Characteristics Of Aerobic Granular Sludge With Different Organic Loadings

As a kind of micor-aggregates of microbes, aerobic granular sludge has many advantages, such as high biological activity, a rich variety of species and coexists aerobic, anoxic and anaerobic environment, which can achieve nitrogen and phosphorus removal under aerobic condition. Aerobic granular sludge may be a promising technology. Recently, aerobic granular sludge has been successfully applied in urban sewage, Salinity wastewater, and brewery wastewater treatment. Besides, aerobic granular sludge has outstanding capacity of remaining micro-organism, and thus could accumulate nitrifiers with a slow growth rate. In traditional processing units, high concentrations or sludge age are frequently applied in order to rich these slow growing bacteria. Nitrobacterium granular sludge may be a promising system to treat high ammonia concentration wastewater. Because the characteristics of aerobic granular sludge relies on the micro-organism species in granule, in this experiment, the author had cultivated aerobic granular sludge with different organic loadings, and the granule type of different dominant species and the characteristics of pollutants removal were investigated.Three indentical sequencing batch reactors (SBRs) were applied in this study with different organic loading rates, namely, in the COD influent for reactors R1, R2, R3 were 600 mg·L-1,200 mg·L-1 and 0 mg·L-1, respectively. The morpholy of aerobic granules and the water quanlity were examined during this the entire experimental period. This work firstly illustrated the formation process of heterotrophic and autotrophic granules, and discussed the microbial species characteristics and differences on wastewater treament in reactors R1 and R3. From the pointview of the microbial cell synthesis and life maintenance, metabolic features of TOC and NH4+-N of heterotrophic granular sludge in R1 and R2 were analyzed.Experimental results show that:1) with the currentexperimental condition applied in the reactor R3, aerobic granules mainly componsed of autotrophic bacteria could be successfully developed. Compared with heterotrophic granular sludge of R1, autotrophic granular sludge showed less diversed species, slow growth rate, small granule size and small equivalent surface area but high density. And the removal rate of NH4+-N was 92% and 87% in R1 and R3, respectively; Howeverthe specific removal effecicency of ammonia in the autotrophic granular sludge (R3) was higher than that of heterotrophic one, and the rate of ammonia in R1 and R3 were108.2mg/(gMLVSS·d) and 579.7mg/(gMLVSS·d), respectively. More complex microbial populations were in R1, and the activity of nitrate nitrogen oxide bacteria (NOB) was restrained, as a result, more NO2--N were accumulated in the reactor. On the other hand, NOB could oxidize NO2--N to NO3--N in R3, and the concentration in the effluent was 38.5mg/L. It was calculated that the ratio of the autotrophic and heterotrophic bacteria was approximately 1:8 in heterotrophic granular sludge (R1).2) In Rl and R2 heterotrophic bacteria predominated, and more than 60% of the organic compound (TOC) was used to maintaining microbe life activity, and organic loading rates slightly influenced the metabolic of TOC in the two reactors. In R1, the removal rate of NH4+-N was to 90%, and among these,30% ammonia was used for cell synthesis, while R2, these values was 79% and 8%, respectively. In R2, organic carbon was insufficient for denitrification, and denitrifying rate was therefore limited, the rate was 19%, resulting in high NO2--N concentration. The denitrifying rate in R1 was 33% in effluent. Therefore, the organic loading rates significantly influenced the ammonia metabolism.