Rapid harvesting of freshwater microalgae using chitosan

doi:10.1016/j.procbio.2013.04.018

Process Biochemistry

Volume 48, Issue 7, July 2013, Pages 1107-1110

https://doi.org/10.1016/j.procbio.2013.04.018 Get rights and content

Highlights

•
Chitosan is used as flocculant to harvest freshwater microalgae.
•
The effect of pH, chitosan concentration and settling time on harvesting efficiency is tested.
•
Harvesting efficiency of 99% is achieved at pH 6.0, 120 mg/L chitosan, after only 3 min operation.
•
Harvesting occurred due to charge neutralization.
•
Flocculation is verified by Scanning Electron Microscopy (SEM) micrographs and by zeta-potential measurement.

Abstract

In this study, chitosan was used as a flocculant to harvest freshwater microalgae Chlorella vulgaris. The recovery efficiency of C. vulgaris was tested at various chitosan concentrations. 120 mg/L of chitosan showed the highest efficiency (92 ± 0.4%) within 3 min. The maximum concentration factor of 10 was also achieved at this dose of chitosan. The harvesting efficiency was pH dependent. pH 6.0 showed the highest harvesting efficiency (99 ± 0.5%). Measurement of zeta-potential confirmed that the flocculation was induced by charge neutralization. This study showed that a biopolymer, chitosan, can be a promising flocculant due to its high efficacy, low dose requirements, and short settling time.

Introduction

Microalgae biomass has been considered as an alternative source of biofuels since long [1], [2], [3]. Due to dilute nature of microalgae culture, harvesting, i.e. biomass recovery from growth medium, is one necessary step, which accounts 20–30% of total biomass production cost [4]. Cost-effective harvesting is challenging due to small size of microalgae cells (3–30 μm in diameter).

Several techniques are available for microalgae harvesting, such as centrifugation, sonication, filtration, air floatation, coagulation, and flocculation. Among these, flocculation is the most striking option, as it is simple and relatively cheap [5], [6]. Flocculants such as aluminum and ferric salts can form flocs with microbial cells including microalgae. Despite high efficiency of such chemicals, their abundant use can contaminate microalgae biomass, which exhibit adverse effects on its subsequent uses such as feed for human and animals [5]. Natural polymers such as chitosan can be a promising alternative to address these challenges [7], [8]. Chitosan is a linear poly-amino-saccharide, which is produced by alkaline deacetylation of chitin [9]. It is insoluble in water and soluble in acids. Generally, chitosan has a viscosity of 20–300 centipoises, molecular weight of (5–19) × 10⁴, density of 0.15–0.3 g/cm³ (in 1% acid solution), and deacetylation degree of 75–85% [10]. Chitosan has distinct advantages over commonly used flocculants for microalgae harvesting [7]. It is cheap, has high flocculation ability, and require low dose for harvesting [10], [11]. It costs only 2 $US/kg. One kilogram of chitosan can effectively treat 500,0000 L of microalgae culture [12]. Moreover, it is biodegradable and has no toxic effects on some downstream applications such as feed for fish and animals.

Several factors such as flocculant type, flocculant dose, settling time, and culture pH affect the harvesting efficiency of microalgae [13]. pH also plays a vital role in flocculation process [3]. pH affects the flocculant interaction with microalgae, and thus, alters the harvesting efficiency [4].

In this experiment, we have explored the potential of chitosan as a flocculant for microalgae harvesting. The effects of flocculant dose, zeta-potential and pH, on harvesting efficiency are also demonstrated.

Section snippets

Strain and growth conditions

Chlorella vulgaris AG30007 UTEX 0000265 was obtained from the University of Texas at Austin, USA. C. vulgaris was cultivated photo-autotrophically in 250 mL sterilized cell culture flasks in a shaking incubator, at 140 rpm, 25 ± 2 °C, and under the illumination of white (Light Emitting diodes (LEDs)). BG-11 medium was used as a growth medium [14].

