Back Washing Of Water Treatment Modules

Back Washing is a term used in water treatment to describe the process by which trapped or filtered contaminants in water during water treatment process are discharge or remove from the water treatment module. Figure 1 below shows a mini water treatment module, while figure 2 below shows a large pressure water treatment module( A Pressure Sand Filter Tank)

Fig. 1. Treatment Module

Fig. 2. Large Pressure Water Treatment Module

Back Washing is a broad term which have different definition and meaning, but, in context to our lesson, it is best describe as above. Back Washing technically involved passing water in a reverse direction against the normal direction of water flow into and out of our water treatment module, during this reverse process the contaminants that were trapped such as particles, debris, flocs, e.t.c are removed or discharged from our water treatment module either into the  environment or into a waste water treatment plant.

Figure 3 shows the back washing of a large Pressure water treatment module

From figure 3 we can see how dirty the water coming out of module is, this is as a result of filtration carried out by the module, it trapped everything particles and flocs, as seen in figure 3  below, the major contaminants in this water is Iron, in some cases the water may be brackish, where we have more of sulphur contaminants. Back washing can be said to be achieved when the water becomes clear as shown in figure 5 and 6. proper rinsing must also be done to achieve more clear water.

Figure 3. Video: Backwashing of Treatment Module

The process called back washing ensures the continuity of our water treatment module over a long period of time, it prolonged the life span and also ensures efficiency, it is like constant renewal or we can also call it a cleaning process.  In some cases depending on the size of water treatment module or nature of contaminants expected, the back washing pump will not be of the same capacity with the pump for normal process flow, since more speed and energy will be required to achieve back washing, in this situation a bigger pump with almost twice the normal capacity for process may be required and installed. In some water treatment plant, a air blower is also installed in the treatment module especially for sand filter tank, one of the advantage of the air blower is that it makes back washing faster and also reduce the quantity of water that will be use for back washing. Air blowing a sand filter tank help to break the mass layers of sand and created enough pores for easy back washing, but, air blowing is not advisable for a purifier modules, as it will scatter the activated carbon bed and results in serious crisis.

Figure 5. Video showing back washing

Figure 6. Showing back washing

Back washing of water treatment module must have duration, depending on the purpose of use and frequency of usage and type of contaminants expected, and also the size of the treatment module, it may be every day, twice a week, once a month or once in two to four months.

Failure to adhere to this period of time set for back washing can be costly, as the case may be, it may results in leakage of trapped contaminants, blockage of treatment module or in some cases will over whelmed the treatment media and may result in total collapse of the system.

 Also back washing of water treatment module must be carried out by a trained person to avoid mistake or damage of plant, and back washing must be done thoroughly,  Back washing is one of the processes in water treatment processes that cannot be ignored or wished away, it is an integral part of water treatment processes that ensures continuity of our water treatment modules, back washing makes water treatment cost effective. No back washing no water treatment.

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