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1.Raw Water Quality

Nutrient

Moderate or large quantities of nutrients such as phosphates, nitrates and organic nitrogen compounds may

act as a fertilizer in a reservoir to stimulate the growth of algae which may cause algal bloom.

The problems related to algal blooms are:

Taste, odor and color,

Increased pH

Shortened filter runs of treatment plants,

Dissolved Oxygen variation,

Organic loading.Thermal Stratification

Thermal stratification develops in lakes and reservoirs when the surface water begins to warm.

The warm surface waters expand and become lighter than the lower waters. The water temperature

difference causes variation in water densities, which create resistance to mixing. This ultimately results in

anaerobic conditions in lower zones.

Test for water quality

Regular analysis of raw water quality preferably once in a week in large water treatment plants is necessary

to identify and correct the problems likely to be faced in the water treatment.

If the fluctuation in quality of water is rapid, the analysis should be undertaken at short intervals.

Turbidity is not a special problem as the dosage of coagulant is adjusted on a daily routine.On the other hand a sudden rise in chloride content will indicate pollution due to sewage.

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In such cases, more confirmatory tests should be taken such as for nitrogen in its various forms, dissolved

oxygen, oxygen absorbed and chlorine demand to decide the occurrence of pollution and to fix the dose of

pre-chlorination needed.

In case of lake as a source the periodical physical and biological examination of samples will indicate if there

is any need for control of algae, which may cause taste and odour problems or clogging of filters.

2 Flow Measuring Devices of Water TreatmentPlant

The preventive maintenance procedures related to Flow measuring devices are listed below:

1. Float sumps should be periodically cleaned to see that silt does not accumulate, which may affectthe proper functioning of the float.

2. Charts and pen recorders should be stocked adequately3. Annual or more frequent calibration of these devices is necessary.4. Annual servicing and checking of the instrument is imperative.

3 Chemical Feeding Unit of Water Treatment Plant

The preventive maintenance procedures related to Chemical feeding unit are listed below:

Alum and lime solution tanks are to be painted annually with anti-corrosive paint.

V-notch weirs, and floats arrangements should be cleaned daily. Setting of the V-notch should bechecked periodically.

Adequate spares for mechanical mixing device should be stocked.

The optimum dosing of coagulant should be determined periodically, in particular there is a change

in water quality based on a proper laboratory study including jar test.

The chemical feeding rate should be controlled depending upon the needs from time to time.

4 Flash Mixer of Water Treatment Plant

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The preventive maintenance procedures related to flash mixer are listed below:

Adequate spares for the mechanical mixing equipment should be kept in ready stock for timelyreplacement when necessary.

Life of equipment such as metallic blades and shafts can be prolonged by periodical painting theequipment with anti-corrosive paints.

5 Flocculator of Water Treatment Plant

The preventive maintenance procedures related to Flocculator are listed below:

Flocculator paddles should be operated continuously to avoid sludge building up.

All metallic parts of the equipment should be painted with anti-corrosive paints once in a year.

Mechanical devices should be lubricated and worn out parts replaced.

In non-mechanical type flocculator with baffles, removing sludge once in six months is necessary.

6. Clarifier or Sedimentation TankThe preventive maintenance procedures related to clarifiers or sedimentation tanks are listed below:

Annual overhauling and repainting of the unit should be done a month or two prior to monsoon.

Sludge line should be kept free of chocking. The line should be flushed with high-pressure water ifchocking is noticed.

The telescopic sludge discharge device, when provided, should be checked for vertical movementand O-rings replaced when leaky.

The traction wheels of the moving bridge should be checked for alignment and rubber wheelsreplaced, if required.

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The units should be worked continuously to protect the mechanical parts from ill effects ofcorrosion, malfunctioning etc., as well as problem of sludge build-up.

Outlet weirs should be kept clean at all times.

Algaecide or bleaching powder may be used for controlling biological growth on weirs

7 Rapid Sand filters of Water Treatment Plant

The preventive maintenance procedures related to Rapid sand filters are listed below:

Defective Gauges

Rate of flow and loss of head gauges frequently get out of order. The operator should be conversant with the

working of these gauges and should be able to do minor-repairs.

Inadequate sand media on Filter bed

Expansion of sand bed during back washing should be kept within the limits to avoid carry over of sand to

wash water trough. Sand bed should never be depleted more than 10 em from the original thickness, when

it is more than 10 em the sand media has to be replenished. The entire bed should be taken out and

additional sand media mixed to give the required effective size and uniformity coefficient.

Air binding

This is caused due to the negative head and formation of air bubbles in the filter sand. This could be

overcome by more frequent back washing during these periods. Provisions should be made wherever

possible to increase the depth of water by about 15 to 30 em. The maintenance of depth of water of at least

105m over sand may eliminate air binding problem. If air binding persists, loss of head may be limited to

1.5 m, which will discourage air binding and ensure reasonable length of filter run.

