Answer Questions for Each Section As Indicated Under the Section Headings

This paper contains 4 sections carrying a total of 40 marks (5 + 6 + 20 + 9).

Answer questions for each section as indicated under the section headings.

Clearly flag your answers by the question numbers (e.g. 3.1b).

Section 1 Algal biotechnology: (5 marks)

Answer 2 out of the following 3 questions (equal marks) on Algal Biotechnology below:

1.1) Algal productivity

For micro-algal cultivation, sketch the productivity (g of biomass/m2/day) as a function of a) irradiance, b) temperature, c) dissolved oxygen.

1.2) Give short answers to all the four questions (1.2a to 1.2d) below

1.2a) In heterotrophic growth, what is the energy source(s) for algal growth?

1.2b) What effect does photosynthetic CO2 uptake have on the pH of the culture?

1.2c) What are the main factors which would give a type II response in algal cultures?

1.2d) If you add nitrate, ammonia and urea to a culture which of these would the algae take up first?

1.3 Algal Growth

The growth curve below is for a culture of Dunaliella salina grown in a 25 L airated carboy-type photobioreactor in the laboratory. The growth conditions were:

Temperature : 25 ± 2) oC

Light: 165 μmol photons.m-2.sec-1 (supplied by cool-white fluorescent lights) on a 12h light: 12h dark cycle.

Initial pH: pH 8.1

Composition of the medium

(all concentrations are in g.L-1)

NaCl 150.0

MgCl2.2H2O 1.5

MgSO4.7H2O 0.5

CaCl2.2H2O 0.2

KCl 0.2

NH4Cl 0.1

H3BO3 0.061

MoO3 0.015

CuSO4.5H2O 0.006

MnCl2.4H2O 0.004

ZnCl2 0.004

Write brief answers to each of the following questions (all are of equal value):

(a) How would you change the culture conditions to increase the growth rate;

(b) How would you change the culture conditions to achieve a higher final cell yield;

Section 2: (6 marks)

Answer all of the 2 questions below:

2.1 Laboratory chemostat operation (2 marks)

In the laboratory class chemostats were operated for the production of the enzyme urease. Explain in detail the chemostat setup, the method of urease measurement and 2 outcomes (results) from your chemostat experiment.

2.2 Bioprocess analysis (4 marks)

An aerobic chemostat was operated at room temperature to degrade hydroxy-butyric acid acid (CH3-CHOH-CH2-COOH) to CO2. The chart below shows the dissolved oxygen concentration plotted against time. At 90 seconds the air supply was stopped.

(a) What is the current hydroxy-butyric acid degradation rate?

(b) Is the chemostat limited by the oxygen supply or by the bacterial activity? Explain your answer.

(c) What is the maximum possible hydroxy-butyric acid degradation rate of this particular chemostat based on its current oxygen supply capacity?

(d) What is the kLa value of the chemostat?

(e) Estimate the critical dissolved oxygen concentration of the bacteria OR their oxygen half saturation concentration (kS)

Section 3: (20 marks)

Answer 5 out of the following 6 questions. Each question carries 4 marks

3.1 Microbial Growth and Cultivation

(a) List the four growth constants of microbes (with units) that allow the prediction of their growth.

(b) Demonstrate with a plot of specific growth rate (µ) against substrate concentration (S) , an example of high and low values of the growth constants. (use a dotted line for a low value and a solid line for a high value of each growth constant).

(c) point out the actual values for each of the growth constants on the plot. (For this, you need to place an arbitrary scale on the Y axis (µ) and the X axis (S).

3.2 Biological nitrogen removal

Nitrogen removal from wastewater is important to avoid pollution of freshwater and marine environments.

(a) Explain the consequences of pollution caused by emission of dissolved nitrogen compounds into the environment such as an ocean lagoon.

Nitrification and Denitrification are processes that play a role in nitrogen removal from wastewater.

(b) Show the reaction equations and point out the electron donor and electron acceptor.

(d) Explain the fundamental problem of attempting nitrogen removal by a single non-controlled process.

(e) Explain in detail at least two advanced treatment processes that can improve the nitrogen removal and keep the electricity costs (for aeration) lower.

