Today is your last chance to turn in the short topic questionnaire!

Transcription

1 In the last class you: Heard about the Water Use Cycle as it relates to this course. We also discussed units for quantifying water quality parameters (ex., mg/l and ppm), and equivalents/l. There were 3 handouts: (i) Problem set #1 (due a week from today), (ii) Directions for finding the course web site, and Friday s lecture notes. Extra copies (a few) are here today and may be downloaded from the course web site. Today is your last chance to turn in the short topic questionnaire! After today you will: Know more about how we quantify water quality a) physical W.Q. parameters b) chemical W.Q. parameters c) biological W.Q. parameters Quiz #1 will be at the end of class today ( 10 min.; use of a 3x5 card with notes is OK) Important correction to Friday s lecture notes regarding the Law of Mass Action: aa + bb! cc + dd; K = [C]c [D] d [A] a [B] b

2 A. ph 1. ph = -log[h + ] Chemical Water Quality Parameters K w 2. H 2 O! H + + OH - [H + ] [OH - ] = K w = (@ 25 o C) pure distilled water has ph = 7; i.e., [H + ] = [OH - ] = 10-7 moles/l 3. Significance - acid-base, range of ph for bio- Also important for corrosion & productivity generally limited to effectiveness of disinfectants B. Alkalinity Concentration in moles/liter We left off here also referred to as Acid Neutralizing Capacity (ANC) 1. Measure of the ability of a liquid sample to Total Alk. = equivalents of neutralize acid to a predefined end-point. acid required to titrate [The resistance to change in ph = buffering.] sample to ph Primarily a result of HCO - 3 and CO -2 3 units = equivalents/ L of sample (bicarbonate) (carbonate) Total Alkalinity = [HCO 3- ]+ 2[CO -2 3 ] + [OH - ] - [H + ] C. Hardness: -characteristics of water attributed to presence of dissolved multivalent cations, e.g., calcium, and magnesium. 1. Possible Ca +2, Mg +2, Sr +2, Fe +2, Mn +2, in most cases Ca +2, Mg +2 account for all hardness. 2. Hardness expressed as equivalent concentration of CaCO 3, e.g., 10 mg/l as CaCO Hardness concern: a) precipitation of soap: 2 Na (soap) + Ca +2 [this was the basis for an = Ca (soap) + 2Na + early test of water quality] b) formation of scales in boilers, hot water heaters, etc. Ca HCO - 3 (+ heat) CaCO 3 (Solid)+ CO 2 + H 2 O

3 mass Mg liter Thought process:! moles liter! equivalents Mg+2 liter +2 1 eq. Ca X 1 eq. Mg +2! moles Ca liter! 3 + 2! 3 +2! 3 60x10 g Mg 1 mole 2.5x10 mole 2 eq. Mg 5x10 eq. x = x = L 24.3 g L +2 mole Mg L +2! mg CaCO 3 (s) liter! x x x x x10 eq. Mg 1 eq Ca 1 mole Ca 1 mole CaCO (s) 100 g CaCO (s) L 1 eq Mg 2 eq. Ca 1 mole Ca mole 0.25 g CaCO3 = or 250 m g/l as CaCO L 3 Example of use of hardness units. Assume a water has 60 mg/l of Mg +2, and you wish to add this amount into a calculation of the total hardness. D. Chlorides (Cl - ) - measure of a common anion, indication of salinity (conductivity is one measure) 1. High concentrations affect taste of water and can enhance corrosion. 2. Chloride is critical in some industrial processes, e.g., papermaking. 2 SO 4! E. Sulfates - measure of another common anion 1. Excessive amounts can cause laxative effect. 2. can be biochemically reduced to H 2 S, causes odor problems and corrosion. F. Metals - primary interest is related to physiological effects (toxic response) on man and aquatic species, e.g., cadmium, copper, lead, mercury, zinc.! Drinking water standards are set based on the effects on people (not aquatic organisms). [in the absence of dissolved oxygen] (rotten egg odor)

