Water treatment and Analysis

MD.AZMERI LATIF BEGM. Sc in Textile Engineering

Specialized in Apparel Manufacturing, Processing and Designing

Water Treatment and Analysis

INTRODUCTION The fresh water is rarely used directly for drinking purposes,

as the water gets contaminated with impurities during its transportation to the city reservoir. Even, the water which is to be used for industrial process also needs a pretreatment. For instance water for textile industry should not contain too much of iron, as it causes staining of fabric. Water for food industry cannot afford to have manganese, as it causes staining of containers and adversely affects the taste and quality of material cooked in that water. The boiler feed water should not contain excess of salts of calcium and magnesium, as they consume more heat due to insulation of containers and pipes by deposition of scales.

Water Treatment and Analysis

A substance that in its purest form is odorless, colorless and tasteless and is needed for survival by every living being. 

Classification of Water:

Water can be classified into three types according to the source: Surface water Subsoil water Deep well water

Surface water:Rain inevitably finds its way into stream, rivers and lakes, all of which are classified as surface water. As is passes over the surface of the earth it carries with it or organic matter in various stages of decomposition. Nitrifying bacteria will in the time convert the organic substances into nitrous which are not objectionable in dyeing and finishing.

Water:

Subsoil water:When in this classification is collected from shallow spring and wells which are about .15m (50ft) or so deep. It is, therefore, surface water which has percolated a short distance through the soil or rock formation.

Deep well water:The deep wells are those which are bored through the subsoil into the water bearing strata beneath.

Water:

The treatment procedure also vary depending upon its use. However, overall picture of water treatment, irrespective of end use shall be considered. An endeavor is made to comprehend the basic chemistry involved in water treatment process. The important stages involved in treatment are as follows: coagulation or flocculation; sedimentation; filtration – slow sand, rapid sand filtration; disinfection – including chlorination and ozonolysis; removal of iron and manganese; softening by lime-soda ash process or deionization method; scale and corrosion control; taste and odor removal; prophylaxiation treatment, i.e., fluoridisation; and specialized treatment for a specific purpose.

Important Steps in Water Treatment

This is the first important step in the water treatment. The principal coagulants used in water treatment consists of aluminum sulphate, ferric chloride, ferrous sulphate. The important reactions involved in flock formation with alum are as follows:Al2(SO4)3 + 3Ca(HCO3)2 → 3CaSO4 + 2Al(OH)3 + 6CO2

Al2(SO4)3 + 3Ca(OH)2 → 3CaSO4 + 2Al(OH)3

Al2(SO4)3 + 3Na2CO3 + 3H2O → 2Al(OH)3 + 3Na2SO4 + 3CO2

Al2(SO4)3 + 6NaOH → 2Al(OH)3 + 3Na2SO4

\

Figure: Water management 

This flock of Al (OH)3 absorbs dirt and color during sedimentation. The reaction with ferric chloride coagulation process is as follows:

2FeCl3 + 3Ca(HCO3)2 → 3CaCl2 + 2Fe(OH)3 + 6CO2

2FeCl3 + 3Ca(OH)2 → 3CaCl2 + 2Fe(OH)3

While with FeSO4 and chlorine,Cl2 + 2FeSO4 + 3Ca(HCO3)2 → 2Fe(OH)2 + 2CaSO4 + 6CO2 + CaCl2 FeSO4 + Ca(OH)2 → Fe(OH)2 + CaSO4

FeSO4 + Ca(HCO3)2 → Fe(OH)2 + CaSO4 + 2CO2

2Fe(OH)2 + ½ O2 + H2O → 2Fe(OH)3 The last reaction in the presence of dissolved oxygen is critical. The effectiveness of a coagulant is

determined by the magnitude of zeta potential. The zeta potential is defined as the charge on ions surrounding suspended particulate matter. The charges are usually negative and are expressed in terms of mill volts.

COAGULATION

Rejection

Accumulatinon

Circulation

Collection

Recycle

Water origin

Applications

Treatment

This treatment does not involve any chemical process, nevertheless it is an important aspect of water treatment. This is physical process of settling of floc. Sedimentation may occur within 15 to 60 minutes duration after vigorous stirring of water with baffles, which in turn expedites the agglomeration process. In this process the color of water is also removed, as colored molecules form basic insoluble salts. The settling tanks are of various sizes and shapes. They have horizontal flow or circular flow or static settling tanks. Sludge clarifier ensures proper circulation and controls the turbulence, or excess of stirring during process of settling. The large particles settle early in comparison with small particles. The shallow depth sedimentation is efficient.

