Research on applications of flat plate photobioreactor model using microalgae for shrimp culture in ninh thuan province combined with biomass recovery masters thesis major sciences and management of the environment

THE JOINT ACADEMIC PROGRAM OF EXECUTIVE MASTER IN
SCIENCES AND MANAGEMENT OF THE ENVIRONMENT BETWEEN
INDUSTRIAL UNIVERSITY OF HOCHIMINH CITY
AND LIÈGE UNIVERSITY

TRAN THI MO

RESEARCH ON APPLICATION OF FLAT PLATE
PHOTOBIOREACTOR MODEL USING
MICROALGAE FOR SHRIMP CULTURE IN
NINH THUAN PROVINCE COMBINED WITH
BIOMASS RECOVERY
Major: EXECUTIVE MASTER IN SCIENCES AND MANAGEMENT OF
THE ENVIRONMENT

MASTER’S THESIS
HO CHI MINH CITY, YEAR 2018


The project was completed at The Industrial University of Hochiminh City
Supervisor’s name: .......................................................................................................
(Write full name and signature)
The thesis was taken at The Industrial University of Hochiminh City date . . . . month .
. . . year . . . . . .
Committee members (name):
1. ......................................................................... - Committee Chair
2. ......................................................................... - Commissioner
3. ......................................................................... - Secretary
(Write full name and signature)

COMMITTEE CHAIR

DEAN OF INSTITUTE OF ENVIRONMENTAL
SCIENCE, ENGINEERING AND MANAGEMENT


ACKNOWLEDGMENT
A completed study would not be done without any assistance. In addition, the efforts of
myselves, there is the enthusiasm of teachers, as well as the support of family and
friends during the research master thesis.
First of all, I would like to express my endless thanks and gratefulness to Prof. Le
Hung Anh, Director of the Institute of Insititute For Environment Science, Engineering
and Management. His kindly support and continuous advices went through the process
of completion of my thesis. His encouragement and comments had significantly
enriched and improved my work. Without his motivation and instructions, the thesis
would have been impossible to be done effectively.
Thanks to Prof. Jean-Luc Vasel, the consultant, was always ready to provide technical
support to me during the course of the thesis.
I would like to state my thanks to Renewable project where supporting and creating
conditions for me to research easily and conveniently, laboratory equipment and a part
of the research cost of the thesis.
Therefore, I gratefully gives acknowledgement to their support and motivation during
the time of doing this research.

1


ABSTRACT
The objective of the research is to evaluate the ability of shrimp culture treatment of
microalgae on flat plate photobioreactor models, from which large scale application in
Ninh Thuan. The research has designed and built the Flat Plate Photobioreactor model

with four different types of fluxes and artificial lighting systems.
The experiments have compared the efficiency of culturing these algae with the Flat
Plate Photobioreactor model in the same laboratory conditions and made the following
conclusions: The study examined a number of different lighting cycles. The lighting
period of 16 hourd and 8 hours produces better and better results in terms of culture
and harvesting of algae, but in reality the outdoor lighting only reaches 8 hours. the
study was conducted on 4 different types of aeration tanks, with data suggesting that
the Flat Plate Photobioreactor is the most efficient way of cultivating algae. The
removal efficiency of pollutants is as follows: Total phosphorus is about 80-85% and
total nitrogen is about 65-70%.
Research results show that Chlorella sp is capable of treating shrimp waste water,
opening up the direction of large-scale study of the topic.

2


CONTENTS
ACKNOWLEDGMENT .......................................................................................................... 1
ABSTRACT ............................................................................................................................. 2
LIST OF ABBREVIATIONS .................................................................................................. 6
CHAPTER 1

INTRODUCTION ........................................................................................ 7

1.1 Overview of shrimp culture ........................................................................................... 7
1.1.1 Situation of shrimp farming in the world ............................................................... 7
1.1.2 Situation of shrimp farming in Vietnam ................................................................ 8
1.1.3 Situation of shrimp farming in Ninh Thuan province ............................................ 9
1.2 Origin, composition and characteristics of shrimp pond effluent ............................... 11
1.2.1 Origins arise.......................................................................................................... 11

