5 Simplest Tests for Controlling Pollution | Environmental Engineering

The following points highlight the five simplest tests for controlling pollution. The tests are: 1. Flame Photometry 2. XRF Analysis 3. Total Organic Carbon Analysis 4. Carbon-Hydrogen Analyser 5. Ion Chromatography Theory & Application.

Test # 1. Flame Photometry

This is a simple test to know the concentration of Alkali metals. The sodium and Potassium are more frequently determined because of their importance of biological systems.

This technique was developed by Bunsan and Kirchhaff in 1860, but Lunelegadh in 1930 established it as an important analytical method for the determination of Alkali metals.

In this method, the solution of sample under test is atomized and finally sprayed into the flame where it imparts colour whose wavelength is characteristic of the elements present in the sample. The intensity of the colour varies with the concentration of the metallic ions in the solution. The diagram of the flame photometer is shown in Fig. 16.1.

The compressed air is blown into the atomizer where it is broken into fine particles is carried with the sample to the mixing chamber. In the mixing chamber, the compressed air meets the fuel gas coming at a certain pressure and the mixture thus formed is fell into the burner for producing flame.

Radiation from the flame passes through a lenses, silt, and filler falls on the photocell. The galvanometer attached to the photocell measured the current development in the photocell by the radiation.

Due to the industrialization of world, the atmosphere becomes more and more sever. Thus now it affects on the living organism in number of undesirable ways. The suspended particles in air are recognized as major pollutants which have a pronounced effect on health and environment. The toxic element as V, As, Sc, Cd, Sb, Hg and Pb traced in the atmosphere producing hazard to human health and on other species.

Public health service have therefore prescribed the tolerance limits for such toxic metallic pollutants in environment samples with increasing the health hazards caused by the foreign substance in air and water, the role of X- Ray fluorescence spectrometry has become increasingly important and has come into extensive use for accurately monitoring the concentration of trace elements in the environment.

The analytical tools with trace metal sansitivition comparatable to x-ray fluorescence include Atomic absorption spectroscopy (AAS), Neutron Activation analysis (NAS) and Optical Emission Spectroscopy. In short each of the three methods has different advantages and has its special role in elemental analysis. To measure the aerosole in atmosphere the use of (XRF) is increasing because a number attribute made it especially attractive.

Test # 2. XRF Analysis:

XRF analysis is based on the measurement of wavelength (or energy) and intensity of characteristics x-ray emitted by a sample which has been excited by photon’s or charged particles such as electrons, protons and particles protons.

This technique can be divided in three areas:

1. X-ray generation (high voltage sealed off D-ray tube, radioisotope source of X- ray tube-fluorescer combination).

2. Wave length measurements.

3. Data interpretation.

Experimental Technique:

In XRF analysis a sample is put in a beam of X-ray to knock on electron out of one of the inner electron shells of the elements in a sample. The hole, left by displaced electrons is usually filled by an electron from an outer electron shell to high energy in the same atom when this happens an X-ray photon or radiation is emitted (fluorescence) whose energy (n sign) or wave length (sign) is characteristics of the elements involved (i.e. 1/Z₂, where z is a atomic number of the elements).

Area of Application:

As we are becoming polluted in air and water but also becoming more concerned with harmful trace elements in agricultural and processed food and in sea-foods. The XRF technique provide an ideal analysis system for samples of foods, fertilizer, solid wastes, soil, plants, forensic and medical science, rock and minerals.

The XRF may be used to identify the contribution from the different sources for the observed concentration of a particular toxic element or elements. One can also obtain information about the mechanism of air diffusion, turbulence, vortex motion etc. and their dependence on geophysical and metrological conditions.

Test # 3. Total Organic Carbon Analysis:

Total carbon analysis is a major tool used to calculate the total organic carbon present in the water, wastewater and in other effluents. Many investigators correlates the TOC with the traditional 5 days BOD or 5 hours COD as an indicator of organic loading. This method is useful for the analysis of samples after getting them from the source.

It is based on the principle that the carbon present in the sample is converted into carbon-di-oxide by carrier gas (oxygen) which is measured by non-dispersive infra-red analyzer. The homogeneous diluted samples when injected in the total carbon channel or inorganic carbon channel which are maintained at temperature of 95°C or 150°C respectively converts the carbon present in the samples into carbon-di-oxide by carrier gas.

