Seasonal response of vegetation on pollutants removal in constructed wetland system treating dairy wastewater

Abstract

Constructed wetland systems provide the ideal solution for small and medium dairy farms as they can be built close to the farm and are easy to manage and use. However, their perfomance is significantly affected by vegetation activity during the year. The aims of the present study were to assess the treatment of dairy wastewater (DWW) by a horizontal subsurface flow system (HSSFs) and the effect of plants in the removal efficiency (RE) of BOD5, COD, total N (TN) and total P (TP), in Sicily (Italy). The HSSFs treated 6/7 m3 per day of wastewater produced by a small dairy farm subsequent to biological treatment. The system included two units which were separately planted with Arundo donax L. and Cyperus alternifolius L. During a three-year study, the main chemical and microbiological characteristics were determined as well as pollutant RE. Plant growth analysis was carried out and biomass production was determined. All DWW parameters showed significant differences between inlet and outlet. In particular, for BOD5 and COD, average RE values were 77.8% and 61.6%, respectively. Arundo donax produced greater biomass than Cyperus alternifolius for both above- (4240.3 g m2/year) and below-ground (6996.3 g m2/year) plant parts. A seasonal variation in RE of BOD5, COD, TN and TP was recorded due to plant growth rates. Our findings highlight that the contribution of plants in pollutant RE tends to vary seasonally.