Effects of hydraulic retention time (Hrt) and packing height on the performance of homemade ceramsite-soil constructed wetland for rural domestic wastewater treatment

Abstract

In this study, homemade ceramsite-soil filler (system A) and a simple soil filler (system B) were applied in vertical upflow constructed wetlands, and their performance in the treatment of rural domestic wastewater were investigated under various HRTs and packing heights. Optimum performance was reached at a HRT of 6.4 d in both systems. The average removal rates of ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) in system A were as high as 90.78, 86.04, and 90.15%, respectively, which were 0.94, 2.21, and 10.62% higher than those in system B. The TN and NH4+-N removal efficiencies of both systems decreased with shorter HRTs, whereas the TP removal efficiency was almost not affected. Along the inlet direction, with increasing packing height, the pollutant removal capacity gradually decreased, and the NH4+-N removal efficiencies in the bottom layers (0-145 mm) of system A and B were 55.88 and 50.22%, respectively, with NH4+-N volumetric loads of 8.63 and 7.76 g/(m3·d). System A contained more nitrifying genera at the genus level, mainly including Stenotrophomonas, Sphingomonas, and Acinetobacter. The addition of ceramsite resulted in a higher treatment efficiency and resistance to hydraulic shock loading.