| Currently,the anaerobic ammonia oxidation process has been intensively explored to maximize its performance as the "first choice" technique of biological nitrogen removal in wastewater.Anaerobic ammonia oxidation bacteria(AnAOB),a significant active functional bacteria of anaerobic ammonia oxidation,has some flaws,including slow growth,a long doubling time,being easily disturbed by the environment,and being difficult to cultivate in practice.The capture of biomass,as well as the high activity of AnAOB,are critical to ensuring the stable and effective operation of anaerobic ammonia oxidation.Microbial immobilization technology is a powerful tool for capturing functioning microorganisms.Biochar(BC)is a renewable resource with a cheaper cost of production than activated carbon and a porous microstructure that is appropriate for microbial immobilization.Iron is a common metal element in the natural environment,and it can stimulate AnAOB activity.As a result,biochar-supported nanoscale zero-valent iron(NZVI@BC)was used as an immobilized material for anaerobic ammonium oxidation microorganisms in this work,and its intrinsic adsorption characteristics for anaerobic ammonium oxidation sludge were identified.The startup and operation characteristics,as well as microbial community differences,of nZVI@BC and BC for anaerobic ammonia oxidation of low-concentration wastewater were compared using a continuous flow experimental device,and the promotion effect of nZVI@BC on anaerobic ammonia oxidation was clarified.Finally,the effect of temperature on the nZVI@BC anaerobic ammonia oxidation nitrogen removal system was investigated.The following are the primary conclusions:(1)It is demonstrated that the physicochemical features of BC and nZVI@BC have a substantial influence on the early adsorption process of anaerobic ammonium oxidation bacteria immobilization by assessing the intrinsic adsorption properties of the materials.The surface of nZVI@BC has a low amount of acidic functional groups,although it has a high iodine adsorption value and pHpzc.The number of microorganisms adsorbed by nZVI@BC is more than that adsorbed by BC at 15～25℃,and vice versa at 30～35℃.The optimal dosage of BC for anaerobic ammonium oxidation sludge adsorption is 33 g/L,whereas the optimal dosage of nZVI@BC is 27 g/L.The adsorption of BC and nZVI@BC on anaerobic ammonium oxidation sludge follows a quasi-second-order kinetic model.The adsorption of anaerobic ammonium oxidation sludge by BC and nZVI@BC is primarily based on chemical adsorption,which is complemented by physical adsorption and controls the adsorption rate.(2)The effects of adding BC and nZVI@BC on the start-up and operating parameters of anaerobic ammonium oxidation were compared by introducing mature anaerobic ammonium oxidation sludge into UASB reactor.During the experiment,the influent NH4+-N and NO2--N concentrations were kept at around 30mg/L and 39mg/L,respectively,while the temperature was kept at around 30℃.The anaerobic ammonium oxidation reaction was successfully initiated after 13 days.R0 removal rates with BC and R1NH4+-N removal rates with nZVI@BC were both over 93%,and NO2--N removal rates were both high.Following the successful start-up,the HRT was reduced from 6 hours to 3 hours,and the nitrogen load(NLR)was doubled.Following the operation,the removal rates of NH4+-N,NO2--N,and TN in the R1 system were 89%,97%,and 80%,respectively,and red sludge with big particles developed at the reactor’s bottom.The Heme C level in R1 reactor is high,at 0.118μmol/mg protein,which is 0.056 μmol/mg protein more than in the BC control group.The anaerobic ammonium oxidation sludge in R1 contains a significant EPS level,owing to the relatively high PN content.High-throughput sequencing analysis reveals that anaerobic ammonium oxidation sludge in R1 contains more OTUs and is more microbially diverse.Candidatus Brocadia,an anaerobic ammonia oxidizing bacteria,is abundant in R1.Because the relative abundance of denitrifying bacteria such as Limnobacter,Denitratisoma,and Pseudomonas is low,the addition of nZVI@BC can inhibit the excessive growth of denitrifying bacteria in anaerobic ammonia oxidation systems,which is beneficial to the maintenance of the anaerobic ammonia oxidation reaction.(3)At 25℃,20℃,and 15℃,the effects of normal and low temperature on the anaerobic ammonia oxidation of nZVI@BC were examined.The results showed that the removal rates of NH4+-N,NO2--N,and TN in the reactor varied significantly with temperature.At 25℃ and 20℃,total nitrogen removal rates in both reactors may progressively recover to around 80%,but at 15.The total nitrogen removal rate of R1 was higher than that of the control group throughout the cooling process,and the ratios of △NO2--N/△NH4+-N,△NO3--N/△NH4+-N fluctuated slightly,indicating that the anaerobic ammonia oxidation reactor with nZVI@BC had strong low temperature resistance,and the addition of nZVI@BC was beneficial to maintain anaerobic ammonia oxidation nitrogen removal.The content of extracellular polymer(EPS)in R1 reactor first decreased and then increased as temperature decreased,whereas the content of EPS in R0 reactor gradually decreased as temperature decreased,but the PN/PS in EPS in both reactors gradually increased as temperature decreased,but the PN/PS in R1 reactor was greater than that in R0.The content of Heme C in anaerobic ammonium oxidation sludge gradually dropped with decreasing temperature,however the content of Heme C in R1 was substantially higher than that in R0.The morphologies of the sludge in the two reactors show that the granular sludge in R1 has greater particle size,a darker hue,and a more compact structure.Furthermore,the SEM image shows that the surface of the sludge in R1 reactor is rich in filamentous bacteria,has many pores,and is rougher.High-throughput sequencing revealed that at low temperatures,R1 had more microbial diversity and species abundance.The number of anaerobic ammonia-oxidizing bacteria Candidatus Kuenenia and Candidatus Brocadia in the two reactors fell gradually as the temperature lowered,although the quantity of two functional bacteria in R1 was much greater than that in R0. |
PDF Full Text Request