SEDIMENTATION

FILTRATION The main role of filters is to retain the particles contained in a liquid

on the surface of filter media or in-depth. Surface filtration requires supporting media, while in-depth filtration is performed through a filter bed. The dissolved solids in the presence of chloride, sulphates of magnesium and sodium increase bed penetration by flock. The real filtration takes place in the first 3 to 4 cm in total height of 80 cm filter bed. The slow sand filters involve filtration of water without previous treatment, while rapid sand filters are used for water which has been previously treated by coagulation or sedimentation. Anthracite coals are used for filtering media along with sand and gravel. The filter beds are usually cleaned by back washing. In rapid filtration, water passes through bed. Washing of filter bed leads to expansion of the filter bed. However, simultaneous air and water washing proceeds without expansion of filter bed.

REMOVAL OF IRON AND MANGANESE From drinking water, Fe and Mn must be removed, as

they cause corrosion of pipes, affect appearance of water, impart metallic taste and cause laundering problems. The paper and textile mills also cannot tolerate their presence in processing water. In underground water, they are present in reduced form for want of oxygen. The metal is present in complex form.

Zeolites are cheaper. Zeolites are complex alumina silicates of alkali metals. The reaction with zeolites are-

Na2Z + Fe+3 → Fe-Z + 2Na+ Na2Z + Mn3+ → Mn-Z + 2Na+

The process of decreasing the hardness of water is called softening. It involves decreasing the concentration of calcium and magnesium salts in water.

The term softening is applied to the process whereby we remove or reduce the hardness or water, irrespective of whether it is temporary (or carbonate) or permanent (or non-carbonate) hardness. We have seen that hardness in water is objectionable because boiling a solution containing Ca2+ and HCO3

- deposits CaCO3 just as in cave formation. In industrial boilers the formation of CaCO3 is an economic headache, because CaCO3 is a poor heat conductor. Fuel efficiency is drastically cut and boilers have been put completely out of action by local overheating due to boiler scale.

SOFTENING OF WATER

Natural water containing large quantities of dissolved salts of calcium and magnesium is called hard water. The salts responsible for hardness are not harmful to man, but when magnesium is present in large quantities; it impairs the organoleptic properties of water. The maximum permissible quantity of magnesium oxide in water is 15 mg/liter . Excess magnesium salts (over 50% of the total volume of liquid) make water softening a difficult problem.

SOFTENING OF WATER

Using hard water for domestic and industrial purposes is undesirable for the following reasons:

A lot of soap is required for washing. The Ca2+ and Mg2+ ions react with soaps, which are salts of fatty acids, to give insoluble precipitates, (C15H31COO)2Ca and (C17H35COO)2Ca, and similar salts of magnesium. Water with a hardness of 7.1 mg-eqiv will require the use of an extra 2.4 g per liter of soap.

The premature wearing out of fabric after laundering in hard waters. The fibers adsorb calcium and magnesium salts and this makes them brittle.

Meat and beans loss much of their nutritional value when boiled in hard waters, the boiling time is increased, and proteins extracted form meat pass into an insoluble form and their assimilation becomes difficult.

The intense corrosion of boilers and hear exchangers because of the hydrolysis of magnesium salts and the increased connection of H+ ions in the solution.

Mg2+ +2H2O → Mg(OH)2 + 2H+

SOFTENING OF WATER

Scale deposits on the surfaces of heat exchangers (boilers, condensers) reduce the efficiency of such equipment. Scale has low heat conductivity and increases fuel consumption. Metal under scale deposits overheats and becomes soft. Boiler tubes begin to budge and crack. The scale should therefore be removed periodically.

 Scaling is connected with the thermal decomposition of bicarbonates, hydrolysis of carbonates, and also decreased solubility in hot water of calcium sulphate, magnesium hydroxide, and silicates of Ca and Mg. The concentration of these substances increases in boiler during water evaporation. Moreover, additional quantities of silicates of Mg and Ca can be formed at high temperatures.

CaSO4 + Na2SiO3 → CaSiO3 + Na2SO4

Salts of Fe, Mn, Al and suspended and colloidal particles are also involved in scale formation. The scale deposit can sometimes be so thick that it almost totally blocks the passage.

SOFTENING OF WATER

One way is to add sufficient quantities of soap. Thus enough steerage ions are added to precipitate all the objection-able Ca2+ ions, leaving the excess soap to carry on the cleansing action.Another way is to boil the water. The temporary hardness, which is attributed to the presence of bicarbonates of calcium and magnesium can be removed simply by boiling the water or by adding lime to the hard water. The soluble bicarbonates of calcium and magnesium decompose on boiling and are precipitated as insoluble carbonates which are allowed to settle and water is filtered off.

Ca(HCO3)2 CaCO3 + CO2 + H2O Mg(HCO3)2 MgCO3 + CO2 + H2O

The major question is how to soften hard water effectively and economically.

