Study On Enrichment And Charateristics Of Ammonia-oxidizing Archaea In Wastewater Treatment Plant

Ammonia oxidation is the key and rate-limiting step in biological wastewaterdenitrification. For a long time, people thought that the main microorganisms involvedin this process were ammonia oxidizing bacteria (AOB). Recently a new kind ofarchaeal which can also achieve ammonia oxidation was found, it was called ammoniaoxidizing archaea (AOA). However, current research focuses on the AOA distribution ofpopulation of AOA, and few on the AOA enrichment and separation, especially forwastewater treatment systems. In order to understand the growth and ammonia oxidationcharacteristics of AOA, this study has enriched AOA from wastewater treatment systems,and examine the impact of factors of growth factors on the AOA and ammoniaoxidation properties.The main subject cultivate AOA from wastewater treatment system via theapproach of the choice of medium, selection of antibiotic and syringe filters. It obtainedhigh purity AOA enrichment culture and AOA reached to3.27×107copies/mL, and AOAcontent is greater than90%. The cloning and sequencing of the obtained high purityenrichment broth show that a single sample AOA flora in archaea amoA genephylogenetic trees, and it belongs to group I.1b, and homology is similar with theHZNAOA7that obtained from East River sediments more than99%, but less than95%with Nitrosopumilus maritimus and Candidatus Nitrososphaera viennensis.It conducts for AOA separating pure exploration experiment from high purity ofthe AOA enrichment broth. With a flat separation method, dilution separation andmicromanipulation separation, pure AOA have not been isolate. This research analyzesreason of difficulty of AOA separate. Because AOA has a long generation time, maybethe medium composition is unsuitable for the growth of purebred AOA,maybe AOAcannot grow without coculture bacteria.It optimizes the influencing factors to the growth and ammonia oxidationcharacteristics of AOA from high purity AOA enrichment broth. The optimal conditionsof growth for AOA are determined by single factor experiment, orthogonal experimentsand comparison test, that is, initial ammonia concentration is1mM, temperature is30℃, pH is7.5, dissolved oxygen concentration is2.65mg/L. The optimal conditionsof ammonia oxidation for AOA is that initial ammonia concentration is1mM,temperature is37℃, pH is8, dissolved oxygen concentration is2.03mg/L. The CODhas no obvious influence on the growth and ammonia oxidation of AOA.Under the ammonia oxidation conditions, the ammonia oxidation rate of unit cell ofAOA is2.53×10-10mg/d, far less than the AOB. Possible reason is that the inhibition of free ammonia on the AOA, different metabolic type from AOB, existence of facultativeheterotrophic nutrition type.