Study On The Factors Affecting The Enrichment Process Of Mixotrophic Anammox Bacteria

The Anaerobic ammonium oxidation(Anammox)biological nitrogen removal technology is both environmentally friendly and cost-effective.It is of great significance in practical engineering as it solves the problems of low carbon sources and high energy consumption.Although Anammox has potential for wastewater treatment,there are technical challenges that hinder its practical application.These include difficulty in enriching Anaerobic ammonium oxidation bacteria,incomplete nitrogen removal,and inability to avoid the negative effects of COD in treating wastewater.Enriching An AOB(Anaerobic ammonium oxidation bacteria)is a challenging task due to its complex nature.The process of nitrogen removal by An AOB is incomplete and is susceptible to the effects of COD when treating actual wastewater.Scholars both domestically and internationally have invested significant effort into improving sludge inoculation,carrier material dosing,and process coupling.In particular,the inoculation of sludge and the injection of small amounts of organic carbon are crucial for practical engineering applications and cost-effective operations.The injection of low amounts of organic carbon and inoculation of sludge have practical significance for engineering applications and operating costs.The effluent typically contains organic matter,and studies have demonstrated that An AOB can utilize acetic acid for mixed-nutrient metabolism.To further utilize Anammox in practical applications,it is crucial to investigate the enrichment of mixed-nutrient An AOB.This study utilized a single-factor rotation method to address the challenges of enriching An AOB and reducing susceptibility to organic contamination.The study also aimed to investigate the factors that influence An AOB enrichment,such as seed sludge,carbon source concentration,and the recovery of mixed-nutrient An AOB activity under refrigerated and high nitrogen loading conditions.The findings of this study can potentially contribute to the large-scale application of Anammox in practical settings.The main conclusions reached are as follows:(1)It is feasible to start up the mixed nutrient Anammox reactor using anaerobic biological iron sludge and ordinary activated sludge at a COD of 15 mg/L.The start-up process for the ordinary sludge system was slightly faster(81 days)compared to the iron sludge system(90days).However,after stable operation,the iron sludge system was found to be more effective in removing total nitrogen compared to the ordinary sludge system.(2)The concentration of carbon source varied between the iron sludge system and the normal sludge system,which affected the effectiveness of the nitrogen removal pathway in each system.In the standard sludge system,the process of enriching mixed nutrient An AOB was found to be successful when normal activated sludge was inoculated in an environment containing sodium acetate concentrations ranging from 0 to 60 mg/L.The reactor start-up times were observed to be in the following order:C2(75 d)<C1(81 d)<C3(117 d).The highest SAA of 2.96 mg N/(g VSS·h)was recorded in C2.In the iron sludge system,an increase in carbon source concentration hindered the enrichment of mixed nutrient An AOB.Reactors R1and R2 were successfully started up after 90 and 96 days,respectively.At the stable operation stage,R1 had a TNRE of 91.74%,which was higher than R2’s TNRE of 89.97%.In terms of SAA,R1 had a rate of 2.80 mg N/(g VSS·h),whereas R2 had a rate of 2.75 mg N/(g VSS·h).In contrast,reactor R3 did not reach the stable operation stage until 120 days of reaction operation and remained in the active stagnation stage.(3)The mixed nutrient Anammox iron sludge system displays a high level of environmental adaptability.Within a brief timeframe,the sludge exhibits strong Anammox performance,as evidenced by its high ammonia removal efficiency(ARE),nitrite removal efficiency(NRE),and total nitrogen removal efficiency(TNRE),which surpasses 90%.These results are highly promising for the future of the Anammox process.(4)At a COD concentration of 10 mg/L,the mixed nutrient Anammox iron sludge demonstrated the ability to withstand a maximum nitrogen removal rate(NRRmax)of 198.47g/m~3/d.Upon increasing the nitrogen influent load(NLR=260 g/m~3/d),the reaction performance deteriorated,resulting in a sharp drop in TNRE to 28.42%.The high concentration of nitrite was identified as the primary factor inhibiting the nitrogen removal performance of the reactor in this experiment.(5)Low concentrations of COD(10-25 mg/L)have been found to alleviate the inhibitory effects of high nitrogen loads to varying degrees.The most effective operating conditions were observed at a COD concentration of 10 mg/L.The study found that the addition of COD had varying effects on TNRE.The reactors with 10 mg/L of COD had the highest TNRE at 80.56%,followed by 15 mg/L at 73.83%,20 mg/L at 70.94%,and 25 mg/L at 47.82%.The specific anoxic ammonium oxidation(SAA)of the reactors also varied with the addition of COD.The SAA of reactors with 10 mg/L,15 mg/L,20 mg/L,and 25 mg/L of COD recovered to 85.09%,81.69%,78.80%,and 47.88%respectively,compared to the optimum stage of nitrogen removal performance.