Comparative Study on the Performances of Modified Vertical Flow–Constructed Wetlands for the Treatment of Domestic Wastewater

The present case study evaluates the treatment efficiency (R%) of vertical flow constructed wetlands (VFCW) with different design considerations for the efficient treatment of domestic wastewater. Four modified VFCW’s were constructed at the pilot scale to study their overall performance with domestic wastewater as the source. Since traditional VFCWs are responsible for increases in nitrates, this study also focuses on the removal of nitrates. These different VFCW’s were termed two stage (TS), two stage-charcoal (TSC), mixed flow (MF), and double stage (DS) VFCWs. The inlet chemical oxygen demand (COD), ${\mathrm{NH}}_3\text{-}\mathrm{N}$, ${\mathrm{NO}}_3\text{-}\mathrm{N}$, ${\mathrm{NO}}_2\text{-}\mathrm{N}$, TN, total organic carbon (TOC), and ortho-P ranged from 300–900, 30–50, 25–50, 30–40, 15–50, 30–120 and $10–15\mathrm{mg}/\mathrm{L}$, respectively, with a pH around 7 and high total coliforms (T-C). The MFCW and DS-VFCW were found to be the most effective in treating almost all the parameters with the highest R% ($>90$). The TS-VFCW showed better treatment of carbon rather than nitrogen compounds (like ${\mathrm{NO}}_3\text{-}\mathrm{N}$). The TSC-VFCW showed better treatment when the system was new, as decreases in R% were observed over time. Statistical analysis with one and paired-sample T-tests were conducted to support similar findings with significance values $<0.05$. The findings from both tests showed that DS-VFCW was the better system compared to the other two for COD, TOC, ${\mathrm{NO}}_2\text{-}\mathrm{N}$, and ortho-P showing $\mathrm{p}=0.000$; whereas, MFCW was the better system to treat pollutants like TN and ${\mathrm{NO}}_3\text{-}\mathrm{N}$. The MFCW and DS-VFCW were both shown to effectively treat ${\mathrm{NH}}_3\text{-}\mathrm{N}$ and T-C.