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Disinfection and sterilization of water

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Sterilization of water is the process that kills, eliminates or deactivates the all form of microorganisms in the water. It is the critical stage for safe potable water. This method must achieve all most 100% deactivation so that prevents the spread of water-borne diseases. On the other hand disinfection means the process that are removing or reducing harmful microorganisms. There are different methods of sterilization. We can divide them into two methods; chemical methods and physical method.

Chemical methods of sterilization

There are various chemicals are used to the sterilization process. The consumption of these chemical can be reduced by installing a filtration system before this stage. Some of the chemical sterilization methods are described here:-

Ozone sterilization of water

Ozone is a highly effective sterilization chemical for water. It has strong oxidizing properties. It can kills wide range of pathogens microorganisms by oxidizing method. Ozone is more powerful disinfectant than chlorine or chlorine dioxide. Moreover it has effective inactivation activities on giardia or cryptosporidium which is not possible by some others chemicals. This method does not affected by pH. After complete the oxidation process, the excess ozone will breaks into oxygen. So it does not create bad taste or odor’s to the water and leaves no solid residue. On the contrary, it added dissolved oxygen into the water which enhances the water’s taste. The disadvantages of ozone are that it is costly, toxic, unstable and must be produced on mill site. It can create irritation on nose even in low concentrations.

Hydrogen peroxide sterilization

Hydrogen peroxide is another ideal sterilizer like ozone. It is a strong oxidant. It destroys microorganisms without leaving any solid particle to the water. The disadvantage of the hydrogen peroxide is that it is unstable, costly and toxic at high concentrations. The vapor of it can affect the eyes and respiratory system. Some metallic peroxide like Na2O2 has better stability and effectiveness than hydrogen peroxide. Na2O2 produces hydrogen peroxide by the reaction with dissolve carbon dioxide. It also produces sodium carbonate which can able to soften the hard water. You can also apply calcium hydrogen and magnesium hydrogen. Some processes use both hydrogen peroxide and ozone commonly to accelerate the ozone decomposition rate which increases the oxidation rate.

Na2O2 + CO2 + H2O → Na2CO3 + H2O2
Na2CO3 + CaSO4 → Na2SO4 + CaCO3

Chlorination sterilization

Chlorination is the most common and cheapest system for sterilization of water. Chlorine input into the water as chlorine gas, sodium hypochlorite or calcium hypochlorite, chlorine dioxide. When inject it forms several chemicals like hypochlorous acid.

Chlorine sterilization

Chlorine is the most widely used disinfectant in municipal water and wastewater treatment. It can destroy pathogens and control nuisance microorganisms. It can also remove iron, manganese, ammonia nitrogen. Chlorine is a toxic gas so need safety facilities. It acts as a quick oxidizing agent. pH can affects on its activities so needs to control the pH. Chlorine reacts with water and form hypochlorous acid which is further break into nascent oxygen. Both of them are powerful germicide.
Cl2 + H2O → HOCl + HCl ; HOCl → HCl + [O]

Calcium and sodium hypochlorite

Sodium hypochlorite is the one of the most commonly used sterilization chemicals. It is easier and safer to use compared with chlorine gas but more expensive. It is chemically unstable which can convert into sodium chlorate. At higher pH the hypochlorite is corrosive which can attack metal pipe. Calcium hypochlorite can be found as powder, granular, liquid and solid form.
Sterilization of water

Monochloramine

Monochloramine is another form of chlorination. When chlorine and ammonia included into the water then it forms monochloramine which can react under well controlled conditions. It is poor sterilization chemical compared with chlorine but last long and protect from bacteria for long time.
NH3 + Cl2 → NH4Cl + NH2Cl
Chloramines hydrolysis in water and give HOCl
Chlorination sterilization of water

Chlorine dioxide

Chlorine dioxide is a powerful disinfectant compared with chlorine but more expensive. It must be produced nearby consuming plant site. It is not more used chemical for sterilization of water due to unstable and costly.

Aeration

Aeration can improves water taste and remove iron, Mn, carbon dioxide, H2S, volatile substances and bad odor. There are two type of aeration, natural and artificial. Natural aeration occurs in river, steam. To create artificial aeration several designs like spray is used. During aeration the water absorbs air. So increases the amount of oxygen into the water. This oxygen causes oxidation of the substances which are responsible for forming odor.

Silver ion method

The disinfect effect of copper and silver ions has been known for long time.

The chemical sterilization methods are precipitation method (With alum, lime, soda ash), Potassium permanganate process, Sodium hydrogen sulphate etc.

Physical sterilization methods

Boiling the water

Boiling is one of the oldest and most commonly used water sterilization techniques. If the water is boiled for about 20-30 minutes then it destroy all type of harmful bacteria and algae. They also remove dissolved gases from the water and improve the water taste. This method is only suitable for normal households but not suitable for industrial and large scale purposes.


UV sterilization

Ultra-violet light has a powerful germicidal action on water. It is one of the latest methods for sterilization of water. When ultraviolet radiation is passing through the water then it is absorbed by the cells and damages the DNA of the microorganisms. Hence they are not enable to grow or reproduce. This physical sterilization method can be applied for groundwater and households water but not suitable for large scale. It does not create solid content in water. The water should be free from suspended particles otherwise it may interfere to come in UV rays contract with microorganisms. The system is costly.

Coagulation water treatment process

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The purpose of coagulation water treatment process is to removes the colloidal particles from water. The water may contain suspended matter, small or large solid particles. Sedimentation and filtration processes can removes most of the solid particles but the small particles that are remains in colloidal suspension cannot removes. If they clump together and form larger particles, then it would be possible to removes easily. But a negative charge prevents them to coagulate; as like two same magnetic poles repulse each other. They are very stable in colloidal system. If we are able to neutralize this charges, then they would be consolidate into coarse formations. For this purpose we add a chemical that produces positive charges. This chemical is known as coagulant. The positive charges of the coagulant neutralize the negative charges on the colloidal particles. As a result the particles are able to coagulate into coarse formations which are easily removable.

The process of consolidation of colloidal particles by neutralizing the charges with a coagulant, so that they can remove from the treated water by sedimentation or filtration is called coagulation. It is a vital part for drinking water and wastewater treatment.

