| Three dimensional biofilm electrode reactor(3D-BER) was a new type of water treatment reactor, based on a large amount of data, this study improved the conventional BER reactor, constructed of a new type of 3D-BER, and used it to treat the nitrate in groundwater. Anode of the reactor was graphite plate, the cathode was stainless steel mesh, and the particle electrode was active carbon, cathode laid in the reactor like spiral pattern, which could increase the contact area between the electrodes effectively, also could increase the current efficiency and enhance the efficiency of denitrification. and used the activated reactor to treat the nitrate nitrogen in groundwater, also analyzed the various factors and optimization of operating conditions, the experimental results showed that the new type of reactor was feasible for treating nitrate nitrogen in groundwater, the nitrate nitrogen removal rate remained at about 83%. The start-up of 3D-BER experiment was divided into two stages: the cyclic cultivation and the continuous water flooding. Firstly used of the denitrification bacteria from wastewater treatment plant, through 8 periods of the passage culture, enriched and sublimated of the denitrification bacteria inoculation fluid, on the electrode appeared a thin layer of film, determined that there was amount of biomass in the reactor, and the inoculation was completed, and changed into continuous water injection. The stability of 3D-BER reactor was studied by adjusting the C/N and current intensity in the experiment of continuous feed water, the results showed that when the influent nitrate concentration was 40mg/L, the current intensity was 40 m A, C/N was 2-10, the removal rate of nitrate was about 99.77%,this time the main denitrification depended on heterotrophic denitrification; When the C/N dropped from 1 to 0, the removal rate decreased but stable at around 50%, then depended on hydrogen autotrophic denitrification. To make use of the synergy of the two, the C/N was one. After two and a half months of inoculating and domesticating the microorganism, the electrode surface was covered with a thick layer of milky biofilm, used optical microscopy and scanning electron microscopy(SEM) determined the main denitrification bacteria in the reactor were pseudomonas、enterobacteriaceae、acinetobacter and micrococcaceae.The removal of nitrate nitrogen in groundwater was studied by using the 3D-BER reactor after cultivation, analyzed the main influencing factors, including influent nitrate concentration, current intensity, hydraulic retention time and influent p H, through the single factor analysis experiment, the following results were obtained:(1) There was an optimal range of nitrate nitrogen concentration in the influent to the remove of nitrate, the removal rate was 90.29%.Lower or higher concentrations could inhibit denitrification.(2) The more current, the more H2, the removal rate of nitrate nitrogen was the highest when the current intensity was 30-45 m A; But at this time the corresponding nitrite nitrogen accumulation and ammonia nitrogen concentration was also the largest. If current was 10-60 m A, the corresponding current efficiency is greater than 100%.(3) Hydraulic residence time was mainly determined the mass transfer time, but also affected the dissolved oxygen in water, the extension of hydraulic retention time was beneficial to improve the efficiency of the reactor, but the time was too long would increase the operating costs, combined with the economic considerations, the residence time was not less than 6h.(4) Influent p H was mainly influenced the growth of the denitrification bacteria, the best p H was 7.0-8.0,the removal rate was 77.37%. The experimental results showed that the effect of p H on the treatment of the reactor was small. This was because the reactor has a p H buffer, so that the reactor internal p H remained at about 7.11.In order to study the interaction between different factors and to find out the influencing factors and the optimum reaction conditions, the study used Plackett-Burman(PB) and Design Box-Behnken(BBD) method to study the influencing factors: evaluated the effects of influent nitrate concentration(A), current intensity(B), hydraulic retention time(C) and p H(D) on the denitrification. It was found that the order of influence was B>C>A>D.Designed N=12 of Plackett-Burman(PB), regarded the removal rate of nitrate nitrogen Y(%) as the response value, the regression equation was as follows:Y(%)=82.9+0.0.271×A-0.528×B+2.07×C-0.856×DDesigned N=15 of Box-Behnken(BBD), regarded the removal rate of nitrate nitrogen Y(%) as the response value, the regression equation was as follows:Y(%)=74.67-3.25×A-8.81×B+5.61×C-4.05×A2+4.33×C2+3.10×AB-3.47×BCThe best reaction conditions: Influent nitrate concentration A=33.43mg/L、Current intensity B=30m A、Hydraulic retention time C=10h,the nitrate nitrogen removal rate was 80%-95%. |
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