ENVE EXAM II Help Session DCC pm

Transcription

1 ENVE-2110 EXAM II Help Session DCC pm

2 Abbreviations Look through lecture notes, book and assignments Examples: (sample test Q1) V, Q, MW, L, CSTR, PFR, batch reactor, C, k, EPA, OSHA, G, SS, TSS, VOC, VSS, S.S., C. V., SDWA, MCL, Alum

3 UNITS Following units are considered: mg/l Ppm ppb Expressed as CaCO 3, P, N or S Molarity (M) Hardness calculation

4 EXAMPLES See your notes, book and homework assignments 3 and 4: EXAMPLE: (sample test Qs 5,6, and 7) Q7: Convert a 1% suspended solids concentration to mg/l.

5 SOLUTION: w w + w 0 x100 =1% w w + w 0 = 0.01 w = (0.01)x(w + w 0 ) = 0.01x1= 0.01x1 g ml x1000 ml L =10 g L =10, 000 mg L

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

7 EXAMPLE: (sample test 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 Ca 2+ and Mg 2+ only. EX. If a solution contains [SO 4 2- ], [K + ], [Ca 2+ ], [Cl - ], and [Fe 3+ ], what ions contribute to hardness? SOLUTION Hardness = [Ca 2+ ] + [Fe 3+ ]

8 MASS BALANCE To understand the concepts of mass balance To understand basic terminology used in predicting concentrations of pollutants in lakes To model pollution in a lake

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 EXAMPLE:COFFEE Two cups of coffee one (375 ml) contains 115 mg of caffeine other (225 ml) is decaf, contains, 1.15 mg of caffeine Combine the two cups of coffee into one very large cup What is the final concentration of caffeine in the coffee in the very large cup?

11 System is the cup ASSUMPTIONS? Fluid in cup is well-mixed Completely mixed system

12 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.

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

14 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.

15 EXAMPLE: POLLUTION IN A LAKE

16 POLLUTION OF A LAKE A lake with a surface area of 1.13 mi 2, is fed by a river with a flow rate of 1,250 cfs. The flow rate in the river exiting the lake is 1,325 cfs. A wastewater treatment plant discharges into the lake at the rate of 75 cfs. The concentration of a conservative pollutant, A, in the plant effluent is 15.0 mg/l. The concentration of A in the influent river is 1.1 mg/l. What is the concentration of A in the lake?

17 Draw a picture What do we know?

18 EXAMPLE: POLLUTION OF A LAKE Draw a diagram What do we know? Q in = 1,250 cfs C in = 1.1 mg/l Q out = 1,325 cfs Q ww = 75 cfs C ww = 15 mg/l Area = 1.13 mi 2 Q in C in Q out C out - Flowrate In (Q ww ) - Concentration in Waste Stream (C ww )

19 EXAMPLE: POLLUTION OF A LAKE What do we need to know?! By stating that pollutant is conservative? - we mean that it is non-reactive.? Is the concentration of A in the river exiting the lake equal to the concentration in the lake? Yes, assume complete mixing C out = C lake? Is concentration in lake constant with time? Yes, at steady-state

20 EXAMPLE: POLLUTION OF A LAKE Assumption: Complete mixing, C out = C lake Q in C in C lake Q out C out Q ww C ww

21 EXAMPLE: POLLUTION OF A LAKE This means that the change in accumulation with respect to time is zero Steady State conditions

22 EXAMPLE: POLLUTION OF A LAKE Need to develop mass balance equation: Rate of Accumulation = Rate In Rate Out Think about: What are the sources and sinks of the pollutant? Rate of Accumulation = Mass in from river + Mass in from wastewater - Mass out from river

23 EXAMPLE: POLLUTION OF A LAKE Assumptions:! No degradation of contaminant! No evaporation of water! No seepage of water (Vol of water in = Vol of water out )! No losses of contaminant (settling, volatilization)! Complete mixing (C lake = C out )! Steady state conditions (d(mass)/dt = 0)

24 EXAMPLE: POLLUTION OF A LAKE Accum. = Mass in from river + Mass in from wastewater - Mass out from river Accum. = d[mass]/dt = Q in C in + Q ww C ww - Q out C out 0 = Q in C in + Q ww C ww - Q out C out

