A Study on Growth Kinetics of Commercial Yeast in Different Test Substrates

1. ICERIE 2017_199
* Correspondingauthor: musfiqur.rahman.alo@gmail.com
Proceedings of the
International Conference on Engineering Research, Innovation and Education 2017
ICERIE 2017, 13 15 January, SUST, Sylhet, Bangladesh
A Study On Growth Kinetics Of Commercial Yeast
In Different Substrates
N. B. Amin1
, M. S. Rahman2
, M. Aminul Haque1
, M. M. Rahman2,*
andM. E. Rahman1
1
Department of Civil Engineering, Leading University, Sylhet, Bangladesh.
Email: nargis.syl@gmail.com
2
Department of Civil and EnvironmentalEngineering, Shahjalal University of Science & Technology,
Sylhet, Bangladesh.
Email: musfiqur.rahman.alo@gmail.com
Keywords:
 Bioaugmentation,
 Yeast ,
 Growth kinetics,
 CSTR,
 Substrates
Abstract:Bioaugmentation is the repetition of adding actively growing,
specialized microbial strains into a microbial community in an effort to increase the
ability of the microbial community to respond to process fluctuations or to degrade
certain compounds, resulting in improved treatment. Yeast or
Saccharomycescerevisae strains causes bio-augmentation of microbes by
replication in wastewater. The aims of this research was to test suitability of
commercial yeast for aiding bio-augmentation in degrading different test substrates
and to determine the growth kinetics of yeast by following high rate batch test
protocol. A simple cost effective Continuously Stirred Tank Reactor (CSTR) has
been built in the laboratory of the Department of Civil Engineering, Leading
University. In experimental assay, four substrates were used i.e. soft drinks,
multivitamin syrup, milk and wastewater in an optimum amount with a fixed
amount of yeast. Growth kinetics of biomass was measured indry weight method
and the experimental results showed an overall biomass yield on different
substrate. The results of the study show a strong potential to demonstrate the
growth kinetics that can be applied as a preliminary treatment stage of wastewater.
1. INTRODUCTION
Yeast (Saccharomyces cerevisiae) is a unicellular fungi which is well known due to its use infood production
industry. Halasz and Lasztity (1991) established that yeast biomass is extensively used as human protein
supplement in human nutrition. Bio-augmentation is the accumulation of bacterial cultural products having
different strains of microorganisms to wastewater with the purpose of providing an adequate amount of mixture
of microorganisms which can help the treatment performance of the waste water treatment system (Novozymes,
2015).Bio-augmentation is crucial for a wastewater treatment system as several previous models for oscillating
microbial cultures(Hjortso and Nielsen, 1995) involve coupling the PBE(population balance
Fig.1 Cell cycle for budding yeast used in deriving cell age distribution models (Zhu et al. 2000)

2. 211 | Amin et. al., ICERIE 2017
equation) for the cell age distribution to the substrate mass balance. The growth rate of yeast in a bioreactor is a
very crucial thing because continuous oscillation of budding yeast can adversely affect bioreactor (Zhu et al.
2000). The simplified cell cycle used in the derivation of the PBE model for budding yeast cultures developed
by (Zhu et al. 2000)illustrating the cell cycle has two control points where at the transition age (at)when a
daughter cell becomes a mother cell capable of under-going budding and after that the division age (ad) when
the budding mother cell produces a daughter cell (Fig.1). However, the growth kinetics of commercial yeast in
municipal waste water augmented with substrate under aerobic condition is a very controversial topic nowadays
which is necessary to be defined asthere are no definitedata for designing a bioreactor perspective the
environment.
2. METHEDOLOGY
Research focuses to observe the growth kinetics of Yeast in different substrates using CSTR (continuously
stirred tank reactor)which is developed in lab. The growth kinetics of yeast is determined from food wastewater
using limited amount of yeastby following high rate batch test protocol. In addition, microbial biomass is a
suitable supplemental protein source obtained from processes in which bacteria, yeasts, other fungi or algae are
cultivated in large quantities. The growth rate of yeast by measuring augmented weight of yeast is a vital part
for wastewater treatment plant as degradation rate of sludge of wastewater achieved by testing samples.
2.1 Experimental procedure
Experimental procedure consists of two key parts where a low cost continuously stirred tank reactor
(CSTR) or bioreactor had been created in lab along with a vacuum filter. Following that other key part of
laboratory tests has been done.
2.1.1 Low cost continuously stirred tank reactor (CSTR)
Using local materials are the significant reason for the low cost bioreactor. The CSTR has been created
using plastic bottle (5 liter), motor, propeller, hard board and plastic pipe. Furthermore the bioreactor has been
fabricated by Glass with glass paper and color. Figure 2, describe the CSTR in details and Figure 3, depicts
the bioreactor after fabrication. However, the vacuum filter has also been made by using local material where
beaker, Buchner funnel, pipes and syringe are the important parts (Fig. 4). Syringe has been working as a pump
which is illustrated on Fig.4.
Motor
Mouthpiece
Propeller
Outlet
Fig.2 Schematic diagram of bioreactor Fig.3 Bioreactor (after fabrication)
Fig.3 Schematic diagram of vacuum Fig.4 Vacuum filter (after fabrication)

