Total Solids, Dissolved Solids and Suspended Solids in Water

Weighing balance

Introduction: 

Environmental engineering is concerned with the solid material in a wide range of natural waters and wastewaters. The usual definition of solids (referred to as "total solids") is the matter that remains as residue upon evaporation at 103~105°C. The various components of "total solids" can be simplified as follows  

 

Component of total solid

Total Solids (TS) are the total of all solids in a water sample. They include the total suspended solids and total dissolved solids. Total Suspended Solids (TSS) is the amount of filterable solids in a water sample. Samples are filtered through a glass fiber filter. The filters are dried and weighed to determine the amount of total suspended solids in mg/l of sample. Total Dissolved Solids (TDS) are those solids that pass through a filter with a pore size of 2.0 micron (1/1000000th of a meter, Also known as a Micrometer) or smaller. They are said to be non-filterable. After filtration the filtrate (liquid) is dried and the remaining residue is weighed and calculated as mg/l of Total Dissolved Solids. 

 

Environmental significance:  

Total solids measurements can be useful as an indicator of the effects of runoff from construction, agricultural practices, logging activities, sewage treatment plant discharges, and other sources. Total solids also affect water clarity. Higher solids decrease the passage of light through water, thereby slowing more rapidly and hold more heat; this, in turn, might adversely affect photosynthesis by aquatic plants. Water will heat up affect aquatic life that has adapted to a lower temperature regime. As with turbidity, concentrations often increase sharply during rainfall, especially in developed watersheds. They can also rise sharply during dry weather if earth-disturbing activities are occurring in or near the stream without erosion control practices in place. Regular monitoring of total solids can help detect trends that might indicate increasing erosion in developing watersheds. Total solids are related closely to stream flow and velocity and should be correlated with these factors. Any change in total solids over time should be measured at the same site at the same flow. Water with total solids generally is of inferior palatability and may induce an unfavorable physiological reaction. It may be esthetically unsatisfactory for purposes such as bathing. Total solids will be higher in highly mineralized waters, which result in unsuitability for many industrial applications. It indicates effectiveness of sedimentation process and it affects effectiveness of disinfection process in killing microorganisms. It is used to assess the suitability of potential supply of water for various uses. In the case of water softening, amount of total solids determine the type of softening procedure. Corrosion control is frequently accomplished by the production of stabilized waters through pH adjustment. The pH stabilization depends to some extent upon the total solids present as well as alkalinity and temperature. 

Solids analyses are important in the control of biological and physical wastewater treatment processes and for assessing compliance with regulatory agency wastewater effluent limitations 

 

Although the waste water or sewage normally contains 99.9 percent of water and only 0.1 percent of solids, but it is the solids that have the nuisance value. The amount of solids in wastewater is frequently used to describe the strength of the water. The more solids present in a particular wastewater, the stronger that wastewater will be. The environmental impacts of solids in all forms have detrimental effects on quality since they cause putrefaction problems. If the solids in wastewater are mostly organic, the impact on a treatment plant is greater than if the solids are mostly inorganic. 

 

In the realm of municipal wastewater, suspended solids analysis is by far the most important gravimetric method. It is used to evaluate the strength of the raw wastewater as well as the overall efficiency of treatment. Furthermore, most waste water treatment plants (WWTP’s) have effluent standards of 10 to 30 mg/L suspended solids which may be legally enforceable. As was the case with municipal wastewater, suspended solids analysis is useful as a means of assessing the strength of industrial wastewaters and the efficiency of industrial wastewater treatment.  

 

Some typical solid concentration

Dissolved minerals, gases and organic constituents may produce aesthetically displeasing color, taste and odor. Some dissolved organic chemicals may deplete the dissolved oxygen in the receiving waters and some may be inert to biological oxidation, yet others have been identified as carcinogens. Water with higher solids content often has a laxative and sometimes the reverse effect upon people whose bodies are not adjusted to them. Estimation of total dissolved solids is useful to determine whether the water is suitable for drinking purpose, agriculture and industrial purpose. Suspended material is aesthetically displeasing and provides adsorption sites for chemical and biological agents. Suspended organic solids which are degraded anaerobically may release obnoxious odors. Biologically active suspended solids may include disease causing organisms as well as organisms such as toxic producing strains of algae. The suspended solids parameter is used to measure the quality of wastewater influent and effluent. Suspended solids determination is extremely valuable in the analysis of polluted waters. Suspended solids exclude light, thus reducing the growth of oxygen producing plants. High concentration of dissolved solids about 3000 mg/L may also produce distress in livestock. In industries, the use of water with high amount of dissolved solids may lead to scaling in boilers, corrosion and degraded quality of the product. 

 

 

Guideline: 

According to Bangladesh Environment Conservation Rules (1997), potable water should not contain more than 1000 mg/l of total dissolved solids (TDS). 

 

Principle: 

The measurement of solids is by means of the gravimetric procedure. The various forms of solids are determined by weighing after the appropriate handling procedures. The total solids concentration of a sample can be found directly by weighing the sample before and after drying at 103°C. However, the remaining forms, TDS and TSS require filtration of the sample. For liquid samples, all these solids levels are reported in mg/L.   

 

A rapid assessment of the dissolved solids content of water can be obtained by specific conductance measurements. Such measurement indicates the capacity of a sample to carry an electric current which in turn is related to the concentration of ionized substances in the water. Most dissolved inorganic substances in water are in ionized form and so contribute to the specific conductance. Although the nature of the various ions, their relative concentrations, and the ionic strength of the water affect this measurement, such measurement can give practical estimate of the dissolved mineral content of water. The TDS content can be approximated by multiplying the specific conductance in micro-Siemens per cm (µS/cm) by an empirical factor varying from 0.55 to 0.90 depending on the chemical composition of the TDS. 

 

Sample handling and preservation: 

Preservation of sample is not practical. Because biological activity will continue after a sample has been taken, changes may occur during handling and storage. Both the characteristics and the amount of solids may change. To reduce this change in samples taken for solids determinations, keep all samples at 4° C. Do not allow samples to freeze. Analysis should begin as soon as possible. 

 

Precautions: 

The following precautions should be observed while performing the experiment.

Water or Wastewater samples which contain high concentrations of calcium, chloride, magnesium or sulphate can rapidly absorb moisture from the air. Such samples may need to be dried for a longer period of time, cooled under proper desiccation and weighed rapidly in order to achieve a reasonable constant weight. We should be aware prolonged drying may result in loss of constituents, particularly nitrates and chlorides. 

Non-representative particulates such as leaves, sticks, fish and lumps of fecal matter should be excluded from the sample if it is determined that their inclusion is not desired in the final result. 

Floating oil and grease, if present, should be included in the sample and dispersed by a blender device before sub-sampling. 

Volume of sample should be adjusted to have residue left after drying as 100 to 200mg. It is mainly to prevent large amount of residue in entrapping water during evaporation. 

Highly mineralized water containing significant concentration of calcium, magnesium, chloride, and/or sulphate may be hygroscopic. Hence prolonged drying, desiccation and rapid weighing. 

We should be aware prolonged drying may result in loss of constituents, particularly nitrates and chlorides. 

 

Apparatus:  

Balance 

Beaker  

Measuring Cylinder  

Filter paper  

Funnel 

Dropper 

 

Procedure:  

Measurement of Total Solids (TS) 

(1) Take a clear dry glass beaker (which was kept at 103°C in an oven for 1 hour) of 150ml. capacity and put appropriate identification mark on it. Weight the beaker and note the weight.   (2) Pour 100ml. of the thoroughly mixed sample, measured by the measuring cylinder, in the beaker.  

