Qaulity of Water Assessment, 2021-02-26.pptx

Qaulity of Water Assessment, 2021-02-26

1. WATER QUALITY ASSESSMENT WMA 318 Prof. O. Martins and Dr O.Z. Ojekunle Dept of Water Res. Magt . & Agromet UNAAB. Abeokuta. Ogun State Nigeria [email protected] https://slideplayer.com/slide/10954136/

2. COURSE CODE : WMA 318 COURSE TITLE : Water Quality Assessment and Pollution Control COURSE UNITS : 2 Units COURSE DURATION: 2 hours per week

3. COURSE DETAILS Course Cordinator : Prof. O. Martins B.Sc., M.Sc., PhD Email:[email protected] Office Location: Room B208, COLERM Other Lecturers: Dr. O.Z. Ojekunle B.Sc., M.Sc., PhD

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5. COURSE CONTENT Solvent properties of water; principles of physico -chemical analysis, major ionic components of natural water. Chemistry of natural waters, water quality requirements, standards for potable water, irrigation and livestock. Types of water, lithological control of surface and ground water. Water Pollution Studies: Sources, fate, pathways and effects of water pollution, Chemical, Mechanical and Biological methods of maintaining and improving water quality. Pre-requisite: CHM 202

6. COURSE REQUIREMENT This is a required course for students in the College of Environmental Resources Management. They are supposed to passed CHM 202 before registering for this course. As a school regulation, a minimum of 75% attendance is required of the students to enable him/her write the final examination

7. READING LIST Eidon D. Enger , Bradley F. Smith 2003. Environmental Science: A study of Interrelationships (Ninth Edition) McGraw-Hill International Edition Publication. William P. Cunningham, Mary Ann Cunningham 2008. Principles of Environmental Sciences, Inquiry and Applications (Fifth Edition) McGraw-Hill International Edition Publication. William P. Cunningham, Mary Ann Cunningham 2008. Environmental Sciences, A Global Concern (Eleventh Edition) McGraw-Hill International Edition Publication.

8. PROPERTIES OF WATER Water is a chemical compound of oxygen and hydrogen and in the gaseous state can be represented by the molecular formula H 2 O. The isotopes of hydrogen and three isotopes of oxygen exist in nature, and if these are taken into account, 33 varieties of water are possible. The physical properties of liquid water are unique in a number of respects, and these departure from what might be considered as normal for such a compound are of the greatest importance with respect to both the existence of life on earth and the operation of many geochemical processes. The boiling point and freezing point of water are both far higher than would be the theoretically expected, considering the low molecular weight of the compound, and the range of temperature over which water as a liquid is wider than might be expected. The reason for these and other departures from “ normal ” behaviour can be gained by more detailed consideration of the molecular structure of the compound.

9. MOLECULAR STRUCTURE OF WATER The spheres representing the ions coalesce to some extent, and the molecule might be thought of as a sphere having two rather prominent bubbles of “ blisters ” attached to it. Te bonds connecting the hydrogen ’ s to oxygen describe an angle of 105 o , so that the two hydrogen are relatively close together on one side of the molecule. Although this representation of the molecule is somewhat empirical it helps to explain some of the abnormal features of the behaviour of water. The molecule has dipolar properties because the positive charge associated with the hydrogen are connected on one side of the molecule, leaving a degree of negativity on the opposite side. Forces of attraction thus exist between hydrogens of one molecule and the oxygen bonds. They hold molecule together in a fixed pattern in the solid state. In contrast to the orderly arrangement of molecules in crystal of ice, the molecules of liquid water are in a chaotic condition of disorder. Hydrogen bonds still remain an important force but their arrangement is continually shifting The cohesive forces represented by the hydrogen bonds impact to liquid water is high heat of vaporization. The forces also tend to prevent the passage to electric currents and impart to the fluid its high dielectric constan t. The attraction between molecules of a liquid is shown at a liquid surface by the phenomenon called Surface tension. The surface of water is 75.6 dynes per centimeter at 0oC and 71.8 dynes per centimeter at 25 o C, which are very high values compared with the many other liquids

