Analysis of effluents in chemical industry
|✅ Paper Type: Free Essay||✅ Subject: Environmental Studies|
|✅ Wordcount: 5259 words||✅ Published: 1st Jan 2015|
This report deals with effluent samples obtained from a Ceramic Industry, and analysis for their physicochemical properties, metallic and non-metallic ions. These parameters were compared with established international standard issued by EHS Guidelines. The heavy Ceramic Industry is an important source of pollutants to the environment. Ceramic wastewaters not only contain high suspended and total solids but also significant amounts of dissolved organics resulting in high BOD or COD loads. The method of testing for these parameters, and consequent laboratory results have been illustrated here with reference to their effect on the surrounding environment. The need for an in depth analysis and measurement of effluents, as a primary step towards wastewater treatment, has been established.
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Manufacturing industries are under continuous surveillance to adhere to environmental standards of pollution and control. In such situations, instead of viewing regulatory controls as extremely restrictive, they can exploit it to their benefit. By projecting itself as pro-environment, the company can work up a positive image and gain advantage against its competitors. From an economic point of view, by finding alternate methods of waste treatment, the company can save costs on disposal procedures. By recycling its wastes, the industry can also cut down on their raw material consumption.
These are but a few reasons why chemical industries should devote their research and technology towards effluent analysis. Only by an assessment of their wastes, the industry would be able to focus on the method of treatment required.
Waste Effluent and Environment Impact
Effluent analysis and monitoring systems should be implemented for all activities that may be recognized as having potential impact on the environment.
Waste treatment and effluent disposal usually depends on a combination of dilution, dissipation, physical, chemical and biological means as a technique to achieve treatment. Inappropriate sitting of treatment plants, ponds and effluent disposal systems can cause nuisance to residents, compromise sensitive landscapes and natural habitats. The potential for nuisance depends on a number of variable factors including prevailing and seasonal weather conditions, topography, separation distances from residences and public facilities, the quantity, concentration and the type of effluent and the nature of the receiving water environment. These factors are required to be assessed in an integrated way when an application for waste treatment and effluent disposal system is considered
Importance of Measurement
The most common disposal methods are landfill and to a lesser extent incineration. Each year approximately 111 million tonnes of controlled waste (household, commercial and industrial waste) are disposed of in landfill sites in the UAE. Some waste from sewage sludge is also placed in landfill sites, along with waste from mining and quarrying. As landfill waste decomposes, methane is released in considerable quantities. Methane is a strong greenhouse gas and contributes to global warming. Furthermore, the leachate fluids formed from decomposing waste can permeate through the underlying and surrounding geological strata, polluting groundwater which may be used for drinking water supplies. Containment landfills however, can limit the spread of this waste leachate.
Initially, Environment Protection Agencies came up with test methods so as to determine the amount of waste effluents released by an industry and the pollution caused by it to the environment. They intend to limit the amount of chemicals that can be hazardous if left in a final effluent and released into the surroundings.
In addition to this, an accurate analysis of the effluents gives an estimate of the kind of treatment and machinery required by the industry for its treatment. It is important to determine the Emission Limit Values (ELV) for every industry so that the effluents released by them to the environment is within permissible limits.
Release of waste effluents to the environment is one of the main problems of the ceramic industry. Environment issues related to ceramic industry mainly include waste water and solid wastes.
Production of ceramics consumes a lot of energy, especially for the operation of a kiln for its grinding operations. Wet milling, though being the preferred method of grinding, releases waste slurry. The ingredients in glazes and the clay body itself are toxic and could be carcinogenic in their raw form.
Process wastewater is mainly generated from cleaning water in preparation and casting units, and various process activities like glazing, decorating, polishing, and wet grinding. Process water is characterized by its turbidity and coloring due to very fine suspended particles of glaze and clay minerals. The potential pollutants of concern include suspended solids (e.g. clay and insoluble silicates
The effluent sludge primarily contains:
Other elemental impurities like Lithium, Strontium, Barium and Manganese are also present. Apart from these inorganic substances, it contains biologically degradable organic matter.