(3) Place the beaker in an oven maintained at 103°C for 24hours. After 24 hours, cool the beaker and weight. Find out the weight of solids in the beaker by subtracting the weight of the clean beaker determined in step (1)  (4) Calculate total solids (TS) as follows:  

 

Measurement of Total Dissolved Solids (TDS) (1)  Same as above (step 1 of total solids).  

Take a 100 ml. of sample and filter it through a double layered filter paper and collect the filtrate in a beaker.  

The repeat the same procedure as in steps (3) and (4) of the total solids determination and determine the dissolved solids contents as follows:  

 

Calculation:   

 

Total solids, TS (mg/l) = mg of solids in the beaker x 1000 / (volume of sample) 

 

Total Dissolved Solids, TDS (mg/l) =mg of solids in the beaker x1000 /(volume of sample) 

 

Total Suspended Solids, TSS (mg/l) = TS (mg/l) – TDS (mg/l)

                              Table

Break Point Chlorination

Introduction: 

Chlorination of public water supplies and polluted waters serves primarily to destroy or deactivate disease-producing microorganisms. Disinfection with chlorine is widely practiced. Chlorination may produce some adverse effects including taste and odor problem. in recent years, chlorination has been found to produce trihalomethanes (THMs) and other organics of health concern (THMs are suspected human carcinogens). Thus, use of alternative disinfectants, such as chlorine dioxide and ozone that do not cause this particular problem, is increasing. 

 

Theory:  

Disinfectant capabilities of chlorine depend on its chemical form in water, which in turn is dependent on pH, temperature, organic content of water, and other water quality factors. Chlorine is used in the form of free chlorine [e.g., chlorine gas] or as hypochlorites [e.g., NaOCl and Ca(OC1)2]. Chlorine applied to water either as free chlorine or hypochlorite initially undergoes hydrolysis to form free chlorine consisting of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion.  

 

Chlorine gas rapidly hydrolyzes to hypochlorous acid according to: 

Cl2 + H2O = HOCl + H+ +Cl–   

 

Aqueous solutions of sodium or calcium hypochlorite hydrolyze too: 

 

14.1 

Ca(OCl)2 + 2H2O = Ca2+ + 2HOCl + 2OH.         14.2 

NaOCl + H2O = Na+ + HOCl + OH–  

 

Hypochlorous acid is a weak acid and will disassociate according to: 14.3 

HOCl H+ +OCl– 14.4 

 

The two chemical species formed by chlorine in water, hypochlorous acid (HOCl) and hypochlorite ion (OCl–), are commonly referred to as “free” or “available” chlorine. 

 

Figure 14.1: Distribution of Chlorine species at 250C 

 

Figure 13.1 shows that Cl2 can be significantly at low pH values (below pH 2); while HOCl is dominant between pH 3 and 6. Between pH 6 and 9, the relative fraction of HOCl decrease, while the corresponding fraction of OCl- increases. In waters with pH between 6.5~8.5, the reaction is incomplete and both species (HOCl and OCl-) will be present. Hypochlorous acid is the more germicidal of the two, especially at short contact time. The dissociation of HOCl is also temperature dependent. The effect of temperature is such that at a given pH, the fraction of HOCl will be lower at higher temperatures.  

 

Reactions of Chorine with Impurities in Water: 

 

Reactions with Ammonia: 

Free chlorine reacts readily with ammonia and certain nitrogenous compounds to form what are collectively known as "combined chlorine". The inorganic chloramines consist of three species: monochloramine (NH2CI), dichloramine (NHCl2) and trichloramine or nitrogen trichloride (NCI3). The presence and concentrations of these combined forms depend on a number of factors including the ratio of chlorine to ammonia-nitrogen, chlorine dose, temperature, pH and alkalinity.  

 

NH3 + HOCI = NH2C1 + H2O; pH 4.5 to 8  14.5 

NH2CI + HOCI = NHCl2 + H2O; pH 4.5 to 8 14.6 

NHCl2 HOCI = NCI3 + H2O; pH < 4.5 14.7 

 

In addition to chlorinating ammonia, chlorine also reacts to oxidize ammonia to chlorine-free products (e.g., nitrogen gas and nitrate) as shown below. 

 

3 Cl2 + 2 NH3 = N2 (g) + 6H+ + 6 CI-  14.8 

4C12 + NH3 + 3H2O = 8C1- + NO3- + 9H+    14.9 

 

The mono- and dichloramines have significant disinfecting power and are therefore of interest in the measurement of chlorine residuals. Combined chlorine in water supplies may be formed in the treatment of raw waters containing ammonia; chlorinated wastewater effluents, as well as certain chlorinated industrial effluents normally contain only combined chlorine. 

 

Reactions with Other Impurities: 

Chlorine combines with various reducing agents and organic compounds thus increasing the chlorine demand which must be satisfied before chlorine is available to accomplish disinfection. 

Fe2+, Mn2+, NO2-, and H2S are examples of inorganic reducing agents present in water supplies that will react with chlorine. Chlorine can react with phenols to produce mono-, di-, or trichlorophenols, which can impart tastes and odors to waters, Chlorine also reacts with humic substances present in water to form trihalomethanes (THMs, e.g., chloroform, brornoform, etc.) which are suspected human carcinogens (Note: According to USEPA, maximum allowable level of THMs in drinking water is 100 µg/L). 

 

Break Point Chlorination 

If chlorine is added to water containing reducing agents and ammonia (either naturally present or added to water to produce combined chlorine), a hump-shaped breakpoint curve is produced as shown in following figure. The different segment of the curve is described as follows : 

 

If the water is free of ammonia and other compounds that may react with chlorine, the application of chlorine will yield free available chlorine residual of same concentration. This is denoted by the ‘no demand line’ or the "zero demand line" (see Fig.). 

Chlorine first reacts with reducing agents such as H2S, Fe-2+, Mn2+ and develops no measurable residual as shown by the portion of the curve from Origin up to point A.  

 

Figure 14.2: Generalized curve obtained during breakpoint chlorination  of water sample containing ammonia  

Addition of chlorine beyond point A results in forming mainly mono- and dichloramines. With mole ratios of chlorine to ammonia up to 1:1 [i.e., C12:NH3-N = 1:1], both mono and di-chloramines are formed. Chloramines thus formed are effective disinfectants and are shown as combined available chlorine residual in figure (From A to B). 

Further increase in the mole ratio of chlorine to ammonia result in formation of some trichloramine and oxidation of part of ammonia to N2 and NO3-. These reactions are essentially complete when 1.5 mole of chlorine has been added for each mole of ammonia nitrogen originally present in water [i.e., C12:NH3-N = 1.5:1]. This is represented by the portion of the curve from B to C. 

Addition of chlorine beyond point C would produce free chlorine residuals and is referred to as "breakpoint chlorination". In other words, chlorination of water to the extent that all ammonia is converted to N2 or higher oxidation state is referred to as "breakpoint chlorination'. 

Addition of chlorine beyond point C would produce free chlorine residuals and is referredto as "breakpoint chlorination". In other words, chlorination of water to the extent that all ammonia is converted to N2 or higher oxidation state is referred to as "breakpoint chlorination". 

