Study Of Lignocellulosic Material Based Algal Biofilm Technology And The Corresponding Influence Factor Of Biomass Production

Algal based bio-energy is recently considered as the most promising replacement for the traditional fossil fuels.However,due to drawbacks like high cost about harvesting the suspended biomass,lower production efficiency,etc.,traditional suspended algal cultivation technology is unsuitable for large scale algal biomass production.Owing to easier harvesting,lower capital construction cost and even less water and energy consumption,algal biofilm technology has been widely studied for algae-based bioenergy production.For biofilm technology,the carrier used for algal attached growth is significantly important.The biomass production performance of a system was directly affected by the cell adhesion rate of carriers.Traditional algal biofilm carriers like metal plate,metal mesh,cotton duct,cotton rope,nonwoven fabric,electrostatic flocking cloth,cellulose acetate/nitrate membrane,etc.,were either expensive and difficult to obtain or un-durable and easy to be corroded.Indeed,this study made the first attempt to develop a new biofilm technology using lignocellulosic materials as biofilm carriers such as pine sawdust?PW?,rice husk?RH?,sugar bagasse?SB?and oak sawdust?OW?,all of which are environmentally friendly,cheap,and renewable with a wide range of distribution around the world.Algal biofilm was cultivated in a self-design four channel algal biofilm photo-bioreactor with PW,RH,SB and OW as carriers.Results indicated that the biomass production using lignocellulosic materials as carriers were all larger than the PMMA and the suspended culture.The lipid contents of the corresponding harvested algal biomass were in the range of 20.10-23.20%,with protein and carbohydrate contents were in the range of 30.35-36.73%and 20.29-25.93%,respectively.PW as carrier obtained the largest productivity,10.92 g·m^-2·day^-1.Using confocal lasers canning microscope for the characterization of the carrier surface indicated that it was mainly due to the surface roughness which enhanced algal cells deposition and protected the early biofilm that promoted the biomass production when with lignocellulosic materials as carriers.In addition,the introduced filamentous fungi might be another reason that cause this higher productivity.Secondly,the toxicity of lignocellulosic materials for the growth of algal cells during biofilm cultivation process was studied.During biofilm cultivation process,lignocellulosic carriers all had a slightly mass loss,which was mainly due to the leaching effect of the medium.Suspended culture of Chlorella vulgaris using the leachate of PW,RH and SB was conducted.Results indicated that the leaching process of PW,RH and SB have no significantly effect on the growth of Chlorella vulgaris.But chemical composition analyze found that the leaching process of PW could inhibit lipid synthesis,with the leaching process of SB and RH could inhibit protein synthesis.However,the leaching process of the three materials all could promote the saturated fatty acid synthesis and inhibit unsaturated fatty acid synthesis,which could optimize the composition of fatty acids.Thirdly,algal biofilm cultivation was conducted in a self-design thirty channel algal biofilm photo-bioreactor using PW and SB as carrier under various particle size and dosage.Meanwhile,the material surface roughness,specific surface area,liquid holding capability and corresponding layer voidage were also characterized to study their relationship with the corresponding formed biofilm productivity.Results indicated that the regrowth mode by using the suspended algal cells in the medium as inoculum for the fresh carrier could obtain much higher biomass productivity(6-16 g·m^-2·day^-1)than growth mode.In addition,the carrier species and particle size affected the biofilm productivity mainly through the material surface roughness,specific surface area,liquid holding capability and corresponding layer voidage.Suitable carrier should with larger surface roughness,specific surface area,liquid holding capability and lower layer voidage as well as particle size.However,optimum operation condition for the selected suitable carrier should depend both on biomass productivity and the cost of carriers.Under the studied condition in this study,the optimum operation condition for PW and SB is 550-380?m&416.67 g·m^-2?particle size&dosage?.At last,the biofilm cultivation using lignocellulosic materials as carrier coupled with multi-physics simulation were conducted to study the mechanism of material surface roughness effect on the algal biofilm cultivation.Results indicated that surface roughness affected cell adhesion mainly through the produced local hydrodynamics in the flow system.Surface roughness caused the significantly change and uneven distribution of the flow vector,which led to the interception of suspended cells by roughness,and the formation of stagnant and reflux zones which cells could be trapped inside.Since initial adhesion was enhanced,the colonization time was shortened,and the biomass production was promoted.