Sustainable wastewater treatment using a new combined hybrid digester – Constructed wetland system

Abstract

Constructed wetlands are one of the most promising decentralised wastewater treatment technologies for single-family homes, rural or peri-urban areas as well as for low-income areas. The present work reports for the first time the combination of a new hybrid anaerobic/anoxic digester (HD) as pre-treatment for a vertical subsurface constructed wetland (VF). Part of the nitrified VF effluent was recirculated to the HD to favour the simultaneous removal of organic matter and nitrogen, intensifying both the HD denitrification and VF nitrification processes. The results indicate that HD was the main responsible for the removal of suspended solids and organic matter, which was completed in the VF up to values always below the discharge limits. Nitrate removal ranged from 64 % to 94 % and ammonium removal from 64 % to 89 %, the former occurring mainly in the HD and the latter in the VF. The combined HD-VF system achieved high overall removal efficiency, reaching 98 % TSS, 94 % COD, 97 % BOD5, 86 % NH4+-N and 43 % TIN on average. Methane emissions were lower than those reported in the literature for CWs. The VF showed no signs of clogging. The system was operated in a sustained manner during a continuous period of 266 days with an average overall surface loading rate of 43.6 g BOD5 m−2 d−1 (range of 29–83 g BOD5 m−2 d−1). The total surface area required was 1.4 m2·equivalent inhabitant−1.