Water Treatment

RO membranes wash/CIP

According to manufacturer guideline membrane life can be 3 to 5 years. To achieve the service life the RO plant should be designed maintaining all guidance and preconditions. Proper Antiscalant selection and accurate dosing is important also to extend membrane life. But scale and fouling materials will be deposited slowly on membrane which need to remove periodically by CIP. Suitable CIP chemicals from reputed manufacturer is now available in ready stock.

CIP chemicals:

Usually three types of chemicals are used for CIP as extremely basic, acidic and neutral biocide. A number of reputed manufacturers produce the chemicals which are available from ready stock. Each products have relevant datasheet which should be followed during membrane washing.

CIP skid with pump & filter suitable for membrane cleaning.
CIP skid with pump & filter suitable for membrane cleaning.

CIP pump selection:

CIP is done with highly acidic and basic corrosive chemicals and SS-304 pump will be damaged very quickly. So it is wise to choose ss-316 or duplex pump for CIP. Usually the CIP is done a 40 meter head and the pump is selected so.


DM PLANT


DM (de-mineralized) & distilled water is required in Pharmaceuticals, power plant, steel industry, fertilizer and other sophisticated process. Usually minerals are removed from raw water to produce DM water. Reverse osmosis system is very much effective for salt removal from raw water & this system is heavily used for industrial water treatment. But all available methods are here:

  1. Cation-anion-mixed bed
  2. Double pass RO/EDI
  3. RO + supercharged resin
  4. RO + DM

Cation/anion/mixed bed with pretreatment:

Raw water contains minerals which remains dissolved in water by forming cation (positive charged) and anion (negative charged). To remove the charged ions cation and anion resin is used in DM plant. The water is pretreated by multi-grade filter if required. Detail water analysis is required to design the DM plant. Depending on alkalinity degasser system may be used to remove dissolved Co2. Usually cation-anion treatment produce water less than 30 microsiemens/cm and mixed bed resin is used to produce water less 10 microsiemens/cm.

Double pass RO:

Usually reverse osmosis is used to remove salinity and dissolved salts from raw water. But in some industries very strict water quality is required and RO pure water is passed again through a second reverse osmosis plant. Double Pass Reverse Osmosis (DPRO) System is the best way to get ultrapure water for industrial use.

In many cases best quality DM water is produced from second pass RO permeate with the combination of EDI (electro de ionization). This water is also used in pharmaceuticals, chemical industries and pharmaceuticals for manufacturing of best quality products.

RO + supercharged resin:

For cost effective plant operation major portion of dissolved minerals are rejected by reverse osmosis plant and the residual minerals are removed by resin bed. In this process RO permeate water is passed through a bed of supercharged resin to provide ultrapure DM water. The resin bed is non-rechargeable and have to replace when exchange capacity exhaust.

RO + DM plant:

In this procedure first permeate of reverse osmosis unit is passed through cation bed, degasser, anion bed and mixed bed.


REVERSE OSMOSIS (RO)

What is RO? RO stands for reverse osmosis and it is particularly opposite of natural osmosisprocess.

What is osmosis? Osmosis is a natural process used in plants for collecting water from environment. In this process water moves from lower salt concentration to higher salt content water solution. This process does not require energy and continues until the salt concentration becomes equal.

So Reverse Osmosis (RO) is named so as it is completely opposite of the osmosis and water from high salt concentration moves to lower salt content through semi-permeable membranes. The process requires energy and so pressurized water is passed through membranes. These are the most up-to-date technology for dissolved salt & salinity removal. Reverse osmosis is used for drinking & industrial purpose. On the other hand demineralized (DM) is used at industry. Electro-deionized (EDI) is a sophisticated technology for best quality DM water production usable after RO treatment.

RO for industryRO plant for surface water treatmentDouble pass ROMobile desalination plantSeawater desalination plant
Complete project for food, beverage & chemical industries.RO plant is used to remove the salinity of river/surface water.Produce best quality permeatePlant is sent to remote location to supply drinking.Produce drinking water at ocean going ship/vessels.





