| Chinese aquaculture is facing the problem of excessive ammonia under high density patterns. This research focuses on the removal of nitrogen and tries to develop a practical method for aquaculture water recirculating, and identified strains that can remove nitrogen quickly for emergency at the same time, the results were as follows.1Two biofilm reactors were developed to cultivate activated aquiculture pond sediments continuously under low DO condition (DO concentration in reactor1was0.8mg/L-1.0mg/L, and in reactor2was0.4mg/L-0.6mg/L). Concentration of ammonium, nitrite and nitrate in the two reactors were monitored during the cultivation. After179days of cultivation, the removal rate of ammonium could reach80%and even more, and the concentration of the effluent nitrite decreased to nearly0mg/L. During the cultivation, the nitrate accumulated in reactor1, but not in reactor2. The contents of ammonium oxidizing bacteria (AOB), denitrifying bacteria and anaerobic ammonium oxidizing bacteria (Anammox bacteria) in the reactors were determined through quantitative PCR. At the end of cultivation, the contents of AOB and denitrifying bacteria in reactor1increased12and12.3times respectively; and the contents of AOB and denitrifying bacteria in reactor2increased53.4and8.3times respectively; but Anammox bacteria was not detected in both reactor. The results suggested that the short-cut nitrification-denitrification was activated in reactor2while the long-cut nitrification-denitrification was activated in reactor1.2Streak plate method and dilution method were used to obtain ammonium removing bacteria from aquiculture pond surface sediment sample. Twenty strains were obtained and one of them was able to remove ammonium efficiently from water. Ammonium concentration bounced back when the culture system was heated at100℃for two minutes, which indicated that ammonium might be removed by flocculation. The results of physiology and biochemical test indicated that the cells of the strain were Gram negative, no spores; Blast results of16S rDNA suggested that the strain was100% homologous with Delftia strain Delftia lacustri DSM21246T (Accession62759). It was concluded this strain belonged to Delftia, and was named as DF10. A series of experiments was conducted to test factors affecting DF10’s flocculation activity, and the results were as follows:1) Medium components such as carbon source and nitrogen source play a crucial role in flocculation activity; DF10could not grow in basic inorganic liquid medium; basic inorganic agar medium with (NH4)2SO4as nitrogen source and Na2CO3as carbon source was the best medium for flocs production, and when the DF10’s inoculating concentration (denoted as OD600) was0.425±0.04, and with initial ammonium concentration of14mg/L, basic inorganic agar medium with acetamide or cirtic acid added could also help to produce flocculants, but the flocculation rate decreased from85%to63%and27%respectively. DF10failed to grow in basic inorganic agar medium without Na2CO3, and could grow but lost the capability to produce flocculants in basic inorganic agar medium without (NH4)2SO4; when cultured in LB medium, DF10release ammonium to ambient environment instead of removing ammonium.2) Applied concentration of DF10had obvious effects on flocculation. The flocculants showed maximum activity when OD600of applied DF10is0.798±0.03, and the flocculation rate could reach97%in17hours with a initial ammonium concentration about14mg/L; and the flocculation rate decreased to85%when the OD600of applied DF10is0.425±0.04.3) Agitation rate had little influence on flocculation.4) Temperature had a significant effect on flocculation of DF10. Best flocculation rate was obtained at30℃-36℃.5) Ammonium concentration influenced flocculation greatly. With28mg/L ammonium concentration,15.42±0.03mg/L could be removed, with7mg/L,14mg/L and42mg/L of intital ammonium concentration,6.88±0.03mg/L,11.92±0.03mg/L and11.76±0.03mg/L ammonium was removed respectively. 6) Flocculation ability of DF10had great pH tolerance and showed maximum activity in the pH range of5-11, otherwise the flocculation rate decreased about23%。... |
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