| Subsurface wastewater infiltration system (SWIS) has merits:low cost, underground water distribution, without influencing ground landscape, combining with greening and ecological construction, easy management etc. which is a kind of ecological treatment technology that has broad application prospects.In this paper, based on the comprehensive analysis of previous studies, operational parameters of SWIS which is fit to areas where soils are sandy and the matrix is river sand are optimized. And by improving the system, the impact of raising the water level, taking intermediate distributary, and adding acetic acid on pollutants removal effect is also studied, which aims to solve the problem of bad denitrogenation effect in previous studies.The specific research content and main results of this paper are follows:The study investigated the pollutants removal effect at different hydraulic loading cycle of 48h,24h,12h,6h. It was found that the removal effect is the worst when the cycle is 48h,and removal effect is better when the cycles are 24h,12h; the removal effect of ammonia nitrogen is the best at 12h where the removal rate is 99.19%, the removal rate of TN is the biggest at 6h, but only 21.18% which means bad removal effect, and the influence to TP is not apparent.The study investigated the pollutants removal effect at different hydraulic loading of 8cm/d, 10cm/d,12cm/d.It was found that SWIS has a weaker anti-shock ability about ammonia nitrogen and a strong anti-shock ability about COD within a certain extent, the removal rate of TN first increases and then decreases with the hydraulic loading decreasing, the influence to TP is not apparent.The study investigated the pollutants removal effect at different temperature of 34-10?.It was found that with temperature decreasing, the removal effect of COD appears weak rising trend on the whole, but in temperature range it appears a sudden falling and slowly rising trend with the temperature droping; the removal rate of ammonia nitrogen gradually declines, the removal rate of TN first increases and then decreases,and the maximum is 27.12% at 20?; the influence to TP is not apparent.The study investigated the pollutants removal effect at different outlet location of 60cm,40cm,20cm. It was found that the removal effect of COD is not affected when the outlet is hightened, the removal effect of ammonia nitrogen and TP are the worst when outlet location is hightened 60cm, the denitrogenation effect is the best when outlet location is hightened 40cm, where the average removal rate is 29.02%. By synthesizing every water quality indicators,40cm is the best outlet location.Having Arranged water inlet at the location of 60cm of matrix, the pollutants removal effect at different diffluent ratio of 3:1,4:1 was investigated.It was found that distributary decreases the concentration of nitrate and nitrite nitrogen, but because of COD/N=2:1 in influent, it has a strong impact on the removal of ammonia nitrogen and TP so that the removal rate of TN is not improved. Distributary has bad impact on the removal of pollutants in this experiment.Arranged water inlet at the location of 60cm of matrix, added acetic acid as carbon source, and then investigated the pollutants removal effect at different replenishment of 0.3mL/d,0.5mL/d,0.7mL/d.It was found that adding acetic acid could obviously improve the removal effect of TN, the optimum replenishment is 0.5mL/d, the concentration of TN is 14.00mg/L, and also the influence to COD is not apparent; adding acetic acid has no impact on the removal of ammonia nitrogen and TP. |
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