The oxidation product (NO3-) of NO pollutant in flue gas used as a nitrogen source to improve microalgal biomass production and CO2fixation

Article abstract of DOI:10.1039/c4ra05491a

In order to eliminate the inhibition effect of the toxic nitric oxide (NO) in flue gas on microalgal growth and CO₂fixation, NO was converted by a wet UV/H₂O₂method to produce nitrate (NO₃^-), which then be used as a nitrogen source for microalgae to improve its growth. The growth ability and biomass compositions of the microalgae cultivated with the produced NO₃^-from NO gas were similar to those of the microalgae cultivated with equivalent moles of commercial NaNO₃. The NO₃^-concentration produced from NO increased with UV lamp power, H₂O₂, and NO concentrations, resulting in an improved microalgal growth. The concentration of NO₃^-from 500 ppm NO wet-oxidized by 6% (v/v) H₂O₂and 55 W UV light was up to 8.8 mM. When the produced nitrate was used as supplementary nitrogen source, the maximum growth productivity of Chlorella PY-ZU1 at 15% (v/v) CO₂reached 1.18 g L^-1per day (0.97 times higher than that cultivated with the standard medium). The peak fixation efficiency of 15% (v/v) CO₂was 69.6% (1.13 times higher than that cultivated with the standard medium). This journal is

Full text of DOI:10.1039/c4ra05491a

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ꢀ
The oxidation product (NO ) of NO pollutant in
3
flue gas used as a nitrogen source to improve
Cite this: RSC Adv., 2014, 4, 42147
microalgal biomass production and CO fixation†
2
Jun Cheng,* Yun Huang, Hongxiang Lu, Rui Huang, Junhu Zhou and Kefa Cen
In order to eliminate the inhibition effect of the toxic nitric oxide (NO) in flue gas on microalgal growth and
2
O
2
method to produce nitrate (NO ), which then be used
3ꢀ
CO
2
fixation, NO was converted by a wet UV/H
as a nitrogen source for microalgae to improve its growth. The growth ability and biomass compositions of
3ꢀ
the microalgae cultivated with the produced NO from NO gas were similar to those of the microalgae
3ꢀ
cultivated with equivalent moles of commercial NaNO
3
. The NO concentration produced from NO
increased with UV lamp power, H
2
O
2
, and NO concentrations, resulting in an improved microalgal
3ꢀ
2
2
growth. The concentration of NO from 500 ppm NO wet-oxidized by 6% (v/v) H
O
and 55 W UV light
Received 9th June 2014
Accepted 29th August 2014
was up to 8.8 mM. When the produced nitrate was used as supplementary nitrogen source, the
ꢀ1
2
maximum growth productivity of Chlorella PY-ZU1 at 15% (v/v) CO reached 1.18 g L per day (0.97
DOI: 10.1039/c4ra05491a
times higher than that cultivated with the standard medium). The peak fixation efficiency of 15% (v/v)
www.rsc.org/advances
CO
2
was 69.6% (1.13 times higher than that cultivated with the standard medium).
17–21
concentrations, on microalgae can be critical.
It was repor-
1
. Introduction
ted that NO in fossil fuel ue gas can be removed and used by
22
2 x 2
Pollutants (including CO , NO , SO
, and ne particles) are the microalgae, Dunaliella tertiolecta. However, for almost all
released into the atmosphere when fossil fuels are burned. As a of the other microalgal species, the presence of NO will lead to
result, environment and human health are seriously harmed. the formation of toxic nitrites or pH decrease in their culture,
17–21,23,24
For example, the greenhouse effect occurs because of excessive therefore, it will hinder their growth and CO
2
xation.