10. PROPERTIES OF WATER Chemical Constitution of Water 1 Ionic and Non Ionic Ionic Anion Cations 2 Major Anions Bicarbonate, Chloride, Sulphate Major Cations Sodium, Potassium, Calcium, Magnesium Non-Ionic SiO 2 , Dissolved gases, oily Substance, Synthetic detergent, etc

11. CHARACTERISTICS OF WATER Hardness Carbonate (Temporary) Hardness CaCO 3 Non Carbonate (Permanent) Hardness CaSO 4 Concentration of Hydrogen-ion, which are expressed in pH units. It is the — Log 10 H + Specific Electrical Conductance - Increases with temperature: values must therefore be related to the same temperature (2%) Colour Alkanity: Ability to neutralize acid; due to the presence of OH-, HCO 3 - , CO 3 2- , Acidity: Water with pH 4.5 is said to have acidity; caused by the presence of free mineral acids and carbonic acids Turbidity: Measure of transparency of water column; indirect method of measuring ability of suspended and colloidal materials to minimize penetration of light through water. Dissolved gasses: O 2 , N 2 , CO 2 , H 2 S, CH 4 , NH 3 , etc.

12. PHYSICAL CHEMICAL PARAMETER Since water is not found in its pure in nature, it is important to determine its combined physical, chemical and biological characteristics. This is done through monitoring of water for its quality. Physical chemical parameter analyzed in natural environments; Atmosphere (rainfall), hydrosphere (river, lakes, and oceans) and Lithosphere (Groundwater) are similar-

13. PHYSICAL CHEMICAL PARAMETER (Cont) Temperature: Measurement is relevant For Aquatic life Control of waste treatment plants Cooling purposes for industries Calculation of solubility of dissolved gases Identification of water source Agriculture Irrigation Domestic uses (Drinking, bathing) Instrument of measurement is thermometer pH: Controlled by CO 2 /HCO 3 - /CO 3 2- Equilibria in natural water. Its values lie between 4.5 and 8.5. It is important Chemical and biological properties of liquid Analytical work Measurement is done in the field. Most common method of determination is the electrometric method, involving a pH-meter. It is important to calibrate the meter with standard pH buffer solutions

14. PHYSICAL CHEMICAL PARAMETER (Cont) Dissolved Oxygen: Water in contact with the atmosphere has measurable dissolved oxygen concentration. It values depends on Partial pressure of O 2 in the gaseous phase Temperature of the water Concentration of salt in the water (the higher the salt content in water, the lower the concentration of dissolved oxygen and the other gases). Measurement is important in Evaluation of surface water quality Waste-treatment processes control Corrosivity of water Septicity Photosynthetic activity of natural water

15. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS Temperature: Temperature affects the density of water, the solubility of constituents (Such as oxygen in water), pH, Specific conductance, the rate of chemical reactions, and biological activity of water . Continuous water quality sensor measure temperature with thermistor, which is a semiconductor having resistance that changes with temperature. Thermistor are reliable, accurate, and durable temperature sensors that require little maintenance and are relative inexpensive. The preferred water-temperature scale for most scientific work ids the Celcius scale. measure temperature to plus or minus 0.1 degree celcius ( o C)

16. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Specific Conductance: Electrical conductivity is a measure of the capacity of water to conduct an electrical current and is a function of the types and quantities of dissolved substance in water. As concentration of dissolved ions increase, conductivity of the water increases. Specific conductance is the conductivity expressed in units of Microsiemen per centimeter at 25 o C. Specific conductance are a good surrogate for total dissolved solids and total ions concentrations, but there is no universal linear relation between total dissolved solids and specific conductance. Specific conductance sensors are of 2 types: contact sensors with electrodes and sensor without electrodes.

17. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Salinity: Although Salinity is not measured directly, some sondes include the capability of calculating and recording salinity based on conductivity measurement. Conductivity has long been a tool of estimating the amount of chloride, a principle component of salinity in water. Salinity is commonly reported using the Practical Salinity Scale (PSS), a scale developed to a standard potassium-chloride solution and based on conductivity, temperature and barometric pressure measurement. Before developing the PSS, salinity was reported in part per thousand/million. Salinity expressed in the PSS is a dimensionless value, although by convection, it is reported as practical salinity unit.

18. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Dissolved Oxygen: Sources of DO in surface waters are primarily atmospheric reaeration and photosynthetic activity of aquatic plants. DO is an important factor in chemical reactions in water and in the survival of aquatic organisms. In surface water, DO concentration typically range from 2-10mg/l. DO saturation decreases as water temperature increases, and DO saturation increases with increased atmospheric pressure. Occasion of super saturation (greater than 100 percent DO saturation) often are related to excess photosynthetic production of oxygen by aquatic plants as a result of nutrient (nitrogen and Phosphorus) enrichment, sunlight and warm water temperature. DO may be depleted in inorganic oxidation reaction or by biological and chemical processes that consume dissolved, suspended or precipitated organic matter. The DO Solubility in saline environments is dependent on salinity as well as temperature and barometric pressure . DO in water that have specific conductance values of greater than 2000 microsiemens/centimeter should be corrected for salinity. The newest technology for measuring DO is the Luminescent sensor that is based on dynamic fluorescence quenching.

19. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) pH: The pH of aqueous solution is controlled by the interrelated chemical reactions that produce or consume hydrogen ions. The pH of a solution is a measure of the effective hydrogen-ion concentration. More specifically, pH is a measure that represents the negative base-10 logarithm of hydrogen-ion activity of a solution, in moles per liter. Solutions having a pH below 7 are described as acidic, and solutions with pH greater than 7 are described as basic or alkaline. Dissolved gases such as carbon dioxide, hydrogen sulphide and ammonia, apparently affect pH. Dagasification (for example, loss of carbon dioxide) or precipitation of a solid phase (for example, calcium carbonate) and other chemical, physical, and biological reactions may cause the pH of a water sample to change appreciably soon after sample collection . The electrometric pH-measurement method, using a hydrogen-ion electrode, commonly is used in continuous water-quality pH sensors. A correctly calibrated pH sensor can accurately measure pH to -+ 0.2 pH units; however, the sensor can be stretched, broken or fouled easily. If the streamflow rates are high, the accuracy of the pH measurement can be affected by streaming-potential effects.

20. MEASUREMENT & RELATIONSHIP OF PHYSICAL CHEMICAL PARAMETERS (Cont) Turbidity: Turbidity is defined as an expression of the optical properties of a sample that cause light rays to be scattered and absorbed, rather than transmitted in straight lines through a sample. ASTM further describe turbidity as the presence of suspended and dissolved matter, such as clay, silt, finely divided organic matter, plankton, other microscopic organisms, organic acids, and dyes. Implicit in this definition is the fact that colour, either of dissolved materials or of particles suspended in the water also can affect turbidity. Turbidity sensors operate differently from those for temperature, specific conductance, DO, and pH, which convert electrical potentials into the measurement of constituent of interest. Submersible turbidity sensors typically direct a light beam from light-emitting diode into water sample and measure the light that scatters or is absorbed by suspended particles in water. Most commercially available sensors report data in Nephelometric Turbidity Units (NTU)/ with a sensor range of 0-1000 and an accuracy of -+5 percent or 2NTU, whichever is greater.

21. WATER QUALITY ASSESSMENT AND POLLUTION CONTROL WMA 318 PART 2

22. Note For any water body to function adequately in satisfying the desired use, it must have corresponding degree of purity. Drinking water should be of highest purity. As the magnitude of demand for water is fast approaching the available supply, the concept of management of the quality of water is becoming as important as its quantity .

