Transfer of oxygen in constructed wetlands applied to wastewater treatment

Abstract

Constructed wetlands are part of the decentralized treatment alternatives for wastewater. It is a technology mainly used in rural areas and research in the field is numerous. GESAD is one of the laboratories working on the subject. The raw influent comes directly from the sewerage of the Pantanal neighborhood basin, then it is guided to a septic tank before arriving in the constructed wetlands. During a determined time, the effluent is discharged on the surface of the filter, in the most homogeneous way possible. The fluid is infiltrated, oxygen exchanges are greater and the oxygenation reactions take place. Nitrification is rolled up in the upper part of the filter, while in the lower zone which is saturated, there is denitrification. The effluent leaves the filter and it is at this moment that measurements are made. These measurements make it possible to obtain the masses of oxygen leaving the filter, consumed and therefore entering. Knowing the surface of the filter it is possible to deduce the flow of oxygen and the yield. The measurements were carried out between March and October 2019. This makes it possible to cover a large period of time. VFCW-PS removal efficiency has increased since 2017, with 98.83% DO removed, 88.6% of COD, 83.4% of NH4+ and 57.8% of TN. Initial DO concentrations (8.21 mg.L-1 on average during the first pulse and 7.12 mg.L-1 during the third pulse) indicate that the filter cannot fully recharge during the 90 minute rest. Therefore, oxygen flow is higher during the first pulse because it is fully recharged with oxygen. The average oxygen intake per unit area per day is 36.23 g.m-2.d-1. This result is enthusiastic because it is comparable to VFCW and Hybrid filters.