The reactions are reversible, but the forward reaction can be made dominant by boiling off the CO2. Boiling, however, is not practical for large scale softening.In the Clark’s process, calculated amount of lime is added to the hard water, whereby the bicarbonates are converted into insoluble carbonates and are removed as above.

Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2 H2O

Permanent hardness is caused by the presence of sulphates and chlorides of calcium and magnesium and can not be removed by merely boiling or adding lime. Special methods are used for the removal of permanent hardness. So the third way to soften water is to precipitate Ca2+ by adding washing soda, Na2CO3. The added CO3

2- ions react with Ca2+ ion to give insoluble CaCO3. If bicarbonate ion is present, the water may by softened by adding a base such as ammonia. The base de–protonates HCO3

- to give CO32-, which then precipitates the Ca2+. A fourth

way to soften water is to tie up the Ca2+ ion so that it becomes harmless. One way to do this is to form a complex containing Ca2+. Certain phosphates, such as sodium phosphate (Na3PO4) act as sequestering agents by forming complexes in which Ca2+ is trapped by the phosphate.

The major question is how to soften hard water effectively and economically.

The fifth and most clever method of softening water is to replace the offending calcium ion by another ion such as Na+. This is done by the process called ion exchange. The ion exchangers originally used for softening water were naturally occurring silicate materials, called zeolites. The giant silicate network of a zeolite is negatively charged and is composed of covalently bound silicon, oxygen, and aluminium atoms. Zeolites are very closely related in structure to the clays, which also show ion exchange. The mobile Na+ ions in the pores can be readily exchanged for Ca2+ ions.

The major question is how to soften hard water effectively and economically.

To understand the principle of cat-ion exchange, consider the structure of a natural zeolite, NaAlSiO4. In it atoms of aluminium, silicon and oxygen are bonded together to form a huge macro anion similar in structure to a macromolecule such as quartz. The negative charge of the anion is balanced by Na+ ions trapped in holes in the anionic lattice. Nothing will happen when pure water is passed through the zeolite because Na+ ions cannot leave the crystal lattice because in that case there would be an unbalance of charge. When hard water is passed, through the zeolite, some of the Na+ ions migrate out of the lattice, being replaced by equivalent number of Ca2+ ions.

Ca2+ (aq) + 2 NaZ (s) → CaZ2 (s) + 2 Na+ (aq)

Thus Ca2+ or Mg2+ ions responsible for hardness can be replaced by two less objectionable Na+ ions. After a zeolite column has been used for some time, more and more of the vacancies in the lattice become filled with Ca2+ ions. Hence an equilibrium is reached beyond which no further exchange of cat ions will occur. The column is regenerated by flushing with a concentrated solution of NaCl. As a result, above reaction is reversed and zeolite is ready for use.

The major question is how to soften hard water effectively and economically.

In this process, the lime treatment is followed by the addition of soda ash (Na2CO3) as result of which calcium ions in the hard water are removed as CaCO3 and magnesium ions as Mg(OH)2. This process is used for the removal of temporary as well as permanent hardness and has been divided into the cold lime process and the hot lime process. The cold lime process is used for partial softening of water, say from 100 ppm to 35 ppm of hardness. The hot lime soda process is employed almost entirely for conditioning the boiler feed water. The reactions involved are:

LIME SODA PROCESS

For Carbonate Hardness:

Ca(HCO3)2 + Ca(OH)2 → 2 CaCO3 + 2 H2O

Mg(HCO3)2 + Ca(OH)2 → MgCO3 + CaCO3 + 2H2O

Since MgCO3 is fairly soluble, it reacts further in the following manner.

MgCO3 + Ca(OH)2 → Mg(OH)2 + CaCO3

For Permanent Hardness:

MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2

CaCl2 + Na2CO3 → CaCO3 + 2NaCl

CaSO4 + Na2CO3 → CaCO3 + Na2SO4

MgSO4 + Na2CO3 + Ca(OH)2 → CaCO3 + Mg(OH)2 + Na2SO4

LIME SODA PROCESS

It is evident from the above reactions, that in case of temporary hardness, each unit of calcium bicarbonate requires one mole of lime, whereas for each unit of magnesium bicarbonate two moles of lime are needed. In the case of permanent hardness, the magnesium salts require one mole each of soda ash and lime, whereas the calcium salts require one mole of sods ash. In other words, for the removal of permanent hardness by Na2CO3, no lime is necessary to remove permanent hardness caused by calcium salts only, but some lime is necessary to remove such hardness caused due to the presence of magnesium salts. If there is excess of lime in the softened water, the water will be made hard due to the presence of soluble Ca(OH)2. Hence it is most essential to add requisite amounts of Ca(OH)2 and Na2CO3 to the hard water. For removing 10 ppm of hardness from one million gallon of water, the following quantities have been proposed.

