Determination of the mean hydraulic retention time at the constructed horizontal flow wetlands using a chemical tracer

Constructed wetland usually has two phases as liquid and solid. Mean hydraulic retention time MHRT is suppose delaying by the solid phase. Aim of this study was to know the flow pattern and phases contribution at the hydraulic efficiency using tracer technique as LiC1 for two constructed horizontal wetland superficial flow CHWSF at pilot scale. Walls were made with concrete and the bed was settled up with gravel and sand. Tracer was injected as impulse signal at the same time in both wetlands 1 and 2. Methodology was figured out recollecting samples at the effluent for a time series and then it were analized at the lab with an atomic absorption spectrometer. Sampling was done for three studies. 1. CHWSF vegetation less. 2. CHWSF submerges influent and 3. CHWSF vegetation growths. The results showed that MHRT values were nearly and similar for all studies such 2,70-1,38-1,33h and 2,84-0,98-1,09h for the wetland 1 and 2, respectively. Tracer recovery mass was varying in a range from 90 to 55% in both. Dispersion number (d) was varying a range between 0,42 to 0,30 for wetland 1, and 0,38 to 0,20 to wetland 2, flow pattern found was pointed out to a dispersed flow to all cases less vegetation growths. Vegetation was promoting either more axial dispersion or less hydraulic efficiency.