Coagulants

Coagulants are the chemicals that are used to removes tiny particles in water. We used different types of coagulants in coagulation water treatment process. Generally, we can categories the common type of coagulant into two groups, aluminium base and iron base. The iron base coagulants include ferrous sulfate (FeSO4.7H2O), ferric sulfate, and ferric chloride. On the other hand aluminium base coagulants include aluminium sulfate (Al2(SO4)3.18H2O), aluminum chloride, sodium aluminate and polyaluminum chloride (PACl). Although some other metal salts as like titanium and zirconium are highly effective, but are costly or rare available.

Coagulation Mechanism

The colloidal particles carry electrical charges; normally negative charge. So the opposite charges coagulant is added to the water to overcome the repulsive charge and “destabilize” the suspension. Usually a metallic salt like alum is added as a coagulant to create positively charged ions. Normally 5-10% solution of coagulant is used. The alum and ferrous sulfate are hydrolysis according to the following equation-

Al2(SO4)3 + 6 H2O ↔ 2Al(OH)3 + 3H2SO4
H+ + HCO3– → CO2 + H2O

FeSO4 + 2 H2O → Fe(OH)2 + H2SO4
H+ + HCO3– → CO2 + H2O
But Fe(OH)2 does not act as coagulant, it oxidized into Fe(OH)3 by consuming dissolved oxygen in water and act as coagulant.
H2O + 2 Fe(OH)2 + ½ O2 → Fe(OH)3
This reaction proceeds easily in an alkaline medium.
Coagulation water treatment process

Factors affecting coagulation water treatment

The process of coagulation of water depends on various factors like pH of the medium, temperature of water, coagulant feed concentration, coagulant dosage, type of coagulant, mass and initial turbidity. Moreover it is also depends on pre-treatment and type of pollutants present.

Effect of pH on coagulation

pH affects on the activities of coagulants. The optimum pH for alum coagulation is 6 to 7.5 whereas 5.0 to 8.0 are for iron. If the alkalinity is lower or higher, then the floc does not form properly. As a result, more coagulant is consumed. In this case, it is beneficial to correct the pH by adding acid or base.

Temperature

Temperature is another factor for coagulation water treatment process. It is more significant at lower turbidity. In case of alum, at low temperatures aluminium hydroxide form a strongly hydrated and very stable sol. So in winter season high coagulant are consumed. When the temperature becomes below the 5⁰C, then alum or ferric salts do not work properly. So it should be consider another coagulant like polyaluminum chloride (PACl).

Type of pollutants

The salt composition of soft water and hard water are not same. Hard water contains Ca2+ and Mg2+ ions. They can alter the charge on the colloidal particles.

Optimum dosage

It is very significant to determine the optimum dosage of a coagulant which will give the maximum clarifying effect. Insufficient amount of coagulant cannot able to destabilize properly of the colloidal particles. On the other hand higher dosage can cause excessive sludge production, corrosion and loss of money.

Type of coagulant

All the coagulants are not suitable for all cases. Different temperatures, pH, type of medium may vary the effectiveness of the coagulant. At lower temperature the polyaluminum chloride (PACl) may be more effective than the traditional coagulants like alum or iron salt. Same way, some pH range can be beneficial to use iron salt instead of alum.

Coagulation jar test

You can determine optimum process condition like dosage, pH by jar test experiments. Generally, it consist several jars filled with equal volume of water. Then test for various dosage of coagulant, pH etc.

Conclusion

Pre-filtration and sedimentation is more effective before the coagulation water treatment process. Moreover, you should follow the following sequence of chemical addition for coagulation of water; firstly add chemicals for pH correction, then add the metal coagulant, after that add the flocculent aid. But remember all the chemicals may not be necessarily for all type of water. In addition, widely many industries practices enhanced coagulation process which is also removes disinfection byproduct (DBP) precursor, color causing compounds.

Determination of chemical oxygen demand of water

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Chemical Oxygen Demand indicates the amount of oxygen required to oxidize all soluble and particulate organic substances in water under specific conditions. All organic compounds may convert into carbon dioxide, water and ammonia. It is a significant parameter to determinate water characteristic. The COD value depends on oxidizing agent, pH, temperature, and period of time. It is expressed as ppm or milligrams per liter (mg/l) of oxygen. There are several methods for determination of Chemical Oxygen Demand but the wet chemical method (dichromate method) is the most common Method.

Principle of chemical oxygen demand

In dichromate method the organic matter in water oxidize with the strong oxidizing agent potassium dichromate under acidic conditions. Normally sulfuric acid is used to achieve the acidity in this COD test method. An additional amount of potassium dichromate are taken, to sure completely oxidation of all organic matter. After complete the oxidation, measure the excess amount of potassium dichromate by titrating with ferrous ammonium sulfate. During the titration the ferroin is used as indicator. At the end point the color of the ferroin changes from blue-green to a reddish brown. The consumption of the dichromate is proportional to the amount of organic matters that are present in the water.
3[CH2O] + 16H+ + 2Cr2O72- → 4Cr3+ + 3CO2 + 11H2O

It is a fast applicable parameter for industrial wastewater, water controlling plant, sewage, rivers, lakes or aquifers but not applicable for drinking water as the lower content of oxidizable organic matter. Frequently, a silver compound like Silver sulfate is used as a catalyst to promote oxidation of certain organic compounds such as linear aliphatic compounds, aromatic compounds and pyridine. Some inorganic materials like chloride, nitrite may interfere with the result of COD. Chloride interference can eliminate by adding Mercuric sulfate whereas nitrite interference can eliminate by adding sulfamic acid.

COD testing equipment and reagents

  1. Water sample
  2. Distilled water
  3. Standard Potassium dichromate solution (0.25N)
  4. Sulfuric acid reagent
  5. Standard ferrous ammonium sulfate (0.25 N)
  6. Ferroin indicator
  7. Mercuric sulfate
  8. Silver sulfate
  9. Water bath
  10. Titration apparatus
  11. 500ml conical flask (Erlenmeyer Flask)
  12. Burette
  13. Pipettes
  14. Pipette bulb
  15. Wash bottle

COD test procedure

  1. Collect the sample water from a source.
  2. Take 500 ml conical flask/ reflux flask and filled with 50ml of sample water.
  3. Place several boiling stones in the reflux flask.
  4. Determinate the chloride ion. If it contains a significant amount then, add 1 g of HgSO4 and 5.0 ml conc. H2SO4; then swirl the mixture until the mercuric sulfate dissolves.
  5. After that place the reflux flask in an ice bath and slowly add 25ml of potassium dichromate solution (K2Cr2O7) with swirling.
  6. Now add 75 ml of a mixture of sulfuric acid-silver sulfate solution to the cooled reflux flask with swirling.
  7. Apply heat to the mixture under reflux in water bath at 150°C temperature for two hours.
  8. Then allow the flask to cool about room temperature and wash the condenser with distilled water. Transfer the mixture into 500 ml Erlenmeyer flask.
  9. Then titrate the excess dichromate with 0.25 N ferrous ammonium sulfate, Fe(NH4)2SO4 solution by using 2 to 4 drops of ferroin indicator. At the end point the color turns from blue-green to reddish brown and take the burette reading. Let the reading is ‘B’ ml.
  10. Run a blank titration similarly. Let the reading is ‘A’ ml.

