epc_fa2011_lecture_5w

epc_fa2011_lecture_5w - Introduction to Water Quality...

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Unformatted text preview: Introduction to Water Quality Management -- To control pollutions from human activities so that the water is not degraded to the point that it is no longer suitable for intended uses. Measurable Quantity and Intended use of the water -- Concerned about the assimilation capacity of a water body for waste loads. WAC (Waste Assimilation Capacity) Total Maximum Daily Load (TMDL) TMDL = ? WLA + ? LA + BL + MOS where WLA = Waste Load Allocation (=Point Source load) LA = Load Allocation (=Non-Point Source load) BL = Background Load (=admissible base load, natural cause) MOS = Margin of Safety (=design buffer/pollutant budget) 1 Water Quality Regulations -- Approaches Effluent-limited (=Treatment based approach) Quality-limited (=Receiving water body based approach) 2 Water Quality Regulations Effluent-limited Regulations -- Waste/Effluent discharges to water must be treated prior to the discharges take place. -- PS orientation -- National Pollutant Discharge Elimination System (NPDES) $12.6 million fine to Smithfield factory (1997/1999) -- VPDES is Virginia’s version of NPDES 3 Water Quality Regulations Quality-limited Regulations -- As long as the receiving water quality meets the water quality standard(s), you can discharge as much. -- Also called “Bubble Policy” (similar to “Carbon Trading” or “Cap and Trade” concepts) -- Concept used in WQ regulations prior to Federal Water Pollution Control Act (FWPCA) of 1972 4 Water Quality Legislation 1) The National Environmental Policy (NEP) Act of 1969 -- EIS requirement 2) The Federal Water Pollution Control (FWPC) Act Amendment of 1972 (P.L 92-500) -- Progressed into Clean Water Act (CWA) as amended in 1977, 1981 and 1987 -- NPDES -- BPT, BAT, BCT and BPWT 3) Safe Drinking Water Act (SDWA) of 1974 (P.L 93-523) Amended 1986, 1996 -- MCL, MCLG and TT concepts -- Surface Water Treatment Rule (SWTR) for filtration -- Regulation on Disinfection By-Products (DBPs) 5 Target Pollutants/Nutrients in Water Major pollutants in the receiving water body can be categorized into four groups 1) Nutrients -- mainly Nitrogen and Phosphorous 2) TSS and Sedimentation 3) Organic Contaminants 4) Inorganic Contaminants 6 Target Pollutants/Nutrients in Water Nutrients -- Nitrogen N2 - molecular N (gas) NH3 (ammonia) or NH4+ (ammonium) – predominant in wastewater NO3- (nitrate) - predominant form in "clean" water NO2- (nitrite) - generally low conc. R-NH3 - (Reactive) organic nitrogen -- Nitrogen transformations -- NH3 is toxic to many aquatic organisms (lethal at 0.1 g/m3) -- NO3 (nitrate) induces Methemoglobinemia, or blue baby syndrome 7 Target Pollutants/Nutrients in Water Nutrients -- Phosphorous -- Algal bloom -- P is often the limiting nutrient N/p ratio -- P is the main cause of eutrophication 8 Target Pollutants/Nutrients in Water Nutrients -- Sedimentation -- Major source of TSS -- Increased turbidity in water treatment process -- Aggrevating/Accelerating factor for acute Algal bloom 9 Target Pollutants/Nutrients in Water Nutrients -- Major Organic Contaminants -- Chlorinated hydrocarbons - Mainly pesticides and herbicides - Resistant to biological degradation - Many have carcinogenic effects -- Trihalomethanes (THMs) - Formed during disinfection of water (=chlorination) - Carcinogenic MCLs established by the EPA (80 μg/L) -- Volatile Organic Chemicals (VOCs) - Industrial chemicals such as benzene, carbon tetrachloride trichloroethylene, vinyl chloride, etc. - Carcinogenic 10 Target Pollutants/Nutrients in Water