Removal Of Agricultural Surface Runoff Pollution By New Biomass Concentration Reactor (BCR) With Internal Circulation Anaerobic And Ultrasound

Agricultural non-point source pollution has become the biggest problem in non-point source pollution in China.According to the data of Ministry of Agriculture and Rural Affairs of the People’s Republic of China（2018）,agricultural non-point source pollution accounts for 51.2%of all non-point source pollution.As one of the main pollution forms in agricultural non-point source pollution,surface runoff has the characteristics of wide distribution,difficult treatment and scattered dispersion.Most agricultural runoff research has focused on the management of fertilizer application,and the development of end technology is far from enough.Therefore,it is urgent and necessary to probe new technologies for agricultural non-point source pollution treatment.In this study,three designed bioreactors including internal circulation（IC）reactor,anoxic packed bed（combined with ultrasound and polybutylene succinate（PBS））and improved biomass concentration reactor（BCR,combined with ultrasound and suspended filler）,are used to treat agricultural surface runoff independently and connectly.The main conclusions are as follows:（1）At normal temperature,the simulated wastewater of agricultural surface runoff was directly fed into the three reactors to investigate the startup of the bioreactor on condition that the carbon to nitrogen ratio is less 5.0.Startup time of designed IC reactor was 20 days.Startup time of anoxic packed bed which using polybutylene succinate（PBS）as a solid phase carbon source for semi-packing,was 14 days.Startup time of improved BCR was 13 days which the biofilm occurred,when the suspending fillers changed from light yellow to yellow-brown and the bacterial micelles appeared in the BCR.The effluent COD was regressed to whether fit to reaction kinetics equation.COD of IC reactor and the improved BCR in startup period were well fitted to the first-order kinetics.While the correlation coefficient of COD at anoxic packed bed was low and was not agree the traditional kinetic equation.The effluent nitrate nitrogen of improved BCR was regressed to fit the Monod Equation for degradation kinetic model.（2）The membrane influence of modified BCR at steady operation state was determined and it was found that there was little effect on effluent NO₃-N,except that all removal rates of effluent COD,NH₄⁺-N,TN and TP were improved with the average increase by 7.40%,2.50%,1.01%and 11.45%,respectively.Based on the reaction kinetic equation,the effluent COD of the BCR at steady operation state was fitted to the first-order kinetics.Moreover,the effluent nitrate nitrogen of improved BCR was regressed to meet the degradation kinetic model of the Monod Equation.（3）By directly combining the anoxic packed bed and the improved BCR with the ultrasonic device under the conditions of no ultrasonic,20 KHz,28 KHz and 40 KHz,actual impact on simulated agricultural surface runoff wastewater were explored.It is found that the ultrasonic frequency of the optimal degradation efficiency of the anoxic packed bed was28KHz,but the optimal condition for the improved BCR was no ultrasonic.The highest correlation between ultrasonic frenquency and parameters on effluent water quality was DO,p H,and NH₄⁺-N for the anoxic packed bed,with the great significant correlation.Because of the obvious negative correlation effect on DO and p H,the degradation of NH₄⁺-N was weakened.The ultrasonic frequency has a positive correlation with nitrogen and phosphorus in the effluent of the improved BCR,which it is significant,especially for the inhibition of NO₃^--N.Moreover,the correlation analysis also shows that the BCR film can increase the effect of ultrasound on the quality of effluent water under ultrasound,by icreased correlation coeffeient of 0.2.On the condition of 20 KHz,28 KHz and 40 KHz,the effluent concentrations of nitrate nitrogen and total phosphorus in modified BCR were regressed to fit the Monod Equation of degradation kinetic model.（4）The simulated agricultural surface runoff wastewater was treated by respectively combining treatment processes of IC reactor,anoxic packed bed under 28 KHz ultrasound,and improved BCR without ultrasound.The average removal rate of COD,NH₄⁺-N,NO₃^--N,TN,and TP in the IC reactor was 90.94%,-25.65%,97.43%,56.36%,and-15.86%,respectively.The average removal rate of COD,NH⁺₄-N,NO₃^--N,TN,and TP in the anoxic packed bed was 89.52%,21.97%,99.09%,74.41%and 14.80%,respectively.The average removal rate of COD,NH₄⁺-N,NO₃^--N,TN,and TP in the effluent of the BCR was 99.22%,82.27%,77.25%,77.23%and 28.98%,respectively.The effluent concentrations of nitrate nitrogen and total phosphorus in improved BCR were regressed to fit the Monod Equation of degradation kinetic model.In this study,the completed treatment process（IC reactor+anoxic packed bed+improved BCR）for simulated agricultural surface runoff has not only high efficient processing capacity using less land area,but also a strong adaptability to the characteristics of agricultural surface runoff.It conclude that the results in this study can be adapted to small-scale distributed processing for agricultural surface runoff according to local agricultural conditions.Therefore,if the completed treatment process is integrated and improved,it can be used and transformed to engineering application according to the requirement in different regions.