Study On Efficiency Of SBR-BAF Hybrid Process For The Treatment Of Wastewater At High Salt Concentrations

Many processes generate high-salinity wastewaters, which contain at least 1% total dissolved solids. High-salinity wastewater is often difficult to treat using biological processes. Organic substants removal in high-salinity wastewater has been widely studied. However, biological nitrogen and phosphorus removal in high salinity wastewater seems to be very poorly studied. And the effect of salt content on bacteriums of active sludge is not clear. Biological treatment processes of high-salinity wastewater at home and abroad were studied and the SBR-BAF hybrid process was chosen for dealing with high salinity wastewater combined the advantages of suspended growth and attached growth process. This can provide a theoretical and practical basis and guidance for the engineering design, operation and management.In this research, the mechanism of removal organic substances, nitrogen and phosphorus is explored using two-sludge SBR-BAF system. During the process of domestication of active sludge in the reactor by gradually increasing salinity, the sludge structures, biologic shapes and settling properties as well as the removal effect of organic substances and total phosphorus and the ability of resistance with salinity were investigated at every experimental salinity level. In the BAF reactor, the influence of nitrification and dinitrification capacity of biofilm and the endurance of high salinity during the process of domestication with high salinity were researched as well as the principle of backwashing during dealing with high salinity wastewaters.Through the above experiments, conclusions are as follows:Firstly, the SBR-BAF system wholly performs well in disposing the organic substances, nitrogen and phosphorus of municipal wastewater. The mean removal efficiencies of COD ,TP, NH4+-N, TN are 96.14%,97.91%,95.40%,65.52% respectively, and the corresponding concentrations of effluent are 19.22 mg/L, 0.17 mg/L, 1.92 mg/L, 14.14 mg/L respectively. Secondly, in SBR reactor, activated sludge in the salt environment after acclimation, the sludge structures, biologic shapes and settling properties will be changed. It was observed that the amount and species of protozoa reduced gradually with the increasing salinity during the acclimation period. The acclimated sludge floc was smaller than the unacclimated sludge. The acclimated sludge had good settling properties. Sludge volumetric index (SVI) was about 30～40 mL/g. When the salt content was lower than 20 g/L, SVI decreased with the increased salt content. While salt content higher than 20 g/L, SVI increased gradually as salinity increased. The bioactivities of acclimated sludge were improved significantly. This experiment demonstrated that PAO could be adapted to the high-salinity environment after long period of acclimation. Good performance could still be achieved for phosphate removal while treating high salinity wastewater. When the salt content was lower than 30 g/L, the concentrations of PO43--P in the effluent were lower than 0.5 mg/L. When the salt content was up to 35 g/L, phosphate uptake rate decreased.Lastly, BAF reactor which was attached by biofilm with high biomass has excellent nitrification and denitrification performance. It is able to quickly adapt to the impact of high salinity. After acclimation, the nitrification and denitrification performance is almost the same as in the salt-free circumstance. In this study, it was found that nitrobacter was more sensitive to high salinity than nitrosomonas. After the process of domestication of sludge in the salt environment, it led to the nitrite accumulation during the course of nitrification when the salinity reached 15 ~ 25g / L. The denitrifying bacterium which is adapted to the freshwater environment had less inhibition than nitrification bacteria during the salinity impact and has less sensitivity to high salinity than nitrification bacteria. BAF has to be backwashed when the headloss increases to 8cm every 15~20 days; After backwashing the recovery is slower in high-salinity environment than in salt-free environment and the higher the salinity, the slower the recovery process.