3. 212 | Amin et. al., ICERIE 2017
2.1.2 Sample preparation and operation system
Beverage (coca-cola), multi-vitamin syrup, milk and wastewater have been selected as testing substrate
where 500 ml of each substrate has been added with 2500 ml of distilled water to maintain experimental
concentration. As a consumer, 25mg/l of yeast has been addedand then stirred 12 hr using continuously stirred
tank reactor (CSTR) at a revolution per minute (RPM) of 4000(Vieira et al. 2012). Meanwhile,100 ml of
samples have been collected at 120 minute interval for testing the consumption rate of yeast. Vacuum filter has
been used to restrain the microbes and then air-dried to examine the weight of dry cell mass.Weight of collected
biomass from the sample has been converted to per liter using general mathematical equations and transformed
to per hour to determine the growth kinetics of commercial yeast.
2.2 Data collection method
For testing part of turbidity reduction, the experiment has been done with Microprocessor Turbidity Meter
(HI 93703 by HANNA Instruments). pH has been tested with pH meter (HI 8014 by HANNA Instruments)
following the standards of AWWA.
3. EXPERIMENTAL RESULTS
Bioaugmentation is a process which helps to degrade the contaminants from the water. Therefore this
process is obtaining more popularity for treating different kind of wastewater. It is one of the prime focuses of
the study and the results acquired from the experiments have shown a positive trend.The study observed that
Fig. 5 Growth kinetics comparison among all substrates
specific growth rate of municipal wastewater is high due to availability of enough food for microbs. As an
illustration, fig.5 isrepresenting the growth kinetics comparison among all the substrates taken into test.
Fig.6 Growth rate profile of Yeast
0
50
100
150
200
250
300
350
400
450
0 2 4 6 8 10 12 14
Biomassconcentration(gm/l)
Augmentation period (hr)
Beverage
Multivitamin Syrup
Municipal waste water
Milk
0
1
2
3
4
5
6
7
8
9
0 2 4 6 8 10 12
Growthrate(gm/hr)
Augmantation period(hr)
Beverage
Multivitamin Syrup
Municipal waste water
Milk

