Accepted Manuscript Review Cultivation of Microalgal Chlorella for Biomass and Lipid Production Using Wastewater as Nutrient Resource Sheng-Yi Chiu, Chien-Ya Kao, Tsai-Yu Chen, Yu-Bin Chang, Chiu-Mei Kuo, Chih-Sheng Lin PII: DOI: Reference:
S0960-8524(14)01692-7 http://dx.doi.org/10.1016/j.biortech.2014.11.080 BITE 14286
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
30 August 2014 7 November 2014 9 November 2014
Please cite this article as: Chiu, S-Y., Kao, C-Y., Chen, T-Y., Chang, Y-B., Kuo, C-M., Lin, C-S., Cultivation of Microalgal Chlorella for Biomass and Lipid Production Using Wastewater as Nutrient Resource, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.11.080
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Cultivation of Microalgal Chlorella for Biomass and Lipid Production Using Wastewater as Nutrient Resource
Sheng-Yi Chiu a,b,, Chien-Ya Kaoa,c,, Tsai-Yu Chena, Yu-Bin Changa, Chiu-Mei Kuoa, Chih-Sheng Lina,* a
Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan
b
Water Technology Division, Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsinchu, Taiwan
c
Agricultural Technology Research Institute, Hsinchu, Taiwan These authors equally contributed to this work
* Author for correspondence: Chih-Sheng Lin, Ph.D. Department of Biological Science and Technology, National Chiao Tung University, No.75 Po-Ai Street, Hsinchu 300, Taiwan Tel: 886-3-5131338 E-mail:
[email protected] 1
Abstract
2
Using wastewater for microalgal cultures is beneficial for minimizing the use of
3
freshwater, reducing the cost of nutrient addition, removing nitrogen and phosphorus
4
from wastewater and producing microalgal biomass as bioresources for biofuel or
5
high-value by-products. There are three main sources of wastewater, municipal
6
(domestic), agricultural and industrial wastewater, which contain a variety of
7
ingredients. Some components in the wastewater, such as nitrogen and phosphorus, are
8
useful ingredients for microalgal cultures. In this review, the effects on the biomass and
9
lipid production of microalgal Chlorella cultures using different kinds of wastewater
10
were summarized. The use of the nutrients resource in wastewater for microalgal
11
cultures was also reviewed. The effect of ammonium in wastewater on microalgal
12
Chlorella growth was intensively discussed. In the end, limitations of
13
wastewater-based of microalgal culture were commented in this review article.
14 15 16 17
1. Introduction As the fast growing world population and economic developments, the demand for
18
energy use of fossil fuel will continue to rise. But, the fossil fuels are not sustainable
19
energy resource in the long term. The burning of fossil fuels can lead to increase in
20
greenhouse gas (GHG) emissions and the environmental impact on global warming
21
(Hill et al., 2006). Renewable energy resources offer clean alternatives to fossil fuels.
22
They produce little pollution or GHG, and they will never run out. Currently, the main
23
of commercially available biofuel, kinds of renewable energy, are bioethanol and
24
biodiesel. Bioethanol is almost derived from sugar cane or corn starch and biodiesel is
25
derived from oil crops including oilseed rape and soybean. However, these crop-based 1
26
biofuels are economically competition with the production and the price of food (Hill et
27
al., 2006).
28
Biofuels derived from microalgae have been proposed as an alternative approach
29
that does not impact on agriculture. Microalgae have been estimated to produce higher
30
biomass productivity than plant crops in terms of land area required for cultivation, are
31
predicted to have lower cost per yield, and have the potential to reduce GHG emissions
32
through the replacement of fossil fuels. The main inputs required for microalgae growth
33
are sunlight, water, carbon dioxide (CO2), and nutrients. Water and inorganic nutrients
34
are identified as important limiting resources for microalgae culture. The nutrients for
35
microalgae cultivation (mainly nitrogen and phosphorus) can be obtained from liquid
36
effluent wastewater; therefore, besides providing microalgae growth environment, there
37
is the potential possibility of waste effluents treatment. This could be explored by
38
microalgae farms as a source of income in a way of wastewater treatment and obtain the
39
nutrients for microalgae growth (Cantrell et al., 2008).
40
1.1. Microalgae for CO2 mitigation
41
Microalgae are one of the earth's most important natural resources. They
42
contribute to approximately 50% of global photosynthetic activity. For autotrophic
43
algae, photosynthesis is a key component of their survival, whereby they convert solar
44
radiation and CO2 absorbed by chloroplasts and used in respiration to produce energy
45
to support growth.
46
During the recent decades, a number of post-combustion CO2 capture methods
47
have been developed using chemical, physical and biological methods (Kumar et al.,
48
2011). In recent years, the bio-regenerative methods using microalgae via
49
photosynthesis have been significant potential made to reduce the atmospheric CO2 to
50
ensure a safe and reliable living environment. In biological methods, particularly 2
51
microalgal photosynthesis, have several merits, such as higher CO2 fixation rates than
52
terrestrial plants and no requirement for further disposal of the trapped CO2.
53
Microalgae-based CO2 biological fixation is regarded as a potential way to not only
54
mitigates CO2 emissions but also shows the potential to produce lipid-rich microalgal
55
biomass as a regenerative energy-source (Ho et al., 2011). One of the most
56
understudied methods of CO2 reduction is the use of microalgae that convert CO2 from
57
a point source into biomass. Microalgae use CO2 efficiently because they can grow
58
rapidly and can be readily incorporated into engineered systems, such as
59
photobioreactors. The CO2 reduction by microalgal photosynthesis and biomass
60
conversion into health food, food additives, feed supplements, and biofuel is
61
considered a simple and appropriate process for CO2 circulation on Earth (Ho et al.,
62
2011). The incorporation of CO2 into energy-reserve components in biomass, such as
63
carbohydrates and lipids, by photosynthesis-driven microalgal fixation of CO2 is the
64
most promising route for CO2 sequestration from flue gas (Chiu et al., 2011; Kao et al.,
65
2014; Kumar et al., 2014) and biogas (Kao et al., 2012a; 2012b).
66
1.2. Microalgae for biofuel production
67
Many microalgae at or near optimal conditions potentially providing the benefits of
68
well-controlling are exceedingly rich in oil (Chisti et al., 2007; Ho et al., 2010), which
69
can be converted to many products such as renewable fuels, such as biodiesel, by
70
transesterification (Chen et al., 2011). The biodiesel produced from algal oil has
71
physical and chemical properties similar to diesel from petroleum, to biodiesel
72
produced from crops of 1st generation and compares favorably with the International
73
Biodiesel Standard for Vehicles (EN14214) (Brennan and Owende, 2010). Biodiesel
74
from microalgae seems to be the only renewable biofuel that has the potential to
75
completely displace petroleum-derived transport fuels without adversely affecting the 3
76
food supply and other crop products. According to some estimates, the yield of oil
77
from algae is over 200 times the yield from the best performing plant/vegetable oils
78
(Singh and Gu, 2010). The production of microalgae to harvest oil for biodiesel has not
79
been undertaken on a commercial scale, but working feasibility studies have been
80
conducted to arrive.
