WQ parameters......

Conductivity

Digital conductivity meter
(Source www.amberscience.com)

Cinductivity is the ability of water to carry an electric current. It can be measured using a conductivity meter. Pure water is not a good conductor of electricity. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about 0.5µScm⁻¹ to 2.0µScm⁻¹. Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases. Thus conductivity increases as water dissolved ionic species.

Typical conductivity of waters:

Distilled water:0.5 µ S cm⁻¹ to 2.0 µ S cm⁻¹

After usage: 2.0 µ S cm⁻¹ to 4.0 µ S cm⁻¹

Normal portable water :50 µ S cm⁻¹ to 1500 µ S cm⁻¹

Industrial waste: > 10000 µ Scm⁻¹

Water pH

   pH is a measurement of how acidic or how basic (alkaline) a solution is. pH is measured on a scale of 0 to 14. Water that is neutral has a pH of 7. Acidic water has pH values less than 7, with 0 being the most acidic. Likewise, basic water has values greater than 7, with 14 being the most basic. A change of 1 unit on a pH scale represents a 10 fold change in the pH, so that water with pH of 6 is 10 times more acidic than water with a pH of 7, and water with a pH of 5 is 100 times more acidic than water with a pH of 7.

Figure : the pH of some solutions

In most industries such as food preservation, beverages, process control. production of chemicals and production of fertilizers, agrochemicals, water pH is a most important factor.

pH Meter

Digital pH meter
(Source:www.saskschools.ca)

pH meter is used to measure pH of a liquid. pH electrode has a glass membrane at the tip. This glass membrane allows to transfer H+ ions. Normally we're measuring the activity of H+ ions, while assuming the solutions are diluted. First we have to calibrate the pH meter using pH=7 and pH=7 or pH=10 buffer solutions. Calibration is the step where check the instrument functions according to the known theoretical relationship. Daily calibrations are recommended for pH meters. Also potential measurements are always depend on temperature. Therefore, it is better to control temperature in potential measurements. 

WQ parameters contd......

Assessment of WQ parameters

o   Preparation for sampling and analysis

o   Sampling

o   Analysis at the site as needed

o   Sample preservation at the site

o   Lab analysis, in replicate

o   Calculation of the final result

o   Statistical treatment

o   Interpretation of result/ judgment of WQ

Preparation for sampling and analysis
       Before we’re going to analyze we have to have good idea about the sampling and analyzing process. We should know how many containers to be taken, what type of bottles to be taken, volume of sample that we need etc.

Ex: when we’re choosing the bottles or containers…

ü  Pesticide analysis- must use a glass bottles

ü  Metal ion analysis- must use plastic bottles because metal ions exchange Na⁺ ions with glass.

ü  DO (Dissolved Oxygen) - fixing should be done at the site and necessary chemicals should be added at the site.

Sampling

source:www.gov.mb.ca

Sample we select should represent the entire water body (should represent the bulk). Therefore, depending on the type of WQ parameter to be measured the volume of the sample and pretreatment method should be decided.

1)      Grab (catch) smaples

o   Sample collected at a particular time and place

o   Only recommended If the water body is completely uniform

o   Not suitable for natural water bodies

2)      Composite samples

o   Combination of grab samples collected at the same sampling point at different times

o   Only recommended of the level pollution is time dependent

o   Recommended for industrial outlets

o   Number of samples will depend on the

·         Industrial process

·         Which step uses more chemicals

·         Idea of the amount of chemical used

·         Number of shifts

3)      Integrated samples

o   Collection of grab samples from many different points at the same time

o   These samples are recommended to investigate water pollution of a natural water body

EX:

Integrated Sampling in a Lake

According to the above example, 

                                Level 1(Top surface)- 13 samples

                       Level 2(drop line1) - 9 samples

                       Level 3(drop line2) - 5 samples

Analise at the site as needed

Source: www.shorelinewa.gov

   Temperature, pH, conductivity, salinity color and tasty can be determined at the sampling site. If the measurements are taken at the site, no preservation requires. If measurements are done at a Laboratory, sample should be stored in a proper manner until the analysis is performed. In some cases special preservation methods are requires to maintain the pollution level unchanged.

