Wetland não-plantada de fluxo vertical com leito de areia e conchas de ostra como pós-tratamento de efluentes para remoção de fósforo

Abstract

The vertical flow constructed wetlands have become a common wastewater treatment choice in the last years, and the filter material’s composition is primordial when considering depuration efficiency. Among several materials that have been studied, oyster shells have great potential for phosphorus removal. This study aimed to evaluate the potential of phosphorus removal of unplanted vertical flow wetlands with oyster shell and sand as filter media. The adsorption capacity of sand samples containing different percentages of oyster were determined by adsorption tests using 50 mg P/L standard solution and applying the results in the Langmuir’s isotherm. The capacities obtained for 0%, 25% and 50% of oyster shells were respectively 91.74, 185.18 and 357.14 mg P/kg. The material containing 50% mass of oyster shells was evaluated in adsorption tests using effluent belonging to ETE Atuba Sul, the adsorptive capacity obtained was equal to 134 mg P/kg. Two vertical flow wetlands with filter media consisting of 50% of oyster shell and 50% sand as filter media were assessed. The columns C2 and C4 were subjected to three cycles of batch application with 6.5 L load of effluent from the ETE in each cycle. The removal percentages varied from batch to batch, from 6.9% to 72.3%. In the evaluation semi-batch system with initial load of 6.5 L, C2 with initial flow of 4.1 mL/s, achieved an average removal of 90.8% while C4 which operated with initial flow of 1.9 mL/s achieved 96.3%. During the operation was verified the presence of air bubbles in the columns. The particle size analysis of the bed material allowed to set the uniformity coefficient (d60/d10). The value of 4.7, pointed to the trend in hydraulic flow problems and clogging.