| In northern China, with the long winter, low temperature and severe weather, it is remarkably difficult for the activated sludge to possess better capacity of nutrients conversion. Compared with activated sludge process, aerobic granular sludge (AGS) obtained better settling property, lower cost and higher biomass retention and contaminants removal efficiency, furthermore, the transfer limitation of substance and oxygen and the formation of temperature gradient inside AGS would be better for microorganisms to tolerate the shock of organic loading and temperature, and finally achieved relatively higher simultaneous nitrogen and phosphorus removal efficiency.Aerobic granular sludge was successfully cultivated in sequencing batch airlift reactor (SBAR) at10℃after40days, the protein content in extracellular polymeric substance (EPS) from AGS was considered as the main factor in granulation. Along with the enhancement of relative hydrophobicity and physical strength, the structure of AGS became more compact which could be helpful for AGS to keep stable. The autofit condition for cultivating AGS was gained by the optimization of SBAR operation, which means OLR was2.4kg/m3·d (influent COD600-700mg/L), HRT was3h and aeration rate was100L/h. SBAR operation can be stabilized for more than100days, moreover, AGS accomplished better contaminants removal capability, the respective COD, NH4+-N and PO43--P removal efficiencies were88.5%,97.8%and97.5%. Rhodobacter changlensis was a kind of psychrotrophs, which was the indigenous flora as well, in addition, Sterolibacterium denitrificans, Dechloromonas denitrificans, Blastobacter denitrificans, Pseudomonas trivialis and Bosea minatitlanensis were the dominant community in SBAR at low temperature.It is difficult to cultivate aerobic granular sludge at low temperature since the bioactivity of AGS was low and the operation of SBAR was complicated. In order to implement the rapid start-up and steady operation of SBAR, four strategies had been selected:1) enhanced by the stored AGS;2) enhanced by metal ions, such as Mg2+and Al3+;3) enhanced by sodium alginate and4) enhanced by bone glue. The results demonstrated that the above strategies could enhance AGS formation by 7-15days, as well as the long-term and stable operation of SBAR. Furthermore, the granules enhanced by bone glue was more effective (cultivated in26-28days) which had the ability to contribute and improve the biological process, the COD, NH4+-N and PO43--P removal efficiencies were86.3%,90.6%and93.8%, respectively.The formation process and sludge characteristics of AGS that cultivated in domestic sewage, saline sewage, normal molasses wastewater, oily wastewater and mixed wastewater combined by domestic sewage and slaughter wastewater were discussed. Relative hydrophobicity, zeta potential and protein content in EPS all increased during the formation process of aerobic granular sludge at low temperature. Therefore, the formation mechanisms of aerobic granular sludge might be concluded:the granulation process of activated sludge was the process of microorganism growth and environment selection. The chemical attraction of hydrophobic sludge aggregates, the electric adsorption of sludge aggregates and the conglutination of EPS were all important during the formation process of aerobic granular sludge. The viscous shear force was significant to lead the sludge aggregates to granular morphology, and the shear force caused by fluid disturbance in internal circulation tube was vital. In addition, it was found that the microorganisms of AGS can tolerate low temperature and possess better microbial activity due to the synthesis of cold shock protein and psychrophilic enzyme.It was notable that the Fourier Transform Infrared (FT-IR) spectra of ASP and AGS were almost the same, both the two kinds of sludge possessed polysaccharides compounds, lipid compounds and amide compounds, which indicated that aerobic granular sludge was suitable for treating real wastewater as activated sludge. Moreover, the Excitation-Emission Matrix (EEM) spectra of ASP and AGS demonstrated that microorganisms could gain better bioactivity due to the higher concentration of soluble microbial by-product-like and the stability of protein content in EPS would be of great significance to sustain AGS with the integrated morphology and compact structure.The aerobic granular sludge was cultivated in real wastewater for almost70days due to the complex components; the AGS was black with the mean diameter of0.8mm, however, the settling property and biomass retention could still be retained. Likewise, the existence of protein content in EPS was important in the formation process of aerobic granular sludge, furthermore, the lipid content in EPS would not influence the structure and strength of AGS. With the better shock resistance of influent, aerobic granular sludge technology gradually became stable which the contaminants removal capacity advanced as well, the COD, NH4+-N and PO43--P removal efficiencies were88.2%,94.0%and92.5%, respectively. The comparatively higher PO43--P removal efficiency was obtained by the combination of Mg, Ca and Fe with P, the adsorption of EPS with phosphorus and the biological phosphorus removal process. Ammonium oxidation bacteria (AOB), nitrite oxidation bacteria (NOB) and phosphorus accumulation organisms (PAO) were all effectively enriched after the granulation of activated sludge, among which NOB content is higher than AOB and PAO I (content higher than90%) was predominant in PAO. Enterobaceter ludwigii, Stenotropomonas humi, Zoogloea ramigera, Malikia spinosa and Comamonas denitrificans were the dominant community in SBAR at low temperature, indicated that AGS possessed better NH4+-N and PO43--P removal efficiencies. |
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