Study On The Mechanism And Application Of Biological Denitrification For Micro-Polluted Water Source By Enhanced Coagulation Process

In recent years,with the rapid development of industrial technology and economic market,a large amount of wastewater has been discharged directly without effective treatment,which has led to excessive ammonia nitrogen in drinking water sources such as lakes and reservoirs.The traditional water purification process,which is composed of coagulation,precipitation,filtration and disinfection,can't solve the problems of these pollutants in the micro-polluted source water effectively and the quality of the effluent water is getting worse.Therefore,in order to prevent and control the modern water pollution problems,improve general water quality,and ensure the safety of drinking water supplies,it is necessary to develop and apply new technologies and processes.However,combined with the actual situation in China,most of the water treatment plants?WTPs?still used traditional process.For many old WTPs,introducing new technologies and processes not only invest lots of cost,but also bring some problems in management.Moreover,there may be a trouble in field limitation for practical engineering.Therefore,improving and strengthening the traditional water treatment process is currently the most economical and effective means to control the water quality of the water plant,and it is also an important development trend for the treatment of micro-polluted water sources.This topic is based on the previous investigation on the treatment methods of traditional micro-polluted water sources and the actual situation of our country.In order to improve the traditional coagulation process,the transformation method of enhanced coagulation coupling biological denitrification was studied.The main results of this research are as follows:?1?The length of the paddle plate would affect the agitation intensity of the impeller to the water.Meanwhile,it would affect the oxygen-enriched ability of the water.Studies showed a significant correlation between the oxygen carrying capacity and the length of the paddle plate.The length gradient,pitch and angle of the paddle plate would affect the dissolved oxygen concentration gradient in the water.When the length gradient of paddle plate was 4,the ratio of paddle plate length was 5:3:1,the ratio of center distance to pool length was 1:8,and the angle between impeller plate and fixed baffle was 90°,the optimum dissolved oxygen concentration gradient could be formed in the water.When the length of the paddle plate was 10 cm,6 cm,2 cm,the pitch of the impeller plate was 3 cm,and the angle was 90°,the best results could be obtained for this experiment.?2?The velocity and turbulent kinetic energy nephograms of the axial and each cross-section in the square and circular flocculation tanks were characterized,which indicated that the new-type mechanical agitator could form a certain concentration gradient of dissolved oxygen in horizontal and vertical.The square flocculation tank was more conducive to the actual coagulation and biological denitrification reactions than the circular flocculation tank.?3?The feasibility of biological denitrification by using the new-type mechanical agitator in the flocculation tank was verified by the contrast experiment between the traditional mechanical agitator and the new-type mechanical agitator in the artificial simulation of the natural micro-pollution source water.With the removal efficiency of COD,NH₄⁺-N and TN as standards,the effect of pH and C/N ratio on the performance of SND and mechanism were investigated.The results indicated that the best removal efficiency of contaminations in effluent was obtained when the pH was 7.5 and C/N was 5:1.And the effluent COD,NH₄⁺-N and TN removal efficiency were 50.95%,24.67%and 9.42%,respectively.?4?In a certain range of PAC dosage,the effluent COD and NH₄⁺-N removal efficiency were higher than those without PAC,which indicated that PAC had synergistic effects on biodegradability of activated sludge.When the dosage of PAC was 20 mg/L,the effluent turbidity was the lowest and the removal efficiency was90.20%.However,the effluent concentration of COD and NH₄⁺-N began to increase rapidly at this time,which indicated that the dosage of PAC had a certain inhibitory effect on the activated sludge.Therefore,the optimal dosage of PAC was 10 mg/L.?5?When the dosage of PAC was 10 mg/L,with the increase of PAM dosage,the effluent turbidity,COD and NH₄⁺-N removal efficiency showed a tendency of increasing first and then decreasing gradually.The removal efficiency of turbidity,COD and NH₄⁺-N reached the maximum when the dosage of PAM were 1 mg/L,1 mg/L and2 mg/L,respectively.When the dosage of PAM was 0.5 mg/L,the effluent turbidity was 0.87 NTU,less than 1 NTU,which had reached drinking water sanitary standard.Considering the economic benefit and treatment efficiency,the optimal dosage of PAM was 0.5 mg/L.In other words,the PAC:PAM was 20:1.?6?The characterization of Zeta potential and the sludge particle size indicated that PAC could promote the growth of sludge floc.The comparative test reflected the PAC could improve the surface structure of sludge and the increase of the sludge particle size enhanced the adsorption capacity of organic matter and ammonia nitrogen on the surface of sludge.In addition,with the increase of PAC dosage,activated sludge ratio aerobic rate increased first and then decreased which showed the PAC could promote the activity of activated sludge in a certain range of dosage.?7?When the PAC dosage was 10 mg/L and the PAM dosage was 0.5 mg/L,the effluent turbidity,COD,NH₄⁺-N and TN removal efficiency increased first and then decreased gradually with the increase of sludge return ratio.The best removal results could be achieved when the sludge return ratio was 20%.