Improved Antibiofouling Properties Of Photobioreactors With Amphiphilic Sulfobetaine Copolymer Coatings

The closed photobioreactors can be used for microalgae culture,due to its precise control of various factors(such as temperature,light intensity,etc.).They have advantages including high utilization of light energy and CO2,effective reduction of pollution rate and the evaporation of water,prevention of external intruder,which work together to achieve high-density culture and increase the success rate of microalgae cultivation.Plastic films are used commonly for photobioreactors,for its easy processing and low cost.However,biofouling behaviour is an inevitable problem in the application of plastic film materials for microalgae culture.Algae cells,extracellular polysaccharides,extracellular proteins and other organic and inorganic substances in the algae liquid system adhered to the surface of the films,leading to a decrease in light transmittance of photobioreactors and deterioration of the culture environment.Therefore,in view of the biofouling problem of photobioreactors,the purpose of this paper is to prepare an amphiphilic zwitterionic copolymer coating,which provides a simple and rapid method for surface modification of photobioreactors,and can be applied for industrial large-scale production.The main points are as follows:In this paper,a series of amphiphilic zwitterionic copolymers(ASC)with different proportions of hydrophilic and hydrophobic monomers were synthesized by semi-continuous seeded polymerization process.The solid content,monomer conversion,average particle size,zeta potential,calcium ion resistance,low temperature stability,solvent resistance and water absorption of the ASC were measured,and the following results were obtained:the solid contents of ASC emulsion were between 28%and 35%,and the monomer conversion rates were more than 80%.ASC had good resistance to calcium ions and low temperature resistance.The average particle size and water absorption rate rose down at first and then rose up with the increasing amount of the hydrophilic monomer and the minimum value appears at ASC-5(when the ratio of hydrophilic and hydrophobic monomers was 2:1),which were 155.1 nm and 7.84%.The ethylene-vinyl acetate copolymer(EVA)films were coated by ASC emulsion and obtained modified EVA films(EVA-ASC).The surface composition of EVA-ASC films were determined by Attenuated Total Reflection-Fourier Transform Infrared spectroscopy(ATR-FTIR)and X-ray photoelectron spectroscopy(XPS).The contact angle changes of EVA-ASC films,which immersed in deionized water for a week were measured by static contact angle meter.The contact angles of EVA-ASC in air were between 76°-100°,performed poor hydrophilicity.However,SBMA showed good water-binding properties in aquatic environment.EVA-ASC-5 had the contact angle of 480°and showed excellent hydrophilicity.The protein resistance properties of EVA-ASC films were tested by Coomassie Brilliant Blue and Quartz Crystal Microbalance with Dissipation(QCM-D)methods.It was found that the anti-adsorption properties were greatly improved of EVA-ASC films compared with EVA unmodified films.The adsorption of EVA-ASC-4(when the ratio of hydrophilic and hydrophobic monomers was 1.8:1)had a minimum value of 8.63?g/cm2,which reduced by 92.1%.The QCM-D method was used to prove that the protein adsorption on the surface of EVA-ASC films were reversible adsorption.The anti-polysaccharide adsorption capacity of EVA-ASC films were measured by phenol-sulfuric acid method.The variation trend was basically the same as that in the protein adsorption experiment.The minimum adsorption value happened at EVA-ASC-4,which was 24.09 ?g/cm2 and decreased by 48.1%compared with EVA films.Using Chlorella sp.as a model algae,the anti-biofouling properties of EVA-ASC films in the culture environment of Chlorella sp.were investigated.The results showed that obvious microalgae biofouling behaviour happened in EVA films,which was observed under microscope after immersion for a week in Chlorella sp.culture system.Slightly adhesion behaviour was observed on the surface of the EVA-ASC-4 film and the cell number of Chlorella sp.reached 1.0875×105 cells/cm2 on the 7th day,which was half of the adhesion cell number on EVA films surface.This paper provided a simple and efficient way to improve the anti-biofouling properties of plastic films for photobioreactors.