Nitrogen pollution in water bodies is becoming increasingly serious, and how to remove nitrogen from water bodies economically and effectively has become a research hotspot. Especially in recent years, with the gradual expansion of aquaculture in China, the content of nitrite and other nitrogen-containing substances in water bodies has been increasing, which inhibits the growth of farm animals and is one of the causes of eutrophication in water bodies. In this study, a strain of bacteria was isolated from the sludge of an aquaculture fishpond and identified asPseudomonas stutzeri, which can efficiently degrade nitrite. After continuous domestication in nitrite mixed solution, the nitrite nitrogen reduction capacity ofP. stutzeriwas significantly improved. Univariate experiments aiming to optimize the degradation conditions indicate that the optimal culture conditions for strain F2 are: medium with a carbon source of sodium succinate; C/N of 18; pH of 8; culture temperature of 28 °C; and shaking speed of 210 rpm in the shaker. Under the optimal culture conditions, the NO2−-N concentration of the culture solution was 300 mg/L, and the nitrite removal rate reached 98.67%. Meanwhile, the results of the nitrogen balance test showed that the strain converted 6.1% of the initial nitrogen into cellular organic nitrogen and 62.3% into gaseous nitrogen.Keywords:nitrogen pollution;nitrite removal;domestication;Pseudomonas stutzeri
Fang Zhou,Xia Zhang,Lisen Zhang,Kaimin Zhang,Junxia Yu,Xinyi Yang,Weiyan Yin,Ruan Chi
Humic acid (HA) is an environmentally friendly and efficient aid leaching agent, however, the mechanism of HA and ammonium sulfate ((NH 4 ) 2 SO 4 ) on rare earth (RE) in-situ leaching process and the effect of HA on ammonium reduction remain unclear. Herein, the potential of HA as an aid leaching agent to optimize the dosage of (NH 4 ) 2 SO 4 and reduce the residual ammonium salt was investigated, controlling the ammonia nitrogen pollution. Moreover, the calculation model of (NH 4 ) 2 SO 4 amount and unit consumption equation were established based on mass action law. The result indicated that the leaching efficiency of RE was increased by 3.96 % in the presence of 0.2 g·L −1 of HA, suggesting there was a synergistic effect between HA and (NH 4 ) 2 SO 4 during the RE leaching process. This effect was further confirmed by the leaching mechanism. Specifically, when the value of mass action quotient ( K t ) increased, the reaction molar ratio ( n ) was decreased as compared with that of pure ammonium sulfate, indicating HA has a promoting effect on the ion exchange reaction between rare earth ions and ammonium ions. Additionally, it was revealed that the (NH 4 ) 2 SO 4 dosage was reduced by 34 % based on the law of mass action. Notably, the optimal (NH 4 ) 2 SO 4 concentration was lowered from 0.1 mol·L −1 for the traditional technology to 0.08 mol·L −1 for this work. These findings provided new insights into strengthening the leaching process of weathered crust elution-deposited rare earth ores by HA, which were valuable for elucidating the interaction mechanisms and realizing the source control of ammonia nitrogen pollution.
After membrane bioreactor (MBR) effluent from landfill leachate was treated with an advanced oxidation process of microwave-activated peracetic acid (MW/PAA), refractory organic compounds were transformed into small molecular organic compounds, which could potentially serve as carbon sources for microorganisms. In this study, a combined biological method involving the use of a MW/PAA process and a semi-aerobic aged refuse biofilter (SAARB) for MBR effluent treatment of landfill leachate was established. The results showed that under optimized MW/PAA process conditions (PAA concentration = 40 mmol/L, MW output power = 160 W), the absorbance removal efficiencies at 254 nm (UV 254 ) and color number (CN) were 42.24 % and 94.09 %, respectively. After the effluent was oxidized by the MW/PAA process and then biologically treated with SAARB, the removal efficiency of total organic carbon (TOC) in comparison with that of the influent reached more than 80 % due to the large amount of bioavailable carbon generated in the MW/PAA process, which promoted denitrification in the SAARB. It improved the removal efficiency of SAARB for nitrogen pollutants (TN, NH 4 + -N, NO 3 - -N, and NO 2 - -N). The oxidized effluent of the MW/PAA process was enriched in some functional microorganisms ( Proteobacteria , Chloroflexi , Actinobacteria , and Firmicutes ) involved in organic compound degradation and nitrogen cycling in the SAARB. The effectiveness of the MW/PAA process combined with biological methods for further treatment of landfill leachate was demonstrated. This study provides practical guidance for the treatment of landfill leachate by advanced oxidation processes combined with biological methods.
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