumps. These chemicals keep the potential scale forming ions in solution, limiting scale formation and build-up on the RO membranes.

Primary Purification System

Process and Water High Purity Water Systems typically use reverse osmosis water systems for primary purification. A carbon trap filter precedes the RO membranes.

RO System

Reverse osmosis water systems consist of a high-pressure pump and motor, RO housings and RO membranes. The pump and motor provide the pressure necessary for the natural osmosis process to be reversed. The RO housings hold the RO membranes and provides concentrate and permeate flow paths or streams. The RO membrane elements provide the semi-permeable membrane that allows the reverse osmosis process to happen. The pressurized feedwater is forced through or permeates the semi-permeable membrane leaving the contaminants contained in the feedwater behind as concentrate in the waste stream. In addition to sending the contaminants to drain, the concentrate or waste stream provides a constant flow across the membrane surface minimizing the build-up of contaminants on the RO membrane surface.

Conductivity Probes are standard equipment on all Process and Water Reverse Osmosis Water Systems. Many system manufacturers consider conductivity probes optional equipment.

The carbon trap filter is a preventive measure used to remove any chlorine that is not removed by the primary carbon filter in the pretreatment system and to remove any resin or media that may inadvertently pass from the multi-media filter, carbon filter or water softener.

Distribution System

Distribution systems used in Process and Water High Purity Water Systems generally include high purity, cone bottom atmospheric storage tanks with 0.2-micron vent filters and pressure transducer level controls, re-pressurization pumps, mixed-bed deionization (DI) vessels with cation and anion IX resin, ultraviolet light (UV) systems and post or final polishing filter housings with absolute rated 0.2-micron cartridge filters.

Atmospheric Storage Tank

The atmospheric storage tanks are used in high purity water systems to collect and store the RO permeate or product water for future use.

The 0.2-micron vent filter prevents contaminants from entering the storage tank when water is removed from the tank and air replaces the water. The level controls turn the RO water system on and off based on the amount of water contained in the storage tank.

Mixed-Bed DI Vessels

Mixed-bed DI vessels are used in high purity water systems to further polish the RO permeate, reducing the total dissolved solid (TDS) levels.

The cation resin is “pre-charged” with positively charged hydrogen ions (H⁺) and exchanges the hydrogen ions for other positively charged ions (eg. Na⁺, K⁺, etc.) in the RO permeate and the anion resin is “pre-charged” with negatively charged hydroxide ions (OH⁻) and exchanges the hydroxide ions for other negatively charged ions (eg. Cl⁻, SO4⁻, etc.) in the RO permeate. The hydrogen ions and hydroxide ions combine to form pure DI water (H⁺+OH⁻=H2O).

The cation resins are regenerated with sulfuric acid or hydrochloric acid and the anion resins are regenerated with sodium hydroxide.

UV System

Ultraviolet light systems are used in high purity water systems to inactivate bacteria and other micro-organisms, preventing them from reproducing.

This reduces the bacteria load in the RO permeate and minimizes bio-film build-up in the storage tank and system piping.

0.2-Micron Polishing Filter

Final polishing filters are used in high purity water systems to remove any sub-micron contaminants still in the DI water, along with any particulate matter picked up by unused DI water returned to the storage tank after flowing through the distribution piping.

Additional or Optional Equipment Used in High Purity Water Systems

Process and Water High Purity Water Systems may contain additional equipment to meet higher water quality requirements or optional equipment requested or preferred by the end-user.

Ultrafiltration Systems

Ultrafiltration systems may be used in high purity water systems in place of traditional pretreatment systems when better pretreatment is desired, higher water recoveries are required or when the system is supplied with challenging feedwater.

These systems can also be used as the primary purification system, replacing the RO and DI components, when lower water quality is acceptable and higher water recoveries are required or desired.

Electro-Deionization (EDI) Systems

EDI systems may be used to replace mixed-bed DI vessels on purified water systems or in conjunction with mixed-bed DI vessels on ultrapure water (UPW) systems.

These systems can be used to reduce operational costs, reduce labor costs and save space.

