Evaluation of phytoremediation potential of <i>Canna indica</i> and <i>Ageratum conyzoides</i> in field-scale hybrid wetlands treating greywater

Constructed wetlands (CWs) offer an eco-friendly wastewater treatment technology which can provide a low-cost alternative to "raw wastewater discharge" which although is increasingly becoming unsustainable, remains the most common practice for urban housing colonies in India. This study demonstrates that despite being a semi-engineered system CWs can provide consistent removal efficiency while treating "grey water", which constitutes the major fraction of the total wastewater generated in an urban housing colony. The lack of field-scale performance data for CWs has kept builders, practicing engineers, and policy makers thus far unconvinced about their true potential beyond scientific publications. The work presented here provides comparative assessment of phytoremediation potential of two macrophytes <i>Canna indica</i> and <i>Ageratum conyzoides</i> while treating grey water emanating from a nearby urban housing colony. How the relative positioning of these macrophytes, upstream or downstream of each other, can influence the wastewater treatment efficiency was also evaluated. Higher removal efficiencies were observed for inorganic nitrogen (43.4%) and phosphate (45.68%) for CWs vegetated with <i>Canna indica</i> while higher sulfate removal efficiency (63.5%) was observed for CWs vegetated with <i>Ageratum conyzoides</i>. For chemical oxygen demand (COD) and total suspended solids (TSSs), removal efficiencies remained consistently above 65% and 80%, respectively.