EAT 131: ENVIRONMENTAL CHEMISTRY

1. EAT 131: ENVIRONMENTAL CHEMISTRY CHAPTER 5: WATER QUALITY PARAMETERS

2. Turbidity • Turbidity is the cloudiness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air. • The measurement of turbidity is a key test of water quality.

3. What is turbid water? • Waters containing suspended matter that interferes with the passage of light through the water (refraction of light) • Caused by a variety of suspended materials that range in size from colloidal to coarse dispersion

4. What causes turbidity? • Human activities that disturb land: - Construction, mining, farming - can lead to high colloidal rock particles/sediment levels entering water bodies during rain storms and create turbid conditions. • Domestic and industrial wastes (organic or inorganic) • Street washing (much inorganic; some organic) • Bacterial growth (by eating organic materials) and other microorgnism feeding upon bacteria • Algal growth stimulated by inorgainc nutrients (N & P) from wastewater discharge/agricultural runoff

5. TURBIDITY Vs FILTERABILITY • Filtration of turbid water is more difficult and costly • High turbidity shortens slow sand filter runs and increases cleaning costs • In high water turbidity, chemical coagulation is needed for rapid sand filters to be effective

6. Multimedia filtration system Slow sand filter

7. TURBIDITY Vs DISINFECTION • Disinfection by clorine, ozone or ultraviolet radiation requires contact between the agent and the organisms to be killed • In cases which turbidity is caused by municipal wastewater suspended solids or runoff from animal farmland, the particles act as shields for the virus and bacteria and protected from disinfectant

8. Standard unit of turbidity • Turbidity is measured in NTU: Nephelometric Turbidity Units. The instrument used for measuring it is called nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample. • Light reaches the detector if there are lots of small particles scattering the source beam than if there are few

9. Measures 0.02 – 40 Nephelometric turbidity unit (NTU)  higher turbidity needs dilution with turbidity free water • A handheld turbidity meter (left-side picture) measures turbidity of a water sample. It is calibrated using standard samples as shown in the three glass vials; 5, 50, and 500 NTUs.

10. Application of turbidity data WATER SUPPLY TREATMENT • Knowledge of turbidity variation in raw water supplies in most important in water treatment plant operation • Water supplies from upland or mountain supplies • Usually have low turbidity; thus no treatment other than chlorination is required • This may change due to concerns with protozoan pathogens • Water supplies from river • Usually require chemical flocculation because of high turbidity • Turbidity measurements are used to determine the effectiveness of daily treatment produced with different chemicals and dosages needed, check on faulty filter operation, and to conform with regulatory requirements • From WHO – the turbidity of drinking water shouldn't be more than 5 NTU, and should ideally be below 1 NTU.

11. DOMESTIC AND INDUSTRIAL WASTE TREATMENT • Suspended solids determination is usually employed in waste treatment plants to determine the effectiveness of suspended solids removal  slow, time consuming, thus not practical for plants requiring frequent chemical dosages • Turbidity measurements  fast, can be used to determine minimum amount of chemical dosages needed to produce high quality effluent

12. COLOUR

13. Coloured water

14. Color of water samples • Dissolved and particulate material in water can cause discoloration. - Dissolved organic compounds called tannins can result in dark brown colors - Algae floating in the water (particles) can impart a green color. - Clay soils (suspended solids) during flood season may cause red color - Iron presents as ferric humate

15. Dye wastes from dyeing operations in textile industry and from pulping operations in paper industry • Surface waters are often coloured to the extent that they are not acceptable for domestic or some industrial uses without treatment

16. The color of a water sample can be reported as: - Apparent color is the color of the whole water sample, and consists of color from both dissolved and suspended components - True color is measured after filtering the water sample to remove all suspended material.

17. Standard colour solutions • Natural coloured waters are yellow-brownish in appearance • Solutions of potassium chloroplatinate (K2PtCl6) tinted with small amount of cobalt chloride yield colors similar to natural colours. Colour produced by 1 mg/L platinum (K2PtCl6) = standard unit of colour • Stock solutions K2PtCl6 that contains 500 mg/L of platinum (= 500 units colour) is normally used, and series of working standards may be prepared from it by dilution.