1.2.2 Composition and characteristics of wastewater ................................................... 12
1.3 Biological methods to treat waste water ...................................................................... 13
1.3.1 Use microorganisms ............................................................................................. 13
1.3.2 Use of animals and plants ..................................................................................... 14
1.4 Overview of Chlorella sp ............................................................................................. 15
1.4.1 Introduce ............................................................................................................... 15
1.4.2. Some forms of farming Chlorella sp ................................................................... 17
1.4.3 Factors affecting the growth and development of microalgae ............................. 18
1.4.4 Application of microalgae .................................................................................... 22
3


1.5. Overview of microalgae application ........................................................................... 25
1.6. Overview of research on Flat Plate Photobioreactor model ....................................... 29
CHAPTER 2

MATERIALS AND METHODOLOGY .................................................... 33

2.1 Time and place ............................................................................................................. 33
2.2 Study materials ............................................................................................................ 33
2.2.1 Shrimp waste water .............................................................................................. 33
2.2.2 Chlorella sp ........................................................................................................... 33
2.2.3 Experimental materials ......................................................................................... 33
2.2.4 Chemicals ............................................................................................................. 34
2.3 Research Methods ........................................................................................................ 34
2.3.1 Specific research methods .................................................................................... 34
2.3.2 Method of data collection ..................................................................................... 36
2.3.3 Data processing methods ...................................................................................... 36
2.3.4 Comparison method, data evaluation ................................................................... 36
2.3.5 Method of determining microbial density ............................................................ 37

2.4 Experimental design .................................................................................................... 38
2.4.1 Experiment 1: Construction of OD growth curve and linear correlation of
microalgae. ............................................................................................................................. 38
2.4.2 Experiment 2: Investigate the effect of the lighting cycle ................................... 38
2.4.3 Experiment 3: Survey of wastewater treatment capacity ..................................... 39
2.4.4 Experiment 4: Study on microalgae biomass harvesting by centrifugation ......... 39
4


CHAPTER 3

RESULTS AND DISCUSSION ................................................................. 41

3.1 Experiment to build growth curve and linear correlation ............................................ 41
3.1.1 Build growth curve ............................................................................................... 41
3.1.2 Linear correlation ................................................................................................. 43
3.2 Change lighting time cycle .......................................................................................... 44
3.2.1 Chlorella1 sp ......................................................................................................... 44
3.2.2. Chlorella2 sp ........................................................................................................ 47
3.3 Survey of wastewater treatment capacity .................................................................... 50
3.3.1 Chlorella1 sp ......................................................................................................... 50
3.3.2 Chlorella2 sp ......................................................................................................... 52
3.4 Biomass recovery experiment ...................................................................................... 53
CONCLUSIONS AND RECOMMENDATIONS ................................................................ 55
A. CONCLUSIONS........................................................................................................... 55
B. RECOMMENDATIONS .............................................................................................. 56
REFERENCES ....................................................................................................................... 58
APPENDIX ............................................................................................................................ 61
A. Some images in the experiment .................................................................................... 61
B. Appendix table of results .............................................................................................. 63

5


LIST OF ABBREVIATIONS

Number

ABBREVIATIONS

CONTENTS

1

Chlorella sp in fresh water

Chlorella1 sp

2

Chlorella sp in salt water

Chlorella2 sp

3

Flat Panel Photobioreactor

Tank 1

4

Air-Lift Photobioreactors

Tank 2

5

Flat Panel Airlift Photobioreactors

Tank 3

Frame And Plastic Bag

Tank 4

6

COD

Chemical Oxygen Demand

7

BOD

Biochemical oxygen Demand

6

CHAPTER 1

INTRODUCTION

1.1 Overview of shrimp culture
1.1.1 Situation of shrimp farming in the world
Total annual harvests in the world today, including fishing and aquaculture, increase
over the years. Shrimp output grew steadily in East Asia in 2011, an average annual
growth of 6% from 2008 to 2011. According to the Food and Agriculture Organization
(FAO) estimated total production - including both natural and farmed fisheries - by
2015 would be around 7.1 million tons, up from 6.9 million tons in 2014. Whereas
shrimp stocks from the sea are near saturation, shrimp farming is playing an
increasingly important role in providing this kind of seafood.
Shrimp farming grows mainly in tropical countries, where favorable climatic
conditions, especially high temperatures throughout the year. About 50 countries
around the world are less likely to breed shrimp. However, large countries are
concentrated in two regions: Eastern Europe, including: China, Thailand, Indonesia,
Vietnam, India, the Philippines, Taiwan, Japan and the western hemisphere, including
Colombia, Mexico, Peru , Bazil.
In recent years, shrimp farming in the world has made great achievements, contributing
significantly to boosting the economic development of developed countries, but
accompanied with great problems are posed as The epidemic, especially early mortality
syndrome (EMS), is explosive in large areas, causing massive losses, the destruction of
mangrove forests, the pollution of water and agricultural land, and the environment.
degradation...
According to GOAL production fell from 3.45 million tons to 3.25 million tons in 2012
(down 5.8%) and 3.21 million tons in 2013 (down 1.1%) due to the impact of EMS in
7