81
Despite microalgae inherent potential as a biofuel resource, many challenges have
82
impeded the development of algal biofuel technology to commercial viability that
83
could allow for sustainable production and utilization. They majorly include: (1)
84
species selection must balance requirements for biofuel production and extraction of
85
valuable co-products; (2) attaining higher photosynthetic efficiencies through the
86
continued development of production systems (Chen et al., 2011); (3) potential for
87
negative energy balance after accounting for requirements in water pumping, CO2
88
transfer, harvesting and extraction; (4) few commercial plants in operation. Therefore,
89
there is a lack of data for large scale plants.
90
1.3. Microalgal biorefinery
91
Microalgal biomass is one of the most potential feedstock for biorefinery, because it
92
can be converted into biofuels and various co-products (Vanthoor-Koopmans et al.,
93
2013). Microalgal biomass can used to produce biodiesel by extracting lipids to
94
transesterification into fatty acid methyl ester (FAME) as biodiesel. Some oleaginous
95
microalgae as nonedible biodiesel feedstock shows great potential due to its high oil
96
yield (5,000-100,000 L ha-1 year-1). The non-lipid fraction of the algal biomass,
97
consisting mainly of protein and carbohydrate, can also be processed to various biofuels,
98
including methane and alcoholic fuels (McGinn et al., 2011). Some microalgal strains
99
are rich in carbohydrates which is a potential feedstock for bioethanol production. The
100
carbohydrates in microalgae mainly come from starch in chloroplasts and 4
101
cellulose/polysaccharides on cell walls. The cellulose/polysaccharides of microalgae
102
should be hydrolyzed to fermentable sugar for bioethanol production. From the point of
103
biofuels, the microalgal cultivation integrated with biorefinery can increase the energy
104
productivity and recycle the CO2 for fuel production to achieve the sustainable
105
development. To achieve high biomass productivity per unit area, higher biomass
106
densities would be needed. Though high biomass density could be achieved in thin-plate
107
photobioreactors and fermenters, the downstream processes, such as dewatering and
108
dying facilities, remain cost and energy intensive processes. Thus, the new
109
cost-effective downstream process should be developed and introduced for biofuel
110
production.
111
In addition to produce energy by microalgal biomass, microalgal biomass can be
112
applied in high valuable products such as food supplements, cosmetics and animal
113
feeds, mainly containing polyunsaturated fatty acids (e.g., DHA and EPA),
114
chlorophylls, carotenoids and phycobilins, among other (Ho et al., 2013; Yen et al.,
115
2013). However, many developed processes focused on obtaining one specific product
116
from microalgal biomass without complete utilization. In other words, the product
117
extraction and conversion processes were developed for one specific product. This
118
mostly means that the other available and valuable components in the microalgae were
119
lost as waste. Thus, integrated processes for complete utilization of microalgal biomass
120
are still need to be developed for enhancement of microalgal biomass utilization
121
sustainability.
122
1.4. Microalgae for wastewater treatment
123
Inorganic nitrogen and phosphorus are is particularly difficult to remove from
124
wastewater. Due to the ability of microalgae to use both wastewater pollutions for their
125
growth, microalgae are particularly useful to reduce the concentration of inorganic 5
126
nitrogen and phosphorus in wastewater (Ahluwalia and Goyal, 2007). Many species of
127
microalgae are able to effectively grow in wastewater conditions through their ability to
128
utilize abundant inorganic nitrogen and phosphorus in the wastewater. Therefore, the
129
mass culture of microalgae can be potentially used for wastewater treatment as a tertiary
130
process (Martin et al., 1985).
131
A complete tertiary process in the wastewater treatment aimed at removing
132
nitrogen and phosphorus is estimated to be about four times more expensive than
133
primary treatment (de la Noüe et al., 1992). It is identical that microalgal cultures offer
134
an elegant solution to tertiary treatment due to the ability of microalgae to use inorganic
135
nitrogen and phosphorus for their growth (Oswald, 1988a; Tam and Wong, 1996). And
136
also, their capacity to remove heavy metals, as well as some toxic organic compounds,
137
therefore, does not lead to secondary pollution. In conclusion, microalgae cultures by
138
wastewater can significantly contribute to the management of water ecosystems by
139
providing an inexpensively environment-friendly system for wastewater treatment.
140
The major advantages of mass cultured microalgae having over conventional
141
aerobic wastewater treatment systems are reduced cost due to the decrease in energy
142
input, low initial capital cost, and low operational cost (Wong and Tam, 1998).
143
However, there are also lot disadvantages, e.g., microalgae cultivation is the space
144
requirement. Since microalgae rely on photosynthesis, the availability of sunlight to
145
reach the microalgae is critical. Therefore, microalgae-based wastewater treatment
146
systems should be performed in low land-cost areas where sunlight and warm
147
temperatures. The potential microalgal wastewater process was shown as the simplified
148
process flow diagram envisioned for typical wastewater treatment, algal wastewater
149
treatment with flue gas mitigation and production of various algal biomass products.
150
The integrated process of using wastewater for microalgae production can be shown as 6
151
the flow diagram envisioned for typical wastewater treatment, microalgal wastewater
152
treatment with flue gas mitigation, and production of various algal biomass products.
153
The typical wastewater treatment can be simply organized into three steps of
154
solid-liquid separation, horizontal anaerobic fermentation and an activated sludge
155
process in aerobic treatment. After the three-step wastewater treatment, the biochemical
156
oxygen demand (BOD) and suspended solids (SS) of treated wastewater were both
157
markedly reduced (Su et al., 1997). The effluent contains nitrogen, phosphorus and
158
other nutrients, and the flue gas consists CO2, both provide the nutrition, including
159
nitrogen, phosphorus and carbon sources, for the cultivation of microalgae. The
160
integrated system of microalgal wastewater treatment incorporated with flue gas was
161
using wastewater and flue gas process; that is not only an environmental-friendly but
162
also a sustainable process for wastewater treatment and CO2 mitigation (Rawat et al.,
163
2011; Razzak et al., 2013).
164 165
2. Wastewater used for microalgae cultures
166
In the past two decades, remarkable efforts have been put into research of
167
microalgae cultivation using wastewater. Some of studies indicated that utilizing
168
microalgae could efficiently remove the nitrogen, phosphorus, and heavy metal
169
elements from wastewater (Cabanelas et al., 2013; Cho et al., 2013; Min et al., 2011;
170
Sun et al., 2013; Wang et al., 2010; Zhu et al., 2013b). Additionally, the nutrient
171
components in wastewater significantly affect the microalgae growth, and their biomass
172
and lipid production (Cai et al., 2013). The nutrient components of different wastewater
173
streams that have been used for microalgal cultivation are discussed as follows.
174
2.1. Wastewater characterization
7
175
Depending on the origin, wastewater used in microalgal cultivations can be divided
176
into three main types as municipal, agriculture and industrial liquid waste products. The
177
wastewater treatment generally consists two or three phases as follows: a primary
178
treatment phase for the sedimentation and/or floatation of solid materials, a secondary
179
treatment phase in which suspended and dissolved organic materials are removed using
180
by physical, chemical and biological processes, and a tertiary treatment phase, such as
181
disinfection and filtration, in which final treatment of the water is performed prior to
182
discharge into the environment (Ramalho, 1977). The treated water discharged from a
183
process of wastewater treatment is known as effluent.
184
There are several common wastes in the effluents of wastewater, including sludge
185
and scum, organic waste, inorganic waste, nutrients, toxins, pathogenic organisms, etc..
186
For microalgal growth, nutrients in wastewater are extremely interest for the more
187
discussion in this review article. Excessive nutrients in the wastewater, such as
188
nitrogen and phosphorus, may cause eutrophication in lakes and upset the balance of
189
the ecosystem (Cai et al., 2013). Nutrients are also the substances that are required for
190
the growth of microalgae. The major nutrients of interest are nitrogen and phosphorous.
191
Nitrogen may be present in effluent as ammonia (NH4 +), organically bound nitrogen or
192
even nitrite (NO2-) and nitrate (NO3-). Phosphorous is presented in influent and effluent
193
primarily in the form of phosphates (PO43-).
194
2.2. Nutrients from wastewater for microalgal cultures
195
The total nitrogen (TN) and total phosphorus (TP) concentrations of wastewater
196
would differ significantly depending on the wastewater type (Table 1). Nitrogen in the
197
form of ammonia and nitrates in wastewater is the most commonly found nitrogen
198
containing chemicals. Ammonium is among the most common chemical forms of
199
nitrogen that can be readily absorbed by most microalgal species and strains. In this 8
200
respect, a cheap source of nitrogen in wastewater or effluent of can be used for
201
microalgal cultivation (Razzak et al., 2013). It may imply that some studies showed
202
wastewater-based microalgal cultures are inhibited with the high concentration of TN,
203
especially high ammonium. However, when the pH of the culture and other growth
204
conditions are controlled, ammonium is a reliable nitrogen source (de-Bashan et al.,
205
2005). In conclusion, regardless of the negative effects on microalgal growth in
206
ammonium-supplementation, it is still the preferred nitrogen source if the
207
environmental parameters for proper development of the culture are controlled (Razzak
208
et al., 2013).
209
Phosphorus is another important element required for microalgae growth and
210
metabolism. Phosphorus is an essential element contributing as ATP in microalgal
211
cells. Therefore, phosphorus availability has a large impact in microalgae growth as it
212
is considerably affected in photosynthesis (Razzak et al., 2013). Phosphorus is usually
213
available in the wastewater as inorganic anions species such as H2PO4- and HPO42-
214
(Martinez et al., 1999).
215
The concentrations of TN and TP which are relatively low (TN: about 15-90 mg
216
L-1; TP: about 5-20 mg L-1) in domestic secondary effluent. The lower TN and TP are
217
the typical water quality of domestic wastewater. The concentrations of TN and TP in
218
the wastewater from livestock breeding and agriculture are usually about 185-3,213 mg
219
L-1 of TN and about 30-987 mg L-1 of TP, such as anaerobic digested poultry litter
220
effluent, swine or dairy manure wastewater. However, these kinds of wastewater
221
always contained nutrients of an extremely high concentration, and thus had to be
222
diluted before they used for microalgal cultivation.
223
2.2.1. Municipal wastewater
9
224
The increasing urbanization and expansion of urban populations has resulted in
225
greater quantities of municipal wastewater, or defined as domestic wastewater. The
226
composition of municipal wastewater varies significantly from one location to another.
227
Municipal wastewater effluent typically contains human and other organic waste,
228
nutrients, microorganisms and household and industrial chemicals. Compared with
229
industrial and agricultural wastewater, there is less nitrogen and phosphorus in
230
municipal wastewater. However, because of the activities of some localized
231
small-scale factories, a significant level of heavy metals such as lead, zinc, and copper
232
will also present in raw municipal sewage. Microalgae cultivation using municipal
233
wastewater as the nutrient sources has been most extensively studied as the main topic
234
of nitrogen and phosphorus removal (Li et al., 2011; Ruiz-Marin et al., 2010).
235
Although, the nitrogen and phosphorus contained in municipal wastewater would be a
236
potential nutrient sources, the complexity, variety and toxicity of the municipal
237
wastewater should be considered for distinct stages of the treatment in order to fit the
238
wastewater discharge standard. Thus, it is no doubt the study of microalgal cultivation
239
using wastewater, the performance of wastewater treatment that remove most toxic
240
components should be also considered (Cabanelas et al., 2013).
241
2.2.2. Agricultural wastewater
242
In general, agriculture is the largest user of water in the world except few regions
243
(Abdel-Raouf et al., 2012). The water carrying waste material from agricultural
244
activities, including animal manure, plant stalks, hulls and leaves, etc.. The
245
large livestock and poultry operations would be a major source of point source
246
wastewater. During the past decades, livestock operations have intensively increasing
247
from small-scale to large-scale. The nitrogen and phosphorus are the main component
248
in the wastewater produced from animal farms (Zhu et al., 2013a). Ammonium and 10
249
organic nitrogen are the main components present in agriculture wastewater. The main
250
form of nitrogen waste in animal waste is ammonium that is almost half of total
251
nitrogen source. Because the animal wastewater produced from the agricultural
252
activities such as animal diet, usage, productivity, and location will significantly affect
253
the nutrient content in animal wastewater (An et al., 2003; de Godos et al., 2009; Wang
254
et al., 2010; Wilkie and Mulbry, 2002; Zhu et al., 2013b).
255
2.2.3. Industrial wastewater
256
There are many types of industrial wastewater based on different industries and
257
contaminants; each sector produces its own particular combination of pollutants.
258
Compared to agricultural wastewater, industrial wastewater varies depending on the
259
source operations. Heavy metal pollutants present in most industrial wastewater;
260
furthermore, nitrogen or phosphorus in industrial wastewater is usually less than
261
municipal or agricultural wastewater (Chinnasamy et al., 2010). The amount of
262
wastewater depends on the technical level of process in each industry sector and will
263
be gradually reduced with the improvement of industrial technologies. The increasing
264
rates of industrial wastewater in developing countries are thought to be much higher
265
than those in developed countries.
266
Due to the complexity of industrial wastewater, the screening and isolation of high
267
tolerance of metal and organic material microalgae species and strains is crucial to
268
achieve high growth efficiency. Nevertheless, only a few literatures studied the
269
microalgal cultivation with high metal tolerance as well as the nitrogen and phosphorus
270
removal (Ahluwalia and Goyal, 2007).
271 272 273
3. Efficiency of microalgal Chlorella growth in wastewater The efficient growth of microalgae in wastewater is dependent on many variables. 11
274
For example, the obviously differ depending on the types and the sources of
275
wastewater. In addition, the variation is also shown in the tolerant capacity of different
276
microalgal species to a particular wastewater condition. Chlorophytes is one of the
277
largest phyla of microalgae, with a variety of species and a wide geographical
278
distribution. Chlorophytic microalgae have been shown to be potential used to a
279
variety of wastewater conditions and very efficiency at nutrients removal from
280
wastewater. The potential microalga strains of Chlorophytes, Chlorella, have been
281
studied enormously and also shown to be effective in nitrogen and phosphorus removal
282
from wastewater with a wide range of initial concentrations (Cai et al., 2013) and the
283
growth of Chlorella species cultured in wastewater have examined in most studies (Wu
284
et al., 2014).
285
For the comparison of different wastewater effects on the microalgal growth, the
286
three different types of wastewater, the nutrient contents and the microalgal Chlorella
287
species and strains used in the recent literatures were summarized in Table 1.
288
Furthermore, the effects of different wastewaters on microalgal Chlorella cultures were
289
organized in Table 2. Then, the efficiency of Chlorella growth in different types of
290
wastewater is reviewed in this section.
291
3.1. Cultures in municipal wastewater
292
In the published literatures, most studies were using municipal wastewater for
293
microalgal cultivation. One of the main reasons is that the municipal wastewater
294
treatment is relatively mature in developed countries. However, the chemical
295
concentrations in municipal wastewater are complex because some municipal
296
wastewater treatment would mix with low concentrations of industrial wastewater that
297
produced in local small factories. Some municipal wastewater would contain a small
298
amount of heavy metal or chemicals, which were diluted by domestic wastewater to fit 12
299
in with ease for biological treatment and wastewater discharge standard (Gizgis et al.,
300
2006). Thus, the effects on the growth of microalgal culture would vary. In this review,
301
we summarized the microalgal biomass production versus different sources of
302
municipal wastewater mainly on the contents of phosphorus and nitrogen.
303
Microalgal Chlorella usually performed a high nutrient pollutions removal and
304
utilized efficiency when the algal cells cultured in domestic wastewater. Lau et al. (1996)
305
studied the ability of C. vulgaris in nutrients removal and reported a nutrient removal
306
efficiency of 86% for inorganic nitrogen and 78% for inorganic phosphorus. It is
307
recently reported that C. vulgaris cultivated by several streams from municipal
308
wastewater yields microalgal biomass from 39 to 195 mg L-1 d-1 (Cabanelas et al., 2013).
309
Cho et al. (2013) also revealed that Chlorella sp. yield the highest biomass production
310
approximately 3.0 g L-1 using 10% anaerobic digestion tanks, and conflux line of the
311
90% wastewaters combined wastewater as nutrients for microalgal cultivation. Li et al.
312
(2011) showed that the biomass productivity of Chlorella sp. growing in the centrate, a
313
highly concentrated municipal wastewater stream generated from activated sludge
314
thickening process, was 0.9 g L-1 d -1. Thus, using municipal wastewater for microalgal
315
culture could be a useful and practical strategy as an advance green treatment process.
316
3.2. Cultures in agricultural wastewater
317
Compared to municipal wastewater, there can be very high in nitrogen,
318
phosphorus, and organic matter in both soluble and solid particle forms in the effluent
319
from agricultural wastewater that is often derived from manure or animal waste. In
320
spite of the high nutrient concentration, studies have demonstrated that the microalgae
321
would be the potential candidate with efficient growth on agricultural waste.
322
Furthermore, microalgae are efficient nitrogen and phosphorus remover from
323
manure-based wastewater (An et al., 2003; Wilkie and Mulbry, 2002). The high 13
324
concentrations of nitrogen and phosphorus of agriculture wastewater, e.g., piggery
325
wastewater, is a potential nutrient source for microalgal growth (de Godos et al., 2009).
326
The higher availability of carbon and nitrogen in piggery wastewater, together with the
327
favorable temperatures and solar irradiations supported higher microalgal biomass
328
productivity. However, the extremely high concentration of NH4+-N in livestock
329
wastewater may be a growth reducing factor. The use of piggery wastewater
330
containing volatile fatty acids, like acetic acid, propanoic acid and butric acid, which
331
provided carbon source in the wastewater, could also be the pH regulator. Huo et al.
332
(2012) used acetic acid as the pH regulator, higher oil content and specific growth rate
333
of C. zofingiensis culture using dairy wastewater can be obtained. In fact, organic
334
carbon source contained in piggery wastewater could provide the mixotrophic
335
condition for microalgae. Lot of the studies showed that the biomass and lipid
336
production significantly enhanced by heterotrophic or mixotrophic cultivation
337
conditions (Perez-Garcia et al., 2011).
338
As we summarized literatures, the studies used agricultural wastewater are not as
339
many as municipal wastewater literatures (Table 1 and Table 2). That may be due to
340
the maturation of well-controlled municipal wastewater treatment and the availability
341
of sewage piping system. However, the properties of agricultural wastewater show a
342
great potential for microalgal biomass and lipid production. This could be the benefit
343
for the countries with intensive pig farming. This is a kind of industrial animal
344
agriculture and the localized wastewater treatment could provide for microalgal
345
cultivation. Zhu et al. (2013a; 2013b) have demonstrated that using microalga C.
346
zofingiensis cultivation combined with piggery wastewater treatment showed the
347
advantage of nutrient removal and the highest productivities of biomass and lipid. The
348
microalgal biomass production could achieve 2.9 g L-1 in a 10-day cultivation. It is 14
349
worthy of note that the diluted piggery wastewater strategy provided an optimal
350
nutrient concentration for C. zofingiensis cultivation. It was also mentioned that the
351
high dilution multiples applied to the digested manure for microalgal growth can be
352
proposed as an effective way to convert high strength dairy manure into profitable
353
byproducts (Wang et al., 2010).
354
3.3. Cultures in industrial wastewater
355
There are few studies using industrial wastewater for microalgal cultivation
356
because the complexity of the contents of industrial wastewater (Table 1 and Table 2).
357
However, there is also many of interest in the use of microalgae as bioremediation for
358
industrial-derived wastewaters, mostly for the heavy metal removal and the
359
biodegradation of organic chemical toxins (hydrocarbons and biocides), rather than
360
nitrogen and phosphorus (Ahluwalia and Goyal, 2007; de-Bashan and Bashan, 2010).
361
In general, microalgal growth rates are lower in many industrial wastewaters because
362
of the low nitrogen and phosphorus concentration and high concentration of toxic
363
compounds. Consequently, there is less potential for utilizing industrial wastewaters
364
for large-scale microalgal mass production (Pittman et al., 2011). But, a huge amount
365
of specifically industrial wastewater is potential resources for microalgae cultivations.
366
Part of the studies focused on the treatment of the industrial wastewater, like
367
textile wastewater decoloring by microalgae as bioremediation. The potential source of
368
industrial wastewater for microalgal cultivation is food processing wastewater, such as
369
soybean processing, brewery and chemical fermentation wastewater (Farooq et al.,
370
2013; Su et al., 2011; Sun et al., 2013). The contents in these industrial wastewaters
371
would be simpler than that of other industrial wastewater, such as carpet mill effluents,
372
iron and steel industrial wastewater, petrochemical industrial wastewater. These
373
wastewaters contain high contents of metals, phenols and chlorinated organic 15
374
compounds those are toxic to microalgal cells as inhibitors. For the further using
375
industrial wastewater with higher concentration of growth inhibitory elements for
376
microalgal cultivation, the adaptive process for microalgal cells or the dilutions of
377
wastewater are needed. In the study, Chinnasamy et al. (2010) used the carpet mill
378
effluent from the city of Dalton, USA, makes up 100-115 million L of wastewater per
379
day. This wastewater was shown to be low enough in toxins and enough phosphorus
380
and nitrogen to support microalgae growth. The data showed that microalge C.
381
saccharophila is able to grow particularly well on the untreated wastewater.
382
Additionally, the contents of food processing wastewater are mainly biological
383
available compounds, such as ethanol, acetic acid and propionic acid, which provided a
384
potential organic carbon source for microalgal cultivation by heterotrophic or
385
mixotrophic cultivation mode.
386 387 388
4. Effects of ammonium and C:N:P ratios in wastewater on Chlorella cultivation We used 3-dimensional reaction surface plots and contour plots to demonstrate the
389
biomass production and productivity of microalgal Chlorella versus a variety of
390
concentrations of NH4+-N and TP in the wastewater used for Chlorella cultures (Fig. 1).
391
In Fig. 1A, the optimal concentration of NH4+-N and TP for biomass production of
392
the Chlorella cultures were between 200 to 400 mg L-1 for NH4+-N and 100 to 200 mg
393
L-1 for TP. However, the NH4 +-N concentration in typical municipal wastewater is just
394
between 10 to 80 mg L-1 (as TN between 16 to 250 mg L-1 in Table 1). The maximum
395
biomass production obtained via municipal wastewater cultivation was approximate 1.5
396
g L-1. This municipal wastewater was obtained as centrate III with 466 mg L-1 of
397
NH4+-N (Cabanelas et al., 2013). However, a higher NH4+-N of the centrate IV (905 mg
398
L-1) contributed to lower biomass production. In addition, Cabanelas et al. (2013) 16
399
showed that as the municipal concentrate with higher NH4+-N above 100 mg L-1, the
400
lower TN removal. However, there is no obvious linear relationship between NH4 +-N
401
removal and biomass production, but it showed a bell-shaped curve pattern for the
402
NH4+-N removal and biomass productivity. The high NH4+-N content in wastewater is
403
as growth inhibitory factor for microalgae because that may contribute to the correlation
404
with pH value. Tam and Wong (1996) showed that the growth of Chlorella was reduced
405
as NH4 +-N > 700 mg L-1 with a pH level below 7. The growth of C. vulgaris in cultures
406
containing NH4+-N was also accompanied with the change of pH value
407
(Przytocka-Jusiak et al., 1977). The dissociation of NH4+ to NH3 occurs at pH level > 8.
408
The lower pH value reduces the formation of NH3 and the nitrogen exists in NH4 + ion
409
form, which is less toxic to microalgal cells. If the nitrogen source as the form of NH3,
410
it would dissipate the pH level within microalgal cells because of high membrane
411
permeability of NH3 (Taiz and Zeiger, 2006). Therefore, cellular mechanism of pH
412
regulation may help the assimilation of NH3 in the wastewater used by microalgae.
413
The optimal condition for biomass productivity of the Chlorella cultures versus
414
NH4+-N is 200 to 400 mg L-1. The values are similar to that of biomass production. The
415
TP concentration for biomass productivity is < 100 mg L-1, this value is little less than
416
that of biomass production (Fig. 1B). However, it can be concluded that the effects of
417
NH4+-N and TP concentrations in wastewater on the Chlorella biomass production and
418
productivity are similar.
419
The carbon:nitrogen (C:N) and carbon:phosphorus (C:P) ratios could be considered
420
when the wastewater is as the nutrient source for the wastewater-based microalgal
421
cultivation. The C:N and C:P ratios in municipal wastewater, such as domestic sewage
422
(C:N is 3.5:1 and C:P is 20:1) and dairy lagoon water (C:N, 3:1 and C:P, 10:1) are low
423
compared to the typical ratios for optimal conditions for microalgae biomass production 17
424
(C:N, 6:1 and C:P, 48:1) (USDA, 1992). This deficient carbon in wastewater would be
425
the restriction for microalgal biomass production; as a result, incomplete assimilation of
426
wastewater nutrients by microalgal cultures occurred. In addition, some published
427
literatures also mentioned that carbon and nitrogen metabolism are linked in microalgae
428
(Fernandez and Galvan, 2007; Perez-Garcia et al., 2011). The reason is that the carbon
429
generated directly from respiration shared each other and the energy was also generated
430
in the TCA cycle (Fernandez and Galvan, 2007). These carbon limitations of C:N and
431
C:P ratios in wastewater could be overcome by waste CO2 addition, like flue gas.
432
C. kessleri culture could successfully remove high concentrations of nitrogen (NH4 +-N
433
or nitrate) from the glucose supplemented wastewater (Lee and Lee, 2002). Thus,
434
sufficient supply of carbon source would be benefit to nitrogen and phosphorus
435
utilization. However, cheaper organic carbon sources need to be looked for, because the
436
cost of the organic carbon substrate is estimated to be about 80% of the total cost of the
437
cultivation medium. Cheap carbon sources, such as crude glycerol from biodiesel
438
industry, sugars from industrial and agricultural waste, acetate from anaerobic digestion,
439
cellulosic materials and cane molasses can be used to replace the expensive pure
440
glucose for the cultivation of mixotrophic algae (Abreu et al., 2012).
441
The typical N/P ratio for optimal conditions for microalgae biomass production was
442
8:1 (USDA, 1992); however, the N/P ratios in most sources of wastewater are close to
443
1:1 (Table 1). It means that the phosphorus source in wastewater is sufficient rather
444
than nitrogen source. This result may also imply that nitrogen source in wastewater
445
would be the limiting factor for microalgal growth.
446 447 448
5. Lipid production of Chlorella cultures in wastewater Although the main focus in the field of using wastewater for microalgae culture is 18
449
to evaluate the viability of microalgae cultivated in wastewater for the inorganic
450
nutrients removal, as the view of sustainable process, it is no doubt that utilization of
451
the produced biomass after wastewater treatment is important to put into consideration.
452
Therefore, the recent studies focused on maximizing the biomass and lipid yield of
453
microalgae has shifted the interest from nutrient removal (Cai et al., 2013).
454
In many studies, the lipid content and production of microalgae cultivated in
455
wastewater was not determined. Table 2 and Fig. 2A demonstrate that the higher lipid
456
contents could be achieved under the wastewater cultivation of lower concentrations of
457
NH4+-N and phosphorus. It is reasonable because that low concentration of NH4+-N
458
during microalgal cultivation is a trigger factor that low available nitrogen (nitrogen
459
deficient condition) contributes to lipid accumulation. Generally, the average lipid
460
productivity of microalgae in the effluent of municipal wastewater was less than
461
10 mg L-1 d -1 (< 10% lipid content). Compared with that, many microalgal species
462
cultured in agriculture wastewater could produce average lipid productivity ranging
463
from 20 to 100 mg L-1 d -1 (Wu et al., 2014). Fig. 2B and 2C show the lipid production
464
and lipid productivity of the microalgal cells under wastewater cultivation.
465
Nevertheless, comparing to the respond pattern of lipid content data in Fig. 2A, these
466
data show a contradict result that higher NH4 +-N in wastewater could generate higher
467
lipid production and lipid productivity of microalgae. However, it is not surprising
468
because the optimal condition range of NH4+-N and phosphorus of respond patterns for
469
lipid production and lipid productivity consist with the response pattern for biomass
470
production and biomass productivity (Fig. 1). This may imply that biomass production
471
and productivity are the dominant factor for the results of lipid production and
472
productivity.
473
However, the lipid production is also dependent on the microalgal species used. 19
474
C. ellipsoidea YJ1 isolated by Yang et al. (2011a) could achieve a higher lipid content
475
of about 40% in domestic secondary effluent. In the study reported by Su et al. (2011),
476
C. pyrenoidosa achieved an average lipid productivity of 236 mg L-1 d-1 under the
477
condition of fed-batch culture using soybean processing wastewater. Additionally,
478
Abreu et al. (2012) reported that C. vulgaris was cultivated in hydrolyzed cheese whey
479
(5 g L-1 glucose and 5 g L-1 galactose), and a lipid productivity about 250 mg L-1 d -1
480
was obtained.
481
Wang et al. (2010) evaluated a batch culture-grown Chlorella sp. on anaerobically
482
digested dairy manure. The total fatty acid content ranged from 9.0% to 13.7% DW
483
(0.141 to 0.233 g L-1) depending on the wastewater concentration used. C. vulgaris
484
grown in an artificial wastewater medium resulted in 20-42% of lipid content (Feng et
485
al., 2011). C. pyrenoidosa was also shown to adapt and utilize high concentrations of
486
organic components in wastewater, resulting in a significant growth potential and lipid
487
production (Su et al., 2011). Farooq et al. (2013) reported that using the two-stage
488
autotrophic-heterotrophic cultivation for C. vulgaris, the lipid productivity was
489
increased from 31 to 108 mg L-1 day. It was also reported that C. pyrenoidosa could
490
attain an average lipid content of 37%, and a high lipid productivity of approximate 0.4
491
g L-1 d -1 using soybean processing wastewater without a supply of additional nutrients
492
(Su et al., 2011).
493
The properties of a biodiesel fuel, including its ignition quality, combustion heat,
494
cold filter plugging point (CFPP), oxidative stability, viscosity and lubricity, are
495
determined by the structure of its component fatty esters. High levels of saturated fatty
496
acids tend to increase the stability of biodiesel because unsaturated fatty acids result in
497
poor oxidative stability. Thus, the biodiesel qualities are dependent on fatty acid
498
composition. The typical fatty acid composition of Chlorella under conditions of 20
499
photoautotrophic and heterotrophic cultivations, nitrogen starvation, and outdoor in a
500
photobioreactor were C16:0, C16:1, C16:2, C16:3, C18:0, C18:1, C18:2, C18:3 (Kao et
501
al. 2012a; Petkov and Garcia, 2007). Among of them, C16:0, C18:0, C18:1 and C18:2
502
are suitable fatty acids for biodiesel production, and these are the most abundant fatty
503
acids in microalgae.
504
The fatty acid profile was shown in Li et al. (2011), for Chlorella sp. cultivated in
505
the centrate, a highly concentrated municipal wastewater, the most abundant fatty acids
506
obtained from algae were C18:2 (14.4-24.4% in total lipid) and C16:0 (15.2-19.1%). C.
507
vulgaris cultivated in the pretreatment of dairy wastewater by UV and NaClO, C16:0
508
was the most abundant fatty acid, ranging from 36.9 to 45.3% of the total fatty acids
509
(Qin et al., 2014). The Chlorella cultures in mixtrotrophic growth with acetic acid
510
regulation having a higher C18:1 (32-35%) which is good for biodiesel production was
511
observed (Huo et al., 2012; Liu et al., 2011). Farooq et al. (2013) reported the main
512
constituents of the lipid extracted from C. vulgaris (UTEX-265) cultivation in brewery
513
wastewater under two-stage photoautotrophic–mixotrophic mode utilizing glucose
514
were C16:0 (20%), C18:1 (44%), and C18:2 (~14%). Above of all studies, the
515
C16–C18 percentage of total fatty acid methyl ester of the Chlorella species
516
wastewater cultivation in heterotrophic or mixotrophic conditions was over 80%,
517
which is an ideal lipid source for biodiesel production (Liu et al., 2011).
518 519 520
6. Limitations of microalgal biomass productivity by wastewater The high biomass production and in some cases of high lipid productivity that have
521
been demonstrated in many of the reviewed studies of wastewater-grown microalgae
522
suggests that there is real potential in the utilization of these high nutrient resources for
523
cost-effective biofuel production (Pittman et al., 2011; Razzak et al., 2013; Singh and 21
524
Gu, 2010; Wu et al., 2014). However, there are some limitations that need to be
525
addressed when wastewater used as the nutrients for microalgae cultures.
526
6.1. Microalgal growth in unsterilized wastewater
527
Microalgae can effectively grow and utilize nutrients in wastewater, providing an
528
attractive means to cultivate microalgae low cost. But, microalgal resistance to biotic
529
pollution is necessary to be considered as an important issue for microalgal growth in
530
wastewater. The biotic pollution is existed or produced by various bacteria, fungi and
531
zooplanktons in wastewater. The microbial existence is the most important
532
characteristic of wastewater (U.S. DOE, 2010; Wang et al., 2013), and also one of the
533
most significant difference between wastewater and culture medium for microalgae
534
culture. However, the growth of microalgae is sometimes restricted by the presentation
535
of bacteria and protozoa in wastewater. Thus, most of the reported data was obtained
536
under sterilized conditions, i.e., the wastewater was treated by autoclave sterilization
537
and/or centrifugation before it was applied for microalgae culture. In laboratory scale, it
538
is easy to sterilize wastewater as microalgal culture broth. But the cost and difficulty
539
would increase exponentially in large-scale microalgal cultivation using wastewater. In
540
order to guarantee stable microalgal growth using wastewater against possible biotic
541
contamination, it is necessary to develop the control techniques of biotic pollution
542
(Wang et al., 2013).
543
The literature showed that C. zofingiensis cultivated in piggery wastewater
544
pretreated by autoclaving and NaClO had no evident difference in the performance of
545
nutrient removal, i.e., microalgal growth and lipid production (Zhu et al., 2013b). The
546
pretreatment of dairy wastewater by UV and NaClO which were feasible for large-scale
547
cultivation was also investigated. The results showed that the highest biomass and lipid
22
548
productivity of C. vulgaris could be obtained by the NaClO-pretreated dairy
549
wastewater.
550
The stability of mass culture is an important issue for wastewater-based microalgal
551
cultures. Zhu et al. (2013b) and Qin et al. (2014) have mentioned that NaClO pretreated
552
wastewater was feasible for microalgal culture, but the hydraulic retention time for
553
NaClO pretreatment need around 15 to 30 min. That means the extra area or volume for
554
the wastewater pretreatment was needed. UV disinfection can instantaneously neutralize
555
microorganisms as they pass by UV lamps submerged in the effluent. The process adds
556
nothing to the water but UV light, therefore there is no impact on the chemical
557
composition or the dissolved oxygen content of the water. If an integrated microalgal
558
cultivation system with wastewater was applied as a continuous flow process, the UV
559
disinfection would be a promising method for wastewater sterilization.
560
6.2. Microalgal cultivation in outdoor system with a large scale
561
The cultivation scale of most recent studies was in the range from several liters to
562
several cubic meters, which means in order to achieve microalgal biomass production
563
under industrial scale it is necessary to enlarge the recent cultivation scale by tens of
564
thousands of times. This, not surprisingly, would bring along a host of problems
565
including political, social and economic as well as scientific (Williams and Laurens,
566
2010).
567
The most important question is what kind of cultivation system could provide
568
microalgal biomass production in a huge scale economically and
569
environmental-friendly. Due to the complexity of construction and the requirement of
570
huge covering area, most of the photobioreactors and microalgal ponds used in recent
571
studies are not possibly suitable for economically industrial-scale microalgal biomass
572
production. Therefore, the R&D efforts on novel cultivation system are very important 23
573
in the future research. The most important limitation is actually caused by light
574
attenuation in the systems of microalgal culture. Therefore, using microalgal species
575
that have the ability to use organic matters in wastewater for heterotrophic growth may
576
be a novel alternative approach to overcome the light limitation (Perez-Garcia et al.,
577
2011).
578
6.3. Life cycle analysis of wastewater-derived microalgal biofuel
579
A critical determinant as to the true potential of algal biofuel production using
580
wastewater resources is whether the process will provide a positive energy output
581
which will also determine the economic viability of the process. It was extremely
582
discussed on the need of life cycle analysis of wastewater-derived microalgal biofuel
583
by Pittman et al. (2011).
584
To date, microalgae-based biofuel production has not yet been commercialized to
585
large-scale. Debates exist regarding life-cycle impacts of large-scale microalgae-based
586
biofuel production, especially the impact on water usage. Yang et al. (2011a) have
587
examined that the life-cycle water and nutrients usage of microalgae-based biodiesel
588
production. Large-scale microalgae biodiesel production has been criticized for the
589
significant amount of freshwater usage (U.S. DOE, 2009). However, microalgae-based
590
biodiesel production may consume much less water than conventional feedstock-based
591
biodiesel production if microalgae are cultivated in wastewater. Without recycling
592
harvested water, the water footprint is approximately 3,726 kg-water/kg-biodiesel, and
593
around 0.33 kg nitrogen and 0.71 kg phosphorus is required (Yang et al., 2011b).
594
Recycling harvest water reduces the water by 84% and nutrients usage by 55%. Using
595
wastewater as microalgae culture medium decreases 90% water requirement, and
596
eliminates the need of all the nutrients except phosphorus. The results confirm the
597
competitiveness of microalgae-based biofuels and highlight the necessity of recycling 24
598
harvested water and using wastewater as water source (Yang et al., 2011b).
599
6.4. Need of efficient techniques for the processes of microalgae following
600
cultivation
601
Besides to the limitations mentioned above, an important issue to be resolved in
602
the applications with microalgae cultivation for biofuel productions is the need for
603
efficient and cost-effective harvesting and processing of microalgae following
604
cultivation. Recovery has been estimated to contribute 20-30% of the total cost of
605
producing the microalgal biomass (Molina Grima et al., 2003). The initial harvesting
606
step is not only costly, but also affects any later processes downstream. The lack of
607
efficient microalgal harvesting systems is the major reason why wastewater-derived
608
microalgal biofuels is not used extensively by the wastewater industry (de-Bashan and
609
Bashan, 2010).
610
Following the microalgal harvesting, the microalgae have to go through a number
611
of further processes. The need for improvements in these further processes still also
612
remains to be largely developed (Brennan and Owende, 2010). Microalgal biomass can
613
be utilized for the production of various biofuels such as bioethanol, biodiesel,
614
biomethane and biohydrogen. However, significant improvements in the efficiency, cost
615
structure and ability to scale up microalgal growth must be made to produce
616
commercially viable biofuels (Pittman et al., 2011). For this purpose, a defined set of
617
technology breakthroughs will be required to develop the optimum utilization of
618
microalgal biomass for the commercial production of biofuels (Singh and Olsen, 2011).
619
In conclusion, lowering the cost of harvesting microalgae and harvesting in a way
620
that allows for the creation of bioproducts remains a large challenge. The choice of a
621
particular harvesting or dewatering method will dictate what upstream conditions must
622
be met (Christenson and Sims, 2011). Thus, the total solution for using wastewater into 25
623
microalgal biofuel production should be concerned. The technologies process evaluation
624
of integrated process systems is still to be carefully investigated.
625 626 627
7. Conclusion Based on current microalgal technologies for biofuel production alone is unlikely
628
to be economically viable or provide a positive energy return. The high biomass and
629
lipid productivity of wastewater-grown microalgae suggests that this microalgal
630
cultivation strategy offers real potential for biofuel generation. Among of municipal,
631
agricultural and industrial wastewater, agricultural wastewater shows a great potential
632
for microalgal Chlorella growth. The ammonium concentration in wastewater would
633
be the dominant factor for the results of microalgal Chlorella biomass and lipid
634
production. However, more efforts should be devoted before the economical and
635
sustainable microalgal biomass and lipid production using wastewater as nutrients
636
resource.
637 638
Acknowledgements
639
The work was financially supported by grants MOST 103-3113-E-006-006 from
640
the Ministry of Science and Technology. This work was also supported in part by the
641
Aim for the Top University Program of the National Chiao Tung University and
642
Ministry of Education, Taiwan.
26
643
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850
Tables and Figures captions
851
Table 1. Nutrients of nitrogen and phosphorus in the wastewater used for the
852
microalgae Chlorella cultivations.
853
Table 2. Biomass and lipid production and productivity of the microalgae Chlorella
854
cultures using wastewater.
855
Fig. 1. Three-dimensional reaction surface plots and contour plots for the biomass
856
production (A) and productivity (B) of the microalgal Chlorella cultured in the
857
wastewater with different NH4+-N and total phosphorous (TP) concentrations. The detail
858
collected data were indicated in Table 1 and Table 2.
859
Fig. 2. Three-dimensional reaction surface plots and contour plots for the lipid content
860
(A), production (B) and productivity (C) of microalgal Chlorella cultured in wastewater
861
with different NH4 +-N and total phosphorus (TP) concentrations. The detail collected
862
data were indicated in Table 1 and Table 2.
36
Figure 1
(A) Biomass production
(B) Biomass productivity
6000 4000 2000 0 -2000
200
500 400 300 200 100
400
500 400 300 200 100
200
400
600
NH4+‐N (mg/L)
800
1500
1000
500
0
-500
0 2000 4000 6000 8000
600
Total phosphorus (mg/L)
800 600
200
500 400 300 200 100
400
600
800
-200 0 200 400 600 800 1000 1200 1400
600
Total phosphorus (mg/L)
Biomass production (mg/L)
8000
-500 0 500 1000 1500 2000
2000
Biomass productivity (mg/L/day)
-2000 0 2000 4000 6000 8000 10000
10000
500 400 300 200 100
200
400
600
NH4+‐N (mg/L)
800
Figure 2
(B) Lipid production
Lipid production (mg/L)
16 14 12 10 8 6 200
150
100
50
200 150 100
3000 2000 1000 0 -1000
150
50
10 12 14 16
200
Total phosphorus (mg/L)
4000
-2000
150
100
50
100
50
200 150 100
400 300 200 100 0 -100 -200
0 1000 2000 3000 4000
150
100
50
-200 -100 0 100 200 300 400 500
500
50
200
Total phosphorus (mg/L)
Lipid content (%)
18
-2000 -1000 0 1000 2000 3000 4000 5000
5000
Lipid productivity (mg/L/day)
6 8 10 12 14 22
20
(C) Lipid productivity
Total phosphorus (mg/L)
(A) Lipid content
50
140 120 100 80 60 40 20
200 150 100
-100 0 100 200 300 400
140 120 100 80 60 40 20
50
100 150 NH4+‐N (mg/L)
200
50
100
150
NH4+‐N (mg/L)
200
50
100
150
NH4+‐N (mg/L)
200
Table 1. Nutrients of nitrogen and phosphorus in the wastewater used for the microalgae Chlorella cultivations Wastewater type
Municipal wastewater
Wastewater source
Microalgae
NH4+-N (mg/L)
TN content (mg/L)
TP content (mg/L)
TN/TP
Centrate Metropolitan wastewater treatment plant
Chlorella sp.
86
132
215
0.6
Li et al., 2011
Centrate Metropolitan wastewater treatment plant
Chlorella sp.
83
116
212
0.5
Li et al., 2011
Pretreated urban wastewater WWTP1
Chlorella sp.
81
84
6
14.0
Cabanelas et al., 2013
Pretreated urban wastewater WWTP2
Chlorella sp.
40
42
6
7.0
Cabanelas et al., 2013
Effluent from primary settler
Chlorella sp.
31
36
3
12.0
Cabanelas et al., 2013
Centrate I
Chlorella sp.
125
130
175
0.7
Cabanelas et al., 2013
Centrate II
Chlorella sp.
125
130
55
2.4
Cabanelas et al., 2013
Centrate III
Chlorella sp.
466
471
55
8.6
Cabanelas et al., 2013
Centrate IV
Chlorella sp.
905
909
55
16.5
Cabanelas et al., 2013
Metro plant centrate
Chlorella sp.
264
290
530
0.5
Min et al., 2011
10% anaerobic digestion tanks and the conflux line of the 90% wastewaters
Chlorella sp. 227
220
250
17
14.7
Cho et al., 2013
Conventional secondary-treatment
Chlorella vulgaris (SAG 211-12)
24
223
330
0.7
Ruiz et al., 2011
Reference
Agricultural wastewater
Industrial wastewater
Conventional secondary-treatment
Chlorella vulgaris (SAG 211-12)
50% piggery wastewater
205
223
330
0.7
Ruiz et al., 2011
Chlorella zofingiensis
148
156
0.9
Zhu et al., 2013
50% piggery wastewater
Chlorella zofingiensis
139
146
1.0
Zhu et al., 2013
50% piggery wastewater
Chlorella zofingiensis
139
146
1.0
Zhu et al., 2013
Dairy wastewater
Chlorella vulgaris
70
71
61
1.2
Qin et al., 2014
10% dairy wastewater
Chlorella zofingiensis G1
5
12
15
0.8
Huo et al., 2012
Digested dairy manure (20x dilution)
Chlorella sp.
112
173
13
13.3
Wang et al., 2010
Digested dairy manure
Chlorella sp.
100
130
18
7.2
Wang et al., 2010
Soybean processing wastewater
Chlorella pyrenoidosa
170
190
46
4.1
Su et al., 2011
Riboflavin manufacturing wastewater
Chlorella pyrenoidosa
885
120
7.4
Sun et al., 2013
Brewery wastewater
Chlorella vulgaris
90
18
5.0
Farooq et al., 2013
Table 2. Biomass and lipid production and productivity of the microalgae Chlorella cultures using wastewater Wastewater type
Municipal wastewater
Wastewater source
Microalgae
Biomass Biomass Lipid Lipid Lipid production productivity content production productivity (mg L-1) (mg L-1 day-1) (%) (mg L-1) (mg L-1 day-1)
Reference
Centrate Metropolitan Chlorella sp. wastewater treatment plant
1175
313
11
120
35.6
Li et al., 2011
Centrate Metropolitan Chlorella sp. wastewater treatment plant
1060
283
11
120
31.2
Li et al., 2011
Pretreated urban wastewater WWTP1
Chlorella sp.
1500
116
Cabanelas et al., 2013
Pretreated urban wastewater WWTP2
Chlorella sp.
1340
117
Cabanelas et al., 2013
Effluent from primary settler
Chlorella sp.
1160
56
Cabanelas et al., 2013
Centrate I
Chlorella sp.
1180
125
Cabanelas et al., 2013
Centrate II
Chlorella sp.
1320
195
Cabanelas et al., 2013
Centrate III
Chlorella sp.
1520
194
Cabanelas et al., 2013
Centrate IV
Chlorella sp.
1180
138
Cabanelas et al., 2013
Metro plant centrate
Chlorella sp.
600
50
Min et al., 2011
Agricultural wastewater
Industrial wastewater
10% anaerobic digestion tanks and the conflux line of the 90% wastewaters
Chlorella sp. 227
3010
400
Conventional secondary-treatment
Chlorella vulgaris (SAG 211-12)
717
95
Ruiz et al., 2011
Conventional secondary-treatment
Chlorella vulgaris (SAG 211-12)
1228
88
Ruiz et al., 2011
50% piggery wastewater
Chlorella zofingiensis
2962
296
37.3
1105
111
Zhu et al., 2013a, b
50% piggery wastewater
Chlorella zofingiensis
2860
286
33.3
987
99
Zhu et al., 2013b
50% piggery wastewater
Chlorella zofingiensis
2005
201
34.8
698
70
Zhu et al., 2013b
Dairy wastewater
Chlorella vulgaris
1870
450
10.3
193
48
Qin et al., 2014
10% dairy wastewater
Chlorella zofingiensis G1
144
29
17.9
26
5
Huo et al., 2012
Digested dairy manure (20x dilution)
Chlorella sp.
1710
81
13.4
233
11
Wang et al., 2010
Digested dairy manure Soybean processing wastewater Riboflavin manufacturing wastewater
Chlorella sp. Chlorella pyrenoidosa Chlorella pyrenoidosa
1391
69
10.1
141
7
Wang et al., 2010
2150
640
37
806
240
Su et al., 2011
1250
254
39.3
491
99
Sun et al., 2013
Brewery wastewater
Chlorella vulgaris
2266
227
26.7
605
61
Farooq et al., 2013
10.8
325
65
Cho et al., 2013
Highlights 1. Agricultural wastewater shows a great potential for microalgal Chlorella growth 2. NH4 +-N in wastewater is the key factor for microalgal biomass and lipid production 3. Optimal N and P concentrations in wastewater for Chlorella cultivation were indicated 4. Limitations of microalgal biomass productivity by wastewater were detail discussed