Industrial Water Supply for Specific Industrial Use

Industrial Water Supply for Specific Industrial Use

IndustrialWater Supply for Specific Industrial Use

Abstract

Treatmentof water meant for drinking and other domestic purposes using reverseosmosis is one of the alternative method of water treatment. Reverseosmosis is one of the most effective methods to reduce the quantitiesof specific metals and ions in water. Some compounds such as nitratesand arsenic can be reduced to safe levels through reverse osmosismethod which comes at a lower cost than convectional distillationmethods. Reverse osmosis is usually used in combination withactivated carbon filtration. A typical reverse osmosis systemconsists of a pre-treatment compartment, the reverse osmosismembrane, water flow regulators, post-treatment filters, supplyfaucet and a storage facility. Reverse osmosis systems requiredpressure to remove contaminants and other dissolved substances inwater.

IndustrialWater Supply for Specific Industrial Use

Bottledwater is mainly derived from underground sources, and hence itsquality varies depending on the nature and chemical composition ofthe material in the ground. Ground water is less vulnerable tocontamination although it can still contain high quantities ofcontaminants such as nitrates, radioactive elements and arsenic.Human activities can also affect the quality of ground water,especially through industrial wastes, and faulty underground chemicalstorage facilities and septic systems. Moreover a sizable proportionof bottled water is derived from surface water reservoirs. Studieshave shown that bottled water that is derived from surface sourceshave a more consistent taste than the water from taps.

ReverseOsmosis (OR) was designed a method of water treatment more than fourdecades ago. RO first emerged as a method of desalinating seawater(Rao,2011).From the moment this technique’s decontaminating potential wererecognized, RO systems began to be commercially produced forpurification of water in homes and industrial use. RO systems weremounted in homes as early as late 1960s (Hameed,2009).RO systems were attractive to many people as viable alternative ofwater purification to the more pricey and energy wastefulpurification techniques. Reverse Osmosis is water purificationtechnology that eliminate a large proportion of contaminants fromwater by shoving the water under substantial pressure via asemi-permeable membrane. It is mainly used to reduce the levels oftotal dissolved sediments and suspensions in water. It is a techniqueof deionizing water by passing it through a membrane (LANXESS,2014).

ProcessDescription. Tohave an in-depth understanding of the process and purpose of RO it isessential to understanding the meaning of osmosis. Osmosis is acritical process that occurs naturally where a hypotonic solution(weaker saline) tends to move to a hypertonic (stronger saline)solution. Osmosis is the main process through which the hairs ofplant roots absorb water from the ground and the mechanism throughwhich the human kidney absorb water from our blood (LANXESS,2014).

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Thediagram above depicts how the process of osmosis works. It isevident that water will tend to move from a hypotonic (lowconcentration) solution to a hypertonic (high concentration) solutionthrough a membrane a membrane, in this case must be semi-permeable soas to allow some water molecules to pass through and not otherparticles. The holes on the semi-permeable membrane are big enough toallow water to pass through and small enough to prevent other largermolecules or particles to pass through (Hameed,2009).

ReverseOsmosis is just as the two words indicate, it is osmosis and reverse. In the natural world osmosis does not need energy to take place, butfor reverse osmosis to occurenergy is required because of the sheer fact that water is moving from the hypertonic solution tohypotonic solution. Energy is needed to push water molecules past thesemi-permeable membrane (LANXESS,2014). The energy required is usually greater than that required innatural process (osmotic pressure) in a bid to de-ionize water.

Thediagram above demonstrates reverse osmosis. When a particular scaleof pressure is applied on a hypertonic solution, water molecules areforced past the membrane and the other contaminants do not passthrough.

Contaminantsnot removed by RO

Eventhough reverse osmosis is a cost effective method of removingcontaminants from water, there are a number of contaminants thatcannot be removed using this method. Contaminants, for exampledissolved gases, such as sulfides and hydrogen are able to passthrough the semi-permeable membrane together with the water (Kimura&amp Sourirajan, 2007).In addition some volatile organic chemicals, pesticides and solventsare not removed by reverse osmosis.

Theefficiency of reverse osmosis membrane in lowering the amount ofcontaminant in the water is based on the chemical properties of theimpurities, concentration of contaminants, the type of the membraneused and the prevailing operating conditions (Kimura&amp Sourirajan, 2007).