Ozone Systems

Ozone systems are used on sanitary systems where bacteria levels must be kept to a minimum.

TOC Reducing UV Systems

TOC Reducing UV Systems are used as ozone destruct units in sanitary systems, to further reduce bacteria levels and prevent bio-film build-up for longer durations in non-sanitary systems or where very low TOC levels are required.

Heat Exchangers

Heat exchangers lower operational costs in sanitary systems and high-temperature systems.

Process and Water offers high quality control panels and instrumentation in the system packages.

Process and Water High Purity Water Systems are available in a variety of piping materials to meet the requirements of most high purity water specifications. They are skid-mounted and come complete with interconnecting piping for ease of installation, while reducing installation time and costs

Posted in Water Treatment

Recovery of an Industrial Reverse Osmosis System

When optimizing the recovery of an industrial reverse osmosis system, it is important to be aware of the mineral and salt ions dissolved in the feedwater, mainly those that can lead to membrane scaling. Calcium and magnesium, which are both contributors to hardness, are perhaps the most common of these ions. As purified water system efficiencies are increased to maximize water recovery and minimize wastewater discharge, salt concentrations rise within the RO reject stream (concentrate) causing scale to deposit on the membrane surface.

An effective component of RO membrane maintenance is the use of membrane chemicals to inhibit membrane fouling and scaling. Membrane chemical use, along with periodic membrane cleaning, and preservation of the membranes during lengthy periods of nonuse, can dramatically increase their life. A strong membrane maintenance program is a great way to reduce the cost of any membrane based water treatment system.

Process and Water offers a broad range of chemicals, formulated to be compatible with all types and brands of reverse osmosis and nanofiltration membranes. For example, XX-100 Antiscalant is effective in controlling inorganic scaling over a large concentration range. It is injected into the feedwater to inhibit these scalants from precipitating and depositing on the membranes. That allows for higher recovery than could be achieved without using an antiscalant. Process and Water XX-100 antiscalant is available in a concentrated version, as well, XX-100C. This version is 10 times more concentrated than the standard XX-100 antiscalent. Process and Water XX-100C is often preferred when storage space is limited or to minimize freight costs.

For challenging feedwaters containing high levels of metal oxides, such as; silica, barium, strontium and , we recommend Process and Water XX-200 Antiscalant. Process and Water XX-250 Antifoulant is ideal for feedwaters with high potential for fouling by fine particulates, silt, colloids, tannins and organic contaminents.

Membrane cleaning can improve membrane performance. Process and Water XXC-10 Membrane Cleaner removes mineral scale, and metal oxides such as iron. AXEON C-20 Membrane Cleaner removes organic material and biological debris.

When a reverse osmosis system is not operating for an extended period of time or placed into storage, it is very important to preserve the membranes; otherwise the membranes become susceptible to microbiological growth or freezing. AXEON M-100 Membrane Preservative is a safe alternative to the use of chemicals such as formaldehyde or sodium bisulfite. AXEON M-100 is compatible with all membrane types and rinses easily from membranes prior to use.

Posted in Water Treatment

Chemical Use for Efficient & Cost Effective Operation of Industrial Water Treatment Systems

When optimizing the water recovery of an industrial reverse osmosis system, it is important to be aware of the mineral and salt ions dissolved in the feedwater, mainly those that can lead to membrane scaling like calcium, barium and strontium. As purified water system efficiencies are increased to maximize water recovery and minimize wastewater discharge, salt concentrations rise within the RO reject stream (concentrate) causing scale to deposit on the RO membrane surface.

An effective component of RO membrane maintenance is the use of membrane chemicals to inhibit membrane fouling and scaling. Membrane chemical use, along with periodic membrane cleaning, and preservation of the membranes, during long periods of inactivity, can dramatically increase their life. A strong membrane maintenance program is a great way to reduce the operational cost of any purified water system.

