The Study Of Electrochemical Microbiosensor Based On Single/Mixed Bacteria To Assess The Water Toxicity

Many countries are facing serious ecological and toxicological problems resulting from the release of complex effluents and toxic substances to the water environment. More and more attention was paid to the development of technologies to detect the toxicity of wastewater. Traditional aquatic acute toxicity tests use the aquatic organism such as fish, rats and invertebrates as the detecting subject. It is time-consuming and expensive, requiring lengthy exposure times and abundance of organisms causing moral controversy. Luminescent bacteria test is currently the most widely used water toxicity detection method and is studied to evaluate the total toxicity of water samples by measuring the strength of the light emitted. Despite its widespread usage for many years, this method was influenced by the opacity, salty and p H value of the solution. It is not an ideal approach for detecting wastewater toxicity. Hence research efforts in recent years have been directed at developing simple, rapid and inexpensive environmental monitoring test technique.In this paper, two kinds of electrochemical microbialsensors were established based on single bacteria strains of E. coli and activated sludge respectively, where potassium ferricyanide was used as mediators. They have the potential for on-line long term monitoring aquatic toxicity. The below results are listed.(1) We took Escherichia coli as a model microorganism which was cultivated in liquid medium for 48 h and then suspended by PBS buffer solution in a test fluid. The experimental conditions were optimized. The concentration of the E.coli OD600=4.0, operation time 20 min, reaction temperature 40 ℃ was adopted in the experiment. The performance for biotoxicity determination of heavy metals and organics were studied under the best test conditions. The IC50 values got by Zn2+、Hg2+、Cd2+、Pb2+ these four heavy metal ions were 5.367 mg/L,2.620 mg/L, 8.222 mg/L and 28.32 mg/L respectively. The IC50 values got by three organic solutions were PA 19.75 g/L; methanol 196.5 g/L; 3,5-DCP 5.152 mg/L. The toxicity order to respiratory inhibition of E.coli was Hg2+ > Cd2+ > Zn2+ > Pb2+ for heavy metals and 3,5-DCP > acetone > methanol for organic substance. The experimental results revealed that the inhibitory effects of toxicants to the E.coli respiration were ordered. We also described the advantages and disadvantages utilizing the single bacteria as subject.(2) Various pollutants were tested using activated sludge containing natural mixed bacteria as subject combined with potassium ferricyanide as mediators. By optimizing the experimental conditions, we investigated the influence of the thalli concentration OD600=1.375, operation time 30 min, culture temperature 35 ℃ and p H=7 in testing solution on water toxicity detection. The suitable testing optimum conditions for aquatic toxicity were determined and a variety of typical toxic(heavy metal ions, organic matter and pesticides) were tested. The toxicity order to respiratory inhibition of E.coli was Hg2+ > Cd2+ > Zn2+ > Pb2+ for heavy metals; 3,5-DCP > acetone > methanol for organic substance and machete > DDT for two kinds of ordinary pesticides. The lower test values showed that the microbial organisms were higher sensitive to the water toxicants. This method showed more sensitive to Hg2+、Cd2+、3,5-DCP、methanol and Machete. Compared with other bioassay, the obtained results verified the feasibility of the technique in addition to the binary mixed toxicity of simulation of real water sample. It has great potential in the actual toxicity of water environment monitoring.