고농도 철강폐수의 생물학적 질산화 공정제어를 위한 환경인자와 미생물 군집 동역학 관계 고찰

Abstract

Biological nitrogen removal is an important aspect of present day wastewater treatment processes. Because the wastewater discharged from industrial fields contains high nitrogen-compound concentration, the attention of stable and efficient performance of the system has been increased. The amount of toxic substances also was considerable factor with nitrogen compounds. Toxic materials affect on the microbial community and then it could lead to the biological process failure.The physiological activity and abundance of the nitrifying bacteria in wastewater processing are critical in the design and operation of wastewater treatment plants, particularly since these microorganisms display low growth rate and high sensitivity to various environmental factors and disturbances. Based on the phylogenetically conserved nature of nitrifying bacterial 16S rRNA gene sequences and their occurrence behavior in nature, ammonia-oxidizing bacteria of the beta-subclass Proteobacteria, and Nitrobacter and Nitrospira genera are regarded as predominant groups of nitrifying bacteria in conventional wastewater treatment plants. The community of nitrifying bacteria of wastewater treatment plants is strongly affected by its surrounding environmental factors such as temperature, pH, characteristics of influent wastewater, substrate concentration, and various toxic materials. This study was conducted to investigate the nitrifying bacterial community and the significant affecting factors in industrial wastewater treatment plant. Based on the results from the full-scale nitrification system, the effects of simultaneous change of environmental factor on nitrification and AOB community were investigated. Finally, the growth kinetics of two AOB cultured in mixed culture were estimated simultaneously and the performance in continuous operation was also simulated to depict change in the concentrations of residual ammonium and two AOB at different hydraulic retention times. In this study, the correlation between nitrifying bacterial community and environmental factors was investigated in full-scale wastewater treatment plant which treats steel-manufacturing wastewater. In the system, the AOB community was constructed with N. nitrosa, N. aestuarii, and N. europaea. The 16S rRNA gene copy number of N. nitrosa, the dominant species AOB, was ranged from 7.8 ⊥ 105 to 2.3 ⊥ 107 copies/ml. The copy number of others was about 10% of the size of N. nitrosa during almost sampling period. Redundancy analysis (RDA), one of the direct ordinations, was applied to reveal the correlation between AOB community and its surrounding environment. The evaluated RDA model could explain 62.4% of AOB variability. Salts contents (K+, Cl-, Ca2+, SO42-), nitrogen compounds (NH4+-N, NO2--N, NO3--N), and temperature were selected the significant factor on the change of AOB population. The correlation between the salts and N. europaea was shown negative correlation and the population size of N. aestuarii has positive correlation with them. Because in salts demand for growth, N. aestuarii was more obligate halophilic bacteria than N. europaea, this result was reasonable. In the correlation with temperature, three AOB was shown different aspects: negative for N. europaea, positive for N. aestuarii, and no relation for N. nitrosa. Based on the data and distribution of sampling points on the RDA triplot, the temperature averaged 32 ∂ 1.4 oC was favorable N. nitrosa, and 27.8 ∂ 4.2 oC was favorable for N. aestuarii. Using RDA to investigate nitrifying bacterial composition and relation with environmental factors provide us the understanding how abiotic parameters affect the microbial community in the biological treatment system. This is an important step to be able to better interpret changes that are seen during process operation. Steel manufacturing industry is one of the primary sources of heavy-metal. Based on the concentration and literatures, zinc was selected for investigating effect on nitrification. Literature values of zinc concentration of inhibition on nitrification were determined in pure cultures or mixed cultures. However, the toxic information would not constants but variables depend on system conditions. Therefore, the effect of zinc on nitrification with respect to the changes in biomass concentration and temperature was evaluated using response surface analysis (RSA). The experimental ranges of three independent variables were determined by the observed values from the steel manufacturing wastewater treatment. RSA and modified ISO9509 methods were applied to establish the combination effect of AOB concentration (3⊥106 to 3⊥107 copies/ml), Zn2+ concentration (0.01 to 3.5 mg/L), and temperature (23 to33oC) resulting in lag period and ammonia oxidation rate (AOR). Various models, from linear to partial cubic, were tested sequentially to estimate the lag period and AOR. The effects of the variables on the lag period were adequately estimated with the partial cubic model based on statistical analysis (P= 0.002 at a 1% a-level, R2=0.978). In case of AOR, the quadratic model was only adequately model with significant statistical values (P= 0.005 at a 1% ？？-level, R2=0.959). From the models and the response surface, the lag period and AOR were significantly affected by the AOB concentration and temperature more than Zn2+ concentration. Although a higher concentrations of Zn2+, the increment of AOB and temperature decreased the inhibition effect of Zn2+ on nitrification. These results can provide a guide for the operation of full-scale wastewater treatment system, especially with quantitative information about the AOB concentration, which has a significant effect on reducing the toxic effects of zinc. The biokinetic of N. nitrosa and N. aestuarii were simultaneous estimated using real-time quantitative PCR (QPCR). Two AOB were detected and monitored in the steel-manufacturing wastewater treatment plant throughout the sampling period. Although the importance of growth kinetic for designing process and predicating operation performance, virtually no biokinetics information on its mixed culture is at hand. Therefore, this study focused on evaluating its biokinetic in mixed culture treating steel-manufacturing wastewater. To provide a set of relevant biokinetic coefficients for modeling, a combination of curve fitting and numerical modeling was used. Because of the lack of information on the competition mechanisms of two groups, we used simple Monod type growth model. From the model with the aids of numerical method, the kinetic values are successfully estimated. The maximum specific growth rates for N. nitrosa and N. aestuarii were estimated 1.63 and 1.06 day-1. These results were very similar with the literature values determined by volatile suspended solids (VSS). The half-saturation constant in this study, however, was greater than that of literature values. The growth kinetic coefficients were used for the simulation in continuous nitrification system at various hydraulic retention times. Assuming the influent ammonium concentration of 300 mg NH4+-N/L, the expected treatment efficiency was above 95% between 10 and 2 days HRT. N. aestuarii was expected to be washout at 5 days HRT.