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Comparison of cell rupturing by ozonation and ultrasonication for algal lipid extraction from Chlorella vulgaris a

b

a

a

Yuanxing Huang , Andy Hong , Daofang Zhang & Liang Li a

School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai, People's Republic of China b

Department of Civil & Environmental Engineering, University of Utah, Salt Lake City, UT, USA Published online: 21 Nov 2013.

To cite this article: Yuanxing Huang, Andy Hong, Daofang Zhang & Liang Li (2014) Comparison of cell rupturing by ozonation and ultrasonication for algal lipid extraction from Chlorella vulgaris, Environmental Technology, 35:8, 931-937, DOI: 10.1080/09593330.2013.856954 To link to this article: http://dx.doi.org/10.1080/09593330.2013.856954

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Environmental Technology, 2014 Vol. 35, No. 8, 931–937, http://dx.doi.org/10.1080/09593330.2013.856954

Comparison of cell rupturing by ozonation and ultrasonication for algal lipid extraction from Chlorella vulgaris Yuanxing Huanga , Andy Hongb , Daofang Zhanga and Liang Lia∗ a School

of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai, People’s Republic of China; b Department of Civil & Environmental Engineering, University of Utah, Salt Lake City, UT, USA

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(Received 26 May 2013; final version received 14 October 2013 ) Cell disruption is essential for lipid collection from cultivated microalgae. This study examines the performance of ultrasonication (US), conventional bubbling ozonation (CBO), and pressure-assisted ozonation (PAO) as a cell rupturing technique to obtain algal lipid from a freshwater unicellular microalgae Chlorella vulgaris, which was grown in BG11 medium at a temperature of 25◦ C and illuminated by artificial lighting with light/dark cycle of 12 h/12 h. Changes in total organic carbon, total nitrogen, total phosphorous, and chlorophyll contents in the algae suspension after ozonation and US treatments were measured to evaluate the effectiveness of cell rupture by these techniques. Lipid yields of 21 and 27 g/100 g biomass were obtained using US and PAO, respectively. Lipid yields of about 5 g/100 g biomass were obtained using CBO. In all rupturing treatments, C16 and C18 compounds were found to be predominant accounting for 90% of the fatty acids. Using US for rupturing, fatty acids of C16:0, C18:1, and C18:2 were predominant, accounting for 76 ± 4.2% of all the fatty acids. Using CBO and PAO involving ozone, fatty acids of C16:0 and C18:0 were predominant, accounting for 63–94% of the products. The results suggest that saturated fatty acid methyl ester (FAME) products are predominant with oxidative ozonation rupturing while unsaturated FAME products of lower-melting points predominant with physical ultrasonic rupturing means. PAO was an effective cell rupture method for biodiesel production with high lipid yield and more saturated hydrocarbon products. Keywords: Chlorella vulgaris; lipid extraction; ultrasonication; pressure-assisted ozonation; cell rupture

1. Introduction Depleting fossil fuels and environmental concerns with carbon emission have initiated interest in biodiesel, which is favourably viewed as biodegradable, sustainable with low sulphur and carbon emission. Raw feedstocks for biodiesel include different categories of plant oil (jatropha, soybean, and palm), animal fat (tallow, lard, and chicken fat), waste cooking oil, algae oil (seaweed), and others. Among them, lipids from microalgae seems most promising because its cultivation has little land requirement but high oil productivity with lower cost.[1,2] To convert microalgae to biodiesel, a series of processes including drying, cell disruption, lipid extraction, and transesterification is required. Cell disruption is particularly important as it facilitates release of the biomass’s intracellular contents for the extraction, and contents of the extracted lipids are highly dependent on the disruption methods.[3,4] Methods of cell disruption include autoclaving, alkaline lysis, homogenization at high pressure, ultrasonication (US), microwave, bead mills, freezing and thawing, osmotic shocks, and sulphuric acid treatment; and these methods were employed with various degrees of success for Scenedesmus obliquus, Botryococcus braunii,

∗ Corresponding

author. Email: [email protected]