CO concentrations in the atmosphere, and this condition has
In recent years, some studies have focused on the alleviation
2
caused problems in terms of environmental and energy aspects. of the effect of NO on microalgae growth. These studies have
Thus, CO2 emissions should be reduced using efficient and shown that the growth and survival of Synechococcus sp. and
economical methods. For microalgae has a higher growth rate Chlorella sp. have improved against exposure to intermittent
(
1 to 3-fold increases in biomass per day), and can x CO
efficiency (2–10%) ten times greater than that of terrestrial sodium bicarbonate. The tolerance of Chlorella KR-1 to
plants (<1%), one of the efficient CO
reduction methods continuous NO exposure can be enhanced by maintaining the
involves the cultivation of microalgae in photobioreactors pH of the culture media at an adequate value (ꢁ7), which is
2
with NO by adding growth stimulators, such as triacontanol and
2
25
2
19
supplied with CO -enriched gas streams, such as those emitted achieved by adding an alkaline solution (NaOH). However, this
2
1–4
from coal-red power plant ue gases. In addition, the CO2 condition can be effective for some specic microalgae only. A
capture process using microalgae has the following advantages: previous study also showed that the presence of NO may lead to
(
i) co-producing high value materials based on biomass, such as the formation of toxic nitrites in microalgae culture, therefore,
5–10
24
biofuel and biogas;
(ii) being an environmental sustainable its inhibitory effect on microalgae growth was evaluated. It
ꢀ
method that can be connected to urban and industrial sewage must take some techniques making NO dissolve into less NO
2
ꢀ
11
cleaning.
Some high CO
but to more usable substances, such as NO
3
.
Advanced oxidation process (AOP) can produce free radicals
2
-tolerant microalgae species have been iso-
However the inhibitory effects of toxic with strong oxidation, such as hydroxyl free radicals (cOH). By a
compounds, such as NO and SO , in addition to high CO
wet AOP using hydrogen peroxide solution with ultraviolet lamp
12–16
lated out.
x
2
2
(
UV/H
2
O
2
), the toxic NO was completely converted into valuable
ꢀ
26–29
NO
3
without generating any other byproduct.
The wet AOP
State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou
(
UV/H O ) has been used in coal-red power plants to simul-
2 2
3
8
†
1
10027, China. E-mail: juncheng@zju.edu.cn; Fax: +86 571 87951616; Tel: +86 571
taneously remove NO, SO and Hg pollutants in ue gas. But
how to deal with and reutilize the large amount of byproducts
(
2
7952889
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra05491a
2
+
nitrate, sulfate and Hg ) is a big problem. Whether the
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3ꢀ
2
oxidation byproduct (NO ) derived from the wet AOP can be following: (1) 3000 ppm of NO and pure N
(used as balance
consumed and used by microalgae has not been reported in gas); (2) mass ow meter; (3) a bubble column reactor (height of
literatures till now. Whether the different oxidation conditions 450 mm and inner diameter of 75 mm); (4) cooling water cycle
(
UV lamp power, H O and NO concentrations) in wet AOP (UV/ system; (5) sand chip gas distributor (outer diameter of 45 mm,
2 2
H
2 2
O ) have important effects on microalgae growth has not height of 30 mm, and average pore size of 0.105 mm to 0.18
been claried. It was rst proposed to reutilize the oxidation mm); (6) UV lamps (UV lamp powers were changed by replacing
ꢀ
byproduct (NO
3
) derived from the wet AOP by microalgae as a and using three sets of UV lamps with different powers (36 W,
supplementary nitrogen source in this paper. This novel process 55 W, and 75 W, Haining Light Factory). All the lamps were of
not only eliminated the effect of toxic NO on microalgal growth the same model (L-L) and of the same wavelength of 253.7 nm);
but also improved microalgal biomass productivity and CO2 and (7) effluent NO scrubber (the residual NO in the mixed gas

xation. The effects of different UV/H O conditions on micro- was further scrubbed using 400 mL mixed solution containing
2 2
ꢀ1
ꢀ1
algal growth and CO xation efficiency were investigated.
KMnO4 (0.05 mol L ) and NaOH (0.1 mol L ; Sinopharm
Chemical Reagent, China) to avoid environmental pollution).
2
2 2
The prepared H O solution with the required concentration
2
. Materials and methods
(
1%, 3%, 6%, and 9%) was placed in the bubble column reactor.
2.1 Strains and media
ꢂ
Temperature was maintained at 25 C by recycling the cooling
Chlorella PY-ZU1, a highly CO -tolerant and fast-growing water. NO concentration (75, 150, 300, and 500 ppm, balanced
2
microalgal species, was used in this study. This strain was with N
obtained by g irradiation and high concentrations of CO
starCS200, China). The NO gas passed uniformly across the
domesticated from Chlorella pyrenoidosa. The cells were sand chip gas distributor into the H solution at a rate of 600
maintained in Brostol's solution (also known as soil extract, mL min . Aer the UV lamp was turned on, H was released,
O, forming hydroxyl free radicals (cOH). These free radicals exhibit
O, 0.175 g of an extremely strong oxidation ability that can convert NO into
KH PO , 0.025 g of NaCl, 40 mL of soil extract, 0.005 g of HNO without generating any other byproduct via the following
) was regulated using a mass ow meter (Seven-
2
2
15
O
2 2
ꢀ1
2 2
O
15,30
SE),
containing 0.25 g of NaNO
3
2 4 2
, 0.075 g of K HPO $3H
0.075 g of MgSO
4
$7H O, 0.025 g of CaCl
2
2
$2H
2
2
4
3
26,31
FeCl $6H O, 1 mL of Fe–EDTA, and 1 mL of A5 solution in 958 reactions (2)–(3).
