PROCESS: 1) SOURCE WATER PUMP & STORAGE:
The First Process is to Pump the raw water from the source which can be Open well, Bore / Tube Well, River Water etc. (Normally River water is the alternative only in case the other two options are not available) to the RAW WATER STORAGE TANK. The pump required would depend upon the uplift of the water & distance required to be covered from the source to the tank.
Raw water tank can be either HDPE Tanks (Example: Sintex tanks) / ZnAl Tanks or Concrete tanks, the Concrete Tanks can be located either in the ground or above the ground level. Having the tanks under the ground level is always feasible. Concrete tanks should be tiled with White tiles and manhole facility to be provided to enable regular cleaning of the tanks.
Storage capacity should be maintained at least twice of the product output per day Example : If Product Output is 2000Lph , the storage capacity installed should be min. 20000 Litres and the storage should be made in individual tanks having double the capacity of the output i.e. 4 nos. of HDPE tank are to be installed of 5000 Litre capacity each.
PROCESS: OPTIONAL): COAGULATION
It is used to cause the suspended solids that may be present in water to coagulate and settle out. By coagulation we mean that the very fine particles of suspended matter come together to become a larger cluster which will settle more easily than the smaller suspended particles. Alum and Lime are normal Coagulants used, this is a optional process and is done in the raw water tank and is done only in case the raw water has more suspended solids which may harm the further filtration process.
PROCESS: 2) CHLORINE DOSING OR OZONE DISINFECTION
Raw water may contain living microorganisms and organics, which are objectionable to the Membrane as it, may cause fouling and further oxidation to deteriorate the performance of the filters and the RO membrane. This Raw water may contain oxidized or unoxidised ferrous which can be converted to ferric oxide with the addition of chlorine, which will further settle down in storage tank. The chemical used for this is Sodium Hypo chloride, which is locally available in market in liquid concentrate or anhydrous form. About 3-5 PPM of sodium hypochlorite solution is dosed in raw water storage tank as standard measure. This reacts with water to form a hypo chlorite acid which acts as disinfecting agent. (Actual quantity of dosage may be obtained from the Plant designers)
This process can be made manually or can be automated depending upon requirement. For automation one no. HDPE hypochlorite solution preparation tank along with one nos. of electronic diaphragm dosing pump is provided. Dosage rate is adjusted as per the actual requirement, which may very on case to case basis.
Ozone is a highly effective oxidizing agent and is a strong disinfectant and can be used in place of chlorine as it does not leave any kind of colour and odour residue in water after treatment and proves to be more efficient than Chlorine. A equivalent Ozone generator is required for this purpose and is dosed online in the piping’s and a UV treatment is given just before the RO to neutralize the effect of Ozone since presence of ozone in water can cause fouling of RO Membranes. This may increase the capital investment initially but has no recurring expense in comparison to the chemical cost required for chlorine and thus is highly recommended for initial disinfection.
PROCESS: 3) PRESSURE SAND FILTER: (TSS)
The chlorinated water is first pumped to this section which is called the Pressure Sand Filter unit which is in series prior feeding to the R.O.Plant. A Pump is used for the purpose to generate the required flow rate and pressure. Pressure Sand Filter Unit is provided for removal of suspended matters & turbidity from raw water. TSS Unit is a vertical Pressure Vessel. Internally, it is fitted with bottom collecting system. A uniform grades silica quartz sand is charged on the supporting media of pebbles and gravel’s. This unit is fitted with frontal pipe work and Multiport Valve externally.
During service cycle water is passed in down ward direction through sand bed, thus entrapping suspended matter & turbid particles. Over a period of time, sand bed gets choked due to suspended matters resulting higher pressure drop and lesser floe. At this stage filter bed need to be backwashes. This is indicated by the pressure drop across the sand bed if the same increases beyond the specified limit (0.5 kg/cm²) or quality of filtered water determinates which ever is earlier. Regeneration process is carried on which involves backwash & rinsing of Sand Bed.
For backwashing: Service water is passed in reverse direction of service cycle to loosen the filtering media bed. Due to this, entrapped suspended matters get free and come out along with effluent water. Backwashing is continued for about 10- 15 minutes or till the effluent coming out is clear.
For Rinsing of Sand Bed: Service water is passed in down ward direction to settle down the sand bed. The effluent water is drained for about 5 minutes time to ensure all unclear water is drained down. This Process is completely done by just changing the valve position of the multi port valve provided
Lesser the velocity higher is the effective filteration, Sand filters used by reputed brands like Bailley, Aquafina, Kinley etc operate sand filters at lower velocity ensuring higher filteration efficiency.
Normally this process is to be carried out after every day operation to enhance the performance of the Filter. The Material of construction can be either Mild Steel, F.R.P. (Fiber Reinforced Plastic) or Stainless Steel, which can be chosen as per requirement.