Performance evaluation of vertical constructed wetland units with hydraulic retention time as a variable operating factor

Abstract

The current research intends to assess the impact of shorter hydraulic retention time (HRTs) and different sized filter material on the pollutant removal performance of two pilot-scale vertical sub-surface flow constructed wetlands (VSSF CW) to treat dairy wastewater. Two CWs (CW-1 & CW-2) were filled with 10 and 20 mm gravels, respectively, planted with Arundo donax, and operated at three different HRTs for treating dairy farm wastewater viz. 6, 12, and 24 h. Over three months, the effluent was tested for TSS, BOD5, TP, and NH4–N removal using standard procedures at regular intervals. Average concentrations of TSS, BOD5, TP, and NH4–N at the final outlets CW-1 and CW-2 were recorded in the range of; TSS: 44.7–118.7 mg L−1, BOD5: 8.1–33.9 mg L−1, TP: 13.7–22.2 mg L−1and NH4–N: 9.1–11.4 mg L−1, respectively. The highest removal of TSS (81.2%), BOD5 (90.2%), TP (65.1%), and NH4–N (82.5%) from wastewater was seen after a 12 h HRT, whereas maximum DO rise (579.0%) was reported after a 6 h HRT in 20 mm gravel-filled CW units. Short HRTs of 6, 12, and 24 h were found to be effective in removing all pollutants from wastewater and maintaining a constant treatment throughout the evaluation period. Results suggest that VSSF CW systems can be operated efficiently under short HRTs while still effectively removing contaminants from dairy wastewater.