Antiscalant selection:

Reverse osmosis membrane is the most critical component of a desalination plant. Depending upon raw water various scales formed on RO membrane sheet. To protect the scaling suitable antiscalant need to select to protect the membrane blockage. Reputed antiscalant manufacturer use projection software for best antiscalant model and dosing rate selection.

Reverse Osmosis (RO) plant is designed based on RO technology to remove salinity and other impurities. Actually reverse osmosis is a membrane based separation of dissolved salts and chemicals. In raw water there are different impurities as – suspended particles with iron is removed by clarification and pretreatment. Particle size up to 1 micron is also removed by micro-filtration. But the dissolved salts, heavy metals-arsenic, chemicals can not be removed by traditional filtration because of their very small size. So membrane is only option in the world to remove these impurities. Usually spiral wound membranes are used in RO plant. Pressurized water is passed through RO membranes (pore size 0.00001 micron) and only water molecules cross the barrier. The membrane have a continuous cross flow which takes the rejected salts/chemicals to drain.

WHO guideline:

According to WHO guideline for drinking the considerable parameters for surface water treatment plant are following:

ParametersUnitValue
pH6.5-8.5
Color(True and Apparent)Pt-Co15
Total Dissolve Solids (TDS)mg/l1000
Chloride(Cl)mg/l600
Total aerobic bacterial countCFU/100 mL1000
Total coliformCFU/100mLAbsent

But there is no fixed standard guideline for industrial use and it varies depending on type of industry and specific industrial use as for drinks, beverages, milk & ice-cream etc. So these standards are obtained from process consultants or equipment manufacturers.

RO Plant Designing Guideline:

  1. Safe designing by software: RO membrane is the costly part of the plant and it is wise to use the membrane 3-5 years to be cost effective. To do so it has to deign according to the membrane manufacturer’s software. The software output indicates the raw water requirement and high pressure pump specification.
  2. Membrane selection: a wide variety of RO membranes are available and type-model selection depends on raw water source, TDS & biological properties. Tap water membrane, Brackish water membrane & Seawater membranes are very common varieties. Each membrane manufacturer provides their product guideline for best model selection.
  3. Good pretreatment: Another important issue is pretreatment which should be good enough to meet SDI (silt density index). Poor pretreatment results membrane damages which leads to financial losses.
  4. Antiscalant selection: The raw water should be analyzed thoroughly and antiscalant is selected accordingly. The scale forming chemicals –iron, silica, calcium, barium etc may present in raw water and antiscalant will be there to protect the membrane from scaling.
  5. CIP is mandatory: CIP (cleaning in place) of membrane is the mandatory part of a RO plant. Using CIP system the membranes can be washed and cleaned using acidic and basic chemicals. According to manufacturer guideline membrane can be used 3 to 5 years. But scale and fouling materials will be deposited slowly on membrane which need to be removed by cip periodically. Suitable cip chemicals from reputed manufacturer is now available from our stock.
  6. Pretreatment selection :Silt density index (SDI) is the parameter for determining the perfection of pretreatment of reverse osmosis system. The maximum permissible SDI is 5 for RO input. If the SDI of RO input water exceeds the allowable limit the scaling factor increases. So pretreatment selection as designing multi-grade filter, iron removal or activated carbon filter are very important for getting low SDI.
  7. Pump selection: Usually end suction centrifugal pump are used for pressure filtration. For chemical dosing non corrosive diaphragm type metering pumps are used. But in some cases for lime dosing non corrosive submersible pumps are used for maintenance free operation in bigger plants. Multistage centrifugal pumps are required to operate the RO plant to provide the pressure. For saline water higher pressure is required and in that cases ring section or plunger type pumps are used. These pumps are manufactured of suitable non corrosive construction depending on raw water quality or salinity.