Central China, Thailand, Vietnam and Malaysia. Production rose significantly in 2014
to -3.49 million tons (up 8.5 percent) mainly due to larger harvests than reported in
China, Vietnam and India. Even so, output will fall again in 2015 due to low harvests
in China, Thailand, Vietnam and Indonesia. [2]
1.1.2 Situation of shrimp farming in Vietnam
Large sea areas have created favorable conditions for the exploitation and development
of aquatic products in Vietnam. Shrimp are suitable habitats in brackish water areas
near the sea. With this feature, the Central, South Central (Khanh Hoa, Phu Yen, Ninh
Thuan, Ba Ria - Vung Tau ...), the Mekong Delta (Long An, Tien Giang, Ben Tre, Tra
Vinh, Soc Trang, Ca Mau, Kien Giang) is the most concentrated shrimp production in
the country.
The rate of surface water surface for aquaculture has increased sharply since the 2000s
with the total area of water surface for aquaculture is nearly 650 thousand hectares to
1054 thousand hectares by 2014.
According to the report, in 2016, the total output of aquaculture in the country is
estimated at over 6.7 million tons, up 2.5% over the same period in 2015. Of which, the
output of mining is nearly 3.1 million tons (up 1.7% over the same period in 2015),
aquaculture output is over 3.6 million tons (up 3.3% over the same period in 2015).
Seafood export turnover is estimated at $ 7 billion, up 6.5% over the same period last
year. Although in the early months of 2016, the fisheries sector has been affected by
droughts and salt water intrusion in the Mekong Delta, which has affected the planned
release of brackish water shrimp as well as the damage to farmers. However, the area
of brackish water shrimp farming in the country is estimated at 700,000 ha increased
0.72% of the plan. The production of brackish water shrimp is estimated at 650,000
tons.
8


Ninh Thuan is the large shrimp breeding center of the country with the production

scale in 2016 reaching the output of 24.1 billion; Most of them are high value
producers such as tiger shrimp (5.1 billion), white shrimp (19 billion), marine fish
species. However, lack of waste treatment facilities, water supply and waste water
drainage systems; Situation of the disease over the years continuously increasing is an
important issue of the province.
However, due to the high economic efficiency from shrimp farming, the aquaculture
area is currently developing spontaneously, the scale and diversified farming methods,
lack of training, full guidance self-priming, leading to environmental pollution.
Spontaneous aquaculture changes the purpose of land use (converting farmland, desert
land into fish and shrimp farming), using unstable water supplies (digging underground
water in the area), releasing into the environment Surrounding a large amount of waste,
polluting the soil, surface water and groundwater. The effects of aquaculture
wastewater have long been assessed but there is no effective solution for many reasons.
In the first six months of 2015, shrimp farmers reduced their stocking density by 30%
to combat EMS and export prices fell. VASEP industry associations accounted for a
decrease of 1.6% in vannamei production during this period over the same period of
2014. [10]
1.1.3 Situation of shrimp farming in Ninh Thuan province
With advantages over the coast of more than 100 km, over the past ten years, the
commercial production of high value seafood and marine products such as lobster,
shrimp, white shrimp, snails ... in coastal communes. The sea of Ninh Thuan province
develops quite fast. It is normal for farmers to earn billions every year. [11]
Due to the geographic advantage surrounding the surrounding mountains, the sea in
Ninh Thuan is less affected when the climate changes, including storms ... so farmers
9


produce and fish in seafood. Phan Rang - Thap Cham, Ninh Hai and Ninh Phuoc
districts have been highly profitable.
According to the statistics of Ninh Thuan Fisheries Department, the whole province