 

Environmental Significance:  

Breakpoint chlorination is required to obtain a free chlorine residual for better disinfection if ammonia is present in a water supply. While free chlorine residuals have good disinfecting powers, they are usually dissipated quickly in the distribution system. For this reason, final treatment with ammonia if often practiced to convert free chlorine residuals to longer-lasting combined chlorine residuals. The difference between the amount of chlorine added to the water and the amount of residual chlorine (i.e., free and combined available chlorine remaining) at the end of a specified contact period is termed as "chlorine demand'. 

 

Apparatus: 

Erlemeyer flask (250 mL)  

Bottle  

Beaker (250 mL)  

Measuring cylinder  

Dropper  

Stirrer 

 

Reagents: 

Starch Indicator  

Standard 0.025 N Sodium thiosulfate  

Potassium Iodine crystal 

Concentrated Acetic Acid 

Chlorine water  

 

Procedure: 

1.) Place 200-mL portion of the water to be chlorinated in each of six 250-mL flasks. 

2.) Add required quantity (as instructed by your teacher) of "chlorine water" (stock solution of bleaching powder in water) in each of the flasks. The chlorine content of the "chlorine water" (determined earlier in the laboratory) would be provided to you by your teacher. Calculate the chlorine dose for each of the six flasks. 

3.) Shake each flask gently and allow to stand for 30 minutes.

4.) Determine residual chlorine of water from each flask by the starch-iodine method as described below: 

 

Starch-Iodine Method: 

The starch-iodine method is based on the oxidizing power of free and combined chlorine residuals to convert iodide ion into free iodine at pH 8 or less, as shown below. 

 

Cl2 + 2I- = I2 + 2 Cl- 

 

In the starch-iodine method, the quantity of chlorine residuals is determined by measuring the quantity of iodine by titration with a reducing agent sodium thiosulfate (Na2S2O3). The end point of titration is indicated by the disappearance of blue color, produced by the reaction between iodine and starch (which is added as indicator during the titration), 

 

I2 + 2 Na2S2O3 = Na2S4O6 + 2 Nal or, I2 + 2S2O32- = S4O62-  + 2I- I2 + 

starch = blue color 

(Qualitative test for the presence of iodine/chlorine) 

 

The titration is carried out at pH 3 to 4, because the reaction with thiosulfate is not stoichiometric at neutral pH due to partial oxidation of the thiosulfate to sulphate. 

 

Procedure for determination of residual chlorine concentration: 

1.) Place 200 mL of the sample in an Erlenmeyer flask. 

2.) Add 'about 1g of potassium iodide (estimated on a spatula) and 2 mL of concentrated Acetic acid to the water. 

3.) Add 0.025 N sodium thiosulfate drop by drop from a burette until the yellow color almost disappears. 

4.) Add 1 mL of starch solution to the water. 

5.) Continue addition of standard sodium thiosulfate (Na2S2O3) solution until the blue color just disappears. 

6.) Record the quantity (in mL) of sodium thiosulfate (Na2S2O3) solution used. 

 

 

Calculation: 

 

Residual chlorine (mg/L) = mL of 0.025N sodium thiosulfate used x M.F.  

M.F 

Table:

Chloride in water

Introduction:

Chlorides occur in all natural waters in widely varying concentration, the chloride content normally increases as the mineral content increases. Upland and mountain supplies usually are quite low in chlorides, whereas river and groundwater usually have a considerable amount. Sea and ocean waters represent the residues resulting from partial evaporation of natural waters that flow into them and chloride levels are very high. Chlorides gain access to natural waters in many ways. The solvent power of water dissolves chlorides from topsoil and deeper formations. Spray from the ocean is carried inland as droplets or as minute salt crystals, which result from evaporation of the water in the droplets. These sources constantly replenish the chlorides in inland areas where they fall. Ocean and seawaters invade the rivers that drain into them, particularly the deeper rivers. The salt water, being denser, flows upstream under the fresh water, which is flowing downstream. There is a constant intermixing of the salt water with the fresh water above. Groundwater in areas adjacent to the ocean is in hydrostatic balance with seawater. Over-pumping of groundwater produces a difference in hydrostatic head in favor of the seawater, and it introduce into the fresh water area. Such intrusion has occurred in many areas of the coastal southern region of Bangladesh.  Human excreta, particularly urine, contain chloride in an amount about equal to the chlorides consumed with food and water. This amount average about 6 gm of chlorides per person per day and increases the amount of CC in municipal wastewater about 15 mg/l above that of the carriage water. Thus, wastewater effluents add considerable chlorides to receiving streams. Many industrial wastes (e.g., tannery waste) also contain appreciable amount of chlorides.  

 

Environmental significance: 

Chlorides in reasonable concentrations are not harmful to human. At concentrations above 250 mg/L they give a salty taste to water, which is objectionable to many people. For this reason, chlorides are generally limited to 250 mg/L in supplies intended for public use. In many areas of the world where water supplies are scarce, source be containing as much as 2,000 mg/L are used for domestic purposes without the development of adverse effects, once the human system becomes adapted to the water. 

 

Guideline: 

According to Bangladesh Environment Conservation Rules (1997), drinking water standard for chloride is 150 - 600 mg/L; but for coastal regions of Bangladesh, the limit has been relaxed to 1000 mg/L. 

 

Principle: (Mohr’s Method) 

This method determines the chloride ion concentration of a solution by titration with silver nitrate. As the silver nitrate solution is slowly added, a precipitate of silver chloride forms.  

 

Ag+(aq) + Cl–(aq) → AgCl(s) 8.1 

 

The end point of the titration occurs when all the chloride ions are precipitated. Then additional silver ions react with the chromate ions of the indicator, potassium chromate, to form a red-brown precipitate of silver chromate.  

 

2Ag+(aq) + CrO42–(aq)→ Ag2CrO4(s) 8.2 

 

This method can be used to determine the chloride ion concentration of water samples from many sources such as seawater, stream water, river water and estuary water. The pH of the sample solutions should be between 6.5 and 10. If the solutions are acidic, the gravimetric method or Volhard’s method should be used. 

 

The end point of titration cannot be detected visually unless an indicator capable of demonstrating the presence of excess Ag+ is present. The indicator normally used is potassium chromate, which supplies chromate ions. As the concentration of CI- ions becomes exhausted, the silver ion concentration increases and a reddish brown precipitate of silver chromate is formed. 

 

2Ag++CrO42- = Ag2CrO4 (reddish brown precipitate) 8.3 

 

This is taken as evidence that all chloride has been precipitated. Since an excess Ag+ is needed to produce a visible amount of Ag2CrO4, the indicator error is subtracted from all titrations. 

The indicator error or blank varies somewhat with the ability of individuals to detect a noticeable color change. The usual range is 0.2 to 0.4 mL of titrant. An error of 0.2 mL will be used in the class. 

 

Precautions:  

A uniform sample size must be used, preferably 100 ml (or 50 mL), so that ionic concentrations needed to indicate the end point will be constant. 

The pH must be in the range of 7 to 8 because Ag+ is precipitated as AgOH at high pH levels and the CrO42- is converted to Cr2O72- at low pH levels, 

A definite amount of indicator must be used to provide a certain concentration of CrO4; otherwise Ag2CrO4 may form too soon or not soon enough. 

The chromate solution needs to be prepared and used with care as chromate is a known carcinogen. 

Silver nitrate solution causes staining of skin and fabric (chemical burns). Any spills should be rinsed with water immediately. 

 

Apparatus: 

Burette  

Measuring cylinder 

Beaker  

Dropper 

Stirrer 

 

Reagents: 

Potassium chromate indicator  

Silver nitrate solution (0.0141 N)  

 

Procedure: 

Take 50 mL of the sample in a beaker and add 5 drops (about 1 mL) of potassium chromate indicator to it. 