3
2
mL of de-ionized water.
H O + hv / 2cOH
(1)
(2)
(3)
2
2
2
.2 System design by which the oxidation product of NO in
ue gas with UV/H is used as a nitrogen source for
microalgal growth
Because of its strong oxidation ability and environmentally
friendly characteristics, UV/H AOP has a wide range of
NO + cOH / HNO
2
, HNO
2
+ cOH / HNO
3
+ cH

2 2
O
NO + cOH / cH, NO + cOH / HNO
2
3
2
O
2
The reaction solution was collected aer 6 h and the
studies in the gas purication eld. Experimental system in remaining H
2
O
2
was removed by ultrasonic wave (SK5210HP,
ꢀ
which the NO in ue gas was converted to NO
3
as nitrogen China). The solution was then used to make the medium for
source for microalgal growth was performed in a bubble Chlorella PY-ZU1 by adding the same quantities of nutrients as
column reactor (Fig. 1). The proposed system comprised the those present in the SE medium. The initial pH of the medium
3ꢀ
Fig. 1 Experimental system in which the NO in flue gas was converted to NO as nitrogen source for microalgal growth.
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was adjusted to 6.5 with 0.1 M NaOH. The SE medium was used was determined using the anthrone method (with glucose as the
8
as the control condition. For the nal AOP runs, NO in the standard). The lipid of the biomass was extracted as described
6
reactor was 500 ppm, H O concentration was 6% (v/v), and UV in a previous study. Fatty acid compositions were determined
2
2
power was 55 W. The medium prepared with the 15 h oxidation by gas chromatography (Agilent 7890A, USA).
2
solution was used as the CO xation medium and labeled
as SE#.
2.5 Calculation of NO oxidation efficiency and residual NO
concentration
3ꢀ
ꢀ
2
.3 NO produced from NO oxidation used as supplement
The NO3 concentrations in the collected solution as prepared
nitrogen source to improve Chlorella PY-ZU1 growth and CO2
xation
in Section 2.2 were analyzed with ion chromatography (MagIC,

Metrohm, Switzerland). The NO oxidation efficiency (mean
ꢀ
value) was calculated according to NO
eqn (6):
3
in the solution using
All of the cultivation experiments were performed in an articial
ꢂ
greenhouse at 27 C. Approximately 270 mL SE medium was
inoculated with 30 mL of Chlorella PY-ZU1 pre-culture in the
M
ꢀ
ꢃ V
NOin
ꢀ
NO3
NO oxidation efficiency ¼
P
(6)
bioreactor (BR, 160 mm ꢃ F56 mm, 300 mL of working
M
ꢀ
volume). For the verication experiments of using NO
3
where MNO3
ꢀ
is the molar concentration of NO in volume V (L)
3
(
derived from NO oxidation by UV/H
2
O
2
) as a nitrogen source
P
ꢀ
2
ꢀ1
of the oxidized solution and
MNOin is the total number of
moles of NO owing into the oxidation reactor. In this study,
for Chlorella PY-ZU1, continuous light of 52 mmol m
s
at the
surface of BR was supplied by four cool white lights combined
ꢀ
NO
3
was the only product of NO oxidation; thus, NO oxidation
with two plant lights (Philips, TLD 36W) that were xed above
ꢀ
ꢀ
2
efficiency also corresponded to NO
3
production efficiency. The
remaining NO concentration (mean value) was calculated using
eqn (7):
the BR. For the other experiments in this study, 68 mmol m
s
3
ꢀ
1
of light was supplied by six cool white lights (Philips, TLD
6W) at the surface of BR. The mixed gas of 15% (v/v) CO
2
containing different NO concentrations was bubbled at a rate of
CNOout ¼ CNOin ꢃ (1 ꢀ NO oxidation efficiency
(7)
ꢀ
1
30 mL min through a long steel pipe (180 mm ꢃ F3 mm). The
NO concentrations were controlled at 0, 75, 150, 300, and 500
ppm by a mass ow meter (Sevenstar CS200, China).