Unlikethe public water system where monitoring is done by bodies to ensureminimum standards are met, in the private sector monitoring the watersystem is the responsibility of the user. In this light,contamination is likely to go unnoticed in a private water systemthan in public. Information on the amount and degree of contaminantsthat maybe present in water should direct the testing process, sinceit is not economically viable to test for all the probablecontaminants in the water (Kimura&amp Sourirajan, 2007). It is paramount toget the information on the nature and degree of contaminants andreasons for removal before identifying the treatment method to beemployed.

TreatmentprinciplesThequantity of water that a reverse osmosis membrane used in homes cangenerate can be more than 30 gallons. The quantity of purified waterproduced is determined by numerous factors such as the prevalentoperating conditions (temperature, pressure and pH) and theconcentration of contaminants in the water fed into the reverseosmosis system (Cancino-Madariagaetal.2011).There are two main measures of performance of a reverse osmosismembrane rejection and recovery rate (Cancino-Madariagaetal.2011).Recoveryrateis a term used denotes the proportion of water that is comes out ofthe RO system. It is important to note that not all the water that isfed into the RO system come out. Part of the water is used aswastewater to cleanse the removed contaminants (Rao,2011).In this light recovery rate is a gauge of efficiency that is estimateusing the following formula:%recovery= [quantity (volume) of treated water/ total volume of water fed intothe system]x 100Recoveryrate can be improved by using a properly designed reverse osmosissystem. This means that more water is produced. Majority of householdreverse osmosis systems are designed with a recovery rate of about20-30 percent (Rao,2011).This means that when 100 gallons of contaminated water are fed intothe reverse osmosis systems the yield (treated water) will be20-30gallons. The 70-80 gallons go into the waste stream. If therejected contaminants are not washed away constantly, the efficiencyof the reverse osmosis system is significantly compromised.Conversely, if the flow of waste s too fast, the recovery rate isalso affected and less water will be treated (Rao,2011).Rejectionrate isthe proportion of contaminant that is rejected and hence does notpass through the RO membrane. The rejection rate for each contaminantis calculated separately, and the summation of this gives the totaldissolved solids. For those water contaminants that pose a healthhazard to people the rejection rate is supposed to be high enough tolower the concentration of such contaminants into safe levels. Inthis vein, the quality of water that is fed into system is veryessential (Rao,2011).For instance, if the water that is fed into the system has a 40mg/lnitrate level, the reverse osmosis membrane with a 80 percentrejection rate would eliminate 40 x 0.8=32mg/l. As can be observedthis would leave 8mg/l of the nitrate in the water that is treated. Anitrate level past 10mg/l is considered to harmful to human healthand hence any reverse osmosis system that allows more than 10mg/lwould be termed as inefficient(Rao,2011).EquipmentsTreatmentsystems can be categorized into two main groupings:

  • Point of entry devices
  • Point of use devices

Pointof use devicesare systems that treat water at the place where it is used, forexample a faucet. Many of the reverse osmosis systems are point ofuse devices that are usually positioned on the countertop or underthe sink. Water treated using the reverse osmosis method is usuallyslightly acidic and hence it requires the installation of plumbingdevices (Hameed,2009).Pointsof entry (POE)are reverse osmosis systems that are designed for water treatment atthe point where it gets into the reservoir. This means that all thewater in the system is treated. POE devices are more expensive andmore difficult to install and run than the point-of –use system.Anemblematic RO system is made up of a pre-treatment compartment, theRO membrane, water- flow regulators, post-treatment filters, supplyfaucet and a storage facility as shown in the diagram above (Hameed,2009).ReverseOsmosis Membrane

Ina RO system the process of selecting the membrane is a crucial aspectof the treatment because it affects the overall performance of theentire system. In many reverse osmosis system, the membranes arecomposed of:

Thinfilm composite (TFC)

Amalgamof cellulose( Cellulose acetate membranes and polyamide membranes)

Theformer has a superior quality and has a higher rejection ratecompared to the latter (Kimura&amp Sourirajan, 2007).Diagram below shows a typical RO membrane made of cellulose.

CelluloseAcetate RO Membrane

TFCmembranesare also more durable due to their great strength. The membranes havea higher resistant to attacks by microbial and are even more tolerantto chlorine, pH, which are the emblematic disinfect water(Bereschenko, 2007). The storage facility has a volume of about 5 gallons. Filters areusually used to remove odor elements and taste and other residualmaterials that may not be removed in the reverse osmosis process.Post-filtration may not be necessary if the AC filters are used atthe pre-treatment phase (Hameed,2009).

