The Deep Treatment Technology Of Both Nitrate And The Residual Organics From Denitrification

According to the serious nitrate pollution situation and the residual organics problems of the traditional denitrifying processes,this paper proposed three different denitrifying processes with the main objective to deeply removing both nitrate and the residual organics from denitrification.1.Denitrifying granular sludge technologySince anaerobic granular sludge has been extensively applied worldwide,this paper proposed that nitrate was firstly treated by granular sludge bed,and then the residual orgaincs from denitrification were further removed by biological contact oxidation and coagulation sediment process.The keypoint of this idea is the sucessful startup and steady operation of denitrifying granular sludge,which were systemically studied in this paper.Well-formed denitrifying granular sludge was obtained within 40 days with methanol as carbon source and flocculent sludge as seed sludge in upflow sludge blanket(USB)reactor.This system showed a good denitrification performance that nitrate and COD removal efficiency were 99%and 91%,respectively when nitrate loading rate(NLR)was 5.0 gNO3-N·L-1·d-1 and influent NO3-N was 100 mg-L-1 with a C/N(COD/NO3-N)at 4.0.As to the sludge floating and channeling phenomena during the cultivation,the measures that improving the seed sludge and controlling the sludge growth rate were adopted respectively to accelerate the formation of good granular sludge.It concluded that ? the stable and aging sludge was better as inoculum.? the sludge loading rate should be within 0.15 gNO3-N gVSS-1·d-1 at the beginning of cultivation.? when fine granules formed,channeling and dead space were usually observed in the sludge bed,so interval air-blowing was advised to improve the mixing effect;? increasing loading rate can accelerate the formation of granular sludge,while the sludge loading rate should be less than 0.25 gNO3-N·gVSS-1·d-1 until dense,mature granular sludge appeared.According to the unstable phenomena of denitrifying granular sludge under high NLRs,the six measures that reducing the size of the granules,increasing the density of the granules,weakening the adhesion effect of sludge to bubbles,reducing temperature,replacing methanol with glucose as carbon source,and decreasing NLR were conducted respectively to improve the stability of the reactor.It indicated that too rapid growth of biomass was the root cause of the flotation of denitrifying granules,and decreasing the growth rate of biomass was able to improve the stability of the denitrifying granules.2.Dentrification-Removing carbon(DN-RC)processIn this paper,an integrated process,called DN-RC process,was proposed through which both nitrate and the residual organics from denitrification can be removed in one sludge system,which consisted of a denitrification tank(DN tank),a removing carbon tank(RC tank),and a sedimentation tank.This process exhibited a good performance that nitrate removal efficiency reached approximately 99%at a high nitrate loading rate of DN tank of 3.0 gNO3-N·L-1·d-1 and a low C/N of 4.0,respectively.The mechanism for the good performance of DN-RC process was studied.The system had a high sludge concentration of 7.0-8.0 gVSS·L-1,and a microbial diversity with rod-shaped bacteria,filamentous bacteria,protozoon,and metazoan,etc.The denitrifying activity remained 25.2 mgNO3-N·gVSS-1·h-1 during anoxic/aerobic alteration,which was almost 1.6 times of the actual removal rate.The added carbon source in DN tank was thoroughly utilized and the residual organics were mainly soluble microbial products(SMP)which were then deeply reduced in RC tank.3.Simultaneous dentrification and removing carbon in one aerobic tank(aerobic denitrification process)The denitrification behavior was investigated by a laboratory-scale aerobic denitrification reactor.The results suggested that nitrate can be removed effectively under aerobic conditions.When air rate was 400 mL·min-1,NLR was 0.5 gN03-N·L-1·d-1,and influent NO3-N was 50 mg·L-1 with a C/N of 7.0,nitrate removal efficiency was more than 99%with an effluent COD less than 10.0 mg·L-1.The effects of air rate and carbon type on aerobic denitrifying process were analysed respectively.It indicated that aerobic denitrifying process was a COD competition process between denitrifying bacteria and carbon oxidizing bacteria.Reducing air rate or selecting easily degradable carbon sources was useful to increase the competitiveness of denitrifying bacteria and was helpful for the aerobic denitrification.The results provide directive significance for improving the nitrogen removal efficiency of the exsiting wastewater treatment plants(WWTP).This study made up the gap of the current denitrifying researches that their effluents always contained a certain amount of the residual organics,and could support and promote the nitrate wastewater treatment.