has 118 rafts / 628 lobster cages, the average yield is about 40 tons / year; About 400
hectares of white shrimp ponds...According to Head of Dang Van Tin Department of
Aquaculture, green lobster farming is growing and bringing high income, because
lobster live in natural day The scarcity, the price to buy expensive varieties, the
breeding time to mature lobster cotton lasts more than a year makes the cost increase.
Although the sale price of lobster from 1.2 to 1.7 million per kg of high economic
value but not stable because the market price of lobster prices are high, resulting in low
interest farmers, so much. Households have switched to green lobster farming. At
present, this breed source is very easy to raise, the price of seed is low, the selling price
when harvest is quite stable from 700-750 thousand VND / kg, the time shrimp farming
is short, high productivity, farmers Interest is more, so many households are excited to
invest in expanding cages to raise.
In the first eight months of 2017, shrimp farming in Ninh Thuan has seen positive
changes, shrimp farming area has increased, there is a change in the target species as
well as forms of farming.
Area of commercial shrimp farming in the first eight months was 789.4 hectares,
reaching 92.9% of the plan and 151% of the same period last year, of which the area of
shrimp farming was 107.8 hectares and 681. 6 ha. The specific area for raising fish is
as follows: Ninh Phuoc 77.0 ha, Thuan Nam 221.5 ha and Ninh Hai 482.6 ha. The
selling price of shrimp was stable so the stocking area increased.

10


1.2 Origin, composition and characteristics of shrimp pond effluent
1.2.1 Origins arise
Brackish water and saltwater aquaculture has been quite developed, the technical level
of farmers and the level of intensive farming has increased, but the awareness of people
about the use of chemicals and antibiotics in shrimp farming is not high; Extinguishing
and treating wastes before discharging into the environment have not been paid due

attention by shrimp farmers.
The amount of waste generated is associated with feed production technology and
shrimp culture systems. Redundant food, shrimp faeces and nutrient metabolism are the
main sources of contaminants. There are also residues of antibiotics and medicines.
Wastewater carries a large amount of nitrogen, phosphorus and other nutrients, creating
super-nutrient, blooming bacteria. The presence of carbonic compounds and organic
matter will reduce dissolved oxygen and increase BOD, COD, H2S, ammonia and CH4
content in the natural basin.
Most of the surplus products in shrimp culture accumulate in pond mud, which is
harmful to shrimp and shrimp farming because the mud is very toxic, hypoxia and
contains many harmful substances such as ammonia, nitrite, H2S, the direct effect of
shrimp is always stress, poor eating, reduced growth rate and susceptible to bacterial
disease and mass death.
The discharge of pond water and pond solid waste in intensive and semi-intensive
shrimp culture to natural canals without treatment will result in sedimentation of the
canal system, polluted natural water environment serious. If the discharge is
continuous, there is no time for the environment to recover, the pathogen is cut, the
organic humus will accumulate as the water environment becomes ephemeral,
intensive shrimp farming and sale. Intensive farming will be at greater risk. On the
11


other hand, the infrastructure serving the shrimp farming areas is not complete, the
irrigation system is the system serving the needs of agricultural cultivation; Many
shrimp farms have no canals, separate canals, even canal sections are sedimented, the
bottom of the canal is higher than the bottom of shrimp ponds. Consequently, the
pathogen still exists in the shrimp pond when the infected ponds discharge into the
environment, so the infection is very high.
1.2.2 Composition and characteristics of wastewater
The composition of shrimp wastewater is not as big as industrial waste water, but due

to the large discharge volume plus the amount of sludge in the pond, the quality of the
surrounding environment is greatly reduced. The cause of environmental pollution in
shrimp farming is due to the high concentration of aquaculture but no plans for water
treatment and lack of attention of the state. Shrimp culture wastewater is rich in organic
matter, suspended solids, H2S, and NH3 produced by the decomposition of organic
matter.
Gases: In the process of raising the use of chemicals have released into the
environment a number of gases under the action of bacteria appear as H2S, NH3, CH4
... these substances are very toxic to ponds and lakes. When shrimp is sick, it is
necessary to use chemicals to remove toxins in ponds or to treat shrimp diseases.
Overdose or overdose will lead to overdose causing some bacteria to develop poorly
for shrimp. In addition, the process of running the explosion engine generates emission
of SO2, NOx, CO...[16]
Mud: Contains many organic substances, antibiotics, chemicals, toxic gases (H2S,
NH3) and many pathogens. The sludge is discharged directly to the untreated soil. Most
shrimp ponds have black or muddy soil in the bottom layer and discharge into nearby
water sources such as rivers and streams after harvesting shrimp causing degradation of
12