4. 213 | Amin et. al., ICERIE 2017
Biomass growth has been increased with time despite the increasing rate depends on the type of substrates. The
graph depicting the biomass growth has been at peak for municipal wastewater where other substrates are
showing a gradual increasing pattern. Correspondingly, a significant amount of increase in augmentation of
biomass observed for almost all the substrates after 8th
hour. However, the food consumption rate of biomass has
been highest for municipal wastewater and steep elevation observed for multi-vitamin syrup. Furthermore, if
growth rate is taken into account then fig.6 exhibits the growth rate of Yeast decreased with time. There are
fluctuations spotted for all the substrates but the initial growth rate has been detected for municipal wastewater
and Milk. Although milk has gradual decrease of growth rate but municipal wastewater regained about 4 gm/hr
of growth rate at the 10th
hour.Adding more, in this study,growth rate of yeast has been calculated using a
common exponential equation as shown in Eq.(1) (Vieira et al. 2012).
( ) = = (1)
Where, ( ) = Biomass at time t (hours), =Initial biomass (gm), µ=Specific growth rate (h-1
). If time is
considered as a variable of the above equation, biomass will be obtained.In this study software analysis has
Fig.7 Specific growth rate profile of biomass
been done using Microsoft Office Excel to find out the specific growth rate (µ) of commercial yeast in different
substrates. Exponential regression curve fitted well within the experimental data and the specific growth rate (µ)
of biomass in soft drinks (beverage), multivitamin syrup, milk, and wastewater are found 0.114 h-1
,0.15 h-
1
,0.036 h-1
and 0.1414 h-1
respectively (Fig.7).
Table 1 Experimental results for Turbidity and pH
Duration (hr) Turbidity (NTU) pH
Multi-vitamin
syrup
Municipal
wastewater
Multi-vitamin
syrup
Municipal
wastewater
0 590 349 2.87 4.45
2 588 345 2.91 4.5
4 582 336 2.92 4.55
6 576 310 2.93 4.6
8 568 290 3.1 4.7
10 555 250 3.45 4.77
12 535 220 4.11 4.8
The study observed bioaugmentation process as a beneficiary while it reduces the turbidity of wastewater as
well as it improves the pH. The standard pH value of drinking water is 6.5-8.5 and turbidity is 10 NTU in
Bangladesh drinking water quality standards (Ahmed et al.2012). Meanwhile from table (1), turbidity of multi-
y = 4.403e0.114x
R² = 0.955
y = 4.560e0.152x
R² = 0.930
y = 7.304e0.141x
R² = 0.927
y = 6.980e0.036x
R² = 0.379
0
5
10
15
20
25
30
35
40
45
0 2 4 6 8 10 12
Biomass(gm)
Augmentation period(hr)
Beverage
Multivitamin Syrup
Municipal waste water
Milk
Expon. (Beverage)
Expon. (Multivitamin Syrup)
Expon. (Municipal waste water)
Expon. (Milk)

5. 214 | Amin et. al., ICERIE 2017
vitamin syrup reduced up to 55 NTU in the time duration of 12 hrs meanwhile in terms of municipal wastewater
it reduced more than 125 NTU which represents the degradation of impurities by biomass. The turbidity and pH
for milk and beverage observed quite equal to 0 hr. Moreover the tests detected that pH at 0 hr improves
gradually along with the increasing time of bioaugmentation. Thus this process may consider as an effective one
for primary treatment of wastewater.
4. CONCLUSION AND RECOMMENDATIONS
Bioaugmentation is a modernprocess researched by several researchers using different technologies and
instruments. In this research work,an attempt has done to determine the growth rate of yeast in various types of
wastewater and observed commercial yeast is suitable for assisting bioaugmentation. Moreover,
bioaugmentation rate found significant for municipal wastewater and multi-vitamin syrup where biomass
increased with the increase of time. The study also reveals that bioaugmentation reduces the turbidity and
improves the acidic condition of wastewater towards standard value. Adding more, the study exhibits the rate of
Bioaugmentation follows the exponential trend during the study period with the specific growth rate(µ) in soft
drinks (beverage), multivitamin syrup, milk, wastewater respectively 0.114 h -1
, 0.15 h -1,
0.036 h -1
, and 0.1414
h -1
. Which portrays exponential equation has strong potential to demonstrate the growth kinetics that can be
applied as a preliminary treatment stage of wastewater. Uniquely this study aids to recover from the failure of
sewage treatment unit using biomass.
5. ACKNOWLEDGEMENTS
Author indebt acknowledge to the authority of Dept. of Civil Engineering, Leading University for their
crucial support.
6. REFERENCES
Ahmed, F.M., and Rahman, M.M. (2012) ‘Water supply And Sanitation’, ITN-Bangladesh.
Halasz, A., and Lasztity, R. (1991)‘Use of yeast biomass in food production’, Boca Raton:CRC Press.
Hjortso, M.A., and Nielson, J. (1995)‘Population balance models of autonomous microbial oscillations’, Journal
of Biotechnology, pp.255-269.
Novozymes (2015) Retrieved February 2, 2015, from Novozymes Web site:
http://www.novozymes.com/en/solutions/wastewater-solutions/What-is-Bioaugmentation/Pages/default.aspx
Vieira, E.D., Andrietta, M.G., and Andriettta, S.R. (2013) ‘Yeast biomass production: A new approach in
glucose limited feeding strategy’, Brazilian Journal of Microbiology, pp.551-558.
Zhu, G.Y., Zamamiri, A.Q., Henson, M.A., and HjortsO, M.A. (2000) ‘Model predictive control of continuous
yeast bioreactors using cell population balance models’, Chemical Engineering Science, pp.6155-6167.