Chlorella PY-ZU1 was cultured in SE# and aerated continu-
30
3. Results and discussion
ously with 15% (v/v) CO in nine-stage sequential bioreactors
2
ꢀ
to investigate the effect of NO3 produced from NO on CO2 3.1 Effects of NO on the growth of Chlorella PY-ZU1

xation. For comparison, Chlorella PY-ZU1 was cultured with SE
medium and aerated continuously with 15% (v/v) CO or with
5% (v/v) CO gas containing 500 ppm NO. The inuent and
effluent CO concentrations were monitored online by a CO
analyzer (Servomex4100, UK). CO xation efficiency was
calculated according to the carbon dioxide difference between
The effects of NO concentrations on the growth of Chlorella PY-
ZU1 and the pH of the culture were examined in the BR (Fig. 2).
Chlorella PY-ZU1 showed a higher tolerance to NO than other
2
1
2
2
2
NO-tolerant algal strains, which could not grow under 150 ppm
2
20
2
NO. When aerated with 15% CO gas containing 150 ppm NO,
biomass concentration of Chlorella PY-ZU1 decreased aer 5
3
0
inuent and effluent as described in a previous study.
days of cultivation, and the pH of culture decreased to 6.27. The
ꢀ
ꢁ
ꢀ1
total output CO2
total input CO2
maximum biomass concentration was 2.03 g L and decreased
by 24.3% to that of microalgae cultivated without NO aeration
CO
2
fixation efficiency ¼ 1 ꢀ
ꢃ 100% (4)
ꢀ
1
(
2.68 g L ). When NO concentration was further increased to
where the total input CO2 ¼ inuent CO concentration ꢃ
2
500 ppm, microalgae could grow but with a 50.7% decrease in
inuent ow rate, and the total output CO
concentration ꢃ effluent ow rate.
2
¼ effluent CO
2
the maximum biomass concentration to that of microalgae
cultivated without NO. The decrease in biomass yield was due to
19,20
pH decrease in the culture caused by NO aeration.
The pH of
2
.4 Analysis of microalgal productivity and biomass
the culture decreased with the increasing cultivation time.
Once the pH of the culture decreased beyond the adequate
range (6.5–7.5 for Chlorella), the microalgae growth was
inhibited. This was why the biomass concentration of Chlorella
PY-ZU1 decreased aer 5 days cultivation with >150 ppm of NO.
However, Chlorella PY-ZU1 showed a higher tolerance to NO
compositions
During cultivation, 10 mL of the samples was dewatered by
centrifugation (Beckman Avanti J26-XP, USA) at 8500 rpm for 10
min and dried at 70 C for 24 h to obtain the weight of the dried
biomass. Biomass concentration (g L ) was calculated from the
microalgal dry weight produced per liter. Growth productivity
ꢂ
ꢀ1
20
than Chlorella KR-1, whose growth was completely suppressed
ꢀ1
when aerated with 15% CO gas containing 300 ppm NO. This
(AGP, g L per day) was calculated using eqn (5):
2
veried that microalgae tolerance to NO depends on the
M
1
1
ꢀ M
2
19
AGP ¼
(5) microalgae species but with a decrease in biomass productivity.
t
ꢀ t
2
Some methods were used to alleviate microalgae growth
where M
biomass concentration at time t
1
is the biomass concentration at time t
1
and M
2
is the inhibition caused by NO, such as controlling culture pH and
25
2
. Total carbohydrate quantity adding some growth stimulators to culture.
Although
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3ꢀ
Fig. 3 Microalgal growth with NO derived from NO oxidation and
commercial NaNO
3
.
Fig. 2 Effects of NO on Chlorella PY-ZU1 growth and pH of the
cultures.
3ꢀ
with H
2
O
2
digestion. Aer 15 h, NO concentration in the
ꢀ
solution reached to 8.8 mM. The total NO
3
concentration in
the medium prepared with this oxidation solution was 11.8 mM,
ꢀ
which could satisfy the NO
3
requirement of Chlorella PY-ZU1
Dunaliella tertiolecta could use NO dissolved in microalgae
culture as a nitrogen source, NO absorbed in the medium could
30
under 15% CO
2
.