Emission and Effluent Guidelines
The following table gives the emission and effluent guidelines for the ceramic industry as provided by the General Environment, Health and Safety Guidelines Document. The chemical concentration of the effluent should not exceed those mentioned below:
Deviation from these levels in consideration of specific, local project conditions should be justified in the environmental assessment.
- Total Dissolved Solids
- Total Suspended Solids
- Oil and Grease
- Biological Oxygen Demand
- Chemical Oxygen Demand
- Heavy Metals, Major Metals and Trace Elements
pH (Power of Hydrogen)
It is the activity of dissolved hydrogen ions. It is measured with an ion-sensitive electrode which responds to hydrogen activity.
Conductivity is the degree to which a water sample can carry an electric current. The magnitude
of the conductivity of a sample is a function of the amount of ions present in the sample. High conductivity can be an indicator of excessive mineralization from either natural or industrial sources. The measure of conductivity is also a good screening test which helps determine which additional testing is required.
Total Solids in an effluent is the measure of the suspended particles and dissolved substances in it. The suspended particles consist of the particulate matter that is retained by a filter and the solids that pass through the filter forms the dissolved substances. It gives an indication of the salinity, turbidity and conductance of the effluent.
ie. TS = Total Dissolved Solids + Total Suspended Solids
Total Dissolved Solids (mg/L) include minerals, salts, cations, anions dissolved in water. To measure TDS, The sample is filtered first and the filtrate is heated in a dish till all the water evaporates leaving behind a residue. The weight of the empty dish should be determined previously. The dish along with the residue is measured again and the difference in weight gives the TDS of the sample.
Total Suspended Solids (mg/L) are solid materials suspended in water that can be trapped by a filter. To measure TSS, the effluent sample is passed through filter of preferably 0.45 micrometers. The filter weight should be determined previously. The residue on the filter is dried at around 100o C till all the water evaporates and the weight is measured again. The difference in the weight of the filter gives the TSS of the sample.
Experimental Values of the Sample Prior to Treatment
- pH = 6.72
- Salinity = 0.7
- Conductivity = 1.67 S /·m
- TSS = 2970 mg/L
- TDS = 1665 mg/L
- Total Solids = 4455 mg/L
(BOD/COD to be performed)
Biological Oxygen Demand
Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live. Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste.
Since it is a measure of the quantity of oxygen required for biodegradation, it can be used to detect the amount of bio-degradable matter.
BOD is measured by either Dilution Test (BOD5) and Manometric Test. BOD5 is the most widely used method of testing.
- 300 ml BOD bottles
- 2 – 5 liter glass bottle with siphon.
- 20 ± 1°C incubator
- DO meter
- Nutrient Solutions:
- Phosphate buffer : Dissolve 8.5 g KH2P04, 21.75 g K2HP04, 33.4 g Na2HP04·7H20, and 1.7 g NH4Cl in approx. 500 ml reagent water. Dilute to 1 L. The pH should be 7.2. Store in 4°C refrigerator.
- Magnesium sulfate solution : Dissolve 22.5 g MgSO4·7H20 in reagent water. Dilute to 1 L
- Calcium chloride solution : Dissolve 27.5 g CaCl2 in reagent water. Dilute to 1 L.
- Ferric Chloride solution : Dissolve 0.25 g FeCl3·6H20 in reagent water. Dilute to 1 L.
- Sample Preparation
- Test the effluent sample for residual chlorine. If detected, employ de-chlorination techniques and check again
- pH of the sample should be between 6.5- 7.5. As needed, dilute the sample with 1 N Sulfuric Acid or 1 N Sodium Hydroxide.
- To prevent loss of oxygen during incubation of these samples, the DO should be reduced by shaking the sample or aerating it with filtered compressed air.
- Dilution water may be prepared immediately before use, or, except for the addition of the phosphate buffer, days or weeks ahead of time. 1 ml of each nutrient solution is added per liter of dilution water. The phosphate buffer is the critical nutrient in stimulating contaminating growths so it must be added the day the water is to be used. Distilled water should be allowed to equilibrate in the incubator or with outside air for at least 24 hours at 20°C before use. To avoid dust or dirt contamination while allowing oxygenation, use a paper towel, cotton plug, or sponge to cover the bottle opening.