Raw water analysis:

It is very wise to have a raw water test report for selection of suitable method, clarifier designing, media selection and successful surface water treatment plant designing. The LIST OF WATER TEST required for this purpose is given here.

SlpH
1.Color(True and Apparent)
2.Total Dissolve Solids (TDS)
3.Total Hardness(EDTA) as CaCO3
4.Chloride(Cl)
5.Total aerobic bacterial count
6.Total coliforms
7.Free Chlorine(Cl2)
8.Ammonia-Nitrogen (NH3-N)
9.Nitrate – Nitrogen (No3 – N)
10.Bi-carbonate(HCo3)
11.Carbonate(Co3)
12.Total Alkalinity as CaCo3
13.Acidity

Filtration flow rate:

Properties of each filter media is different and water loading rate differs from others. Standard filtration rate 5 GPM/min/Sq.ft. But for perfect plant designing the allowable flow rate should be considered from corresponding filter media datasheet.

Vessel diameterAllowable water flow rate
10 inch600-1200 L/H
12 inch1000 – 2000 L/H
14 inch1200-2500 L/H
16 inch1500-3000 L/H
18 inch2000-4000 L/H
20 inch2500-5000 L/H
24 inch3500-7000 L/H
30 inch5500-11000 L/H
36 inch8000-16000 L/H

Media selection:

bore-well water contains different impurities as iron, manganese, suspended particles etc and the media selection is dependent on the details chemical analysis report. Usually the BIRM media is efficient and cost effective for iron removal plant. But the requirement of pH, alkalinity and other parameters should be considered from its datasheet before designing. Depending on the chemical parameters Manganese zeolite/quantum filtration media can also be used. Other regular media are graded sand, anthracite & activated carbon. All datasheet are available in download.

Note: Manganese zeolite need activation.

Vessel selection & no. of vessel:

Standard filtration rate is 5 british gallon/min/Sq.Ft. So the vessel should be selected within maximum allowable flow rate. FRP filter vessel with multiport valve is available now which can be used for small to medium plant design. Multiport valves is manual or programmable which gives the benefit of automatic backwash. FRP is cost effective to mild steel/SS vessels and it is maintenance free also. For higher capacity plant multiple FRP vessels are used to divide the water flow or custom made FRP is used. Alternatively large horizontal filter vessels are made of mild steel with epoxy paint/rubber lining.

Filtration flow rate:

Properties of each filter media is different and water loading rate differs from others. Standard filtration rate 5 GPM/min/Sq.ft. But for perfect plant designing the allowable flow rate should be considered from corresponding filter media datasheet.

Vessel diameterAllowable water flow rate
10 inch600-1200 L/H
12 inch1000 – 2000 L/H
14 inch1200-2500 L/H
16 inch1500-3000 L/H
18 inch2000-4000 L/H
20 inch2500-5000 L/H
24 inch3500-7000 L/H
30 inch5500-11000 L/H
36 inch8000-16000 L/H

Vessel Size & Cost Calculation:

This automatic formula can assist to design a plant with minimum knowledge. Using the calculation it is easier to select vessel diameter with filter media requirement and approximate budget also.

CALCULATE VESSEL DIAMETER:

For oxidation & traditional sand filter: One filter vessel is required and the flow rate should be 5-8 GPM/Sq.Ft. The filter water may have 0.5 mg/liter iron.

For using Birm: One filter vessel is used at flow rate of 5-8 GPM/Sq.Ft. The filter water iron concentration will be less than 0.3 mg/liter.

For using manganese zeolite: One manganese filter and one sand filter is required. The filtration rate should not exceed 10 GPM/Sq.Ft. The filter water iron concentration may be within 0.3 mg/liter. Manganese zeolite must be activated after installation.