water quality without control of diseases. When the black mud layer is taken to the
shrimp farming area without good management of waste, they return to the pond when
heavy rain.
Water: In shrimp farming using antibiotics, chemicals (potassium, chlorine) they will
be present in waste water. Water rich in nutrients should produce H2S, NH3 and waste
water contains more SO42-, HCO3-, NO2- toxic if not treated before discharging into the
surrounding environment. Long-term exposure to water will be eaten, dry skin,
cracked, hardened. In water, H2S reaches 0.001ppm for a continuous time, reducing the
reproductive capacity of the shrimp, while NH3 is converted to NO2- by nitrosomonat
and forming methemoglobin, which reduces the amount of oxygen to the cell. In

shrimp wastewater contains organic matter such as N, P. Total N, P produced per
hectare for semi-industrial (yield 2 tons) about 13 and 43 kg, so the effluent discharge
nourish and reduce the amount of oxygen in the water. In addition, shrimp waste water
has

odor

due

to

microorganisms

decomposing

organic

substances,

algae,

phytoplankton, dead bacteria and antibiotics, chemicals present in wastewater.
Normally, mud is discharged directly to the land or river without treatment, causing the
diseased shrimp to die soon after shrimp.
1.3 Biological methods to treat waste water
1.3.1 Use microorganisms
Use of microorganisms, the collection of extracellular enzyme components of
microbial growth; extracellular enzymes; Biological nutrients, minerals that activate
the original growth and active catalysts have the effect of dissolving organic soluble
and insoluble matter from shrimp faeces, the leftovers accumulate to create stability,

Maintaining water quality and water color in ponds. This solution has two directions:

13


Aerobic method: Use aerobic microorganisms to treat. Researchers Phan Thi Hong
Ngan and Pham Khac Lieu (Hue University) applied aerobic treatment technology with
submerge aerated fixed bed (SAFB), using modified aerobic activated sludge Good
results of brackish water aquaculture were 73.7%, 97.4% NH4-N. Aerobic methods
have long retention times that facilitate the growth and activity of nitrifying bacteria.
Anaerobic method: use anaerobic microorganism for treatment. This is a commonly
used method for wastewater treatment, especially the Upflow Anaerobic Sludge
Blanket (UASB). This technology distributes waste water from the bottom up through
the anaerobic sludge layer to carry out the decomposition of organic matter by
anaerobic microorganisms. The phase separation system separates the solid-liquid-gas
phase to remove the gases, transports the slurry to the bottom of the tank and leads the
water back to the treatment. Research by Mirzoyan N. and Gross A. Published at
NCBI, the UASB reactor is well suited for brackish water aquaculture, reducing 81%
suspended solids (TSS), 98% COD, 92% volatile.
1.3.2 Use of animals and plants
It is possible to carry out the absorption of pollutants based on the process of
metabolism in the ecosystem through the food chain. Often people use phytoplankton,
algae or algae to absorb nitrogen, phosphorus and carbon, etc. in wastewater to
increase biomass. A study by the Nha Trang Institute of Materials Science on the
ability of environmental treatment in shrimp farming ponds shows that seaweed can
absorb large amount of ammonium salt at high speed. After 24 hours, with a density of
400 g / m2, the ammonia content in the water was reduced by more than 20%. As of
Thursday, ammonia levels have dropped by more than 80% and by 10 am am 10% less
than initially. For phosphate, absorbed 30-60% after 24 hours. The study by Ngo Thi
Thu Thao and colleagues on the effect of combined culture of seaweed and white

shrimp larvae concludes that algae helps improve the quality of the environment and
14


