Performance of a multi-stage hybrid wetland system for the treatment of a dairy effluent

This work evaluates the performance of a pilot-scale hybrid wetland (HW) system for the effluent treatment from a dairy industry, located in Santa Fe (Argentina). The system consists of three stages in a serial configuration: vertical flow (S1) – free water surface (S2) – horizontal subsurface flow (S3) wetlands. The HW was operated during nine months. Wastewater, plant and sediment samples were taken from the system. Main pollutant concentrations were determined in wastewater. N and P concentrations were determined in plant tissues and in sediments to evaluate the accumulation in the system. The mean COD, BOD, TN, and TP removals in the whole HW system were 91 %, 94 %, 76 %, and 64 %, respectively. Organic matter concentration decreased due to aerobic and anaerobic degradation processes in all stages, mainly in S2. S1 presented proper conditions for nitrogen compounds interconversions by ammonification and nitrification processes. The highest total nitrogen removal was achieved in S2. Plant uptake contributed significantly to nutrient retention in S2 and S3. In S2, sediment did not participate significantly in nutrient retention. Phosphorus removal showed the lowest system efficiency. The obtained results determine the system performance under site-specific conditions, which contributes to the scaling process of the treatment wetland. •The final quality of a dairy effluent was improved using a multi-stage HW system.•VF stage enhanced the biodegradability of refractory compounds.•FWS and HSSF stage were the main contributors for TN removal.•Plant uptake was a key process for nutrient removal from wastewater.•The obtained results are useful for scaling the HW under site-specific conditions.