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

•VFCW planted with Vetiveria zizanioides was used for nitrate removal.•Nitrate removal occurred with DO at 5.2 ± 1.2 mg O2 L−1 in influent.•Nitrate load removal under various HL and hydraulic retention times.•Effect of nitrate load applied on nitrate load removal was observed.

A vertical flow constructed wetland (VFCW) planted with Vetiveria zizanioides (0.24 m2 × 0.70 m) intended to receive a synthetic wastewater with high nitrate concentration was used to study the influence of the 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 HL were used, from 148 ± 5 to 473 ± 5 L m−2 d−1; accordingly, nitrate load increased from 12.4 ± 0.7 g m−2 d−1 to 39.9 ± 0.7 g m−2 d−1. The nitrate load removal occurred in all trials, increasing proportionally to HL and nitrate load applied, reaching a maximum value of 11.9 ± 0.7 g m−2 d−1 at a nitrate load applied of 20.4 ± 1.2 g m−2 d−1 and HL of 239 ± 7 L m−2 d−1. Beyond that maximum, a further increase in HL or nitrate load applied led to a considerable decrease in nitrate load removal. Anaerobic conditions were not detected and denitrification was observed even at 5.2 ± 1.2 mg L−1 O2 in influent. Toxicity signs in Vetiveria zizanioides leaves were never detected and the results obtained suggest that the used plant absorbs and assimilates nitrogen from wastewater. Although Vetiveria zizanioides is not commonly used in constructed wetland, it proved to be very a robust, efficient and promoting system, encouraging further studies.

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