improve the quality of shrimp and biomass. At 400-800 g/m3, it is suitable for
combined culture.
In the food chain, people also use first-class animals in coastal waters such as clams,
blood cockles, mussels, oysters.... to consume phytoplankton and improve bottom
sediment or live fish species. plankton, mullet, tilapia, etc. Research by Duong Thi
Thanh (Ho Chi Minh City University of Technology) shows that Tetraselinmis sp. and
bivalve molluscs is a suitable solution to treat industrial shrimp waste water,
environmental protection. Hue University of Agriculture and Forestry also has research
on the ability of organic matter processing of tilapia, mullet and snail in intensive waste
water shrimp culture. The results showed that, with effluents having dissolved oxygen
parameters, NH3, BOD5, COD, TSS, coliform exceeded the limit of circular
44/2010/TT-BNNPTNT và QCVN 11:2008/BTNMT many times, using a suitable ratio
of subjects have helped the water after treatment meet the requirements, although the
coliform indicator is still higher than the allowed threshold.
1.4 Overview of Chlorella sp
1.4.1 Introduce
1.4.1.1 Scientific classification
Table 1.1. Scientific classification [23]
Domain

Eukaryota

Regnum

Plant

Divisio

Chlorophyta

Class

Trebouxiophyceae

Ordo

Chlorellales

Familia

Chlorellaceae

Genus

Chlorella
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1.4.1.2 Characteristics
Chlorella is a genus of single-celled green algae belonging to the division Chlorophyta.
It

is

spherical

in

shape,

about

2

to

10 μm in

diameter,

and

is

without flagella. Chlorella contains the green photosynthetic pigments chlorophylla and -b in its chloroplast. Through photosynthesis, it multiplies rapidly, requiring
only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. [21]
Chlorella is a potential food source because it is high in protein and other essential
nutrients; when dried, it is about 45% protein, 20% fat, 20% carbohydrate, 5% fiber,
and 10% minerals and vitamins. Mass-production methods are now being used to
cultivate it in large artificial circular ponds.
1.4.1.3 Role
Chlorella has the potential and can be used as a source of food and energy as it has the
potential for photosynthesis, which in theory can reach 8%, which can compete with
other crops such as plants. Cane. It is also an attractive food source because it has high
levels of protein and other essential nutrients; When dried, it contains about 45%
protein, 20% fat, 20% carbohydrate, 5% fiber, 10% minerals and vitamins.

It is a rich and varied food supplement that helps the body regulate itself and balance
its tolerance and excretion. This helps the body to recover health quickly, creating good
resistance to many diseases and environmental pollution.
Characterized by single-celled microorganisms, photosynthetic growth through
photosynthesis, or heterodox, or both. Chlorella has the ability to accumulate heavy
metals and thus remove toxic compounds from wastewater. In addition to being a
natural source of food for aquaculture, they also enhance oxygenation through
photosynthesis under daylight. In some cases algae also play a role in eliminating

16


pathogens. Therefore, Chlorella can be used primarily to remove nutrients (removal of
nitrogen and phosphorus) in aquaculture waste water treatment.
Today, algae are also used to feed cattle and poultry, produce biofuels to clean energy.
1.4.2 Some forms of farming Chlorella sp
1.4.2.1 The open system
Natural ponds: using natural ponds and ponds for culturing ponds, not using agitators
but low productivity.

Figure 1.1. Open system [24]
Round tanks: Chlorella aquaculture in circular tanks with aeration system for high
productivity but high construction costs, energy consumption.
Pond system: Aquaculture in artificial pond system with water depth of more than
15cm. Productivity is usually 20-25 g/ m3 /day. High export value, however, depends
on the weather. Dry season evaporates quickly, especially in the dry season, so it is
difficult to control temperature
1.4.2.2 The closed system
This system has a high illumination rate of over 90%.

17


Figure 1.1. Closed system [25]
The system allows to limit direct contact with air and contaminated parts (dust,
microorganisms ...) between the algae and the external environment.
Advantages:
Increased illumination efficiency due to increased surface contact area.
Achieve high biomass.
Increase the sterility of the culture system.
Increases the efficiency of CO2 conversion.
Reduce exposure.
Disadvantages: high investment costs.
1.4.3 Factors affecting the growth and development of microalgae
1.4.3.1 Light
Light is an essential key for growth of microalgae. Microalgae uses light to process the
photosynthetic, but the light energy cannot be stored by microalgae, so the light should
be supplied sustainably. The microalgae cannot use all the supplied light because
microalgae cannot absorb all the photons, and too much light will cause light inhibition
for the surface layer of microalgae. [19]

18


Like other higher plants, light is one of the important contributors to photosynthesis.
Algae have the effect of increasing the intensity of light. When the light intensity is
low, the true rate of photosynthesis will be balanced with the respiratory rate. This is
called a point offset. Depending on the type of algae, the optimal illumination range
and the appropriate lighting time. Typically, algae are fed in the light intensity of 1,000
- 10,000 lux, with lighting time of 16 - 24h / day.