Process and Water offers a broad range of chemicals, formulated to be compatible with all types and brands of RO membranes and nanofiltration membranes. For example, XX-100 Antiscalant is effective in controlling inorganic scaling over a large concentration range. It is injected into the feedwater to inhibit these scalants from precipitating and depositing on the membranes. That allows deionization systems and other high purity water systems to operate at higher water recovery rates than could be achieved without using an antiscalant. Process and Water XX-100 antiscalant is available in a concentrated version, as well, XX-100C. This version is 10 times more concentrated than the standard XX-100 antiscalent. Process and Water XX-100C is often preferred when storage space is limited or to minimize freight costs.

For industrial water treatment systems operating in challenging feedwaters, containing high levels of metal oxides, silica, calcium, barium and/or strontium, we recommend Process and Water XX-200 Antiscalant. Process and Water XX-250 Antifoulant is ideal for feedwaters with high potential for fouling by fine particulates, silt, colloids, tannins and organic contaminants.

Membrane cleaning can improve the performance of industrial reverse osmosis systems. Process and Water XXC-10 Membrane Cleaner removes mineral scale, and metal oxides like iron and manganese. Process and Water XXC-20 Membrane Cleaner removes organic matter and other biological foulants.

If a commercial or industrial reverse osmosis system is out of operation for more than a week or two or it is placed into long-term storage, RO membrane preservation is an important consideration. Otherwise permanent damage due to freezing or microbiological growth will result in early RO membrane replacement. Process and Water XXM-100 Membrane Preservative is a safe alternative to chemicals such as sodium bisulfite or formaldehyde. Process and Water XXM-100 is designed for use with all membrane types and minimizes rinse time when restarting purified water systems.

Posted in Water Treatment

Benefits Of Weak Base Anion Resin in Industrial Wastewater recycling

Ion Exchange technology can be used in industrial wastewater treatment plants to exchange one ion for another for the purpose of demineralization of the incoming process rinse waters from a plating, anodizing or precision manufacturing process. There are basically two types of ion exchange industrial rinse water recycle systems, one which is uses strong base anion resins and another that uses weak base anion exchange resins. While weak base anion resins do not remove as much silica or C02 as a strong base (used in city water deionization systems) they have great capacity and are a very good neutralizer of strong acid rinses such as nitric, hydrochloric and sulfuric that are present in many industrial metal finishing and anodizing process plating lines.

 

When ion exchange is used in a dual separate bed system for recycling rinse water, many clients are concerned with frequency and volume of ion exchange resin regeneration due to the cost of chemicals and treatment of the waste water. The two major benefits with a weak base anion resin is it use less chemical (sodium hydroxide) for regeneration and generates less waste water that will need to be treated, evaporated or hauled away. In addition to this the water quality although does not make pure DI water still returns a high quality of water that can be use in most process rinse environments. This in turn reduces the capital cost for the equipment purchase and the ongoing cost to operate such a specialized state of the art recycling treatment process.

Process and Water specialized in designing, fabricating and commissioning state of the art industrial wastewater recycling systems. Each of our high quality products are made in our state of the art U.S.A. facility in East Bridgewater, MA, by our experienced engineering & production team.

Posted in Water Treatment

The benefits of treating Industrial Waster using a Slant Plate Clarifier.

Process and Water Industrial Wastewater Slant Plate Systems and Clarifiers are designed to provide low cost, yet extremely efficient solids removal from a wide range of waste and process liquids.

Slant Plate Clarifier - Process and Water - Eastbridgewater MA
The key advantage of Industrial Wastewater slant plate clarifiers over conventional types of clarifiers is the use of a series of inclined plates. These plates are able to provide a large settling area for particles and allow for a more compact footprint, greatly reducing the floor space needed for accomplishing the same result.

In fact, this Industrial Wastewater inclined plate design allows the settling area, or surface area, to be as much as 10 times more than the actual floor space occupied by the clarifier. This significant reduction of the required floor space is achieved by reducing separation between plates to just two inches, and stacking the settling surfaces at an angle.

 

The advantage to the slant plate design is getting the maximum square footage out of your production floor space, which translates into greater efficiencies and cost savings for your operation. Because the slant plate clarifier uses inclined plates, it is often referred to as an “inclined plate clarifier.” A slant plate clarifier is also referred to as an “SPC.”