The percentage of carbon present in samples is given in terms of CO₂ which is measured by non-dispersive infra-red analyser. The difference of readings between total carbon and inorganic carbon given organic carbon present in the samples. The fig. shows the flow diagram of the TOC analyser.

The following process is useful to TOC:

I. Preparation of working solution:

For the total organic carbon analysis two types of sample solutions are used.

A. Organic carbon stock solution:

Dissolve 2.125 gm of AR grade anhydrous potassium biphthalate (KHC₈H₄O₄) in CO₂, free water dilute to 1 litre. This stock solution contains 1000 mg/l (ppm) organic carbon stock. The stock solution of other concentration can be prepared by appropriate dilution.

B. Inorganic Carbon Stock Solution:

Dissolve 4.404 gm of AR grade anhydrous sodium carbonate (Na₂CO₃) in 500 ml of CO₂ free water and add 3.497 gm. AR grade anhydrous sodium-bi-carbonate to the flask and dilute to 1 litre with CO₂ free water. This solution of other concentration can be prepared by approximate dilution.

Sample Preparation:

When the sample contains appreciable amount of suspended solid it must be blended and 10 drops of conc. HCL added for removing large concentration of inorganic carbon. If the sample has large concentration of organic carbon, the sample may be diluted by CO₂ free water as sample should not contain total carbon more than 10,000 ppm.

Operation:

Open shut off valve on oxygen cylinder and set cylinder regulator for output pressure of 10 psi, the pressure regulator of both channels have to set up at 3 to 5 psi and flow control valves at 100 to 150 cc/min. Place main power switch ‘ON’. Turn ‘ON’ non-dispersive analyser and recorder.

The set point of high temperature furnace switch at ‘ON’. Turn ‘ON’ non-dispersive analyser and recorder. The set point of high temperature at 150°C. Allow sufficient warm up time for stable drift free operation.

The instrument is then standardized for full scale span of 1000 ppm or 100ppm for Total Carbon and 100 ppm for inorganic carbon by injecting 20 microlitre of standard stock solution.

Turn sample selector valve to Total Carbon position. Rinse syringe with CO₂ free distilled water and then with sample. Take 20 microlitre of sample in syringe and inject in the Total Carbon Channel port after removing plug and inject it in one stock. Let the syringe be in that position until the peak for Total Carbon Channel and inorganic carbon channel.

The difference between the two registered peaks given the total Organic Carbon present in it in terms of CO₂. At least three successive injection should be done for one sample in each port to minimize the error.

Test # 4. Carbon-Hydrogen Analyser:

The determination of carbon and hydrogen in organic material depends simply on burning the sample in an existing atmosphere and measuring the combustion products carbon-di-oxide and water. There are many methods in the field to determine the carbon and hydrogen but the recent advanced instrument for the micro analysis is known as ‘carbon hydrogen analyzer’ the instrument is very sensitive and MICRO analysis is done very quickly. This instrument can be used for the analysis of environmental organic pollutants for carbon and hydrogen determination.

A definite amount of sample is put in the .capsule crimped at both ends placed in combustion tube and heated in a stream of oxygen. The resulting products as carbon dioxide and water are absolved in weighed contrary hydrous Magnesium chlorate and these are weighed again after absorption is complete. Thus giving the weight of water and carbon dioxide produced and hence the percentage of carbon and hydrogen in the original sample.

The apparatus for the determination of carbon and hydrogen is sketched as shown in the fig. which consists of following three parts:

a. Scraber Tube:

This tube is used to pure the supply of oxygen. A 1/3 portion of the tube is tilled with Ascarite (sodalime) and anhydrone (dehydrate) separated by a thin layer of cotton plug. The water and carbon-di-oxide from the incoming oxygen in cylinder are absolved in this tube and purified oxygen is allowed to go in the system.

b. Absorption Assembly:

This assembly is made of three tubes. These are pyrex glass tubes provided with inlet and outlet and ground glass stoppers which allow inlet and outlet to be opened or closed. First tube be filled with anhydrome (dehydrate) and packed with a small cotton plug at both ends. 1/3 portion of the second tube is filled with Ascarite (sodalime) separating each by thin layer of cotton wad.