The light that acts on the microalgae through the pigment system in chloroplasts, the
number and size of algae that play a major role in determining the chlorophyll content
of each microalgae, the intensity of light is The light intensity plays an important role,
but the demand for it varies depending on the depth and density of the algae in the
culture medium.
1.4.3.2 Salinity
Sea algae have a high salt content, with a variety of algae that are capable of being
domesticated and cultured in freshwater habitats, with large numbers of green algae
(Fabregas, 1984). According to Coutteau (1996), algae can live and grow in new
environments with a lower salinity of up to 15 ppt. The optimum salinity for algae
grows from 20 to 24 ppt. According to Tran Suong Ngoc and colleagues (2007),
Tetraselmis is thought to be algae with a salt capacity of 6 - 53 ppt. Tetraselmis gracilis
reproduces at salinity ranges from 9 to 30 ppt and Chlorella distributes broadly at
salinity from 5 to 30 ppt. However, in algae culture, to develop the best algae, the
salinity difference should be less different than where they are distributed.
1.4.3.3 Temperature
In addition to environmental factors such as light, temperature also contributes
significantly to the development of algae. Algae grown in the appropriate temperature
environment develop rapidly, the length of algae extends. In contrast, the temperature
19


lies within the tolerance of the algae, the cells of the algae are hypoechoic or
hypotonic, leading to the algae being stunted or dead (Pham Thi Diem Phuong, 2012).
Each algae has its own optimum temperature range. According to Truong Sy Ky
(2000), algae can be kept at around 20 - 30oC. Lavens and Sorgeloos (1996) suggest
that saltwater algae, including Tetraselmis, grows well in the range of 16 -270C for
Chlorella vulgaris under natural light conditions of 25-300C. However, algae grow
slowly when they rise to 400C and below 250C. Experiment on the effect of salinity and
temperature on the growth rate of Tetraselmis tetratheles from Mohd Adib Fadhid B

Azian in 2007, Tetraselmis tetratheles developed at a temperature between 20 and 300C
is quite stable and does not grow well. At about 330C, at this temperature the algae
grow slowly and decay rapidly. According to Coutteau (1996), the appropriate
temperature for algae development is 16 - 350C and the optimum temperature for algae
growth is 20 - 240C. Temperatures are lower than 160C, algae are slow to grow and
algae will die when temperatures are above 350C. In addition, raising algae in the room
will easily control the temperature, while outdoor weather can change abnormally.
According to Diem (2011), the suitable temperature for Isochrysis galbana is 10 - 350C
but the optimal temperature is about 25 - 300C. When outdoor temperature algae were
raised to optimum algae productivity of 270C, while temperatures higher than 320C or
lower than 190C algae yield significantly decreased.
1.4.3.4 pH
pH is the indicator of algae growth. According to Coutteau (1996) [7] , algae can live
within the pH range of 7-9, but the optimum pH is from 8.2 to 8.7 for chlorella algal
pH of 6-8.5 if pH is unstable. The cells break down and the algae die unexpectedly.
Therefore, in the algae culture system we need to add CO2 to stabilize the pH below 9
during algae development. According to Oh_Shama (1986), when ammonium or
nitrate is used as the nitrogen supply for algae, it leads to the pH of the medium. The
20


