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Environmental Engineering Exam III Help Session

This help session covers various topics related to environmental engineering, including abbreviations, hardness calculation, mass balance, wastewater treatment, BOD5 test, and WW pre-treatment design. Examples and calculations are provided to assist with understanding.

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Environmental Engineering Exam III Help Session

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  1. ENVE-2110 EXAM III Help Session DCC337 11-12-13 4-5 pm

  2. Abbreviations • Look through lecture notes, book and assignments • Examples: (sample test Q1) • BOD5, P, seed, t, DOb,t, DOb,i, f, DOs,t, DOs,I, NOD or NBOD, COD or CBOD, WW, WWTP, TSS, VSS, TKN, NPDES, EPA, CSTR, MW, Q, V, batch reactor, OSHA, VOC, C.V., S.S., SS, vs, type I settling, X, m, rg, S, Ks, mmax, AS, WAS, RAS, SRT, qc, OD, media, TF, RBC

  3. UNITS • Following units are considered: • mg/L • ppm • ppb • Expressed as CaCO3, P, N or S • Molarity (M) • Normality (N) • Hardness calculation

  4. EXAMPLES • See your notes, book and homework assignments 3 and 4: EXAMPLE: (sample test Q9) Q9: Calculate the normality (N) of 123 mg/L CaCO3.

  5. SOLUTION:

  6. HARDNESS • Notes and book: • Understand the meaning • A sum of all polyvalent cations • Be able to calculate hardness:

  7. EXAMPLE: (sample test II Q10) What is hardness? SOLUTION: • Characterization of water that does not lather well. • Causes scum and scale. • Hardness is the sum of all polyvalent cations in a water sample • Typically modeled with Ca2+ and Mg2+ only. EX. If a solution contains [SO42-], [K+], [Ca2+], [Cl-], and [Fe3+], what ions contribute to hardness? SOLUTION Hardness = [Ca2+] + [Fe3+]

  8. MASS BALANCE • To understand the concepts of mass balance. • To understand basic terminology used in predicting concentrations of pollutants in WW systems . • To model pollution in a reactor.

  9. LAW OF CONSERVATION OF MATTER • Disregarding nuclear reactions, matter can neither be created nor destroyed. • The mathematical representation of this law is called a materials balance or mass balance.

  10. SYSTEMS • Picking a system: what do you want to know?; what data is available? • System boundaries are defined so as to make calculations simple. The system within the boundaries is called the control volume.

  11. Control Volume: what is within the dotted lines Cup 2 Cup 1

  12. MATERIALS BALANCE • For environmental processes, the basic equation is: • Accumulation = Input – Output - Decay and each of these terms refers to a mass quantity (make sure units match) within the system (memorize this). • The system could be the planet or it could be a cell or anything in between.

  13. STEPS • Draw a picture • Include all flows in • Include all flows out • Assume: well mixed and S.S • Flow in = flow out

  14. What if the chemical is degrading? • chemical transformation of compound to another • can occur by a living organism (biodegradation) • can occur “abiotically” (chemical, photo-degradation, etc.) • Often “first order” – cell death is first order or -kdX

  15. Reaction Terms • Sedimentation • Volatilization • Bio-uptake • Degradation

  16. WASTEWATER TREATMENT • SOURCE WATER • Different sources from domestic to industrial • PRETREATMENT • SCREENS • GRIT CHAMBER • EQUALIZATION TANK • PRIMARY TREATMENT • SEDIMENTATION • SECONDATY TREATMENT • BIOLOGICAL TREATMENT • AS, TF, PONDS • SECONDARY SETTLING • TERTIARY TREATMENT OR ADVANCED TREATMENT • DISINFECTION • FILTRATION • NITROGEN CONTROL • PHOSPHOROUS REMOVAL • DISTRIBUTION

  17. WASTEWATER TREATMENT • BE ABLE TO DESIGN: (old exam Qs 10,12-14) • Grit removal • Equalization tank(s) • Primary settling tanks • TF, AS or ponds • Secondary settling tanks • Understand the concepts behind tertiary treatment or advanced treatment • Effluent

  18. BOD • Know why BOD is important • How to calculate BOD5 • Where in the WW treatment processes BOD is removed • BOD5 TEST • 5-day test • BOD bottle volume typically 300 mL • Seed = microbes + nutrients • Be able to calculate BOD with and without a seed • Be able to calculate • Dilution factor = P =volume of WW sample/300 mL (volume of WW + dilution water with or without seed)

  19. TYPICAL BOD VALUES

  20. BOD5 EXAMPLE • Determine the BOD5 value for a 12 mL WW sample when it is placed in a standard BOD bottle filled with dilution water. The bottle had an initial dissolved oxygen concentration of 1.8 mg/L. A blank run parallel showed no change in DO over the incubation period.

