Performance efficiency and water quality index of a two-stage horizontal subsurface flow constructed wetland system polishing anaerobically treated brewery effluent

The disposal of untreated or partially treated brewery wastewater can cause pollution problems to the receiving water bodies. The objective of this study was to evaluate the effectiveness of a two-stage horizontal subsurface flow constructed wetland (HSSFCW) system planted with Cyperus alternifolius and Typha latifolia in polishing an up-flow anaerobic sludge blanket (UASB) reactor treating brewery effluent in Kombolcha, Northern Ethiopia. The system was integrated with the UASB reactor, and its performance efficiency was monitored for a year using standard methods. The first-order kinetic model was used to correlate the influent and effluent pollutant concentrations and estimate the areal rate constant (kA) by fitting the experimental data to the model. The HSSFCW's water quality index (WQI) and oxygen transfer rate (OTR) were also calculated. The findings showed that HSSFCW removed 89% total suspended solids (TSS), 92% chemical oxygen demand (COD), 83.6% total nitrogen (TN), 92.9% ammonium – nitrogen (NH4+ − N), 74.4% total phosphorous (TP), and 79.5% orthophosphate (PO43−). Literature comparable OTR values were obtained for each HSSFCW stage with a total OTR value of 23.5 g−2d−1. Effluent concentrations of COD, TN and NH4+ − N were reasonably correlated (R2 ≥ 0.85) to influent concentrations. The calculated kA (md-1) for TSS, COD, TN, NH4+ − N, TP, and PO43− were 0.26, 0.26, 0.11, 0.18, 0.08, and 0.08, respectively. Further polishing of the effluent with two-stage HSSFCW has shifted the WQI from a good to excellent water quality rating and thus, can be used as a sustainable polishing technique for agro-process wastewaters.