Slant Plate Clarifier System Design - Process and Water - Eastbridgewater MA

As part of our portfolio of Industrial Wastewater product we do offer full tunkey treatment packages that include pH and ORP instrumentation and chemical injection to aid in precipitating heavy metals from waste water.

Our Industrial Wastewater Slant Plate Clarifier series is designed to be tough and dependable, while at the same time being sensitive to tight budgets and maximizing production space. We have many models available, each with different flow capacities, to cover a wide range of design flow needs. Our gravity plate Clarifier models and industrial wastewater treatment systems range from 5 to 400 GPM. Each of our high quality products are made in our state of the art U.S.A. facility in East Bridgewater, MA, by our experienced engineering & production team.

Posted in Water Treatment

Process and Water – Case History 1069

20 GPM Copper and Ferric Chloride

Etching, Water Recycling Technology
Through Ion exchange

Introduction

The cost and maintenance associated with recycling metal bearing waste streams has decreased in recent years. This case history will press upon the technical and financial aspects of recycling metal bearing rinse waters. It is Process and Water’s belief, that by understanding the “theory” and environmental impact of water recycling, more companies will follow this path into the new millennium.

Ion Exchange Treatment

The water recycling system Process and Water designed recycles 100 % of all rinses associated with the etching process. All copper and ferric chloride rinses are double counter flow with a retainer to assist in the reduction of etching solution drag out. The inorganic (copper and ferric chloride rinses) constituents cascade to the sump tank where it is then pumped from the etchers directly to an ion exchange feed tank. In an etching process the use of non-volatile organics are required. These organic components coat the etched substrate and give it a protective layer. As with all organics present in the use of ion exchange, pretreating with carbon is imperative. This organic rinse water from the stripper/developer and benzotriazole are fed to two 4.0 ft3 FRP columns of organo clay and carbon at 8 gallons per minute. At this flow rate the organic absorption unit will run at 2 gallons per minute, per cubic foot. This is a sufficient amount of media and volumetric flow rate to efficiently absorb all organics present. The organic treatment phase can be backwashed with city water. Having the ability to backwash insures that the columns will not saturate prematurely. The previously organic rinse water is then fed to the ion exchange feed tank.

The etching rinse water is now ready for treatment. The water will be pumped using a dual set of centrifugal pumps with a double face corrosion resistant seal. A pressure transducer controls the feed tanks. This pressure transducer is wired back to the control system and converts pressure into feet (each psi = 2.31 feet). This will in turn control the function of the feed pumps. If the feed tank should drop to a low-level point, an automatic actuated ball valve opens to allow the passage of make up water. The city water is treated through a standard deionization (SDI) make up system.
The water is fed through a 5 micron pre-filter for sedimentation removal. The ion exchange unit is designed with two dual bed exchangers. Each cation exchanger houses 14 ft3 of a polystyrene cross-linked strong acid cation resin. The basic function of the strong acid cation resin is to exchange hydrogen for all cations present in the feed stream. Each of the anion exchangers contains 21 ft3 of a macroporous weekly basic anion resin. As with most metal finishers the need for 5 to 8 meg water is not required for recycling. The weak basic anion resin effectively removes acids such as chlorides, sulfates, and nitrates, but will not exchange hydroxide for all present anions. The capacity is a tremendous benefit of the week basic anion. Standard strong basic anions can hold 18,000 kilograins per ft3. The weekly basic anion resin has a capacity of 35,000 kilograins per ft3. With almost twice the holding capacity, the resin we selected cut down the frequency and volume associated with a regeneration without sacrificing quality. This system was designed for 20 gpm but currently is only running at 15 gpm.