- The BOD bottle is filled by slowly adding sufficient dilution water so that the stopper can be inserted without leaving an air bubble
- Completely fill two BOD bottles with dilution water to be incubated as blanks.
- Incubation and Dissolved Oxygen Determination
- Calibrate DO meter each day of use and check membrane of probe. Record the barometric pressure each day of analysis.
- Determine the DO of the two dilution water blanks and all sample bottles
- Place the samples and the 2 dilution water blanks in a 20 ± 1°C incubator for 5 days. Fill water seals with dilution water and cap to reduce evaporation from seals. Check daily, add water to seals if necessary.
- Before removing the caps, pour off the water above the cap.
- After 5 days, determine the DO of the two dilution water blanks and the sample bottles.
The BOD is calculated using the difference between the initial and final dissolved oxygen levels in the sample. This value is multiplied by the dilution factor which is the ratio of bottle volume to sample volume.
Chemical Oxygen Demand
The determination of Chemical Oxygen Demand (COD) is widely used in municipal and industrial laboratories to measure the overall level of organic contamination in wastewater. The contamination level is determined by measuring the equivalent amount of oxygen required to oxidize organic matter in the sample. COD differs from BOD in that it measures the oxygen demand to digest all organic content, not just that portion which could be consumed by biological processes.
A COD test measures all organic carbon with the exception of certain aromatics (benzene, toluene, phenol, etc.) which are not completely oxidized in the reaction. COD is a chemically chelated/thermal oxidation reaction, and therefore, other reduced substances such as sulfides, sulfites, and ferrous iron will also be oxidized and reported as COD. NH3-N (ammonia) will NOT be oxidized as COD.
COD can be measured by the closed reflux titrimetric method and the closed reflux colorimetric method
The heater, or reactor, is used to obtain fast organic reactions. Since it is vital that the reaction take place at 150°C (±2°C) for 2 hours it is important to ensure accurate pre-heating.. The reactor is equipped with a timer to notify the operator when the reaction is completed.
A sample is refluxed in strongly acidic solution with a known excess of potassium dichromate
(K2Cr207). After digestion the remaining unreduced K2Cr207 is titrated with ferrous ammonium sulphate to determine the amount of K2Cr207 consumed and the oxidizable matter is calculated in terms of oxygen equivalent.
This procedure is applicable to COD values between 40 and 400 mg/L. Higher COD values can be obtained by careful dilution or by using higher concentrations of dichromate digestion solution
When a sample is digested, COD material in that sample is oxidized by the dichromate ion. The
result is the change in chromium from the hexavalent (VI) to the trivalent (III) state. Both chromium species exhibit a color and absorb light in the visible region of the spectrum. In the 400 nm region the dichromate ion (Cr2072-) absorbs strongly while the chromic ion (Cr3+) absorbs much less. In the 600 nm region it is the chromic ion that absorbs strongly and the dichromate ion has nearly zero absorption.
This method covers the ranges from 0 to 15000 mg/L 02
- 0- 150 mg/L near 420 nm
- 0-1000 (1500) mg/L near 600 nm
- 0-15000 mg/L near 600 nm
The US Environmental Protection Agency specifies that the only acceptable reportable measuring method for COD is the colorimetric dichromate method. Advantages in using this method include high accuracy, certifiable results and abate chloride interference.
The chemical oxygen demand (COD) test is widely used as a means of measuring the organic strength of domestic and industrial wastes. This test allows measurement of a waste in terms of the total quantity of oxygen required for oxidation to carbon dioxide and water. It is based upon the fact that all organic compounds, with a few exceptions, can be oxidized by the action of strong oxidizing agents under acid conditions. The amino nitrogen will be converted to ammonia nitrogen. However, organic nitrogen in higher oxidation states will be converted to nitrate.
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During the determination of CID, organic matter is converted to carbon dioxide and water regardless of the biological assimilability of the substances. For example, glucose and lignin are both oxidized completely. As a result, COD values are greater than BOD values and may be much greater when significant amounts of biologically resistant organic matter is present. Wood-pulping wastes are excellent examples because of their high lignin content.