  21. What is the volume of a standard BOD bottle? 300 mL • What is a blank? BOD bottle that contains only dilution water or dilution water with seed. Allows you to see if there is any contribution to oxygen demand from dilution water only. • What is dilution water? Dilution water is what is added to BOD bottle to top off to 300 mL. It contains trace elements for bacterial metabolism. May also contain inoculum of microorganisms (not always required) called “seed”. • How long is a typical BOD test? 5 days

  22. Calculate the BOD5 of WW:

  23. BOD5 with “seed” • Understand the equation: (check your notes and book)

  24. DESIGN of WW

  25. PRETREATMENT • BAR RACKS • No design criteria • Know what they are • Purpose • Trash racks, manually cleaned racks and mechanically cleaned racks • Grit Chamber • Know why they are used • Depth: 2-5 m • L:W ratio: 3:1 to 5:1 • Q = 3 min

  26. Equalization • Not a treatment process. • Use to improve the effectiveness of both secondary and tertiary treatment processes. • WW does not flow in at a constant flow rate. • Equalizing the flow using a separate tank. • No specific design criteria other than functional, in-line or off-line.

  27. PRIMARY TREATMENT • Primary settling tanks (clarifier) • Number tanks > or = 2 • Circular or rectangular • Detention time = 1.5-2.5 hrs • Depth usually = 15 ft • L:W ratio = 3:1 to 5:1 • Sludge removal • 62% removal of TSS • 35% removal of BOD

  28. SECONDARY TREATMENT • Biological treatment • AS • TF • Ponds • Secondary clarifier

  29. Activated Sludge (AS) • Has flow in • Has RAS in • Has flow out • Has RAS out

  30. EXAMPLE: Design a secondary settling tank dimensions for a rectangular settling tank, area and volume assuming the return activated sludge flow of 1.3 MGD and flow in 3.5 MGD. • Calculate the total flow using mass balance. • Draw a schematic of the settling tank with RAS • State your assumptions! • Show your work!

  31. SOLUTION Flow balance, S.S. assumption: Flow IN = Flow OUT Question asked total flow?

  32. DESIGN • If v0=1,200-1,700 gal/ft2 d • Assume 1,300 gal/ft2 d • Assume Q = 2 hrs HEIGHT:

  33. VOLUME: Assume 2 tanks V(per tank)=26,738 ft3

  34. L:W RATIO: (3:1 to 5:1) • Assume 4:1 • L=4W

  35. TANK DIMENSIONS

  36. TRICKLING FILTER • TF: • Bed of coarse material • Rocks, plastic, stones • WW applied on the top • Circular • 80% removal (varying depending on the media) • Depth<6ft • Area=Q/Qloadingrate or Q/0.09 gal/min ft2 • D2=4A/P

  37. TF EXAMPLE • Determine the area and loading rate of a low-rate TF that has a diameter of 35.0 m and depth of 1.5 m. The flow rate is 1,900 m3/d and the influent BOD5 is 150 mg/L.

  38. LOADING RATE:

  39. PONDS • Aerobic ponds • Anaerobic ponds • Facultative ponds

  40. SECONDARY CLARIFIER • SAME AS PRIMARY CLARIFIER

  41. TERTIARY TREATMENT • Disinfection • Filtration • Nitrogen control • Phosphorous removal

  42. Disinfection • Chlorine is added to WW • Cl2 + H2O = HOCl + H+ + Cl- • results in a pH drop (decrease) • Detention time = 15 min • Depth = 3 m (typically) • To deactivate reproduction of microbes (not necessarily kill them)

  43. FILTRATION • Can be different types • Surface filters • Deep bed filters • Membrane filters • Carbon filters • More or equal to 2

  44. BATCH REACTOR • Assumptions: • Well-mixed • Uniform composition • Constant volume • Noting in or out • 1-st order • 2-nd order • See sample exam Q9 • Be able to recognize, draw and label

  45. CSTR • Assumptions: • Completely mixed • Uniform concentration throughout the reactor • Water enters and leaves the reactor at a given volumetric flow rate of Q (volume/time) • Mass or quantity = CiV • Average r = r • Able to define terms with units • Be able to recognize, draw and label

  46. During S.S. conditions: • See examples from sample exam – Q 2

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