Add standard (0.0141 N) silver nitrate solution to the sample from a burette, a few drops at a time, with constant stirring until the first permanent reddish color appears. This can be determined by comparison with distilled water blank. Record the mL of silver nitrate used. 

If more than 7 or 8 mL of silver nitrate solution are required, the entire procedure should be repeated using a smaller sample diluted to 50 ml with distilled water. 

 

Calculation: 

 

Chloride, Cl- (mg/L)  = (mL of AgNO3 used - "error" or "blank") x Multiplying Factor (M.F.) 

 

Where, M.F.  

 

 

                      Table

biochemical oxygen demand

Introduction: 

The biochemical oxygen demand determination is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic organisms in a water body to break the organic materials present in the given water sample at certain temperature over a specific period of time. 

BOD of water or polluted water is the amount of oxygen required for the biological decomposition of dissolved organic matter to occur under standard condition at a standardized time and temperature. Usually, the time is taken as 5 days and the temperature is 20°C. 

The test measures the molecular oxygen utilized during a specified incubation period for the biochemical degradation of organic material (carbonaceous demand) and the oxygen used to oxidize inorganic material such as sulfides and ferrous ion. It also may measure the amount of oxygen used to oxidize reduced forms of nitrogen (nitrogenous demand). 

 

Environmental significance: 

BOD is the principle test to give an idea of the biodegradability of any sample and strength of the waste. Hence the amount of pollution can be easily measured by it. Efficiency of any treatment plant can be judged by considering influent BOD and the effluent BOD and so also the organic loading on the unit.  

 

Application of the test to organic waste discharges allows calculation of the effect of the discharges on the oxygen resources of the receiving water. Data from BOD tests are used for the development of engineering criteria for the design of wastewater treatment plants. Ordinary domestic sewage may have a BOD of 200 mg/L. Any effluent to be discharged into natural bodies of water should have BOD less than 30 mg/L. This is important parameter to assess the pollution of surface waters and ground waters where contamination occurred due to disposal of domestic and industrial effluents. Drinking water usually has a BOD of less than 1 mg/L. But, when BOD value reaches 5 mg/L, the water is doubtful in purity. The determination of BOD is used in studies to measure the self-purification capacity of streams and serves regulatory authorities as a means of checking on the quality of effluents discharged to stream waters. 

The determination of the BOD of wastes is useful in the design of treatment facilities. It is the only parameter, to give an idea of the biodegradability of any sample and self-purification capacity of rivers and streams. The BOD test is among the most important method in sanitary analysis to determine the polluting power, or strength of sewage, industrial wastes or polluted water. It serves as a measure of the amount of clean diluting water required for the successful disposal of sewage by dilution.  

 

Guideline:  

According to Bangladesh Environment Conservation Rules (1997), drinking water standard for biochemical oxygen demand (BOD) is 0.2 mg/L (at 20°C). For wastewater effluent allowable concentration of BOD varies from 50- 250 mg/L depending on discharge point of the effluent (e.g., inland water, irrigation land, public sewer etc.)   

 

Principle: 

The sample is filled in an airtight bottle and incubated at specific temperature for 5 days. The dissolved oxygen (DO) content of the sample is determined before and after five days of incubation at 20°C and the BOD is calculated from the difference between initial and final DO. The initial DO is determined shortly after the dilution is made; all oxygen uptake occurring after this measurement is included in the BOD measurement.  

 

Since the oxygen demand of typical waste is sever hundred milligrams per liter, and since the saturated value of DO for water at 20uC is only 9.1 mg/L, it is usually necessary to dilute the sample to keep final DO above zero. If during the five days of experiment, the DO drops to zero, then the test is invalid since more oxygen would have been removed had more been available. 

 

The five-day BOD of a diluted sample is given by, 

 

BOD5 = [DOi - DOf] × D.F.    11.1 

 

Here,  

Dilution factor (D.F.) = 

 

In some cases, it becomes necessary to seed the dilution water with microorganisms to ensure that there is an adequate bacterial population to carry out the biodegradation. In such cases, two sets of BOD bottles must be prepared, one for just the seeded dilution water (called the "blank") and the other for the mixture of wastewater and dilution wader.  The changes in DO in both are measured. The oxygen demand of waste water (BODw) is then determined from the following relationship: 

 

BODm × Vm = BODw × Vw + BODd × Vd 11.2 

 

Where, BODm, is the BOD of the mixture of wastewater and dilution water and BODd is the BOD of the dilution water alone; Vw and Vd are the volumes of wastewater and dilution water respectively in the mixture and Vm = Vw + Vd. 

 

Sample handling and preservation: 

Preservation of sample is not practical. Because biological activity will continue after a sample has been taken, changes may occur during handling and storage. 

If Analysis is to be carried out within two hours of collection, cool storage is not necessary. If analysis cannot be started with in the two hours of sample collection to reduce the change in sample, keep all samples at 4° C. 

Do not allow samples to freeze. Do not open sample bottle before analysis. Begin analysis within six hours of sample collection.  

 

Apparatus: 

BOD bottle  

Beaker (250 ml)  

Measuring cylinder  

Dropper  

Stirrer 

 

Reagents: 

Manganous sulfate solution  

Alkaline potassium iodide solution  

0.025N sodium thiosulfate  

Starch solution (indicator)  

Concentrated sulfuric acid. 

   

Procedure: 

Fill two BOD bottles with sample (or diluted sample); the bottles should be completely filled. Determine initial DO (DOi) in one bottle immediately after filling with sample (or diluted sample). Keep the other bottle in dark at 20°C and after particular days (usually 5-days) determine DO (DOf) in the sample (or diluted sample). Dissolved oxygen (DO) is determined according to the following procedure: 

Add 1 mL of manganous sulfate solution to the BOD bottle by means of pipette, dipping in end of the pipette just below the surface of the water. 

Add 1 mL of alkaline potassium iodide solution to the BOD bottle in a similar manner. 

Insert the stopper and mix by inverting the bottle several times. 

Allow the "precipitates" to settle halfway and mix again. 

Again allow the "precipitates" to settle halfway. 

Add 1 mL of concentrated sulfuric acid. Immediately insert the stopper and mix as before. 

Allow the solution to stand at least 5 minutes. 

Withdraw 100 mL of solution into an Erlenmeyer flask and immediately add 0.025N sodium thiosulfate drop by drop from a burette until the yellow color almost disappears. 

Add about 1 mL of starch solution and continue the addition of the thiosulfate solution until the blue color just disappears. Record the ml. of thiosulfate solution used (disregard any return of the blue color). 

 

 

Calculation: 

 

Dissolved oxygen, DO (mg/L)  

 

= mL of 0.025N sodium thiosulfate added x Multiplying Factor (M.F.) 

 

Calculate BOD of the sample according to Eq. – 11.1 or Eq. – 11.2.  

      Table

ChemicalOxygen demand

Oxygen sample

Introduction: 

The chemical oxygen demand (COD) test allows measurement of oxygen demand of the waste in terms of the total quantity of oxygen required for oxidation of the waste to carbon dioxide and water. The test is based on the fact that all organic compounds, with a few exceptions, can be oxidized by the action of strong oxidizing agents under acid conditions. 

 

Organic matter + Oxidizing agent = CO2 + H2O 12.1 

 

The reaction in Eq.-1 involves conversion of organic matter to carbon dioxide and water regardless of the biological assimilability of the substance. For example, glucose and lignin (biologically inert substance) are both oxidized completely by the chemical oxidant. As a result, COD values are greater than BOD values, especially when biologically resistant organic matter is present. 

