Effect Of Sludge Biochar On Nitrogen And Phosphorus In Bioretention And Its Mechanism Analysis

Urban rainwater is the main cause of urban waterlogging and water pollution.As one of the important measures of low impact development and urban rain flood management,biological detention pool plays a good role in urban rain water treatment and control.At present,a great deal of research has been done on the bioretention,which has a better and more stable removal effect on the total suspended matter,heavy metal,oil and pathogenic bacteria in water,while the removal effect of nitrogen,phosphorus and other nutrients is relatively unstable.Biochar,as a widely used adsorbent,acts on many pollutants good adsorption collection.This paper explores the adsorption performance between the modified filler soil added with sludge biochar and standard filler soil.Placing the two fillers in the biological retention tank to operate to explore the impact of the height of the submerged area,the concentration of pollutants,and the cycle of alternating dry and wet operation on the device.A simple characterization analysis of sludge selection,pyrolysis temperature,pyrolysis time and biochar was carried out on sludge bi ochar leaching.Finally,the optimization of the packing structure was carried out,and the nitrogen and phosphorus treatment performance of the biological retention tank after the optimized structure was explored.Studies have shown that the modified packing with 4%(w/w)addition has a certain effect on the adsorption of ammonia nitrogen and phosphate under static adsorption conditions,and the changes between fillers and ions in water are not significantly.The application of sludge biochar to biological detention tanks requires exploring its optimal pyrolysis conditions.The naturally air-dried sludge was pyrolyzed at 500? for 3h prepared sludge biochar with the largest specific surface area and the least nitrogen and phosphorus released after leaching.The setting of the submerged area is of great significance for the removal of nitrate ions from the bioretention.The maximum difference of nitrate removal rate before and after setting is about 20%.However,the setting of submerged areas has a negative effect on the removal of phosphate.The setting of the height of the submerged area has a certain influence on the removal of ammonia nitrogen by the improved filling soil.The single modified filler soil can only improve the removal of nitrate in rainwater by 4.35%~18.78%,which is somewhat lower than the standard filler soil in the removal of ammonia nitrogen and phosphate.In addition,the modified filler soil will release other properties of P during rainfall,affecting its effluent quality.Alternating dry and wet operation has a greater impact on the removal of ammonia nitrogen and phosphate by the modified filler soil.After a long-term drought,the removal rate drops to about 60%,and it takes a longer period of humidification to restore its operating effect.Applying sludge biochar to the upper half of the bioretention tank filler,the removal of ammonia nitrogen,nitrate nitrogen and phosphate can reach 88.62% ~ 97.52%,83.18% ~ 89.83%,97.85% ~ 99.16% respectively at the height of 300 mm submerged area.Reasonable setting of the addition of sludge biochar can improve the removal effect of traditional biological retention tanks on nitrate and ammonia nitrogen,and at the same time provide new ideas for the sludge resource utilization.