Enrichment And Impact Factors Affecting The Metabolic Activity Of Anammox Bacteria

Anaerobic ammonium oxidation(ANAMMOX)is considered to be an economical and efficient way of nitrogen removal.However,the growth of anammox bacteria is slow,the requirements for propagation are relatively strict,and the enrichment is challenging,limiting the popularization and application of the anammox process.Because of this,this paper optimized the enrichment conditions of anammox bacteria,deeply analyzed the community structure of the enriched bacteria,and further explored the physiological characteristics of anammox bacteria.What's more,this paper investigated the effects of p H value,temperature and substrate concentration on the activity of anammox bacteria,which can lay a theoretical foundation for the efficient enrichment of anammox bacteria.In this study,the enrichment of anammox bacteria was studied in an expanded granular sludge bed(EGSB)reactor with activated sludge as inoculum.Under the conditions of 5.0 mmol·L^-1 concentration of ammonia nitrogen(NH₄⁺)and nitrite nitrogen(NO₂^-),30?culture temperature and p H 7,the EGSB reactor was started to enrich anammox bacteria through intermittent operation and continuous operation.Subsequently,the initial NH₄⁺and NO₂^-concentrations increased from 5.0 mmol·L^-1 to 20.0 mmol·L^-1,and the hydraulic retention time(HRT)decreased from 12 h to 8h reached a stable operation state.The removal rates of NH₄⁺and NO₂^-were 91.5%and 98.3%,respectively.The removal rates of NH₄⁺and NO₂^-were 2.90 mmol·g^-1·d^-1 and 3.48 mmol·g^-1·d^-1,respectively.The MLVSS in the system also increased from3.18 g·L^-1 to 5.85 g·L^-1.The 16S r RNA gene sequence results showed that 37.59%of the anammox bacteria were Planctomycetes;At the genus level,Candidatus?Kuenenia and unclassified?Candidatus?Brocadiaceae accounted for24.96%and 9.36%,respectively.The results showed that the optimum p H range of anammox bacteria was 7.0-7.5.The activity and reaction rate of anammox bacteria in weak alkaline condition s was higher than in acidic conditions.The optimum temperature range of anammox is30?-35?,and its reaction rate and microbial activity will be seriously inhibited under high and low-temperature conditions.The initial NO₂^-concentration and NH₄⁺concentration have a great influence on the Anammox process.Compared with the influence of NH₄⁺concentration,NO₂^-concentration has a more serious restriction on the growth and metabolism of anammox bacteria.The anammox population was more sensitive to NO₂^-.In general,the optimal p H,temperature,NO₂^-concentration and NH₄⁺concentration in the substrate were 4.0 mmol·L^-1 and 10.0 mmol·L^-1,respectively,and the corresponding maximum anammox reaction rates were 0.1784mmol·g^-1·d^-1,0.1923 mmol·g^-1·d^-1,0.2718 mmol·g^-1·d^-1 and 0.6420 mmol·g^-1·d^-1,respectively.