23. Contaminant Are physical, chemical, biological or radiological substances found as unwanted residue in or on a substance. Pathogens: Are micro organisms that can cause diseases e.g bacteria Metals (Metals that are harmful in relatively small amounts are labeled toxic)

24. Disease caused by contaminants Salmonella Typhi Typhoid fever Vibro Cholera Cholera Entameoba histolytica Amoeba Dysentery Escherichia Coli (E. Coli) Gastroenterits Enterovirus Polio Hepatitis Infestious Hepatitis Heavy Metal Cancer

25. Water Purification Process Abstraction: Abstraction involves pumping and transportation of raw water, a process with high rate of electrical energy consumption. It occurs at the intake. Screening: Is defined as the process whereby relatively large and suspended debris is removed from the water before it enters the plant. Aeration: Aeration (Air Stripping) is a physical treatment process whereby air is thoroughly mixed with water to removed dissolved gasses and odour. Coagulation: Addition of chemical to remove suspended solids. Flocculation: A chemical flocculent, such as aluminium sulphate, is mixed rapidly with the water to remove mud. Sedimentation: Also known as clarification- is the gravity-induced removal of particles. Filtration: Involves the removal of suspended particles from water by passing it through a layer or bed of a porous granular material e.g sand. The filter water the passed through nozzles, the nozzles and sand in the filter beds must be cleaned periodically (This is known as back washing). Chlorination: After filtration, the water looks much more cleaner than it was in the dam or river but it may not yet be healthy to drink because it may contain unseen micro-organism (bacteria) that are dangerous to the human body and can serious illness (such as diahorrea) 4.5 liters – 1 Gallon. 1 Liter – 100cl. 1 m3 – 5 drums or 200 liter volume.

26. WATER QUALITY OBJECTIVES AND REQUIREMENT A major advantage of the water quality objectives approach to water resources management is that it focuses on solving problems caused by conflicts between the various demands placed on water resources, particularly in relation to their ability to assimilate pollution. The water quality objectives approach is sensitive not just to the effects of an individual discharge, but to the combined effects of the whole range of different discharges into a water body. It enables an overall limit on levels of contaminants within a water body to be set according to the required uses of the water.

27. WQ Criteria For some other water quality variables, such as dissolved oxygen, water quality criteria are set at the minimum acceptable concentration to ensure the maintenance of biological functions.

28. Examples of the development of national water quality criteria and guidelines in Nigeria In Nigeria, the Federal Environmental Protection Agency (FEPA) issued, in 1988, a specific decree to protect, to restore and to preserve the ecosystem of the Nigerian environment. The decree also empowered the agency to set water quality standards to protect public health and to enhance the quality of waters

29. Hardness is usually expressed in term of milligram per liter of calcium carbonate, CaC03; grains per gallon are also used to express hardness concentration. Water with more than 300mg/L of hardness is generally considered to be hard, and water with less than 75mg/L is considered to be soft. Very soft water is undesirable in public supply because it tends to increase corrosion problem in metal pipes; also, some health official believe it to be associated with the incident of the heart disease.

30. Dilution In water pollution control, it is often necessary to predict the BOD concentrations and the DO levels downstream from a sewage discharge point. One of the first computations needed for this involves the effect of dilution. Assuming that pollutant is completely mixed in the streamflow (at a point just below the end of the mixing zone), one can calculate the diluted concentration of any water quality parameter using the following mass balance equation: cd = (csQs + cwQw)/(Qs + Qw) where cd = diluted concentration or temperature cs = original stream concentration or temperature cw = waste concentration or temperature Qs = stream discharge Qw = waste discharge

