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Preliminary Study of Nitrifying Bacterial Sensor

Author: XieJiaZuo
Tutor: WangPing；LiHanDong
School: Central South University of Forestry Science and Technology
Course: Biochemistry and Molecular Biology
Keywords: nitrifying bacteria cellular fatty acid composition GC bacterial membrane immobilization biosensor toxicity determination
CLC: X703
Type: Master's thesis
Year: 2010
Downloads: 55
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Abstract

With the rapid development of modern industry, more and more toxic chemical emission poured into water causing increasingly serious water pollution. Assessment or prediction of the exogenous chemicals impact to the environment is an important task of environment protection activities. Usually, off-line analysis is used to traditional environmental monitoring. Not only it has operational complexity and high cost, but also it is not suitable for on-site rapid testing and continuous online analysis. Nitrifying bacteria is obligate aerobic, so it is vulnerable to external environmental factors such as heavy metals, pesticides, organic pollutants which can affect the nitrification process through inhibiting the nitrification enzymes. This is often used for toxicity test, therefore it is of great significance to isolate bacteria which can be used for toxicity-test from environment.In this paper, we had identified the strain from sludge of a pond in Beijing after enrichment, separation, screening. Then we did some analysis of factors on nitrification including pH, temperature, bottling capacity and inoculation. Besides, we investigated complex formulation, physiological and biochemical characteristics, degradation conditions of the high dominant degradation bacteria. Based on these studies, we had prepared highly efficient nitrifying bacteria bio-films which could be made of nitrifying bacteria sensor combined with a dissolved oxygen meter. Then we investigated the responsiveness of nitrifying bacteria sensors in different concentrations of organic and inorganic compounds. The main conclusions follow:From the pond sludge in Beijing, through screening and separation we got 4 highly efficient nitrifying bacteria:F1, F4, Y2, Z1. After identification of whole-cell fatty acids and physiological and biochemical experiments, we initially identified that F1 and F4 belong to Rhodococcus, Y2 belong to Pseudomonas, Z1 belong to Micrococcus.Strains F1, F4, Y2, Z1 can reach a higher nitrification rate at 35℃ after 21 day culture, but low temperature is not suitable for their growth and reproduction. As being affected by their growth environment and domesticated environment, alkaline environment is suitable for growth of the strains, the optimal pH ranges from 8 to 9. These 4 strains are aerobic bacteria. With the increase of dissolved oxygen in the medium, the NH4+-N degradation ability of strain increase significantly.General terms orthogonal test result shows that the best condition of NH4+-N degradation rate of complex bacteria is temperature (35℃), pH (8.5); bottling capacity (20mL/250mL); inoculation amount (25%); NH4+-N degradation rate (70.02%). The order of factors affecting nitrification effect is as follow:bottling capacity> temperature> pH> inoculation. The effect of bottling capacity and temperature are greater, but pH and inoculation volume is relatively obvious.Optimization of membrane fixed carrier ratio of experimental analysis shows that:when it is on the condition of PVA 16%, CA 0.6%, NaNO3 2%, CaCl2 75%, there is a best performance of membrane response,△DO can reach to 1.13mg/L.Through a preliminary study about nitrifying bacteria sensor response to HgCl2 and phenol with different concentrations, it is found that nitrifying bacteria sensors always have obvious response to both inorganic toxic (HgCl2) and organic toxic (phenol). With the increase of their concentration, the inhibition impact to respiration rate of nitrifying bacteria becomes stronger and stronger. When HgCl2 solution is 0.09mol/L, the DO sensor value is almost flat line. This shows that nitrifying bacteria respiration rate is almost completely inhibited by Hg2+. When the phenol solution is 0.12mol/L, the DO value of nitrifying bacteria sensor is almost flattened showing that the respiratory rate of nitrifying bacteria is greatly inhibited too.

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