Both the ends are packed with a small cotton plug. 1/10 portion of the third tube is filled with anhydrome and remaining portion with the magnese-di-oxide (MNO₇) separated with a thin layer of cotton wad. Again both ends are packed with cotton wad.

c. Combustion Tube:

The combustion tube is made of transparent Quartz and held up in vertical position with open end up. A roll of silver wire gauze having 1 wide and necessary diameter to fit the bore of the combustion tube is inserted in end of the tube is then tilled with silver tungstane- magnesium oxide up to the bottom of the enlarged bulb on shown in Fig. The quarter chips of 8-20 mesh are poured into the combustion tubes.

Operation:

The unit is connected to a oxygen supply cylinder. The furnace starts heating gradually after the electric power is switched on and attains the temperature of 900°C by gradually advancing the setting of the furnace control knob. The absorption tubes are connected to the unit in order as shown in Fig. The oxygen cylinder is opened in order of their relation to the oxygen flow through the system. The oxygen flow rate is adjusted to 100 ml/min.

After three minutes a buzzer sound indicates the end of the operation. Thus ensuring the completion of sweep cycle. The same is repeated 2-3 times to bring the whole system in condition before the sample in run. After the initial conditioning, absorption tubes are detached for initial weighing and replaced immediately and locked.

As soon as the operating button is pushed, an intense flash of light is emitted indicating rapidly burning of the sample inside the combustion tubes. After completion of the sweep cycle, the stoppers of the absorption tubes are closed and reweighed. The increase in weight indicates the presence of carbon dioxide and water.

The percentage of carbon and hydrogen is calculated as follows:

Test # 5. Ion Chromatography Theory & Application:

Chromatography is a technique for the separation of the components of a mixture by which the components molecule migrates between stationing phase and mobile phase. In liquid chromatography mobile phase is liquid and stationary phase is either solid or liquid.

Ion chromatography provides powerful class of liquid chromatography having many methods for the analysis of organic and inorganic ions. Several works have been done to solve the problem of separation and detection of ions either independently or in integrated fashion.

Three major approaches are:

1. Suppressed ion chromatography

2. Non suppressed ion chromatography

3. Indirect detection ion chromatography

The principles and working of them are as following:

I. Suppressed ion chromatography the reactions are solved by the use of ion-exchange method. This is an oldest method.

In this method, the simple ion exchange of a sample X and mobile phase ions with the charged group of the stationary phase as:

X + R^x Y: Y + R⁺X: anion exchange

X⁺+ R Y⁺: Y⁺+RX⁺: cation exchange

In anion exchanging separation, the weekly interact ions which the ion exchanger, retained on the column mobile phase ion. The sample ions X are in attached with the mobile phase ions Y’. for the ionic sites R’ of the ion exchanger during the processing the sample ion retained for longer period in anion exchanging. In cation exchange the sample ions Y + are exchanged with the mobile phase ions X+, for the ionic sites R- of the ion exchanger, at the time of separation and detection of ions.

A conventional method is used for detecting the ions in the back-ground of water. The analysis of anion is done by employing a lower capacity anion exchanger as separating column. The conventional microporous strong cation exchanger in the H+ form for the stripper and sodium-carbonate or sodium-hydroxide are mobile phase.

The separating column contain a core of syrendivinyl benzene polymer (S/DVB) which as sulphonic acid group on its surface. This groups held small aminated latex particles ectrostatically. Animation converts the neutral latex particles into anion exchanger. The packing compressed of sulphonated S/DVN core (20-30 diameter) covered with a monolayer of anion exchange late x particals (0.1-0.5 diameter).

Separation is achieved by conventional ion exchange competition, carbonate ions acting as counter ions. When the effluent passed through the suppressor sodium carbonate got converted to carbonic acid a low conductivity eluent and sodium salts (sulphates, nitrates etc.) were converted to their conductance and detection by conductivity detector.

The second column called as suppressor complicates the use of ion chromatography. The suppressor column needed periodic regeneration and small attempts were made to tackle these problems by employing a counter current regenerated shell and tube device, incorporative sulphonated polyetrylene in exchange hollow fibres.

In this case sodium carbonate passed down word to the core of hollow cation exchange membrane and an acid stream on the outer side flowing upwards continuously supplying hydronium ions to exchange for sodium ions across the membrane. The leakage of anion is prevented by the Donnam exclusive effect, which operates in ion exchange membrane system and made more effective by employing dilute acid regenerating stream.

These column allows continuous operation with varying interference from base line drips. The device remained very difficult to fabricate. The anion hallow fibres for cations are also used for routine analysis.