31. A fundamental concept in science is the law of conservation of matter . This means that when there is no appreciable conversion of mass into energy, the sum of the masses of substances entering into a reaction must always equal the sum of the masses of products of reaction. Even if there in no chemical reaction occurring, the law of conservation underlies the concept of mass balance (also called material balance), and is useful in environmental technology Mass balance calculations play an important role in the design and operation of water, sewage, air and solid waste treatment processes. In treatment systems, the physical, chemical, and biological processes usually occurs in vessel or tanks called reactors, and the particular reactions or processes are referred to as unit processes . In the simplest case, it can be said that the input must equal the output, or, in other words, “ what goes in must go out. ” If this does not occur, there must be an accumulation (depletion) of the material in the reactor equal to the difference between the input and output, or accumulation = input-output. Since, in this kind of situation, the composition of material in the reactor changes with time, it is referred to as an unsteady-state operation. In the steady state operation, it can be assumed that the rates of input and output are constant, as is the composition of the completely mixed reactor. Suppose, for example, two pipes containing salt solutions discharge into a tank in which the two solutions are completely mixed, and the third pipe carries the mixture out of the tank

32. The solution in the first pipe has a concentration of c1 mg/L and that in the second pipe has a concentration of c2 mg/L. the flow rate of the pipes are Q1 and Q2 respectively. The concept of mass or material balance can be applied to determine the concentration of the mixed solution discharged from the tank because under steady-state conditions, the total amount of salt entering the tank must be equal to the total amount leaving the tank. In other words, since the salt neither decays nor reacts with other substance (in this example), the concentration of salt in the mixture in the tank stay constant over time. The product of concentration of volume flow rate equals the mass flow rate because mg/L X L/d = mg/d where the volume flow rate in this example is expresses in terms of liter per day, or L/d. for convenience here, consider that the time interval is 1 day. Then the product of c1 X Q must equal the mass of salt entering the vessel in 1 d from the first pipe. Similarly, c2 X Q equals the mass of salt entering the tank from the second pipe. The total mass of salt entering the tank in 1 d, that is, the input , must be equal to the sum from the two pipes, or input = c1 X Q1 + c2 X Q2.

33. The total mass of salt leaving the tank equals the product of the concentration in the mixture c3 and the volume flow rate leaving the tank. Because water is actually incompressible, however, that flow rate must be Q1 + Q2. Therefore, the output of salt is c3 X (Q1 + Q2). Because the concept of mass or material balance applies here and output = input, the following relationship is obtained: c3 X (Q1 + Q2) = c1 X Q1 + c2 X Q2 Solving the above equation for c3 by dividing both sides by (Q1 + Q2), we obtained the following mass balance equation c3 = (c1 X Q1 + c2 X Q2)/Q1 + Q2 Mass balance calculation can be applied to the natural environmental systems, such as streams, rivers, lakes and even the atmosphere e.g Stream pollution.

34. EXAMPLE: The BOD5 of an effluent from a municipal sewage treatment plants is 25mg/L and the effluent discharge is 4 ML/d. the receiving stream has a BOD5 of 2 mg/L and the stream flow is 40 ML/d. compute the combined 5-day BOD in the stream just below the mixing zone. SOLUTION: Applying cd = (csQs + cwQw)/(Qs +Qw) cd = (2 X 40 + 25 X 4)/ 40 X 4 = 180/44 = 4.1mg/L Where cd represent the diluted BOD5 in the combined flow EXAMPLE: A river has a dry-weather discharge of 100 cfs and a temperature of 25oC. Compute the maximum discharge of cooling water at 65oC that can be discharged from a power plant into the stream. Assume the legal limit on the temperature increase in stream is 2oC SOLUTION : The maximum allowable stream temperature is 25 + 2 = 27oC Applying mass balance equation cd = (csQs + cwQw)/(Qs +Qw) 27 = (25 X 100 + 65 X Qw)/100 + Qw 200 = 38Qw : Qw = 5.3 cfs The discharge of warm water cannot be exceed 5.3 ft3/s if the stream temperature is not to increase more than 2oC