There is 14 ft3 of strongly acidic cation resin in each of the cation vessels. At this flow rate, the exchange process of hydrogen for positively charged cations(+) equals (1.07) gallons per minute, per cubic foot. As with most acidic waste solutions there is a greater amount of negatively charged anions(-) than positively charged cations(+). For this reason, a greater volume of weekly basic anion resin is present in each anion vessel. The anion resin will exchange OH(-) for negatively charged anions(-) present in the waste stream at (0.71) gallons per minute, per cubic foot. At a feed TDS (total dissolved solids) of approximately 300 mg/l (600 Mhos) this efficiently exchanges all dissolved solids to an average of 25 mg/l (50 Mhos).

The “treated” water is fed through a post macroporous filter for possible resin leakage. The now clean water is continuously recirculated through an ultraviolet disinfection unit for bacteria control. Stagnant water can promote the growth of bacteria very quickly; continuously recirculating the water through the UV lamp decreases the growth probability. The treated water is pumped back to the etching process through a pressurized pumping system, 15 gpm, at 60 psi. A pressure transducer (mentioned above) monitors the transfer tank and pump from high and low level alarms.
Ion Exchange Chemical Regeneration
Ion exchange resins are widely used due to their ability to be chemically regenerated. Cation exchange resins are regenerated with a positively charged acid (H(+)). The two most commonly used acids are sulfuric (H2SO4), and hydrochloric (HCl). HCl was selected over H2SO4 for its ability to regenerate the resin without causing sulfate precipitates on the cation resin bed. Both the cation and anion resin beds are regenerated with deionized water to insure proper chemical to contaminant exchange. Before regeneration it is important that the column being regenerated is backwashed. This backwash will “fluff” the resin bed and discard any colloidal matter present. A sample port is used to observe the backwash water. All of the water generated from the backwash is recycled to a holding tank where it can be used for make up water or additional water for the decationized dual bed rinse explained later. The backwash water is passed through a macroporous filter to remove any sediment present. When the water becomes relatively clear the backwash is complete. The cation regeneration is ready to be initiated, and volumes are as follows:
14 ft3 of Cation resin with Hydrochloric Acid treatment: 10% maximum @ 10 lbs. ft3 = 45 gallons with 32% Hydrochloric Acid. 4.0 GPM of water to 1.5 gallons of 32% HCL=5.5 GPM total for 30 minutes.

Through automated controls in our Allen Bradley PLC, we are able to recover a large percentage of the regenerant for reuse. During the coarse of the cation regeneration and slow rinse a volume of 125 gallons is recovered from the 325 generated. The regeneration is followed by a deionized slow rinse. This slow rinse allows for further exchange to take place and rinses the free acid off the resin bead. After the anion regeneration phase a dual bed fast rinse is performed. A fast rinse will not have to be completed during the cation regeneration.
Anion resins are regenerated with a negatively charged hydroxide chemical (OH(-)). With the use of sodium hydroxide (NaOH) we are able to exchange negatively charged anions off the resin for (OH(-)). As with the cation regeneration, the anion resin bed must be back washed before sodium hydroxide regeneration. All of the water generated from the backwash is recycled to a holding tank where it can be used for make up water or additional water for the decationized dual bed rinse explained later. The backwash water is passed through a macroporous filter remove any sediment present. The anion regeneration volumes are as follows:
21 ft3 of Anion resin with sodium hydroxide treatment: 6% @ 10 lbs. per cu ft. = 35 gallons with 50% sodium hydroxide. 7.3 GPM of water to .67 of 50% NaOH=7.97 GPM total for 30 minutes.

Through automated controls in our Allen Bradley PLC, we are able to recover a large percentage of the regenerant for reuse. During the coarse of the anion regeneration and slow rinse a volume of 150 gallons is recovered from the 450 generated. The regeneration is followed by a deionized slow rinse. This slow rinse allows for further exchange to take place and also rinses the free hydroxide off the resin bead.
After the dual bed deionizer is regenerated a decationized fast rinse is performed. The water that was recovered from the cation and anion regeneration will be used in the decationized fast rinse. The water is fed through a centrifugal pump to the dual bed exchanger where it is recirculated for 45 minutes. A TDS meter inline monitors the incoming total dissolved solids. If the feed TDS becomes greater than 1500 mg/l an alarm will sound and the decationized rinse water is diverted to the regeneration waste holding tank. Deionized water is fed to the recirculation tank if a low-level point is reached. A level pressure transducer controls the function of the make up water valve. When complete the dual bed exchanger regenerated is ready for operation.

