Nitrate removal in vertical flow constructed wetland planted with Vetiveria zizanioides: Effect of hydraulic load.

Abstract

tA vertical flow constructed wetland (VFCW) planted with Vetiveria zizanioides (0.24 m2× 0.70 m) intendedto receive a synthetic wastewater with high nitrate concentration was used to study the influence ofthe hydraulic load (HL) increase on nitrate load removal, keeping a low carbon nitrogen ratio (C/N).The inlet nitrate concentration was kept constant ([NO3−] = 83 ± 7 mg L−1) and four different levels of HLwere used, from 148 ± 5 to 473 ± 5 L m−2d−1; accordingly, nitrate load increased from 12.4 ± 0.7 g m−2d−1to 39.9 ± 0.7 g m−2d−1. The nitrate load removal occurred in all trials, increasing proportionally to HLand nitrate load applied, reaching a maximum value of 11.9 ± 0.7 g m−2d−1at a nitrate load appliedof 20.4 ± 1.2 g m−2d−1and HLof 239 ± 7 L m−2d−1. Beyond that maximum, a further increase in HLornitrate load applied led to a considerable decrease in nitrate load removal. Anaerobic conditions werenot detected and denitrification was observed even at 5.2 ± 1.2 mg L−1O2in influent. Toxicity signs inVetiveria zizanioides leaves were never detected and the results obtained suggest that the used plantabsorbs and assimilates nitrogen from wastewater. Although Vetiveria zizanioides is not commonly usedin constructed wetland, it proved to be very a robust, efficient and promoting system, encouraging furtherstudies.