Celluloseacetate membranes have a higher fluxand as such a smaller area of membrane is needed for reverse osmosis.These membranes are also resistant to small concentration ofcontaminants such as chlorine which means that they are free ofmicrobes. Cellulose acetate can also produce a product with residualchlorine that hampers consequent re-growth (Hameed,2009).

Polyamidemembranes are the best alternatives inenvironments where temperatures are high (above35&nbspoC).This type of membrane does not tolerate chlorine but this does notmean that it can be attacked by microbes. Polyamide membranes arecan also tolerate a wider pH range compared to cellulose acetate(Hameed, 2009).

Modernreverse osmosis systemscome with monitoring lights and gauges to give a signal when thestorage facility is full to prevent wastage of water throughoverflowing. Given that reverse osmosis treatment method requiressignificant volume of water consideration must be given to theadequacy of the water coming to the system. The waste water comingfrom the system together with the contaminants eliminated in thetreatment process can be connected to the drainage system (Hameed,2009).

Itis important to also note that microbial can clog the reverse osmosismembrane, a phenomenon that is referred to as bio-fouling. This meansthat the systems must be regularly disinfected with products that are provided by the manufacturers. When bio-fouling is detected earlyit is possible to clean and restore the RO membrane into a good form(Al-Bastaki, 2004).Nonetheless, when the membrane is torn away a replacement isrequired. If the water fed into the system has high concentration ofsalts and other dissolved substance it is important to pre-treat thewater with a recommended softener to increases the life of the ROmembrane. Majority of the modern RO system are usually fitted with amonitor that shows water that has high dissolved substances. Thereare some monitors that can give the user the expected membrane lifeby continuously measuring the water treated since the last ROmembrane was last replaced (Hameed, 2009).

CaseStudy

Abraajwater facility was established in 2002 after the acquisition of thenew technology bottling firm (NTBC). Abraaj is a well known companyin the security and real estate business in the Middle East andIndia, and is one of the leading investment firms listed in theKuwait security exchange market (AbraajWater, 2015). Abraaj boosts of state of artwater treatment technology in the market. The company is a certifiedfirm in compliance with international standards by credited agenciessuch as the United States FDA. The company maintains s a highdiscipline for safe drinking water that is has been approved bycertified laboratories in Kuwait and the United States (AbraajWater, 2015). Abraaj is one of the mainsuppliers of water to the United States army, Saudi Arabia and Iraq.Abraaj has also met the requirement to export its water to theEuropean Union and Africa. Temperatures in a country like Kuwait canreach 50 degree Celsius during the hot season meaning that waterconsumption is high, through the year. Abraaj uses two stages reverseosmosis to filter water from underground sources. Water is producednaturally through the hydrologic cycle, and when it passes throughsoils, sands, rocks in the mountains it dissolves salts and mineralspresent (Abraaj Water, 2015).Abraaj derives its water from the surface sources and mimics thehydrologic cycle, through elaborate system of distillation. Waterfrom the surface is disinfected and purified to produce 100 percentdistilled water (Abraaj Water, 2015).Some of the water is combined with recommended levels of salts androcks to achieve the right mineral balance to produce mineral water.Abraaj can reduce the cost of purifying water by deploying reverseosmosis to remove contaminants in water that is fed to the system.

Summary

Treatmentof water meant for drinking and other domestic purposes using reverseosmosis is one of the alternatives for large water purifying firmssuch as Abraaj. Reverse osmosis is one of the most effective methodsto reduce the quantities of specific metals and ions in water. Somecompounds such as nitrates and arsenic can be reduced to safe levelsthrough reverse osmosis method which comes at a lower cost thanconvectional distillation methods. Reverse osmosis is usually used incombination with AC filtration. Choosing the apt RO system should bebased on water assessment and analysis of the firm’s needs andcondition. Regular assessment and replacement of the RO membrane iscritical in maintaining a functional RO system. This ensures that thesystem is effective in removing contaminants and reducing the levelof bacterial contamination of the RO system. Abraaj has successfullyemployed RO system in its water plants and the company has attainedimmense benefits over the years. Nonetheless, more need to be done toamplify the use of RO system in the plant, especially in theproduction of bottled mineral water.

References

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