Physical Parameters Relevant to Water Analysis, Chemistry tutorial

Introduction

Water appears to be the most necessary of the 3 indispensable matters (air, water and food) to man. Even though there is a general observation that with no air, man can barely survive for a very few minutes (that is, between three to five minutes) and without food, he might survive for up to 50 days. Though, it is as well a general facts that without water  on the  wet  surfaces of  alveoli  in humans  or  gills in  fish for instance,   intercellular  oxygen  exchange  is  impossible.  Several other biochemical reactions that are vital to life are water-dependent. Water is also needed for day-to-day running of vital domestic, industrial and agricultural activities.

Water needless to  say,  is  so  important  for  both  the  sustenance and continuity of life, hence, having a good understanding of chemistry and analysis  of  water  is  vital  to  sustainability  of  man  and  his  various activities (in the face of the fact that less than 2percent of the total water available on the surface of the earth is appropriate for drinking). Apart from the seeming "localization" of the two per cent good water, technological advancement and quick industrialization through their concurrent pollution tendencies have situated the bounded good water under serious stress.

Notable Physical Parameters of Water

Turbidity

The term 'turbid' is applied to waters containing suspended matter that interferes with the passage of light through the water or in that visual depth is restricted. Turbidity might be caused via a broad diversity of suspended substances ranging in sizes from colloidal to coarse dispersions, depending upon the degree of turbulence. In lakes or other water existing under comparatively quiescent  conditions,  most  of  the  turbidity is due to  colloidal  and extremely fine dispersions; in river under flood situations, the turbidity is as a consequence of to comparatively coarse dispersion, while glacier-fed rivers and lakes, turbidity is due to colloidal coarse particles created via the grinding action of the glacier. As rivers descend from mountainous areas to the plains, they receive contributions of turbidity from farming and other operations, which disturb the soil. Under flood conditions, great amounts of topsoil are washed to receiving streams. Much of these materials  is  inorganic  in  nature  and  includes  clay  and  silt,  but considerable amounts of organic matter are included. As the rivers progress toward the ocean, they pass through urban areas where domestic and industrial treated and untreated wastewaters might be added. Such wastewaters often enclose huge quantities of both organic and inorganic substances that generate turbidity. Street washings contribute much turbidity as well.

Organic substances reaching rivers serve as food for bacteria. The consequential bacterial expansion and other microorganisms that feed upon the bacteria create extra turbidity. Inorganic nutrients such as nitrogen and phosphorus present in wastewater discharges and agricultural runoff stimulate the growth of algae which also contribute to turbidity.

Significance of Turbidity in Public Water Supplies

Aesthetics: Any turbidity in a sample of drinking water is automatically associated with possible wastewater pollution and the health hazards occasioned by it.

Filterability: Filtration of water is rendered more difficult and costly with increasing turbidity.

Disinfection: To be effective, there must be direct contact between a given disinfectant (e.g. chlorine, ozone, chlorine dioxide or UV radiation) and the organisms it has to kill. In cases where turbidity is caused by municipal wastewater suspended solids or runoff from animal feed lots, many of the pathogenic organisms might be encased in the particles and remain protected from the action of the disinfectant.

Method of Turbidity Determination

Instrumental method that employs the principle of nephelometry is used. A light source illuminates the example and one or more photoelectric detectors are utilized by a readout device to indicate the intensity of scattered light. A particular formation polymer suspension is used as a standard. Turbidity in treated drinking water must never exceed one nephelometric turbidity unit (NTU).

1 NTU = 1mg SiO2/L.

Applications of Turbidity Data

Water Supply: Knowledge of the turbidity variation in raw-water supplies   is   of   prime   importance to water treatment plant operations. Such measurements are used in conjunction with other information to determine whether a supply requires special treatment through chemical coagulation and filtration before it may be used for a public water supply.

Determination of Effectiveness of Coagulants: Water supplies obtained from rivers usually require chemical flocculation because of high turbidity. Turbidity measurements are used to determine the most effective and economical chemical to use.

