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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 11, November 2013)
Eutrophication Treatment by Algae Farming
Ranjini Menon1, Prof. Nita Mehta2
Department of Chemical Engineering, Thadomal Shahani Engineering College
At this point, oxygen-demanding bacteria take over the
ecosystem, decomposing the algae and using up dissolved
oxygen in the process. These bacteria increase the
biological oxygen demand (BOD) of the ecosystem. BOD
is the amount of oxygen required for the decomposition of
organic compounds by microorganisms in a given amount
of water and measured in milligrams of oxygen consumed
per litre of water.
Biological oxygen demand is important because it
affects the amount of dissolved oxygen available to all
species in an aquatic ecosystem. A higher BOD indicates a
lower level of dissolved oxygen. This lower concentration
of oxygen causes many fish to suffocate, and as they die,
the number of oxygen-demanding decomposers increases
even more.
Abstract-- Eutrophication caused by the imbalance of
chemicals, from disposed wastes in lakes and ponds, along
with the presence of sunlight gives a boost to the growth of
microalgae in the lake. Algae farming can be carried out by
creating open ponds or photo bioreactor (PBR). On further
treatment, the harvested algae can be converted into biodiesel.
Such a productive result to waste water treatment can be
carried out at varied locations where the optimum operating
conditions for micro algae farming are satisfied.
I. INTRODUCTION
The rapid accumulation of wastes into a water body
causes ecological imbalances or notable changes in its
nutrient level which in turn leads to a phenomenon known
as ‘Eutrophication’. Eutrophication is the natural aging
process of a body of water such as a bay or lake.
The word ‘eutrophication’ has its root in two Greek
words: ‘eu’ which means ‘well’ and ‘trope’ which means
‘nourishment’.
This process results from the increase of nutrients within
the body of water which, in turn, create plant growth. The
plants die more quickly than they can be decomposed. This
dead plant matter builds up and together with sediment
entering the water, fills in the bed of the bay or lake making
it shallower. Normally this process takes thousands of
years.[1]
III. ALGAE CULTURE
Algae are a group of plant like organisms that live in
water and can make their own food through photosynthesis
(using sunlight to make food from simple chemicals).
When additional phosphates are added to a body of water,
the plants begin to grow explosively and algae takes off or
"blooms."
Many of the waste products often contain
nitrates and phosphates. Both nitrates and phosphates are
absorbed by plants and are needed for growth. However,
the human use of detergents and chemical fertilizers has
greatly increased the amount of nitrates and phosphates that
are washed into our lakes and ponds. When this occurs in a
sufficient quantity, they act like fertilizer for plants and
algae and speed up their rate of growth.
II. T YPES OF EUTROPHICATION
Eutrophication is of two main types, cultural and
artificial eutrophication.
Cultural eutrophication is an unnatural speeding up of
this process because of man's addition of phosphates,
nitrogen, and sediment to the water.
Artificial eutrophication involves the artificial
enrichment of the system and harvest of the nutrients as a
crop at the desired trophic level. [2]
The ecological imbalance formed in the water body due
to the pollution caused leads to an algal bloom over the
surface of the water body. The algae bloom occurs as the
algae accumulates into dense, visible patches near the
surface of the water, prohibiting light from penetrating
deeper areas of lake or stream. Some fish are unable to
survive without this light, but for them an even more
serious problem arises when the algae begin to die.
Pre Treatment of Waste Water
The waste water cannot feed algae directly and must first
be processed by bacteria, through anaerobic digestion. If
waste water is not processed before it reaches the algae, it
will contaminate the algae in the reactor, and at the very
least, kill much of the desired algae strain.
In biogas facilities, organic waste is often converted to a
mixture of carbon dioxide, methane, and organic fertilizer.
Organic fertilizer that comes out of the digester is liquid,
and nearly suitable for algae growth, but it must first be
cleaned and sterilized.
551
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 11, November 2013)
The utilization of wastewater and ocean water instead of
freshwater is strongly advocated due to the continuing
depletion of freshwater resources. However, heavy metals,
trace metals, and other contaminants in wastewater can
decrease the ability of cells to produce lipids
biosynthetically and also impact various other workings in
the machinery of cells. Agricultural-grade fertilizer is the
preferred source of nutrients, but heavy metals are again a
problem, especially for strains of algae that are susceptible
to these metals. In open pond systems the use of strains of
algae that can deal with high concentrations of heavy
metals could prevent other organisms from infesting these
systems. It has even been observed that strains of algae can
remove over 90% of nickel and zinc from industrial
wastewater in relatively short periods of time.[3]
Chlorella sp. has been studied for use in CO2
sequestration. It was reported that Chlorella sp. can be
grown under 20% CO2 conditions. The species has been
used as a health food. CO2 tolerance of Dunaliella sp. also
has been examined and the species has been used in the
industrial production of b-carotene
Further potential applications of micro algal products are
the utilization of secondary metabolite, fertilizer and
biofuel production. In addition to CO2 sequestration,
another potential strategy to offset operational costs, is to
develop multi-functional systems such as waste treatment
and aquaculture farms, functions. Since economic
feasibility is one of the major issues to realize biological
mitigation systems, seeking additional value for the system
is an important criterion. [6]
Types of Algae used for Algae Farming
The main branches/lines of algae are:
IV. METHODS OF ALGAE C ULTURE
Algae are cultured by mainly two methods i.e. either
under natural conditions or in an artificially induced
environment. [4]The two methodology of algae culture are:
(i) Open Ponds
(ii) Photo Bio-Reactor (PBR)
 Chromista :
This line includes the brown algae, golden brown algae,
and diatoms. The plastids in these algae contain
Chlorophylls A and C. These form one of the most
prominent lines of algae.