Regeneration wastewater

During the regeneration, a total of 800 gallons was generated, with 35 % recycled for the decationized rinse. This recycling process will reduce the historical volumes of regeneration with a “final fast rinse” by 500 gallons. The now contaminated 800 gallons from regeneration must be treated. There is much free HCl in the regenerant wastewater. The pH of this waste solution is approximately (1) to (2) pH units. The pH must be adjusted to between (7) and (9), in order to successfully treat the solution. The wastewater will be treated through a closed atmospheric evaporator. The closed system will concentrate the solution and the distillate will be condensed through a heat exchanger. This distillate can be used for future make up water. There are level controls internally that adjust the solution being fed to the unit. All components are controlled by an Allen Bradley PLC with modem capabilities. The closed evaporator reduces the volume of regenerant wastewater by 90%. Furthermore, there was no air discharge permitting required the customer is RCRA (Resource Conservation and Recovery Act) exempt. Due to this exemption, the customer forgoes the environmental and financial obligation of filing for an air discharge permit.

Ion Exchange System Controls

The ion exchange dual bed deionizer is controlled with an Allen Bradley SLC 500 controller. A DTAM digital display is present for visual inspection of the level percentage in the primary system tanks. Level requirements can be changed with the touch pad of the DTAM display. During the regeneration the DTAM display can be used to inspect stages and make alterations if needed. An influent/effluent total dissolved solids meter monitors the feed and discharge water quality. The meter is looped to a dual pen chart recorder, where a permanent record is kept of the influent/effluent TDS. A dual electrode pH meter is also present in the influent and effluent of the ion exchange unit. As mentioned previously, a percent chemical cell is part of the regeneration sequences. This meter monitors % HCl and % NaOH during the regeneration process and allows the operator to better observe actual chemical dosage without using a hydrometer or checking the chemical feed reservoirs. The newly designed control system was a key component to the operator friendly environment the customer required.

Conclusion

Process and Water closed the loop of a company that lacked the ability to discharge to a sanitary POTW sewer. In addition they understood the importance of recycling their wastewater. The initial capital cost was the only liability. They saw the financial and environmental payback of water recycling. More companies’ upper management must become more enlightened, and not blindfolded only by the capital involved in water recycling. There is more to look at than financial pay back. We all share a responsibility in achieving environmental stability.

Posted in Water Treatment

Lower Costs in Reverse Osmosis Based Wastewater Treatment Systems

Innovations in Microfiltration Unlock Higher Performance and

Lower Costs in RO-based Wastewater Recycling Systems

 

By Tom Belmont, CEO of Process and Water

 

Introduction

As the pressure on fresh water supplies continues to grow worldwide, industries and municipalities are experiencing the negative effects.  These include more frequent water supply shortages, limits on the capacity of municipal wastewater treatment plants, and escalating costs for water and effluent treatment.  One of the most promising strategies for offsetting some of these impacts involves the use of advanced membrane technologies.

This paper discusses some of the technical aspects of these advances, and how membrane technologies are increasing the efficiency and reliability of industrial wastewater recycle systems while also lowering their operating costs.

Wastewater Recycle Challenges

Among the various recycling alternatives, much of membrane development over the past several years has centered on reverse osmosis (RO), which functions to separate most, if not all, substances in wastewater.  RO is a more cost-effective technique for handling wastewater with high total dissolved solids (TDS) than other treatment alternatives.  But one issue has caused persistent operational issues for RO systems.  That issue is membrane fouling.

Extensive research has been done to determine the factors that affect membrane fouling. These factors include ionic composition, salt concentration, and the presence of organic components, and suspended solids and colloids.  Various applications have been studied for the handling of ground water, surface water and sea water.  But very little has been done to examine membrane fouling with the complex and constantly changing chemical mixtures in industrial wastewater flows.

