SUmber Dan Kualitas Air

Water :Resource and Characterisic

Utilitas

Water resources• vary in regional/local patterns of availability• dependent on topographic & meteorological

conditions• dependent on the physical features of the

earth and on the earth’s geological structure

3 types of water resources:

1. Surface water

2. Ground water

3. Sea water

Utilitas

Water quality characteristics

• Physical

• Chemical

• Biological

Utilitas

Physical characteristics

• Temperature

• Turbidity

• Suspended solid

• Taste and odor

Utilitas

Chemical characteristics

• pH

• Alkalinity

• Hardness

• Conductivity

• Dissolved organic, inorganic materials & gas

SCALING

CORROSION

Utilitas

pH

• Indicates the hydrogen ion concentration in water

• pH > 7 scaling

• pH < 7 corrosion

Utilitas

Alkalinity

• A measure of the water’s ability to absorb hydrogen ions without significant pH change

• Water alkalinity is determined by carbonate ions and hydroxyl ions (OH-)

• The carbonate system is comprised of the following chemical species:– Aqueous carbon dioxide CO2 (aq)

– Carbonic acid H2CO3

– Bicarbonate ion HCO3-

– Carbonate ion CO32-

Utilitas

A series of alkalinity reaction

CO2(aq) + H2O H2CO3 H+ + HCO3-

HCO3- H+ + CO3

2-

CO32- + H2O HCO3

- + OH-

If there is a source of solid CaCO3, then the solubility reaction for CaCO3(s) applies in the system:

CaCO3(s) Ca2+ + CO32-

Utilitas

• From the equations, it can be seen that CO2 and three forms of alkalinity are all part of one system that exist in equlibrium

• A change of concentration of one ions will result in a change in pH

Utilitas

CO2 pH 4.5 – 8.5 HCO3

- pH 4.5 – 9.5 CO3

2- pH 8.5 – 14 OH - pH 9.0 -- 14

Utilitas

Alkalinity (mol/L) = [HCO3-] + 2[CO3

2-] + [OH-] – [H+]

where concentrations in the brackets are [mol/L]

If the concentrations are measured in terms of equivalents, or in mg/L as CaCO3:

Alkalinity (meq/L) = (HCO3-) + (CO3

2-) + (OH-) – (H+)

Utilitas

Analysis

• Using sulfuric acid (H2SO4)

• Alkalinity P (end point pH : 8.3)

CO3- HCO3

-

• Alkalinity M (total alkalinity, end point pH : 4.5)

HCO3- H2CO3

If P alk = 0 all of the alkalinity is bicarbonate

Utilitas

Utilitas

Hardness

• The presence of multivalent cations, most notably Ca and Mg ions

• 2 problems:– The reaction between hardness and soap

produces a sticky, gummy deposit (soap curd)– Ca2+ and Mg2+ precipitate while heated

reduces efficiency of HE

Utilitas

HardnessThere are 2 types of hardness based on the anions1. Carbonate hardness (CH) temporary

hardness. It can be removed by simply heating the water.

associated with HCO3- & CO3

2-

Ca2+ + 2HCO3- CaCO3 + CO2 + H2O

bicarbonate Ca bicarbonate

2. Noncarbonate hardness (NCH)

Utilitas

Total hardness (TH) = Ca2+ + Mg2+

NCH = TH – CH

CH = HCO3- + CO32-

Utilitas

Hardness commonly expresses as mg/L

CaCO3

Equivalent weight =

mg/L of X as CaCO3 =

n

weightmolecularoratom

meqmgXofweightequivalent

meqCaCOmgLmgXofionconcentrat

/

/0.50/ 3

Utilitas

Hardness classification

Descriptionhardness

meq/l mg/L as CaCO3

Soft < 1 < 50

Moderately hard 1 – 3 50 – 150

Hard 3 – 6 150 – 300

Very hard > 6 > 300

* Masters, G.M. 1998. Introduction to environmental engineering and science. p281

Utilitas

Conductivity

Electrical conductivity: a measure of the ionic activity of a solution in terms of its capacity to transmit current

Can be used to predict total dissolved solid

Units: micromhos/cm

Utilitas

Relationship between TDS & conductivity varies according to

solution concentration

Conductivity (mhos/cm)

TD

S (

mg

/L)

Dilute solution Concentrated solution

Utilitas

Water Saturation Index

Saturation Index is a means of evaluating water quality data to determine if the water has a tendency to be corrosive or to form a chemicals scale

The evaluation is based on the pH, alkalinity, hardness, total dissolved solid or conductivity

There are many type of saturation index, the most commonly used is :Langelier saturation indexRyznar saturation index

Utilitas

Langelier saturation index

• The saturation index (SI) can be calculated as follows :

• Whereas pHs = theoritical pH or pH at saturation can be determined from graph or by calculation

SI = pH – pHs

Utilitas

Utilitas

Utilitas

SI values and recommended treatment

www.water-research.net/corrosion.htm

SATURATION INDEX DESCRIPTION RECOMMENDATION

-5 Severe corrosion Treatment recommended

-4 Severe corrosion Treatment recommended

-3 Moderate corrosion Treatment recommended

-2 Moderate corrosion Treatment may be needed

-1 Mild corrosion Treatment may be needed

-0.5 None-mild corrosion Probably no treatment

0 Near balanced no treatment

0.5 Some faint coating Probably no treatment

1 Mild scale coating Treatment may be needed

2 Mild to moderate coating Treatment may be needed

3 Moderate scale forming Treatment advisable

4 Severe scale forming Treatment advisable

Utilitas

Ryznar saturation index

• The Ryznar Stability index is an empirical method for predicting scaling tendencies of water based on a study of operating results with water of various saturation indices

• This index is often used in combination with the Langelier index to improve the accuracy in predicting the scaling or corrosion tendencies of a water.

Stability index = 2pHs - pH = pHs - Langelier's Saturation pH

Utilitas

Utilitas

Biological characteristics

• Microbiological contaminants

• Microorganisms:– Non-pathogenic– Pathogenic

• Coliform bacteria (typically e.coli) are used as indicator organisms

• The presence of coliform suggests that the water is contaminated

Utilitas

Summary

Ground water Characteristic Surface water

Low turbidity High

High mineral Vary

Low dissolved O2 Vary

Low microorganism High

Stable temp & chem Unstable

Low pollutant High