Gauging the Amount of Chemicals: Turbidity measurements help to gauge the amount of chemicals needed from day to day in the operation of treatment works. This is particularly important on "flashy" rivers where no impoundment is provided. Measurements of turbidity in settled water prior to filtration is helpful in controlling chemical dosages so as to prevent excessive loading of rapid sand filters.

Checking Faulty Filter Operation:  Turbidity measurements of the filtered water are needed to check on faulty filter operation and to ensure conformity to regulatory requirements.

Effluent Control: Turbidity measurements offer a quick means of determining the levels of suspended solids in an effluent so as to know the minimum amount of coagulants needed to produce high-quality effluent

-Colour:

Many surface waters, particularly those emanating from swampy areas, are often coloured to the extent that they are not suitable for domestic or some industrial uses without being treated to remove the colour. The colouring materials, many of which are humic substances, result from contact of water with organic debris, such as leaves, needles of conifers and woods, all in various stages of decomposition.  Iron is sometimes present as ferric humate and produces a colour of high potency. Natural colour exists in water primarily as negatively charged colloidal particles and its removal can readily be accomplished by a coagulant having a trivalent metallic ion such as aluminum or iron.

Surface waters may appear highly coloured because of coloured suspended matter when in reality they are not. Rivers that drain areas of red clay soils become highly coloured during times of flood. Colour caused by suspended matter is referred to as apparent colour while colour caused by vegetable or organic extracts that are colloidal is called true colour. At times, surface waters may become coloured by the presence of dyes from textile industries and pulping operations in the paper industry which leads to production of liquors containing lignin derivatives and other materials in dissolved form.

Significance of colour in public water supplies

i. Disinfection problem: Waters containing colouring matter derived from natural Substances undergoing decay in swamps and forests are not considered to possess toxic properties. However, disinfection by chlorination results in the formation of chloroform, other trihalomethanes and a   range of  other chlorinated   organics,   leading  to  problems  of  much  current concern.

ii. Problem of aesthetic unacceptability: The natural colouring materials impart a yellow-brownish appearance somewhat like that of urine to water. This makes consumers to seek other sources  of  drinking  water  if  the  public  water  supply  is  not aesthetically  acceptable no matter how safe it may be from the hygienic  viewpoint.  The   alternative  sources  sought  by consumers  may  be  springs  or  wells  with  uncertain  levels  of pathogenic organism. Waters intended for human use should not exceed 15 colour units.

Standard colour solutions

This is done by preparing a stock solution of potassium chloroplatinate (K2PtCl6) that contains 500mg/L of platinum. Cobalt chloride is added to provide the proper tint. The colour produced by 1mg/L of platinum (in the form of K2PtCl6) is taken as the standard unit of colour. The stock solution has a colour of 500 units, and a series of working standard is prepared from it by dilution. A matched set of colour-comparism tubes, called Nessler tubes are usually used to contain the standard. A series ranging from 0 to 70 colour units is employed. Samples with colour  less  than  70  units  are  tested  by  direct  comparison  with  the prepared standards. For samples with a colour greater than 70 units, a dilution is made with demineralised water and colour calculation is made, using a correction factor for the dilution employed.

Suspended matter in samples must be removed to enable determination of true colour. This is usually accomplished by centrifuging; filtration is not recommended because of possible adsorption of colour on the filtering medium.

Applications of Colour Data

Consumption Specifications: The decision about whether to treat  a water sample further to meet the World Health Organization  (WHO) guideline of 15 colour units for drinking water can be taken from the colour data obtained.

Indicator of Possible Formation of Toxins:  Colour in natural waters is an indirect indicator of the potential for trihalomethane formation during disinfection with chlorine.  A  water  supply  is generally  desired   with  a  colour  low  enough   so  that  chemical treatment will not be required and trihalomethane formation will not constitute a burdensome treatment problem.

Designs of Treatment Plant: Before a chemical treatment plant is designed, research is conducted to ascertain the best chemicals to use and amounts required. Colour determinations serve as the basis of the decisions. Such data are necessary for proper selection of chemical feeding machinery and the design of storage space.

