Study On Mixed Culture And Performance Of Two Different Species Of Heterotrophic Nitrifiers

With the rapid development of China’s industrial process, wastewater containing nitrogen is pouring into the rivers and nitrogen pollution increasingly serious. Biological denitrogenation, the most widely used process of wastewater treatment, has disadvantages of slow-startup and extra addition of carbon sources, etc. And many novel nitrogen-removal processes, such as simultaneous nitrification and denitrification（SND）, have been conducted to overcome these limitations. Therefore, it is necessary to explore microorganisms with the capability of heterotrophic nitrification and aerobic denitrification（HN-AD）.Two strains with the capability of HN-AD, Penicillium sp. L1 and Acinetobacter sp. Y1, were investigated in this paper. Optimum conditions for Penicillium sp. L1 to remove NH₄⁺-N are initially evaluated. Then compound microorganisms were constructed in the optimal way which the degradation rates of NH₄⁺-N, TN, and COD were selected as evaluation indexes. Eventually, these compound microorganisms are used to remove NH₄⁺-N and NO₃--N. The conclusions were drawn as followings:1. Study on optimum conditions for Penicillium sp. L1 to remove NH₄⁺-N:The degradation efficiencies of TN and COD and the growth of mycelial pellets were determined by inoculation method, C/N ratio, initial p H level, and Ca CO3 addition. The values were set as follows: two inocula—spore（dose, 1%, 2%, and 3%） and pre-cultured spore（pre-cultured time, 24 h, 36 h, and 48 h）; C/N ratios—12, 24, 36, and 48; p H values—1, 3, 5, 7, and 9; Ca CO3 addition—0 mg/L, 50 mg/L, 100 mg/L, 200 mg/L, and 1000 mg/L. The removal efficiencies of TN and COD reached 98.85% and 90.01% when the initial concentration of NH₄⁺-N was 130 mg/L under the following conditions: C/N 36, p H 5, inoculation with 48 h precultured spore and 0 mg/L Ca CO3. The pellet diameter reached 4.5mm. And these pellets were tight and not easily broken. Moreover, the removal efficiencies of TN and COD reached 94.92% and 81.25% when the initial concentration of NH₄⁺-N was 400 mg/L.2. Optimization way to compound Penicillium sp. L1 and Acinetobacter sp. Y1:Three ways of combination were studied, i.e., simultaneously inoculation of two strains, compounding two strains of different growth status, and adsorption. In this study, NH₄⁺-N was selected as sole nitrogen source. Conclusion was obtained that adsorption was the optimum way. The degradation efficiencies and rates of TN and COD were indicators. The average removal rate of TN and COD by compound microorganisms combined in adsorption way reached 7.10 mg-N/L/h and 102.33 mg-C/L/h which 4.69 mg-N/L/h and 15.83 mg-C/L/h by Acinetobacter sp. Y1, correspondingly in first 12 h. Thus, compound microorganisms were superior to Acinetobacter sp. Y1.3. Nitrogen-removal performance of compound microorganisms:Mixed mycelial pellets were used to remove NH₄⁺-N and NO₃--N. Mixed mycelial pellet（a）（inactivated mycelial pellet adsorbing Acinetobacter sp. Y1） and mixed mycelial pellet（b）（un-inactivated mycelial pellet adsorbing Acinetobacter sp. Y1） can be recycled to degrade NH₄⁺-N. Mixed mycelial pellet（a） performed better which high-efficiency of NH₄⁺-N removal was observed in seven cycles and the mixed mycelial pellet even remained stable after 120 r/min shaking for 20 days. Mixed mycelial pellet can denitrify under high dissolved oxygen（DO） concentration（120 r/min） and low DO concentration（0 r/min） and performed better than Acinetobacter sp. Y1.