Thus one of the chief limitations of COD test is its inability to differentiate between biodegradable and non-biodegradable 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. 

The major advantage of COD test is the short time required for evaluation. The determination can be made in about 3 hours rather than the 5-days required for the measurement of BOO. For this reason, it is used as a substitute for the BOD test in many instances. 

 

Environmental Significance:  

"COD is often measured as a rapid indicator of organic pollutant in water; it is normally measured in both municipal and industrial wastewater treatment plants and gives an indication of the efficiency of the treatment process. COD has further applications in power plant operations, chemical manufacturing, commercial laundries, pulp & paper mills, environmental studies and general education. 

 

Guideline: 

According to Bangladesh Environment Conservation Rules (1997), drinking water standard for chemical oxygen demand (COD) is 4.0 mg/L. For wastewater effluent allowable concentration of CBOD varies from 200- 400 mg/L depending on discharge point of the effluent (e.g., inland water, irrigation land, public sewer etc.) 

 

Principle: 

Potassium dichromate or potassium permanganate is usually used as the oxidizing agent in the determination of COD. In this class potassium permanganate would be used in the determination of COD. Potassium permanganate is selective in the reaction and attacks the carbonaceous and not the nitrogenous matter. 

In any method of measuring COD, an excess of oxidizing agent must be present to ensure that all organic matter is oxidized as completely as possible within the power of the reagent. This requires that a reasonable excess be present in all samples. It is necessary, therefore, to measure the excess in some manner so that the actual amount can be determined. For this purpose, a solution of a reducing agent (e.g., ammonium oxalate) is usually used.  

 

Apparatus: 

Beaker (250 mL)  

Dropper 

Stirrer 

 

Reagent: 

Diluted sulfuric acid solution 

Standard potassium permanganate solution 

Standard Ammonium Oxalate solution 

 

Procedure:  

Pipette 100 mL of the sample into a 250 mL Erlenmeyer flask. 

Add 10 mL of diluted sulfuric acid and 10 mL of standard KMn04 solution. 

Heat the flask in a boiling water bath for exactly 30 minutes, keeping the water in the bath above the level of the solution in the flask. The heating enhances the rate of oxidation reaction in the flask. 

If the solution becomes faintly colored, it means that most of the potassium permanganate has been utilized in the oxidation of organic matter. In such a case, repeat the above using a smaller sample diluted to 100 mL with distilled water. 

After 30 minutes in the water bath, add 10 mL of standard ammonium oxalate [(NH4)2C204] solution into the flask. This 10 mL ammonium oxalate, which is a reducing agent, is just equivalent to the 10 mL potassium permanganate (oxidizing agent) added earlier. The excess of reducing agent [(NH4)2C204] now remaining in the flask is just equivalent to the amount of the oxidizing agent (KMn04) used in the oxidation of organic matter. 

The quantity of ammonium oxalate remaining in the flask is now determined by titration with standard potassium permanganate. Titrate the content of the flask while hot with standard potassium permanganate to the first pink coloration. Record the mL of potassium permanganate used. 

 

Calculation: 

COD (mg/L) =

Alkalinity in Water

Alkalinity Ph Chart

Introduction:  

Alkalinity is primarily a way of measuring the acid neutralizing capacity of water. In other words, its ability to maintain a relatively constant pH. The possibility to maintain constant pH is due to the hydroxyl, carbonate and bicarbonate ions present in water. The ability of natural water to act as a buffer is controlled in part by the amount of calcium and carbonate ions in solution.  

Carbonate ion and calcium ion both come from calcium carbonate or limestone. So water that comes in contact with limestone will contain high levels of both Ca++ and CO32- ions and have elevated hardness and alkalinity. 

 

Environmental significance: 

Alkalinity is important for fish and aquatic life because it protects or buffers against rapid pH changes. Higher alkalinity levels in surface waters will buffer acid rain and other acid wastes and prevent pH changes that are harmful to aquatic life. Large amount of alkalinity imparts bitter taste in water. The principal objection of alkaline water is the reactions that can occur between alkalinity and certain actions in waters. The resultant precipitate can corrode pipes and other accessories of water distribution systems. 

 

Wastewaters containing excess caustic (hydroxide) alkalinity are not to be discharged into natural water bodies or sewers. Alkalinity as carbonate and bicarbonate of saline water is very important in tertiary recovery processes for recovering petroleum. Alkaline water offers better wetting to the formation rock and improve oil release. As an additional benefit, ions that provide alkalinity absorb on rock surfaces occupying adsorption sites and decrease the loss of recovery chemical by adsorption. The alkalinity value is necessary in the calculation of carbonate scaling tendencies of saline waters. 

 

The alkalinity acts as a pH buffer in coagulation and lime-soda softening of water. In wastewater treatment, alkalinity is an important parameter in determining the amenability of wastes to the treatment process and control of processes such as anaerobic digestion, where bicarbonate alkalinity, total alkalinity, and any fraction contributed by volatile acid salts become considerations.  

 

Principle: 

The alkalinity of water can be determined by titrating the water sample with sulphuric acid of known values of pH, volume and concentrations.  Based on stoichiometry of the reaction and number of moles of sulphuric acid needed to reach the end point, the concentration of alkalinity in water is calculated. When a water sample that has a pH of greater than 4.5 is titrated with acid to a pH 4.5 end point, all OH-, CO32-, and HCO3- will be neutralized.  

 

For the pH more than 8.3, add phenolphthalein indicator, the colour changes to pink colour. This pink colour is due to presence of hydroxyl ions. If sulphuric acid is added to it, the pink colour disappears i.e. OH- ions are neutralized. Then add methyl orange indicator, the presence of CO32- and HCO3- ions in the solution changes the colour to yellow. While adding sulphuric acid, the color changes to slight orange ting, this color change indicates  that all the CO32- and  HCO3- ions  has been neutralized. This is the end point.  

   

Apparatus: 

Burette with Burette stand and porcelain title  

Pipettes with elongated tips  

Conical flask  

Measuring cylinders  

Beakers  

Dropper 

Stirrer 

 

Chemicals 

Standard0.02N sulphuric acid   

Phenolphthalein  indicator 

Methyl orange indicator 

 

Sample handling and preservation:  

Preservation of sample is not practical. Because biological activity will continue after a sample has been taken, changes may occur during handling and storage. To reduce the change in samples, keep all samples at 4°C. Do not allow samples to freeze.  Analysis should begin as soon as possible. Do not open sample bottle before analysis. 

 

Procedure:  

Measure 50 ml or 100 ml of your sample into a 250 mL beaker or erlenmyer flask. Place your sample onto a stir plate (make sure to put a bar magnet in the flask). 

Measure initial pH of your sample. If the sample pH is below 8.3 (if above 8.3, do step 3 first), add several drops of methyl orange indicator. If the color of the solution turned yellow, titrate your sample with 0.02 N H2SO4 (you may need to dilute the acid provided in the lab) until the color changes to slightly orange ting (pH 4.5). Record the total volume of acid used for the titration.  

Measure initial pH of your sample. If the sample pH is above 8.3, add several drops of phenolphthalein indicator. If the color of the solution turned pink, titrate your sample with 0.02 N H2SO4 or HCl (you may need to dilute the acid provided in the lab) until color changes from pink to clear (pH 8.3). Record the volume of acid used for the titration. Then, proceed with step 2.  