18. Sample with colour less than 70 units are tested by direct comparison with prepared standards • If colour greater than 70 units, a dilution is made with demineralized water to bring the resulting colour within standard ranges. • Calculation of colour is made using the dilution factor. • A series ranging from 0–70 colour units is employed and will serve for several months, if protected from dust and evaporation Apparent colour is determined on the sample directly, but true colour is determined after centrifuging the sample to separate suspended solids

19. Colour measurement

20. Color Removal • Filtration with membranes having 0.45 micron pores can effectively treat problems associated with particulates, apparent color. • Even in situations with dissolved organics, true color, conventional treatment processes (coagulation, flocculation, sedimentation and filtration) can remove a substantial portion of color • Biological treatment – anaerobic & aerobic processes • Advance Oxidation Processes – ozonation, fenton process, UV-vis + TiO2 • Adsorption - Activated carbon can be used, but depending on the level of color, activated carbons can have a short life time in this service.

23. Application of colour data • Colour is aesthetically displeasing and unacceptable for domestic supplies, while many industries require color-free water • However, removal of colour is an expensive matter when capital investment and operating costs are considered • So, colour data is one of the parameters to satisfy client that appropriate treatment are needed to produce an acceptable supply • Colour determinations also can be the basis of making decision in designing chemical treatment plant; chemicals and the amount to be used; as well as for design of storage space

24. pH

25. What is pH? • pH is a measure of how acidic/basic water is. • The range goes from 0 - 14, with 7 being neutral. pH of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base. • pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water that has more free hydroxyl ions is basic. • Important factor: chemical and biological processes in wastewater treatment

26. pH concept pH = -log {H+}  px = -log10x = log10 1/x pH = log 1/{H+} Pure water at 25C; {H+} = 10-7; {OH-} = 10-7; Kw = 1x10-14 at 25C -log{H+} + -log{OH-} = -log Kw pH + pOH = 14 Kw changes with change in temperature, thus pH of neutrality change as well; at 0 C = 7.5 and at 60 C = 6.5

27. Measurement of pH • Hydrogen electrode is the absolute standard to determine pH • A wide variety of indicators (e.g. methyl orange; phenolphthalein; litmus paper) were calibrated with hydrogen electrode to determine colour characteristics at various pH levels • Determination of pH values by using indicators that exhibit different colour changes in a particular range is fairly accurate • pH is reported in "logarithmic units," each number represents a 10-fold change in theacidity/basicness of the water

28. Coloured indicator (e.g. litmus paper) • It has the property of changing its color to red with acidic substances and to blue with basic ones. • On the packet of the litmus paper, there is a color scale which indicates the color assumed by the paper as a function of the pH High side, a strip dipped in a solution of baking soda. Bottom side, a strip dipped in vinegar. indicator paper

29. Commercial models of pH meters (a) Small battery-operated model for use in the field or laboratory. (b) Line-operated laboratory benchtop model. (a) (b) Setting the pH meterBefore using it, the instrument has to be checked and possibly adjusted. For this purpose, the electrode of the meter is immersed in suitable buffer solutions with known pH (usually pH 7; 4; 10).

30. Adjustment/Treatment of pH

31. Hardness • Hard water is water that has high mineral content (in contrast with soft water). • Hard water minerals primarily consist of Ca2+ (CaCO3 and CaSO4 ) & and Mg2+(CaMg(CO3)2), and sometimes other dissolved compounds such as bicarbonates and sulfates. • The simplest way to determine the hardness of water is the lather/froth test: soap or toothpaste, when agitated, lathers easily in soft water but not in hard water.

32. What does hard water do? • The minerals contained in hard water settle out as a deposit of hardness scale wherever the water is heated or when cold standing water evaporates. • Examples of this include; • white marks, stains and scale on sinks, baths, toilet bowls and around the base of taps • blocked shower heads • scale deposits on kettles and water heating elements • clogging of pipe

33. Cause and source of hardness • Hardness is caused by multivalent metallic cations • Such ions are capable of reacting with soap to form precipitates and with certain anions present in water to form scale • Principle hardness causing cations: calcium(II) > magnesium(II) > strontium(II) > iron(II) > mangan(II) • Major anions associated with the cations: bicarbonate > sulphate > chloride > nitrate > silicate

34. Public health significance • Hard water is generally not harmful to one's health. • Their use for cleaning purposes is quite unsatisfactory, unless soap costs are disregarded

