Simultaneous Nitrate Removal And Cr(VI) Reduction In Pure Cultures Of Chelatococcus Daeguensis TAD1

Nitrate and hexavalent chromium are two key pollutants in water. When they exist at thesame time, it can both increase the destructive effects to the environment, and increase theprocessing difficulty. At present, chemical method is the main way to simultaneously removenitrate and heavy metal ions, but the cost is too high, and it is easy to create the secondarypollution. In this paper, the feasibility of simultaneous Cr(VI) reduction and nitrate removalby aerobic denitrifier TAD1was demonstrated. Aerobic denitrifier TAD1was a strain ofChelatococcus daeguensis, isolated from flue gas denitrification biological trickling filtersystem of coal-fired power plant.Sodium succinate and nitrate nitrogen were the best carbon and nitrogen source for strainTAD1respectively. The stable phase of strain was delayed because of the existence ofhexavalent chromium, and Cr(VI) reduction was mainly occurred in the logarithmic phase.Strain TAD1could remove Cr(VI) in the premise of TAD1having the microbial activity, andmainly relied on its own growth metabolic activity. Compared to the Cr(VI) reduction ratio bycultivating strain, the Cr(VI) reduction ratio by the cells and filtrates of cultivated strain wasmuch lower. The single cosxist of copper, zinc and nickel ion could inhibit strain reducinghexavalent chromium, and a variety of ions coexistence increased the degree of inhibition.After adding biodegradable adsorption materials, Cr(VI) removal rate by TAD1wasimproved.The parameters affecting simultaneous removal of Cr(VI) and nitrate by strain TAD1was investigated, such as C/N, initial Cr(VI) concentration, temperature, pH, rotate speed.The results showed that with the increase of C/N, nitrate and Cr(VI) removal rate and removalratio were increased, and under the condition of low C/N, microbial denitrification was morelikely to be suppressed. For C/N15, bacterial growth mass reached the maximum, and thedenitrification rate was94.53%, at the same time,15mg/L Cr (VI) could be removedcompletely. With the increase of initial Cr(VI) concentration, nitrate removal rate and removalratio both decreased, while Cr(VI) reduction rate firstly increased, then decreased. when theinitial Cr(VI) concentration was15mg/L, Cr(VI) reduction rate reached the maximum, and itreached1.01mg/(L h) in initial12hours. In addition, the temperature in45-50C, pH in7-9,rotational speed in150-180rpm was more conducive to simultaneous removal of Cr(VI) andnitrate by strain TAD1. Under optimized conditions, the concentration variation of COD, TNand total chromium was analyzed. The results showed that the removal ratio of COD, TN andtotal chromium could reach86.99%,37.50%,14.82%respectively. Part of nitrogen turned into N2or N2O, hexavalent chromium was mainly reduced to soluble trivalent chromium.