| The integrated floating fixed-film and activated sludge(IFFAS)process based on suspended biological carrier combines the advantages of both biofilm and activated sludge,which has attracted extensive attentions in recent years.The start-up phase,biomass and microbial characteristics of IFFAS have essential impacts on the sewage treatment efficiency.However,there are some problems in this process,such as long start-up time,unstable biofilm structure,low bioactivity and so on.One of the causes for these disadvantages is that the raw materials of suspended carriers are of poor biocompatibility,which makes it difficult for biofilm formation.In order to improve the efficiency of biofilm formation,increase biomass and/or enhance bioactivity of IFFAS,a new type of suspended carrier with good electrophilicity and hydrophilicity was made,and a new method to improve the nitrification and denitrification performance of IFFAS based on quorum sensing was developed.The relevant operation conditions were adjusted to strengthen the denitrification capacity of IFFAS process,and the microbial mechanism involved in the process was explored.The main conclusions were shown as follows:(1)A new type of suspended carrier was prepared by blending and screw extrusion technology with high-density polyethylene(HDPE)as the basic raw material,polyquaternium-10,natural clinoptilolite and tal were used as the modified material.The results showed that the Zeta potential of the modified carrier was +11.7±1.1 m V,which was more conducive to the attachment of negatively microorganisms than the conventional carrier with negative potential.The contact angle of the modified carrier surface was 73.2 °,which was more hydrophilic than the conventional carrier with contact angle of 95.4 °.Therefore,the biological affinity of the modified carrier was significantly improved compared with the conventional carrier.In addition,the modified carrier obtained a certain adsorption capacity of ammonia nitrogen due to the addition of natural clinoptilolite.(2)Biomass analysis results showed that the growth rate of biomass on the surface of the modified carrier was significantly faster than that of the conventional carrier under the same operating conditions,and the content of polysaccharide and protein were slightly higher than that of the conventional carrier.It indicated that AHLs signal molecules added to the reactor could enhance the adhesion of microorganisms to a certain extent and accelerate the formation of biofilm.(3)The pollutant removal performance of IFFAS system filled with modified carriers was investigated by adjusting dissolved oxygen(DO)and C/N ratio.The results showed that it was favorable for IFFAS to achieve better simultaneous nitrification and denitrification performance when DO concentration was properly reduced;IFFAS with modified carriers was more suitable for sewage treatment with low C/N ratio;AHLs added to IFFAS system could not only improve the nitrification rate,but also improve the denitrification rate.The system revealed better denitrification effect at low dissolved oxygen(DO=0.8±0.3 mg/L)and low carbon nitrogen ratio(C/N=4).The effluent COD,NH4+-N and TN could generally meet the wastewater emission standard.The results of high throughput analysis showed that the abundance of Nitrospirales in the biofilm on the modified carrier was more abundant than that of the conventional carrier,and the addition of AHLs could improve the nitrification efficiency of Nitrospirales and promote the growth of denitrification bacteria(Rhodocyclales,etc).(4)AHLs were added to the IFFAS process based on modified carrier and the intermittent aeration mode was adjusted to promote the simultaneous nitrification and denitrification performance.Results showed that denitrification of the IFFAS system can be improved by adjusting the aeration duration on the basis of ensuring the effluent NH4+-N meeting the discharge standard,thus improving the simultaneous nitrification and denitrification capability of the system. |
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