Chemical oxygen demand calculation

COD in mg/L= 8000 (A-B) N / V

Where,
A is the volume of FAS used in the blank sample, in milliliters.
B is the volume of FAS in the original sample, in milliliters.
N is the normality of FAS solution.
V = milliliters of sample used for the test.

Relation between BOD and COD

Now a days, water is contaminant by various type of organic substances. Chemical Oxygen Demand is an important water quality parameter as like BOD. But we cannot get a clear picture of all type of organic substances from the BOD values alone whereas COD values gives a better result. Because, biodegradable and non-biodegradable substances are includes in COD values. Consequently, COD values are larger than BOD. Moreover, the measurement of COD requires a shorter time about 2-3 hours. On the other hand bod requires longer time period 5 days. The higher the chemical oxygen demand, the higher the amount of pollution in the water.

Brand New COD-572 Chemical Oxygen Demand Meter Analyzer

Biochemical Oxygen Demand – BOD determination

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There is a close relationship between dissolved oxygen and biochemical oxygen demand. BOD is the amount of dissolved oxygen required to break down the organic material of the sample water by aerobic biological organisms at certain temperature over a specific time period. Generally this parameter is determined with the consumption of oxygen by the micro organism during 5 days of incubation at 20⁰C. It is expressed as milligrams/liter or ppm. It is also known as biological oxygen demand. You should remember that BOD is an indicator and not a pollutant.
biochemical oxygen demand

Importance of BOD

BOD is the best and reliable method to determine the level of pollution by the organic waste. Although it has some natural limitation but it is a significant method. It is important method to analysis the sewerage, industrial, effluent and extensive pollutant water. If one liter of sample water consumes 100mg of oxygen to biodegrade of organic matter, then the BOD is 100 ppm. The BOD value of drinking water should have less than 1 ppm. On the other hand the BOD value of raw sewerage runs from 200 ppm to several hundred ppm.

BOD indicates the amount of pollution of water bodies. Lower BOD indicates the water is good quality for aquatic life or little aerobic activity whereas higher BOD indicates the water is highly polluted. When the BOD is higher, then DO becomes lower. All the aquatic animals rely on this dissolved oxygen to live. So the reduction of DO in the water can bring a negative effect on the fish and other aquatic life. When it is drops below a certain level, the aquatic life are unable to continue at a normal rate. Aquatic organisms become stressed, asphyxiate, and may die.

Sources of organic materials

Common sources of organic materials are plant decay, leaves, grass clippings, woody debris; animal wastes; wastewater from residential areas, food processing plants, dairy plants, pulp and paper mills, canneries; septic systems leakage; fertilizer runoff and urban storm-water runoff. These organic materials run into water bodies and increases oxygen demand. Dead algae or other organisms are also part of the decomposition cycle. They are responsible for water pollution because they stimulate the growth of micro organisms that can increase the biochemical oxygen demand. All most all natural water contain small amount of organic materials.

Determination of BOD

The most common and popular method for determination of Biochemical Oxygen Demand is Standard Method which is recognized by U.S. EPA and leveled as 5210B. It is not a accurate quantitative test, although it is widely used as an indication of water pollution.

BOD test procedure

  1. At first analyzed and conditioned the water sample to ensure favorable growth conditions for bacteria, which may include adjustment for pH (6.5-7.5), neutralization of residual chlorine, or reduction of DO in supersaturated samples. If there is no or less oxygen in any sample then oxygen is provided to the sample water. To provide oxygen entered air into the water sample with fusion tube up to 5 minutes or the DO level up to 7 ppm.
  2. If BOD is higher than DO, then dilute the sample water with BOD free water (distilled water) to lower the BOD level.
  3. Then added the appropriate amount of seed bacteria. The selection of micro organisms (seed bacteria) is very important and the results are obviously not reproducible.
  4. Determination the initial DO (D1) of one portion of the sample.
  5. Then rest of the dilute sample filled into a 250-300ml incubation bottle. The sample incubates for 5 days in the dark room at 20 °C to prevent DO production via photosynthesis. You can cover the sample bottle completely with aluminum foil.
  6. After the 5 days, the sample is removed from the incubator and the bottles uncork, then take the final dissolved oxygen (D2) reading.
  7. The difference between the first and the last of the samples is called the BOD.

BOD calculation

Calculate the BOD from the DO depletion and volume of sample used following the formula below:
BOD calculation
Where:
D1 is the DO of the sample after dilution (ppm).
D2 is the DO of the diluted sample after 5 day incubation (ppm).
B1 is the DO of diluted seed sample after preparation (ppm).
B2 is the DO of diluted seed sample after 5 day incubation (ppm).
f is the ratio of seed volume in dilution solution to seed volume in BOD test on seed.
P is the decimal dilution factor. [For example, if a sample of 100 ml dilute into 500 ml, then P = 100/500 = 0.20].

BOD of some collected sample from different sources:

Sample BOD Remarks
Normal water 0-3 Acceptable
River water 5-20 Polluted
Sewerage water 50-100 Very bad water
Industrial water 150-1000 Worst water

Aquarium water treatment

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There are different sources of aquarium water. All are not suitable for it. So treatment is necessary. Moreover, you have to feed the fish. This can also create problems. The main aquarium water problems are algae, ammonia, nitrite, nitrate, phosphate, hardness, pH, alkalinity and temperature. In addition you have to always remember that not to add too many fish at a time or do not overcrowd and overfeed. These will create problems to your aquarium.

Aquarium water test

It is necessary to test your aquarium water regularly. This can be daily, weekly or monthly. The important tests are ammonia, pH, nitrite, and nitrate. These test should be perform weekly. You have to test temperature regularly.

