Denitrification potential evaluation of a newly indigenous aerobic denitrifier isolated from largemouth bass Micropterus salmoides culture pond

This work evaluates the application potential of a new indigenous aerobic denitrifi er, strain Pseudomonas CW-2, isolated from a largemouth bass culture pond. The rate of ammonium-N removal by strain CW-2 was approximately 97% at a DO concentration of 5.2 mg/L. Furthermore, when nitrate and ammonia coexisted, the strain gave priority to assimilating ammonia, and thereafter to denitrifi cation. Under optimal cultivation conditions, citrate and acetate were the carbon resources, C/N was 8, dissolved oxygen was 5.2 mg/L, and pH was 7; the removal rate of ammonium reached nearly 90%. The changing patterns of different bacteria in strain CW-2-treated and the control pond water were also compared. Lower levels of ammonia, nitrite, and phosphates were observed in the treated water as compared with the controls. Meanwhile, phylum-level distributions of the bacterial OTUs revealed that P roteobacteria, Bacteroidetes, Planctomycetes, and N itrospirae continuously changed their relative abundances in relation to carbon and the addition of strain CW-2; this finding implies that the conventional denitrifi cation process was weakened under the ef fects of carbon or the presence of strain CW-2. We propose that strain CW-2 is a promising organism for the removal of ammonium in intensive fish culture systems, according to our evaluations of its denitrifi cation performance.

Pseudomonas mendocina LYX:A novel aerobic bacterium with advantage of removing nitrate high effectively by assimilation and dissimilation simultaneously

The problem of nitrate accumulation in aerobic tank and total nitrogen excessive discharge in effluent was very common in traditional livestock and poultry farming wastewater treatment systems owing to the lengthy process flow and low process control level.A strain LYX of aerobic bacterium was isolated from the activated sludge of a wastewater treatment system in a pig farm,which could remove nitrate effectively in aerobic tank and was identified Pseudomonas mendocina by 16S rRNA sequencing.Under the condition of nitrate as the sole nitrogen source,this strain removed over 90%of NO_(3)^(−)-N with an initial concentration of 110 mg/L under aerobic conditions within 48 hours.Among them,37.9%of NO_(3)^(−)-N was assimilated into Bio-N,about 51.9%was reduced to gaseous nitrogen and less than 0.5%of nitrogen was replaced by NO_(3)^(−)-N and NH_(4)^(+)-N,9.7%NO_(3)^(−)-N remained in the effluent at the end.At the same time,four key genes(napA,nirK,norB and nosZ)related to nitrate nitrogen removal were expressed during the denitrification process of P.mendocina LYX,in which the transcription level of the indicator genes of this aerobic denitrifying bacterium(napA)was the highest.In addition,it was found with the 15N tracer technique that inoculation of this strain on sludge increased the amount of nitrogen loss from 9.26 nmol N/(g·h)to 23.835 nmol N/(g·h).Therefore,P.medocina LYX is a potential bioagent for advanced nitrogen removal by assimilating and reducing nitrate simultaneously in aerobic tanks.

Aerobic N_2O emission for activated sludge acclimated under different aeration rates in the multiple anoxic and aerobic process

Nitrous oxide（N_2O） is a potent greenhouse gas that can be emitted during biological nitrogen removal. N_2O emission was examined in a multiple anoxic and aerobic process at the aeration rates of 600 m L/min sequencing batch reactor（SBRL） and 1200 m L/min（SBRH）.The nitrogen removal percentage was 89% in SBRLand 71% in SBRH, respectively. N_2O emission mainly occurred during the aerobic phase, and the N_2O emission factor was 10.1%in SBRLand 2.3% in SBRH, respectively. In all batch experiments, the N_2O emission potential was high in SBRLcompared with SBRH. In SBRL, with increasing aeration rates, the N_2O emission factor decreased during nitrification, while it increased during denitrification and simultaneous nitrification and denitrification（SND）. By contrast, in SBRHthe N_2O emission factor during nitrification, denitrification and SND was relatively low and changed little with increasing aeration rates. The microbial competition affected the N_2O emission during biological nitrogen removal.