Nutrients -- Inorganic Contaminants -- 1 -- Inorganic contaminants include both suspended and dissolved materials -- Suspended inorganics are undesirable for aesthetic reasons, but their primary effect on water quality is within their abilities to shield microorganisms from disinfectants. -- Dissolved inorganics that have health effects include aluminum, arsenic, barium, cadmium, chromium, fluoride, lead, mercury, nitrate, selenium, and silver. -- Solubility of the inorganics at a particular pH influences the metal transport in the environment. 11 Target Pollutants/Nutrients in Water Nutrients -- Inorganic Contaminants -- 2 Lead (Pb) - Batteries, paint pigment, methyl ethyl ketones - Cause disorders on the nervous system - Lead is regulated in a Treatment Technique (TT) Mercury(Hg) - Direct industrial discharges and agricultural runoff - Bio-accumulate in fish and humans - Mercury acts directly on the mucous membrane, causing gastrointestinal irritation or inflammation accompanied by pain and vomiting. MCL is 0.002 mg/L. Cadmium (Cd) - Smelting operations, electroplating, corrosion of galvanized pipes runoff from waste batteries and paints - Cause diarrhea and, over time, liver and kidney damage. MCL is 0.005 mg/L. 12 Target Pollutants/Nutrients in Water Nutrients -- Inorganic Contaminants -- 3 Chromium (Cr) - Chrome plating, steel fabricating, paint pigments and leather tanning - Cause allergic dermatitis. MCL is 0.1 mg/L Arsenic (As) - Smelting operations, pesticides, semiconductor manufacturing, petroleum refining, wood preservatives, animal feed additives, herbicides and erosion of natural deposits - Fatal to humans at high concentrations. Skin damage; circulatory system problems; increased risk of cancer. MCL is 0.05 mg/L. An example of skin damage caused by long-term effects of arsenic in drinking water 13 Target Pollutants/Nutrients in Water Nutrients -- Inorganic Contaminants -- 4 Fluoride - Erosion of natural deposits; discharge from fertilizer and aluminum factories - High concentrations can cause permanent discoloration and loss of teeth, embrittlement of bones. Children may get mottled teeth. MCL is 4.0 mg/L Radionuclides - Radium-226 and Strontium-90 - All contribute to the increased risk of cancer - Treatment Technique (TT) - MCLs range from 20,000 pCi/L (picocuries per Liter) for Tritium, 3H (which passes through the body) to 5 pCi/L for radium (which accumulates in the bones) 14 Quick Recap 1) Total Maximum Daily Load (TMDL) TMDL = ? WLA + ? LA + BL + MOS 2) Effluent- and Quality-limited Regulatory concepts. 3) Clean Water Act (CWA) and Safe Drinking Water Act (SDWA) 4) Nutrients = Organic + Inorganic substances 15 Dissolved Oxygen (DO) Modeling in Natural Systems -- DO (Dissolved Oxygen), C is the amount of molecular oxygen dissolved in water. (and available for oxidation/decay by aerobic heterotropes) -- DO is one of the most important water quality parameters. -- DO = f(temperature) - DO decreases as water temperature increases - Colder water has a higher DO conc. than warmer water “Good" quality water = 8 to 10 mg/L “Average” = 6.5 to 8 mg/L “Below average" or “Impaired” = < 4 mg/L (VA Min. Req.) -- DO Source and Sink 1. 2. 