Simultaneous Nitrification And Denitrification In MBBR Of Continuous Flow Using Novel Biocompatible Carriers

Simultaneous nitrification and denitrification?SND?has been considered as one of the promising biological processes for nitrogen removal from wastewater.The moving bed biofilm reactor?MBBR?based on biological suspended carriers has been developed to overcome the deficiencies and combine the advantages of both activated sludge process and fixed bed biofilm reactor.MBBR can provide longer sludge retention time for the slow-growing nitrifier and an anaerobic environment for denitrifier during continuous flow operation,which are appropriate for SND.Suspended biocompatible carriers are the core part of successful continuous flow MBBR-SND,however,normal carriers?usually made of HDPE?have inherent drawbacks such as slow biofilm formation rate and poor biocompatibility,which is adverse for nitrogen removal efficiency in these reactors.In this thesis,a kind of novel biocompatible carrier prepared by blending with modified materials were used to observe the biofilm formation properties,and the nitrogen removal performance of MBBR-SND in continuous flow conditions was investigated by measuring the effluent concentrations of COD,NH₄⁺-N and TN in different DO concentrations,temperatures and C/N ratios.The results of Sequencing Batch Moving Bed Biofilm Reactor?SBMBBR?biofilm formation experiment showed that the hydrophilicity,eletrophilicity and biological affinity of the noval carrier were better than the normal carrier,and the the biofilm formation rate of novel carriers was faster.The effluent of the reactor R₁ using novel carriers could meet the first level A of“Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant”?GB18918-2002?on the 14th day,which was 8 days earlier than the control reactor?using normal carriers?,which shortened the start-up time of the reactor.The effects of DO,temperature and C/N on the nitrogen removal efficiency of the reactor were investigated in the continuous flow MBBR-SND reactor?pH was 7-8 and HRT was 8 h?.At low DO levels?0.5-1.0 mg/L?,relatively short HRT?8 h?,appropriate temperature?21-25°C?and C/N?>7?,the removal efficiencies of COD,NH₄⁺-N and TN of the reactor R₁ were 90.5%,88.6%and 76.6%,respectively,which met the national first level A standard,on the contrary,the R₀ using normal carriers could not reach the first level A standard.High-throughput sequencing results showed that compared with R₀,the bacterial diversity and richness of reactor R₁ were significantly improved.The relative abundance of autotrophic nitrification and anoxic denitrifying bacteria increased by 3.64%and 8.4%respectively in the experimental reactor.Moreover,there was a higher proportion of heterotrophic nitrifying bacteria?Rhodobacterales,16.9%,5.1%higher than R₀?and aerobic denitrifying bacteria?Sphingomonadales,3.0%,R₀ little difference from R₁?in the biofilm of R₁,which further promoted the N-removal performance in R₁.The actual domestic sewage treatment experiment showed that effluent COD concentration of both reactor R₀ and R₁ could meet the first level A standard?<50 mg/L?at low DO level?0.5-1.0 mg/L?,relatively short HRT?8 h?and the appropriate temperature?21°C-25°C?.However when the C/N increased to 4,the effluent NH₄⁺-N concentration of the reactor R₁ reached the first level A standard whereas the effluent TN efficiency is stable,was close to the first level B standard.This study lays a foundation for the application and popularization of SND technology based on novel biocompatible carriers,and promotes the development of related microbial mechanisms.It is of great significance for the efficient and stable removal of TN in wastewater and the alleviation of the environmental nitrogen pollution.