1 Preparing for the PE Exam Biological Systems (10% of exam) Cady R. Engler, P.E. Bio & Ag Engineering Dept. Texas A&M University

2 Topics Biological Processes ~5 questions Principles of organic and biochemistry Aerobic and anaerobic processes Ergonomics Environmental and Ecological Systems ~3 questions Environmental assessment techniques Awareness of ecological processes

3 Topics Principles of organic and biochemistry Thermal properties – food and biomaterials Mass and energy balances Heat and mass transfer Kinetics  Enzyme reactions  Growth  Death

4 Topics Aerobic and anaerobic processes Bioreactor systems Oxygen transfer Anaerobic treatment

5 Topics Ergonomics Human/machine interaction  physical capabilities  visual requirements

6 Topics Environmental assessment techniques Measurement of organic matter Measurement of other nutrients Effect of scale

7 Topics Ecological processes Mass and energy balances Limiting nutrients

8 Thermal properties Water psychrometrics Biomaterials

9 Mass and energy balances Heat and mass transfer These may appear in several different sections of the exam.

10 Enzyme Kinetics Michaelis-Menten model s = substrate concentration v = reaction velocity v max = maximum reaction rate K M = Michaelis-Menten (saturation) constant

Michaelis-Menten enzyme kinetics KMKM First order Zero order

12 Michaelis-Menten Kinetics Example 1 An enzyme that follows simple Michaelis-Menten kinetics has the following parameter values: v max = 116 mg/L·s K M = 5.2 mg/L Determine the initial reaction rate with a substrate concentration of 100 mg/L.

13 Michaelis-Menten Kinetics Example 1 (cont.)

14 M-M Kinetics – Example 2 The figure below shows reaction rates as a function of substrate concentration for an enzyme catalyzed reaction. Estimate v max and K M for the enzyme.

15 M-M Kinetics – Example 2 From inspection of the plot: v max ≈ 3.25 mol/L·min K M = v = 0.5 v max = mol/L

16 Enzyme Kinetics May use reciprocal (Lineweaver-Burk) plot for evaluation of parameters

17 Evaluating kinetic parameters Lineweaver-Burk plot

18 M-M Kinetics – Batch Reaction Substrate concentration as a function of time can be found by integrating the kinetic equation with s = s 0 at t = 0 :

19 Enzyme Kinetics Inhibition of enzyme reactions Competitive Non-competitive Substrate Other Immobilized enzymes – diffusion effects Surface Internal (porous particles)

20 Growth Kinetics Exponential growth of microorganisms Monod model for dependence of growth rate on substrate concentration

21 Monod growth kinetics

22 Growth Kinetics Maintenance requirements of organisms must be considered in many systems (equivalent to adding a death term): Growth rates may be subject to inhibition – similar to enzyme kinetics

23 Yield Coefficients Yield of cell mass per mass of substrate consumed: Other yield coefficients can be defined in a similar manner.

24 Bioreactor Systems Batch reactor: for Monod kinetics (note that both s and x vary with time)

25 Batch Reactor Generally, μ = μ max for batch growth since s >> K S for most of the growth period

26 Bioreactor Systems Continuous stirred tank reactors (CSTR) (assuming no maintenance requirement) µ = specific growth rate D = dilution rate θ = mean residence time washout occurs when D ≈ µ max

27 CSTR – Monod Kinetics

28 CSTR – Monod Kinetics When grown under a specific set of conditions, an organism has the following growth characteristics: μ max = 0.3 h -1 K S = 0.45 g/L The feed to a CSTR has a substrate concentration of 100 g/L. Determine the maximum dilution rate if the substrate concentration in the effluent is not to exceed 1 g/L.

