Performance of Pilot-scale Constructed Wetlands for Treating Paper Mill Effluent

Abstract

Wastewater discharged from the paper industry generates substantial volumes, ranging between 75 and 225 m³ per ton of product, containing high levels of organic content (COD 480-4450 mg/L), chloride (80-980 mg/L), and a variety of volatile fatty acids (approx. 950 mg/L), cellulose (approx. 1,200 mg/L). The objective of this study was to investigate the efficiency and reaction coefficients of the free water surface flow constructed wetlands (FWS CWs) for removing pollutants such as color, dissolved solids, suspended solids, chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), and nitrogen (TKN). Three pilot-scale units were established, each containing sand as the media and planted with (1) Narrowleaf cattail (Typha angustifolia L.), (2) Loop-root mangrove (Rhizophora mucronata Lam.), and (3) Unplanted control. Upon evaluating the system's performance, it was observed that the FWS CWs effectively reduced contaminants in the factory effluent, particularly color, COD and TKN. The color removal efficiency ranged from 31.15-93.55% (56.86+18.31), 17.86-89.25% (54.30+21.39%), and 27.87-91.40% (58.11+18.84%) for control, cattail, and mangrove unit, respectively. Regarding COD removal, the efficiencies ranged from 31.15-93.55% (56.86+18.31), 17.86-89.25% (54.30+21.39%), and 27.87-91.40% (58.11+18.84%) for control, cattail, and mangrove unit, respectively. Both COD and color removal efficiency presented no statistically significant differences observed among the three units (P > 0.05). The removal efficiency of TKN was 40.00 and 85.74%, 20.00 and 85.71%, and 80.00% and 85.71% for control, cattail, and mangrove unit, respectively. The reaction kinetics of color removal appear to align with both Plug Flow Reactor (PFR) and Continuous Stirred Tank Reactor (CSTR) models. Rate constants for color removal were calculated for the control and mangrove units, as no color removal was observed in the cattail unit. For the mangrove unit, the first-order reaction rate constants were 0.021 d⁻¹ for the PFR model and 0.023 d⁻¹ for the CSTR model, while for the control unit, they were 0.030 d⁻¹ for the PFR model and 0.035 d⁻¹ for the CSTR model. COD reduction can be described by the CSTR model, with first-order reaction rate constants of 0.140 d⁻¹ for the control unit, 0.131 d⁻¹ for the cattail unit, and 0.143 d⁻¹ for the mangrove unit.