Effect of filter media and hydraulic retention time on the performance of vertical constructed wetland system treating dairy farm wastewater

Abstract

This study deals with the dairy wastewater treatment using laboratory scale vertical flow (VF) constructed wetlands with the <i>Canna indica</i> plantation over wetland beds due to phytoremediation capabilities. Three laboratory scale VF CWs (CW-A, CW-B and CW-C) each with an area of 0.135 m2 filled with gravel (CW-A: 20 mm; CW-B:10 mm gravel) and sand (CW-C) receiving 0.04 m3 d-1 dairy wastewater were operated for the wastewater purification. Each unit was operated at three hydraulic retention times (HRTs) i.e. 12 h, 24 h and 48 h for assessing its effect on wastewater purification . Among all units, removal rates fluctuated as: total suspended solids (TSS): 64.2–74.5%; biochemical oxygen demand (BOD): 45.3 – 63.1%; ammonium nitrogen (NH4–N): 29.6 – 56.5% and phosphate phosphorous (PO4–P): 20.5 – 57.8% at different HRTs. Increase in HRT showed better removal of pollutants in all CWs. Moreover, maximum removal of pollutants excluding TSS and NH4-N was achieved in CW-B at 48 h HRT. CW-B with similar HRT provided maximum removal of PO4-P (57.8%), BOD (63.1%) and chemical oxygen demand (COD): 67.4%. Increase in the size of filter media, from sand (0.25 mm) to 20 mm gravel resulted in higher removal of NH4 -N from wastewater.