In combination with the filter vessels multi-grade filter with graded quartz sand media and anthracite is used for suspended particles removal. Activated carbon filter with granular activated carbon made of coconut shell, iodine value 1000 mg/liter is used to remove organic matter, color and odor from water.

Consumables cost:

RO antiscalant & cartridge filter are the common consumables in plant operation. But actual requirement varies from plant to plant. Other consumables are bi-carbonate, caustic, biocide, membrane cleaner etc required at less frequently.

Source of chemicals:

Most of the water treatment chemicals are imported items and procurement of genuine, quality products is the key to success. Chemicals from reputed manufacturers may be little bit costly but applies at low dosages thus minimizing operating cost. These chemicals do not contain impurities and not harmful for membranes or other sensitive water treatment plant.

Frequently used chemicals for water treatment plants are:

  • Aluminimum sulfate
  • Lime powder
  • Polymer
  • Floculant
  • Ferrous sulfate
  • RO antiscalant
  • Bag filter
  • Sodium bi-carbonate
  • Membrane CIP chemicals
  • Sodium hypo chlorite
  • Ferric chloride

Quality chemicals are supplied allover Bangladesh. Please contact us for chemical requirement with dose adjustment.

Operation &Maintenance:

very important considerable parameters are free chlorine content, pH, SDI and salinity. Usually sand filter, multigrade filter, activated carbon or other filters are used in plants which need to backwash daily. The filter should backwash until the input and drain water seems to like same. It is better to backwash filter vessel with stored filter water for better and quick backwash. For big filter vessels air compressor/blower can also be used before backwashing for best result.

Media change:

Practically the life of media depends on its operation time, level of maintenance and quality of filter media. Graded sand is the most common filter media and is suggested to change yearly. Manganese media can be used 2-3 years. BIRM media will be good for use 3-4 years. Activated carbon need to change within 1-1.5 years.

Electric control panel:

This is the most important part of a project. Control panel ensures the smooth operation of the plant. Usually control panel operate the pump, motor, blower or other electric equipment with operational safety. If overload or dry run protector is fixed properly, the electrical items will stop in case any problem but will not burn.

System or process automation is another important role for water treatment plant. Different types of water level controller and indicators can be used to control the whole plant in automatic mode. So for getting comfort in project operation the control panel should be designed and commissioned by professional experts.

Software based design:

Membrane manufacturing is a big industry and very reputed manufacturers are producing different types of ro membranes and providing excellent technical services. Most manufacturers provide software for ro plant designing which can be used for error free plant designing.

Consultancy services:

We can provide consultancy services for design, drawing, tender preparation, site supervision as required by client. According to the provided drawing client himself or contractor can execute the job

RO plant for industry

Industrial water can be broadly divided as drinking water usable for food industry and others for chemical/industrial purpose.

RO plant for food industry:

Reverse osmosis water treatment plant is one of the best established process for drinking water production. Drinking water is the key requirement of food industry for production of Jar water, bottled water, drinks, beverages & other food items. Practically reverse osmosis can remove salts, harmful chemicals and pathogenic bacteria, viruses from water and ensure safe drinking water. So during the plant designing biological safety plan is very important.

Usually good pre-treatment is installed before RO plant to protect the membrane damage and ensure water quality also. The pretreatment processes are raw water disinfection, clarification, multi-grade filter, iron removal, activated carbon filter and microfiltration. But the process largely varies upon raw water availability, its quality and drinking water requirement.

pH adjustment of RO water:

Usually RO water pH is lower than 7.0 due to incorporation of carbon di-oxide and in some cases pH need to adjust to meet the requirement. The adjustment can be done using de-gasser, chemical dosing or lime bed etc. Automatic dosing pumps can be used with ORP controller to increase pH. In some cases de-gasser is used to remove the carbon di-oxide for industrial use. But for drinking water sodium bi-carbonate is preferred.