Tap water
Tap water may include chlorine and chloramines because most of the municipal water is treated with chlorine to kill harmful bacteria or other pathogens. These chemicals can harm to fish and biological filter. So these chemicals should be removed before using them into aquarium. You can use different chlorine neutralizer or a chlorine remover such as dechlorinator, sodium thiosulphate, as a chemical additive. You have to make sure that you use a right dechlorinator because all dechlorinators does not remove chloramine from the water.

Water Changes
You can change up to twenty percent of the water each week depends on water quality.
Aquarium water treatment

Algae Treatment

A small amount of algae can be a source of fish food in the aquariums. So it is not harmful to fish, though it may look odd. On the other hand, excessive amount of algae growth is harmful to fish or other aquatic animals. Water, light, and nutrients are responsible to overgrowth of algae in the aquariums. It is the common problem in aquariums and ponds. So before aquarium water treatment you have to know what the root cause is.

Sometimes you can able to remove algae in manually. If it is not possible then you can use different chemicals to remove but you should bear in mind that the entire chemical is not suitable for all type of aquarium animals. Some are suitable for fish but they are not suitable for snails, live plants, shrimp, lobsters or any other invertebrate. So carefully uses the chemicals. Otherwise it will create great problems. If you have algae problems then you need to Phosphates test.

Ammonia problems

High Ammonia level in aquarium is one of the most serious problem. It can bring health problems of the fish or aquatic lives, even death of them. Newly set up aquarium will go through a process that some of biological colonies begin to grow quickly which are responsible for increasing ammonia in the tank. Moreover, too many new fish added at a time, die off bacterial colonies, filter fails due to power or mechanical failure are also responsible for increasing ammonia. Loss of appetite, red or purple color, tiredness, lay at the bottom and fish gasp for breath at the water surface are main symptom of the ammonia increases.

If the ammonia reaches risky level, then it should be taken a necessary action to reduce it. You can use different ammonia binder to decrease the ammonia level. For example available form of ammonia binders are liquid and filtration media. You can use the ammonia binder when the ammonia is extremely high whereas the filtration media can be used when levels are elevated, but not immediately critical. It should not exceed 0.30ppm.
aquarium water treatment
Seachem Prime 500ml

Nitrite problems
Nitrites is the another major killer of aquarium water fish. When the level increases then the fish blood reduces its ability to carry oxygen. Brown gills, rapid gill movement are the main symptoms. It is better to keep nitrite level up to 0.6 ppm. Above 1.0 ppm may be dangerous to fish. You can reduce excess nitrite by changing partial water. Moreover you can also reduce toxicity of nitrite by adding salt to the water.

Nitrates
Nitrates are less toxic then ammonia or nitrites. It does not directly affects on the fish at lower level. But at higher level, it may effects on their growth and can decreases oxygen levels. Nitrates will help to overgrowth of algae, even at low level like 10 ppm. If nitrate levels exceed 50 ppm then it should be reduced. You can reduce the level of nitrates by changing a portion of water or using filter media. Test monthly to keep the levels within the safe range. It produces through the nitrogen cycle. The main symptoms are loss of appetite, lay at bottom of tank, and rapid gill movement.

Nitrogen Cycle
Your aquarium water should have well balanced with beneficial bacteria for nitrogen cycle. These bacteria break down the unhealthy elements within the water. The cycle has three stages. The cycle begins with fish and their feces, urine, and uneaten food which are converted into ammonia compound shortly. Then these converted into Nitrite with the help of Nitrosomonas bacteria. At last stage the nitrites converted into Nitrates. This nitrogen cycle is a vital part of every aquarium.
aquarium water treatment
API Quick Start Water Conditioner for Aquariums

pH
pH is one of the important parameter for aquarium. There is no exact pH range. It may differ on the sources of the fish. Salt water and fresh-water fishes need different pH. Normally salt-water fish needs higher pH like 8.0 or above. On the other hand fresh-water fish needs lower pH ranges like 7.5 or below. pH is not a static parameter, it can change with time. If the pH increases then you can consider it may be increases ammonia. Moreover, fish and plant waste, water evaporation, topping off water, CO2 and water hardness can changes the pH.

To lowering the pH you can use acids or filtered water that has low buffering capacity. Otherwise you will not achieve your target. Buffering media would tent to remain same pH. To raise the pH you can use a base like sodium bicarbonate. As this base is a partial soluble compound so you can get benefit of buffering the water. If the pH does not match for specific spices of fish then it may stress on the fish. Sometimes you can loss fishes. It is better to test once a month. Generally, 6.0 to 8.5 pH level is excellent for fishes.

Phosphate problems
Including well maintained aquarium all of the aquariums are present phosphate. It may be organic or inorganic. The fish waste, uneaten food, plant decay, phosphates containing lower quality foods, dying algae, dead fish and pH buffers can increases phosphate levels. Sometimes it also depends on water sources. It does not directly harm to the fish. It helps to overgrowth of algae by providing nutrient.

If the phosphate level is too elevated, you can reduce it by using phosphate control additives or carbon filter media. Moreover, water changes and properly tank maintenance will also help to reduce it. The ideal levels of phosphate are 0.1 ppm or below.
aquarium water treatment
Blue Life USA Phosphate Rx Aquarium Treatment

Cloudy water
Occasionally, some fine particles like dirt, sand, silt or any other debris can creates the cloudy aquarium water. It makes the aquarium odd looking. To resolve this problem you can use flocculants, because different filter media does not able to remove these fine particles. The flocculants accumulate them which are removable.

Heavy metals
Trace amount of certain heavy metals like zinc, copper, lead and cadmium in the water are important to the health of fish and the stability of the water chemistry. But very high levels can be a problem as well.
aquarium water test
API Freshwater Master Test Kit
Temperature
Temperature is another important parameter for aquarium water. If it is quickly changes then it will harmful to fish or aquatic lives. You can use aquarium heater to keep stable water temperature.

Dissolved oxygen in water

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Dissolved oxygen (DO) means the amount of oxygen that is dissolved in the water. Oxygen is the essential element to all animals. No animals can survive without it. Dissolved oxygen in water makes aquatic life possible. Human being takes oxygen from the air with the lungs. On the other hand, Fishes take dissolved oxygen through their gills. Gills work better if the water contains more oxygen. Hence to growth and reproduction of aquatic life must have sufficient levels of dissolved oxygen (DO) in the water. Otherwise, it becomes harder for animals to get the oxygen. It is not visible to us. Moreover it is not the oxygen component of the water molecule H2O. It is express as milligrams per liter (mg/L) or ppm.

