| The biological flocculation and adsorption process, which is developed based on the rapid organic matter adsorption by activated sludge, can remove organic matters in domestic wastewater significantly at lower investment of infrastructure and operation costs. Its application is beneficial for reducing the investment of infrastructure and the operation costs simultaneously to construct wastewater treatment plants (WWTPs). At present, most studies on such a process are focused only on system structure, reactor configuration and influencing factors, such as solids retention time (SRT), hydraulic retention time (HRT). However, its working principle is not yet clearly understood and its kinetics is not sufficient. Also, a mathematical model for describing this process is not available and the results are ununiversal. Through systematic experiments, the key parameters of the biological flocculation process were optimized and a universal mathematical model was developed in this study. The developed model was further proven to be reasonable and accurate with a pilot-scale study, which indicated the results are universal. Main results of this study are as follows:1. A laboratory-scale study was performed after analyzing the key parameters of the biological flocculation and adsorption process. The influences of ratio of gas/water, coagulation time, activation time, SRT and recirculation ratio on the system performance were evaluated. The optimized parameters were determined as follows: gas/water ratio 10:1, coagulation time 30 min, activation time 2 h, SRT 6 d and recirculation ratio 40%-50%.2. The adsorption characteristics of activated sludge in the biological flocculation and adsorption process were investigated. The suspended and colloidal organic matters were adsorbed effectively. The absorption capability was improved greatly after activation. The adsorption of organic matters by activated sludge followed the pseudo-second-order kinetics. The adsorption rate constant kads was 0.816 g COD/mg.MLVSS.h at 20℃. The adsorption ratio decreased 10%after the addition of inhibitosr, indicating that the microbial biodegradation occurred in the process. The heterotrophic bacteria yield coefficient was estaimated as 0.69 g COD/g COD and sludge yield was high.3. Based on ASM1 and the working principle of the biological flocculation and adsorption process, a mathematical model, which included biological adsorption and hydrolysis processes, was developed. The carbon sources of system were analyzed on the basis of kinetic equation and mass balance. The results of sensitivity analysis demonstrated that YH,μH, kH, KX, KS, kads,μA, bA were more sensitive. The model was calibrated and verified with the experimental data. The optimized simulation results were found to be:coagulation time of 40 min, activation time of 1.5 h, SRT of 6 d.4. A pilot-scale biological flocculation and adsorption system was well designed, installed and operated based on the results of the bench-scale study and mathematical model simulation. The removal efficiency of suspended solids, chemical oxygen demand (COD), CODss decreased significantly with an increase in hydraulic loading rate, and the removal rate of SS and CODss changed slightly. The removal efficiency of COD and SS remained high, while the removal efficiency of SCOD decreased with an increase in sludge loading rate when it was in a range of 2-20 kgCOD/kgMLSSd. The average COD, NH3-N and PO43--P removal efficiency were 70%,15%and 40%, respectively, at a recirculation ratio of 50%. At a recirculation ratio of 25%, the average COD, NH3-N and PO43--P removal efficiency was 65%,10%and 20%, respectively. The biological flocculation process had a resistance to shock loadings. The results of the pilot-scale study further demonstrated that the developed model was reasonable and accurate and was able to provide a theoretical foundation for its design and. operation in WWTPs.
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