Optimization of FucoPol bioreactor production and exopolysaccharide applications

Abstract

FucoPol is an exopolysaccharide (EPS) produced by the bacterium Enterobacter A47, composed of sugars (fucose, galactose, glucose and glucuronic acid) and acyl groups (succinyl, pyruvyl and acetyl), and with a high average molecular weight (>106 Da). The first main goal of this thesis was to investigate the effect of the phosphorus (P) concentration on FucoPol production. Production assays were performed under different concentrations of this nutrient: from 0.8 to 2.6 g.L-1(standard concentration). The conditions implemented did not affect Enterobacter A47 growth, but a reduction of the EPS synthesis was observed: 24% less polymer when 2 and 1.3 g.L-1 of P were used, and 44% for 0.8 g.L-1 of phosphorus. A slight reduction to 2.0 g.L-1 in the phosphorus concentration did not affect the polymer’s composition, neither the molecular weight. However, the EPS obtained from the assays with fewer P showed less fucose content and was richer in glucose. Secondly, this thesis aimed to assess the flocculation properties of FucoPol. The flocculation rate of FucoPol was determined using a kaolin clay suspension (5 g.L-1) in the presence of CaCl2. Flocculation rate values above 70% were achieved with a low bioflocculant dosage of 1 mg.L-1, for pH values in the range 3-5, and temperature within 15-20 ºC. The bioflocculant was also shown to be stable after freezing/thawing and heating up to 100 ºC, for 20 min. The work performed in this thesis also had as an objective to explore the metal binding efficiency of the polysaccharide. FucoPol revealed a good performance in the biosorption of cobalt, copper and zinc. The polysaccharide was an excellent biosorbent of lead so this metal was chosen for further studies, namely the impact of EPS dosage, Pb2+ initial concentration, pH and temperature. Optimal FucoPol concentration of 5 mg.L-1 was found to uptake 18645 mgmetal.g-1EPS from an 100 mg.L-1 Pb2+ solution, at pH 2.3. Moreover, FucoPol presented a great sorption performance in the range of temperatures between 5 and 45 oC.