© 2013 Taylor & Francis

and Chlorococcum sp.[5–8] Exploration of new techniques such as supercritical fluid extraction with carbon dioxide continues to aim at improving extraction of lipid from microalgae.[9] Ozonation has been widely used in water treatment for disinfection and oxidative removal of contaminants. Recently, ozonation has been found to be effective for volume reduction of waste-activated sludge.[10,11] Pressureassisted ozonation (PAO), a recently developed technique, is capable of solubilizing cellular materials of activated sludge at high efficiency via rupturing cell wall.[12] PAO employs repetitive pressure cycles (PC) to deliver ozone to the treatment vessel; in such a closed vessel containing the biomass an ozone gas mixture was compressed to reach a pressure of 1.0 MPa in the headspace (compression) to be followed immediately by venting (decompression) to complete one pressure cycle. During continuous pressure cycles, the integrity of activated sludge flocs was destructed, and the microorganisms were disrupted via strong cell lytic activity of ozone that led to release of cell contents and subsequent oxidation.[13,14] To date, ozonation as a cell disruption technique for microalgae for the purpose of lipid extraction has not been

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extensively reported, and the research on cell disruption by PAO is much lacking. PAO is expected to cause both chemical and direct mechanical damage to microalgae cells; however, the parameters influencing the microalgae cell disruption and lipid recovery have not yet been settled. The objective of this study is to evaluate the feasibility of using PAO to disrupt cells of Chlorella vulgaris for lipid recovery. The results in terms of lipid extraction efficiencies are compared with conventional methods of US and conventional bubbling ozonation (CBO) to determine the benefits of this new rupturing technique.

2. Experimental section 2.1. Chemicals and reagents Hexane, acetic ether, and methanol of HPLC grade were purchased from Sigma-Aldrich Co. (USA). Chemicals KOH, NaNO3 , K2 HPO4 , MgSO4 · 7H2 O, CaCl2 · 2H2 O, citric acid, ferric ammonium citrate, Na2 EDTA, Na2 CO3 , H3 BO3 , MnCl2 · 4H2 O, ZnSO4 · 7H2 O, Na2 MoO4 · 2H2 O, CuSO4 · 5H2 O, and Co(NO3 )2 · 6H2 O of analytical grade were from Sinopharm Chemical Reagent Co. (Shanghai, China). Fatty acid methyl ester (FAME) standard sample GLC-10 for Gas Chromatograph/Mass Spectrometer (GC/MS) identification; and potassium indigo trisulphonate for spectrophotometric quantification of ozone were from Supelco (Bellefonte, PA, USA).

2.2. Cultivation of C. vulgaris Algal seed, Seed I, of C. vulgaris was provided by Chinese Academy of Aquatic Research Institute (Wuhan, Hubei, China). For algae growth, 5 mL of Seed I was diluted with BG11 medium at a ratio of 1:5 and cultivated for two weeks to obtain Seed II; then 10 mL of Seed II was diluted with BG11 medium at a ratio of 1:10 and cultivated for another two weeks to get Seed III. Finally, 20 mL of Seed III was diluted with BG11 medium at a ratio of 1:100 and cultivated for about two months for the biomass to reach harvest stage for cell disruption experiments. The medium BG11 contained these nutrients in g/L: NaNO3 , 1.5; K2 HPO4 , 0.04; MgSO4 · 7H2 O, 0.075; CaCl2 · 2H2 O, 0.036; citric acid, 0.006; ferric ammonium citrate, 0.006; Na2 EDTA, 0.001; Na2 CO3 , 0.02; and 1 mL of trace element solution, which consisted of in g/L H3 BO3 , 2.86; MnCl2 · 4H2 O, 1.86; ZnSO4 · 7H2 O, 0.22; Na2 MoO4 · 2H2 O, 0.39; CuSO4 · 5H2 O, 0.08; and Co(NO3 )2 · 6H2 O, 0.05. Algae cultivation was carried out in an automated incubator (SAFE PGX-350B, Safe Instrumental Ltd., Zhejiang, China) at 25◦ C, illuminated by artificial lighting (light intensity of 9600 lx) with light/dark cycle of 12 h/12 h. Algae growth was monitored by absorbance measurements at 540 nm using a spectrophotometer (723N, Jingke Industrial Co., Ltd, Shanghai, China), while the algal biomass concentration was determined by measurements of total suspended

solids (TSS) per Standard methods,[15] and the following lipid yields calculation was based on the dry biomass.

