Research On Plant Fallen Leaves As Solid Carbon Source For Bioremediation Of Urban Surface Water

Eutrophication in city surface water is becoming a serious problem in manycountries. Nitrate removal is a key process in preventing eutrophication. An essentialrequirement for the reduction of nitrate is the presence of a carbon source that canbe oxidized as an electron donor. Unfortunately, most city surface water lackbiodegradable COD, which can be efficiently utilized by denitrifying bacteria. The citysurface water in Shanghai lack the electron donor, which is indispensable in theprocess of nitrate denitrification. The city surface water in Shanghai serverly lackcarbon source to the extent that the ratio of BOD5/TN in surface water is only1.1,and the decrease tendency will not be changed recently.In this work, city park and garden waste （mainly fallen leaves） was examinedthe potential to be used carbon source in the process of denitrification. Two differentverification ways were investigated. The first way used shacking bottle to examineleaching solution of fallen leaves whether can be used as carbon source or not. Thenair lifted biofilm reactor with ceramic honeycomb carrier was used reexamine theelectron donor’s performance in the procedure of degradating nitrate.（1）Fallen leaves of Platanus orientalis,Cinnamomum camphora,DahurianLarch can release COD when they were submerge into water. For Cinnamomumcamphora77.4mg COD was released per gram.58.8mg· g^-1for Platanus orientalis;52.2mg· g^-1for Dahurian Larch. The releasing process of COD is swift.80%COD wasreleased in the first24hours. Some organic acid was found in the leaching solution.The main organic acid was fumarate and other were citric acid, oxalic acid and malicacid according to the analysis by HPLC.（2）Outside influencing factors will change the leaching process of phoenixtree fallen leaves. The rising temperature favors the releasing of organicmaterical,while the increase of pH and solid-liquid ratio inhibit the releasing ofCOD,those three factor’s influencing force on carbon release varies, pH>solid-liquid>temperature.（3）The average nitrate removal rate was2.19mg NO₃^-N/h and2.052mg NO₃^-N/h,when the leaching solution of Platanus orientalis, Cinnamomum camphorawas used as carbon source during denitrification, while the rates were2.29、2.26and1.87mg NO₃^-N/h respectively with methanol, acetic acid and glucose as carbonsource. The rate with the leaching solution was slightly slower than that withmethanol and acetic acid, but faster than that with glucose. The experimental resultsindicated that7.5mg equivalent of COD from the leaching solution of Platanusorientalis fallen leaves were met for1mg nitrate reduction and there was no nitriteaccumulation during the denitrification.（4）The color of leaching solution of fallen leaves is identified by visiblespectrophotometry. The related coefficient between absorbance and concentrationis0.9922.Those plant pigment in leaching solution can be degradated by O3, andremoval rate is15.97degree/h, the removal rate isn’t increased by O3/UV.Thedegradation product of plant pigment is organic acid, so the pH of solution goesdown. The removal rate of nitrate is2.1408mg/h,2.35mg/h and2.32mg/hrespectively with UV, O3, O3+UV as pretreat method for leaching solution of fallenleaves. The degradation rate increased by63.94%,when pretreat method of O3aeration was applied.The best pretreat time is90min.In conclusion,the leaching solution of Platanus orientalis andCinnamomum camphora fallen leaves can act the role of the carbon source in theprocess of denitrification. The color of leaching solution can be effectively removedby O3aeration method and increase the biodegradability of the leaching solution,which has board application and meaningful prospect for the future research.