Effects of riverbed and lake bottom sediment thickness on infiltration and purification of reclaimed water

摘要

Municipal wastewater reuse has been an important way to enhance water pollution control and water conservation in China. However, many pollutants, such as N, P, chemical oxygen demand (CODCr), and 5-day biochemical oxygen demand (BOD5), are contained in the reclaimed water that can pollute the groundwater environment around rivers and lakes supplied with reclaimed water. Therefore, an environmentally friendly method to control infiltration and purification is quite necessary. Original sediment is one potential option. Therefore, in this study, the effects of sediment thickness at 5, 10, and 20 cm were studied for water infiltration and purification processes in riverbed media. The results indicate that the infiltration efficiency of the riverbed media was reduced when the sediment formed gradually and reached an appreciable level. The thickness was kept at 5-20 cm, and the ranges of the removal efficiencies for BOD5, CODCr, ammonium-nitrogen, nitrate-nitrogen, total nitrogen, and total phosphorus were 47.7-69.0, 49.9-62.7, 90.6-92.5, 30.5-45.8, 42.7-63.1, and 62.2-77.9%, respectively, by a sediment and soil pillar of riverbed media. The removal efficiencies increased by increasing the sediment thickness, and the final infiltration rates were over 10(-4) cm/s. The riverbed infiltration remained steady even when thickness was beyond 20 cm, and the purification effect was obvious. The ammonium-nitrogen removal efficiency of the riverbed filtration system did not appear to have an unlimited increase with the increase in sediment thickness. Generally, the existence of a nitrification and denitrification interface was located in the sedimentary layer, and it remained anaerobic at the bottom over a 10-cm thickness. Because ammonium-nitrogen was involved in nitrification, the nitrate-nitrogen concentration of the percolate tended to increase at the beginning of experiments. As the adsorption and nitrification took place, over 90% of ammonium-nitrogen was removed in the riverbed infiltration system through attachment to sediments. The experimental results could be used as references in river regulation.