2.3. Cell disruption Algae cell disruption was conducted using three different methods, namely PAO, CBO, and US. In PAO, 200 mL of C. vulgaris suspension was added into a 1-L closed, stainlesssteel reactor and subjected to successive pressure cycles of compression and decompression using an ozone–air mixture, as previously described.[16] Figure 1(a) illustrates the system set-up: an ozone–air stream was generated from dry, filtered air by an ozone generator (3A-OA-10, Tonglin Technology, Beijing, China) and fed into the reactor at 2 L min−1 by an air compressor (Aizhong Machine Co., Ltd, Shanghai, China) to achieve the designated pressure (e.g. 0.6 MPa) in the headspace; once attaining the pressure, the headspace was rapidly vented to ambient pressure thus completing one pressure cycle as shown in Figure 1(b). The number of pressure cycles and the compression pressure were varied to identify good conditions for rupturing C. vulgaris cells. CBO was carried out by bubbling of the ozone–air stream into the same reactor at ambient pressure. In US treatment, 80 mL of C. vulgaris suspension was taken from the incubator, placed in a glass beaker, and subjected to US using an ultrasonicator (JYP-1200L, Zhixin Instrument Co., Ltd, Shanghai, China). The sonication probe was inserted into centre of the suspension and operated at 20 kHz and acoustic power of 360 W. The ultrasonicator worked in a 5 s on/ 5 s off mode controlled by a timer. Experiments were conducted in batch mode at room temperature of 15 ± 2◦ C. 2.4.

Lipid extraction

Following rupturing of algal cells by PAO, US, or CBO, the suspension was centrifuged at 14,000 rpm for 30 min; the supernatant containing the lipid was decanted and extracted by liquid–liquid extraction [17] using 50 ml of a 1:1 (v/v) solvent mixture of hexane and acetic ether. The extract was evaporated using a rotary evaporator (RV 10 DS25, IKA, Germany) under vacuum at 25◦ C. The crude lipid residue was measured gravimetrically to obtain the weight (Wlipid ) on an electronic balance (BSA224S-CW, Sartorius, Bohemia, NY). Lipid yield (Y ) was calculated bythe following equation:  Y

g lipid 100 g biomass

 =

Wlipid × 100, TSS × V

(1)

where V is the suspension volume (L). The collected lipid was converted to FAME via transesterification reaction. The lipid was dissolved in 1 mL of hexane and added with 200 μL of a 2-M KOH in methanol solution and vigorously mixed for 2 min with a

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933 Magnetically coupled stirrer

(a)

Vent Pressure gauge Gas inlet Ozone generator

Cell suspension Flow meter Reactor Air compressor

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(b)

Compression / decompression cycles

Compression: Ozone/air mixture was introduced in to the closed reactor containing microalgae suspension

Figure 1.

Decompression: Once At ambient pressure, reaching target pressure, ready to start another the head space is rapidly pressure cycle vented, causing expanding gas bubbles to appear

Experimental setup of PAO and operation: (a) setup and (b) operation of compression and decompression.

vortex mixer (VORTEX-6, Scientific Instrument, Shanghai, China). The upper layer was carefully removed for composition analysis. Analyses of FAME composition were performed using a Gas Chromatograph (7890A, Agilent, CA, USA) equipped with a Chrompack capillary column (DB-5MS, 0.25 μm × 30 m × 0.25 mm, Agilent), an inert Triple-Axis Mass Spectrometer Detector (5975C, Agilent), and an autosampler (7683B Series Injector, Agilent) assembly. A 1-μL sample was injected in the splitless mode with an injector temperature at 270◦ C. Helium was used as the carrier gas at 1 mL min−1 . The oven temperature was programmed initially at 50◦ C for 1 min, increased to 180◦ C at 15◦ C min−1 , increased to 230◦ C at 7◦ C min−1 , increased to 300◦ C at 30◦ C min−1 , and then held at 300◦ C for 10 min. The MS was operated in scan mode with mass range of 20– 500 a.m.u. The compounds were identified by comparison of spectra with NIST library and standard FAME samples. Relative contents of the FAME product were calculated according to Chinese national standard methods (GB/T 17377-2008).[18]

2.5.

Analysis

To evaluate cell rupture effect after treatment, the centrifuged supernatants of the untreated and treated

suspensions were determined for total organic carbon (TOC), ammonia (HACH method10031), nitrate (HACH method 10020), nitrite (HACH method 10019), total nitrogen (TN), dissolved phosphorous (DP) (HACH method 8048), total phosphorous (TP) (HACH method 8190), and chlorophyll concentrations. TOC and TN were measured by a TOC/TN analyzer (Multi N/C 3100, Jena, Germany). Chlorophyll contents were quantified by absorbance measurements using a spectrophotometer and calculated by Arnon [19] as shown in the following equation: Total chlorophyll (mg L−1 ) = 20.2 A645 + 8.02 A663 , (2) where A645 and A663 represented absorbance at 645 and 663 nm, respectively. The untreated and treated algae suspensions were observed by scanning electron microscope (SEM) (S-4800, HITACHI, Japan). Ozone concentration was determined by the indigo colorimetric method.[15] 3. Results and discussion 3.1. Algae disruption When algae cells are ruptured, the intracellular substances such as protein, lipid, and inorganic salts are released to the aqueous medium, changing its organic carbon, nitrogen, and phosphorous concentrations. Thus, changes (most often

