Preliminary evaluation of constructed wetlands for nutrients removal from olive mill wastewater (OMW) after passing through a sand filter

The current study was carried out to test the removal of nitrogen and phosphorus from olive mill wastewater (OMW) by combination of sand filter and a mixture of aquatic plants (Phragmites australis, Typha latifolia and Arundo donax). The experimental pilot was composed of two serial systems: sand filter followed by vertical flow constructed wetlands (VF-CWs). The sand filter was filled with 50 cm of sand and 10 cm of gravel in the top and the bottom of the filter. The second step of the treatment consists of a tank (1 x 1 x 1 m(3)) filled with 20 cm of gravel and 60 cm of soil, planted with a mixture of aquatic plants at a density of 8 young plants/m(2) for each plant and irrigated twice in the week by 20L of preliminary filtered OMW. During all experiment, OMW was diluted with domestic wastewater at a ration 1/1 (v/v). Mean diluted OMW concentrations were 2.05 g/L, 1.52 g/L, 1.94 mg/L, 1.70 mg/L, 0.22 g/L, 0.30 g/L, 26.78 g/L and 20.47 g/L for TKN-N, NH4+-N, NO2--N, NO3-N, ortho-phosphate (OP), Total phosphorus (PT) total COD and dissolved COD respectively. Despite the rather high influent concentrations, the performance of the sand filter was very effective since it achieved average removals of about 60.4%, 74.4%, 80.61%, 97.85%, 96.45%, 79.75% and 76.75% for NTK, NH4+, NO3-, PO43-, PT total COD and dissolved COD respectively. The presence of aquatic plants was more efficient in removing of nutrients and organic load. The average elimination of experimental system (sand filter + VF-CWs) in terms of flow was 62.48% for NTK, 90.43% for NH4+, 77.25% for NO3-, 98.51% for PO43-, 97.53% for PT and 99.05% for total COD. In general, this study shows potential application of the experimental system to achieve nutrient and COD removal from OMW. Although the percent removal of organic matter and nutrients from OMW was very high, final OMW concentrations remained high, thus preventing their use for irrigation or immediate disposal into the environment.