ABSTRACT

1. http://www.hulsdairy.com/Digester3.htm http://algae.ucsd.edu/Blog1/Blog-3-Sapphire.html http://msutoday.msu.edu/news/2008/msu-leverages-public-private-funds-for-farm-waste-to-energy-project/ http://www.britannica.com/blogs/2009/10/hitchcock-loved-algae-toxic-tuesdays-a-weekly-guide-to-poison-gardens/ R#1 : μmax = 0.337 d-1 ; α = 1.42 L/g • R#2 : μmax = 0.369 d-1 ; α = 1.185 L/g • R#3: μmax = 0.326 d-1 ; α = 0.917 L/g R#4: μmax = 0.367 d-1 ; α = 1.25 L/g ALGAL BIOREFINERY WITH EXOPOLYSACCHARIDE PRODUCTION – Studies on algae growth and polysaccharide saccharification Cesar M Moreira*1, Nguyet Doan1, Shambhu Rajeev1, Yingxiu Zhang2, Mingrui Zhao2, Brian Wolfson2, Spyros Svoronos2, Edward Phlips3, Pratap Pullammanappallil1 1Agricultural and Biological Engineering; 2Chemical Engineering, 3School of Forest Resources and Conservation, University of Florida, Gainesville, Fl 32611 the growth rate under the described conditions. Sampling was carried out at 24 hour intervals with sampling size maintained at 1.5 ml. The sample optical density was determined using a Milton Roy Spectronic 401 Spectrometer using λ=540 nm. Enzymatic saccharification was applied to the algal broth and freeze dried algae exopolysaccharide. Cellulase, hemicellulase, pectinase, amylase and a combination of them were used. The pH was adjusted to 4.5 the temperature was 50 °C and the studied time of reaction were 4 hours and 24 hours. In all the cases 24 hrs showed a bigger amount of reduced sugars. The DNS method was used to determine reduced sugars. The use of algae as an alternative source of bioenergy (e.g., biogas or bioethanol) has a large potential. However, algae biomass for energy is still in its infancy. Key issues affecting large scale algae based production of bioenergy are: selection of species, cultivation and harvesting techniques and conversion technology. RESULTS INTRODUCTION ABSTRACT Four runs each in duplicate were carried out. Air and 1% CO2 were sparged at 0.5 L/min. The temperature was kept constant at 30 °C. A bank of two 20 W fluorescent lamps giving off 60 μmol photon m-2s-1 and four LED PAR 38 18 Watts giving off 1,200 μmol photon m-2s-1 lights kept on a 13/11 on/off. Batch were used to determine A laboratory scale, temperature controlled assembly (Figures 1 and 2) with four photobioreactors was constructed for cultivating Synechococcus BG011. The photobioreactors can be operated in batch, semi-continuous or fed-batch mode, by sparging gas with different CO2 concentrations and exposed to controlled light intensity. The apparatus has now been operational for over a year and has successfully cultured several batches with each batch growth lasting two or three weeks without any contamination. The growth of Synechococcus BG011 is affected by light intensity and CO2 enrichment. At a light intensity of 1,200 μmol photon m-2s-1, the specific growth rate is about the same for all the reactors, but the inhibition factor decreases in CO2 enriched reactors. The doubling time was 1.9 days. Specific growth rate increased by 50% at light intensity of 1,200μmol photon compared to light intensity of 60μmol photon m-2s-1 provided by conventional fluorescence lamps. At low light intensity ( 60 μmol photon m-2s-1 ) the specific growth rate was less than at high light intensity regardless of the CO2 concentration suggesting that light was limiting rather than CO2. Ash free dry weight, afdw, (algae cell and polysaccharide) was about 3 g/L when cells were grown at high light intensities and 1% CO2 atmosphere. The exopolymer is a mixture of carbohydrates and proteins; it sugars like: glucose, arabinose, glucoronic acid. The molecular weight distribution was observed to be >100 kDa = 3.2% of afdw, and rest between 100 and 30 kDa The exopolymer can be saccharified using commercially available cellulase, hemicellulase, pectinase and amylase. The sugar released depended on the enzyme used. Combination of enzymes released more sugars than individual enzymes. A combination of cellulase and pectinase released sugars amounting to 13% of the afdw. Growth rate of the hypersaline nitrogen-fixing exopolysaccharide producing cyanobacteria Synechococcus BG011 wasshown to be affected by light intensity. At low light and high light intensities the growth rate of cyanobacteria growing under air or enriched CO2 environment is about the same; however, when increasing light intensity the specific growth rate of cultures increases. In every run growth appeared to be inhibited as ash free dry matter concentration increased. Ash free dry weight (AFDW) increased from 0.7 g/L when grown with air and low light to 3 g/L when grown in a 1% CO2 atmosphere and higher light intensity. The secreted exopolymer is a mixture of protein and carbohydrates made up of sugars like: glucose, arabinose, and glucoronic acid. These exopolymers were saccharified using available commercial cellulase, hemicellulase, pectinase and amylase. Using a mixture of these enzymes a maximum recovery of 13% of the total available organic matter was attained without any other pretreatment. METHODS CONCLUSIONS Fig 2. Four bioreactors within the laboratory scale assembly. Fig 1. A schematic diagram of the laboratory scale, temperature controlled photobioreactor assembly Fig 3. Biomass concentration during batch growth under air and 1% CO2 enriched air diurnal cycle of 13 hours of light and 11 hours of darkness at light intensity of a) 60 μmol photon m-2 s-1 b) 1,200 μmol photon m-2 s-1 . The experimental data is fit to an exponential growth function of the form: X = X0*e(μmax*t) /(1+α*X0*(e(μmax*t)-1)) where: μmax = maximum specific growth rate; X0 = initial biomass concentration; α = inhibition factor; Δt = time period ; X =biomass concentration This research investigated the cultivation of a unique hypersaline nitrogen–fixing exoplysachharide producing cyanobacteriumSynechococcus BG 011 and methods to saccharify the exoplysaccharide. Advantages of the Synecchoccus BG011 include: PHLIPS ET AL., 1989 R#1 : μmax =0.508 d-1 ; α = 0.745 L/g  1) Can be cultivated under hypersaline conditions thereby avoiding contamination in large scale ponds. 2) Fixes nitrogen, so there is no need to add nitrogen containing nutrients for cultivation, thus saving costs. 3) Produces extracellular polysaccharide which could simplify processes for separating and recovering the product.   4) The algae suspension containing polysaccharide can be fed to an anaerobic digester for biogas production. The biogas can be cleaned  through utilization of CO2 in algae cultivation as shown in Figure 4  or the polysaccharide can be saccharified and used as feedstock for fermentation. (Figure 4).  The CO2 from fermentation could be used for algae growth  FUTURE WORK NOTE: being αan inhibitory factor it could account for shading effect due to increasing cell concentration, polysaccharide formation or carbon source limitation. It is not clear at the present stage of the research what may be the possible explanation. • On-going research is focusing on optimization of conditions for growth and exopolymer production, characterization and separation of exopolymer, and development of optimal saccharification techniques. • The algae suspension is being anaerobically digested to determine biogas production and yield. Table 1. Sugar released after treatment of exopolymer with commercial enzymes. Two substrates were used in this study. In one case the maturing algae suspension was used without any processing. In the second case the maturing algae suspension was freeze dried and the freeze dried powder was used as a substrate for enzyme reactions. Fig 4. Schematic diagram of the anaerobic digestion operation