Means of Ensuring Economical Operations:  Colour determinations on the raw and treated water or wastewater govern the dosages of chemicals used, to ensure economical operation and to produce low-colour water that is well within accepted limits.

-Taste and Odour:

The sensations of taste and smell are closely related and often confused. Hence, a wide variety of tastes and odours may be attributed to water by consumers.  Substances that produce an odour in water will almost invariably import a taste as well. The converse isn't true, as there are many mineral materials, which produce taste but no odour.

Significance of Taste and Odour in Water Supply

Consumers find taste and odour aesthetically displeasing for obvious reasons.  Because water is thought of as tasteless and odourless, the consumer associates taste and odour with contamination and may prefer to use a tasteless, odourless water that might in fact pose more of a health threat. Odours produced by organic substances might pose more than just aesthetic problem since some of those substances are carcinogenic.

Sources of Taste and Odour

Many substances through which water comes into contact in nature or during human utilize may lead to perceptible taste and odour. These include minerals, metals and salts from the constituents of wastewater. Inorganic substances are more likely to produce tastes unaccompanied by odour. Alkaline materials impart a bitter taste to water, while metallic salts might provide a salty or bitter taste.

Organic materials, on the other hand, are probable to create both taste and odour. A multitude of organic chemicals might cause taste and odour troubles in water, by petroleum-based products being prime offenders. Biological decomposition of organics might effect in both taste and odour producing liquids and gases in water. Principal among them are the reduced products of sulphure that impart a "rotten egg" taste and odour. As well, indeed species of algae secrete an oily substance that may effect in both odour and taste. The combination of 2 or more substances, neither of which would create taste or odour via itself, may sometimes consequence in taste and odour problems for instance organics and chlorine can exhibit this synergistic result.

Measurement of Taste and Odour

Direct measurement of substances that create tastes and odours can be complete if the causative agents are recognized. Several kinds of analysis are available for measuring taste-producing inorganic. Measurement of taste and odour-causing organics can be made using gas or liquid chromatography. Because chromatographic analysis is time-consuming and need expensive equipment, it isn't routinely performed on water samples, but should be done it problem organics are suspected.  

Though, since of possible synergistic consequences, quantifying the sources of organics doesn't necessarily quantify the nature or intensity of taste and odour. Quantitative tastes that employ the human senses of taste and smell can be utilized for instance the 'threshold odour number' (TON).

Various amounts of odorous water are poured into containers and diluted with enough odour-free distilled water to create a 200 mL mixture. An assembled panel of five to ten "noses" is utilized to find out the mixture in that the odour is just barely perceptible to the sense of smell. The TON of that example is then computed using the formula

TON = A + B /A

where A = the volume (ml) of odorous water

and B = the volume of odour -free water required to produce a 200 ml mixture.

Application of TON Data

Potable water is supposed to be taste and odour free. Though, United States Environmental Protection Agency (USEPA) doesn't have a maximum standard for TON. A TON of three has been recommended via the Public Health Service and serves as a guideline rather than a legal standard.

Temperature

Temperature isn't employed to estimate directly either potable water or wastewater. It is, though, one of the most significant parameters in natural surface-water systems. The temperature of surface waters governs to a huge extent the biological species present and their rates of activity.  Temperature has a result on most chemical reactions that take place in natural water system. Temperature as well has a pronounced result on the solubilities of gases in water.

Sources of Temperature

The temperature of natural water systems responds to many factors, the ambient temperature (temperature of the surrounding atmosphere) being the most universal. Generally, shallow bodies of water are more influenced via ambient temperatures than the deeper bodies. The utilize of water for dissipation of waste heat in industry and the subsequent discharge of the heated water might consequence in dramatic, though perhaps localised, temperature changes in receiving streams. Elimination of forest canopies and irrigation return flows can as well effect in raised stream temperature.

Impacts of Temperature

Cooler waters generally have a wider diversity of biological species. At lower temperatures, the rate of biological activity these as food supplies utilizations, expansion, reproduction, and so on, is slower. An amplify of 100C is usually sufficient to double the biological activity, if necessary nutrients are present.

