Optimization Of Operational Parameters For An Anoxia Activated Sludge－biological Aerated Filter Process

Anoxic activated sludge-biological aerated filter （AAS-BAF） that comprised of ananaerobic activated sludge chamber and a post nitrification BAF, has been deemed as aninnovative biological process treating domestic wastewater, due mainly to that it can notonly take full advantage of carbon source in the raw wastewater, but also extend theoperational cycles effectively. Notwithstanding, it was recognized that phosphorusremoval in biological way in this process is rather difficult, and then additionalenhanced chemically phosphorus removal is necessary. According to the previousexperimental results achieved in our group, FeSO4is evident as an effective chemicalfor phosphorus precipitation, also has a certain positive effect on denitrificationefficiency, sludge dewaterability and settleability. However, some correlated operationalparameters, including FeSO4dosage points, feeding inlet points, internal recirculationratio and points, as well as their synergistic interaction, in the AAS-BAF process have tobe optimized, by which to elevate its cost-effectiveness and stability during actualapplication.In this study, four operational modes were selected to evaluate the effectiveness ofthe AAS-BAF process, and corresponded optimized conditions were obtained. Firstly,series of static batch tests were carried out to determine the best parameters in everymode, based on the total nitrogen and phosphorus removal efficiency. Afterwards, theseoptimized parameters were adopted in the dynamic lab-scale AAS-BAF process toexamine the treatment performance and to get the optimized mode. Finally, a pilot-scaleprocess was operated under the optimized mode to study the system stability and toassess the economic feasibility.The experimental results in the static tests showed that FeSO4dosage have rathergood capability in TN and TP removal, indicated by a stably low SP and NO₃^--Nconcentration in effluent that averaged about0.4mg/L and0.3mg/L, respectively, inmodes1,3, and4. In contrast, although a good denitrification efficiency could beobserved in mode2, phosphorus removal and the ferrous oxidation werenon-synchronous, resulting in a relative lower phosphorus removal efficiency.In the lab-scale dynamic experiments, treatment performance, especially in theterms of TN and TP removal efficiency in the AAS-BAF under mode1,3, and4wereevaluated through a continuous operation, during which combined dosing of1000mg/Lalkalinity and0.5mg/L PAM were employed to enhance the flocculation. The resultsdisplayed that the TN and TP removal efficiency under mode3and4are consistentlyhigher than those of modes1, whose carbon utilization rate seems as to be constrained by PAM addition. Considering the better sludge dewaterability and settleability in thesystem, mode4was considered as the optimized condition.After that, the pilot-scale AAS-BAF system was operated to examine the realwastewater treatment performance under this optimized condition. It is noted that theAAS-BAF process have an excellent removal efficiency in pollutants, which stablyconformed to the national one-class A wastewater discharge regulation, even while theprocess HRT decreased from7.5hr to3.4h, and the internal recycle ratio was about300%. Compared with the performance of SZ-BAF, the treatment cost could be savedup to0.17RMB per ton wastewater, which was quit attractive for the wastewatertreatment engineering.