Modified First Stage of French Vertical Flow Constructed Wetlands performance during extreme operation conditions

Abstract

This study applied two Modified First Stage of French Vertical Flow Constructed Wetlands pilots for the treatment of sewage coming from a combined sewer system under extreme hydraulic loads and medium temperatures at high altitude. Particularly, the pilot-scale experiment was conducted within nine months after their start-up period of four months. During this period, two different high hydraulic loading rates (0.94 m d-1 and 0.56 m d-1) representing 2.5 and 1.5 times the design values respectively, were applied to investigate the impact of HLRs on the performance of the treatment system. The observed performances for COD and TSS removals were satisfactory, with average values of 53% and 66% respectively. Moreover, reducing the HLR resulted in higher removal efficiency for COD (from 46% to 64%) but not for TSS (from 67% to 64%). From these findings, it is suggested that high HLRs can be applied for the First Stage of the French System without compromising the operation of the units and obtaining satisfactory results, especially in case of diluted wastewater and severe area restrictions.