One of the chief limitations of the COD test is its inability to differentiate between biologically oxidizable and biologically inert organic matter. In addition, it does not provide any evidence of the rate at which the biologically active material would be stabilized under conditions that exist in nature.
History of the COD Test
Chemical oxidizing agents have long been used for measuring the oxygen demand of polluted waters. Potassium permanganate solutions were used for many years, and the results were referred to as oxygen consumed from permanganate. The oxidation caused by permanganate was highly variable with respect to various types of compounds, and the degree of oxidation varied considerably with the strength of reagent used. Oxygen-consumed values were always considerable less than 5-day BOD values. This fact demonstrated the inability of permanganate to carry the oxidation to any particular end point.
Ceric sulfate, potassium iodate, and potassium dichromate are other oxidizing agents that have been studied extensively for the determination of chemical oxygen demand. Potassium dichromate has been found to be the most practical of all, since it is capable of oxidizing a wide variety of organic substances almost completely to carbon dioxide and water. Because all oxidizing agents must be used in excess, it is necessary to measure the amount of excess remaining at the end of the reaction period in order to calculate the amount actually used in t he oxidation of the organic matter. It is relatively easy to measure any excess of potassium dichromate, an important point in its favor.
In order for potassium dichromate to oxidize organic matter completely, the solution must be strongly acidic and at an elevated temperature. As a result, volatile material originally present and those formed during the digestion period are lost unless provision is made to prevent their escape. Reflux condensers are ordinarily used for this purpose and allow the sample to be boiled without significant loss of volatile organic compounds.
Certain organic compounds, particularly low molecular weight fatty acids, are not oxidized by dichromate unless a catalyst is present. It has been found that silver ion acts effectively in this capacity. Aromatic hydrocarbons and pyridine are not oxidized under any circumstances.
Chemical Oxygen Demand By Dichromate
Potassium dichromate is a relatively cheap compound that can be obtained in a high state of purity. The analytical-reagent grade, after drying at 103 oC, can be used to prepare solutions of an exact normality by direct weighing and dilution to the proper volume. The dichromate ion is a very potent oxidizing agent in solutions that are strongly acidic. The reaction involved in the usual case, where organic nitrogen is all in a reduced state(oxidation number of -3), may be represented in a general way as follows:
CnHaObNc + dCr2O2-7 + (8d +c)H+ —— nCo2 + (a+ 8d-3c)/2 H2O + cNH+4 + 2dCr3+
Where d = 2n/3 +a/6 – b/3 – c/2.
For these and other reasons, dichromate approaches an ideal reagent for the measurement of COD.
Selection of Normality
COD results are reported in terms of milligrams of oxygen, Since the equivalent weight of oxygen is 8 g, it would seem logical to use a N/8 or 0.25 N solution of oxidizing agent in the determination so that results can be calculation in accordance with the general procedure. Experience with the test has shown it has sufficient sensitivity to allow the use of a stronger solution of dichromate, and a N/4 or 0.25N solution is recommended. This allows the use of larger samples by doubling the range of COD that can be measured in the test procedure, since each milliliter of a 0.25 N solution of dichromate is equivalent to 2 mg of oxygen.
In any method of measuring COD, an excess of oxidizing agent must be present to ensure that all organic matter in oxidized as completely as is within the power of the reagent. This requires that a reasonably excess be present in all samples. In it necessary, of course, to measure the excess in some manner so that the actual amount reduced can be determined. A solution of a reducing agent is ordinarily used.
Nearly all solutions of reducing agents are gradually oxidized by oxygen dissolved from the air unless special care is taken to protect them from oxygen. Ferrous ion is an excellent reducing agent for dichromate. Solutions of it can be best prepared from ferrous ammonium sulfate which is obtainable in rather pure and stable form. In solutions, however, it is slowly oxidized by oxygen, and standardization is required each time the reagent is to be used. The standardization is made with the 0.25N solution of dichromate. The reaction between ferrous ammonium sulfate and dichromate may be represented as follows:
6Fe2+ + Cr2O2-7 + 14H+ —- 6Fe3+ + 2Cr3+ + 7H2O
Both the COD and BOD tests are designed to measure oxygen requirements by oxidation of organic matter present in the samples. It is important, therefore, that no organic matter from outside sources be present if a true measure of the amount present in the sample is to obtained. Since it is impossible to exclude extraneous organic matter in the BOD test and impractical to do so in the COD test, blank samples are required in both determinations.
