Experimental Research On Biochar Strengthening UASB-Constructed Wetland Dispersion Treatment Of Rural Domestic Sewage

In this thesis,the collection and treatment of rural domestic sewage is difficult,the centralized treatment rate is low,and the single treatment technology has the problems of blocked treatment facilities and unstable pollutant removal rate.By using Up-flow anaerobic sludge blanket（UASB）as the pretreatment unit of constructed wetland,the UASB-constructed wetland combined process was formed,and its treatment effect on rural domestic sewage was studied.The main research contents of this paper include the construction of three groups of UASB reactors（R0,R1,R2）with different biochar addition,in which reactor R0 does not add biochar,R1 adds biochar at 10 g/L,and R2 adds biochar at 20 g/L,to explore the strengthening effect of biochar on the start-up and operation process performance of UASB reactors,and to explore the influence of environmental conditions on the treatment effect of UASB reactors by changing the hydraulic retention time of influent,influent C/N and environmental temperature.At the same time,through the construction of"UASB-constructed wetland"combined device,the treatment effect of laboratory scale and pilot test combined device on actual rural domestic sewage was studied respectively.The main results of the study are as follows:（1）Adding biochar can shorten the sludge granulation time.At the initial stage of start-up of reactors R1 and R2（influent COD concentration is 300 mg/L）,mature particles with a diameter of 2 mm were formed,accounting for 1.22%and 3.04%respectively,while R0 was not formed in the control group.Meanwhile,the removal rates of NH₄⁺-N in reactors R0,R1 and R2 are 66.38%,69.34%and 73.53%respectively.In addition,the standard deviation of COD and NH₄⁺-N concentration in the effluent of the reactor is R2≈R1>R0.Therefore,with the increase of biochar addition,the sludge granulation time is advanced,and the removal effect of COD and NH₄⁺-N is stable.（2）The mixture of biochar and anaerobic sludge can enhance the adsorption performance and mechanization strength of mature particles.In the stable operation stage,the proportion of mature sludge in reactors R1 and R2 is 6.41%and 24.28%higher than that in control group R0,respectively.At the same time,with the increase of influent COD concentration,the COD removal rate of reactor R2 is close to 90%,which is higher than that of control group R0 and reactor R1.When the influent NH₄⁺-N concentration was increased to 26.47±1.7 mg/L,the removal rate of NH₄⁺-N in reactor R2 reached 60.81%,while that in control group R0 was only 56.49%.Under the conditions of low C/N ratio and different temperatures（15℃,25℃,35℃and 45℃）,the removal rate of COD and NH₄⁺-N in reactor R2 is higher.Therefore,during the stable operation,the addition of biochar is beneficial to the stable operation of the reactor,which makes the reactor sludge more granular.At the same time,biochar as a carrier can strengthen the anaerobic ammonia oxidation performance,and the reactor R2 with the addition of biochar of 20g/L has better removal effect on COD and NH₄⁺-N.（3）The average concentration of COD and NH₄⁺-N in the effluent of laboratory scale test is 76.75±9.06 mg/L（100mg/L;80 mg/L secondary standard）,0.16±0.12 mg/L（5mg/L;8 mg/L first-class standard）.The average concentrations of COD,NH₄⁺-N,TP and TN in the effluent of pilot test were 59.29 mg/L（60 mg/L first-class standard）and 0.17mg/L（5 mg/L;8 mg/L first-class standard）,0.45 mg/L（1.0 mg/L;1.5 mg/L first-class standard）and 11.92 mg/L（20 mg/L first-class standard）.Therefore,the concentrations of COD,NH₄⁺-N in laboratory scale and COD,NH₄⁺-N,TP,TN in the effluent of pilot-scale test combination device can reach the standards of Discharge Standard of Pollutants for Urban Sewage Treatment Plants（GB18918-2002）and Discharge Standard of Water Pollutants for Rural Domestic Sewage Treatment Facilities（DB51/2626-2019）.