Research On Perchlorate And Nitrate Reduction By Mixed Sulfur-carbon Three-dimension-electrode Biofilm

Perchlorate and nitrate are contaminations that have been found in many surfaceand underground water. Perchlorate mainly comes from solid propellant rockets andfireworks; nitrate mainly comes from agriculture, livestock farming waste, sewageirrigation and other social activities; the produce of fertilizer contained potassiumnitrate and fireworks will also cause the emission of perchlorate and nitrate.Perchlorate can interfere with the body through making impact on thyroid iodide;nitrates in human body can be easily reduced to toxic nitrite, which could cause thedeformation of red blood cells to lose their oxygen capacity. In recent years, usingmicrobiological methods to remove perchlorate and nitrate get the attention of manyscholars.On the basis of biological and electrochemical methods, the test combined sulfurautotrophic process and electrochemical hydrogen autotrophic process to put forwarda new process, which was named mixed sulfur-carbon complex three-dimensionalelectrode biofilm, and putting emphasis on the correlation between sulfur autotrophicdenitrifying-bacteria and perchlorate-reducing-bacteria and hydrogen autotrophicdenitrifying-bacteria and perchlorate-reducing-bacteria. and comparatively analyzingthe effect of hydraulic retention time (HRT) and current intensity on perchlorate andnitrate treatment under the conditions of deoxygenated influent water and nodeoxidation influent water, respectively; so as to optimize the operating parameters ofthe combined process.When the influent NO3--N was28mg/L, the correlation between the bacteria ofperchlorate degradation and denitrification was analyzed. When setting the current at10mA, the final effluent NO3--N concentration was below the detectableconcentration when varying HRT from12h to2h, and the removal efficiency wasclose to100%, which indicates that the reactor can tolerate the shock of loading rate; however, the effluent NO3--N concentration increased when the HRT was shortened to1h; setting HRT at1h, the effluent NO3--Nconcentration increased slightly with thecurrent from10mA to25mA，the better removal efficiency could be indicated by theeffluentNO3--N at4mg/L, meeting the sanitary standard for drinking water(GB5749-2006). The pH decreased overall, and was stable at7.6at the end of theprocess; the ORP decreased with the change of HRT, but less affected by the current,finally stable at-300mV. When setting HRT at1h, current at25mA, using thedomesticated denitrifying bacteria to degrade ClO4-of1.25mmol/L(124.4mg/L), theresults show that the effluent ClO4-concentration gradually decreased, and was stableat0.97mmol/L(96mg/L), and no intermediate product was formed. This indicatesthat the anaerobic sludge bacteria domesticated by nitrate can effectively reduceperchlorate, but not completely.Using Aeration to removal the oxygen in the influent water of the reactor tomake the dissolved oxygen (DO) at0.5~0.6ppm or less, and to research the effectsof HRT and current intensity on the degradation of ClO4-and NO3--N. When settingthe current at10mA, the effluent ClO4-and NO3--N concentrations increasedgradually with HRT decreasing from12h to2h, the effluent SO42-concentration atfirst increased then decreased; the effluent pH decreased with the shorten leng of HRT.When setting HRT at2h, change the current intensity at the range of10~35mA, theremoval effiency of ClO4-and NO3--N increased slightly, however, the effluent SO42-concentration was not obviously affected. The perchlorate was reduced to Cl-completely during the whole period, and the effluent SO42-concentration at the end ofthe process was stabilized at170mg/L, which meets the water standards; the effluentpH and ORP met the required microbial anoxic environment. Compared withinoculation sludge, the microbial bacteria in the reactor are mainly proteobacteria, andthe superior strains are Desulfocapsa sp. Cad626、 Thiobacillus thioparus andRhodococcus sp. DTB; what’s more, there appeared new strains-Rhodococcuserythropolis、Epsilon proteobacterium49MY、hodococcus erythropolis、Sulfuricelladenitrificans (T)、Flavobacteriales bacterium CF-1and Thiobacillus thioparus.Another reactor was set for comparison test, in which the influent was not deoxy and contained DO at2.5~3.0ppm, but the influent concentration and operatingconditions are the same as the former reactor. The effluent ClO4-and NO3--Nconcentration increased when shortening the HRT from12h to2h, but decreased asthe current from10mA to35mA. Comparative analysis shows that the treatmentefficiency of aeration deoxygenated condition is better than undeoxygenatedprocessing. The effluent SO42-concentration at the end of the process was stabilized at160mg/L, and the pH was between7.9and8.1, the ORP of the reactor could meet theanaerobic metabolic condition; the ClO4-and NO3--N concentration decreased alongthe reactor from the bottom to the top. In the reactor, proteobacteria accounted for64%of the bacteria, and the superior strains were beta proteobacterium5Z-C1、Marinomonas sp. JL-55and Thiobacillus sp. K6.2; Compared with the inoculationsludge, the new strains included Thiomicrospira denitrificans、 Thiobacillusthioparus、 Sulfurimonas sp. Go25-1、 Rhodococcus erythropolis and Vibrio Harvey.