Calculate both Phenolphthalein Alkalinity and Total Alkalinity using the formula provided above.  

 

Calculation: 

 

Phenolphthalein Alkalinity (mg/L as CaCO3) 

= Multiplying Factor (MF) x milliliter of 0.02N H2SO4(added up to pH 8.3) 

 

Total Alkalinity (mg/L as CaCO3) 

  =Multiplying Factor (MF) x milliliter of 0.02N H2SO4(added up to pH approx. 4.5)

Where, M.F.

     Table

Arsenic in water

Introduction: 

Presence of elevated levels of arsenic in groundwater (especially from shallow aquifer) has become a major concern in Bangladesh. Arsenic pollution of groundwater is particularly challenging in Bangladesh since tubewell water extracted from shallow aquifers is the major source of drinking water for most of its population. The rural water supply is almost entirely based on groundwater supply through use of hand pump tubewells; the urban water' supply is also heavily dependent on groundwater. In Bangladesh, the arsenic in groundwater is of geologic origin and is probably only apparent now because it is only the last 20 - 30 years that groundwater has been extensively used for drinking in rural areas.  

 

Weathering of arsenic-rich base metal sulphides in the upstream of the Ganges basin appears to be a major source of arsenic-rich iron oxyhydroxides in the sediments of Bangladesh. Use of phosphate fertilizer can potentially enhance release of arsenic as a result of replacement of arsenic by phosphate ions on the adsorption sites of iron oxyhydroxides. Natural and anthropogenic processes that may lead to release/mobilization of arsenic in the subsurface are being investigated. 

 

Arsenic occurs in water in several different forms. Depending upon the pH and the redox potential, Eh. Some of the most important compounds and species are shown in Table 1.  

Table 1: Arsenic compounds and species and their environmental and toxicological importance in water.

In groundwater, arsenic primarily exists as inorganic arsenic. Inorganic trivalent arsenic, [As(III)] or arsenite is the dominant form in reducing environment; while inorganic pentavalent arsenic [As(V)] or arsenate is the dominant form in oxidizing or aerobic environment. In groundwater environment where the conditions are mostly reducing, a significant part of the arsenic exists as As(III).  

 

Environmental significance: 

Arsenic is a major environmental pollutant and exposure occurs through environmental, occupational and medicinal sources. Airborne exposure is small except in polluted locations. Food exposure can be significant but, particularly in fish and shellfish, it is mostly in organic forms that are relatively nontoxic. Drinking water remains the most significant source worldwide, and large numbers of people are subject to serious exposure from this source. Toxicity consists mostly of neuropathy, skin lesions, vascular damage, and carcinogenesis. Vascular lesions are the result of endarteritis (blackfoot disease). This appears to be more prevalent in developing rather than developed countries and may be related to nutritional deficiencies. Skin cancer is the most clearly associated malignancy related to arsenic exposure from drinking water; however, bladder, lung, liver, and kidney tumors also appear to be related. There is no particular remedial action for chronic arsenic poisoning. Low socioeconomic status and malnutrition may increase the risk of chronic toxicity. 

Guideline: 

According to ECR 1997, drinking water standard for arsenic in Bangladesh is 50 μg/L(or 0.05 mg/L). The WHO guideline value for arsenic in drinking water is 10μg/Land the USEPA is also planning to revise its standard from50 μg/Lto10μg/L. 

Analytical Methods for Measuring Arsenic:  

The most commonly used method for detection of arsenic concentration water may be categorized as follows:  

Inductively coupled plasma (ICP) method  

Hydride generation atomic absorption spectrophotometric method  

Graphite furnace atomic absorption spectrophotometric method  

Hydride generation-scraper-spectrophotometric (SDOC) method  

Hydride generation-scraper-indicator paper-field kit.

The first three methods involve high-cost equipment and provide more accuracy and lower detection limit (minimum detection limit, MDL = 1 μg/L). The last two methods are relatively low cost methods but accuracy of determination is less.  

Inductively coupled plasma (ICP) method  

An ICP source consists of a flowing stream of argon gas ionized by applied radio frequency field typically oscillating at 27.1 MHz. The water sample is atomized at temperature about 6000 to 8000.0 K. The light emitted from ICP Hydride generation atomic absorption spectrophotometric method is focused on entrance slit and using radio frequency determines absorbance of arsenic.  

Hydride generation atomic absorption spectrophotometric method  

In this method arsenic is reduced to gaseous arsine in a reaction vessel. The method is  two types: i) manual hydride generation and ii) continuous hydride generation. In manual  method zinc is added to speed the reaction whereas continuous in continuous hydride  generation no zinc is needed. In continues measurement hydride generator a peristaltic  pump is used to meter and mix reagents and a gas-liquid separator unit uses flow of  argon to strip out hydrogen and arsine gas.  

 

Hydride generation-sera per-spectrophotometric (SDDC) method 

Minimum detectable quantity for this method is 1 micro gram As. This method essentially  involves: conversion (reduction) of all arsenic in water into As(III) and generation of arsine gas in the form of arsenic hydride (AsH3). Absorbance of red-coloured complex produced by passing of arsine gas through a solution of silver diethyl-dithiocarbamate (SODC) is measured in a spectrophotometer at 535 nm wavelength.  

Hydride generation-scraper-indicator paper-field kit  

A simple and reasonably accurate method for arsenic measurement Similar to SOOC  method all arsenic in water is converted to As(III) and generates arsine gas which is then  passes through a filter paper soaked in mercuric bromide.  

 

Laboratory Measurement of Arsenic by Arsenic Tool kit Method:  

In the class arsenic measurement by arsenic tool kits will be conducted. The kit involves the generation of arsine (AsH3) from inorganic arsenic species by reduction with Zn and HCl. The arsine then reacts with a test strip containing HgBr2 to produce a color that is compared with a color scale for quantitation.  

 

Apparatus: 

1. Arsenic toolkits 

 

Procedure: 

Add reagent to Reaction Bottle and shake vigorously.  

Insert the strip into the turret and close it. Let it sit 10 minutes.  

Select the As concentration on the chart that matched the color of the test strip most closely. The reference chart provided with the kit displays the yellow to brown range of colors expected for As concentrations of 0, 10, 25, 50, 100, 200, 300, 500, and 1000 μg/L. 

 

   Table

Chemical coagulation in water: (Alum Coagulation)

 

Introduction: 

Chemical coagulation is a treatment method widely used for removal of small sized and colloidal impurities from water. Surface water generally contains a wide variety of colloidal impurities that may cause the water to appear turbid and may impart color to the water. Colloidal particles that cause color and turbidity are difficult to separate from water because the particles will not settle by gravity and are so small that they pass through the pores of most common filtration media. In order to be removed, the individual colloids must aggregate and grow in size so that they can settle by gravity. Chemical agents are used to promote colloid aggregation by destroying the forces that stabilize colloidal particles. 

 

The process of destroying the stabilizing forces and causing aggregation of colloids is referred to as chemical coagulation. Coagulation involves reduction of electrical forces of repulsion and promotion of "chemical type" interaction between colloids, which eventually results in settling of the colloids and accomplishes removal of turbidity and color. At higher coagulant doses, "charge reversal" is possible which may result in re-suspension of the colloids. Hence optimum coagulant doses are determined through laboratory model tests where the water to be treated are subjected to a range of doses of a coagulant and the removal efficiencies are observed. 

 

Many authors use the term "coagulation" to describe the process by which the charge on particles is destroyed, and the term "flocculation" to describe the aggregation of particles into larger units. The chemical used for this purpose is called are called coagulants. The most common coagulants used in water and wastewater treatment are aluminum and ferric salts such as alum, ferric chloride and ferric sulfate. 

