| The effluent quality of low C/N domestic sewage treated by the traditional biological denitrification process is difficult to meet the standards because of insufficient carbon source.Moving bed biofilm reactor(MBBR)requires less aeration.which can reduce the inefficient utilization of carbon sources and energy consumption.Therefore,the biofilm-culturing startup characteristics and shortcut nitrification kinetics of two MBBRs with Kaldnes packing and polyhedral hollow sphere packing were compared by investigating biofilm biofacies,the component and content of extracellular polymer(EPS)in biofilm,removal efficiency of NH4+-N and COD,so as to construct a shortcut nitrification system suitable for stable growth of ammonia oxidizing bacteria(AOB).In order to further improve the denitrification performance of MBBR in treating low carbon wastewater,reed,silvergrass,corncob and grapefruit peel were selected as experimental solid carbon sources,and their carbon release,nitrogen release,adsorption and denitrification property were measured and studied under static and dynamic conditions respectively.Therefore,solid carbon source which provided stable carbon sources and did not cause secondary pollution to the environment was screened.Finally,it was added to MBBR to realize the combination of shortcut nitrification and denitrification with solid-phase denitrification.The main conclusions were as follows(1)Compared with hollow sphere packing,the removal rates of NH4+-N and COD in the MBBR reactor with K2 packing were 94.46%and 82.51%respectively.The biofilm in K2 packing had more compact structure,and higher protein and polysaccharide contents in EPS,which could achieve stable and efficient shortcut nitrification.The corresponding kinetic analysis also showed that MBBR filled with K2 filler had better substrate degradation ability(2)The release experiments of solid carbon source showed that the reed had lower carbon release,whereas shaddock peel with softer texture and loose structure was not suitable for external carbon source.Carbon and nitrogen releases of corncob and silvergrass did not significantly increase the water loading,and the leaching solution contained a large number of trace elements and protein-like substances which were beneficial for microbial growth and degradation.Therefore,they were suitable for MBBR denitrification carbon sources(3)The solid carbon source adsorption experiments confirmed that the microorganisms carried by corncob had strong adsorption and transformation ability to nitrogen in the wastewater,and the ability was gradually enhanced with the increase of NO2--N concentration in influent water.Nitrogen in the wastewater was mainly adsorbed by silvergrass,and the effect of microorganisms carried by silvergrass itself was very small(4)Denitrification experiments showed that the denitrification system with K2 packing biofilm and corncob solid carbon source had more advantages than silvergrass in nitrogen removal.When the concentration of NO2--N was 10-30 mg/L,the removal rate of nitrogen was over 99%.However,the concentration of NO2--N was 30-60 mg/L,which adversely affected the denitrification performance of the system.With the increase of retention time,the concentration of NO3--N gradually decreased to less than 10 mg/L.In addition,the rough and porous surface structure of corncob has good microbial adhesion.Therefore,corncob was selected as denitrifying solid carbon source of MBBR and the carrier of microorganisms(5)The corncob was fixed by polyethylene filler and then added into MBBR to treat synthetic wastewater which do not contain any carbon source.The denitrification effect of MBBR was better than that of MBBR with sucrose and sodium acetate as carbon source.The average concentrations of NH4+-N and NO3--N in the effluent of the reactor were less than 1 mg/L,the average concentration of NO2--N decreased to 3.65 mg/L,which was decreased by 69.78%,and the average concentration of effluent COD was 30 mg/L.The mian component content of EPS in MBBR's biofilm with corncob was also increased significantly.The protein and humus contents of the compact extracellular polymer(TB-EPS)were 1.51 and 1.53 times than that of the original biofilm.The results showed that corncob as denitrification solid carbon source and microbial carrier for MBBR was beneficial to construct high-efficiency nitrogen removal system by combining shortcut nitrification and denitrification with solid-phase denitrification. |
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