934 Table 1.

Y. Huang et al. Changes of TOC, ammonia, nitrate, nitrite, TN, DP, and TP per unit TSS after various treatments.

Treatment

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US for 30 min CBO for 30 min (aqueous ozone conc. 12.4 mg L−1 ) PAO (0.8 MPa, 80 PC) (aqueous ozone conc. 2.2 mg L−1 )

TOC Ammonia Nitrite Nitrate TN DP TP (mg/g TSS ) (mg N/g TSS ) (mg N/g TSS ) (mg N/g TSS ) (mg N/g TSS ) (mg P/g TSS ) (mg P/g TSS ) 230 120

0 1

0 −9.8

−6.2 24

15 17

0.25 0.1

390

0.7

−9.8

14

97

0.34

increases) of TOC, ammonia, nitrate, nitrite, TN, DP, and TP contents in the centrifuged medium before and after cell disruption were measured that reflected the released intracellular substances and disruption efficiencies, as given in Table 1. A significant increase in organic nitrogen accompanied by a small decrease in inorganic nitrogen in the aqueous medium after 30 min of US indicated cell rupture and release of cell contents. The increase in organic nitrogen was corroborated by an increase in dissolved phosphorus along with a significantly higher increase in total phosphorus after treatment, which also suggested significant contribution to the phosphorous content by organic phosphorus that originated from release of cell contents. The same pattern of released cell substances was observed in CBO and PAO treatments. These results suggested the occurrence of cell rupture and release of cell contents. Rupturing of algal and bacterial cells by US under different conditions was reported.[20,21] When using PAO for cell disruption, increases in TOC, TN, and TP in the medium were much higher than those with CBO or US, suggesting enhanced rupturing of cells with ozonation in pressure cycles. Figure 2 shows SEM images of a unicellular C. vulgaris cell in the suspension prior to treatment with its smooth

Figure 2. SEM micrographs of C. vulgaris cells before treatment (upper left), after US (upper right), after CBO (lower left), and after PAO (lower right).

3.6 9.1 18

spherical surface (upper left), after US for 30 min with recesses on the roughen surface (upper right), after CBO for 30 min with separation of the shrivelled cell from its cell wall (lower left), and after PAO (0.8 MPa, 80 PC) with complete cell rupture into cell fragments revealing punctured openings (lower right). All the three methods can rupture the algal cells but through different ways and to different degrees. The rough surface of the US treated cells was caused by shear force, while shrivelled cells after CBO treatment was caused by the high oxidation ability of ozone from outside. PAO can force the dissolved ozone gas migration through the cell walls and leading to complete cell rupture during pressure cycles.

3.2.

Lipid extraction

C. vulgaris is widely recognized for its potential in commercial lipid production because of its nature of rapid growth, high lipid productivity, and contamination resistance.[22] Following cultivation, lipid extraction from the algal cells is needed with efficiency but without excessive, unwanted transformation of the lipid. The yield and composition of lipid obtained from C. vulgaris after being subjected to US, CBO, and PAO under different conditions were investigated; the results are shown in Figure 3 and Table 2. Using US as shown in Figure 3(a), lipid yields were 7.7, 11, 14, and 21 g/100 g biomass at contact times of 5, 10, 30, and 60 min, respectively, indicating increasing lipid content in the medium with increasing contact time that has increased the extent of cell rupture. Thus, C. vulgaris was amenable to rupture by US, which had been understood to provide mechanisms including cavitation and acoustic streaming at high acoustic power (e.g. at 360 W and 20 kHz as used in this study). The effectiveness of US in cell rupturing was related to the supplied power, contact time, as well as the cell’s characteristics. Figure 3(a) reveals that the trend of increasing chlorophyll in the medium followed that of lipid yield. Therefore, the intensifying green colour that indicated increasing chlorophyll content in the supernatant has provided a convenient, rapid estimation of the extent of cell rupturing by US treatment. During ozonation of a green algae Scenedesmus quadricauda, Plummer and Edzwald [23] observed cell lysis