4 G. Iron and Manganese - two metals of interest for nuisance and economic reasons rather than toxicity. Ferrous iron Ferric iron This is an oxidation reaction. Fe +2 The change in ion charge results Mn +2 + O Fe +3 red 2 Mn +4 blue from the loss of electrons. groundwaters precipitates Fe(OH) 3 (s) and MnO 2 (s) nitrate, nitrite, ammonia H. Nitrogen (NO - 3, NO - Blue baby disease. Both 2, NH 3 ) 1. Nutrient for algal growth - eutrophication. NO - 3 and NO - 2 react with 2. Oxygen demand (NH 3 NO - 3 ). hemoglobin converting it 3. NO - 3 toxicity to new-born infants to methemoglobin that (methemoglobinemia). can not bind oxygen. I. Phosphorus - mostly PO -3 4, primary concern is as an algal nutrient. Ithaca Journal Thursday, January 27, 2005 Construction is now complete and plant operators have been evaluating the efficiency of P removal as a function of iron dose. Some key points: v the southern end of Cayuga Lake is on a federal list of impaired waterways. Reason: excessive phosphorous and silt. v $4.9 million project. Goal = 50 to 75% reduction in phosphorous input. v Main P sources = Ithaca and Cayuga Heights wastewater treatment plants. Major source of P in sewage is builders added to detergents to tie up Ca and Mg. v Treatment process involves adding FeCl 3 which will produce Fe(OH) 3 (s). The Fe(OH) 3 (s) will adsorb dissolved P compounds and can be separated by sedimentation.

5 In order to renew its New York State permit for Lake Source Cooling, Connell had to agree to fund a study of the sources and fate of phosphorus in Cayuga Lake. J. Fluoride 1. Demonstrated reduction in dental cavities in children. Approx. desired level = 1 mg/l. 2. High concentration can cause mottling of teeth (brown spots), higher concentrations can cause skeletal fluorosis. K. Organic compounds 1. Oxygen demand - biochemical oxygen demand (BOD). - chemical oxygen demand (COD). 2 Dissolved Organic Carbon (DOC) Total Organic Carbon (TOC). Particulate Organic Carbon (POC) 3. Low level organic compounds - toxic, carcinogenic. These are specific compounds or compound classes such as: PCBs (polychlorinated biphenyls), PAHs (polynuclear aromatic hydrocarbons) THMs (trihalomethanes), etc. CHCl 3 Cl x Cl x

6 Biological Water Quality Parameters A. Waterborne diseases, e.g., typhoid, cholera, bacillary dysentery, hepatitis, poliomyelitis. An example close to home. 50 years after the Broad Street pump (1903) there was a typhoid epidemic in Ithaca. 83 people died, over 1,300 had the disease, and Cornell closed down for 1 semester. We could analyze a water sample for each of these types of pathogen (plus others), but the expense would be very high. B. Indicator organism 1. MPN multiple tube fermentation 2. Membrane filter technique 3. Fecal/non-fecal coliform BIOLOGICAL WATER QUALITY PARAMETERS Biological characterizations are (in general) relatively recent as a basis for defining water quality. Ex. Baltimore circa 1896: The city chemist, using solely chemical means to judge the quality of water, judged that it was satisfactory and above the normal in quality He measured parameters such as: total volatile solids, chloride, nitrate (NO 3- ) and ammonia nitrogen (NH 3 ). [These parameters, as measured then, compare with the concentrations in today s Baltimore water supply]. However, in 1896 the water source was contaminated by runoff from watersheds fertilized with manure. The water was described as having a putrescent odor and taste. The water was clearly bacterially contaminated and physically objectionable. These quality aspects were not apparent based upon chemical analyses. Use of chemical parameters as the sole determination of water quality persisted in some areas of the U.S. until the late 1920 s. The water had SO 4-2 in it, growth of bacteria consumed O 2 creating conditions under which SO 4-2 could be microbially converted to H 2 S

7 BIOLOGICAL WATER QUALITY PARAMETERS *Indicator Organisms Nature of the problem: We can t possibly analyze a water for every possible pathogen? Why? 1. Tests are different for different organisms and difficult to perform. Therefore, cost = time + money Economics 2. Tests are not always very sensitive. If numbers of pathogens are low (and they usually are) they may not be detected. Therefore, negative results do not prove you are safe. Detection An ideal answer to the problem would be to use a bacterial organism which was easily identified to indicate whether or not pathogens were present. What characteristics would be desirable in an indicator organism? 1. Easy to measure, cheap and fast Always be present when pathogens are present, and never be found when pathogens are absent (same source). Survive in a given habitat as long as pathogens (same sensitivity to environmental stress and disinfectants). Be innocuous (safe to work with).

