cell surface and exopolymer characterization of laboratory stabilized activated sludgefrom a beverage

Fermentor-stabilized activated sludge from an industrial beverage bottling plant was grown on three different food sources: normal plant waste water, plant wastewater containing high sucrose concentrations, and a synthetic glucose-based feed stock. Surface charge, hydrophobicity, and exopolysaccharide composition were measured on the stabilized bacterial flocs. Cell surface charge was measured by electrophoretic mobility, dye exchange titration, and a standard colloid titration, while cell hydrophobicity was determined using the bacterial adhesion to hydrocarbons (BATH) test. Exopolysaccharide profiles were determined by measuring concentrations of glucose, galactose, mannose, glucuronic, and galacturonic acids in digested exopolymer extractions using HPLC. Changes in the physical surface properties of the bacteria and the chemical composition of the extracted exopolymers were correlated with differences in the three food sources. Cell surface hydrophobicity was similar for cultures grown on different plant wastewaters, while the culture grown on synthetic food produced less floc hydrophobicity. Electrophoretic mobility measurements, charge titrations, and dye exchange titrations showed different total surface charge as well as varying charge availability. Additionally, total surface charge and total exopolysaccharide concentrations appeared less dependent on food source than the food-to-mass ratio. High concentrations of biodegradable food produced dispersed growth and high concentrations of exopolysaccharides that contributed to poor settling. introduction Settling in an industrial activated sludge system requires mixed bacterial cultures with the appropriate chemical and physical properties to agglomerate and settle in the secondary clarifier. A small portion of this settled sludge is wasted to produce the desired solids residence time in the basin, and these wasted solids are often dewatered with the aid of a polymeric flocculant. The efficiency of this dewatering process depends on properly matching the polymeric flocculant to the surface characteristics of the bacterial flocs. Therefore, knowledge of floc surface properties as a function of wastewater composition helps in selecting the best flocculant. Surface charge and hydrophobicity are important properties used to map flocculants to secondary sludge. These properties can be measured by several methods, but all methods require the biological floc to be perturbed from its normal environment before taking the measurement. Similar properties that are measured using different procedures often disagree, and these differences can be caused by perturbations in floc environments as well as nuances associated with the different molecular probes and conditions used to make the measurements. Fortunately, these dissimilar methods can yield complimentary information that creates a clearer picture of the bacterial surface when combined. Additional chemical measures can identify chemical components that contribute to these physical properties, and any correlation between physical properties and chemical composition can be used to