[Evolution of Extracellular Polymeric Substances of the Activated Sludge with Calcium Ion Addition During Set-up Period of Sequencing Batch Reactors].

Great attention has been paid to accelerate the start-up period and enhance floc properties and structural stability in activated sludge reactors with the aid of inorganic chemical agents such as calcium ion. The laboratory-scale sequencing batch reactors (SBRs) were operated continuously for 35 days to investigate the effect of calcium ion (Ca) on the physicochemical properties and evolution of extracellular polymeric substances (EPS) of activated sludge during set-up period. When compared to the control (non-calcium ion addition), the addition of 150 mg·LCa to the influent significantly increased the mixed liquid suspended solids (MLSS) and the mixed liquid volatile suspended solids (MLVSS) by 89.6% and 75.6% on 28 d, respectively, and decreased the sludge volume index (SVI) by 47.9% following SBRs set-up. Compared with the control system, the contents of EPS, polysaccharides (PS) and proteins (PN) were increased by 76.4%, 28.8% and 31.6% under the condition of Ca dosage of 150 mg·L. The PS/PN ratio was 68.8 for Ca addition, compared to only 36.6 for the control reactor. Analysis using three-dimensional excitation emission matrix fluorescence spectroscopy and Fourier transform infrared spectrum revealed that Ca addition changed the compositional characteristics of EPS. Results from this study provided a fundamental knowledge basis for the improvement of the settling properties of activated sludge with calcium ion addition.