LIME SODA PROCESS

Ca(HCO3)2 hardness (expressed CaCO3) – 521 lbs of lime.

Mg(HCO3)2 hardness (expressed as CaCO3) – 1040 lbs of lime.

Calcium non-carbonate hardness (expressed as CaCO3) – 900 lbs of soda ash.

Magnesium non-carbonate hardness (expressed as CaCO3) – 900 lbs of soda ash, 520 lbs of lime.

LIME SODA PROCESS

The cat ion exchange resin in H+ form, is used while anion exchange resin is used in OH- hydroxyl form. A strongly acidic resin (like vinyl styrene DVB copolymer with sulphonation) is used as cat ion exchanger, while basic anion exchanger (also vinyl styrene base with labile OH – group) is used for removal of anions. The important reactions are:

H2R + CaCl2 → CaR + 2HCl

H2R + MgCl2 → Mg-R + 2HCl

H2R + CaSO4 → CaR + H2SO4

H2R + MgSO4 → MgR + H2SO4

Then water is passed on anion exchanger RNH3OH

DEIONIZATION OR DEMINERALIZATION METHOD

Industrial water treatment Plant(WTP)

WTP contains three filter these are given below: 1) Multimedia filter : Only stone remaining in this filter of tank.2) Activated Carbon filter : Activated carbon in upper side & stone in lower side.3) Resin filter (Softener vessel) adjusted with NaCl vessel: Resin in upper side & stone in lower side.

Procedure :At first water come inside the multimedia filter by input pipe. Then water pass to second tank means carbon tank. Here polluted water must be purified and pass to the next tank or Resin tank. It is very important tank for wtp. In this tank, Resin must be given for washing water. Wastage of other tank and polluted water wastage are remove in this tank by extra pressure. Resin hold the ca, mg in attach with it. After that it hold clean water supplied. Next supply to clean water(hardness of water must be 5 above). Incase of Resin damage, then it can not hold ca, mg, at this time supply of water to dyeing must be stopped. At this moment additional tank is used with the resin tank. Here used (NaCl - 550 kg + Water 1500 Lt). It is used to clean the resin tank. It is also used to increase the activity of resin tank.

After this treatment, all Salty water should be drained by pressure. Then water is used to dyeing section supply again. This system is also called back wash. Water treatment plant is used for the removal of Water hardness, creosote and pesticides from the liquid phase in a timber treatment facility. A storage tank is used for smoothing the flow, from where the water is pumped into a chemical dosing system for pH adjustment. At this stage, ferric sulphate is added to form a precipitate with suspended solids, which is subsequently flocculated by the addition of polyelectrolyte.

Water is then pumped through series operated sand filters, which provide the final stage of suspended solids removal and protect the granular activated carbon (GAC) filters from particulate contamination. Series operated GAC filters are then used to remove the dissolved creosote and pesticides from the water. To ensure compliance with specification levels, the water is sampled and analyzed after the first GAC filter. The second GAC filter acts as a guard bed.

The key features of these products are :•Range of activity levels and pore size distributions provide a flexible approach to adsorption •Excellent product hardness to resist mechanical attrition •Spent material can be thermally reactivated

Water Hardness Test : Equipments :•Solution (TH-C)•Indicator (TH-B)•Buffer soln (TH-A)

Test :•Water : 10 ml•Buffer : 3 drop

Indicator : something Soln making

Details are given below:

Test Procedure : At first water should be taken. After that Buffer must be added only 3 drops. Next add something indicator. If in this time color will appear blue means hardness zero. On the other hand if color will appear in violet means hardness is present. At this time solution TH-C added in according to drop. Per drop grading of this solution is 5. If the blue color come by adding TH-C 1 drop then this water hardness is 5. So much added this solution then hardness is also more.

HOW YOU MEASURE WATER HARDNESS?

First of all, take 5ml water in a bottle than added 5 drop of buffer solution and 1 drop of indicator.

Then add EDTA (Ethylene di amine Tetra Acetic Acid) by injection. Injection is pointed 0.01 to 1.

Finally calculate by giving result how many EDTA are needed to change the color.

5 ml water+5 drop of buffer solution+1 drop indicator

Water Hardness=Water volume*used EDTA

=300*0.07

=21 ppm(parts per million)StandardSoft water=<60ppmMedium soft=60-120ppmHard Water=120-180ppmVery hard=>180ppm

if we use 10 ml water then multiply 500. If we use 5 ml water

Then multiply 300.

Water Treatment Process Flow diagram :

Thank

You

All

AZMIR