Higher DO level can increases the taste of drinking water. So many water companies try to keep higher dissolved oxygen in water. In the case industries dissolved oxygen is not good sign, it may corrosion the water pipes. It is also corrosive to boiler.

Sources of dissolved oxygen

Oxygen enters into the water by following ways (1) direct absorption from the atmosphere, (2) rapid movement, or (3) release of oxygen from aquatic plants during photosynthesis.

Photosynthesis: in presence of light and chlorophyll green plants and some bacteria produce Oxygen and glucose by using carbon-di-oxide and water. It is recognized as Photosynthesis process.

CO2 + H2O → O2 + C6H12O6

Moving water such as mountain stream or river is greatly contact with atmospheric air. Therefore they are able to mix with air that tends to dissolve more oxygen. On the other hand stagnant water contains less dissolved oxygen.

Dissolved oxygen levels in water

The solubility range of oxygen is about 5-14 ppm. Sufficient amount of dissolved oxygen is important to all forms of aquatic life. If the levels drop below 5.0 ppm then it would stress to aquatic life. Lower concentrations cause greater stress. If the oxygen levels go to below 1-2 ppm then large amount of fish may die. On the other hand 8-9 ppm is generally good fishing waters to support a large diverse fish population. Most aquatic animals cannot live in the areas where the dissolved oxygen level is less than 0.2 ppm. This is anoxic. Moreover, it will increase the solubility of many toxic elements such as lead, zinc, copper, hydrogen sulfide, ammonia, cyanide. In addition it can also alter the structure and diversity of aquatic communities. Although too much dissolved oxygen concentrations is a very rare but it may creates gas bubble disease of fish.

Dissolved oxygen test procedure

You can measure Dissolved Oxygen in different ways. Electronic meter is one of the important methods. It does not measure oxygen directly, it measure the partial pressure of oxygen in the water. Then it would convert to oxygen mass weight concentration. The BOD is another significant method. It determines the oxygen requirements during a specified period of organic matter degradation. The other methods are drop bottle (iodometric), a microburet, or a digital titrator. The amount of oxygen dissolved in water is often expressed as ppm or mg/l.
Dissolved oxygen in water
Extech 407510 Dissolved Oxygen Meter

Factors affecting dissolved oxygen in water

Several natural and man-made factors affecting dissolved oxygen in water such as temperature, nutrient pollution, altitude, salinity, organic waste.

Photosynthesis

The photosynthesis process occurs in presence of light and chlorophyll. Therefore huge amount of oxygen produces during day time. On the other hand the photosynthesis process terminates during night time. But at this time the respiration process occurs and consumes oxygen. As a result DO level higher at day time and lower at night time. Turbidity (due to suspended solids) can restrain the sunlight to go into the water that limits the photosynthesis process.

Temperature

There is a significant relationship between water temperature and DO concentrations. Oxygen easily dissolves in cool water. Cold water can holds more dissolved oxygen than warmer water. Moreover the solubility of oxygen in water decreases with the increases of temperature.

Seasonal changes

Seasonal changes is the another factor that affecting dissolved oxygen concentrations in water. During summer season the water becomes warmer. Therefore at this time water contains less DO. Conversely the water becomes cooler at the time of winter season. So this time the water holds more oxygen. Rainy seasons also effects on oxygen concentrations. As the rain water interact with the atmospheric oxygen then it tends to higher the dissolved oxygen level.

Altitude

The atmospheric pressure decreases at higher altitude. When the atmospheric pressure decreases then the solubility of oxygen in water also decreases. So the amount of oxygen decreases at higher altitudes than at low altitudes.

Salinity

Waters with high amounts of salt holds less oxygen than fresh water. Reason, the solubility of oxygen decreases if the salinity of the water increases. Hence the freshwater like lakes, streams, and tap water generally contains higher concentrations of DO than the ocean. Higher suspended solids in the water also decrease the DO.

Moving water

The ocean, rivers and streams water are moving water. When this water is moving then they contact with air. Oxygen concentrations are much higher in air than in water, which are about 21% and 5-14 mg/l respectively. This huge difference of concentrations helps to dissolve the oxygen into the water. Moreover the volume and speed of moving water can also affect on dissolved oxygen levels.

Organic waste

The water may contain a lot of organic waste including leaves, grass, dead plants or animals, organic chemicals and sewage. Microorganisms like Bacteria decompose these materials by taking up oxygen. Therefore the levels of dissolved oxygen drop in the water body.

Fertilizer

Fertilizer runoff from farm fields and lawns may decrease The DO. As like land plants the aquatic plants also grow better with these nutrients. These large amounts of nutrients such as nitrate and phosphate help to produce great quantities of algae. When these aquatic plants die, then the bacteria decompose them by using large amounts of DO. This process is known as eutrophication. As a result Dissolved Oxygen levels can drop too low.

Arsenic in drinking water

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Higher level of arsenic in drinking water is dangerous for health. It is a semi-metal element. In general it is naturally found in the earth’s crust. It is odorless, tasteless and colorless. So you are not able to conform if your drinking water is contaminant to the arsenic. You can only determine the presence and concentration of arsenic in water with the laboratory analysis. It should be kept arsenic levels in drinking water as low as possible. If you are living a higher arsenic containing area then you should read the test report if your water is public. On the other hand if your water system is private then you should test the water so that you can know what you are drinking. Your local or county health department and many private certified laboratories offer water testing for arsenic.

The both type of organic and inorganic arsenic are available but organic type of arsenic is not found in drinking water. Normally organic arsenic is found in different types of foods. There are two types of inorganic arsenic is found in ground water. These are As3+ (arsenite) and As5+ (arsenate).

If you notice high level of arsenic in your drinking water, then you need to look for an alternate water source. This water must be lower levels of arsenic. Several short-term and long-term solutions are available. You can install in home water treatment device to reduce arsenic in drinking water. Otherwise you have to purchase bottled water for drinking and cooking purposes until you installed a permanent one.
Arsenic in drinking water

Source of arsenic in water

The main source of drinking-water is lakes, streams, rivers or underground. Arsenic can enter these drinking water sources through the arsenic rich rocks, agricultural arsenic based pesticides and industrial practices such as mining, wood preservatives, textile, transistor, semiconductor, pigments. Environment is another source of arsenic. It can enter into the environment as a dust through the burning of fossil fuels, mining, waste burning, and pesticides. These arsenic particles get into water through the water flows of rain or snow. It seeps into groundwater. Usually groundwater contains higher amount of arsenic than surface water.