 

The common metal salt alum (aluminum sulfate) is a good coagulant for water containing appreciable organic matter. The chemical formula used for commercial alum is Al2(SO4)3.14H20. Once dissolved in water, aluminum forms hydroxo-complexes and solids [e.g., Al(OH)3(s), Al(OH)2+, Al(OH)2+, Al(OH)4-; and as a result pH of water is lowered, especially if alkalinity of water is low,. Theoretically, each mg/L of alum consume approximately 0.50 mg/L (as CaCO3) of alkalinity, For water with low alkalinity, this may result in significant reduction in pH that may interfere with formation of aluminum hydroxide flocs. If the alkalinity is insufficient, coagulant aids such as lime [Ca(OH)2], soda ash (Na2CO3), activated silica and polyelectrolytes are used to provide the necessary alkalinity. Iron coagulants can be operated over a wider pH range and are generally effective in removing turbidity and color from water. However, they are usually more costly. 

 

Environmental Significance: 

Besides efficient removal of turbidity and color, coagulation with alum and ferric chloride or ferric sulfate is also widely used for removal of heavy metal ions (e.g., lead, arsenic) from water. In this process heavy metal ions are primarily removed by adsorption (and Subsequent precipitation) onto coagulated flocs of metal (either aluminum or iron) hydroxides. Coagulation with alum and ferric chloride / sulfate is being successfully used for removal of arsenic from water. 

 

Principle: 

Treatment of water by coagulation involves - 

Determination of optimum dose of coagulant by jar test. 

Determination of power input for the flocculator.  

 

In the class jar test to determine optimum coagulant dose will be carried out, it is important to determine the optimum dose to avoid charge reversal and resuspension colloids. Optimum coagulant dose is considered as the amount of coagulant which produces water with lowest turbidity. 

 

Apparatus: 

Coagulation (stirring) device 

pH meter 

Turbidity meter 

Glass beakers (1000 mL) 

 

Reagent: 

1. Standard Alum solution. 

 

Procedure: 

1. Determine pH and turbidity of the water to be treated. You may be instructed to determine color and arsenic concentration of the water to be treated (if removal efficiencies of these parameters are to be determined). 

2. Fill six 1000 mL beakers each with 500 mL water to be treated, 

3. Add required (as instructed by teacher) coagulant (standard alum solution) to each beaker. 

4. Mix the samples in the beaker with the help of the stirring device. Subject the samples to one minute of rapid mixing followed by 15 minutes of slow mixing (about 40 rpm). 

5. Allow the flocs to settle down for about 15 minutes. Observe the characteristics of the flocs and the settling rates. 

6. Collect the supernatant from each beaker and measure pH and turbidity of each. You may be instructed to measure color and arsenic concentration of the supernatant samples (if removal efficiencies of these parameters are to be determined). 

7. Plot pH versus alum dose in a graph paper and observe effect of alum dose on pH. 

8. Plot turbidity (NTU) versus the coagulant (alum) dose (mg/L) in a graph paper. Determine optimum dose of alum from this plot. 

     Table

BRICKS TEST

Theory: 

Brick is a very common construction material obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning them at a required temperature. Due to high strength and durability, easy availability and low cost; they are nowadays widely usedfor building construction. 

On the basis of their size, IS 1077:1992 classifies bricks into two categories, i.e. modular and non-modular type. The sizes of modular brick are selected in conformity with the metric system considering 100 mm module as the basis of all dimensional standardization. The standard modular sizes of Indian bricks are:

Without mortar : 190 mm × 90 mm × 90 mm

With mortar: 200 mm × 100 mm × 100 mm

However, bricks of non-modular sizes are also available in India, which satisfies other requirements of the code, but not the requirements regarding dimension. The standard sizes of non-modular bricks varies region to region basis. In Odisha the standard size of non￾modular bricks available is 225 mm × 125 mm × 75 mm (without mortar). This size may vary slightly due to drying shrinkage. 

To assess the size of the brick, at least twenty numbers of whole bricks is taken at random from the stock. All blisters, loose particles of clay and small projections shall be removed. Then they shall be arranged upon a level surface successively as shown in Figure 

10 in contact with each other and in a straight line. The overall length of the assembled bricks shall be measured with a steel tape or other suitable inextensible measure sufficiently long to measure the whole row at one stretch. Measurement by repeated application of short rule or measure shall not be permitted. For a good quality of brick, tolerances in dimensions are allowed within ± 3.0 %. 

Measurement of sizes of brick

   

Bricks used in construction work should have adequate compressive strength to resist lateral and vertical loads. Ordinary bricks are designated on the basis of average compressive strength as follows:

The compressive strength of any individual brick tested shall not fall below the minimum compressive strength specified for the corresponding class of brick. To access the compressive strength of the bricks, load is applied over the flat side keeping mortar filled face facing upwards.

Water absorption of a brick is defined as the ratio of weight of water absorbed to the dry weight of the unit under a given method of treatment in a standard period of time. Water absorption indicates degree of porosity in a brick. Strength, stiffness, unit weight and other properties decrease with porosity. For good quality of bricks, after immersion in cold water for 24 hours, the water absorption should not be more than 20% by weight efflorescence of bricks is usually seen as a white powder (salts of crystallization) caused by water soluble salts as Sulphates of Calcium, Magnesium, Sodium, Potassium etc. and Sodium Chloride. These salts are deposited on the surface of the bricks on the evaporation of water. Efflorescence decreases strength and stiffness of bricks. The liability to efflorescence is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or ‘serious’ in accordance with the following definitions:

Objective:

 To estimate dimension, tolerance, compressive strength, water absorption, and efflorescence of bricks.

Reference: 

IS 3495 (Part-1 to 4):1992.

Apparatus: 

(1) Dimensions and tolerance: Measuring tape, trowel and brush. 

(2) Water absorption: Weighing balance, metal tray about 5 cm deep, ovens.

(3) Compressive strength: Compression testing machine

(4) Efflorescence: A shallow flat bottom dish or tray.

Material: 

(1) Dimensions and tolerance: Bricks (20 nos.)

(1) Water absorption: Bricks and water.

(2) Compressive strength: Bricks, cement, sand, water and two 3 mm thick plywood sheets.

(3) Efflorescence: Bricks and water. 

Procedure: 

For dimension and tolerance test: 

1. Collect at least twenty numbers of whole bricks at random from the stock. 

2. Remove all blisters, loose particles of clay and small projections from the 

surface of the brick. 

3.Arrange the bricks upon a level surface successively as shown in Figure 1 in 

contact with each other and in a straight line. 

4. Measure the overall length of the assembled bricks with the steel tape.

Measurement by repeated application of short rule or measure shall not be 

permitted. If, for any reason it is found impracticable to measure bricks in one 

row, then divide the samples into rows of 10 bricks each and measure them separately to the nearest millimetre. Then, add all these dimensions together.

For water absorption test: 

5. Dry the specimen in a ventilated oven at a temperature of 105 to 115o C for 24 

hours. Then cool it to the room temperature and determine its weight (W1).

6. Immerse the dried specimen completely in clean water at a temperature of 27 ±2 o C for 24 hours. Then remove the specimen, wiped of any traces of water and measure its weight (W2). This weighing shall be completed within three minutes after the specimen has been removed from water. Determine percentage of water absorption.

