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1 Water Chemistry 5 Evaluating Water Quality WATER QUALITY ASSESSMENT Water quality: Water quality: physical, chemical, biological characteristics Acceptable quality varies with intended use, for example: Recommended Threshold Odor Number is for drinking water is 3 whereas it is 0 for brewing 1

2 PHYSICAL CHARACTERISTICS: Turbidity Turbidity – the clarity of water Transparency of natural water bodies is affected by human activity, decaying plant matter, algal blooms, suspended sediments, and plant nutrients T bidit id i i ti t f t t l d d T ur bidit y prov id es an i nexpens i ve es ti ma t e o f t o t a l suspen d e d solids TSS concentration Turbidity has little meaning except in relatively clear waters but is useful in defining drinking-water quality in water treatment Secchi disk measures how deep a person can see into the water (feet). Reflects euphotic zone. Can’t be used in shallow water. Other methods for measuring turbidity are Jackson Turbidity Units (JTU) depth candle can be seen Nephlometer Turbidity Units (NTU) light scattering from a tungsten lamp (white light) Formazin Nephelometric Units (FNU) light scattering from an LED (light emitting diode, infrared) calibration uses microspheres of the polymer formazin Units are roughly equivalent Duration of Turbidity is an Important Factor http://waterontheweb.org/under/waterquality/turbidity.html 2

3 Nephlometer Turbidity Units (NTU) PHYSICAL CHARACTERISTICS: Color Blue - Transparent water with low dissolved solids 3

4 PHYSICAL CHARACTERISTICS: Color Red - An iron mine pit lake in northeast Minnesota (some algae cause red color) PHYSICAL CHARACTERISTICS: Color Left - Reddish-Orange - iron Precipitate from AMD Right - Reddish Silt in Malaysia River 4

5 PHYSICAL CHARACTERISTICS: Color he Brown-Yellow Amazon River Green-Blue Tapajos meets t Brown-Yellow = dissolved organic materials, humic substances aying plant material from soil, peat, or dec PHYSICAL CHARACTERISTICS: Color Green due to water rich in phytoplankton and other algae http://www.ozestuaries.org/indicators/Images/swan_algae.jpg gy/wetlands/basics/importance.html www.samford.edu/schools/artsci/biolo 5

6 PHYSICAL CHARACTERISTICS: Color Verbal descriptions of color are unreliable and subjective r Recommendation is for EPA Secondary Drinking Wate color of less than 15 Platinum Cobalt Units (PCU) 1 unit - the color of distilled water containing 1 milligram of platinum as potassium chloroplatinate per potassium chloroplatinate per liter liter Color is reduced or removed from water through the use of coagu lation, settling and filtration techniques PHYSICAL CHARACTERISTICS: Solids Total Solids (TS) - the total of all solids in a water sample Total Suspended Solids (TSS) - the amount of filterable solids t l filt d i d d i h d er samp i n a wa t i l e, filt ers are d r i e d an d we i g h e d Total Dissolved Solids (TDS) - nonfilterable solids that pass through a filter with a pore size of 2.0 micron, after filtrati on the liquid is dried and residue is weighed EPA Secondary Drinking Water Recommendation is for TDS of less than 500mg/L Volatile Solids (VS) - Volatile solids are those solids lost on heating to 500 degrees C - rough approximation of the amount of organic matter present in the solid fraction of wastewater 6

7 PHYSICAL CHARACTERISTICS: Temperature Temperature should be measured in the field Temperature affects a number of water quality parameters Such as dissolved oxygen which is a chemical characteristic www.woonasquatucket.org/waterqualitydata2005.htm AESTHETIC CHARACTERISTICS: Odor Taste Evaluated Volume Threshold Odor is 200mL Number TON Compound Odor # when odor is first Geosmin from algae Earthy Grassy noticed when # of parts of sample Musty 2-methylisoborneal from starting with a dilute mixed with distilled algae sample in which water per 200mL of odor cannot be odor cannot be i x t it ure m Fishy mines from algae A detected Bleachy Chlorine from 1 200 (undiluted) disinfectants 2 100 Fruity Aldehydes from EPA secondary ozonization 3 70 standard for Iron or Manganese Rusty Metallic 4 50 drinking water Iron bacteria Earthy 6 35 Ammonia Ammonial Ammonial Ammonia 8 8 25 25 Rotten Eggs Hydrogen Sulfide from 12 17 organisms/minerals 24 8.3 Organic Sulfides Rotten Cabbage 5.7 35 Methane gas Garlic 450 Skatole Fecal 70 2.8 (a compound in feces) 100 2 7