Community based desalination:

In coastal areas of Bangladesh drinking water availability is a critical issue. In many areas groundwater is not available or saline which is not drinkable. In those areas surface water is also saline and salinity is being increased day by day. So small desalination plants are installed in rural areas to provide safe drinking water to the affected people. The plants are designed in such a way that local peoples are capable to operate and maintain the plant. Usually peoples collect drinking water at a minimum charges which bear the maintenance load.

RO plant for industrial use:

Now a day’s industrialization is going on in Bangladesh. In many industries treated water is required for very sensitive usage and very strict water quality is required for many products. Best quality of water is required for pharma, power plant, chemical industries, agro industries, fertilizer, steel etc. To meet the required quality usage of reverse osmosis is increasing day by day. In many industries RO water is further processed by DM plant or distillation plants. Procurement or installation of RO plant is relatively easy but the plant should be economically viable. The business feasibility of the plant depends on the perfection in plant designing. We are designing & installing RO plant according to international practice to make your business profitable.

Raw water source is different in different industrial areas in Bangladesh. Deep tube well is very common raw water source but river water is also used. Depending on raw water source and chemical quality the plant is designed. The treated water quality is also considered during the design. There are raw water crisis in many industrial zone and special water saving features are added with the plant. Reverse osmosis with low rejection is considered in this case and RO wastewater is also recycled in many factories. Usually good pre-treatment is installed before RO plant to protect the membrane damage and ensure water quality also. The pretreatment processes are raw water disinfection, multi-grade filter, iron removal, activated carbon filter and microfiltration.

Antiscalant selection:

Reverse osmosis membrane is the most critical component of a desalination plant. Depending upon raw water various scales formed on RO membrane sheet. To protect the scaling suitable antiscalant need to select to protect the membrane blockage. Reputed antiscalant manufacturer use projection software for best antiscalant model and dosing rate selection.

Quality of RO output:

There is no fixed water quality for RO output water. Because RO membrane reject 90-99% dissolved salt from raw water. As raw water TDS (total dissolved solid) varies place to place and RO output varies accordingly. The percentage of rejection varies for ro membrane model, element number & array type.

RO plant for deep well water treatment

In true sense reverse osmosis is used to remove salinity and unwanted dissolved chemicals from raw water. The bore well water in southern area of bangladesh contain excess salinity, chloride and in some cases arsenic also. Reverse osmosis system can be used for treatment of this raw water to meet the WHO guidelines. RO membranes are supposed to use for dissolved salt removal and absolutely not feasible to remove iron and suspended particles. So for bore well water treatment the usual process is Aeration, iron removal, multigrade filter, activated carbon, microfiltration and finally reverse osmosis. But the process largely varies upon raw water availability, its quality and drinking water requirement. In case of heavy iron and other impurities clarifier can be used to get clarified water.  To get the best result from ro plant it should be designed professionally by membrane manufacturer software. Antiscalant selection and its dose should be adjusted perfectly to protect membrane blockage. CIP(cleaning in place ) is a mandatory attachment for ro plant and it can be used to wash the ro membranes with branded cleaning chemical from reputed manufacturer.

RO plant for surface water treatment:

In bangladesh river is the major surface water source. Reverse osmosis is not required if the river water is non Saline. But due to tidal effect, weather change and reducing upstream flow river water becomes Saline in coastal areas. In most coastal areas better alternative water source is not present ŕnd municipal water supply also depends on river water.  So surface water is primarily treated by clarifier based surface water treatment plant and then feed to reverse osmosis system for salinity removal. Designing of ro plant for surface water is little bit different from underground water. For membrane safety the concerned parameters are disinfection, SDI and membrane cleaning system.

