The infiltration–percolation process based on different filter design is generally implemented in arid climate countries for primary and secondary wastewater treatment. Semi-saturated sand filters can compete with planted filters in terms of removing some pollutant loads, but they need routine clogging that a pebble filter can avoid. Two semi-saturated mesocosms have been tested in secondary urban wastewater treatment during several seasons in Mediterranean climate, one with sand, the other with pebbles, having respective porosity/specific area of 0.17/0.633 m−1 and 0.24/0.099 m−1. By applying specificorganic loads of 29.36 and 32.54 g m−3 day−1 of COD (chemical oxygen demand) in the same order, the sand filter showed significantly better performance in terms of removal of total phosphorus (TP; 75.8 ± 20.80%, 0.564 ± 0.248 g m−2 d−1, 3.016 ± 1.324 g m−3 day−1), total nitrogen (TN; 47.94 ± 15.43%, 17.72 ± 14.52 g m−2 day−1), COD (137 ± 61.26 g m−3 day−1), and total suspended solids (TSS; 53.83 ± 26.60 g m−3 day−1). However, the pebble filter has similar performance in terms of areal export of TSS and COD, and significantly exceeds the sand filter in terms of volumetric removal of TN (4.124 ± 2.998 g m−3 day−1). It is less evapo-transpiring (7.52 ± 8.04 mm day−1) and has a relatively higher hydraulic retention time. Both semi-saturated filters tested can be used in similar conditions to unsaturated ones for the removal of suspended solids, with an advantage for the removal of total phosphorus and biodegradable organic load for the semi-saturated sand filter. Therefore, they may constitute a solution for decentralized wastewater treatment and a non-conventional source of water.
عبد السلام النبيلي | Abdeslam Ennabili | 5754