NO3- uptake will lead to an increase in the pH of the medium and vice versa. The
uptake of NH4+ will lead to a decrease in pH. In the algae culture system, pH should be
<7.8 (Tran Suong Ngoc et al., 2007).
1.4.3.5 Aeration mode
In the artificial culture medium the above factors are ensured through aeration. The
goal is to ensure adequate supply of CO2 for organic algae, limiting pH change as a
balance between CO2 and HCO3 (Coutteau, 1996)[7] .At the same time, under the
effects of aeration, algae is limited to settling down and limiting temperature
stratification. However, the volume of culture that is mixed varies with the supply of

gas, while the strong or weak aeration depends on the type of algae at each stage of
algae growth.n the natural environment, under the action of wind and tide, stratified
water tides help algae provide enough nutrients and light for photosynthesis. In the
artificial culture environment, the factors are guaranteed. In aeration, aerobic culture is
very important because air is a carbon source for photosynthesis to provide CO2 as a
balance between CO2 and HCO3 to stabilize pH and aeration in the medium. Makes
nutrients and cells distribute evenly in the environment to reduce shading or
photosynthesis and to avoid temperature stratification in the out door culture system.
1.4.3.5 Diet composition
The macronutrients (C, N, P, K, S, C, Mg, Na, Ca and Fe) và Trace elements (Zn, Cu,
Ni)affect the growth of algae in which trace elements are required, Or stimulates the
action of many enzymes, promotes biosynthesis of chlorophyll and reduces the
chlorophyll breakdown by increasing the stability of the chlorophyll-linker complex
with proteins.Just like higher plants, phytoplankton should have high concentrations of
minerals such as N, P, S, Ca, Mg… for their simultaneous growth with other
substances at lower concentrations such as Cu, Zn, Mn …Normally, these
micronutrients are present in the natural environment in sufficient quantities for the
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normal growth of phytoplankton, But when other factors intervene, especially the
pollution caused by human activity at levels higher than the normal level, it will cause
the inhibitory effect on growth.
In the macronutrients, N and P are the most important. N plays an important role in the
composition and structure of proteins, a component of photosynthesis and enzyme
systems. N is a component of amino acids, nucleotides, hormones,….Carbon N
deficiency is not used for the synthesis of N from nitrate and ammonium salts. If
ammonium is the only nitrogen source for algae, the pH environment will be
significantly reduced, affecting their growth.
1.4.4 Application of microalgae

1.4.4.1 Application of microalgae in food technology
Microalgae are a rich source of carbohydrates, protein, enzymes and fiber. Besides,
many vitamins and minerals like vitamin A, C, B1, B2, B6, niacin, iodine, potassium,
iron, magnesium and calcium are abundantly found in microalgae. Being such a rich
source of essential nutrients, they are a major source of food, especially in Asian
countries like China, Japan and Korea. Green micro-algae have been used as nutritional
supplement or food source in Asiatic countries for hundreds of years. Nowadays, they
are consumed throughout the world for their nutritional value. [12]
Compared with traditional wastewater treatment methods, the use of algae for
wastewater treatment has the following important benefits:


Compared with sludge processing and other secondary processing processes,

using algae is a low cost method of removing phosphate compounds as well as nitrogen
compounds and pathogens..

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

Traditional wastewater treatment processes include energy-consuming aeration,

while the algae wastewater treatment produces the oxygen required by aerobic bacteria,
using Algae are an effective way to digest nutrients in wastewater and provide oxygen
from photosynthesis to aerobic bacteria.


In conventional wastewater treatment facilities, sludge often contains harmful

solid waste, which will eventually be disposed of in the landfill. Whereas the sewage
treatment facilities by algae, which produce sludge are algae biomass with high energy
content, can be further processed for the production of fertilizers or biofuels, Algae
also do not use chemicals and the whole process is quite simple, producing only
minimal amount of sludge.


Traditional wastewater treatment plants, which contribute significantly to the

formation of greenhouse gases and algal waste water treatment facilities, also emit CO2
but are much smaller in CO2. Algae consume, so that the whole process of algae
processing does not arise but also consume CO2.
1.4.4.2 Other environmentally friendly applications of microalgae
Algae can be used to seize fertilizers in agricultural wastewater, after collection,
algae are again used as fertilizer.
Because algae grow well under harsh conditions and do not require much
nutrients, they can be cultivated in areas that are not suitable for agricultural
production, so there is no competition for cultivated land. Otherwise, when cultivating
algae, one can use waste water without the use of agricultural water.
Unlike other crops, algae do not depend on seasonal conditions, algae can grow
well wherever the weather is warm and sunny..
Algae can also be cultivated in seawater or in the desert. Algae can also be
cultured in wastewater and water containing phosphates, nitrates, or other
contaminants.

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