8 CHEMICAL CHARACTERISTICS ical parameters are: Commonly measured chem – pH – Alkalinity – Alkalinity Hardness – Nitrates, Nitrites, & Ammonia – – Phosphates – Dissolved Oxygen & Biochemical Oxygen Demand Portable laboratories and test kits Chemical Characteristics: pH The pH of water determines the solubility of many ions and biological availability of chemical constituents such as nutrie nts (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium) EPA secondary drinking water recommendation 5 pH 6 5 ~ 8 5 pH 6 . 5 ~ 8 . 8

9 Chemical Characteristics pH Scaling/Corrosion – Influences whether a water will be scale-forming or corrosive Langelier Saturation Index (LSI) Determines if calcium carbonate will precipitate – • LSI LSI – pH pH pH = pH s s • pH = actual pH value measured in the water • pH = pH of the water in equilibrium with solid CaCO 3 s If LSI > 0 calcium carbonate will precipitate • If LSI < 0 calcium carbonate won • t precipitate ’ pH 114 –no precipitate pH –precipitate pH s s Ryznar Index Index Ryznar Determines the degree of scale formation versus corrosion – • RI = 2 pH – pH s If RI < 5.5 heavy scale will form • • If 5.5 < RI < 6.2 scale will form corrosive very corrosive scale neutral scale heavy • If 6.8 < RI < 8.5 water is corrosive 6.2 6.8 8.5 5.5 • If RI > 8.5 water is very corrosive RI Scaling/Corrosion – Chemical Characteristics pH pH of the water in equ ilibrium with solid CaCO 3 − 2 2 + + ⎞ ⎛ ⎞ ⎛ [HCO γ [HCO ] ] ] K [C γ [C K a ] 2 − + 3 2 Ca HCO ⎟ ⎜ 3 = pH − log S ⎟ ⎜ K SP ⎠ ⎝ − 2 + ] ][CO [H 3 K where equilib = = constant 2 − H ] [ ] CO [CO 3 3 = coeff activity γ i K solubility = product SP 9

10 Determine the Langelier & Ryznar indexes for the Denver water supply Conc. (mg/L) Conc. (mol/L) Constituent TDS TDS 179 - 179 +2 -3 1.05 x 10 42 Ca -3 - 1.89 x 10 115 HCO 3 pH = 7.9, Temp = 20 ° C the value of pH DeterminethevalueofpH Determine S Determine the Langelier index Determine the Ryznar index Carbonate Equilibrium Constants as a Function of Temperature K K K K T, ° C 1 m sp 2 -11 -7 -9 8.13 x 10 53.02 x 10 2.75 x 10 -11 -9 -7 7.08 x 10 3.46 x 10 3.24 x 10 10 -7 -11 -9 3.72 x 10 3.80 x 10 15 6.03 x 10 -7 -11 -9 4.17 x 10 4.17 x 10 5.25 x 10 20 -3 -9 -7 -11 4.68 x 10 25 1.58 x 10 4.57 x 10 4.47 x 10 -7 -11 -9 6.03 x 10 5.07 x 10 40 3.09 x 10 -7 -11 -9 5.07 x 10 1.82 x 10 60 7.24 x 10 − 2 − + + ][HCO [H ][CO ] CO [H [H ] ] 3 2 3 3 K K K = = = = = = K K K 1 2 m − ] CO [H ] [CO ] [HCO 3 aq 2 2 3 pH = 7.9 Conc. (mol/L) -3 +2 Ca 1.05 x 10 = Solubility product for CaCO K 3 sp - -3 1.89 x 10 HCO 3 − 2 + Now calc: Calculated activities: ⎞ ⎛ γ γ K ] [Ca [HCO ] − + 2 3 2 Ca HCO ⎟ ⎜ 3 pH log = − S γ 0.93 = ⎟ ⎜ − = γ 0.75 + 2 K HCO SP Ca 3 ⎠ ⎝ 10

11 Chemical Characteristics: RedOx Potential REDOX Ox Red idation + Redox = uction - Oxidation : substance loses or donates electrons (e ) - Reduction : substance gains or accepts electrons (e ) Oxidation Is Loss Reduction Is Gain OILRIG Oxidation Is Loss Reduction Is Gain OILRIG Redox reactions can be thought of as reactions involving transfer of oxygen + = 2Mg O 2MgO 2 more convenient to y y enerall g yg y it is In solution chemistr consider redox reactions as electron transfers 2 + 3 − + e = + Fe Fe The redox potential is a number defining how much gaining - a system might do – essentially activity of or losing of e electrons (unit in volts) Chemical Characteristics RedOx Potential Eh Redox Potential can be measured on site Redox Potential (Eh) can be calculated using the Nernst equation: RT 0 lnK + = = lnK E Eh + E Eh sp nF 0 C & 1 atm pressure) ° = standard potential (at 25 where E R = gas constant (kcal/(mol•K) T = temperature (K) F = Faraday constant (23.1 kcal/V) n = number of electrons transferred in the reaction (or ½ reaction) o K = solubility product sp ∆ G − r r = ) (l K K og (l ) SP 2.303RT rally ranges from -400 to 800 millivolts (mV) Eh of groundwater gene Measure Eh during purging and immediately before and after sampling using a direct-reading meter because purging can aerate the water and change the chemistry 11

