The Research On Oily-Wastewater Treatment By Immobilized Microorganisms

With the development of industry, the quantity demand of oil is more and more. Oil brings huge economic increase, and does great harm to ecology environment at the same time. People have paid more attention to oil pollution damages in the field of ecology environment and people health, and the method and technology of remediation to oil contamination is becoming the puzzle for environment researchers. Now immobilized microorganisms technology has obtained a certain breakthrough in the field of oily-wastewater treatment.Immobilization systems are intended to entrap materials such as microorganisms or enzymes into a defined space and in this way microorganisms or enzymes can retain activity and be reutilized several times over a long period of time. Immobilized microorganisms can increase the biodegradation rate through a high microorganism loading and offer protection from extreme pH and toxic compounds.Especially this paper researched the application of immobilization technology in oily-wastewater treatment.In this study, oily-wastewater is object of study. The oil biodegradation ability of two bacteria conserved in laboratory is examined; the biodegradation efficiency of oil between free and immobilized microorganisms using sodium alginate immobilization method is compared; the method of chitosan tectorial membrane, which reinforce the strength of microorganisms immobilized bead, is studied preliminary. The results of this paper will could provide a theory support for the practical application of oil-wastewater bioremediation. The main conclusions are as follows:(1):two bacteria named W-1 and W-2 are identified as Rhosococcus sp. and Bacillus cereus sp. respectively, by morphological, biochemical and physiological characteristics. From the growth curve of two bacteria, we can see that W-1 and W-2 grow quickly in enrichment media, reaching stable phase after 7 hour. So, it is suitable to use bacteria incubated 7-8 hour as seed bacteria. And the optimal growth conditions for W-1 and W-2 are about 35℃,pH 7.5-8.5,salinity 2% and 4%, respectively, W-2 have more salt tolerance than W-1. (2):the oil biodegradation rate of W-1 and W-2 is declining with the increase of oil concentration in wastewater, is increasing with the increase of biodegradation time. After 7 days biodegradation, the oil biodegradation rate of W-1 and W-2 can reach 32% and 45%,respectively in the media containing 300 mg·L-1 standard oil.The optimal oil degradation conditions are similar to their growth condition, indicating that maximum degradation rate is correlated with maximum growth rate, consistent with the oil being the sole source of carbon.(3):the adsorption quantity of active carbon to W-2 is tested, which is 10.9×108 cell/g at 25℃,so immobilization method containing active carbon not only can increase the strength of immobilized bead but also reinforce microorganisms immobilization by active carbon absorbing bacteria. The optimal immobilization condition are:crosslinking temperature,25℃;crosslinker pH,5-6;crosslinking time, 24 h; the volume ratio of immobilized bacterial to gels is 1:5.Meanwhile, the speed of immobilized microorganisms reactivation is accelerated by adding inorganic salt.(4):the influence of pH, temperature and salinity to microorganisms beads (MB) biodegradation is investigated in the mineral salt media(MSM)containing 0.3% standard oil.The results show that the adaptable range of pH is 6-9, that of temperature is 30-50℃,that of salinity is 2-5% for immobilized W-2,which are more tolerant than free; the biodegradation rate of free W-2 reach about 40% and that of immobilized W-2 reach above 70%,which increase more than 30%.(5):because of existing low strength, easy decomposition for immobilized microorganisms beads, beads strength is reinforced by the method of chitosan tectorial membrance.The results show that the optimal tectorial membrance conditions are chitosan with 85% deacetylated degree and with 0.8% concentration; tectorial membrance time with 1.5 h. After tectorial membrance, the strength of beads are improved obviously and the beads can reuse twice.