Operation and Maintenance manual of Water Treatments plant consisting of features of Operation and Maintenance of individual components of the water treatment supply system is necessary for adopting in the O & M of the water treatment systems. The Operation and maintenance features of the following water treatment components are discussed in the following subsections.
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.
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.
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.
On the other hand a sudden rise in chloride content will indicate pollution due to sewage.
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.
The preventive maintenance procedures related to Flow measuring devices are listed below:
The preventive maintenance procedures related to Chemical feeding unit are listed below:
The preventive maintenance procedures related to flash mixer are listed below:
The preventive maintenance procedures related to Flocculator are listed below:
The preventive maintenance procedures related to clarifiers or sedimentation tanks are listed below:
The preventive maintenance procedures related to Rapid sand filters are listed below:
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.
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.
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.
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).
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.
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.
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 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.
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.
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. .
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.
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 walk through 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.
The preventive maintenance procedures related to clear water reservoirs are listed below: