Raikova Et Al., 2016. Towards - An - Aviation - Fuel - Through - The - Hydrothermal
Raikova Et Al., 2016. Towards - An - Aviation - Fuel - Through - The - Hydrothermal
Raikova Et Al., 2016. Towards - An - Aviation - Fuel - Through - The - Hydrothermal
net/publication/305366235
CITATIONS READS
8 1,139
5 authors, including:
Valeska P Ting
University of Bristol
95 PUBLICATIONS 1,512 CITATIONS
SEE PROFILE
Some of the authors of this publication are also working on these related projects:
Gas sensing using porous materials for automotive applications View project
All content following this page was uploaded by Sofia Raikova on 03 May 2018.
9
Towards an Aviation Fuel Through the
Hydrothermal Liquefaction of Algae
S. Raikova1, C.D. Le2, J.L. Wagner1, V.P. Ting3 and C.J. Chuck3
1
Centre for Doctoral Training, Centre for Sustainable Chemical Technologies, Department of
Chemical Engineering, University of Bath, Bath, United Kingdom, 2Department of Oil Refining and
Petrochemistry, Hanoi University of Mining and Geology, Hanoi, Vietnam, 3Department of Chemical
Engineering, University of Bath, Bath, United Kingdom
entire algal biomass, including proteins and car- hydrocarbon fuels, including aviation kerosene.
bohydrates, to generate algal oils. However, However, the nitrogen content is substantially
although both gasification and pyrolysis are higher in algal bio-oils than alternative terres-
effective for processing of dry feedstocks such trial oils, and as such, removal of the
as lignocellulose, they are unappealing from an N-compounds in the bio-crude is one of the
economic standpoint due to the high mass frac- most significant challenges that must be over-
tion of water in algal feedstock, and the need come in order to advance HTL technology for
for energy-intensive drying [6]. biofuel production from microalgae.
In contrast, thermochemical processes con- HTL can be used to process biomass at a
ducted in the presence of water, such as hydro- concentration of ca. 1025 wt% in water,
thermal gasification, hydrothermal reducing the energy consumption of biomass
carbonization, and HTL, are more suitable for preparation by 88% (with respect to using dry
wet feedstocks. HTL, in particular, has recently biomass) if a 16% slurry is generated using
been examined for the processing of whole centrifugation and processed without further
microalgal feedstocks, and can offer significant drying steps [7]. The mild temperatures used
energetic cost savings, as lipid content and in HTL are well within the range of tempera-
overall biomass productivity are often inversely tures encountered in many conventional oil
related [6]. It utilizes water at sub-/near-critical refinery operations [8], and as such, HTL pro-
conditions (200374 C, 528 MPa) as both the cessing for algal biomass can be made energy-
reaction medium and solvent for a host of efficient and easily scalable. Liu et al. evalu-
simultaneous reactions, converting algal bio- ated the life cycle performance of lab-, pilot-,
mass into a bio-crude oil, alongside a nutrient- and full-scale scenarios, finding significant
rich aqueous phase, a solid char, and a number improvements in Greenhouse Gas emissions
of gaseous products (Fig. 9.1). The bio-crude oil with respect to gasoline and corn ethanol, and
produced is acidic, highly viscous, and contains a potential Energy Return on Energy Invested
high proportions of N and O. Much like pyroly- of B2.5 for the full- scale scenario [9], subject
sis oil, this bio-crude can be catalytically to the optimization of a closed-loop system
upgraded to produce various fractions of incorporating energy and nutrient recycling.
9.2.1 Reaction Mechanism These are highly reactive, and rapidly poly-
merize and form liquid bio-crude, gaseous,
HTL employs water at near-critical condi- and solid products [1517]. At higher reaction
tions as a reaction medium and solvent. At temperatures and longer reaction times, repo-
near-critical conditions, the solvent properties lymerization, condensation, and decomposi-
of liquid water change substantially (including tion of substances from different phases may
changes in dielectric constant, density, diffu- occur. This results in an increase of the solid
sivity, polarity, viscosity, H-bonding, and H1 and gas yields and reduction of the bio-crude
donor capabilities), transforming it from a yield [1820]. Dehydration reactions, leading
polar, highly H-bonded solvent to exhibiting to oxygen content reduction, also play a key
behaviour more typical of a nonpolar organic role in improving the quality of the bio-crude.
solvent. In this form, it can act as a solvent for
a range of organic reactions and facilitate the
breakdown of biomass to bio-crude [10]
(Fig. 9.2). 9.3 HYDROTHERMAL
The prevention of vapour formation at high LIQUEFACTION OF MICROALGAE
pressure means the enthalpy associated with
the phase change of water is largely reduced, Bio-crude yields and properties are depen-
giving vastly increased energy efficiencies for dent on the algal species and its composition.
HTL processing over pyrolysis [12]. However, operational parameters, such as
HTL is comprised of hundreds of simulta- reaction temperature, heating rate, retention
neous reactions, which are not well- time, the initial biomass loading, and the pres-
characterized in the literature. In hot ence of catalysts also have a significant effect
compressed liquid water (near the critical on yields [14]. A wide range of operating con-
point of 374 C and 22.1 MPa), there are two ditions have been explored, with liquefaction
competitive reactions: hydrolysis and repoly- typically carried out in high pressure batch
merization [13,14]. The former is more impor- reactors. Oil yields are generally calculated as
tant and dominant at the early stages of the a weight percentage of the feedstock weight,
process, when the microalgae is decomposed using either the dry (d) or the dry ash-free
and depolymerized into small compounds. (daf) weight as a basis.
9.3.1 Effect of Biomass Composition on respect to initial lipid content, further reinfor-
Bio-Crude Oil Production cing the advantages of hydrothermal processing
over lipid extraction for algal biodiesel [22].
It has been previously shown that bio-crude Higher heating values (HHV) of 2535 MJ/kg
yields from HTL of microalgae can be strongly are typical for bio-crude, and higher lipid levels
correlated to the biomass composition. The lipid in the biomass appear to correspond to higher
fraction of the biomass is much more readily HHV, although the two properties are not line-
converted into bio-crude than other biomass arly related. Li et al. found, under optimal con-
components, with a study by Biller and Ross ditions, Nannochloropsis and Chlorella bio-crude
reporting that conversion efficiencies of different HHVs were 31.5 and 34.2 MJ/kg, respectively,
algal components to bio-crude oil were in the with a maximum HHV of 37 MJ/kg. Although
order lipids . proteins . carbohydrates [15]. this constitutes a significant increase with
This explains the particularly high yields respect to the starting biomass (22.4 and
obtained from lipid-rich microalgae. However, 32.3 MJ/kg initially), it still falls short of the
as HTL utilizes all biomass components, a high energy content of mineral crude (4148 MJ/kg)
lipid content is not essential for obtaining good [27]. Interestingly, higher bio-crude yields do
bio-crude yields, in contrast to algal biodiesel, not necessarily correspond to better oil proper-
which relies entirely on lipids. This effect has ties; Nannochloropsis processed at 350 C yielded
been demonstrated by Yu et al., who reported a 34% oil with an HHV of 38.1 MJ/kg, while 46%
yield of 39.0% bio-crude oil from an algae strain oil was obtained at a processing temperature of
containing only 0.1% lipids [21]. Utilizing the 310 C, with a much lower HHV of 27.7 MJ/kg
entire algal biomass for processing lifts the con- [25] (Table 9.1).
straints on high-lipid algal strain selection, and The numerous simultaneous reactions occur-
can significantly reduce cost and energy require- ring under HTL conditions lead to a bio-crude
ments of cultivation by using faster-growing containing a diverse range of chemical com-
strains or algal communities. pounds, the main constituents of which have
Although the specifics of the effects of bio- been found to be C5C16 cyclic nitrogen com-
mass composition remain unclear, a number of pounds, C15C33 branched and unbranched
studies have examined the role of the different hydrocarbons, branched oxygenates, aromatic
component fractions (eg, lipids, proteins, and compounds, and heterocycles [26]. Brown et al.
carbohydrates) in bio-crude production via carried out a detailed analysis of bio-crude pro-
HTL. Most liquefaction processes under opti- duced by liquefaction of Nannochloropsis sp.
mized conditions have resulted in bio-crude Over 90 compounds were detected using
yields around 3045% [15,2225], regardless of GCMS, although some lighter organics are
algae strain [12], although, notably, Li et al. likely to have been lost during sample extrac-
obtained yields of 55% for Nannochloropsis sp. tion, and heavier compounds may not have
under HTL at 260 C for 60 min and at 25% algal been detected by GC. A brief overview of the
loading, and 83% for Chlorella sp. (220 C, major compounds is presented in Table 9.2.
90 min, 25% algal load) [26]. The two algal spe- Elevated heteroatom (O and N) content with
cies have very different compositions respect to mineral crude oil is typical of bio-
(Nannochloropsis contains protein, lipids, and crude oils [9,10,29]. Higher O and N levels give
carbohydrates in an approximate ratio of rise to undesirable fuel properties, such as high
52:14:22, whereas the same components in acidity and viscosity [24], and the increased
Chlorella have a ratio of 9:60:13), but in both diversity of chemical composition can nega-
cases, bio-crude yield was enhanced with tively affect combustion performance, storage
Spirulina Biomass only 42.26 5.86 3.47 47.26 1.15 20.4 [25]
Spirulina 300 C, 1012 min, 20% TS, DCM 32.6 68.9 8.9 6.5 14.9 0.86 33.2 [24]
extraction
Chlorella 350 C, 60 min, 10% TS 35.8 70.7 6.8 5.9 14.8 0.0 35.1 [23]
Nannochloropsis 350 C, 60 min, 10% TS 34.3 68.1 8.8 4.1 19.0 0.0 34.5 [23]
Spirulina 350 C, 60 min, 10% TS 29 73.3 9.2 7 10.4 0.0 36.8 [15]
Spirulina 220 C, 20 bar, 30 min, 25% TS 38 59.15 5.50 10.47 18.19 1.22 28.7 [25]
Spirulina 310 C, 115 bar, 30 min, 25% TS 38 71.29 8.01 7.66 16.82 0.81 35.2 [25]
Spirulina 350 C, 195 bar, 30 min, 25% TS 30 70.69 8.05 7.22 10.06 0.77 34.3 [25]
Indole
Methylindole
1-Pentadecene
Heptadecane
Isomers of 2-phytene
Myristic acid
Phytane
(Continued)
Palmitoleic acid
Palmitic acid
Oleic acid
Stearic acid
Cholest-4-ene
Cholest-5-ene
Cholesta-3,5,-diene
Cholesterol
(Continued)
9.3 HYDROTHERMAL LIQUEFACTION OF MICROALGAE 223
TABLE 9.2 (Continued)
Major Compound Structure
Cholest-4-en-3-one
Cholest-4,6-diene-3-one
stability, and economic value [24,29]. The het- produced via HTL presents numerous advan-
eroatom content of the bio-crude can generally tages compared to lipid extraction, the product
be attributed to the high O and N content of the needs significant upgrading to obtain a
starting biomass, although there is not always a suitable aviation fuel [24]. An alternative solu-
direct correlation: Chlorella biomass containing tion posed by Garcia Alba et al. suggests that
1.9% N was processed to bio-crude with a 0.3% proteins could be extracted prior to HTL pro-
N content, while Nannochloropsis (7.5% N ini- cessing and sold as a high-value co-product in
tially) resulted in a bio-crude with 5.4% N. a biorefinery paradigm [13]. However, this
Chlorella bio-crude was also found to have a clearly has implications for bio-crude volumes,
higher O content (11.5% compared to 9.5% for particularly when low-lipid algae such as
Nannochloropsis), although the O content of the Spirulina are used.
biomass was 21.8%, compared to 29.1% for
Nannochloropsis [26].
9.3.2 Effect of Microalgal Loading on
Additionally, the elevated N content of bio-
Product Formation
crude of up to 11%, arising from the proteins
in the starting biomass (compared to around One of the key benefits of wet biomass pro-
0.1, and seldom above 1%, for mineral crude) cessing in comparison to lignocellulosic bio-
[30,31], limits its direct usability as a fuel, as it mass or dry processing is that microalgae
can lead to increased NOx emissions. forms a slurry with water, which can be easily
Significantly, higher nitrogen levels may con- pumped and flowed through the reactor.
tribute to catalyst poisoning, making these bio- Particularly for continuous HTL operation,
crude oils unsuitable for co-refining in existing determination of the optimal loading of micro-
refineries [12,31]. Hence, although bio-crude algae in the slurry is crucial.
From the literature, many factors such as holding temperature triggers bio-crude pro-
the scale of the reactor and economics need to duction. After reaching a maximum value for
be considered with the selection of the micro- the bio-crude yield, further increase in the
algal load used in HTL. Hence, there is no holding temperature inhibits biomass
clear connection between the microalgal load liquefaction.
(total solid fraction, TS) in the feed and the The optimization of holding temperature
bio-crude yield. Studies of HTL of algae per- varies depending on microalgal species; how-
formed over a large range of microalgal loads ever, in the majority of cases, compared to a
(ranging from 4% to 50%) have apparently bio-crude yield obtained at ca. 350 C, lower
yielded contradictory results [6]. For example, holding temperatures (B310320 C) gener-
Jena et al. concluded that an increase of the ated higher bio-crude yields. This effect was
biomass fraction in the feed by 10% resulted in observed by Dote et al. [35], and subsequently
a jump of more than 20% in the bio-crude by Minowa et al. [36], who observed that
yield [32], though the opposite findings were yields of bio-crude oil from the liquefaction of
reported by Garcia Alba et al. [13]. Dunaliella tertiolecta increased from 30.9% to
The optimum ratio of microalgae and water 43.8% when increasing the holding tempera-
in the feed is presumably dependent on species ture from 250 C to 300 C, but dropped to
and reactor design. A high microalgal loading 42.6% when processing temperature was
would be economically beneficial, due to reduc- increased further to 340 C [36].
tion of the water content of the feed, leading to a These findings are mirrored in the work of
reduction in the energy required for heating the Gai et al. for each retention time examined, oil
water, and a correspondingly higher volume yields from Chlorella pyrenoidosa increased
efficiency and productivity of the HTL reactor when holding temperature was increased from
[12]. However, there is expected to be an upper 260 C to 280 C, and proceeded to decline
limit due to mass transfer limitations and the when reaction temperatures were brought to
formation of blockages in continuous thermo- 320 C [37]. The authors suggested that with
chemical conversion [33]. Continuous liquefac- increasing temperatures, more secondary
tion studies have shown that while some decomposition reactions may be triggered,
practical operational issues of reactor blockage resulting in the production of gases and char
may occur at microalgal loads above 5 wt% in rather than oils. Regrettably, they were not
the feed [31], processing of microalgae slurries able to satisfactorily confirm this using the gas
with microalgal loads of up to 35% (obtaining a yields obtained in their investigation, owing to
bio-crude yield of up to 63.6%) are possible [34]. the high experimental error.
Another key consideration on the loading of In addition, the holding temperature has a
microalgae is the cost of drying the original feed- strong influence on the bio-crude properties:
stock, which plays a significant role in dictating increasing the temperature results in a decline
the most suitable loading achievable. in oxygen content and consequently increases
the HHV of the oil [36,38]. The nitrogen con-
tent in turn appears to increase with holding
temperature, likely due to the promotion of
9.3.3 Effect of Holding Temperature on
protein decomposition at high temperatures,
Microalgal Processing although the opposite effect has been reported
The holding temperature has a remarkable in other studies [21].
influence on the yield and properties of HTL The length of time the reaction is held at
products. In general, an initial rise in the temperature also has a significant effect on
chemical, and pharmaceutical industries [60]. alkenes, fatty acids, ketones, aldehydes,
Lammens et al. have also evaluated the poten- nitriles, amides, and nitrogen heterocycles
tial of algal proteins as a source of high-value such as indoles and pyridines [62,63]. In addi-
bio-based chemicals, such as N-methylpyrroli- tion, due to the high boiling point range of the
dinone, N-vinylpyrrolidinone, and acrylonitrile oils, most reports have only achieved partial
[61]. Overall, there is significant scope for characterization [6,64]. Elemental analysis is
extraction of higher-value materials from therefore one of the most reliable methods to
macroalgae prior to conversion to fuels, and achieve a like-for-like comparison of different
the application of a biorefinery concept could crude oils and of the performance of different
increase the value of the seaweed biomass and upgrading studies.
improve the economics of production of bioe-
nergy from macroalgae, thereby leading to a
more rapid commercial realization of algal-
9.5.1 Upgrading of Bio-Crude Oil
derived biofuels.
Produced by the HTL of Microalgae
Only a few studies have investigated the
9.5 CHARACTERISTICS OF BIO- upgrading of HTL oils from microalgae
CRUDE OIL FROM (Table 9.3), with the majority of these studies
HYDROTHERMAL LIQUEFACTION conducted in batch and achieving only partial
OF ALGAE nitrogen removal. While the choice of catalyst
was found to impact the physical properties of
The bio-crude oil produced by the HTL of the reaction products, it had little impact on
microalgae requires significant upgrading the denitrogenation performance itself [66].
before it can enter the conventional fuel stream Instead, the degree of denitrogenation appears
and be used to produce aviation kerosene. The to be mainly dependent on the reaction tem-
high levels of nitrogen (typically between 4% perature, which suggests that these reactions
and 8%) and sulphur (up to 1%), in particular, are thermally controlled [66]. Unfortunately,
must be almost completely removed if the the high temperatures also result in a signifi-
resulting fuels are to comply with emission cant reduction in the hydrogen content of the
standards. The crude bio-oils from HTL of oils, presumably due to an increase in the aro-
algae can be blended with fossil oil and matic content of the reduction product above
upgraded to conventional kerosene and other desirable levels. Potentially, the poor perfor-
hydrocarbon fuels in a conventional refinery. mance of the selected catalysts under these
While it is true that these facilities are capable conditions could lead to insufficient hydrogen
of processing oils with high levels of sulphur, being provided for complete hydrogenation. It
common industrial catalysts are not able to tol- has also been suggested that the accumulation
erate the high levels of oxygen and nitrogen of ammonia may be limiting the complete
seen in the bio-oils. Therefore, at least partial reduction of nitrogen compounds [69].
upgrading of the oils is required to reduce the Nonetheless, more recent studies have demon-
oxygen and nitrogen concentrations to a level strated the full catalytic upgrading of bio-
comparable to fossil crude oil before they can crude directly to suitable hydrocarbon fuels.
be sent to a refinery for fractionation. Research has focused on both in situ heteroge-
Detailed chemical analysis of the oils is dif- neous catalysis and hydrotreatment of the bio-
ficult, as they can contain up to several hun- crude after separation [70]. Duan and Savage
dred compounds, including phenols, alkanes, reported on the use of a 5% Pd/C catalyst for
Bio-crude from 5.32 0.56 8.35 HZSM-5 400500 C 4.35 MPa Batch 0.54 h 1.62.71 Bdl 0.392.81 [65]
HTL of (050 wt% (hydrogen)
Nannochloropsis loading)
at 350 C for 1 h
Bio-crude from 4.80 0.48 8.07 Pt/C, Mo2C, 430530 C 3.5 MPa Batch in 26 h 1.503.61 Bdl 0.135.31 [66] Temperature
HTL of HZSM-5 (hydrogen) supercritical has biggest
Nannochloropsis (520 wt%) water (water/oil impact on oil
at 340 C for 4 h mass ratio of 4:5) properties
Bio-crude from 4.89 0.68 6.52 Pt/C (25 wt 400 C 3.4 MPa Batch in 4h 2.172.79 Bdl 4.314.71 [67]
HTL of %), HCl, (hydrogen) supercritical
Nannochloropsis NaOH water (water/oil
at 320 C for 4 h mass ratio of 1:1)
Bio-crude from 7.3 Nd 7.8 Pt/γ-Al2O3 400 C 6 MPa Batch in 1h 2.45.8 N/A 4.717.9 [8] With formic
HTL of (040 wt%) (hydrogen) supercritical acid, reacted
Chlorella sp. at HCOOH water with the crude
350 C for 1 h (088 wt%) (043 wt%) algal oil
resulting in
increased yield
Bio-crude from 0.26.3 Nd 1039 HZSM-5 600 C Pyrolysis probe 0.020.14 N/A 0.080.30 [68] Elemental
HTL of (SiO2/ (heating rate: calculated
Desmodesmus Al2O3 5 280), 20 C per second, from structure
sp. at zeolite: pyrolysis time: of compounds
200375 C for sample mass 10 s) identified
560 min ratio of 20:1 by GC
Bio-crudes 4.04.7 0.30.5 5.38.0 Co-promoted 125170 C 13.6 MPa Bench-scale LHSV of ,0.050.16 ,50 ppm 0.81.2 [34]
from HTL of MoS2 on (1st quarter in hydroprocessing 0.140.20 h21
Nannochloropsis fluorinated of reactor); hydrogen system
sp. at alumina 405 C (Main flow
344362 C, in support reactor)
continuous
reactor
230 9. TOWARDS AN AVIATION FUEL THROUGH THE HYDROTHERMAL LIQUEFACTION OF ALGAE
hydrotreatment of algal bio-crude oil, finding oil over a temperature range of 350450 C,
that the bio-crude HHV from Nannochloropsis with a residence time of 60 min [72]. While the
was significantly improved from approxi- total nitrogen content was not affected by the
mately 37 MJ/kg to 44 MJ/kg, with corre- thermal treatment, the total oxygen content
sponding improvements in the kinematic was significantly reduced from 5.7% in the
viscosity, and significant reductions in N, O, bio-crude to 0.2% in the product oil treated at
and S content. However, these results were 400 C. Thermal treatment was also found to
achieved over long retention times of up to 4 h reduce the total acid content, as well as the
and 80 wt% catalyst loadings, and the yield boiling point range of the bio-crude oils, mak-
was substantially decreased [71]. Other studies ing them more volatile and less viscous. In
have centred around supported Pd catalysts, addition, trace metals were partly removed
though more recently, Li and Savage reported from the bio-crude. Similar findings were also
the upgrading of algal crude oil produced by reported by Bai et al., who used a two-step
HTL using HZSM-5, generating a paraffin-like process to hydrothermally treat the bio-crude
oil composed of .95 wt% C and H, which oil [73].
retained 80% of the energy content of the ini- These findings demonstrate that it is possi-
tial bio-crude and was suitable for use as a liq- ble to process the HTL bio-crude in a similar
uid fuel [65]. way to heavy crude oil, continuously treating
A number of studies have attempted to in a number of subsequent processes, includ-
upgrade crude bio-oils produced by the lique- ing thermal treatment, hydrotreatment, and
faction of Nannochloropsis sp. [66,67] or hydrocracking, to make fractions suitable for
Chlorella sp. [8] in the presence of supercritical further processing towards production of dif-
water. It was hoped that the reaction of water ferent commercial products, such as gasoline,
with hydrocarbons would generate additional diesel, and jet fuel.
hydrogen which, in turn, would promote the In a similar effort, promising results were
removal of heteroatoms from the bio-crude. achieved during the continuous hydrotreating
However, while the presence of water did not of bio-oils produced by the HTL of various
appear to have a beneficial effect on the deni- strains of Nannochloropsis over sulphided
trogenation performance, it was found to CoMo catalyst supported on fluorinated alu-
increase the oxygen content of the reaction mina [34]. Single-stage upgrading at 405 C
product [8]. The best results in the presence of with a space velocity of 0.20 h21 and a pres-
supercritical water were obtained over Pt/C sure of 14 MPa in excess hydrogen produced
catalyst at 530 C with a reaction time of 6 h, oils with a nitrogen content ranging from
with almost complete sulphur removal and a 0.07 wt% to 0.25 wt%. An even lower nitrogen
reduction in nitrogen content from 4.0% to content could be achieved by pretreating the
1.5% [66]. In contrast, upgrading of a liquefac- oil at temperatures between 125 C and 170 C
tion oil obtained from Nannochloropsis in the in the first quarter of the reactor, before con-
absence of water over an HZSM-5 catalyst, at version at 405 C. While this study demon-
500 C, and with a reaction time of 4 h, resulted strated that almost complete denitrogenation
in a reduction in the nitrogen content from of microalgal crude oils can be achieved under
5.3% to 1.6% [65]. continuous conditions, further studies are
Alternatively, Roussis et al. performed required to verify these findings and optimize
experiments to thermally treat HTL bio-crude the reaction conditions.
Elliott et al. developed a bench-scale contin- 9.7.1 Algae Cultivation and Waste
uous system for HTL of algal biomass in 2013 Water Treatment
[34]. The system included the combination of a
CSTR and a plug-flow reactor, with integrated Significant value could be added by com-
modules for catalytic upgrading and sulphur bining the microalgal production process with
stripping. This more complex hybrid HTL a secondary objective, such as waste water
reactor configuration was developed as a treatment, the recovery of metals from mining
direct result of plugging problems experienced waste, or carbon sequestration from power
previously with a plug-flow reactor system. plant effluents. Waste water treatment in par-
The solids and bio-crude product were sepa- ticular could provide substantial quantities of
rated without the use of solvents through the algal biomass, without requiring the addition
use of an in-line filtration unit. The group was of costly nutrients. The environmental remedi-
able to operate at far higher loadings than ation industry has vastly expanded in recent
Jazrawi et al. (up to 35%), obtaining maximum years, with the remediation market in the
bio-crude yields of 63.6% using a specially cul- United States alone generating an estimated
tured Nannochloropsis strain. The group pre- $12.8 billion in 2010, of which waste water
sented a proposal for a biorefinery, with water treatment represented just under 50% [75].
and nutrients in the post-HTL water recycled Wastewater treatment via algal remediation
into the algal growth stage, although the lends itself well to synergistic combination
model did not explore the potential of using with biomass production, and numerous
the CO2-rich gaseous phase as the CO2 source investigations into the cultivation of algae on
to supplement algal cultivation [34]. industrial, municipal, and agricultural waste
waters have already been carried out [76,77].
Global municipal waste water production
amounts to approximately 300 billion m3, of
9.7 PROCESS INTEGRATION FOR which just over 50% is currently treated [78].
AN ADVANCED BIOREFINERY Assuming an average biomass yield of 1 g/L,
and a liquefaction yield of 30%, complete con-
Despite the many potential benefits of algal version of the existing waste water treatment
biofuel technology, for costs and sustainability facilities could result in an annual bio-crude
benefits to be optimized, secondary value production of up to 90 billion L.
streams must be considered. Conventional In addition, waste water treatment using
crude oil refineries generate a wide range of microalgae has been proven to be highly effec-
products, including paraffin, lubricants, gases, tive in reducing the concentration of N and P
sulphuric acid, petrochemicals, and feedstocks pollutants, which are used as nutrients, in the
for plastic manufacture, alongside fuels. effluent [79]. Compared to conventional meth-
Similarly, algal fuel production has the poten- ods such as chemical precipitation or the pro-
tial to co-produce high-value chemicals, such duction of an activated sludge, forming waste
as proteins, vitamins, and trace minerals in products which are often disposed of by land-
addition to liquid fuels [5]. However, few fill, microalgal treatment provides a much
industries have the economic capacity to more sustainable route as it allows the efficient
accommodate high volumes of co-products. recycling of these nutrients [77].
The only industries on a similar scale to fuels Metal recovery from mining waste could be
are mining, agriculture, plastics, and environ- another lucrative secondary function of micro-
mental remediation. algae cultivation. A number of studies have
energy-intensive production [92]. As a result, TABLE 9.4 Nutrient Content of HTL Process Water
nutrient provision for algal cultivation is a (Spirulina, 300 C) Compared to Standard Growth Media
key sustainability concern [93], and nutrient 3N-BBM 1 V [86]
recovery is a crucial step in making third- HTL Process Water 3N-BBM 1 V
generation biofuel production viable [94]. Nutrient Conc./ppm Conc./ppm
In hydrothermal processing, high protein
TOC 15123
levels in the feedstock can lead to accumula-
tion of light organics in the aqueous phase Total N 8136 124
[26] (up to 50% of biomass carbon has been NH1
4
6295
found to accumulate in process water) [86],
PO32 2159 135
leading to reduced bio-crude yields and 4
[5] A.A. Adenle, G.E. Haslam, L. Lee, Global assessment of [18] S. Zou, Y. Wu, M. Yang, C. Li, J. Tong,
research and development for algae biofuel production Thermochemical catalytic liquefaction of the marine
and its potential role for sustainable development in microalgae Dunaliella tertiolecta and characterization of
developing countries, Energy Policy 61 (2013) 182195. bio-oils, Energy Fuels 23 (2009) 37533758.
[6] D. López Barreiro, W. Prins, F. Ronsse, W. Brilman, [19] D. Zhou, L. Zhang, S. Zhang, H. Fu, J. Chen,
Hydrothermal liquefaction (HTL) of microalgae for Hydrothermal liquefaction of macroalgae
biofuel production: state of the art review and future Enteromorpha prolifera to bio-oil, Energy Fuels 24
prospects, Biomass Bioenergy 53 (2013) 113127. (2010) 40544061.
[7] L. Xu, D.W.F. Wim Brilman, J.A. Withag, G. Brem, S. [20] K. Anastasakis, A.B. Ross, Hydrothermal liquefaction
Kersten, Assessment of a dry and a wet route for the of the brown macro-alga Laminaria Saccharina: effect of
production of biofuels from microalgae: energy balance reaction conditions on product distribution and com-
analysis, Bioresour. Technol. 102 (2011) 51135122. position, Bioresour. Technol. 102 (2011) 48764883.
[8] P. Duan, X. Bai, Y. Xu, A. Zhang, F. Wang, L. Zhang, [21] G. Yu, Y. Zhang, L. Schideman, T. Funk, Z. Wang,
et al., Catalytic upgrading of crude algal oil using Distributions of carbon and nitrogen in the products
platinum/gamma alumina in supercritical water, Fuel from hydrothermal liquefaction of low-lipid microal-
109 (2013) 225233. gae, Energy Environ. Sci. 4 (2011) 45874595.
[9] X. Liu, B. Saydah, P. Eranki, L.M. Colosi, B. Greg [22] G. Yu, Y. Zhang, L. Schideman, T.L. Funk, Z. Wang,
Mitchell, J. Rhodes, et al., Pilot-scale data provide Hydrothermal liquefaction of low lipid content micro-
enhanced estimates of the life cycle energy and emis- algae into bio-crude oil, Am. Soc. Agric. Biol. Eng 54
sions profile of algae biofuels produced via hydro- (2011) 239246.
thermal liquefaction, Bioresour. Technol. 148 (2013) [23] P. Biller, R. Riley, A.B. Ross, Catalytic hydrothermal
163171. processing of microalgae: decomposition and upgrad-
[10] A.A. Peterson, F. Vogel, R.P. Lachance, M. Fröling, M. ing of lipids, Bioresour. Technol. 102 (2011) 48414848.
J. Antal Jr., J.W. Tester, Thermochemical biofuel pro- [24] D.R. Vardon, B.K. Sharma, J. Scott, G. Yu, Z. Wang, L.
duction in hydrothermal media: a review of sub-and Schideman, et al., Chemical properties of biocrude oil
supercritical water technologies, Energy Environ. Sci. from the hydrothermal liquefaction of Spirulina algae,
1 (2008) 3265. swine manure, and digested anaerobic sludge,
[11] J. Wagner, Production of transport fueld via the hydro- Bioresour. Technol. 102 (2011) 82958303.
thermal liquefaction of microalgae and subsequent [25] S.S. Toor, H. Reddy, S. Deng, J. Hoffmann, D.
upgrading reaction (PhD confirmation report), 2014. Spangsmark, L.B. Madsen, et al., Hydrothermal lique-
[12] C. Tian, B. Li, Z. Liu, Y. Zhang, H. Lu, Hydrothermal faction of Spirulina and Nannochloropsis salina under
liquefaction for algal biorefinery: a critical review, subcritical and supercritical water conditions,
Renewable Sustainable Energy Rev. 38 (2014) 933950. Bioresour. Technol. 131 (2013) 413419.
[13] L. Garcia Alba, C. Torri, C. Samorı̀, J. Van Der Spek, [26] H. Li, Z. Liu, Y. Zhang, B. Li, H. Lu, N. Duan, et al.,
D. Fabbri, S.R.A. Kersten, et al., Hydrothermal treat- Conversion efficiency and oil quality of low-lipid
ment (HTT) of microalgae: evaluation of the process high-protein and high-lipid low-protein microalgae
as conversion method in an algae biorefinery concept, via hydrothermal liquefaction, Bioresour. Technol. 154
Energy Fuels 26 (2012) 642657. (2014) 322329.
[14] S. Zou, Y. Wu, M. Yang, C. Li, J. Tong, Bio-oil produc- [27] J.G. Speight, Handbook of Petroleum Analysis, first
tion from sub- and supercritical water liquefaction of ed., Wiley Interscience, New York, NY, 2001.
microalgae Dunaliella tertiolecta and related properties, [28] T.M. Brown, P. Duan, P.E. Savage, Hydrothermal
Energy Environ. Sci. 3 (2010) 1073. Liquefaction and Gasification of Microalga
[15] P. Biller, A.B. Ross, Potential yields and properties of Nannochloropsis sp., Energy Fuels 24 (2010) 36393646.
oil from the hydrothermal liquefaction of microalgae [29] G.W. Huber, S. Iborra, A. Corma, Synthesis of trans-
with different biochemical content, Bioresour. portation fuels from biomass: chemistry, catalysts,
Technol. 102 (2011) 215225. and engineering, Chem. Rev. 106 (2006) 40444098.
[16] A. Demirbas, Mechanisms of liquefaction and pyroly- [30] J.S. Ball, M.L. Whisman, W.J. Wenger, Nitrogen con-
sis reactions of biomass, Energy Convers. Manage. 41 tent of crude petroleums, Ind. Eng. Chem. 43 (1951)
(2000) 633646. 25772581.
[17] Y.F. Yang, C.P. Feng, Y. Inamori, T. Maekawa, [31] C. Jazrawi, P. Biller, A.B. Ross, A. Montoya, T.
Analysis of energy conversion characteristics in lique- Maschmeyer, B.S. Haynes, Pilot plant testing of con-
faction of algae, Resour. Conserv. Recycl. 43 (2004) tinuous hydrothermal liquefaction of microalgae,
2133. Algal Res. 2 (2013) 268277.
[59] R. Morchio, C. Cáceres, Macroalgae current state in oil: a catalyst screening study, Fuel 120 (2014)
Latin America. International Workshop on Sustainable 141149.
Bioenergy from Algae. Berlin, Germany, 2009. [74] K.S. Ocfemia, Y. Zhang, T. Funk, Hydrothermal pro-
[60] K.A. Jung, S.-R. Lim, Y. Kim, J.M. Park, Potentials of cessing of swine manure into oil using a continuous
macroalgae as feedstocks for biorefinery, Bioresour. reactor system: development and testing, Am. Soc.
Technol. 135 (2013) 182190. Agric. Biol. Eng. 49 (2006) 533541.
[61] T.M. Lammens, M.C.R. Franssen, E.L. Scott, J.P.M. [75] United States International Trade Commission,
Sanders, Availability of protein-derived amino acids Environmental and Related Services—Investigation
as feedstock for the production of bio-based chemi- No. 332-53, USITC Publication 4389, 2013.
cals, Biomass Bioenerg. 44 (2012) 168181. [76] W.T. Chen, Y. Zhang, J. Zhang, G. Yu, L.C.
[62] Z. Hu, Y. Zheng, F. Yan, B. Xiao, S. Liu, Bio-oil pro- Schideman, P. Zhang, et al., Hydrothermal liquefac-
duction through pyrolysis of Blue-Green Algae tion of mixed-culture algal biomass from wastewater
Blooms (BGAB): product distribution and bio-oil char- treatment system into bio-crude oil, Bioresour.
acterization, Energy 52 (2013) 119125. Technol. 152 (2014) 130139.
[63] U. Jena, K.C. Das, J.R. Kastner, Effect of operating [77] J.K. Pittman, A.P. Dean, O. Osundeko, The potential
conditions of thermochemical liquefaction on bio- of sustainable algal biofuel production using waste-
crude production from Spirulina platensis, Bioresour. water resources, Bioresour. Technol. 102 (2011) 1725.
Technol. 102 (2011) 62216229. [78] Aquastat, Food and Agriculture Organization of the
[64] A.E. Harman-Ware, T. Morgan, M. Wilson, M. United Nations, 2014.
Crocker, J. Zhang, K. Liu, et al., Microalgae as a [79] L. Wang, M. Min, Y. Li, P. Chen, Y. Chen, Y. Liu, et al.,
renewable fuel source: fast pyrolysis of Scenedesmus Cultivation of green algae Chlorella sp. in different waste-
sp., Renewable Energy 60 (2013) 625632. waters from municipal wastewater treatment plant,
[65] Z. Li, P.E. Savage, Feedstocks for fuels and chemicals Appl. Biochem. Biotechnol. 162 (2010) 11741186.
from algae: treatment of crude bio-oil over HZSM-5, [80] V.K. Gupta, A. Rastogi, Biosorption of lead(II) from
Algal Res. 2 (2013) 154163. aqueous solutions by non-living algal biomass
[66] P. Duan, P.E. Savage, Catalytic treatment of crude Oedogonium sp. and Nostoc sp.—a comparative study,
algal bio-oil in supercritical water: optimization stud- Colloids Surf. B Biointerfaces 64 (2008) 170178.
ies, Energy Environ. Sci. 4 (2011) 1447. [81] V.K. Gupta, A.K. Shrivastava, N. Jain, Biosorption of
[67] P. Duan, P.E. Savage, Upgrading of crude algal bio-oil in chromium (VI) from aqueous solutions by green algae
supercritical water, Bioresour. Technol. 102 (2011) Spirogyra species, Water Res. 35 (2001) 40794085.
18991906. [82] D.B. Johnson, K.B. Hallberg, Acid mine drainage
[68] C. Torri, D. Fabbri, L. Garcia-Alba, D.W.F. Brilman, remediation options: a review, Sci. Total Environ. 338
Upgrading of oils derived from hydrothermal treat- (2005) 314.
ment of microalgae by catalytic cracking over H-ZSM- [83] K. Sbihi, O. Cherifi, A. El gharmali, B. Oudra, F. Aziz,
5: a comparative PyGCMS study, J. Anal. Appl. Accumulation and toxicological effects of cadmium,
Pyrolysis 101 (2013) 2834. copper and zinc on the growth and photosynthesis of
[69] P.-Q. Yuan, Z.-M. Cheng, X.-Y. Zhang, W.-K. Yuan, the freshwater diatom Planothidium lanceolatum
Catalytic denitrogenation of hydrocarbons through par- (Brébisson) lange-bertalot: a laboratory study, J.
tial oxidation in supercritical water, Fuel 85 (2006) Mater. Environ. Sci. 3 (2012) 497506.
367373. [84] S. Raikova, H. Smith-Baedorf, R. Bransgrove, O.
[70] P. Duan, P.E. Savage, Hydrothermal liquefaction of a Barlow, F. Santomauro, J.L. Wagner, et al., Assessing
microalga with heterogeneous catalysts, Ind. Eng. hydrothermal liquefaction for the production of bio-
Chem. Res. 50 (2011) 5261. oil and enhanced metal recovery from microalgae cul-
[71] P. Duan, P.E. Savage, Catalytic hydrotreatment of tivated on acid mine drainage, Fuel Process. Technol.
crude algal bio-oil in supercritical water, Appl. Catal. 142 (2016) 219227.
B Environ. 104 (2011) 136143. [85] D. Aitken, B. Antizar-Ladislao, Achieving a green
[72] S.G. Roussis, R. Cranford, N. Sytkovetskiy, Thermal solution: limitations and focus points for sustainable
treatment of crude algae oils prepared under hydrother- algal fuels, Energies 5 (2012) 16131647.
mal extraction conditions, Energy Fuels 26 (2012) [86] P. Biller, A.B. Ross, S.C. Skill, A. Lea-Langton, B.
52945299. Balasundaram, C. Hall, et al., Nutrient recycling of aque-
[73] X. Bai, P. Duan, Y. Xu, A. Zhang, P.E. Savage, ous phase for microalgae cultivation from the hydrother-
Hydrothermal catalytic processing of pretreated algal mal liquefaction process, Algal Res. 1 (2012) 7076.