Despite their critical capability to produce re-usable water, many large RO-based recycling installations have experienced difficult operational problems in the field. The most common problems include unreliable filtration production, decrease in salt rejection, the need for frequent membrane cleaning, and premature membrane failure. Each of these issues contributes to higher operating costs and lower long-term effectiveness. In some cases, the problems were significant enough to cause shutdowns at water recycle plants.

The primary cause of this performance degradation and failure is that RO membranes generally have low tolerances for a broad range of incompatible components in water. These substances, if not removed prior to the RO phase of the process, will cause scaling, fouling or permanent degradation of the RO membrane. Recognizing this problem, and to avoid its ramifications, suppliers of reverse osmosis membranes suppliers have established feed water quality criteria for RO systems. While these criteria are helpful, they do not prevent incompatible elements from finding their way into feed water flows.  When they do, and feed water quality falls out of specified ranges, the industrial customer winds up owning the problem.

The ever-increasing demand for higher-quality, lower-cost industrial wastewater recycle options has paved the way for innovations with RO.  One area in which newer membrane technologies are driving significant performance improvements and cost reduction is microfiltration (MF) pre-treatment for RO systems.  Because of its versatility, robust nature and high filtrate quality, tubular microfiltration is well on the way to replacing the more traditional equipment used to remove unacceptable substances in the RO pretreatment process.  These include gravity clarifiers, media filters, lime softeners and ion exchangers.

One key characteristic of MF is that many agents that are incompatible for RO can be converted into microfiltration-compatible material and efficiently removed prior to the RO phase.  MF and RO can work effectively in tandem, but only if the system is designed to properly support the necessary chemical reactions.

Chemical Reaction Development

Based on the types and quantities of fouling substances identified in the wastewater, a chemical treatment process is developed to counteract each of the fouling factors. The array of chemical treatment options includes precipitation, adsorption, chemical reduction, pH adjustment and microbial control.  When several fouling agents are present, the chemistries for dealing with each substance are evaluated for their compatibility and combined effect. Treatment processes are usually carried out in two- or three-phased chemical reactions. The chemical treatment typically includes some combination of the following processes:

  • Lime softening – – Hardness precipitation for scaling c
  • Magnesium hydroxide – Silica colloid adsorption for fouling prevention.
  • Dithiocarbamate – Heavy metal precipitation and bio-growth control.
  • Powdered activated carbon – Organic reduction, oxidant destruction and bio- film prevention
  • Fe/Al coagulation – Precipitates and colloid agglomeration for membrane filtration enhancement
  • pH Adjustment – pH operating zone optimization for the integrated reactions

 

How the Membrane MF Process Works

After the chemical reactions are completed, the pretreated wastewater is processed through MF membrane filters that are designed to separate the incompatible precipitates from the water. The wastewater is pumped at a high velocity (12-15 feet per second) through membrane modules such as those shown in Figure 1. These modules are connected in a series, with inlet pressures that are typically around 45-50 psig.  This creates a turbulent flow of water that moves parallel to the membranes surfaces. This pressurized, turbulent flow produces a high-shear scrubbing action which minimizes deposits of solids on the membranes’ surfaces.

During operation, clear filtrate water permeates through the membrane, while suspended solids are retained in the re-circulation loop, and then purged for further de- watering. The membranes are automatically cleaned in two ways.  First, they are cleaned with chemicals when the flux drops to below the specified design level.  Second, these systems have automatic back-pulse mechanisms that provide physical surface cleaning by periodically reversing the direction of the filtrate flow. These automated cleaning functions are key components in the design of these systems and critically important to their reliability and long-term performance.

 

The Next Generation of MF Membranes

One of the biggest challenges for MF manufacturers is in the application and control of the pore forming technique in the membrane production process.  A recognized and well-documented problem for many MF products is their tendency to bleed fine particles through their membranes until the larger pores are plugged by the solids.  This issue usually occurs after the chemical cleaning or back-pulse processes, and results in premature flow decline, low-flux operation and out-of-spec performance.