Incrustation of media

This problem of incrustation of sand particles may arise as in the case of water softening with lime soda

when sand particles get coated with material that is difficult to remove by normal backwash. Remedy lies in

washing the filter occasionally with sodium hydroxide (10 kg/ m2 area of bed) or bleaching powder (20 kg/

m2 area of bed).

Cracking of sand beds

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This occurs when water is lowered below the surface of the sand. Cracks in a filter bed under water may also

arise due to cementing of grains by some materials in the applied water. The vulnerable portion is near the

walls, since the sand is drawn away from the walls. The rate of flow increases through cracks allowing

heavier deposits of solids at these points resulting in unequal distribution of the wash water. This can be

avoided by the use of hand rake or by draining of bed and removing clogged sand.

Bumping of filter beds

Sometimes careless or indifferent operation of the filter bumping or lifting of the filter beds when switching

on the back wash cycle is adopted. This type of inadequate cleaning process should be discouraged.

Mud-balls

These are caused by the general build-up of materials not removed in back-wash. Mud balls accumulate at

or near surface and in course of time clog the entire sand media. Proper coagulation and settling of feed

water could considerably reduce mud-ball formation. Surface wash or surface raking at intervals helps

reduce mud ball formation. Compressed air scouring for more than 3 minutes also effectively decreases mud

ball concentration.

Sand boils

Sand boils are caused when disproportionately large discharges of wash water rush towards expanding the

sand and displacing the gravel. This situation arises mainly due to poor distribution of wash-water from

under-drain system.

Slime growths

When slime growths are noticed on filters, the bed is cleaned in the normal way and water is lowered to the

level of the sand bed. Then common salt is distributed evenly over the surface of sand using 7 kgl m2 of

filter area, after which the wash water valve is opened until water rises about 15 cm above the sand level.

The water is allowed to remain for 2 hours to dissolve the salt and then lowered to the bed level to be

retained for 24 hours after which it is thoroughly back-washed before placing into service.

Backwashing

The waste wash water drains should be kept free of clogging or sediment. The requisite up-flow velocity of

backwash water should be maintained at the design rate for proper cleaning of the sand.

Backwashing of filters in water treatment should not be based on arbitrarily fixed time scheduled but the

frequency should be in accordance with the filtrate quality and head loss measurement. Duration of cleaning

should be dependent upon the turbidity of the wasted water. .

8 Chlorinators of Water Treatment Plant

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The preventive maintenance procedures related to water treatment chlorinator and chlorine house are

listed below:

The chlorine demand of the filtered water is to be satisfied and optimum free residual chlorine maintained to

render water completely safe.

The operator should be careful in administering calculated doses accurately.

Periodically chlorine dose should be monitored weekly to ensure adequate chlorine residual at the drinking

tap; assuming adequate filtration and chlorine contact time, the residual of total chlorine should be 0.5 mg/L

or the residual free chlorine should be 0.2 mg/L;

Bubbling the chlorine gas through the filtered water stored in the clear water reservoir by dipping rubber

tubes connected to chlorine cylinder must be avoided. Chlorine application should be done through a

chlorinator only.

Chlorinators require periodical adjusting; The chlorinator should be maintained properly.

If the unit is out of order, it should be repaired immediately.

Since chlorine gas is heavier than air it is likely to sink to the floor. Hence providing and maintaining

arrangement for forcing air from top and driving chlorine gas from the floor through ventilators located at

the floor level is necessary.

Safety requirements

Whenever dealing with gaseous chlorine, safety is an important issue. Ammonia should be kept handy for

checking for leaks. Chlorine cylinders storage building should be well ventilated. It the operator must walkthrough an area with chlorine in the air, he or she should use a breathing apparatus. If no breathing

apparatus is available, the operator should keep his head high. since chlorine is 2.5 times as heavy as air

and will tend to sink to the ground.

9 Clear Water Storage Reservoirs

The preventive maintenance procedures related to clear water reservoirs are listed below:

Water level recorder should be kept in working order at all times.

During the pumping of water the water level in the reservoir should be maintained at the lowestlevel as possible so that overflow and wastage of water when the pump is suddenly shut down could

be prevented.

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Roof of the clear water reservoir is always kept at least 60 cm above the surrounding ground levelto prevent rainwater flooding over the roof.

Roofing should be periodically checked to ensure that no leakage is there so that pollution can beprevented. Top of roof should be sloped in such a way to prevent stagnation of rainwater;

Ventilator outlets should be regularly checked and cleaned to guard against mosquito breeding andbird droppings.

Cleaning of sump and reservoirs should be done regularly at least once in six months.