As alternate new membrane technology using an electric field to accelerate the ion transports employed in this technology the potential is set up across the two membrane and then the cations are putted out of the channel across the membrane and replaced by hydronium ions. This system contains shorter length for the reaction (lower dead volume), has higher exchange capacity and is applicated to both cation and anions.

Non-Suppressed Ion Chromatography:

The ion chromatographic system with suppressed column is generally complicated and costly. Thus for the laboratory the conventional system with HPLC used for analysis of ions. Fritze used conductivity detector in conjunction with low capacity rasions (XAD-1) in separator column for the micro level analysis of the anions such as chloviclen bromide sulphates, nitrates etc. These anions detected in the back ground of low conductivity elements such as potassium citrate, potassium phthalate or potassium benzoate (pH 6.0).

Analysis by non-suppressed systems depends on existence of significant measurable difference between sample ions and the prevailing eluent ions. For improving sensitivity low capacity exchanger match the low ionic strength eluent employed which enable detection of small amounts of samples and proper displacing ions can display a useful difference in equivalent conductance in comparison with common inorganic ions.

Investigations have revealed that the simple mineral acids (1-10 mM) suit as mobile phase for anion analysis. pH adjustment in the range 3.5 to 6.0 can be used to vary the ionic strength and hence elution characteristics.

Silica columns with bonded quaternary amine functionalities have been developed as low capacity anion exchangers. The most favoured elution is O-phthalic acid (1-10 mM). The choice of eluent, working pH range and linear range of sample loading are severely restricted for silica based column packing. However, its efficiency is very high around 10,00 plated/ meter (for NO₃).

These columns can be used with other detectors. In single column operation the control of eluent is possible through the process. The conductivity detectors used for this method require a large electronic offset range for nulling the background conductivity of the eluent and small cell current to minimize heat dissipation in the cell and resulting base line driff and noise. The good results can be obtained of the detector by using low background conductivity stability.

Indirect Detection Ion Chromatography:

Inorganic ions such as Nitrates (NO₃), Nitrites (NO₂), Bromides (Br), Bromates (BrO₃), Fluoride (F), Thyocynates (SCN), Chlorides (CI), Sulphates (SO₄), Phosphate (FO,) observe very ultraviolet radiation. This is a low sensitivity method.

In this method ultraviolet detector is used with a mobile phase with very low absorbance at monitoring wave length. When the sample contain chromospheres eluate and pass through the detector the absorption of light take place and positive peak is recorded. When the mobile phase is light ionic species transparent and if the ion display light absorbing ion by ion exchange then the solvent and solute mixture will be less recorded.

The ultra-violet absorbing technique inorganic ions can be detected by using conventional variable wave length detectors. The phthalic acid is used at lower pH-values at concentration of 5 × 10⁴ on which provides monogram detection limits for the chloride and nitrates ions in 12 to 15 minutes.

The ultraviolet detector is used in the region 285-300 mm for such analysis and the normal procedure is that the detector must be filled with eluent to enable the change in absorbance to be measured.

6. Microprocessor:

There is lots of confusion between ‘chips’, ‘microprocessor’, ‘microcomputers’. To be able to discuss the application of micros, it is important for a system analyst to be fully aware of the difference between the various terms.

The word which is most often (mis-) used is ‘chips’, or ‘silicon chip’; what is a chip and for what can one be used? Early (first generation) computers were based on valves and were notoriously unreliable, yet they brought such an increase in computing power that it mattered little if they were unavailable for 99 percent of the time the remaining one percent made it worthwhile.

The discovery of the transistor led to the second generation of computer systems, with much increased reliability and decreased size, but the hardware still consisted of separate capacitors, diodes, resistors, and so on, that is of ‘discrete components’.

Advances in technology meant that number of components could be put on a single water (‘chip’) of semi-conductor, usually silicon, and this led to the third generation of a computer systems, consisting of ‘integrated circuits’.

The number of circuits which could be put on a single chip increased rapidly, and the various stages are generally known as ‘medium scale integration’ (MST), ‘large scale integration’ (LST) and more recently, ‘very large scale integration’ (VLSI). As the density of components increased, it became feasible to put more and more complex circuits on a single chip, until a whole processor could be fabricated on a single chip.