3.3 Control of bioprocesses

Microbial processes need to be controlled very strictly in many cases. High cell density cultures of E. coli, SND and anaerobic digestion were examples requiring control Explain for two of the processes:

(a) what needs to be controlled

(b) what needs to be measured

3.4 Process Control in High Cell Density Cultures

High cell density cultures require high level of oxygen and feed supply. Towards the end of the culture feed supply is given “on demand” as both, over supply and under supply will mean the process does not run optimally.

(a) Explain how such an “on demand” feed supply can be done by using feedback control loops based on oxygen measurements. Give instructions detailed enough to allow a technician to operate the process under optimum conditions

(b) Give an example where this feeding technology is used and what the problems are when too much feed is added.

3.5 Energetics calculations

The interspecies hydrogen transfer as it occurs during anaerobic digestion involves reactions that are close to the thermodynamic equilibrium, at which the Gibbs Free Energy change (ΔG) of a reaction is zero. The (ΔG) of a reaction can be calculated and depends on the Standard Gibbs Free Energy Change ((ΔGo) and the concentrations of products and substrates. For the interspecies hydrogen transfer between bacteria, hydrogen gas (H2) is the substrate for one species while it is the product for the other species.

(a) Sketch a plot that demonstrates how the ΔG depends on the hydrogen concentration for each reaction. Show a line that represents ΔG=zero.

(b) Explain, by referring to the plot, the effect of hydrogen concentration on the energetics of both reactions, and at which H2 concentrations the hydrogen transfer can work.

3.6 Fermentation pathways

Lactic acid fermentation and butyric acid fermentation are microbial sugar fermentation processes that occur when food material such as milk and vegetables are stored in the absence of oxygen.

(a) Explain why one process is desired, the other not.

(b) Explain the principle of electron flow of these fermentation pathways.

(d) How much growth (g of biomass/ mol of glucose) would you expect per mol of glucose fermented via these two fermentations and why?

Section 4: (9 marks)

Answer 6 out of the following 8 questions. Each question carries 1.5 marks

4.1 Using unusual electron acceptors

Comment on the capabilities of bacteria to use insoluble solid electron acceptors or electron donors. Give an example showing the electron transfer reaction. Point out the industrial relevance of this bio-reaction.

4.2 Aerobic chemolithotrophic reactions

Explain what chemolithotrophic bacteria are and what their role is in geobiochemical cycles. Give 3 examples of reactions that they catalyse.

4.3 Biofuel (5 min)

Both, algae and bacteria can be used to generate biofuels. Point out key differences between the two approaches (“pros and cons”). Point out what the electron donor and acceptors are both phototrophic and heterotrophic production of biofuels.

4.4 Product Yield Prediction

The aerobic oxidation of a brewery wastewater consisting essentially of 25 mM ethanol (CH3-CH2OH) solution as the organic pollutant will require how much oxygen per L of wastewater? Refine your answer by a) neglecting and b) including the likely growth of microbial cells.

4.5 Electron Balance

The anaerobic digestion of an organic substance produced 20,000 L of methane gas. How much oxygen would have been necessary to degrade the same compound?

4.6 Process monitoring and control

A proportional- integral- differential controller (PID) can be used in bioprocesses to control process parameters such as dissolved oxygen concentration or pH to a desired set-point.

(a) Explain how the three different elements (P, I, D) work and give at least one advantage and one disadvantage of each element.

(b) Give an example of a process, parameter to be controlled and the need for its control.

4.7 Bio-geo-chemical cycles

Under anaerobic conditions bacteria can carry out anaerobic respirations in which electron acceptors other than oxygen are used.

(a) Give examples of 3 anaerobic respirations by pointing out the electron accepting half reaction showing the electron acceptor, the number of electrons reacting and the reduced end product.

(b) Explain the ecological/industrial significance of the reaction.

4.8 Biomass recycle

What is the advantage of biomass feedback (recycle) in bioprocesses. What is its potential effect on productivity? Give an example of its industrial use. Give an example of how the biomass can be separated from the mixed liquor in the reactor.

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