3. Microbial metabolism (=deoxygenation) Atmospheric reaeration via diffusive flux (=reoxygenation) Algal production of oxygen and respiration (diurnal DO cycle) 16 DO Deficit, D Concept -- DO deficit, D is the difference between a saturation concentration of the oxygen and current concentration of DO in the water at a given water temperature. -- DO deficit, D tells us how much O2 can be further dissolved into the water at a given temperature. D = Cs - C DO Deficit Curve DO Deficit, D (mg/L) Do Dc (Critical DO Deficit) xo tc Downstream distance (x) Time of travel (t) 17 DO-BOD Relationship -- BOD (Biochemical Oxygen Demand) represents the amount of oxygen required by microorganisms to oxidize any organic matter discharged/presented in a water during a specified period of time, usually in five days (i.e., BOD5). -- BOD is an indirect measure of the amount of organic matter present in a water. -- We need to be able to measure/estimate this oxygen demand (via BOD) prior to any discharge so that we know exactly how much pollutants can be accepted by the water without causing harmful effects. Pollutant budgeting or TMDL 18 BOD Characteristics -- 1 L0 BOD Exerted (= yt) BOD, L (mg/L) Yt = BODt = L0 ‐ Lt BOD Remaining (= Lt) Lt 0 0 Time (days) L0 = BODu Lt = BOD remaining at time t yt = BOD exerted at time t = BODt = amount of O2 consumed in oxidation at time t dL = − kL dt Lt t dL = − k ∫ dt L L0 0 ∫ ⎛L ⎞ L ln L Lt = ln ⎜ t ⎟ = − k t ⎜L ⎟ 0 ⎝ 0⎠ L t = L 0 e − kt = BOD Remaining at time t 19 BOD Characteristics -- 2 L t = L 0 e − kt = BOD Remaining at time t y t = L 0 - L t = L 0 - L 0 e − kt = L 0 [1 - e − kt ] = BOD Consumed at time t = BOD t Example) 5-day BOD = BOD5 = y5 = L0 [1 – e( -k*5 days)] With known BOD5 and k, find L0 (=BODu) first 20 Streeter and Phelps DO “Sag” Model -- Streeter and Phelps were early developers of DO model (1925); most of existing O2 dynamic models are variations of this original model. -- Two basic components of the model; 1) Oxygen Sink - assumes that DO is lost only due to BOD exertion (=deoxygenation) kd = Deoxygenation rate constant 2) Oxygen Source - assumes that the atmosphere is the only source of O2 to be dissolved into the water via diffusive flux (=reaeration) kr = Reaeration rate constant 21 S-P DO “Sag” Model Deoxygenation Rate Constant, kd Bosko's equation Kd = Deoxygenation rate constant at 20°C (day-1) k = BOD rate constant at 20°C (day-1) v kd = k + η h v = Average stream velocity (m/sec) h = Average stream depth (m) η = Bed activity coefficient Temperature adjustment for kd kd = kd T 20o C θ T − 20 T = Water temperature in °C kd T = Deoxygenation rate constant at temperature T kd 20°C = Deoxygenation rate constant at 20°C θ= Temperature adjustment coefficient θ = 1.135 for 4-20°C θ = 1.056 for 20-30°C 22 S-P DO “Sag” Model Reaeration Rate Constant, kr O'Conner and Dobbins equation kr = Reaeration rate constant at 20°C (day-1) 3.9 v 0.5 kr = h 1 .5 v = Average stream velocity (m/sec) h = Average stream depth (m) Temperature adjustment for kr kr = kr T 20o C θ T − 20 T = Water temperature in °C kr T = Reaeration rate constant at temperature T kr 20°C = Reaeration rate constant at 20°C θ= Temperature adjustment coefficient θ = 1.024 23 DO “Sag” Curve (=Oxygen Sag Curve) -- 1 DO saturation concentration (Cs) DO Sag Curve C0 Dc (Critical DO Deficit) DO, C (mg/L) Cmi n Reoxygenation Response to DO Deficit Deoxygenation due to BOD removal 0 0 xo tc Downstream distance (x) Time of travel (t) Dc = critical deficit (= Max. D) Cmin. = Cc= critical DO conc. (= Min. DO conc.) tc = critical time (time at which Dc and Cc reached) xc = critical distance (location from discharge point where Dc and Ccoccur) 24 DO “Sag” Curve (=Oxygen Sag Curve) -- 2 Accumulation = Inflow - Outflow + Deoxygenation + Reaeration ∂ CA ΔV = QC x - QC x + Δx + rD ΔV + rR ΔV ∂t 0 = -Q dC − k d L t + k r (C s − C ) dV dC = − k d Lt + kr (C s − C ) dt dD dC =− = k d Lt − k r D dt dt dD + k r D = k d L0 e − k d t dt D= [ k d L0 − k d t e − e − kr t + D o e − kr t kr − k d 25 DO “Sag” Curve (=Oxygen Sag Curve) -- 3 -- Spatiotemporal approach (= Analysis and Design orientation) D= [ k d L0 − k d t e − e − kr t + D o e − kr t kr − k d -- Point-estimation approach (= Regulation/Compliance orientation) Dc = kd L0 e − k d tc kr ⎡k ⎛ k − kd 1 ln ⎢ r ⎜ 1 − D o r kr − k d ⎢ k d ⎜ k d L0 ⎣⎝ x c = u × tc tc = - Which DO conc.? (How bad?) ⎞⎤ ⎟⎥ ⎟ ⎠⎥ ⎦ - When Dc occurs? - Where Dc occurs? 