First Two Years of Operation of Subsurface Flow-constructed Wetland System with Methane Fermentation Digestion Effluent Treated by Polymeric Flocculation

Abstract

In this study, we used a subsurface flow-constructed wetland (CW) to improve the energy efficiency and reduce the required processing area of digestion effluent from a methane fermentation system (e.g., a biogas power generation facility) , treated by polymeric flocculation. One of the objectives was to evaluate the water purification efficiency. Our data show that the CW treatment decreases the biological oxygen demand (BOD) more than 99%. The total N was reduced by 61.6% as a result of the CW treatment. However, NO₃-N tended to remain, which seems to be caused by a lack of carbon availability for the additional denitrification in the latter stage of the CW. There nitrification was already advanced, as the C/N ratio in the feedstock was low. Total phosphorus was reduced by 97.7% in CW. Furthermore, the polymeric flocculation treatment reduced the required area by 30% conversion in oxygen transfer rate (OTR) based on BOD and NH₄-N load. Thus, the CW area could be reduced by 40%, as estimated from the survey results of several real-scale CWs. Furthermore, 51% of the generated electrical power remained available.