Study On The Degradation Of Cyanide By Immobilized Cells

As cyanide is highly toxic to living organisms, wastewater containing cyanide must be treated before discharging into the environment in order to protect the environment and water bodies. The application of highly-effective-cyanide-degradation stains to the treatment of cyanide offers the environmentally friendly technique, which meets the requirement of the ecological safety. Particularly, the use of biological treatment in combination with immobilization could strongly enhance the conversion of toxic or recalcitrant pollutants into environmentally acceptable substances. In this study, the immobilization of a cyanide-degradation stains identified as Alcaligenes sp. DC02 and the construction of the bioreactor were investigated including the application of photo-spectrometer in the complicated medium system, the screening of suitable immobilized carriers and the optimization of the biodegradation conditions, the analysis of degradation end-product and dynamic model and the construction and operation of bioreactors.The glucose, protein and the extract of yeast existed in the cell-culture medium and their concentrations were proved to employ an effect on the cyanide analysis if the samples were not pretreated by distillation, however, the result from such a analysis process still could reflect the relative cyanide concentration. It made no difference that the analysis was done with the phosphate buffer as the medium or with NaOH solution.Polyurethane foam was screened to the suitable carrier and the immobilization could be realized by incubating cells with the polyurethane foams. The immobilized biomass was determined to be 0.35g dry weight/g polyurethane foams. The optical temperature and pH for the biodegradation by the polyurethane-foam-immobilized Alcaligenes sp.DC02 were 35 ℃ and 8.0, respectively. Moreover, the degradation rate of the immobilized cell was the same as that of the free cell for the low-concentration cyanide solution while the degradation rate of the immobilized cell was much higher forthe high-concentration solution. The degradation rate of the immobilized cell increased 2.4 fold than that of free cells for 1200 mgCNVL. The increase of the biodegradation rate might result from enhancement of the adsorption of the cyanide by the polyurethane foam on the biodegradation process.Ammonium (ammonia) was proved to be one of end-products in the biodegradation by Alcaligenes sp.DC02. The quantities ratio of ammonium generated to the cyanidedegraded was approximately 1:1, suggesting that the biodegradation was realizedcompletely and two possible mechanisms might be involved in cyanide degradation. Examination of the kinetics illustrated that the cyanide biodegradation followed the kinetics equation of first-order reaction. However, the kinetic constant of the immobilized cells was considered to be the overall mirror of different factors such as the physical absorption and the degradation by the microorganisms.Three kinds of bioreactor have been constructed and operated for a long period. In the sequencing batch reactor(SBR) simulated in the shaker, the immobilized cells could keep active after 20 days with 93 % of degradation rate. The continuous fixed bed reactor(CFBR) was operated smoothly for 13 days with 90% of degradation rate for 111.3mgCN7L. When the continuous stirred tank reactor (CSTR) was introduced to the long-time degradation, it was found that the bioreactor efficiency improved so that the bioreactor could run stably for about 50 days and then the cell adsorbed on the carrier would gradually die and remove from the carrier. When the proliferation of the cell was conducted at the same time during the degradation operation, the efficiency and stability of CSTR enhanced greatly so that the biodegradation rate could still attain above 93% for 300mg/L of the input cyanide concentration for 48 days.