26 Streeter and Phelphs DO “Sag” Modeling Procedure -- 1 1) As always, draw a simple mass balance diagram first, and summarize all given parameters directly in the diagram. 2) Are the effluent (or wastewater) temperature and the receiving water temperature the same? If not, calculate the mixed temperature first by using a mass balance. (Q*Temp) 3) If effluent (or wastewater) BOD is given as BOD5, calculate a corresponding BODu. 4) With the mixed temperature (from 2 above), find the saturation value of DO (=Cs) from the Table A-3 (page 979). 5) Find initial DO Deficit, D0 at mixing point. 6) Find initial BOD, L0 at mixing point. 27 Streeter and Phelphs DO “Sag” Modeling Procedure -- 2 7) If kd and kr are not given, calculate them first using Bosko (for kd) and O'Conner and Dobbins (for kr) equations. 8) If the mixed temperature (from 2 above) is not equal to 20ºC, adjust kd and kr values to the mixed temperature. 9) Find the time of travel, t from the mixing point to the target location downstream (t = x/u). 10) All set and ready to go -- put calculated parameters to Street and Phelp's DO sag curve equation to find DO deficit (=D) at target location. 11) DO at target location is the difference between Cs and D. 28 Streeter and Phelphs DO “Sag” Modeling Procedure -- 3 12) Compare calculated DO at the target location vs. assimilative capacity of river (= required water quality criterion), and determine whether DO at target location is O.k. (i.e., either greater than or equal to the assimilative capacity) or not (i.e., less than assimilative capacity) 13) To find the critical (=worst case) DO, calculate a critical time of travel, tc by using equation. 14) Using tc, calculate the critical DO deficit, Dc. 15) Using Dc, find the critical DO = Cs - Dc 16) Correspondingly, find the critical distance, xc where the critical DO would occur by using velocity and distance 29 Streeter and Phelphs DO “Sag” Modeling Typical Problem-Solving Approaches Analysis & Design Approach - Forward pollutant accounting (=to “find”) - With an initial mixed concentration from the loading/waste discharge, calculate BOD-DO concentration profile downstream-wise cumulatively reflecting all existing and planned loadings/waste discharges in their entirety to the target location and beyond Regulation and Compliance Approach - Backward pollutant budgeting (=to “set”) - With a required/desired concentration at the target location downstream, calculate BOD-DO concentration profile upstream-wise by accounting/balancing all existing loadings/waste discharges back to the first loading/discharge location in question (=permittee) 30 Quick Recap -- 1 1) DO = f(temperature) 2) Concept of DO Deficit, D 3) BOD Remaining, Lt vs. BOD Consumed, yt 4) DO Source and Sink Streeter and Phelphs DO Sag Curve 5) Spatiotemporal vs. Point-estimation approaches in DO Sag modeling 31 Quick Recap -- 2 6) Use MB for calculating initial mixed conditions! 7) To calculate DO Deficit, D at a given location/time use the full S-P DO Sag equation D= [ k d L0 − k d t e − e − kr t + D o e − kr t kr − k d 8) To calculate the “worst” (=critical) conditions, use Dc = kd L0 e − k d tc kr ⎡k ⎛ k − kd 1 ln ⎢ r ⎜ 1 − D o r ⎜ kr − kd ⎢ k d ⎝ k d L0 ⎣ x c = u × tc tc = ⎞⎤ ⎟⎥ ⎟ ⎠⎥ ⎦ 32 ...
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