Geoscience Reference
In-Depth Information
14.1.2.9.5 Chemical Equations Encountered in Water/Wastewater Operations
Cl
2
+ H
2
O ↔ HCl + HOCl
NH
3
+ HOCl ↔ NH
2
Cl + H
2
O
NH
2
Cl + HOCl ↔ NHCl
2
+ H
2
O
NHCl
2
+ HOCl ↔ NCl
3
+ H
2
O
Ca(OCl)
2
+ Na
2
CO
3
↔ 2NaOCl + CaCO
3
Al
2
(SO
4
)
3
+ 3CaCO
3
+ 3H
2
O ↔ Al
2
(OH)
6
+ 3CaSO
4
+ 3CO
2
CO
2
+ H
2
O ↔ H
2
CO
3
H
2
CO
3
+ CaCO
3
↔ Ca(HCO
3
)
2
Ca(HCO
3
)
2
+ Na
2
CO
3
↔ CaCO
3
+ 2NaHCO
3
CaCO
3
+ H
2
SO
4
↔ CaSO
4
+ 2H
2
CO
3
Ca(HCO
3
)
2
+ H
2
SO
4
↔ CaSO
4
+ 2H
2
CO
3
H
2
S + Cl
2
→ 2HCl + S
°
↓
H
2
S + 4Cl
2
+ 4H
2
O → H
2
SO
4
+ 8HCl
SO
2
+ H
2
O → H
2
SO
3
HOCl + H
2
SO
3
→ H
2
SO
4
+ HCl
NH
2
Cl + H
2
SO
3
+ H
2
O → NH
4
HSO
4
+ HCl
Na
2
SO
4
+Cl
2
+ H
2
O → Na
2
SO
4
+ 2HCl
14.1.2.10 Chemical Dosages (Water and Wastewater Treatment)
Chemicals are used extensively in water/wastewater treatment plant operations. Water/wastewater
treatment plant operators add chemicals to various unit processes for slime growth control, cor-
rosion control, odor control, grease removal, biochemical oxygen demand (BOD) reduction, pH
control, sludge bulking control, ammonia oxidation, bacterial reduction, and fluoridation, among
other reasons. To apply any chemical dose correctly it is important to be able to make certain dosage
calculations. One of the most frequently used calculations in water/wastewater mathematics is the
conversion of milligrams per liter (mg/L) to pounds per day (lb/day) or pounds (lb) dosage or load-
ing. The general types of mg/L to lb/day or lb calculations are for chemical dosage, BOD, chemical
oxygen demand (COD), or suspended solids (SS) loading/removal; pounds of solids under aeration;
and waste activated sludge (WAS) pumping rate. These calculations are usually made using either
of the following equations:
mg/L × Flow (MGD) × 8.34 lb/gal = lb/day
(14.12)
mg/L × Volume (MG) × 8.34 lb/gal = lb
(14.13)
If mg/L concentration represents a concentration in a flow, then million gallons per day (MGD) flow
is used as the second factor. However, if the concentration pertains to a tank or pipeline volume,
then million gallons (MG) volume is used as the second factor.
14.1.2.10.1 Chlorine Dosage
Chlorine is a powerful oxidizer commonly used in water treatment for purification and in wastewa-
ter treatment for disinfection, odor control, bulking control, and other applications. When chlorine
is added to a unit process, we want to ensure that a measured amount is added. The amount of
chemical added or required can be specified in two ways:
• Milligrams per liter (mg/L)
• Pounds per day (lb/day)
To convert from mg/L (or ppm) concentration to lb/day, we use the following equation:
mg/L × MGD × 8.34 lb/gal = lb/day
(14.14)
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