Abstract: To explore groundwater environmental risk of watererosion sandy soil amended with municipal sewage sludge and further verify the feasibility of municipal sewage sludge as ameliorant to sandy soil, a saturated leaching test in simulated soil columns was carried out based on the improvement effect of sewage centrifugal dewatering sludge on sandy soil. Sewage centrifugal dewatering sludge was mixed with the sandy soil at a portion of 15% (wet weight) to prepare 0-20 cm soil layer. The quality of exudate was analyzed by means of saturated leaching, and its environmental risk to groundwater was assessed with the improved sandy soil as the surface soil. The results showed that nitrogen had a big, persistent risk. The proportion of nitrate nitrogen in total nitrogen was high. TN content was positively correlated with nitrate nitrogen content (r=0.997, P<0.01). Nitrosation happened in deep soil, greatly increasing the risk of nitrite nitrogen pollution of groundwater. Furthermore, the peak value of TP in exudate was 0.18 mg·L^-1, being about 2.6 times the control. The COD content was positively correlated with nitrite nitrogen and TP (r=0.630, P<0.05; r=0.677, P<0.05). The carbon source represented by COD was the main limiting factor affecting the risk of nitrite nitrogen and TP in groundwater; however, sludge hydrolysis and acidification reduced the pH of exudate and increased the exudate COD content, which further increased the risk to the groundwater. The peak value of COD in exudate was 46 mg·L^-1, being about 2.5 times the control. There was a positive correlation between pH and COD (r=-0.760, P<0.01). The risk of heavy metals to groundwater was higher at the end of the experiment, showing a certain delayed effect. The sandy soil improved with 15% proportion of municipal sewage sludge would have a somewhat environmental risk to the groundwater during the oversaturated leaching process. Thus, some certain pollution prevention and control measures should be taken to control the risk.

Key words: sediment, particulate matter, microorganism, diagenetic state., amino acid