Microfilter systems produced by Process and Water are designed to overcome this problem.  The designs were developed after extensive R&D, QA control and field testing, and in collaboration by Duraflow, Process and Water’s membrane supply partner, these modules effectively eliminate operational problems related to pore formation.

Process and Water’s MF (Microfilter) offerings are manufactured in a tubular configuration capable of handling high concentrations of solids.  The fabrication process starts with preparation of a solution containing specialized polymers and other chemicals that enhance membrane formation. The fabrication process involves precision application of the solution to the porous, polymeric tubes in a highly controlled environment. Through a proprietary, pore-forming process, micro-porous membrane are formed on the inside surface of the support tubes. This results in very narrow pore distribution throughout the membranes.  In fact, more than 99% of the pores in the MF modules are less than 0.2 microns in diameter.

The specialized solution and application procedures effectively eliminate all of the unwanted large pores in membranes. This allows the near-total removal of unacceptable components for more consistent adherence to feed water quality criteria. The manufacturing process also results in membranes with much higher numbers of pores per square inch of surface area. This enables the membranes in Process and Water MF systems to operate consistently at twice the operating flux of other MF systems. In addition, this feature means that these Process and Water systems require roughly half as many membranes to filter the same amount of water as other such systems.  Lastly, the manufacturing process forms a very strong chemical bond between the membranes themselves and polymeric tube surfaces. This produces a highly durable MF filter material that can extend a continuous operation for 5 to 10 years without membrane replacement.

Reverse Osmosis Process

Pretreated wastewater in these systems is typically pressured between 200 to 600 psig and processed through thin-film composite or cellulose acetate RO membranes.  The feed stream is separated into permeate (clean water) usually 75 to 80 % of the feed (recovery), and concentrated brine containing the separated salts (reject).  The permeate water generated by these systems is cleaner and less conductive than that of most municipal water supplies.  That said, the nature of customers’ specific wastewater requirements, and their objectives for recycling and reuse, must be the primary factors that drive the system design, chemical reactions, and membrane configurations for their RO systems.

MF – RO Installations

A large number of installations have successfully combined proper chemical reaction with Process and Water’s high-flux, tubular microfiltration and RO systems for recycling of wastewater from various industries (Figure 2).  Following are examples of selected installations.

  • Anodizing – A major Aerospace supplier Universal Alloys manufacturer in Romania, operates a 45 GPM MF/RO system for removal of anodizing wastewater and 95% recycle of combined wastewater.
  • Electroplating – A large job shop in New York operates a 40 GPM MF/RO system for removal of heavy metals and 65% recycle of combined wastewater.
  • Consumer electronics – An electronic connector manufacturer in operates a 30 GPM MF/RO system for removal of heavy metals and 70% recycle of combined wastewater.
  • Power generation– A power plant in California operates a 500 GPM MF/RO/EVAP system for removal of hardness/silica and 100% recycle of cooling tower blow-

Conclusion

Microfiltration, when coupled with an appropriate chemical pretreatment can provide a cost-effective, high-performance method for pretreatment of industrial wastewater RO systems. Compared to conventional wastewater treatment operations, MF systems have smaller footprints and lower operating costs. In addition, high quality and consistent filtrate produced by modern MF systems leads to improved overall performance of the RO system.  As has been proven true in the field, a well-protected RO membrane can be operated effectively for several years before replacement is required.

Against the backdrop of today’s global water supply issues, companies across all industry segments are realize that it makes good business sense to become more self-sufficient through the recycling of the water resources they use to support their production processes.  Whatever the industry or the specific requirement, Process and Water is ready to help customers meet their production water challenges with MF-RO systems that are among the most innovative in the industry.

About the Author

Process and Water is a leading provider of innovative water purification, wastewater treatment and regulatory compliance solutions for customers in the commercial and industrial sectors.  As CEO, he sets the Company’s strategic direction and oversees all aspects of its operations, including the design, manufacture, and delivery of solutions built with cutting-edge fluid handling and process purification technologies.

Posted in Water Treatment