Development of a horizontal seepage test system of constructed wetland and research on the seepage characteristics based on micro-pollution water

Abstract

Horizontal subsurface flow constructed wetlands (HSFCW) were widely used as an effective biotechnology for wastewater treatment. However, clogging of the substrate bed was a key factor restricting its application. In this study, a horizontal seepage test system was independently developed, which was used to reveal the development trends of hydraulic resistance in HSFCW, as well as changes in permeability coefficients with time. The relationship between the average permeability coefficient and purification effect was further analyzed. The results showed that the new test system has proved the law of resistance development in HSFCW. The distribution characteristics of the isobaric surface indicate that the blockage of the HSFCW gradually spreads from the lower part to the lower part. The seepage resistance of homogeneous subbed in HSFCW was mainly concentrated in the front end. The growth rate of hydraulic loss in the core zone ranged from 0.685 to 19.515 cm·month−1, the growth rate in the transition zone ranged from 0.223 to 0.695 cm·month−1, and little change occurred in the safety zone. At the end of the HSFCW operation, the widths of the core, transition, and safety zones account for approximately 20–30 %, 50–70 %, and 10–20 % of the entire wetland length, respectively. Meanwhile, the SS removal rate stabilized at over 92 %, when the average permeability coefficient reached 41.45 m·d−1. The removal rate of COD and TN was higher when the average permeability coefficient is between 59.45 and 41.45 m·d−1 and 27.08–59.45 m·d−1, respectively. This study provided a horizontal testing method to accurately understand the changes in the seepage field in HSFCW.