| The integrated floating film and activated sludge process(IFFAS)based on suspended biological carrier has attracted much attention concerning the continuous reduction of C/N ratio of urban sewage and the more strict discharge standards.Although the process can achieve better nitrogen removal by simultaneous nitrification and denitrification(SND),there are still some disadvantages,such as slow biofilm formation and rapid consumption of external carbon source,which resulting in unsatisfied total nitrogen(TN)removal.On this basis this study aims to develop a new type of carbon source slow-release carrier to further strengthen the biofilm formation as well as to upgrade the structure of IFFAS reactor to develop a new two-units IFFAS reactor.The operating conditions were improved to slow down the consumption rate of external carbon source and promote the storage of bacteria internal carbon source and improving the SND performance under lower C/N ratio.The main results are as follows:(1)The carbon source slow-release carrier was prepared by adding natural zeolite,polyquaternary-10,bamboo powder,and polybutylene succinate(PBS)into polyethylene.Compared with the conventional carrier,the novel carrier exhibited weaker hydrophobicity,stronger positive electricity,larger roughness,higher surface free energy and the ability of carbon source slow-release.It proved theoretically that the modified carrier had stronger initial adhesion to bacteria.In addition,the results of biofilm formation experiment showed that compared with the conventional carrier,the modified carrier not only showed higher specific bacteria growth rate,biofilm quantity and extracellular polymer(EPS)content,but also had more compact bacteria distribution on its surface.These results further indicated that the modified carrier strengthened the biofilm formation process and accumulated more biomass.(2)For the two-units IFFAS process,the mode of alternating influent and aeration was adopted(taking the reactor R1(only activated sludge was filled)as the control).Under the influent conditions of TN concentration of 40 mg/L and C/N ratio of 5-6.5,the IFFAS reactor R3(filled with modified carrier)showed better SND performance,and TN removal efficiency(59.9-65.9%)was 12.3-13.5% higher than IFFAS reactor R2(filled with traditional carrier).The storage and consumption curve of poly-β-hydroxybutyrate(PHB)in one operation cycle showed that the two-units IFFAS process could not only promote the storage of carbon source in bacteria cells,but also slow down the consumption of carbon source in anoxic unit.In addition,the results of fluorescence in situ hybridization(FISH)showed that the relative abundance of functional bacteria(nitrifiers and denitrifiers)in R3 system was higher than that in R1 and R2.(3)In order to further optimize operation mode of the two-units IFFAS process,intermittent aeration(220 min aeration and 180 min non-aeration,with the ratio of 1.22)was adopted and reduced the consumption of electronic donors to a certain extent.When achieving stable phase,the TN removal efficiencies of R1,R2 and R3 increased to 51.4%,61.9% and 63.1%,respectively.On this basis,the step-feed mode was used and resulted in further increased TN removal performance.The changes of EPS components showed the increase of protein content and functional groups types despite the main components of SND biofilm did not changed significantly.This variation improved the stability and complex of biofilm,which further enhanced the and anti-shock ability of two-units IFFAS. |
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