Organic pollutants removal from olive mill wastewater by a combined system of a sand filter and an aquatic plant system

The objective of this study consisted of testing the potential of a sand filter to decrease the organic pollutants in olive mill wastewater (OMW) diluted to 50% with domestic wastewater, and to polish the treatment by using a mixture of aquatic plants: Phragmites australis, Typha latifolia and Arundo donax. The experimental pilot consists of a sand filter followed by a planted system. The sand filter is filled with 50 cm of sand and 10 cm of gravel at the top and the bottom of the filter. The feed (4 cm•j-1) is done sequentially according to a one-day wet/three days dry cycle. In order to activate the degradation processes in the sand filter, OMW are diluted to 50% with domestic wastewater. The second step of the treatment consists of a tank (1x1x1 m3) 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 two times in the week by 20 L of pre-filtered OMW. The results show that the sand filter ensures a neutralization of the OMW pH, which passes from 4.79 to 7.68. The enrichment of the sand by the micro-organisms ensures an important mineralization of the organic matter. After ten weeks of operation of this system without clogging sign, the rate of abatement of the TSS, total COD, dissolved COD and phenolic compounds was about 70%, 79%, 76% and 81% respectively. Completion of the treatment by the mixture of three plants shows an increase in the pH, electric conductivity and a significant elimination of the total COD (99,7%), dissolved COD (99,5%), TSS (94%) and polyphenols (95%). With regard to OMW treatment efficiency, the treatment of the OMW by the combination of two systems (sand filter and planted system) results in a significant removal of the organic load of the OMW.