35. Methods of determination • Hardness is expressed in terms of CaCO3 • 2 standard methods: • Calculation method • Divalent ions (M2+) are analysed using AAS, ion chromatography or ion specific electrodes • Hardness caused by each ion is calculated Hardness (in mg/L) = M2+ (in mg/L) x 50/EW of M2+ • EDTA titrimetric method • The solution of ethylenediaminetetraacetic acid (EDTA) or its sodium salt is used as titrating agent • EDTA are chelating agent that form extremely stable complex ions with Ca2+ and Mg2+ and other divalent ions causing hardness M2+ + EDTA  [M .EDTA]complex • Dyes, Eriochrome Black T or Calmagite serve as indicators to show when all hardness causing ions have been complexed M2+ + Eriochrome Black T  (M . Eriochrome Black T)complex blue red

36. Methods of determination

37. Types of hardness • Calcium and magnesium hardness are the greatest portion of the hardness in natural waters • If Ca hardness is determined, Total Hardnes = multivalent metallic cations Total hardness – Ca hardness = Mg hardness • Carbonate and Non-carbonate hardness • Carbonate hardness is the hardness of water caused by the presence of carbonate (CO32-) and bicarbonate (HCO3-) ions. • It is chemically equivalent to bicarbonate plus carbonate alkalinities (or called temporary hardness) • Amount of hardness in excess of carbonate hardness is noncarbonate hardness; i.e. cations associated with sulfate, chloride, and nitrite ions (or called permanent hardness) Noncarbonate hardness = total hardness – carbonate hardness

39. Permanent hardness is hardness (mineral content) that cannot be removed by boiling. It is usually caused by the presence in the water of calcium and magnesium sulfates and/or chlorides which become more soluble as the temperature rises. • Temporary hardness is caused by a combination of calcium ions and bicarbonate ions in the water. It can be removed by boiling the water or by the addition of lime (calcium hydroxide).

40. Treatment of water hardness • Permanent hardness can be removed using a water softener or ion exchange column. • Water softeningis the act of reducing the dissolved calcium, magnesium, and to some degree manganese and ferrous iron ion concentration in hard water. A common water softener is sodium carbonate (Na2CO3). • Ion exchange - where the calcium and magnesium ions are exchanged with the sodium ions in the column.

42. Application of hardness data • Basis for recommending the need for softening processes • The types and relative amount of the hardness in water determine the most economical softening process to be used (design considerations) • Hardness data serve as basis for routine control of softening processes

44. Biochemical Oxygen Demand(BOD)

45. BOD • BOD: The amount of oxygen used by microbes in the oxidation of organic matter • BOD is the most important parameter in water pollution control. As an indication of the quality of water • Determines the pollution strength of domestic and industrial wastes in terms of the oxygen that will be required if discharged into natural watercourses in which aerobic conditions exist. • Quantitative relationship between amount of oxygen required to convert an amount of organic compound to carbon dioxide, water and ammonia:

46. BOD measurement • The BOD sample is measured by determining the amount of O2 consumed from a sample of water placed in a BOD bottle (air tight container) and kept in incubator (temperature 20oC, no light) for 5 days. • Light must be excluded to prevent algal growth that may produce O2 in the bottle • BOD may be measured directly in a few samples but in general a dilution is required

47. BOD measurement • To ensure that all other conditions are equal, a very small amount of micro-organism seed is added to each sample being tested. This seed is typically generated by diluting activated sludge with de-ionized water. • Diluting the sample with oxygen saturated de-ionized water, inoculating it with a fixed amount of seed, measuring the dissolved oxygen (DO) and then sealing the sample to prevent further oxygen dissolving in. • The sample is kept at 20 °C in the dark to prevent photosynthesis for 5 days, and the DO is measured again. The difference between the final DO and initial DO is the BOD.

48. Dilution water: - phosphate buffer, MgSO4, CaCl2, and FeCl3 solutions - before use, bring dilution water temperature to 20 + 3°C. Saturate with DO by shaking in a partially filled bottle or by aerating with organic-free filtered air.

49. Calculation of BOD 1) BOD5 (mg/L) = D1-D2 (when no seed or dilution is used) D1=initial DO in sample D2=final DO in sample 2) BOD (mg/L) = (D1-D2)/P (when unseeded dilution water is used) P= mL pipeted/300 mL 3) BOD (mg/L) = [(D1-D2)-f(B1-B2)]/P (when seeded dilution water is used) B1=initial seed DO in control B2=final seed DO in control f = fraction of seed in the incubated sample = (volume of seed in diluted sample)/(volume of seed in seed control) P= Vol. sample/vol. mixture

50. Application of BOD data • Principle test applied to domestic and industrial waste to determine strength in terms of oxygen required for stabilization • Serves regulatory authorities in monitoring the quality of streams and effluents discharged into such waters • Important consideration in design and costs of biological treatment facilities