Nitrogen Removal from Secondary Effluents Through a Simple and Double Filtration on Sand Filter

Abstract

AbstractTo cope with water scarcity, wastewater reuse is one of the most promising supply-management practices. Several techniques are used for the purification of domestic wastewater, and our research work focused on the infiltration–percolation technique, which is a biological treatment process with a culture fixed biomass. The main purpose of the present study was to investigate the performance of this treatment process regarding particularly the removal of nitrogen from the wastewater treatment plant of Zarat. A comparative study was carried out to evaluate the effect of the double filtration (on 50 cm of sand) on the nitrogen removal efficiency, compared to the simple filtration (on 1 m of sand). Three PVC columns (internal diameter 20 cm and length 120 cm) were used to simulate wastewater treatment by media-based filtration. Each column was packed with a drainage layer (medium gravel), a transition layer (fine gravel), and a filtration layer (sand). Operating the two filter columns in series (50 cm of sand) resulted in a better effluent quality than a simple filter column (1 m of sand). The total nitrogen and ammonia removal efficiencies by filter columns 1 and 2 in series amounted to 97% and 96%, respectively. Analyses of the percolating water showed that overall removal of nitrogen increased significantly with the infiltration depth, emphasizing that the highest nitrogen removal efficiency occurred mainly in the upper layers of the filter bed. However, after a double filtration, the decrease in the total nitrogen and ammonia was accompanied by an immediate increase of significant nitrate content (\({\text{NO}}_{3}^{ - }\)). These results are very encouraging for the urban wastewater treatment for agricultural reuse, even with a high residual NO3 concentration since it will be an interesting contribution to fertilization in nitrogen nutrients since they are well assimilated by plants.KeywordsWastewater treatmentInfiltration–percolationNitrogen removalSand filtersDouble filtration