The medium pH was adjusted by adding either 1 M H₂SO₄ or 1 M NaOH. Cell suspension was stirred for 10 min at 100 rpm on an orbital shaker. The mass cultivation

Effect of chitosan dose

The effect of chitosan dose on harvesting efficiency of C. vulgaris was investigated. Various concentrations (30, 60, 90 and 120 mg/L) of chitosan were tested. The corresponding percentage ratios of chitosan dosages to microalgae biomass were 3%, 6%, 9% and 12%. A control experiment (without chitosan) was also performed as a reference. A dramatic decrease in optical density was found just after 3 min settling time. The optical density decreased with increase in chitosan dose. We have presented

Discussion

Flocculation is a widely used process for microalgae harvesting. Flocculation is induced by inorganic or polymeric flocculants. Despite versatile applications of such flocculants, there are some limitations with their use. Inorganic flocculants (e.g. alum and ferric chloride) are toxic and produce large amount of sludge, while polymeric flocculants are expensive to use. Biopolymers, on the other hand are cheap, efficient, and environmentally friendly [22]. Chitosan is one promising choice due

Conclusions

Chitosan holds tremendous potential for high biomass recovery from microalgae culture. Low dose requirement and short settling time are the distinct advantages of chitosan over commonly used flocculants. Microalgal culture can be concentrated up to 10 times at optimal pH (6.0) and flocculant dose (120 mg/L chitosan). Further studies should be carried out to explore the possible ways to reduce the chitosan dose for cost-effective microalgae harvesting.

Acknowledgement

This work was financially supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government Ministry of Education, Science and Technology (MEST) (NRF-2012M1A2A2026587).

References (33)

X. Zhang et al.
Harvesting algal biomass for biofuels using ultrafiltration membranes
Bioresour Technol
(2010)
Z. Wu et al.
Evaluation of flocculation induced by pH increase for harvesting microalgae and reuse of flocculated medium
Bioresour Technol
(2012)
D. Vandamme et al.
Flocculation of Chlorella vulgaris induced by high pH: role of magnesium and calcium and practical implications
Bioresour Technol
(2012)
C.-D. Wu et al.
Enhanced coagulation for treating slightly polluted algae-containing surface water combining polyaluminum chloride (PAC) with diatomite
Desalination
(2011)
L. Heng et al.
Algae removal by ultrasonic irradiation–coagulation
Desalination
(2009)
C.K.S. Pillai et al.
Chitin and chitosan polymers: chemistry, solubility and fiber formation
Prog Polym Sci
(2009)
L.M. Lubián
Concentrating cultured marine microalgae with chitosan
Aquacult Eng
(1989)
L. Xu et al.
A simple and rapid harvesting method for microalgae by in situ magnetic separation
Bioresour Technol
(2011)
S. Salim et al.
Ratio between autoflocculating and target microalgae affects the energy-efficient harvesting by bio-flocculation
Bioresour Technol
(2012)
R.K. Henderson et al.
The impact of differing cell and algogenic organic matter (AOM) characteristics on the coagulation and flotation of algae
Water Res
(2010)

J. Morales et al.

Harvesting marine microalgae species by chitosan flocculation

Aquacult Eng

(1985)

F. Renault et al.

Chitosan for coagulation/flocculation processes – an eco-friendly approach

Eur Polym J

(2009)

H. Tang et al.

Antibacterial action of a novel functionalized chitosan–arginine against Gram-negative bacteria

Acta Biomater

(2010)

A.L. Ahmad et al.

Optimization of microalgae coagulation process using chitosan

Chem Eng J

(2011)

B. Bolto et al.

Organic polyelectrolytes in water treatment

Water Res

(2007)

K. Kurita

Chemistry and application of chitin and chitosan

Polym Degrad Stab

(1998)

Cited by (122)

