Basic Concepts in Water Chemistry. Dissolved Oxygen (DO) ESM 202. Understanding. Water Quality Parameters. Management. O 2 (gas) O 2 (aq)

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1 Management ESM 202 Understanding Water Quality Parameters Value of Monitoring Water Quality Parameters Human Health Sustainable management Restoration Remediation 1 2 Water Quality Parameters Dissolved Oxygen Temperature Biochemical Oxygen Demand Nutrients: N & P Minerals: Anions & Cations Trace Elements Toxic Organic Compounds Coliform Bacteria, other Microbes, Viruses Solids (TDS, SS) Alkalinity, Hardness Turbidity Color Taste and Odor 3 Dissolved Oxygen (DO) O 2 (gas) O 2 (aq) 4 Increasing Temp Increasing Salinity High DO Low DO Basic Concepts in Water Chemistry 6

2 Basic Concepts Equilibrium K = A + B = C + D [C] [D] [A] [B] Thermodynamic equilibrium Reversible vs. irreversible = Products Reactants Basic Concepts Concentration in aqueous or solid systems [HCO 3 ] = mol / L = M Convert from mol/l to g/l using the Molecular Weight (MW), g/mol Concentration in gas phase: P CO2 = atm 7 8 Dissolution Dissolution O 2 dissolution in water O 2 (aq) O 2 (g) CO 2 dissolution in water: CO 2 (aq) = CO 2 (g) P K H,O2 = O2 = [O2 (aq)] atm = 663 atm. L/mol 3.15 x 10 4 mol/l P CO2 K H = [CO2 (aq)] = 26.9 atm L/ mol mg/l g/mol = x 10 3 g/l = mol/l g/mol 9 10 Oxygen Demand Oxygen Demand How much Oxygen is needed to degrade a load of pollutant? Chemical Oxygen Demand (COD) Biochemical Oxygen Demand (BOD) Nitrogenous Biochemical Oxygen Demand (NBOD) Total Oxygen Demand (TOD) 11 C a H b O c N d S e + x O 2 a CO 2 + 1/2 b H 2 O + d NO 3 + e SO 4 12

3 Chemical Oxygen Demand Biochemical Oxygen Demand Quick test to determine Oxygen Demand Strong oxidizing agent in acidic medium with catalyst (silver sulfate) No info on biologically oxidizable matter Issues Some organic matter is quite inert Interference from minerals in water C a H b O c N d S e + Cr 2 O 7 Cr 3+ + a CO 2 + 1/2 b H 2 O + d NO 3 + e SO 4 Measures rapidly biologically oxidizable organic matter Usually expressed as 5day BOD = BOD 5 Depending on BOD concentration and water characteristics: Dilution Essential nutrients (N, P, K, Fe, etc.) Bacterial seed EZ BOD Nitrogenous BOD Simply Place a sample of the microbial biomass into the test bottle with the wastewater Insert integrated DO probe Follow instructions that appear on the liquid crystal display (LCD) Test provides a quantitative prediction of BOD5 (based on correlation to BOD5) For specific plant conditions Data collected in 15 to 60 minutes Nitrogenous Oxygen Demand Twostep oxidation of ammonia: Effect of BOD in a River Pollutant discharge NH /2 O 2 Nitrosomonas NO + H 2 O + 2 H + NO + 1/2 O 2 Nitrosobacter NO 3 NH O 2 NO 3 + H 2 O + 2 H + Can inhibit nitrification to measure CBOD and NBOD separately 17 18

4 Microorganisms Microorganisms E. coli used as an indicator of water quality: normal inhabitant of intestines of many animals Indicator of presence of fecal matter Total coliforms are typically reported Cost of testing for all possible microorganism is $$$$ Coliform test Results reported as Most Probable Number (MPN) per 100 ml Incubation at moderate temperature (35 o C) for 48 hr Test does not account for normally occurring microbes which also respond to lactose New developments to deal with these issues 22 Sediments 23

5 Turbidity Turbidity Water clarity is an indicator of drinking water quality In the field, use a Secchi disk In lab, measure transmission of light through a standard cuvette Colloidal particles scatter light Colloidal particles may harbor pathogens, toxics (metals, pesticides), radionuclides Hardness Hardness Correlated with TDS Represents total concentration of Ca and Mg, and is reported in equivalent CaCO 3 Other ions (Fe 2+ ) may also contribute Hard water leaves solid deposits (boilers, hot water pipes, heaters, fixtures) and requires more soap Hard water is less corrosive Soft Moderate Hard Very Hard < 50 mg/l = mg/l = mg/l > 300 mg/l Treatment usually left to consumer (domestic, industrial, etc.) depending on needs What is? Concentration of H + Measured on a log scale Actually, an inverse log = log 10 ([H + ]) = 7 means [H + ] = 10 7 mol H + /L What does it mean? 29 30

6 Natural conditions Acidic Temperate forest soils ( 46) Raindrop through clean atmosphere ( 55.5) Sulfur vents ( 4) Alkaline Arid soils ( 811) Limestone dominated soils ( 79) Ocean ( 88.5) Human (anthropogenic) changes to Acid rain (deposition) Acid mine drainage Discharge of acidic or alkaline wastewater Open mining of limestone Cattle feedstock yards (NH 3 ) Fossil fuel combustion Dissociation of Water Why does it matter? controls the chemical form (species) of many compounds Low leads to faster dissolution (weathering) of surrounding minerals Releases potentially toxic elements Changes in biodiversity High Can increase concentration of ammonia, toxic to fish Increased precipitation of metals H 2 O + H 2 O = H 3 O + + OH K w = [H 3O + ] [OH ] [H 2 O ] [H 2 O ] = [H + ] [OH ] = log 10 (K w ) = pk w = pc Diagram = 6 pc Diagram = 8 pc pc H+ = 6 pc [H + ]= 10 6 M pc H+ = 8 [H + ]= 10 8 M [H + ] [H + ] [OH ] [OH ] 35 36

7 Macro Nutrients Macro Nutrients Common Forms of Nitrogen: Ammonia/Ammonium NH 3 / NH + 4 Nitric Acid/Nitrate HNO 3 / NO 3 Nitrous Acid/Nitrite HNO 2 /NO 2 Organic Nitrogen Phosphate PO 3 4, HPO 4 37 Ratio of Uptake of Nutrients (typical): C : N : P 100 :16 :1 38 Dissociation Acids: HNO 3 + H 2 O = H 3 O + + NO 3 pc Diagram for NH 3 K HNO3 = [H + ] [NO 3 ] [HNO 3 ] = 101 mol/l pk HNO3 = 1.0 pc [NH 4+ ] [NH 3 ] Bases: NH 3 + H 2 O = NH 4+ + OH K NH3 = [OH ] [NH 4+ ] = mol/l pk [NH NH3 = ] 39 [OH ] [H + ] 40