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8

20

6

15

4

10

2

5

0

0

n

US

i 5m

n

n

US

i 0m

1

i 0m

3

US

n

US

i 0m

6

8

8

6

6

4

4

2

2

0

0

n

O1

CB

n

n

i 0m

O3

O6

CB

(c) 40 30

-2

i 0m

i 0m

CB

Yield (g lipid/100 g TSS)

D Chlorophyll (mg/g TSS)

10

D Chlorophyll (mg/g TSS) Yield (g lipid/100g TSS)

-2

D Chlorophyll (mg/g TSS)

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(b) 10

40 D Chlorophyll (mg/g TSS) Yield (g lipid/100g TSS)

30

20

20

10

10

0

0

Yield (g lipid/100 g TSS)

D Chlorophyll (mg/g TSS)

D Chlorophyll (mg/g TSS) Yield (g lipid/100g TSS)

Yield (g lipid/100 g TSS)

25

(a) 10

C C C C C C 0P 0P 0P 0P 0P 0P a 8 Pa 8 Pa 8 Pa 8 Pa 4 Pa 2 P M M M M M M 0.8 0.4 0.6 0.6 0.2 0.6

Figure 3. Lipid yields and chlorophyll changes of C. vulgaris suspension after being subjected to various treatments.

and improved coagulation. Using cyanobacteria Microcystis aeruginosa cultured in the laboratory, Miao and Tao [24] showed destruction of cell membrane via ozonation, resulting in the release of intracellular cytoplasm as measured by increased volatile organic contents. In this research as shown in Figure 3(b), CBO of C. vulgaris resulted in lipid yields of 5.0, 5.4 and 5.6 g/100 g biomass after contact times of 10, 30, and 60 min, respectively, which were lower than those obtained from US treatment. Previous research on ozonation of activated sludge suggested sequential and concurrent actions that involved disintegration of suspended solids, solubilization of the solids, and mineralization of the

935

released soluble organic matter.[25] With increasing contact time, more algal cells were ruptured, and the released lipid would be continually mineralized or transformed into polar organic acid compounds that were not extractable by the organic solvent. This was clearly shown as chlorophyll largely disappeared after ozonation, with only a small amount of chlorophyll detected at 10 min and none after 30 and 60 min of ozonation. This result was consistent with ozonation of M. aeruginosa, in which 72% of chlorophyll a was removed even at a low ozone dose of 1 mg L−1 in 30 min.[24] High-pressure (48–85 MPa) homogenization was found effective for rupturing of algal cells in a short time.[3,26] Rupturing of cells with the assistance of pressure would be more desirable when the pressure could be deployed at the lower range, e.g. at 90% of the total as given in Table 2. Other fatty acids of C12, C14, C15, C17, C20, C24, C25, and C26 were also detected, but they contributed only 3.2–7.4% of all fatty acids from C. vulgaris. Among fatty acids of C16 and C18, saturated hydrocarbons were of 36–41%, while unsaturated ones were of 55–57%. Moreover, C16:0 (i.e. fatty acids of 16 carbon atoms with zero double bonds), C18:1, and C18:2 were most abundant, accounting for 29–33%, 16–26%, and 21–27% respectively. The general fatty acids profile of C. vulgaris was similar to that of Chlorococcum sp. with different ratios, containing 63% of C18:1, 4% of C18:2, 4% of C16:1, and 3% of C18:0.[9] The differing composition according to rupturing method provides an opportunity to adjust to desirable final compositions of biodiesel if algal lipids from different kinds of algae are mixed at the proper ratios. For example, in cold areas, unsaturated hydrocarbons with lower melting point produced through US process could account for more ratio in the final biodiesel product, while in tropical region, saturated ones resistant to oxidation provided by PAO could occupy more ratio. When CBO was used for rupture, saturated C16:0 and C18:0 represented 32–43% and 44–55% in fatty acids, which were very different from the composition obtained through US rupture. Only small amounts of unsaturated C18:1, C18:2, and C18:3 were detected with CBO for 30 min, which was likely due to oxidation by ozone.

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Y. Huang et al. Table 2.