In modern business concept equipment are compact, takes less space and economic also. So the lamella clarifier has been developed with higher flow rate in less space to minimize the water treatment cost. Lamella clarifier can be prefabricated with mild steel or FRP for small plants. But in industry the rectangle RCC clarifier is constructed with several baffle wall, flocculation zone, sludge hopper and water overflow zone for clear water collection. FRP Lamella sheet or PVC tube settlers are placed at 1-2 inch internal distance and 45 degree angle in the clarification zone of the clarifier. The raw water is coagulated with dosing chemicals as lime, alum, polymer/flocculent to build flocks in flocculation zone. The water is then passed through the tube or channel placed at inclined position which prevent the sludge to move upward and only clear water goes upward. The sludge is settled at bottom and collected in sludge hopper.

Lamella clarifier with tube settler and RCC tank

Filtration system:

The clear water from clarifier is stored in clear water reservoir and is pumped through sand filter or multi-grade filter & activated carbon for filtration. The vessel can be made of FRP, mild steel or stainless steel etc. Usually vertical filter vessels are used for filtration but horizontal filter vessels are also used for higher flow rate in large water treatment plant.  The clear water contains little bit suspended particles which is removed by multi-grade filter. The filter vessel is equipped with graded stone, pebbels, graded sand, coarse/fine silex, anthracite etc. Granular activated carbon with around 1000 mg/gram iodine value is used as filter media in activated carbon filter vessel which removes organic matter, color & odor. The filter water can be treated further for RO plant/DM plant/water softener etc as required for industrial purpose.

Disinfection:

Surface water contains biological matter and bacterial count is relatively higher. So disinfection is mandatory to kill pathogenic bacteria. Hypo solution/bleaching power/chlorine gas can be used for this purpose. These chemical have residual effect which will not allow bacteria to grow in pipeline. But for RO membrane the free chlorine is harmful and have to be removed by de-chlorination system.

River/lake/surface water intake:

There are no fixed and definite system for surface water intake system and completely dependent upon site condition. Usually a pump house is constructed at riverside where the water level variation is not significant. In many cases underground pump house is required to meet the suction head of the intake pump. Floating pump house can be used to intake water from River/lakes with tidal variation/flush flood where water level variation is remarkable. Other better alternative systems are using vertical turbine pumps/non clog submersible pump or making bore well at riverside. Finally the outcome is a combination of space availability near river/lakes, water level variation, required delivery head & flow of the intake pump and the distance of intake to WTP site etc.

Mobile desalination plant

Reverse osmosis desalination plant is a trusted source of drinking water. So during natural calamities these type of plants are used at affected areas to supply drinking water. The plant is installed either in a covered van or in a trolley to be mobile. The plants are suitable to produce safe drinking water from any raw water even from drain or seawater.

Reverse osmosis desalination plant is a trusted source of drinking water. So during natural calamities these type of plants are used at affected areas to supply drinking water. The plant is installed either in a covered van or in a trolley to be mobile. The plants are suitable to produce safe drinking water from any raw water even from drain or seawater.

Basic components of the RO system are pre-treatment unit, RO unit and power source. In the mobile unit different compact pre-treatments are used as MGF (multigrade filter), UF (ultrafilter) etc. The RO system is installed in the container with membrane CIP unit also. In most cases the unit contains a diesel generator to provide power for the RO unit. These plants can start operation in a site within hours at emergency.

Seawater desalination plant

This is the actual desalination plant and suitable to use at Naval ship, islands, tourist locations or coastal belts etc. The key features of the plant is:

  1. It can be operated at very high TDS as 40,000 mg/liter.
  2. Higher operating pressure is required due to high TDS.
  3. Special saline resistant and corrosion free pumps are used to pressurize the water.
  4. The electromechanical equipment including pipeline used in desalination plant are non-corrosive and pressure resistant.

Positive displacement pumps (plunger pumps) are used for smaller desalination plant, capacity ranges 500 – 5000 liter/hour.

Skid mounted seawater desalination unit usable at naval ship, commercial vessels and other seawater treatment.

Double pass RO

In many cases best quality DM water is produced from second pass RO permeate. This water is also used in pharmaceuticals, chemical industries and pharmaceuticals for manufacturing of best quality products.

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