| At present,the total nitrogen concentration in secondary effluent from municipal sewage plant can only achieve less than 35mg/L,which is much higher than the available resources utilization index(<10mg/L).Moreover, a series of problems easily occurred as the secondary effluent aways was discharged to the nearby water body, such as the algal bloom, eutrophication and odor. These problems not only threaten the human health and life, but also restraint reusing water resource.Therefore, it’s imminent that the research on deep nitrogen removal technology of the secondary effluent would be done.The 3DBER technology which demands less carbon source as the addition of the current is more applicable to the further denitrification of secondary effluent with low C/N ratio.The 3DBER often need high current in order to obtain a desired effect of nitrogen removal.But, high current intensity caused the problem hydrogen inhibition, carbon electrolysis which led effluent chroma and polarization of electrode which increased mass transfer resistance.In order to strengthen the nitrogen removal rate of biofilm electrode process(3DBER), two multi-electrode biofilm reactors(Multi-DBER-1, Multi-DBER-2) were designed based on the existing theories at home and abroad. Aiming at solving the problem of inhibition of hydrogen, carbon electrolysis and polarization of electrode,some new improvements were made in the spects of reactor structure and electrodes space arrangement for improving the nitrogen removal efficiency of 3DBER process on the secondary effluent.By contrastively running Multi-DBER-1 、 Multi-DBER-2 and 3DBER, the following three contents are studied as well as molecular biology technology. Such as : ○1 the startup characteristics of Multi-DBER; ○2 the effects of electric current, C/N ratio, pH and HRT; ○3 the biofilm denitrifying bacteria diversity in Multi-DBER-1 and Multi-DBER-2 under the optimal operating condition.Research results:(1)When the startup was completed,the TN removal rate of Multi-DBER-1and Multi-DBER-2 were 94.87% and 94.19%,respectively; the effluent organoleptic character was good;the TN removal rate of 3DBER was 88% with bad effluent organoleptic character.(2)The test results showed that current,C/N ratio,pH and HRT had some certain effects on nitrogen removal of the three denitrification reactors.Compared with 3DBER, Multi-DBER-1 and Multi-DBER-2 can acquire higher denitrification result at different factor conditions.In addition, The TN removal rate of Multi-DBER-1 and Multi-DBER-2 were respectively 76% and 86.97% under the optimal condition that the current was 200 mA and HRT was 9h.The 3DBER can acquire 61.99% removal rate at its optimal 200 mA and 9h conditon.(3)The β-proteobacteria dominated in Multi-DBER-1 and Multi-DBER-2 reactors. Futhermore,those figures were 72.86% and 58.57%,respectively.Except for uncultured bacterium,the denitrifying bacteria which could use hydrogen or organics accounted for 31.43% and 48.57%;21.43% and 37.14%,respectively.It’s mainly to complete the nitrogen removal in the system by auautotrophic and heterotrophic denitrifying bacteria.Above all, Due to some changes in the structure, Multi-DBER-1 and Multi-DBER-2 reactors which started quickly not only acquired higher optimal current, shorter optimal HRT, delayed the hydrogen inhibition, and slowed the carbon electrolysis and polarization of electrode. Thus, the target of enhancing denitrification effect was obtained. What’s more, the new reactors displayed their own superiority at electric energy consumption, intermediate product and by-product.The analysis about operation characteristics and mechanism of nitrogen removal of Multi-DBER-1and Multi-DBER-2 from macroscopic operation effect and microorganism aspects not only can provide strong theoretical guidance for the application of 3DBER technology, but also gave support for the further denitrification of secondary effluent and contribute to raising the water quality by improving the present situation of high nitrogen in reclaimed water. |
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