Arsenic occurs naturally in soil and bedrock in many parts of the United States, including parts of upper New England (Massachusetts, New Hampshire, Maine), New Jersey, Florida, and large parts of the Upper Midwest, the Southwest (like Nevada), and the Rocky Mountains. It occurs extensively in some countries like Bangladesh, India.

Effects of arsenic in water

Contact with high levels of arsenic in drinking water can causes many long-term and short-term health effects such as thickening and discoloration of the skin, nausea, stomach pain, diarrhea, Vomiting, decreased production of blood cells, abnormal heart rhythm and blood vessel damage, numbness in the hands and feet, Partial paralysis, Blindness, skin rash. Several types of cancers are related to arsenic such as bladder, lungs, skin, kidney, nasal passages, liver, and prostate cancer. Many studies in Bangladesh, Taiwan, Chile and Argentina on arsenic support for cancers. Bangladesh is one of the higher arsenic containing country where arsenic obtained up to 1 ppm. The health risk depends on the concentration of arsenic, amount of water, length of consuming time and individual sensitivity to arsenic.

When you consume arsenic contamination water then bloodstream distributes it throughout the body. It does not able to enter into the body through the skin during showering or by inhalation during bathing. Therefore, it is safe to use the water during showering, bathing and other household work, if the arsenic level is over 0.01 ppm. We found high arsenic levels at nails and hair in our body. Here, arsenic accumulate over long-time. Our body releases a great amount of arsenic through the urine. Moreover, a small amount of arsenic removes through the skin, hair, nails and sweat.

Arsenic levels in water

Environmental Protection Agency (EPA) of USA approves a lower standard of 10 ppb or 0.01 ppm of arsenic in drinking water. Previously it was 50 ppb. It reduces to 10 ppm due to threat of bladder and lung cancer. This level protects consumers from the health effects of long term constant contact to arsenic. Consuming above 0.01 ppm arsenic containing water for a long-term will increases chronic health problems. If it is more than 0.01 ppm, then you should look for another water source or install home treatment equipment. Children and pregnant women are greater risk of arsenic.

Arsenic test

Arsenic in drinking water is odorless, tasteless and colorless. The only way to tell if arsenic is present is to test for it. If you are living in arsenic containing area then it is recommended that you should test your water. To arsenic test you should contact your regional public health office or commercial labs. Moreover, you have to conform that they can measure low level arsenic (as low as 1-2 µg/L). If your water is municipal supply water then you should contact the local drinking water authorities to know the arsenic level.
Removing arsenic from water
iSpring RCC7 Built in USA WQA Gold Seal Certified 5 Stage Reverse Osmosis Water Filter, 75 GPD, Transparent 1st Stage & Designer Faucet

Removing arsenic from water

There are two types of arsenic in water. These are arsenic-3 and arsenic-5. Among them arsenic-3 is very difficult to remove from water. Therefore, it must be converting into arsenic-5 to remove. Oxidation is the appropriate method to convert arsenic-3 to arsenic-5. The most common oxidants are liquid chlorine (bleach), hydrogen peroxide, and ozone. Among them chlorine is the most readily available oxidant for home water treatment. The other factor to removing the arsenic in drinking water is the possible presence of other element as like iron and manganese. It may act as a hinder the effectiveness of arsenic removal. So you must remove it from the water before arsenic treatment.

The available systems for removing arsenic from water are anion exchange, reverse osmosis, activated alumina and other types of adsorptive media filters. These systems are categories into two types; point-of-entry treatment (POET) and a point-of-use (POU). The POET system treats the entire household water. On the other hand, POU treats kitchen tap water. You can contact your local health department or a water treatment company to determine which type of arsenic removing system works best in your area. All the systems have advantages and disadvantages. People use the POU treated water only for drinking and cooking purpose.

Anion exchange:

In this system arsenic is exchanged by the chloride. Generally people use it to treat water for the entire house. It requires little maintenance. When arsenic replaces all the chloride ions, then it is required to regenerate the resin. Normally we we use a suitable chloride containing compound such as NaCl solution as regeneration medium. It is one of the best methods to remove arsenic in drinking water.

Reverse osmosis (RO):

Generally we installed reverse osmosis as a point-of-use treatment system. Usually, it needs pre-filtration system to remove sand and gravel that can foul the RO membrane. It is ineffective to removing arsenic-3.
Removing arsenic from water
APEC – Top Tier – Built in USA – Ultra Safe, Premium 5-Stage Reverse Osmosis Drinking Water Filter System (ROES-50)

Adsorptive media filters:

There are several types of adsorptive media available such as activated alumina (AA) and granular iron oxide. Commonly we use it for point-of-use treatment systems. These systems are also not able to remove the arsenic-3. It is more expensive than reverse osmosis system. The adsorptive media filter consist an adsorptive media cartridge that can be replacing about every 6-12 months. This ongoing cost is the drawback of this system. The granular iron oxide system effectively removes arsenic from water in both POET and POU systems. It is easy to operate and maintain.

3 Stage 20″ Big Blue Whole House Activated Alumina Water Filter w/ Radial Flow Carbon Block – Removes Fluoride, Arsenic, Sediment, Chlorine, & Chloramines

Distillation process

As like permanent hardness arsenic does not remove by boiling water. It will increase the concentration of arsenic in water as the water evaporates at 100 ⁰C. But you can apply the distillation method to produce several gallons of arsenic free water per day. In this case you have to boil the water then condensate the water.

Conclusion
After above and related discussion we may come to the conclusion that the problems of arsenic in drinking water is a great problem of international. WHO, many NGO and other UN-system organizations are working in many countries to remedies the problems of arsenic in water. However, taking massive actions against arsenic contamination is a must.

