Cover Page

The Hydrologic Cycle

Meteroric Water

Ground Water

Surface Water

Hardness

Ion Exchange Softeners

Iron

Iron Removal

Manganese

Manganese Removal

Hydrogen Sulfide

Hydrogen Sulfide Removal

Chlorides and Sulfates

Sodium

Fluorides

Turbidity

Removal of Turbidity

What is meant by pH?

Alkalinity

Removal of Alkalinity

Acidic Water

Removal of Acidity

Objectionable Tastes and Odors

Nitrates

Bacterial Contamination

Forms of Lower Plant Life in Water

Forms of Lower Animal Life in Water

Decontamination by Chlorination

Decontamination by Reverse Osmosis

Reverse osmosis works through a technique called membrane separation. Raw water enters a module housing the cellulose acetate membrane system. Normal water pressure, or boosted pressure, forces the water against the semi-permeable membrane and only clean water molecules pass through the pores in the membrane. Impurities are rejected and flushed away.

The following tables show typical rejection rates of salts, organics and dissolved gases:

Typical Membrane Rejection/Passages

Salts

CATIONS Name	Symbol	Percent Rejection	Percent Passage (Average)	Maximum Concentration Percent
Sodium	Na+	94.96	5	5-10
Calcium	Ca+2	96.98	3	*
Magnesium	Mg+2	96.98	3	*
Potassium	K+1	94.96	5	5-10
Iron	Fe+2	98.99	2	*
Manganese	Mn+2	98.99	2	*
Aluminum	Al+3	99+	1	10-20
Ammonium	NH4-1 **	88.95	8	3-8
Copper	Cu+2	98.99	1	10-20
Nickel	Ni+2	98.99	1	10-20
Zinc	Zn+2	98.99	1	10-20
Strontium	Sr+2	96.99	3	-
Hardness	Ca and Mg	96.98	3	*
Cadmium	Cd+2	96.98	3	10-20
Silver	Ag+1	94.96	5	*
Mercury	Hg+2	96.98	3	-
ANIONS Chloride	Cl 1	94.95	5	5-8
Bicarbonate	HCO3 1	95.96	4	5-10
Sulfate	SO4 2	99+	1	5-15
Nitrate	NO3 1 * *	85.95	10	3-6
Fluoride	F 1	94.96	5	5-8
Silicate	SiO2 2 * *	80.95	10	-
Phosphate	PO4 3	99+	1	10-20
Bromide	Br 1	94.96	5	5-8
Borate	B4 O7 2 * *	35.70**	-	-
Chromate	CrO4 2 * *	90.98	6	8-12
Cyanide	CN 1 * *	90.95**	-	4-12
Sulfite	SO3 2	98.99	1	5-15
Thiosulfate	B2 O3 2	99+	1	10-20
Ferrocyanide	Fe(CN)6 3	99+	1	10-20

* Must watch for precipitation, other ion controls maximum concentration.
** Extremely dependent on pH; tends to be an exception to the rule. 

Organics

	Molecular Weight	Percent Rejection	Maximum Concentration Percent
Sucrose sugar	342	99.9	30-35
Lactose sugar	360	99.9	30-35
Protein	10,000 Up	99.9+	50-80
Glucose	180	99	15-20
Phenol	94	***	-
Acetic acid	60	***	-
Formaldehyde	30	***	-
Dyes	400 to 900	99.9	-
Biochemical Oxygen Demand	(BOD)	90-99.9	-
Chemical Oxygen Demand	(COD)	99.9	-
Urea	60	40-60	Reacts similar to salt
Bacteria & virus	500,000-50,000	99.9+	-
Pyrogen	1000-5000	99.9+	-

*** Permeate is enriched in material due to preferential passage through the membrane.

Gases, Dissolved

Carbon dioxide	CO2	30-50%
Oxygen	O2	Enriched in permeate
Chlorine	CI2	30-70%