8 The ideal indicator organism does not exist, but what we do have is the Coliform group of bacteria. It s important to note that many pathogenic organisms that infect humans are excreted in their fecal matter. These organisms are enteric, i.e., they originate in the intestinal tract. Coliform organisms also originate in the intestinal tract. Coliforms are non-pathogenic (generally) but occur in great numbers. Ex. 1/3 to 1/5 of weight of fecal matter = coliform bacteria. There is roughly a 5 x 10 6 to 5 x 10 8 /1 ratio between coliforms and pathogens such as those which cause typhoid (Salmonella typhosa). Therefore, (conclude) we can (and do) use coliforms as an indicator organism. Any water with high coliform content is suspect. Coliforms are relatively hardy and persist as long or longer than most pathogens. Therefore, coliforms have several of the characteristics of an ideal indicator. Problem: Coliforms can have other sources than fecal matter. Some example coliform organisms are: Escherichia coli (E. coli): normally found in gut of man and animals Enterobacter aerogenes: Found in gut of man & animals and in soil Enterobacter cloacae: Found in soils

9 Therefore, if we analyze for total coliforms we could get a false positive. Since some coliforms have a soil origin it is necessary to differentiate between total coliforms and fecal coliforms. This is usually done by increasing the incubation temperature of the test from 35 C (for total) to 44.5 C (for fecal). Soil organisms won t grow at the higher temperature (more on this in a minute). Also change chemical composition of test medium Summary re. Coliforms as an indicator: Advantages 1. Coliforms are found in the gut of man and animals (enteric) common origin 2. Coliforms are excreted in high numbers and coliform concentration >> pathogens detection OK Advantages (continued) 3. Absence of coliforms indicates a water safe from pathogens (coliforms are as hardy or are longer lived than pathogens) 4. Initial coliform concentration is proportional to the degree of pollution 5. Coliforms are non-pathogenic Disadvantages 1. Some coliform species are widely distributed in nature found in soils, plants and grain multiple sources No. Safe to work with (relatively). A few strains of E. coli produce toxins that attack the cells of the intestinal tract. These organisms are the main causes of Travelers diarrhea. Coliforms die off in exponential manner. 2. Timing and extent of pollution cannot be time ascertained from coliform concentration. Why? Low numbers could indicate: a) a small, recent source b) a large some time in the past. c) a large some distance

10 A test based on the ability of coliform bacteria to ferment lactose and produce gas. Two main ways: I. Multiple tube Fermentation: Inverted tube collects gas. inoculate H 2 O sample ANALYSIS FOR COLIFORM BACTERIA dilute 1 ml 1 ml 1 ml 1 ml 1 ml /10 1/100 1/1000 1/10,000 1 ml Goal = dilution to extinction; want a statistical likelihood that a 1 ml sample will not contain bacteria Typical dilutions water: up to 10-4 waste water: up to 10-6 etc etc Gas found in 24 hr. in any tube Presumptive Test lactose broth Positive Presumptive Test incubate Gas found in any tube in 48 hr. lactose 35 o C Doubtful Presumptive Test No Gas found in any tube in 48 hr. Negative Presumptive Test Gas found in 24 hr. in any tube Presumptive Test Positive Presumptive Test Gas found in hr. hr. in any tube Doubtful Presumptive Test At this stage, the test for fecal coliform can be done by inoculating a 2nd series of tubes (containing EC medium) and 44.5 o C for 48 hr. Confirmed Test Completed Test Streak on Endo agar Transfer from all tubes showing gas Production Gas found No gas found in incubate in hr. in 48 hr. in 35 o C 48hr. brilliant green any tube tube lactose bile broth Positive Negative Confirmed Transfer from all tubes Confirmed Test Test showing gas production Gram stain = Gram-negative incubate No typical short straight rods coliform Typical coliform colonies colonies hr. hr. Negative Completed Test Positive Completed Test Note: overall, it takes 6 days to complete the test Gram-negative bacteria have thin cell walls and a higher lipid content.