Swimming pool chlorine stabilizer

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Cyanuric acid used as a swimming pool chlorine stabilizer. The Chlorine sanitizes the pool water and keeps the water clean and safe for the swimmers. In presence of sun light and high temperatures it is very unstable; it breaks down into inactive components and losses its effectiveness. Therefore to maintain the chlorine level for water disinfection, we have to add more amount of chlorine. It increases the chemical cost. The pool Cyanuric acid reacts with the free chlorine and forms a compound to give it more stability in sunlight. Consequently, it reduces the loss of free chlorine in presence of UV light. In other words, it reduces the cost of pool water maintenance. If you neglect it then you will loss huge amount of chlorine.

Cyanuric acid is also known as CYA. The chemical formula of it is (CNOH)3. It is white and odorless solid. It has lower pH.

As the sunlight doesn’t enter the indoor pools, so you do not need stabilized the pool. In this case 5-10 ppm Cyanuric acid is enough. It will lessen the chloramines formation.

Without stabilizer a pool can loss about 80-90% of its free chlorine within a few hours in presence of UV rays.
Swimming pool chlorine stabilizer
In The Swim Pool Chlorine Stabilizer and Conditioner – 10 lb. Bag

Cyanuric acid test
It is recommended that you should regular test of your swimming pool chlorine stabilizer to keep the appropriate levels. The chemical test for pool cyanuric acid is very easy. You can determine it with the test strips. If the stabilizer level is too low then you have to add the required amount to bring the level up.

Pool stabilizer levels
The acceptable pool stabilizer levels are 30 – 80 ppm. To properly maintain the ideal level is about 35-50ppm. The ideal level may differ depends on region. For example, in northern areas the ideal range is 20-40 ppm. On the other hand, in some region the acceptable is up to 100ppm. Low or high cyanuric acid in pool is not recommended, both are harmful to pool.

High cyanuric acid in pool

Higher swimming pool chlorine stabilizer levels can slower the effectiveness of chlorine. Therefore it is not able to kill bacteria and micro-organisms, and prevent algae. Moreover, it also increases the cloudiness of pool water. In contrast there is no evidence that it is carcinogenic. If the pool stabilizer level cross the 100ppm, then your chlorine can turn into ineffective.

Swimming pool chlorine stabilizer
Natural Chemistry Liquid Swimming Pool Stabilizer and Conditioner – 1 Gallon

Lowering cyanuric acid in pool
There is no chemical available in the market to lower the stabilizer. You should regular monitoring it to maintain the acceptable level. You can follow the following method to lowering the swimming pool chlorine stabilizer.

Replace with fresh water: You can replace a portion of pool water with fresh water. However the replacing of water is very costly.

Used non-stabilized chlorine product: Different stabilized chlorine products are available in the market such as dichloro or trichloro products. These types of stabilized chlorine products may contain up to 5% or higher stabilizer. They could increases the level of Cyanuric acid. Hence, if the level is too high, you should use non-stabilized chlorine product when needed. You should know that regular backwashing helps to stay the pool stabilizer level lower.

Low cyanuric acid in pool

We know that low cyanuric acid in pool can’t able to stabilize the chlorine properly. Therefore, free chlorine can be released into air. As a result it cannot do sanitized pool water perfectly. If the cyanuric acid test shows that the level is low, then you have to need add the stabilizer. For example to raise about 20ppm for a 3000 gallons swimming pool, you have to add about 200 gm. Swimming pool chlorine stabilizer is dropped due to drain, backwash, splashout or winterization.


Determination of permanent hardness of water

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The available methods for determination of permanent hardness of water are O’Heners method, EDTA method and Soap titration method. Initially we have to know; what is hardness? –Hardness is due to presence of bicarbonate, sulphates, chlorides and nitrates of calcium and magnesium. It is expressed in ppm (part per million) as calcium carbonate. There are two types of hardness:

  1. Temporary hardness
  2. Permanent hardness

Bicarbonate of calcium and magnesium is responsible for temporary hardness whereas sulphates, chlorides and nitrates of calcium and magnesium are responsible for permanent hardness. The salt of Na, K and NH4- do not reacts with soap; hence the presence of these salt do not creates hardness of water.

Determination of permanent hardness of water by O’hehners method
Theory: At first, the water is boiled to remove temporary hardness. When the water is boiled then, the Bicarbonate of calcium and magnesium are change into non-dissolve carbonate.
Ca(HCO3)2 → CaCO3 + H2O + CO2
Mg(HCO3)2 → MgCO3 + H2O + CO2

After that, added Na2CO3 solution. This chemical reacts with dissolved calcium and magnesium salts and converts them into insoluble carbonate.
CaCl2 + Na2CO3 → CaCO3 + 2NaCl
MgCl2 + Na2CO3 → MgCO3 + 2NaCl
The residue Na2CO3 is then determined by titrating against a standard acid. The reduction in the amount of soda added is equivalent to permanent hardness.
Burette for determination of permanent hardness of water

BrandTech 4761161 Borosilicate Glass 50mL Titrette Bottletop Burette, with Titration and Recirculation Valve

Apparatus

  • Beaker
  • Weighing Balance
  • Burette with stand
  • Pipette
  • Conical flask
  • Hot plate

Chemicals

  • N/10 Sodium carbonate solution
  • N/10 HCl acid

Indicator

  • Methyl orange

Procedure:

  1. Take 50ml of water sample into a 500ml beaker and boil for 15 min.
  2. Add 50ml of N/10 Na2CO3 solution into it with stare.
  3. Separate the precipitate with filter paper and wash the precipitate 3-4 times with a little distilled water. Take the filtrate and cool the solution to room temperature. Then, take it into a 250ml volumetric flask and dilute it up to the mark with distilled water.
  4. Take 50ml in a conical flask from volumetric flask with a pipette and titrate it against N/10 HCl using Methyl orange indicator. At the end point the color of the solution turns into reddish yellow.
  5. Take the burette reading. Let, it is v ml.
  6. For blank titration, take 50ml of N/10 Na2CO3 solution into a 250ml volumetric flask and dilute it up to the mark with distilled water. Take 50ml in a conical flask from it with a pipette and titrate it as same process against N/10 HCl using Methyl orange indicator.
  7. Determine the consumed N/10 Na2CO3 solution from the difference of this two reading.