12 Redox reactions in groundwater are usually controlled by microbial activity so Eh depends upon and influences rates of biodegradation some geochemical activities Eh can be an indicator of (e.g. sulfate reduction) Eh of groundwater indicat es location of contaminant plumes undergoing anae robic biodegradation to lower Eh in the plume than upgradient due to lower Eh in the plume than upgradient due Biodegradation can reduce contaminants in groundwater (natural and enhanced) Eh-pH DIAGRAM ° Stability limits of water at 25 C 1.4 and 1 bar 1.2 At conditions above the top 1.0 dashed line water is is water , line dashed 0.8 oxidized to O 2 Natural 0.6 At conditions below the water 0.4 bottom dashed line, water is Water is stable 0.2 Eh (volts) reduced to H 2 0.0 No natural water can persist -0.2 limits stability outside these stability limits outside these -0.4 for any length of time -0.6 Water in nature is usually -0.8 between pH 4 and pH 9 02468101214 pH 12

13 1.4 1.2 Eh-pH conditions 1.0 of waters in various 0.8 environments environments . 6 0 06 0.4 0.2 Eh (volts) 0.0 -0.2 4 0 04 . - -0.6 -0.8 02468101214 pH Eh-pH DIAGRAM Eh-Ph diagram can be 1.4 used to show the fields 1.2 of stability for solid & 1.0 3+ Fe p ecies p dissolved ionic s 0.8 0.6 in Iron will be mobile 0.4 groundwater only under 2+ Fe(OH) (s) Fe 3 0.2 Eh (volts) the Eh-pH conditions 0.0 3+ 2+ and Fe are Fe where -0.2 stable in the diagram 04 4 . 0 - er s tl d (i (i .e. un d y l t rong -0.6 acidic conditions at any reducing Eh , or under -0.8 conditions under 02468101214 typical pH conditions ) pH 13

14 Chemical Characteristics: HARDNESS high multi-valent ion content Hard water is found in about 85% of USA Prevents lathering/sudsing - hotter water and extra rinse cycles may be may be required required Fabric appearance declines & life may be reduced Minerals may clog pipes & cause excessive wear on moving parts Solutions: Distill water to remove the calcium and magnesium – Distill water to remove the calcium and magnesium – Soften the Water - Replaces calcium and magnesium ions with sodium or potassium ions – Cation exchange Strong adsorption » » » Weak adsorption + +3 + +2 + +2 + > K > Ca = NH > Na >H > Mg Al 4 Web images from various commercial water softening web sites 14

15 HARDNESS measured in grains per gallon gpg 1 grain of hardness = the amount of calcium and magnesium equal in weight to a kernel of wheat 1 grain = 64.8 mg of calcium carbonate dissolved in 1 gallon = 1 part in 70,000 parts of water = 14.3 ppm Classification mg/l or ppm grains/gal Sft 0 17 1 0 1 S o ft 0 - 17 . 1 0 - 1 Slightly hard 1 - 3.5 17.1 - 60 Moderately hard 60 - 120 3.5 - 7.0 Hard 120 - 180 7.0 - 10.5 Very Hard 180 & over 10.5 & over http://water.usgs.gov/owq/hardness-alkalinity.html 15

16 Chemical Characteristics: NITROGEN (N) Nitrogen gas (N ) makes up 78.1% of the Earth’s atmosphere 2 required by all plants and animals for An essential nutrient formation of amino acids (the molecular units that make up protein) protein) ) or N must be "fixed" (combined) in the form of ammonia (NH 3 nitrate (NO ) to be used for growth 3 + + bacteria = 2NH + H + 8H – N 2 2 3 - + NH + O – + bacteria = NO + 3H + 2e- 2 3 2 + - - +2e- O + bacteria = NO + 2H + H – NO 2 3 2 Ammonia NH (extremely toxic) continually changes to ammonium 3 + (relatively harmless) and vice versa, relative NH 4 concentration depends on temperature & pH At higher temperatures and pH, more N is in the ammonia form NITROGEN cycle 5 main processes cycle nitrogen through the bio atmos & geosphe re nitrogen fixation nitrogen uptake (organism growth) nitrogen mineralization (decay) nitrification d en it ditifiti ifi ca ti on r Animal Protein Decay Protein Atmos- Biotic N Industrial N Ammonia Plants & pheric NH 3 fixation fixation Microbes N N 2 2 Denitrifying Lightning bacteria Nitrites - NO 2 Nitrates Nitrifying - NO 3 bacteria /ch29/1_nitrogen_cycle.swf http://www.mhhe.com/bio sci/genbio/tlw3/eBrid ge/Chp29/animations 16