A very marked change in oxidation-reduction potential (ORP) occurs at the end point of all oxidation-reduction reactions. Such changes may be readily detected by electrometric means if the necessary equipment is available. Oxidation-reduction indicators may also be used; Ferroin (ferrous 1,10-phenanthroline sulfate) is an excellent one to indicate when all dichromate has been reduced by ferrous ion. It gives a very sharp brown color change that is easily detected in spite of the blue color produced by the Cr3+ formed on reduction of the dichromate.
Although an oxidizing agent is used in the measurement of COD, it does not figure directly in the calculation of COD. This is because a solution of reducing agent must be used to determine how much of the oxidizing agent was used, and it is simpler to relate everything to the reducing agent in this case, because its strength varies from day to day and its normality is seldom, if ever, exactly equal to 0.25N.
Calculation of COD is made using the following formula :
COD(mg/L) = 8000 (blank titr. – sample titr.) [norm. Fe(Nh4)2(SO4)2] —– mL sample
Methods to Reduce Hazardous Waste Generation
The COD test can generate a large volume of liquid hazardous waste. In the past, common practice was to dilute completed samples with tap water and discharge them down the drain with a good flushing of water. This meant that considerable quantities of acid, chromium, silver, and also mercury (added for chloride complexation) could reach a treatment plant and perhaps surface waters. For this reason, drain disposal is now discouraged and sometimes prohibited, and so spent solutions must be stored, packaged and disposed into approved hazardous waste storage sites. It is possible to reduce this problem by recovering silver and mercury from the samples, but this requires proper permitting. In order to reduce this problem, alternate procedures can be used. “Standard Methods” now offers two closed reflux methods in which smaller sample and reagent volumes are used. Refluxing here is conducted in sealed containers. However, the principles are essentially the same as in the more historical open-reflux method. In order to maintain sufficient sensitivity with the reduced volumes, the concentration of the ferrous ammonium sulfate titrant is reduced. In one variation, a colorimetric rather than a volumetric procedure is used. This takes advantage of the change during organic oxidation from orange color of Cr(VI), which absorb at 420 nm. Measurements of color change from sample oxidation at either wavelength can be used for quantification. Although costs of prepared reagents for the closed flux COD procedures from commercial companies tend to be high, many analysts prefer them in comparison with reagents for the conventional reflux procedure because of their easy in use and reduction in quantities of resulting waste chemicals requiring disposal.
While these considerations tend to support the use of the closed reflux procedure, a similar variation can be made with the open reflux procedure as well. Here, for example, a 10 mL rather than a 50mL samples can be used. In this case, only 5 mL of dichromate solution is added together with only 15 mL of Ag+ amended concentrated sulfuric acid. By reducing the concentration of the ferrous ammonium sulfate titrant from 0.25 N to 0.025 N, suitable sensitivity can still be maintained. The sample reflux apparatus as used with larger samples works satisfactorily here. With this modification, only one-fifth of the volume of waste solutions are generated, and little sacrifice in analytical precision is made.
Certain reduced inorganic ions can be oxidized under the conditions of the COD test and thus can cause erroneously high results to be obtained. Chloride causes the most serious problem because of its normally high concentration in most wastewaters.
6Cl- + Cr2O2-7 + 14H+ —- 3Cl2 +2CR3+ + 7H2O
Fortunately, this interference can be eliminated by the addition of mercuric sulfate to the sample prior to the addition of the other reagents. The mercuric ion combines with the chloride ions to form a poorly ionized mercuric chloride complex
Hg2+ + 2Cl- —— —– HgCl2 (aq)
In the presence of excess mercuric ions the chloride-ion concentration is so small that it is not oxidized to any extent by dichromate.