1ml 0.1N HCl ≡ 0.005005g CaCO3

Calculation:
Volume of N/50 Na2CO3 used for removing permanent hardness in 50ml of water sample
=50 -43.5 = 6.5 ml
Normality of water due to permanent hardness:
N1V1 = N2V2
N1 × 50 = N/50 × (6.5)
N1 = 6.5 /50 × 50 = 0.0026
Amount/Lit = N × Eq.wt
= 0.0026 × 50 = 0.13 gm/lit
Mg/lit = 0.13 gm/lit × 1000mg/1gm = 130 mg/lit
As,
1mg/lit = 1ppm
Permanent hardness = 130 ppm
Result: the given sample of water contains 130ppm permanent hardness.

Determination of permanent hardness of water by EDTA method:
The temporary hardness can be removed by boiling. The permanent hardness is determined first by precipitating the bicarbonates of Ca2+ and Mg2+ by heating and filtering off.

Procedure:

  1. Take 100ml of water sample into a beaker and boil gently for 15-20 minutes.
  2. Cool the solution then filter and wash the precipitate several times. Collect both the filtrate into a 250ml volumetric flask and level upto the mark with distilled water. Then, shake well.
  3. Take 50ml of solution from volumetric flask with pipette and place into a conical flask.
  4. Add 1-5ml NH4OH/NH4Cl buffer solution. It increases the pH level and should be 10. Check the pH with standardize pH meter.
  5. Add 2-3 drops 0.1M Mg-EDTA solution and 3-4 drops Eriochrome Black T indicator. Then, shake well and the color becomes wine red.
  6. Fill up the burette with standardized 0.01M EDTA solution. Record the initial burette reading and titrate the water sample with this standard solution.
  7. At the end point the color of the solution turns into blue from wine red. Titrate carefully near the end point.
  8. Take the final burette reading. Let, it is V1 ml.
  9. Repeat the titration process at least three times.
  10. You can run a blank titration for more accurate result. Let, it is V2 ml.

Water sample Vs EDTA

Serial No Volume of water sample (ml) Burette readings (ml) Volume of EDTA solution (ml)
Initial Final
1
2
3

Permanent hardness calculation:
In case of blank titration, the calculate volume of EDTA required by sample water, V = (V1-V2)ml
The permanent hardness can be calculated by using the following formula.
1ml 0.01M EDTA ≡ 1.00mg CaCO3
∴ Vml 0.01M EDTA = V ᵡ 1.00mg CaCO3

The 100ml sample water is dilute into a 250ml volumetric flask
Hence, 50ml dilute water = 100 ᵡ 50/250 ml = 20ml sample water

Now, 20ml of sample water ≡ V ᵡ 1.00mg CaCO3
∴ 1000ml of sample water ≡ V ᵡ 1.00mg ᵡ 1000/20 CaCO3
≡ V ᵡ 1.00 ᵡ 50 ppm CaCO3

Result
Amount of permanent hardness present in the given water sample = ppm

Determination of total hardness of water

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To determine the Total Hardness of Water, EDTA is the easiest method. Reason, EDTA reacts with all metal without alkali metal and the proportion is 1:1. The main cause of water hardness is dissolved salts of calcium and magnesium. Moreover the other ions like Strontium, Iron, Barium and Manganese also contribute of water hardness. Traditional it is measured by the amount of soap that is required to produce leather. The EDTA method is more accurate and more rapid.

Mn+ + Na2H2EDTA → [M-EDTA](4-n)- + 2Na+ + 2H+

There are two types of hardness: (1) temporary hardness and (2) permanent hardness.
The temporary hardness is due to the presence of Ca(HCO3) or Mg(HCO3) or both. On the other hand, permanent hardness is due to the presence of sulphates, chlorides and nitrates of calcium and magnesium (as like CaCl2, CaSO4, MgCl2 and MgSO4) in water.

To determine the Total Hardness of Water with EDTA method initially an inorganic acid is added to convert temporary hardness into permanent hardness.
Ca(HCO3)2 + 2HCl → CaCl2 + H2O + 2CO2

At pH 10, EDTA forms colorless, water soluble stable complexes with calcium and magnesium ions. When the indicator Erichrome black T dye is added into the hard water, then the indicator forms unstable complex with calcium and magnesium ions and the solution turn into wine red. If there is no hardness the color becomes blue which is original color of indicator. Now, when this solution is titrated against EDTA, then the calcium and magnesium ions started to form a stable metal-EDTA complex. After all the free calcium and magnesium ions are consumed, the EBT is replaced by EDTA from the unstable complex and liberates the free Eriochrome Black-T. Then the water color change from wine red to blue that indicates the end point.

Apparatus:

  • Conical Flask
  • Funnel
  • Burette
  • Sand
  • Beaker
  • Pipette
  • Graduated cylinder
  • Hot plate stirrer
  • Wash bottle
  • Spatula

Chemicals:

  • Buffer solution
  • Inhibitor
  • Eriochrome black T indicator (blue color)
  • NaOH
  • Standard EDTA Solution 0.01M
  • Magnesium sulphate

Procedure:

  1. Take 50ml of water sample into a conical flask.
  2. Then add 2-3ml 1:1 HCl and boil for 2 min.
  3. Cool the solution and neutralized with the dil NaOH.
  4. Add 1-5ml NH4OH/NH4Cl buffer solution. The pH should be 10. Check the pH with standardize pH meter. (you can also add an Inhibitor, after the buffer solution)
  5. Add 2-3 drops 0.1M Mg-EDTA solution and 3-4 drops Eriochrome Black T indicator. Then, shake well and the color becomes wine red.
  6. Fill the burette with standardized 0.01M EDTA solution. Record the initial burette reading and titrate the water sample with this standard solution.
  7. At the end point the color of the solution turns into blue from wine red. Titrate carefully near the endpoint.
  8. Take the final burette reading. Let, it is V1 ml.
  9. You can run a blank titration for more accurate result. Let, it is V2 ml.

Total hardness calculation:

Serial No Volume of water sample (ml) Burette readings (ml) Volume of EDTA solution (ml)
Initial Final
1
2
3

In case of blank titration, the calculate volume of EDTA required by sample water, V = (V1-V2)ml
The total hardness (temporary + permanent) can be calculated by using the following formula.

1ml 0.01M EDTA ≡ 0.001001g CaCO3
∴ Vml 0.01M EDTA = V ᵡ 0.001001g CaCO3

Now, 50ml of water sample ≡ V ᵡ 1.001mg CaCO3
∴ 1000ml of water sample ≡ V ᵡ 1.001mg ᵡ 1000/50 CaCO3
≡ V ᵡ 1.001 ᵡ 20 ppm CaCO3