Humidais construídos para a depuración de augas residuais urbanaseliminación de nitróxeno, ensaios biolóxicos e respirometría en diferentes configuracións híbridas

Résumé

Nowadays there are still numerous lacks in the understanding of the mechanisms of depuration as in the methods of design of the constructed wetlands (CWs), especially in relation to the application of hybrid systems. The goal of the present research is to contribute to a better knowledge of treatment CWs, through the following specific goals: a) the development of laboratory methodologies aimed at describing the processes and obtaining kinetic and stoichiometric parameters, b) obtaining these kinetic and stoichiometric parameters for a synthetic substrate simulating domestic wastewater; and c) the advance in the conception and design of hybrid CW systems. Aerobic, anoxic and anaerobic essays, as well as respirometric techniques were developed and applied in order to characterize these systems. CWs were simulated at lab scale through down flow columns that allow reproducing the real conditions, both of hydraulic saturation and non-saturation, of hybrid systems constituted by several units in series. In addition, attention was paid to parameters related with medium clogging and greenhouse gas emissions. Hybrid CWs including subsurface horizontal flow (HF) and vertical flow (VF) steps look for effective nitrification and denitrification through the combination of anaerobic/anoxic and aerobic conditions. Several CW configurations including single pass systems (HF+HF, VF+VF), the Bp(VF+HF) arrangement (with feeding by-pass) and the R(HF+VF) system (with effluent recirculation) were tested. The percentage removal of TSS, COD and BOD5 was usually higher than 95% in all systems. The single pass systems showed TN removal below the threshold of 50% and low removal rates (0.6-1.2 g TN/m2·d), except the VF+VF system which reached 63% and 3.5 g TN/m2·d removal but only at high loading rates. Bp(VF+HF) system required by-pass ratios of 40-50% and increased TN removal rates to approximately 50-60% in a sustainable manner. Effluent recirculation significantly improved the TN removal efficiency and rate. The R(HF+VF) system showed stable TN removals of approximately 80% at loading rates ranging from 2 to 8 g TN/m2·d.