Fatty acids quantity and composition of C. vulgaris ruptured by different methods. Relative content of fatty acids (%)

Rupture by US – 5 min US – 10 min US – 30 min US – 60 min CBO – 10 min CBO – 30 min CBO – 60 min PAO – 0.2 MPa, 80 PC PAO – 0.4 MPa, 80 PC PAO – 0.6 MPa, 80 PC PAO – 0.8 MPa, 80 PC PAO – 0.6 MPa, 40 PC PAO – 0.6 MPa, 20 PC

C16:0

C16:1

C16:2

C16:3

C18:0

C18:1

C18:2

C18:3

Others

31 33 32 29 39 32 43 41 41 46 40 28 34

0.9 1.1 0.3 2 ND ND ND ND ND ND 3.1 8.5 4.5

2.1 2.4 2.8 1.8 ND ND ND ND 7.1 ND ND ND ND

6.2 6.5 5.4 11 ND ND ND ND 1 ND ND ND ND

9 8.3 8.6 7.9 55 44 47 52 39 46 49 35 42

26 24 21 16 ND 3 ND ND 4.3 ND ND 11 4.9

21 21 27 26 ND 8 ND ND ND ND ND 14 7.3

0.4 0.3 0.4 0.1 ND 7.2 ND ND ND ND ND ND 1.2

3.5 4.0 3.2 7.4 6.2 5.8 10.3 7.7 7.6 7.8 7.9 4.6 6.0

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Note: ND, not detected.

Unsaturated organic compounds in extracts were likely to be attacked by the electrophilic ozone molecule and thus unsaturated compounds were reduced in the final products. When PAO was used for cell rupture, C16:0 and C18:0 were predominant, accounting for 28–46% and 35–52%, respectively, of the products that were similar to results achieved by CBO. Again, unsaturated hydrocarbon products were less than those using US treatment; this was explained by the oxidative mechanism of ozone. Besides C16 and 18, fatty acids of other carbon numbers were found to be in small amounts of 4.6–7.9%. Unsaturated long-chain hydrocarbons are prone to oxidation but they possess lower melting points that are favourable for utilization in cold regions, while saturated hydrocarbons possess resistance to oxidative degradation.[27] It appears that by utilizing the proper cell rupturing conditions, i.e. controlling the extent of oxidation by ozone, the lipid quality could be balanced such that the FAME biodiesel could be controlled for desirable oxidative stability and for low-temperature utilization. 3.3. Mechanisms of cell rupture For cell rupture with US, cavitation phenomenon has been suggested as the main mechanism which provides shear stress developed by viscous dissipative eddies from shock waves of imploding cavitation bubbles.[7] CBO ruptures algal cells by ozone’s oxidative reaction that compromises cell membrane’s ability to regulate permeability of substances eventually leading to outflow of cytoplasm. With PAO treatment of microalgae, the rupture mechanism is similar to one for rupture of activated sludge as suggested by Cheng et al.,[12] which includes enhanced migration of dissolved gas across membrane into cells under compression and expansion of gas developed from within the cells during decompression. Significant increases in soluble TOC, TN, and TP observed after PAO treatment of

biomass, namely microalgae and activated sludge, affirmed PAO as a viable cell rupturing technique. A maximum lipid yield of 27 g/100 g biomass was observed for PAO under 0.6 MPa and 80 cycles, which was higher than US and CBO processes.

4. Conclusions US, CBO, and PAO were found useful for rupturing cells of C. vulgaris for the purpose of algal lipid release. Changes (particularly increases) of TOC, ammonia, nitrate, nitrite, TN, DP, TP, and chlorophyll in the supernatant after rupturing treatment have reflected the extent of cell rupture. CBO resulted in smaller lipid yield of 5.0–5.6 g/100 g biomass, while US and PAO resulted in 21 and 27 g/100 g biomass, respectively. Compared with PAO process, CBO was not a favourable cell rupture process for lipid extraction from algae since it resulted in a relative low lipid yield. Fatty acids of C16 and C18 were predominant products. However, more unsaturated products were found with US as a rupturing technique, while saturated products with CBO and PAO.

Funding This work was supported by the National Natural Science Foundation of China [grant number 51208299]; Science & Technology Commission of Shanghai Municipality [grant number 11JC1408700]; Shanghai Municipal Education Commission and Shanghai Education Development Foundation [grant number 11CG52].

Supplemental data Supplemental data for this article can be accessed doi:10.1080/09593330.2013.856954.

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Comparison of cell rupturing by ozonation and ultrasonication for algal lipid extraction from Chlorella vulgaris.

Cell disruption is essential for lipid collection from cultivated microalgae. This study examines the performance of ultrasonication (US), conventiona...
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