35. COMPUTATION OF MINIMUM DO It is important to be able to predict the minimum dissolved oxygen level in a polluted stream or river. For Example, if a new sewage treatment plant is to be discharge its effluent into a trout stream, it is possible that conventional (secondary) treatment levels will not remove enough BOD to prevent excessively low DO downstream. To determine if some form of advanced treatment is required to preserve the stream for trout spawning and survival, it is necessary to compute the minimum DO caused by the sewage effluent and to compare it to the allowable value for trout streams. One technique used to describe and predict the behaviour of a polluted stream uses the so-called Streeter-Phelps equation. This equation is based on the assumption that the only two processes taking place are deoxygenation of BOD and the reaeration by oxygen transfer at the surface, as previously discussed. Two key formulas from the Streete-Phelps model of stream pollution and oxygen sag follow. Figure 5.11 illustrate some of the variables in these equations. The minimum DO in the stream is the difference between the saturation DO level and the critical oxygen deficit. The formulas are

36. COMPUTATION OF MINIMUM DO (Cont) Tc= Dc= Where tc = Time it takes for the critical oxygen deficit or minimum DO to develop, d Dc = Critical oxygen deficit, mg/L Di = Initial oxygen deficit at time t = 0 just below the point of waste discharge into the stream, mg/L BODL = Ultimate BOD in the stream just below the point of waste discharge, mg/L k1 = Deoxygenated rate constant, d-1 k2 = The reaeration rate constant, d-1

37. COMPUTATION OF MINIMUM DO (Cont) The value of k1 if generally taken to be the same as the rate constant for the BOD reaction in this equation BODt = BODL X (1-10-kt); it can be determined in the laboratory. The value of k2 depends on the velocity and the depth of the flow and can be determined from field studies or by an appropriate formula. The reaeration rate constant k2 can be vary from about 0.1 for the sluggish to about 4.0 for a swallow turbulent stream. Both rate constants, k1 and k2 depend on temperature. The equation tc and Dc look complicated, and they are. They are presented here to illustrate the power of mathematics as a tool for modeling the environment and helping solve water pollution problems. But as complicated as they may appear, the Streeter-Phelps equations are not completely accurate representations of the oxygen profile in a polluted stream or river. Other factors that affect the oxygen balance include photosynthesis and respiration of rooted plants and algae and the oxygen demand of benthic (bottom) deposits. Equations that have been developed to include these factors are even more complicated than the equation tc and Dc

38. COMPUTATION OF MINIMUM DO (Cont) EXAMPLE: The BODL in a stream is 3 mg/L and the DO is 9.0 mg/L. The streamflow is 15mgd. A treated sewage effluent with BODL =50mg/L is discharged into the stream at a rate of 5 mgd. The DO of the sewage effluent is 2 mg/L. Assuming that k1 = 0.2, k2 = 0.5, and the saturation DO level is 11 mg/L, determine the minimum DO level in the stream. For a stream velocity of 0.5 ft/s, how far downstream does the minimum DO occur? SOLUTION: First, it is necessary to compute the diluted BODL and DO using the Mass Balance Equation BODL = (15 X 3 + 5 X 50)/15 + 5 = 295/20 = 14.8mg/L DO = (15 X 9 + 5 X 2)/15 + 5 = 145/20 = 7.3 mg/L Now compute the initial oxygen deficit as Di = saturation DO – Initial DO = 11.0 – 7.3 = 3.7mg/L Applying the Streeter-Phelps Model Equations for tc

39. COMPUTATION OF MINIMUM DO (Cont) Tc= = = (0.33)log 1.56 = 0.64 d It will take about 0.64 d (roughly 15hours) for the minimum DO to occur. Now applying next Streeter-Phelps Model Equation for Dc gives Dc= = 9.87 X (0.745 – 0.479) + 3.7 X 0.479 = 2.63 + 1.78 = 4.4 mg/L The minimum DO in the stream is the difference between saturation DO and the critical oxygen deficit, or 11.0 – 4.4 = 5.6 mg/L. At a velocity of 0.5 ft/s, in 0.64 d the distance downstream for the minimum DO is 0.64 d X 24 h/d X 3600 s/h X 0.5 ft/s = 27659 ft approximately 5 million.