WQ parameters will be discussed in next posts.............

Water Quality (WQ) Parameters..

What is Water Quality (WQ)?

   Water quality is a term used to describe the chemical, physical, and biological characteristics of water. Although scientific measurements are used to define a water's quality, it's not a simple thing to say that "this water is good," or "this water is bad."

These scientific measurements are known as WQ parameters.

Basically there are 3 types of water quality parameters.

   1. Physical Parameters (sample do not change while measuring)

    Ex:- Temperature, color, odor, taste, pH, turbidity, conductivity etc.

    

   2.  Chemical parameters ( Sample undergoes chemical changes)

    
    Ex:- acidity, alkalinity, BOD, COD, nitrate, sulphate, phosphate, metals, hardness, pesticides, oil/grease, phenol.

   3. Biological parameters
       Ex:- E-coli, coliform


Basically there are two methods for determine WQ parameters quantitatively. First one is the classical methods. This methods do not use instruments except balance.
    Ex:- Gravimetric, titrometric methods etc.

Other method is the Instrumental method. This methods always need instruments.

Instrumental Methods

Basic methods are,

·     Electrochemical methods

~Instrument that are used to measure electrical properties are used in this method.

~Ex: conductometry, potentiometry, voltametry and amperometry.

·     Spectroscopic methods

~Wave properties (wavelength, wave number, frequency etc.) are used as the independent variable.

~Ex: UV/ Visible, IR, NMR etc.

·     Radiochemical methods

~Measure the content of radioactive substances and radioactive properties.

·     Miscellaneous methods

~Turbidity, Circular dichroism (CD), polarimetry, refractive index (RI)

TABLE 1. INSTRUMENTAL TECHNIQUES
Method	Response
Potentiometry:	Many chemical reactions produce electric energy, a battery for example. The amount of chemical to produce a measured potential is calculated.
Coulometry:	The amount of electrical current and the duration over which it flows is a measure of the amount of chemical substance producing the current.
Conductimetry:	The number of charged chemical components in a solution determines the resistance or conductance of a solution to the passage of electrical current.
Voltammetry:	The magnitude of electric potential necessary to cause the breakdown of a chemical substance and the current resulting from that breakdown are related to the amount of chemical present.
Ultraviolet, visible, infrared, and x-ray spectometry:	The extent to which these rays are absorbed by a sample depends upon the amount of sample present
Thermogravimetry:	The loss in weight of a substance as it decomposes upon heating is proportional to the amount of substance initially present.
Nuclear magnetic resonance:	For chemicals showing magnetic properties the strength of the magnetism is related to the amount of substance present.
Nuclear activation analysis:	The amount of radioactivity produced by a substance is proportional to the amount of material emitting radiation.
Mass spectrometry:	The intensity of each component fraction present as a chemical is broken apart relates to the amount initially present.

WQ analyzing lab

Why do we need to assess the Quality of waters?

Because we must judge whether the water we use has the sufficient quality we use has the sufficient quality for the intended use. Therefore, the quality required depends on the use of water.Also water that is perfectly good to wash a car with may not be good enough to serve as drinking water at a dinner party. When the average person asks about water quality, they probably want to know if the water is good enough to use at home, to play in, to serve in a restaurant, etc., or if the quality of our natural waters are suitable for aquatic plants and animals.

BOI and CEA are the institutions that are responsible for formulated guide lines, consult parameters of other countries and also consult health aspects from certain organizations (WHO).

TABLE 2: DRINKING WATER STANDARDS (Sri Lanka Standards for potable water – SLS 614, 1983)

(Source: BOI Sri Lanka)

Highest desirable level: This is the level we would like to see. If a pollution parameter has value below the highest desirable level there will be no health problems.

Maximum permissible level: This is the legal limit. If the pollution parameter has a value above, this legal action can be taken.

Maximum tolerance limit: This is the limit above which cannot be tolerated by legal authorities.

Assessment of WQ parameters will be discussed in the next posts….