For compressive strength test: 

7. Remove the unevenness observed in the bed faces to provide two smooth and 

parallel faces by grinding. Immerse in water at room temperature for 24 hours. 

Remove the specimen and drain out any surplus moisture at room temperature. 

8. Fill the frog and all voids in the bed face flush with cement mortar having 

cement sand ratio 1:3. 

9. Store under damp gunny bags for 24 hours followed by immersion in water for 

3 days. Remove the bricks and wipe out traces of moisture. 

10. Place the specimen with mortar filled face upward, between two 3 mm thick plywood sheets, carefully centred between platens of the testing machine. 

Apply load axially at a uniform rate of 14 N/mm2/min and note the maximum 

load at failure. Find compressive stress after dividing total load (in N) by loaded surface area (mm2) For efflorescence test: 

11. Place the end of the brick in the disk or tray. The depth of immersion in water 

shall be 25 mm. 

12. Keep the whole arrangement at a temperature 20oC to 30oC until all the water in the dish is absorbed by the specimens and the surplus water evaporates. 

13. When the water has been evaporated and the bricks appear to be dry, place a 

similar quantity of water in the dish and allow it to dry evaporate as before. 

14. Examine the bricks for efflorescence after the second evaporation and report the results as the definition given in Table 3. 

Observations: 

Table 1: Observations on dimension and tolerance

Nos. of bricks tested : ________

Standard sizes of bricks taken: ______ mm × ______ mm × ______ mm. 

Table 4: Observations on efflorescence test

The percentage of area where efflorescence occurred is : ________ %. Thus the degree of efflorescence is ___________. 

Note: Carefully observe the brick that have undergone efflorescence test. And estimate the 

percentage of efflorescence area.

 Calculation:

• The dimensions of given bricks are : ______ mm × ______ mm × ______ mm 

• Compressive strength for the brick specimen is: __________ N/mm2

• Percentage of water absorption for the brick specimen is : ________ % by weight. 

• Degree of efflorescence for the brick specimen is found: __________

Conclusions: 

• The given bricks has dimensions ______ mm × ______ mm × ______ mm and the 

tolerances in dimensions are bellow/ above 3.0%. Thus the bricks are of good quality/ are not of good quality.

• The lowest compressive strength observed by the bricks specimen is __________ N/mm2

. Thus, the brick belongs to _______ class. 

• The percentage of water absorption for the brick specimen is less than/ more than 20% by weight. Thus, bricks are of good quality/ are not of good quality.

• The rating of efflorescence for the brick specimen is _______. This is acceptable/ 

not acceptable for good quality of bricks. 

Precautions: (Discuss about the precautions to be taken while conducting this experiment) 

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-

-

-

Questions: 

1. What are the characteristics of good bricks? 

2. What is efflorescence in bricks? What are its causes and remedies? 

3. What are the limits for water absorption and compressive strength for various classes of bricks?

4. Why frog filling is necessary for testing of compressive strength? 

5. Describe various field tests performed to check the quality of bricks.

SPLITTING TENSILE STRENGTH OF CONCRETE

Theory: 

Splitting tensile strength is generally greater than the direct tensile strength and lower than the flexural strength (modulus of rupture). Splitting tensile strength is used in the design of structural light weight concrete members to evaluate the shear resistance provided by concrete and to determine the development length of the reinforcement. This test method consists of applying a diametrical force along the length of a cylindrical concrete at a rate that is within a prescribed range until failure. This loading induces tensile 

stresses on the plane containing the applied load and relatively high compressive stresses in the area immediately around the applied load. Although we are applying a compressive load but due to Poisson’s effect, tension is produced and the specimen fails in tension. Tensile failure occurs rather than compressive failure because the areas of load application are in a state of triaxial compression, thereby allowing them to withstand much higher compressive 

stresses than would be indicated by a uniaxial compressive strength test result. Thin, bearing strips are used to distribute the load applied along the length of the cylinder. The maximum load sustained by the specimen is divided by appropriate geometrical factors to obtain the splitting tensile strength.

Arrangement for loading of splitting tensile test specimen

Objective:

To determine splitting tensile strength of cylindrical concrete specimens.1q

Reference:

IS: 5816 - 1999, 

IS: 1199-1959, 

SP: 23-1982, 

IS: 10086-1982. 

Apparatus:

Cylindrical mould confirming to IS: 10086-1982 for splitting tensile strength, 

tamping rod, metallic sheet, universal testing machine.

Material: 

Cement, sand, aggregate and water, grease

Procedure: 

1. Sampling of Materials: Samples of aggregates for each batch of concrete shall be of the desired grading and shall be in an air-dried condition. The cement samples, on arrival at the laboratory, shall be thoroughly mixed dry either by hand or in a suitable mixer in such a manner as to ensure the greatest possible blending and uniformity in the material.

2. Proportioning : The proportions of the materials, including water, in concrete 

mixes used for determining the suitability of the materials available, shall be 

similar in all respects to those to be employed in the work

3. Weighing: The quantities of cement, each size of aggregate, and water for each batch shall be determined by weight, to an accuracy of 0.1 percent of the total 

weight of the batch.

4. Mixing of concrete: The concrete shall be mixed by hand, or preferably, in a 

laboratory batch mixer, in such a manner as to avoid loss of water or other 

materials. Each batch of concrete shall be of such a size as to leave about 10 

percent excess after moulding the desired number of test specimens.

5. Mould: The cylindrical mould shall be of 150 mm diameter and 300 mm 

height conforming to IS: 10086-1982.

6. Compacting: The test specimens shall be made as soon as practicable after 

mixing, and in such a way as to produce full compaction of the concrete with 

neither segregation nor excessive laitance.

7. Curing: The test specimens shall be stored in a place, free from vibration, in 

moist air of at least 90 percent relative humidity and at a temperature of 27° ± 

2°C for 24 hours ± ½ hour from the time of addition of water to the dry ingredients.

8. Placing the specimen in the testing machine: The bearing surfaces of the 

supporting and loading rollers shall be wiped clean, and any loose sand or 

other material removed from the surfaces of the specimen where they are to 

make contact with the rollers.

9. Two bearings strips of nominal (1/8 in i.e 3.175mm) thick plywood, free of 

imperfections, approximately (25mm) wide, and of length equal to or slightly 

longer than that of the specimen should be provided for each specimen.

10. The bearing strips are placed between the specimen and both upper and lower 

bearing blocks of the testing machine or between the specimen and the supplemental bars or plates.

11. Draw diametric lines an each end of the specimen using a suitable device that 

will ensure that they are in the same axial plane. Canter one of the plywood strips along the centre of the lower bearing block.

12. Place the specimen on the plywood strip and align so that the lines marked on 

the ends of the specimen are vertical and centred over the plywood strip.

13. Place a second plywood strip lengthwise on the cylinder, centred on the lines marked on the ends of the cylinder. Apply the load continuously and without shock, at a constant rate within, the range of 689 to 1380 kPa/min splitting tensile stress until failure of the specimen

14. Record the maximum applied load indicated by the testing machine at failure. 

Note the type of failure and appearance of fracture.

Observation

• Length of Specimen (l): _______ mm

• diameter of the specimen (d): _______mm

Results: 

• The average 7 days tensile strength of concrete sample is : _______ MPa 

• The average 28 days tensile strength of concrete sample is : _______ MPa 

Precautions: 

(Discuss about the precautions to be taken while conducting this experiment) 

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-

-

-

Questions: 

1. What is the relationship of splitting tensile strength of concrete with its compressive strength?

2. What is the significance of splitting tensile test experiment?