17 Chemical Characteristics: NITROGEN (N) Maximum Contaminant Level (MCL): nitrite-N : 1 mg/L nitrate-N : 10 mg/L nitrite + nitrate (as N) : 10 mg/L Sources: Fertilized areas; Sewage disposal; Feed lots; N cycle Potential Problems: Infants <6mo convert nitrate to nitrite due to higher pH in their Infants <6mo convert nitrate to nitrite due to higher pH in their digestive system & could become seriously ill, and may die if untreated because the nitrite diminishes oxygen caryying capacity of their blood Excessive concentrations can lead to eutrophication Chemical Characteristics: PHOSPHATES Secondary Drinking Water Standard EPA recommendation – total phosphate should be <0.05 mg/L (as phosphorus) in a stream where it enters a lake or reservoir – total phosphate should not exceed 0.1 mg/L in streams that do not discharge directly into lakes or reservoirs Sources: Erosion; Fertilizer; Sewage; Feed lots; Detergents Potential Problems: Excessive concentrations can lead to eutrophication >4g/day may cause gastrointestinal discomfort & decrease bone density 17

18 EUTROPHICATION n or phosphorus) resulting in excessive increase in nutrients (typically nitroge plant growth and decay, re ducing oxygen availability Eutrophication can cause too much plant growth either making fo od sources for fish inaccessible or literally suffocating them due to oxygen depriv ation ©DigitalVision Sources: http://www.whoi.edu/oceanus/viewArticle.do?id=2487 (left) and /IMG/photo_04.gif (right) http://www.unep.or.jp/ietc/publications/short_s eries/lakereservoirs-3 18

19 Chemical Characteristics: DISSOLVED OXYGEN Dissolved Oxygen DO mg/L – only gas routinely measured in water samples (depends on temperature, salinity, and pressure) Analysis should be perfor med on site immediately after sampling Oxygen enters the water by photosynthesis of aquatic biota transfer across the air - water interface transfer across the air water interface DO < 5mg/L stresses aquatic life (the lower the concentration, the greater the stress) DO dependence on Temperature www.woonasquatucket.org/waterqualitydata2005.htm 19

20 Biological Characteristics: FECAL COLIFORMS Harmless bacteria ~ present in large numbers in feces and intestinal tracts of humans and animals other warm - blooded other warm - blooded animals Environmental Impact – indicator of contamination with human or animal fecal material – may indicate contamination by pathogens or disease producing bacteria or viruses Criteria Swimming ~ fewer than 200 colonies/100 mL – Fishing and boating ~ fewer than 1000 colonies/100 mL – Domestic water supply ~ fewer than 2000 colonies/100 mL – – Drinking water 0 colonies/100mL Biological Characteristics: BIOCHEMICAL OXYGEN DEMAND (BOD) Biological Oxygen Demand is a measure of oxygen used by microorganisms to decompose organic waste (add a micororganism dead leaves, plants, dead plants, leaves, samples , seal sample seed to seed to all samples seal sample all from air, store in dark to prevent grass clippings, manure, photosynthesis, subtract seeded sewage, or food waste control, measure decrease in DO) Nitrates & phosphates are plant nutrients so may contribute to high BOD levels When BOD levels are high, dissolved fish and other ⇒ oxygen oxygen decreases decreases ⇒ fish and other aquatic organisms may not survive An index of the degree of organic pollution in water BOD level of 1-2 ppm - very good BOD level of 3-5 ppm - moderately clean BOD level of 6-9 ppm - somewhat polluted 20

21 Biological Characteristics Specific to Surface Water Benthic macroinvertebrates are examined to assess the biological attributes of water quality. Their presence indicates a high quality of water, while their absence suggests water may be polluted. Hess sampler http://www.cotf.edu/ete/modules/water q3/WQassess2a.html Water Quality Information References Colorado Department of Public Health and Environment - Water Quality Control Division – htt p ://www.cd p he.state.co.us/w q /w q hom.as p pp qqp U.S. EPA - National Primary Drinking Water Regulations http://www.epa.gov/safewater/mcl.html – U.S. Geological Survey - National Water Quality Assessment Program – http://water usgs gov/nawqa/ http://water . usgs . gov/nawqa/ U.S. Department of Agriculture – Water Quality Information Center http://www.nal.usda.gov/wqic/ – 21

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