Nitrite ix oxidized to nitrate and this interference can be overcome by the addition of sulfamic acid to the dichromate solution. However, significant amounts of nitrite seldom occur in wastes or in natural waters. This also holds true for other possible interferences such as ferrous iron and sulfide.
Application of COD Data
The COD test is used extensively in the analysis of industrial wastes. It is particularly valuable in surveys designed to determine and control losses to sewer systems. Results may be obtained within a relatively short time and measures taken to correct errors on the day they occur. In conjunction with the BOD test, the COD test is helpful in indicating toxic conditions and the presence og biologically resistant organic substances. The test is widely used in the operation of treatment facilities because of the speed with which results can be obtained.
BOD Vs. COD
To measure oxygen demand, biochemical oxygen demand (BOD) relies on bacteria to oxidize readily available organic matter during a five-day incubation period. COD uses strong chemicals to oxidize organic matter. Generally, COD is preferred to BOD for process control measurements because results are more reproducible and are available in just two hours rather than five days. By the time you have the results from a five day test, the plant conditions are no longer the same, so real time monitor and control cannot be relied upon by the use of BOD. COD is a quick and easy and the process at the wastewater treatment plant can be optimized and controlled with real time accuracy.
BOD simulates the actual treatment plant process by measuring the organic material microorganisms can oxidize. Although COD is comparable to BOD, it actually measures chemically oxidizable matter. The COD test is not a direct substitute for the BOD test; however, a ratio usually can be correlated between the two tests. This requires COD versus BOD testing over a specified period of time.
For industrial samples, COD is the only feasible test because of the presence of bacterial inhibitors or other chemical interferences, which would interfere with a BOD determination. Many industrial laboratories find that parallel COD and BOD testing is beneficial because the COD test can be used to target a specific BOD range.
The Ceramic Industry is a major source of pollutants to the environment. Industrial Wastes unless treated pose a threat to the environment and are extremely hazardous if left untreated. Hence evaluation of the same is of utmost important. The composition of the effluents should fall within the Emission Limit Values as specified by EHS Guidelines.
Analysis of effluents forms the primary phase of Wastewater Treatment. It indicates the type of treatment required and gives an estimate of the machinery and infrastructure to be laid. Only through a thorough assessment the industry would be able to gauge the various possibilities of treatment and recycling.
Summary and Future Research
The study so far has identified the importance and need for effluent analysis as the first step towards treatment systems. The chemical composition of effluents released from the Ceramic Industry have been estimated and their ELV’s mentioned. The tests and methods of analysis have been explained in depth and simulated in the laboratory so as to determine the chemical concentration levels of the effluent sample prior to treatment.
Further tests will include an analysis of the treated samples and verification with the standard values issued by EHS Guidelines. In addition, ICP atomic spectroscopy will be used to identify the presence of elemental contaminants and a report of the same will be provided to the Ceramic Company for their reference.
- Metcalf & Eddy, Inc., George Tchobanoglous, Franklin Burton, H. David Stensel, “Wastewater Engineering Treatment and Reuse”, 4th ed. McGraw-Hill.
- Lenore S. Clescerl, Arnold E. Greenberg, Andrew D. Eaton, “Standard Methods for Examination of Water & Wastewater”, 20th ed. Washington, DC: American Public Health Association.
- Environmental, Health and Safety Guidelines for Ceramic Tile and Sanitary Ware Manufacturing (pdf).
- M.L. Nollet, “Handbook of Waste Analysis”, 2nd ed, McGraw-Hill Publications.
- Sawyer, McCarty & Parkin, “Chemistry for Environmental Engineering and Science”, 5th edition. McGraw-Hill Publications.
Importance of Quantitative Measurements
Quantitative measurements serve as the keystone of engineering practice. Environmental engineering and science is perhaps most demanding in this respect, for it requires the use of not only the conventional measuring devices employed by engineers, but, in addition, many of the techniques and methods of measurement used by chemists, physicists, and some of htose used by biologists.
Every problem in environmental engineering and science must be approached initially in a manner that will define the problem. This approach necessitates the use of
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