25 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

26 EXAMPLE: POLLUTION OF A LAKE Same problem as #2, lets assume that this time contaminant is reactive Q in C in Need to consider degradation (also called decay), assume first order kinetics with a rate constant of 0.005hr -1 Q ww C ww C lake Q out C out

27 EXAMPLE: POLLUTION OF A LAKE Accum. = Mass in from river + Mass in from wastewater - Mass out from river - Mass lost to decay Accum. = d[mass]/dt = Q in C in + Q ww C ww - Q out C out - Mass lost to decay

28 EXAMPLE: POLLUTION OF A LAKE Accum. = d[mass]/dt = Q in C in + Q ww C ww - Q out C out - Mass lost to decay First order decay: dc/dt = -kc Assuming the volume is constant, then Mass lost to decay = V dc/dt = -kc out V 0 = Q in C in + Q ww C ww - Q out C out - kc out V

29 Control Volume: what is within the dotted lines rain evaporation river Marauders Lake river seepage condominiums

30 REACTION TERMS Sedimentation Volatilization Bio-uptake Degradation

31 WATER TREATMENT Be able to define and draw all the stages in a water treatment plant: (see old exam Q2) SOURCE WATER SCREENS RAPID MIX FLOCCULATION SEDIMENTATION FILTRATION DISINFECTION STORAGE DISTRIBUTION

32 WATER TREATMENT BE ABLE TO DESIGN: (old exam Qs 3-6) Rapid mix tanks Flocculation/sedimentation tanks (old exam Q12) Know the disinfection kinetics equation and understand it Understand the reasoning behind water treatment

33 JAR TEST Know what Jar Test is used for Jar test: (old exam Question 13) 6 beakers Dosing of coagulant Alum Iron Polymers Plotting data for optimum dose Stable vs. destabilized particles Coagulant Measurement

34 Be able to understand TYPE I settling descrete TYPE II settling flocculent TYPE III settling Zone/hindered SETTLING

35 DESIGN EXAMPLE 4.75 Two parallel flocculaton basins are to be used to treat a water flow of m 3 /s. If the design detention time is 20 minutes, what is the volume of each tank? See solution provided.

36 DESIGN EXAMPLE 4.76 Two sedimentation tank operate in parallel. The combined flow to the tanks is m 3 /s. The volume of each tank is 720 m 3. What is the detention time in each tank? See solution provided.

37 DESIGN EXAMPLE 4.74 What is the volume required for a rapid mix basin that is to treat 0.05 m 3 /s of water if the detention time is 10 s? See solution provided.

38 DESIGN EXAMPLE 4.82 The town of Eau Gaullie has requested proposals for a new coagulation water treatment plant. The design flow for the plant is m 3 /s. The average annual water temperature is 19 C. The following design assumptions for a rapid-mix tank has been made: 1. Number tanks = 1 2. Tank configuration: circular with liquid depth = 2Xdiameter 3. Detention time = 10s 4. Velocity gradient = 800 s Impeller type: turbine, 6 flat blades, N p = Available impeller diameters: 0.45, 0.60, and 1.2 m 7. Assume B = H/3

39 DESIGN RAPID-MIX SYSTEM 1. Water power input in kw 2. Tank dimensions in m 3. Diameter of the impeller in m 4. Rotational speed of the impeller in rpm

40 EXAMPLE: (Question 11 sample exam II) Explain TYPE II settling. SOLUTION: Particles flocculate during settling Particles grow in size Settling velocity changes Flocs settle

41 EXAMPLE: (sample exam II question11) Where can you find type II settling? SOLUTION: Alum or iron coagulation in settling tank

42 BATCH REACTOR Assumptions: Well-mixed Uniform composition Constant volume Noting in or out 1-st order 2-nd order C = C 0 exp "kt [ ] C = C 0 1+ C 0 kt See sample exam Q9 Be able to recognize, draw and label

43 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 = C i V Average r = r Able to define terms with units dm j dt = Q i C i " Q o C o ± r V Be able to recognize, draw and label

44 During S.S. conditions: C i " C o # ± r = 0 See examples from sample exam Q 2

45 PFR Assumptions: Uniform longitudinal velocity profile Mixing is rapid enough that X-sec. can be considered wellmixed No interaction between adjacent fluid elements in the direction of flow Equation: "C j "t = #v "C j "x ± r C = C 0 " kt Be able to recognize, draw and label