Adaptability Study On Bark As A Carbon Source For Denitrification In Advanced Treatment Of Sewage Plants

Currently, in the process of municipal sewage treatment often encounter the problemof the lack of carbon source, and that will cause the low efficiency of nitrogenremoval. Traditional additional carbon source such as methanol、acetic acid will bringsome problems so that researchers prefer to use natural organic matter. The process ofdenitrification is determined by the release of organic carbon source contained in thecellulose material, so the focus of this study is to explore the laws of the release ofcarbon source, such as the content、the reaction rate and the factors which is related tothe release of carbon source.This test has used vertical flow constructed wetland system which was filled by firbark, and it just singly changed the HRT or the nitrate loading of the system, and eachfactor was divided into five stages. The purpose was to research the influence of thetwo factors to the release of organic carbon source. The main conclusions could bedrawn as follows:（1）After the biofilm stage, the bark was put into the wetland system. The period ofdomestication was divided into four stages. In this four stages, the concentration ofNaAc was from200mg/L to0mg/L. When the system eventually reached a steadystate without external carbon, the denitrification efficiency was about43%.（2）The result showed that the carbon concentration and the HRT satisfied the equation:C=28.574ln（t）+34.475. In this test, when the HRT was from0.75d¹.12d, the releaserate of per liter bark would increase as the HRT improved, and when it was1.12d⁴.48d, the trend would be otherwise, the best HRT was1.12d. Throughout thetest, the release of per liter bark in the reactor per day reached a maximum of39.85mg, and a minimum of16.48mg. The consumption rate of organics in thereactor was30mg/（L·d）. The effluent COD_cr concentration didn’t have a significantchange when the HRT changed, so it was considered that the bark would not causesecondary pollution.（3） In order to research the influence of nitrate loading, it was found that themaximum range of COD_cr concentration was45.23mg/L⁴7.14mg/L. The releaserate of per liter bark and nitrate loading satisfied the equation: y=1.063x+9.798.When NaNO₃concentration was180mg/L，the average COD_cr content of per liter bark in the reactor reached a maximum of41.22mg per day. The maximum rate ofconsumption of organics was37.02mg/（L·d） as the maximum was21.59mg/（L·d）.The study showed that the change of nitrate loading would not cause secondarypollution.（4）When it took effluent of secondary sedimentation tank as the influent of system,the nitrate removal efficiency could maintain at about60%, and the COD_crconcentration of effluent could meet the standards. The COD_cr concentration was16.17mg/L¹7.57mg/L, and the amount of the release of bark per day was40.28mg.