| In wastewater treatment, the extracellular polymeric substances (EPS) of microorganism in both the activated sludge and biofilm systems are closely related to sludge characteristics. With respect to improving the operation of a bioreactor, it is important to understand the differences of EPS properties between the activated sludge and biofilm, and the effects of EPS on sludge characteristics and the quantity of biofilm. This study thus compared the EPS properties with the sludge characteristics in three systems--activated sludge, biofilm, and their concurrent system.This study firstly proposed extractions for low speed centrifugation products (LSCP), soluble EPS (SEPS) and Bound EPS (BEPS) in order to examine the effects of different layers of EPS on sludge characteristics. Heating extraction was chosen for the BEPS extraction because of the greater quantity of the BEPS extracted and because of the lowest DNA proportion.The evaluation of test parameters on bacterial adhesion to hydrocarbons (BATH) method using sludge samples was conducted. Results showed that the relative hydrophobicity (RH) of activated sludge was more stable at a wavelength of 600 nm, and a minimum standing time of 20 min gave stable results. N-octane and phosphate-urea-magnesium (PUM) buffer were found suitable as the hydrophobic and aqueous phase respectively. The volume ratio of the hydrophobic to the aqueous solution is suggested to be 1/10. An optimized procedure is then recommended.Feeding with poor organic substance synthetic wastewater in an experimental equipment, the effects of nutrients (COD/N/P) on the composition of EPS and sludge characteristics were studied. When the COD/N ratio changed from 120/5 to 120/24, the activated sludge performed better with the sludge volume index (SVI) value lowering from 164 to 105. Meanwhile the effluent suspended solids (ESS) increased from 5mg/L to 18mg/L, indicating that the bioflocculation of sludge became worse. A decreasing content of protein and a doubling content of humic and polysaccharide in EPS were found in this period. Phosphorus depleted conditions (COD/P=120/0.2) resulted in a rapid increase in SVI, indicating sludge bulking. Both doubling content of humic and decreasing content of polysaccharide in EPS were detected. The analysis of the microbial community structure of the activated sludge showed that the filamentous bacteria were dominant under this condition. A larger amount of protein content in total EPS was associated with poorer settleability, and the humic content in total EPS had significant negative correlation with the bioflocculation of sludge. Thus it can be concluded that the polysaccharide in LSCP had a positive correlation to the settleability and a negative one to the bioflocculation of the sludge, suggesting an important effect of the outermost layer EPS of the cell on sludge characteristics.Different performance of four carriers with various structures and materials were shown in a pilot-scale equipment. The amount of total EPS of biofilm in the inclined columnar type carrier was the greatest, with the greatest quantity of biofilm. Furthermore among the EPS of different layers for the four carriers, the protein was the composition showing the greatest variation.In the investigation of the surface properties of two carriers in a full-scale suspended carrier bioreactor, carrier A exhibited more hydrophilic surface and carried higher surface potential than carrier B. The amount of EPS of biofilm on carrier A was greater than that on carrier B, and the difference of EPS of the two biofilms was mostly caused by the significant difference of protein composition. The EPS of biofilm on suspended carriers was much greater than that of activated sludge in the same chamber. The protein content of biofilm EPS was 1.5 times of that of activated sludge. Results showed that sludge relative hydrophobicity (RH) increased with protein content and the total content of EPS of biofilm in suspended carriers, and the same relationship was true between the RH and the content of protein and DNA in BEPS. These result confirmed that the microorganisms on carrier had better adhesive properties than those in activated sludge.Although using the same combined packing, the EPS of biofilm coming from the three treatment stations were quite different due to the different kinds of wastewater. Nonetheless almost the same content of protein of three biofilm on combined packing were detected--approximately 50mg/g-VSS. Humic and DNA content of SEPS of biofilm in combined packings were also significantly correlated to RH of the sludge. Using the same elastic packing, the EPS of biofilm in wastewater treatment plant was much greater than that in the water treatment plant. |
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