Chlorella PY-ZU1 cultivated in the SE#
ꢀ2 ꢀ1
medium under 52 mmol m
s
of continuous light and 15%
ꢀ
ꢀ
22
be converted to NO
2
and then oxidized to NO
3
.
This
CO2 for 11 d exhibited a peak growth productivity and
oxidation process was extremely slow. The improvement effect
produced from NO on Chlorella PY-ZU1 did not
overcome the toxic effect of NO. Thus, a much faster NO
ꢀ1
maximum biomass concentration of 0.76 g L per day and 5.48
ꢀ
of little NO
3
ꢀ1
g L , respectively. These values were almost equal to those of
ꢀ1
ꢀ1
Chlorella PY-ZU1 (0.73 g L per day and 5.31 g L , respectively)
cultivated in the SE medium with 11.8 mM commercial NaNO
oxidation method will be needed.
3
.
In addition, the growth curve of Chlorella PY-ZU1 cultivated
3ꢀ
ꢀ
3
.2 Conrmation of using NO (derived from NO oxidation
with NO
3
produced from NO is consistent with that of the
[Fig. 3(b)].
by UV/H
2
O
2
) as a nitrogen source for Chlorella PY-ZU1
Chlorella PY-ZU1 cultivated with commercial NaNO
3
The total carbohydrate quantity of the dried biomass of
Chlorella PY-ZU1 cultivated with NO3 produced from NO
41.57%, w/w biomass) was almost equal to that of the Chlorella
During UV/H
2
O
2
AOP process, the remaining H concentra-
2 2
O
ꢀ
tion in the solution was decreased with the oxidation time,
resulting in a decrease in NO
process of 500 ppm NO oxidized by 55 W UV/6% H O , the NO
3
production rate was stabilized at 0.427 mM h and 53% of NO
ꢀ
26
(
3
production efficiency. In the
ꢀ
PY-ZU1 cultivated with commercial NaNO (43.57%; data not
3
2
2
ꢀ
1
shown). The lipid contents in the two biomasses were 18.11%
and 17.92%, respectively. The biodiesel compositions from
these two kinds of biomasses were analyzed (Table 1). The fatty
ꢀ
was converted into NO
3
in the rst 6 h [Fig. 3(a)]. In the next
ꢀ
6
h, the NO
3
production rate gradually decreased to 10.65%
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acid proles indicated the presence of C16: 0, C16: 1, C16: 2, Therefore, a further increase in UV lamp power only has a little
ꢀ
C16: 3, C18: 0, C18: 1, C18: 2, and C18: 3. Palmitic acid, oleic impact on NO3 production and thus a little effect on the
acid, linoleic acid, and linolenic acid were considered as the growth of Chlorella PY-ZU1.
main components, which ranged from 12% to 24% of the total
H
2
O
2
+ cOH / HO
2
c + H
2
O
(8)
(9)
fatty acids. These results indicated that oxidation product of NO
derived from NO in ue gas by UV/H ) can be used as a
nitrogen source for Chlorella PY-ZU1 instead of the commercial
NaNO
(
2 2
O
2 2
cOH + cOH / H O
3
.
3ꢀ
Similarly, the NO production efficiency derived from NO
3
.3 Effects of different NO conversion conditions on the
(300 ppm) by UV/H
56.60% to 79.33% and the derived NO
2
O
2
(55 W of UV for 6 h) increased from
ꢀ
growth of Chlorella PY-ZU1
3
concentration
3ꢀ
2 2
increased from 2.70 mM to 3.79 mM [Fig. 4(c)] when H O
concentration increased from 3% to 6%. This nding resulted
The NO concentration produced from NO increased with
2 2
increase of lamp power, H O , and NO concentration. As a
result, microalgae growth was improved. Under UV light irra-
in an evident increase in the maximum biomass concentration
ꢀ1
ꢀ1
of microalgae from 3.43 g L to 3.85 g L [Fig. 4(d)]. However,
a further increase in H concentration from 6% to 9% did not
increase the maximum biomass concentration (stabilized at
diation, H O can release cOH free radicals. cOH free radicals
2
2
ꢀ
26,29
2 2
O
exhibit strong oxidation ability to convert NO to NO
high concentration of produced NO
biomass yield during microalgae cultivation.
.
A
3
ꢀ
3
in AOPs results in a high
ꢀ
1
30,32
3.91 g L ). This is mainly because appropriate H
tration may cause a reaction such as eqn (1) in the solution.
