Effects of hydraulic retention time and indigenous substrates on the treatment performance of constructed wetlands planted with Cyperus alternifolius for healthcare wastewater remediation

Abstract

Due to persistent contaminants in healthcare wastewater (HWW), conventional treatment technologies are ineffective. Yet few studies utilize local materials, and none have compared pumice versus ignimbrite substrates with Cyperus alternifolius in horizontal subsurface flow constructed wetlands (HSSFCWs). Four pilot-scale systems (2.8 m × 0.8 m × 0.6 m) with volcanic substrates (ignimbrite and pumice), with and without Cyperus alternifolius , were established. The constructed wetland units operated at a loading rate of 0.01125 m 3 /day. Chemical oxygen demand (COD), total suspended solids (TSS), turbidity, nitrate (NO₃⁻), and phosphate (PO₄³⁻) were measured using standard methods at hydraulic retention times (HRTs) of 4, 8, 12, and 24 days. Data were analyzed using two-way ANOVA with Tukey’s post-hoc test (α = 0.05). At a 24-day HRT, the planted pumice bed (W4) achieved promising removal results for COD, TSS, turbidity, NO₃⁻, and PO₄³⁻ 98.6%, 98.3%, 96.2%, 99.8%, and 97.9%, respectively. Whereas the planted ignimbrite (W2) system also performed well: 95.8% for COD, 96.9% for TSS, 91.8% for turbidity, 96.3% for NO₃⁻, and 94.2% for PO₄³⁻. The effects of HRT and wetland type were statistically significant ( p < 0.0001). The comparison between wetland units was also tested using Tukey’s test: W4 statistically enhanced removal compared with W2 ( p < 0.0112) and the unplanted units ( p < 0.05). Overall, the planted pumice bed system provides better removal efficacy. This low-cost, nature-based solution demonstrates significant potential for sustainable HWW treatment in resource-limited settings. We recommend field-scale implementation with 24-day HRT using planted pumice beds, alongside long-term performance monitoring under varying influent loads to optimize design parameters for healthcare facilities.