Treatment of olive mill wastewater by coagulation–flocculation with aluminum sulphate / aluminum polyhydroxichlorosulfate and effect on phytotoxicity

Abstract

In the present study, coagulation floculation was examined using two different coagulants: aluminum sulphate (Al2(SO4)3) which is widely used on an industrial scale for olive mill wastewater (OMW) treatment, and polyhydroxichlorosulfate aluminum (Aln OHm Cl3n-m-2k (SO4)k) popularly known as WAC. The coagulant WAC is already used in the treatment and purification of water, but it has never been tested for the treatment of OMW. The phytotoxicity study of OMW (before and after treatment) to wheat seeds showed that the toxic compounds of this effluent affect both the seed germination and the seedling growth. The root length was more sensitive to OMW than the shoot length. However, the toxicity of this effluent has been greatly reduced after treatment with WAC (growth was inhibited at concentration of 80%) compared to another OMW treated with aluminum sulfate. The highest percentages of germination have been observed in the seeds irrigated by OMW treated with WAC. This study also showed that the phytotoxicity decreased with dilution (5% - 40% for raw OMW, 5% - 50% for OMW treated with aluminum sulfate, and 5% - 60% for OMW treated with WAC). Finally, the experimental results obtained show that the dilution and the treatment by the WAC coagulant (2.50 g; pH between 6.50 and 7.50) are two important processes to reduce the phytotoxicity effect of OMW.