At elevated temperature and enhanced metabolic rates, organisms that are more proficient at food utilisation and reproduction flourish, while other species decline and are perhaps removed altogether. Accelerated growth of algae often recurs in warm water and can become a difficulty when cells cluster into algae mats. Natural secretion of oils via algae into the mats and the decay creations of dead algae cells can effect in taste and odour problems. Higher-order species, such as fish, are affected dramatically by temperature and by dissolved oxygen levels that are a function of temperature. Game fish usually need cooler temperatures and higher dissolved-oxygen levels.  

Temperature changes influence the reaction rates and solubility levels of chemicals; most chemical reactions involving dissolution of solids are accelerated via enhanced temperatures, while the solubility of gases, on the other hand, reduces at elevated temperatures.

Solids in Water Supplies

The total solids in a liquid example contain total dissolved solids and total suspended solids. Total dissolved solids are substances in the water that will pass through a filter through a 2.0 µm or smaller nominal average pore size. The substance retained via the filter is the total suspended solids.

The amount and nature of melted and suspended matter occurring in liquid material fluctuate deeply. In potable waters, most of the matter is in melted form and consists mostly of inorganic salts, small amounts of organic matter and dissolved gases. The total dissolved solids content of potable waters generally ranges from 20 to 1,000 mg/L, and as a rule, hardness raises via total dissolved solids.

Unlike the measurement of total suspended solids where sample drying is conducted at 103 to 1050C, total melted solid analysis for water supplies is conducted at 1800C. The cause for the higher temperature utilized in the latter is to eliminate all mechanically occluded water. Here, organic matter is generally extremely low in concentration and losses due to the higher drying temperature will be tiny.

Significance of Solids Determination

  • Water through a total solid content of less than 500 mg/L is most desirable for domestic utilize. A higher total solid content imparts taste to the water and frequently has a laxative and sometimes the reverse result upon people whose bodies aren't used to the higher levels.
  • Water with a high dissolved solid content tends to stain glassware and has adverse impacts on irrigated crops, plants and grasses.
  • The suspended solids analysis is used to ensure that an important wastewater discharge requirement is met.
  • In cases in which water softening is required, the kind of softening process might be dictated via the melted solid content, because precipitation techniques reduce the solids and exchange methods enhance the solids.
  • Corrosion control is frequently completed via the production of stabilized waters through pH adjustment. The pH stabilization based, to an extent, upon the total solids present as well as the alkalinity and temperature.

Determination of Solids in Water Supplies

Dissolved solids are the main concern in water supplies; thus, the total solids determination and the exact conductance measurement are of greatest interest. Hanged solids tests are seldom made since of the small amounts present. They are more easily estimated via measurement of turbidity.

Total solids

The determination of total solids is simply made through evaporation and drying of a calculated example in a tarred container. Utilize of platinum dishes is extremely recommended since of the ease through which they can be brought to steady weight before utilize. Vycor ware is a good substitute, but the employ of porcelain dishes has to be avoided since of their tendency to transform weight.

Specific conductance

A speedy evaluation of the melted solids content of a water supply can be attained through precise conductance measurements. These measurements specify the capacity of an example to carry an electric current, which in turn is related to the concentration of ionized materials in the water.

Most dissolved inorganic materials in water supplies are in the ionized form and so donate to the specific conductance. Even though this measurement is influenced via the nature of the diverse ions, their relative concentrations and the ionic strength of the water, these measurements can provide a practical estimate of the variations in dissolved mineral content of a specified water supply. As well, via utilize of an empirical factor, precise conductance can permit a rough estimation to be made of the dissolved mineral content of water examples.

Dissolved and Suspended Matter

In cases where turbidity measurements aren't sufficient to give the essential information, the suspended solids might be computed via filtration through a glass-fibre filter. Another technique is to filter an example of water through filter paper and find out total solids in the filtrate. The dissimilarity between total solids in unfiltered and filtered examples is a compute of the suspended solids present.

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