PNP-degrading Bacterium And Its Application In Wasterwater Treatment And Soil Pollution Remediation

In recent years, environmental pollution and security issue have become the focus of theattention, how to effectively avoid pollutants that would cause damage of human healthdeposit into the environment has become an urgent problem that needs to be solved. As thedeveloping of the chemical industry, a large amount of toxic and refractory organics inindustrial wastewater have been discharged into the environment. The substances which canexist in a long-term in the natural environment have adverse impact on animal, plant andhuman health. At present, the control of toxic and refractory organics in wastewater is animportant issue of the Water-Pollution-Control. The nitro phenol (p-Nitrophenol, PNP) is oneof the important raw materials in industries, such as chemical, printing, dyeing, medicine andexplosives, and it is a long term residual pollutant in soil and water of the environment whichpose a threat to plants, animals and human health. The nitro phenol used in the productionprocess could be carried into environment with the discharge of industrial wastewater.Bioremedition technology is the mainly use biological organisms to the treat pollutants, andeventually the pollutants would be contaminated decomposition of harmless process, and theadvantage is about it is that it is quickly, efficiently, economical, practical, safety and simple.Some scholars are dedicated to the study of biological degradation of nitro phenol, but thePNP in the soil pollution reports really little. In this paper, enrichment culture method andsewage treatment plant oxidation ditch were used, and the efficient bacterial strains of PNPdegradation were screened from the activated sludge. There are many bacterial strains thatwere screened from the activated sludge can effectively degradation of nitro phenol (PNP),but among all the strains Z-1in all the strains had the best degradation performance, theresults are as follows:(1) PNP as the only carbon source and energy of the bacteria growth, through thephysiological and biochemical characteristics, and ultimately the bacterial strain Z-1wasdetermined for optimal strain, and identified by PCR, according to16S rDNA sequenceanalysis, strain Z-1was identified as Rhodococcus sp.. The optimal degradation conditionswere inoculation amount4%~8%, temperature15~35°C, pH6~11, PNP concentration100~500mg/L. Under the optimal condition, the degradation effect was better, and the straincould tolerate the PNP concentration of1000mg/L.(2) The metabolic pathway of high efficiency degradation bacterium was confirmed,mainly through two kinds of ways, and the4-nitro catechol way was conformed to degradePNP in this paper. The degradation performance of the immobilized bacterium Z-1mainlyeffected by environmental factors: the initial concentration, pH, temperature and other factors.Under the optimal operation conditions, the remove of the PNP in wastewater reached above90%.(3) The mixture of PVA and sodium alginate was used as the carrier, and orthogonalexperiment was used to determine immobilized optimal conditions of bacterium Z-1. Theresult are as following: PVA was90g/L, sodium alginate concentration was1.0%, H3BO3+ CaCl2concentrations were4.0%+3.0%, the proportion of embedding agent and bacteria liquidwas30:1, calcification time was12h, the embedding balls were made by the conditions abovehad the optimal degradation effectiveness and mechanical properties.(4) The degradation conditions of PNP wastewater for the embedding balls to wasdetermined. The optimal conditions were inoculation amount8%, temperature30~35°C,pH6~8, rotation peed120~160r/min. In the single factor effect, the degradation efficiency ofPNP wastewater by immobilized bacterium was higher than the free bacterium. Thissuggested that the tolerance of immobilized cells was better, compared to the free bacterium,in the salinity, temperature, pH and other conditions. The reason is that the surface of thecarrier increased the contact area, and also protected the bacterium in the embedding ballsfrom the toxicity of the substrate, so that the degradation performance of immobilized ballwas improved.(5) Immobilized balls in enrichment medium trained after3d in constant temperature and120r/min speed continuous oscillation5h, the balls had completely no broken phenomenon,which indicated that the mechanical strength of the immobilized balls was high could affordthe impact of the wastewater streams. Putting the immobilized balls into the solution ofcertain amount of peacock blue and crystal violet, the peacock blue and crystal violet couldreach the centre of the balls in30min which also indicated that immobilized balls had anexcellent transfer performance of.(6) The degradation of PNP in soil was studied under the simulating conditions. PNPcaused obvious inhibition of the microorganism in early stage. After30d of degradation, thecarbon source using ability was significantly enhanced. The degradation speed of Z-1of PNPin the soil was also accelerated. The PNP inhibition to soil microbes was eliminated. PNPcould reduce microbial diversity in the soil, but the addition of Z-1could restore andimproved soil microbial diversity, which indicated that adding Z-1to the soil environmentwas an effective way to restore the PNP polluted soil. The relationship of indigenous bacteriaand pollutants had a balance in the soil. Inoculated with bacteria Z-1was a solution to aneffective remediation method of PNP contaminated soil. In the degradation process, thedifferent soil enzyme activity was accompanied by changes in the PNP concentration.Meanwhile, the results showed a different trend of microorganisms in the soil during thedegradation of the PNP in the soil environment. The influence of micro-organisms played notonly the existence of a catalytic role, but also came with the inhibition.