29 CSTR – Monod Kinetics

30 Bioreactor Systems CSTR with recycle (e.g., activated sludge) D > µ max when washout occurs

31 Bioreactor Systems Plug flow reactors (PFR) Behave as batch reactors with reaction time equal to residence time c = concentration of component C u = linear velocity of fluid

32 Microbial Death First order death (decay) kinetics N = number of viable organisms Assumes constant temperature Sterilization time depends on size of system since the number of viable organisms is proportional to size

33 Food Sterilization D = decimal reduction time = time to kill 90% of viable organisms

34 Food Sterilization D is a function of T (temperature) Over range of T used for sterilization where z is the change in T required to change D by a factor of 10

35 Food Sterilization – example 1 For food spoilage organisms, a typical value for z is 10°C. If D = 0.22 min at 121°C, determine D at 137°C.

36 Food Sterilization F is the thermal death time or time required to obtain a stated reduction in the population of organisms or spores usually expressed as a multiple of D often written with subscript denoting T and superscript denoting z :

37 Food Sterilization – example 2 An acceptable economic spoilage rate for a particular food product was obtained with a process having F 0 = 7 min. Determine the processing time required at 115°C. Note that F 0 is defined using typical values for food spoilage organisms and sterilizing conditions:

38 Food Sterilization – example 2

39 Food Sterilization – example 3 A food product contains an average of 10 spores per can prior to sterilization. If a spoilage rate of 1 can in 100,000 is the target, determine F 280 for the process. D 250 = 1.2 min and z = 18°F.

40 Food Sterilization – example 3

41 Oxygen Transfer Oxygen transfer must balance oxygen uptake at steady state: k L a = volumetric mass transfer coefficient c L * = O 2 concentration at saturation c L = O 2 concentration q O2 = oxygen demand of cell mass x = cell mass concentration

42 Oxygen Transfer Oxygen transfer rate affected by temperature solute concentrations type of aerator mixing intensity

43 Anaerobic Treatment Anaerobic digestion converts organic matter to methane and carbon dioxide Composition typically 60% CH 4, 40% CO 2 Trace amounts of H 2 S also formed Biogas yield 3 – 8 SCF/lb VS (0.2 – 0.5 m 3 /kg VS)

44 Anaerobic Treatment Anaerobic processes generally slower than aerobic with retention times >50 days for anaerobic lagoon days for mesophilic digester <10 days for thermophilic digester

45 Anaerobic Treatment Anaerobic lagoon design (similar refs) ANSI/ASAE EP JUL99, Design of Anaerobic Lagoons for Animal Waste Management, ASAE Standards Agricultural Waste Management Field Handbook, USDA-NRCS, Chapter 10, Agricultural Waste Management System Component Design: ftp://ftp.wcc.nrcs.usda.gov/downloads/wastemgmt/ AWMFH/awmfh-chap10.pdf

47 Organic matter measurement BOD (5 day) oxygen consumed by microbial growth BOD 5 = [DO t=0 -DO t=5 ] sample - [DO t=0 -DO t=5 ] blank COD oxygen consumed by chemical oxidation VS (volatile solids) loss of mass after thermal oxidation

48 BOD Example Given the following data, determine the BOD for a waste water sample that was diluted by a factor of 10: Dissolved oxygen (mg/L) Time (d)Diluted SampleSeeded sample

49 BOD Example

50 Other nutrients Nitrogen Total Kjeldahl nitrogen Ammonia nitrogen Nitrate and nitrite Phosphorus Orthophosphate Total phosphorus Mass balances, limiting nutrients, eutrophication

References Shuler, Michael L., and Fikret Kargi, Bioprocess Engineering Basic Concepts, 1 st or 2 nd Edition, Upper Saddle River, NJ: Prentice Hall, 1992 or Heldman, D.R., and D.B. Lund, Handbook of Food Engineering,New York: Marcel Dekker, Toledo, R.T., Fundamentals of Food Process Engineering, 2 nd Edition, New York: Van Nostrand Reinhold, Metcalf & Eddy’s Wastewater Engineering: Treatment, Disposal, and Reuse, 3 rd or 4 th Edition, New York: McGraw Hill, 1991 or ANSI/ASAE EP JUL99, Design of Anaerobic Lagoons for Animal Waste Management, ASAE Standards Midwest Plan Service, Livestock Waste Facilities Handbook (MWPS – 18).