Open Ponds:
Algae are grown or cultivated in open ponds such as
raceway – type and lakes. Raceway ponds may be less
expensive. Raceway-type ponds and lakes are open to the
elements. Open ponds are highly vulnerable to
contamination by other microorganisms, such as other algal
species or bacteria. Thus cultivators usually choose closed
systems for monocultures. Open systems also do not offer
control over temperature and lighting. The growing season
is largely dependent on location and, aside from tropical
areas, is limited to the warmer months.
Open pond systems are cheaper to construct, at the
minimum requiring only a trench or pond. Large ponds
have the largest production capacities relative to other
systems of comparable cost. Also, open pond cultivation
can exploit unusual conditions that suit only specific algae.
For instance, Spirulina sp. thrives in water with a high
concentration of sodium bicarbonate and Dunaliella salina
grow in extremely salty water. Open culture can also work
if there is a system of harvesting only the desired algae, or
if the ponds are frequently re-inoculated before invasive
organisms can multiply significantly.
 The Red Line:
This is an early branch of marine algae containing just
Chlorophyll A. Red algae can often be seen coating wave
washed rocks. A characteristic of red algae is that their
plastids contain only one type of chlorophyll —
chlorophyll a. This is different from green algae and plants
which have both chlorophyll a and b.
 Dinoflagellates :
These evolved on a separate line that includes the
ciliated protists.
 The Euglenids:
This independent line of single celled organisms that
include both photosynthetic and non-photosynthetic species
 The Green Line:
They are related to plants. Like plants and green algae,
they have chlorophylls A and B.
Commercial Value of Algae
Some microalgae species, such as Chlorella, Spirulina
and Dunaliella have commercial values. It is expected that
commercial profit from biomass production will offset
overall operational costs for CO2 sequestration.
552
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 11, November 2013)
This allows the reactor to operate for long periods. An
advantage is that an alga that grows in the log phase is
generally of higher nutrient content than old senescent
algae. Maximum productivity occurs when the exchange
rate (time to exchange one volume of liquid) is equal to the
doubling time (in mass or volume) of the algae.
Different types of PBRs include [4]:



Fig. 1 Schematic representation of Open Pond Systems [4]
Enclosing a pond with a transparent or translucent
barrier effectively turns it into a greenhouse. This solves
many of the problems associated with an open system. It
allows more species to be grown; it allows the species that
are being grown to stay dominant; and it extends the
growing season – and if heated the pond can produce year
round.
Tanks
Polyethylene sleeves or bags
Glass or plastic tubes
Optimum Conditions for Culturing Micro-Algae
Parameters
Range
Optima
16-27
18-24
12-40
20-24
Temperature
(°C)
Photo Bio-Reactor (PBR):
A PBR is a bioreactor which incorporates a light source
to carry out the cultivation.
Virtually any translucent container could be called a
PBR; however the term is more commonly used to define a
closed system, as opposed to an open tank or pond. Since
PBR systems are closed, the cultivator must provide all
nutrients, including CO2.
Salinity
(g.l-1)
1,000-10,000
Light
intensity (vol.& density
(lux)
2,500
dependent)
5,000
Photoperiod
16:8
(light
(minimum)
:
dark,
hour)
pH
-
24:0 (maximum)
7-9
8.2-8.7
Factors Determining Growth Rate of Algae
i. Light - Light is needed for the photosynthesis process
ii. Temperature: There is an ideal temperature range that
is required for algae to grow
iii. Medium/Nutrients - Composition of the water is an
important consideration (including salinity)
iv. pH - Algae typically need a pH between 7 and 9 to
have an optimum growth rate
v. Algae Type - Different types of algae have different
growth rates
vi. Aeration - The algae need to have contact with air, for
its CO2 requirements
Fig. 2 Schematic representation of the algae production in a tubular
photo bioreactor [4]
A PBR can operate in batch mode, which involves
restocking the reactor after each harvest, but it is also
possible to grow and harvest continuously. Continuous
operation requires precise control of all elements to prevent
immediate collapse. The grower provides sterilized water,
nutrients, air, and carbon dioxide at the correct rates.
553
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 11, November 2013)
vii.
viii.
Mixing - Mixing prevents sedimentation of algae and
makes sure all cells are equally exposed to light
Photoperiod: Light & dark cycles [3][4]
The algae also have to be concentrated 30-fold. The
harvest of the algae must be done with minimal or no
chemical inputs to limit contaminants in the fuel
produced. An efficient, low-cost harvest technology is
needed.
V. H ARVESTING O F ALGAE
Algae can be harvested using micro-screens,
by centrifugation, by flocculation and by froth flotation.
Interrupting the carbon dioxide supply can cause algae to
flocculate on its own, which is called Auto Flocculation.
Water that is more brackish or saline requires larger
amounts of flocculants. Flocculation is often too expensive
for large operations. Alum and ferric chloride are some of
the chemical flocculants used for this purpose.
In froth flotation, the cultivator aerates the water into
froth, and then skims the algae from the top.
Ultrasound and other harvesting methods are currently
under development. [5]
Harvesting microalgae poses one of the big
technological challenges. After detailed research it has
been calculated that 20% to 40% of pond biomass must be
harvested daily.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
554
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J. Glenn Songer, Rodney F. Smith and N.M.Treiff, Sewage
Treatment by Controlled Eutrophication, Microbial Bacterial Study,
1974
R.A. Andersen, Culturing of Microalgae in Outdoor Ponds, Algal
Culturing Techniques, London, 2005
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Chauhan & R. Abitha, Sustainability of Large-Scale Algal Biofuel
Production in India , Journal of the Indian Institute of Science, 2012
Eiichi Ono, Joel L. Cuello, Selection of Optimal Micro Algae
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2003