COMPONENTS OF WATER TREATMENT PLANT

SEDIMENT FILTER

the first thing that incoming tap water encounters, and as the name implies it filter out sediment.

1. If sediment filter bypassed , the sediment would then rapidly clog the activated carbon filter, making it much less useful and potentially risking damage to the RO membrane.
2. Sediment filter also prevents sediments from getting through that might coat the inside of the reverse osmosis membrane..
3. Typical sediment filters used for this application have pore sizes in the 0.5 to 1 um (micrometer, or millionth of a meter) range. If the water contains a lot of sediment, it is sometimes useful to have a series of sediment filters with steadily decreasing pore size, increasing the lifetime of the filters.

5 um filter is used in our laboratory.

CARBON BLOCK: ACTIVATED CARBON WORKS BY SURFACE ADSORPTION

1. The next filter in line typically contains activated carbon.
2. The primary purpose of this activated carbon is to break down the chlorine and chloramine in the tap water and effective in removing large amounts of organic materials. If not removed, these compounds may damage the RO membrane. They will also pass through the remaining filters (RO and DI) fairly readily, and so can end up in the final filtered water
   

Carbon filter types:

1. Powdered block filters and granular filter.
2. carbon block more effective than granular owing to its increased surface area.

REVERSE OSMOSIS MEMBRANE

1. Reverse osmosis membranes consist essentially of a sheet of porous organic polymer. A variety of different materials is used commercially, including
   1. cellulose acetate/triacetate blends (sometimes called CTA): inexpensive and resistant to oxidation by chlorine.
   2. thin film/thin layer composites (sometimes called TLC or TFC): more costly, but have high impurity rejection. They must be protected from chlorine and chloramine.
   3. modified polysulfone (sometimes called SPSF): generally optimal only in special such as soft water source

RO membrane is a semipermeable membrane, allowing water to pass through while rejecting contaminants that are too large to pass through the tiny pores inthe membrane.Reverse osmosis membrane is of microscopic size (0.0001 micron)allowing only pressurized water molecules to pass and bigger molecules are rejected . Size of smallest bacterium is 0.02 um
RO membrane removes 95-99% of organics , bacteria and other particulate matter and 90-97% of all ionized and dissolved minerals but fewer of gaseous impurities

DEIONIZING RESINS

1. The final filter in an RO/DI system is the deionizing resin.
2. DI resin traps all charged molecules passing through it, and leaves uncharged (neutral) molecules free to pass through.
   1. Water , for example, passes through it, as would other
   2. uncharged inorganic molecules such as oxygen (O2), nitrogen (N2) and chloramine (NH2Cl, if any remained from the previous filters).
   3. Uncharged organic molecules also pass through a DI resin, including ethanol (CH3CH2OH), methanol (CH3OH), methane (CH4), propane (CH3CH2CH3), carbon tetrachloride (CCl4), and methylene chloride (CH2Cl2). I
3. Ions such as sodium (Na+), copper (Cu++ or Cu+), ammonium (NH4+), phosphate (PO4—), silicate (Si(OH)3O-), and acetate (CH3CO2-) all get caught.
4. All atoms or molecules that are in rapid and significant equilibrium with their charged forms will be caught and removed just as their charged forms are. These include ammonia (NH3) caught as ammonium, silicic acid (Si(OH)4) caught as silicate, carbon dioxide caught at least partially as bicarbonate (HCO3-) or carbonate (CO3–), and acetic acid (CH3CO2H) caught as acetate, etc.
5. To catch these ions, the resin consists of porous beads that have fixed charges attached to them. The counterions to these fixed charges start off as H+ and OH- in a fresh resin. Normally, there are different beads intended to bind cations and anions. In a mixed bed DI resin, the beads are mixed together in a single filter. In a separate bed system, each bead type will be in a different filter, thereby potentially allowing the DI to be recharged .

(RSO3)H + Na+ —–> (RSO3)Na + H+
(RNR3)OH + Cl- ——> (RNR3)Cl + OH-

Mixed bed deionizers usually produce water with a specific resistance that exceeds 10 Mohm/cm.

0.2 MICRON FILTER

Polyethersulfone (PES) membranes are hydrophilic filters constructed from pure polyethersulfone and available in pore sizes raing from 0.03 micron to 5.0 micron.

UV FILTER

UV Filter is incorporated so as to kill any live bacteria, spores and viruses

CONDUCTIVITY METER

Used to measure conductivity of the water from the output tube measured in microsiemens/cm or as TDS in ppm

CONDUCTIVITY IS RECIPROCAL OF RESISTIVITY

1. Conductivity(S/cm) = 1/Resistivity(Ohms-cm)
2. Conductivity(S/cm) = ppm x 2

NCCLS SPECIFICATIONS FOR REAGENT GRADE WATER

Microbiological content : The microbiological content of viable organisms , as determined by total colony count after incubation at 36 ± 1 'C for 14 hrs followed by 48 hrs at 25 ± 1 'C and reported as colony forming unit/mL (cfu/mL)
Specific resistance or resistivity: The electrical resistance in ohms measured between opposite faces of a 1.00 cm cube of an aqueous solution at a specified temperature . For these specifications , the resistivity will be corrected for 25'C and reported in Mohm/cm. The higher the amount of ionizable materials, the lower the resistivity and higher the conductivity.
Particulate matter : When water is passed through a membrane filter with a mean pore size of 0.2 um, it is considered to be free of particulate matter.
Organic material : When water is passed through a bed of activated carbon, it is considered to contain minimum organic material .

QUALITY , USE AND STORAGE OF REAGENT GRADE WATER

Type III :

1. Used for glassware washing.Final rinsing should be done with with water suitable for the intended glassware use .
2. May be used for certain quantitative procedures such as for general urinanalysis.

Type II :

1. Used for general laboratory testing not requiring Type I water.
2. Storage should be kept minimum.
3. Storage as well as delivery systems should be constructed to ensure minimum of chemical or bacterial contamination.

Type I :

1. Should be used in test methods requiring minimal interference and maximum precision and accuracy.eg. Trace metal determination, enzyme measurements, electrolyte measurements and preparation of all calibrators and solution of reference materials.
2. Should be used immediately after production.
3. No specifications for storage are given because it is not possible to maintain high resistivity while drawing off water and storing it.