2 2
Therefore, within a certain range, the increase in H O
2 2
O concen-
ꢀ
NO
% H
Chlorella PY-ZU1 under 15% CO
increased (Fig. 4). The maximum biomass concentration of
3
, the oxidation product derived from 300 ppm NO with
for 6 h, could increase the biomass productivity of
as UV lamp power was
6
2 2
O
ꢀ
26
concentration can improve the yield of NO3
increased the biomass growth of Chlorella PY-ZU1. Once H O2
,
and then
2
2
5
2
ꢀ1
ꢀ1 concentration exceeding a certain value, any further increase
microalgae was evidently increased from 3.45 g L to 3.85 g L
Fig. 4(b)] as UV lamp power increased from 36 W to 55 W.
However, with further increasing the UV lamp power from 55 to
5 W, the growth rate of maximum biomass concentration
gradually decreased. Two main reasons could explain the
results. On one hand, under UV light irradiation, H can
may cause side reactions as eqn (8) and (9) which lead to a
[
27
decrease in the oxidation ability of free radicals. Therefore,
further increase in H
2
O
2
concentration only had little effect on
7
ꢀ
the yield of NO
3
and a slight impact on biomass production of
Chlorella PY-ZU1.
2 2
O
ꢀ
NO3 production efficiency decreased from 91.26% to
26
release cOH free radicals by eqn (1) reaction. The cOH free
53.00% [Fig. 5(a)] as NO concentration increased from 75 ppm
radicals have extremely strong oxidation ability to convert NO
ꢀ
to 500 ppm because of the limitation of NO residence time and
into NO3 according to eqn (2) and (3). Therefore, compared
26,31
ꢀ
cOH free radicals.
However, the derived NO
3
concentration
with the reaction system without UV light, addition of UV light
can greatly enhance NO conversion into NO
increasing UV lamp power can improve the energy density per
unit in solution, thus produce more effective photons and cOH
free radicals. Therefore, the NO
an increase in UV lamp power.
biomass concentration of Chlorella PY-ZU1 was increased. On
ꢀ
from NO increased from 1.09 mM to 4.22 mM; thus, the
3
. Furthermore,
maximum biomass concentration of Chlorella PY-ZU1 increased
ꢀ1
ꢀ1
from 3.05 g L to 4.15 g L [Fig. 5(b)].
ꢀ
3
produced rate increased with
Consequently, the maximum
3ꢀ
xation by Chlorella PY-ZU1 cultivated with NO
2
2
6,31
3.4 CO
derived from NO oxidation
the other hand, once the power of UV lamp exceeds a certain When 500 ppm NO was directly aerated into microalgal
value, some side reactions, such as eqn (8) and (9), may occur in culture, biomass production was decreased by 50.7% to that
27
ꢀ1
the solution, leading to a great loss of cOH free radicals.
of 2.68 g L of microalgae cultivated without aerated NO
3ꢀ
Table 1 Compositions of lipids in microalgae cultivated with commercial NaNO
3
and NO derived from NO oxidation
3ꢀ
NO derived
Conditions
Commercial NaNO
3
from NO oxidation
Lipid content (% of dry biomass)
17.92
18.11
Lipids composition (% of total lipid)
C16: 0
C16: 3
C18: 0
C18: 1
C18: 2
C18: 3
Others (C16–C24)
Total
23.85 ꢄ 0.29
7.02 ꢄ 0.34
3.15 ꢄ 0.26
15.88 ꢄ 0.75
15.52 ꢄ 0.83
12.77 ꢄ 0.34
21.8 ꢄ 0.63
100
22.37 ꢄ 0.10
6.80 ꢄ 0.29
3.17 ꢄ 0.01
14.82 ꢄ 0.76
14.76 ꢄ 0.57
12.65 ꢄ 0.46
25.4 ꢄ 0.45
100
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2 2
3ꢀ
Fig. 4 Effects of UV lamp power and H O concentration on NO production and microalgal growth.
(
Fig. 2(a)). By contrast, biomass production increased when appropriate CO concentration for the mutant Chlorella PY-ZU1
2
15,30
5
00 ppm NO was converted into nitrate by UV/H
2
O
2
as a was up to 12% (v/v).
