Feeding mode influence on treatment performance of unsaturated and partially saturated vertical flow constructed wetland

Abstract

This study aimed to evaluate the influence of two different feeding modes on wastewater treatment performance and oxygen consumption rate (OCR) of the unsaturated (UVF wetland) and partially saturated (SVF wetland) vertical flow constructed wetlands operated in parallel under subtropical climate for four years. Each wetland had a superficial area of 7.5 m2 and was planted with Typha domingensis. Both units have a filter media depth of 0.75 m, composed by sand (effective diameter of 0.29 mm and uniformity of 4). UVF wetland operated typically unsaturated, while SVF wetland had the bottom part saturated (57% of total depth). Two feeding modes were evaluated for both wetlands. The feeding mode was operated within the limits recommended by the German standard, with a hydraulic loading rate (HLR) of 75 mm d−1 and specific pulse volume (SPV) of 19 L m−2 for both wetlands and a specific hydraulic loading rate (SHLR) of 8 and 9 L m−2 min−1 for UVF and SVF wetlands, respectively. Meanwhile, the second feeding mode was applied for both wetlands, being an HLR of 103 mm d−1, 26 L m−2 of SPV, and 4 L m−2 min−1 of SHLR. The load removal efficiency of SVF wetland was higher than the UVF wetland for all parameters and feeding modes. No statistical difference was identified for OCR values between wetlands and feeding mode. The results showed that operating UVF and SVF wetlands with a SHLR around 4 L m−2 min−1 and SPV equal of 26 L m−2 is preferable. This fact could represent a significant reduction in inlet pumping power requirements and also less superficial area requirements.