Chitosan-β-cyclodextrin composite flocculants dual-drive for efficient microalgae harvesting: Structural evidences, dehydration process, E-DLVO model behavior and biomass utilization
2024, Separation and Purification Technology
Flocculation is one of the promising methods for harvesting microalgae. In this study, a series of grafted cationic chitosan-cyclodextrin composite flocculants (CTS/β-CDs) with different structural properties were prepared from chitosan and cyclodextrin. The results showed that the harvesting efficiency of CTS/β-CD-1 for C. vulgaris reached 99.91%. The chain type of polymeric flocculants with moderate graft chain lengths (L = 10–20) and tighter branched chain density distribution (D = 1.0–1.8) was favorable for C. vulgaris harvesting. The addition of CTS/β-CDs caused the discrete C. vulgaris cells to be flocculated and aggregated, and the reorganization of particles resulted in larger particles after flocculation, improving the dewatering performance of microalgae flocs. CTS/β-CDs had no significant inhibitory effect on the extraction of lipids, proteins and carbohydrates, and did not affect the extraction and quality of fatty acid methyl esters, and the re-cultivation experiments of the harvested water showed that chitosan-based flocculant was able to effectively reduce the cost of microalgae harvesting. Electrostatic interactions and bridging were the main harvesting mechanisms between CTS/β-CD-1 and C vulgaris. E-DLVO modeling suggested that flocculation is mainly a result of electrostatic and acid-base interactions when the distance between particles is small. At higher pH, the harvesting efficiency of CTS/β-CD-1 with C. vulgaris decreased. The study contributes to a better understanding of the structure–activity relationship between the structural characteristics of flocculants and the harvesting performance.
Direct biohydrogen production from chitosan harvested microalgae biomass and an isolated yeast
2024, Energy Conversion and Management
There is a bottleneck in recovery microalgae biomass from cultivations to recovery bioenergy the low metabolites yields achieved still lacks low operating cost. Optimization of the harvesting process such as coagulation-flocculation is crucial to find the conditions of a chemical compound for biomass and metabolites recovery and suitable or easy assimilation by microorganism for biohydrogen production. Dose, pH, flocculation velocity, flocculation and settling times are relevant factors that influence over biomass and metabolites recovery and define the requirements of the harvesting process in terms of invested energy.
The aim of this study is to get the efficiency of biomass and biomolecules separation by using the response surface methodology for three chemical compounds such as ferric chloride, aluminum sulfate and chitosan. The design presented recovery efficiencies highest as 99 % for all the coagulants. A selection of coagulant conditions yields augmentation a carbohydrates content subsequently transformed to biohydrogen. The mix of microalgae and chitosan presented high carbohydrates increase or a low effect on carbohydrates determination in comparison to those harvested using other flocculants, where the microalgae biomass was washed because of precipitates formation. The biohydrogen produced from untreated harvested microalgae biomass with chitosan was of 1.958 ± 0.2 mmol/L using isolated indigenous yeast Candida sp. by using the chitosan concentration to recovery the maximum biomass concentration (0.02 g/L), was of 2.4 ± 0.1 mmol/L of H₂. Under these conditions, the energy reduction was from 0.15 kWh/m³ to 1.2 kWh/m³, 35 % to >80 % less in comparison with other flocculants applied. In this context, the findings demonstrated that applying an organic flocculant for microalgae harvesting even lacking high biomass and carbohydrates yields, the biomass can be enriched and improved leading for a sustainable and direct route to produce a potential biofuel.
Development of a novel Fe@urea nanocomposite for effective harvesting of high lutein-producing microalgae biomass
2024, Chemical Engineering Journal
An Innovative microalgae biomass harvesting is addressed through a newly developed Fe@urea nanocomposite (NC) with high lutein and lipid content. The persistent challenge of scaling up microalgae harvesting for large-scale commercial production is undertaken by coating Fe₃O₄ nanoparticles (NPs) with urea, significantly enhancing biomass harvesting efficiency. This improvement aligns with increased NH₂⁺ groups on the NC's surface, demonstrating superior performance compared to conventional Fe₃O₄ NPs, especially at pH 4. Characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and zeta potential analysis validate the efficacy of the Fe@urea NC. The elemental composition was analyzed through energy-dispersive X-ray spectroscopy (EDX) to confirm effective urea coating on the NC surface. Remarkably, enhanced Fe@urea-mediated harvesting within one minute is achieved through NH₂⁺-assisted interactions. Optimization experiments varying NC concentrations and culture pH, guided by the Langmuir model, showcase the NC's multifaceted solution, excelling under a magnetic field and also via self-flocculation. Cell viability tests confirm lutein-enriched microalgae cell integrity during harvesting at pH 4, preventing product leaching. This synthesized Fe@urea NC presents an efficient and viable method for microalgae harvesting, holding promising implications for large-scale microalgae biorefinery applications.
Microalgal harvesting for biofuels – Options and associated operational costs
