Design of a Combined Constructed Wetland System and Its Application on Swine Wastewater Treatment

Abstract

To treat heavy-loaded wastewater from small-scale livestock farms, a combined constructed wetland system was designed, which includes series of hybrid constructed wetlands made up of surface flow (SF) and subsurface flow (SSF) compartments, as well as two anaerobic units, also in series, as its pretreatment. The combination of multitype and multistage treatment units and the division of the wetland area into compartments in a horizontal baffled layout prolongs the hydraulic retention time (HRT), reduces clogging and short-circulating, and keeps specific operation conditions for each unit, including loading input, bacteria, padding material, and vegetation. The system demonstrates various benefits, such as efficiency, simplicity, flexibility, low cost, and easy management, which were demonstrated by a pilot system for the treatment of wastewater from a small-scale pig farm. The first running result showed excellent removal efficiency and removal rate for organic materials in terms of chemical oxygen demand (CODcr) and biological oxygen demand (BOD5), nutrients in terms of total nitrogen (TN), ammonia nitrogen (NH3-N), and total phosphorus (TP), and heavy metals in terms of Cu and Zn. The effluent met relative standards for all aforementioned indicators except for TP. Heavy input load and limited plant uptake could be the main reasons for the failing to meet the standard for TP. Solutions to this issue include adding one or more SF compartments before and after the SSF units, using special padding material economical in cost and with strong sorption capacity, and replacing the padding material regularly.