The earliest such devices, built at the beginning of the 1970s, were very slow and were four-bit processor (whereas, for example, a mainframe might be 32 bits.). Their principle use was in control application, and the limited instruction set (a few dozen typically) was aimed at this type of application. A four bit addition took around 10 (sign-s).

It was not long before eight-bit processor was produced. These had more instructions and were faster than their four-bit predecessors. As different technology evolved, these eight-bit processors were improved significantly, particularly in terms of the processing speed and the range of instructions.

Current eight-bit processors take 1 -2 (sign) for operations such as addition and, as well as the more common instruction, often have facilities for using binary-coded decimal operands and instructions to move large blocks of data around memory. More powerful 16bit micros are now becoming available. There are many misleading claims about the power of specific micros and many machines which are described as 32-bit wide external data bus.

As the packing density of Components increases, more and more logic can be accommodated on a single chip and a typical processor chip might contain the control processor unit (CPU), the arithmetic/logical unit, input/output control, address control and over 200 bits of CPU memory (registers and flags).

But this is not sufficient for a computer system, and there in lies the difference between a ‘microprocessor’ and ‘microcomputer’, terms which are often confused of used (incorrectly) as synonyms.

At the very least, a microcomputer requires, in addition to the CPU. A power supply (often a single 5 V supply is enough), some primary storage [read only memory (ROM) or random-access memory (RAM) and input/output circuits. In practice, rather more is required, particularly some form of ‘backing storage’ such as cassette tape, floppy disks of hard disks.

Advantage of microprocessor in analytical instrument:

1. As the size of the microprocessor is small thus the instrument base on it are compact in size.

2. Operation of the instrument becomes easy. By operating just a few switch the instrument starts functioning.

3. Range of the measurement becomes wider.

4. Since the automatic parts are zero thus the corrosion of alignment is left.

5. Since the microprocessor can make actual programs by it no use of logarithmic amplifier is necessary.

6. Due to the considerable researches in the field of microprocessors the new circuits provide more facilities.

7. Machines on the microprocessor having large amount of primary storage capacity (64 k to 512 k) for the data.

8. The microprocessor can also control the external data logging device like recorder, teletypewriter etc. coupled with the main instruments.

Digital Display of Instruments:

In the digital instruments, the signal is first converted into digital form (if required) and is then processed by using special electronic circuits- Integrated Circuits performing various complex logic operations like AND, OR NAND, Triggering, Counting, Decoding, etc., and finally given to special indicating units like 7 segment LED (Light Emitting-Diodes).

The signal value is thus displayed directly in digits. Liquid Crystal Display glows while Liquid Crystal Display (LCD) requires a small amount of external light. With Digital Display, measurement becomes very simple without scope of any personal error. Furthermore, the digital signals can be amplified indefinitely and stored accurately. Also because of ON-OFF character of digital circuits, the drift and stability problems are inherently negligible.

Precaution and remedies of microprocessor based instruments:

Protection from Humidity:

Humidity causes disturbance on the performance of instruments. In some cases, it may cause permanent damage to some instruments. In humid condition the fungi grow on some sensitive parts and damage the instruments. The corrosion also takes place which affect on the circuits of microprocessor. It causes short circuit problems.

Sensitive parts may allow stored in dry and cool environment in desiccators etc. Relative humidity of 60% or less is recommended for the analytical instruments. It advantages to give every day warm up of about one hour to the electronic instruments. The warm up not only stabilise the circuit operation but also avoids to building of humidity.

Improper Temperature:

Improper temperature affects on the instruments. The instrument should be kept within a specified range of 5°C to 40°Cof operating temperature. They should be housed in good ventilated rooms and never exposed directly in the sun. It has been observed that instruments give very stable and satisfactory results when operated at a steady temperature of 25°C.

Improper Operating Voltage:

The voltage in our country is not suitable and fluctuations over a quite wide range. The instruments should be protected against the wide fluctuation of supply, voltage by using voltage stabilisers. The supply voltage fluctuation can not only cause unstable readings.

Case must be taken while connecting the power cords to the three pin plug. This is particularly necessary because power cords of instruments of UK and other European countries use quite often different colours like yellow, blue, brown than our conventional green, red, black.

Protection from Dust:

Electronics circuits, high resistance, contacts and specially optical imparts like mirror, lenser, gratings are very much affected by dust. The instrument should be installed in air- conditioned rooms provided with linoleum to minimise the dust problem.