2024, Algal Research
Microalgae are a source of a range of natural products, including biofuels, but financial and technical limitations can make large-scale production challenging to commercialize. A significant limitation is the practical and economical bulk harvesting of microalgae from the cultivation medium. Based on chemical and energy demands, common harvesting processes can have high costs due to microalgae having a similar specific gravity as their medium, negative surface charges and significant variability between strains.
Determining the cost-effectiveness of harvesting methods is complicated as many publications commonly quote harvesting as costing 20–30 % of the operational cost, regardless of the method of biomass production (e.g., open ponds, bioreactors, etc.) or the harvesting method selected. This non-specific statement does not reflect that specific harvesting methods will have different operational costs. This paper aims to provide a more accurate, method-specific cost analysis of the harvesting stage operating costs to help in the economic analysis of microalgae production systems.
The four primary harvesting mechanisms currently used, centrifugation, flocculation, flotation, and filtration, are assessed for their energy and chemical consumption. Centrifugation, flocculation, flotation, and filtration had an average biomass recovery of 92 %, 95 %, 92 % and 91 % and an energy requirement range of 1–8 kWh m⁻³, 0.1–6.7 kWh m⁻³, 0.015–7.6 kWh m⁻³ and 0.1–5.9 kWh m⁻³, respectively. Furthermore, the operational costs, based on energy requirements and the use of flocculants, were 0.448–1.086 USD m⁻³, 0.014–16.65 USD m⁻³, 0.08–31.3 USD m⁻³ and 0.013–0.791 USD m⁻³, respectively. Finally, the biomass production costs were calculated as ranging between 0.02–0.177 USD kg⁻¹, 0.006–35.05 USD kg⁻¹, 0.169–26.95 USD kg⁻¹ and 0.02–3.00 USD kg⁻¹ for centrifugation, flocculation, flotation, and filtration microalgae harvesting technologies, respectively.
Efficient magnetic flocculation for microalgae harvesting using a novel composite flocculant of Fe<inf>3</inf>O<inf>4</inf>-based starch-grafted-cationic polyacrylamide
2023, Journal of Water Process Engineering
As a flocculant for algae harvesting, a novel magnetic starch-grafted-cationic polyacrylamide composite (MAG@ST-g-CPAM) was developed in this study, and the harvesting efficiency of the composite was assessed with comparison to starch, Fe₃O₄ magnetite nanoparticles, cationic polyacrylamide and starch-grafted-cationic polyacrylamide. The feeding ratios for flocculant synthesis were optimized, and impacting factors were examined. Magnetic particles were recovered for cyclic use, and the effect of MAG@ST-g-CPAM flocculation on water reuse was examined. The results showed that MAG@ST-g-CPAM flocculation successfully achieved harvesting efficiencies of 93.2 % and 97.3 % at doses of 25 mg/L and 30 mg/L, respectively, which were superior to those of other flocculants. The optimized feeding ratio of acrylamide:Fe₃O₄:starch was 6:4:3. The late exponential algal growth solution with a pH range of 5–6 was most favorable for algae flocculation. A total of 93.7 % of Fe₃O₄ magnetite nanoparticles was recovered at pH = 3, and flocculation facilitated the reuse of water by effectively eliminating fulvic acids from the culture solution. This study demonstrated that MAG@ST-g-CPAM is a promising flocculant for algae harvesting.
Research progress on the magnetite nanoparticles in the fields of water pollution control and detection
2023, Chemosphere
Magnetite nanoparticles (MNPs) have shown increasing application in the fields of water pollution control and detection due to their perfect combination of interfacial functionalities and physicochemical properties, such as surface interface adsorption, (synergistic) reduction, catalytic oxidation, and electrical chemistry. This review presents the research advances in the synthesis and modification methods of MNPs in recent years, systematically summarizes the performances of MNPs and their modified materials in terms of three technical systems, including single decontamination system, coupled reaction system, and electrochemical system. In addition, the progress of the key roles played by MNPs in adsorption, reduction, catalytic oxidative degradation and their coupling with zero-valent iron for the reduction of pollutants are described. Moreover, the application prospect of MNPs-based electrochemical working electrodes for detecting micro-pollutants in water were also discussed in detail. This review addresses that the construction of MNPs-based systems for water pollution control and detection should be adapted to the natures of the target pollutants in water. Finally, the following research directions of MNPs and their remaining challenges are outlooked. In general, this review will inspire MNPs researchers in different fields for effective control and detection of a variety of contaminants in water.

View all citing articles on Scopus

View full text

Short communicationRapid harvesting of freshwater microalgae using chitosan

Highlights

Abstract

Introduction

Section snippets

Strain and growth conditions

Effect of chitosan dose

Discussion

Conclusions

Acknowledgement

Bioresour Technol

Bioresour Technol

Bioresour Technol

Desalination

Desalination

Prog Polym Sci

Aquacult Eng

Bioresour Technol

Bioresour Technol

Water Res

Aquacult Eng

Eur Polym J

Acta Biomater

Chem Eng J

Water Res

Polym Degrad Stab

Short communication
Rapid harvesting of freshwater microalgae using chitosan