Effect of pollutant loading rate and macrophyte uptake on the performance of a pilot-scale hybrid wetland system for the final treatment of dairy wastewater

Abstract

Commonly, conventional treatment methods may not be sufficient for dairy wastewater treatment. This could be improved by applying a hybrid wetland (HW) system. The aim of this work was to evaluate the effect of different inlet loading rates on organic matter and nutrient removal efficiency from dairy wastewater treated by a pilot- scale HW system under real conditions. The HW system was composed of vertical subsurface flow (VF) and horizontal subsurface flow (HSSF) wetlands. Two different surface loading rates (SLRs) were applied to the HW system. Low SLR (COD 87.6 g m 2 d 1) and high SLR (COD 130.5 g m 2 d 1) were used in order to evaluate the effect of inlet load on pollutant removal efficiency in terms of the SLR and surface removal rate (SRR). For bothSLRs, wastewater samples were taken at the inlet and outlet of each stage of the HW system. Besides, plant samples were taken at the beginning and the end of each feeding strategy from each wetland to assess nutrient accumulation in different plant tissues. In general, for all pollutants an increase in SRR was observed as the SLR increased. The highest SRR values reached for VF/HSSF were: 45.04/20.15, 2.75/0.22, 1.83/0.72 and 1.11/0.04 g m 2 d 1 for COD, NH4 +-N, Org-N and SRP, respectively. Nutrient concentrations showed a significant increase in plant tissues. Both the VF and the HSSF stages play a fundamental role in the HW system. In addition to organic matter degradation, ammonification, and nitrification-denitrification processes, plant uptake could be an important mechanism to remove pollutants from wastewater. Further research focused on the management and operation of wetlands will be carried out to improve these results.