CO xation experiments were performed in a nine-stage
. Overall, the maximum biomass sequential bioreactor described in the previous studies.
concentration and peak growth productivity of Chlorella PY- The sequential bioreactor was lled with SE# medium and
supplement nitrogen source for microalgae under continuous
2
ꢀ
2
ꢀ1
15,30
light of 68 mmol m
s
ꢀ1
ꢀ1
ZU1 were 5.40 g L and 1.18 g L per day. These depen- operated for 2 days without microalgae to determine the abiotic
dent parameters increased by 107.7% and 96.7%, respectively, removal of CO . Hence, the abiotic removal of CO should be
2
2
compared with those of the microalgae cultured in the SE eliminated in the calculation of CO2 xation efficiency by
ꢀ
1
ꢀ1
medium (2.68 g L and 0.60 g L
per day, respectively) microalgae.
In the nine-stage sequential bioreactor, the CO
Although Chlorella can tolerate up to 50% concentration of efficiency of the microalgae cultivated at 500 ppm NO was
, the biomass concentration does not reach a higher value lower than that of the microalgae cultivated without NO
(
Fig. 6).
2
xation
CO
(
2
ꢀ1
33
almost <1 g L ). That makes CO
difficult. The appropriate concentration of CO
2
mitigation by microalgae (Fig. 6). The peak CO
2
xation efficiency of 26.2% was
xation efficiency
2
for microalgae decreased by 19.9%, whereas the mean CO
2
growth is always below 10%. Anjos et al. optimized CO -miti- of 17.3% was decreased by 33.2%. However, when 500 ppm
2
ꢀ
gation by Chlorella vulgaris P12 under different CO concen- NO was converted into NO3 by UV/H O as a supplement
2
2
2
trations (ranging from 2% to 10%). Results showed that 6.5% nitrogen source for Chlorella PY-ZU1, CO xation efficiency
2
3
4
was the most appropriate CO
When Chlorella pyrenoidosa was cultivated with SE medium, medium without NO. The peak and mean CO
experiments also showed that 6% was the most appropriate CO ciency were 69.6% and 52.3%, respectively, increased by
concentration. In order to increase the ability of Chlorella to 112.8% and 101.9% compared with those of the microalgae
grow under higher CO concentrations, Chlorella pyrenoidosa cultivated in the SE medium without aerated NO (32.7% of
2
concentration for Chlorella P12.
was higher than that of microalgae cultured in the SE
2
xation effi-
2
15
2
was mutated by nuclear irradiation and domesticated with high the peak CO xation efficiency and 25.9% of the mean CO2
2
concentrations of CO2 in our previous study. The most xation efficiency).
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Fig. 6 CO
vated with NO
2
fixation and biomass growth of Chlorella PY-ZU1 culti-
ꢀ
3
derived from NO oxidation.
4. Conclusions
ꢀ
NO pollutant in ue gas could be converted into useful NO3 by
ꢀ
UV/H O oxidation. The NO product can be used as a nitrogen
2
2
3
source to improve microalgal growth and CO
2
xation ability.
ꢀ
When NO
3
derived from 500 ppm NO oxidation was used as a
xation
efficiency of Chlorella PY-ZU1 were increased by 96.67% (1.18 g
nitrogen source, the peak growth productivity and CO
2
ꢀ
1
L
per day) and 112.8% (69.6%), respectively. This nding
provided information regarding environmental and economical
benets to culture microalgae with waste carbon and nitrogen
sources (exhaust CO gas and NO oxidation products) in ue
2
gas.
Acknowledgements
3ꢀ
This study was supported by the National Natural Science
Foundation of China (51176163, 51476141), National High
Technology R&D Program of China (2012AA050101), Interna-
Fig. 5 Effects of NO concentration on NO production and micro-
algal growth.
tional Sci.
2012DFG61770), Zhejiang Provincial Natural Science Founda-
xation tion of China (LR14E060002), Program for New Century Excel-
2
&
Tech. Cooperation Program of China
(
Ramanan et al. has demonstrated an increase in CO
efficiency by maneuvering chemically aided biological seques- lent Talents in University (NCET-11-0446), Specialized Research
tration of CO . Chlorella sp. showed the peak CO xation effi- Fund for the Doctoral Program of Higher Education
2
2
35
ciency of 46% at input CO concentration of 10%. Chiu et al. (20110101110021), Science and Technology Project of Guangxi
2
replaced a half of the culture broth with fresh medium every day Province (1346011-1).
to enhance growth rate of Chlorella sp. and CO
CO xation efficiency of Chlorella sp. was 16% at input CO
concentration of 15%. In this study, the produced NO
2
reduction. The
2
2
36
ꢀ
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