40- thumb rules/standards you must know in water treatment plant

1-Clarifier (HRSCC) outlet pH is 1 to 1.5 units lesser than inlet pH or out let pH is 10 to 15% lesser than inlet pH

2-Clarifier outlet water conductivity increases by 115 to 125% than its inlet water conductivity

3-Hardness of water at clarifier outlet decreases slightly (1 to 3 ppm) than its inlet water

4-Losses in clarifier = Inlet water X 2%

5-Detention time in clarifier =The time it takes for a drop of water to travel from inlet to outlet

Detention time = Clarifier tank volume M³ / Flow rate M3/day

Actually clarifiers are designed for detention time for 3 to 4 hours. If clarifier inlet flow increases detention time reduces & vice versa

6-For reverse osmosis

• Permeate water pH=Inlet water pH X 80-85%
• Permeate water conductivity =Inlet water conductivity X 5-15%
• Reject water pH =Inlet water pH X 105 to 110%
• Reject water conductivity = Inlet water conductivity X 325 to 350%

7-Pressure drop in RO cartridge filter will be 0.1 to 0.2 kg/cm2
Water treatment plant chemicals & their functions

8-RO membrane pores opening will be 0.0001 microns

9-UF membranes pores opening will be 0.01 to 0.1 microns

10-Ro plant recovery rate = (Feed water flow-Reject water flow) X 100 / Feed water

11-Salt passage in RO = Concentration in permeate water X 100 / Concentration in feed water

12-Salt rejection in RO = (1-Salt passage) X 100

13-In a RO plant reaction time for chemicals is minimum 15-20 seconds, so dosing taps should be at least 20 meter before the RO unit (RO inlet line)

14-For SAC: Outlet water pH = Inlet water pH X 70-75%

15-For SAC: Outlet water conductivity = Inlet water conductivity X 130-150%

16-For SBA: Outlet water pH = Inlet water pH X 140-150%

17-Feed water or Boiler water TDS = Conductivity X 50-60%

18-Standard pressure drop in DM plant vessels (SAC, SBA, MB etc) is 0.4 to 0.6 kg/cm2

19-Pressure drop in UF membranes is 0.1 to 0.3 kg/cm2

20-Whatman paper required for SDI is of cellulose nitrate membrane having pore size 0.45 microns & 47 mm diameter

21-Colloidal silica is in un-dissolved form & non reactive, it is removed in clarifier

22-Reactive silica is in dissolved form, is removed in RO, SBA & MB

23-A change of 1 pH value represents the change of 10 times in relative acidity or alkalinity.

For example: pH 4 is 10 times acidic than pH 5

24-Higher pH of water causes scaling & lower pH causes corrosion

25-Acids & alkalis have tendencies of increasing or decreasing the conductivity of water

For example: Water of pH 10 has more conductivity than that of pH 7

26-In DM plant SBA is always kept after SAC:

The cat ion resin is usually located before the anion resin. If the water contains any hardness traces, then it reacts with OH- of anion resin forming Hydroxide. And hydroxide has less solubility; it precipitates in the alkali environment.

27-For DM plant if DM plant Degasser is provided if inlet water has bicarbonates > 150 ppm, if it is less then there is no necessary of degasser tower.

28-On every 1 degree rise in water temperature its conductivity increases by 4 to 5 micS/cm

29-M alkalinity should be less than 20% of TDS

30-Silica in drum water = 0.4 X OH alkalinity

31-2 X P-M = 0 or negative, indicates no hardness in water

32-Conductivity = 6 X PO₄ in drum water
50-Selected QnA for WTP operators & Chemists

33-Standard parameters of water in steam drum at various operating pressure

Sl No.	Parameter	UOM	P = up to 35 Kg/cm2	P=35-45 kg/cm2	P = 45-67 Kg/cm2	P =67-100 kg/cm2	P = >100 kg/cm2
1	pH in drum		9.5-10.2	9.5-10.2	9.5-10.2	9.5-9.8	9.5-9.8
2	Conductivity in drum	MicS/cm	500	250	150	100	50
3	TDS in drum	ppm	250	125	75	50	25
4	Hardness in drum	ppm	Nil	Nil	N	N	N
5	Silica in drum	ppm	<15	<10	<5	<1	<0.6
6	Chloride in drum	ppm	Nil	Nil	Nil	Nil	Nil
7	Oil & Grease in drum	ppm	Nil	Nil	Nil	Nil	Nil
8	Hydrazine (N2H4) in feed water	ppm	0.01-0.2	0.01-0.2	0.01-0.2	0.01-0.2	0.01-0.1
8	Residual phosphate in drum	ppm	18-20	15-18	10-15	6-10	5-7

34-Standard parameters of feed water/Condensate water

Sl No.	Parameters	UOM	Values
1	pH		8.5-8.8
2	Conductivity	MicS/cm	3-5
3	TDS	ppm	1.5-2
4	Hardness	ppm	Nil
5	Silica	ppm	0.02
6	Chloride	ppm	Nil
7	Oil & Grease	ppm	Nil

Also read Power plant thumb rules