Wastewater Treatment in a Sub-Surface Flow Constructed Wetland: Nutrient Removal Analysis

Abstract

Constructed Wetlands (CWs) treating the wastewater and minimizing the environmental degradation is a very economical and eco-friendly technique. In order to understand the treatment efficiency of these engineered systems, a six month study (December 2014-May 2015) was carried out. The objective of this investigation was to evaluate the removal efficiency of contaminants from municipal wastewater by two main phytoremediation plants i.e. Lammncea and Typha lattifolia. Targeted wetland was located in NUST (National University of Science and Technology) Sector H-12 Islamabad Pakistan, having the capacity for receiving municipal wastewater from a population of 6000, generating 0.2 MGD wastewater. The water quality parameters were studied at four units pilot scale unit, lab scale unit, parallel unit and control unit. The evaluated parameters were; Chemical oxygen demand (COD), Total suspended solids (TSS), Total dissolved solids (TDS), Electric conductivity (EC), pH, Total phosphates (TP), Dissolved oxygen (DO), Temperature, Total coliforms, Fecal Coliform and nutrients (ammonia, nitrate and orthophosphate). Control unit running as reference showed no removal efficiency which strengthened the fact that plants were responsible for treatment of waste water. In all the cases parallel unit, comparatively showed the maximum removal efficiency due to more retention of wastewater. For both the plants typha and duckweed most significant removal efficiencies were recorded as, TSS (63 and 72%), DO (46 and 49%), TDS (40.61 and 34.9%), COD (69 and 62%), TP (64 and 81%), fecal coliform (97 and 98%) and total coliforms (98 and 97%). Removal percentage for nutrient parameters (ammonia, orthophosphate, and nitrate) were higher at lab scale than that of pilot scale because of controlled lab conditions. Results generated for six months studies depicts that seasonal fluctuation played a major role in contaminant removal , it was high in summers due to improved plant growth.