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Olive mill wastewater pretreatment by combination of filtration on olive stone filters and coagulation–flocculation

ABSTRACT In the present study a new combined process, comprising filtration of raw olive mill wastewater (OMWW) on two successive olive stone (OS) filters followed by a coagulation–flocculation, was developed in order to perform an efficient pretreatment of OMWW. The results show that the use of OS filter leads to a higher removal of total suspended solids (TSS) and fatty matter (FM) from the raw OMWW (about 82.5% and 73.8%, respectively) and a depletion of total phenolic compounds (TP) and chemical oxygen demand (COD) (11.3% and 23.2%, respectively). The coagulation–flocculation was then applied to improve the removal of TP and COD from the filtered OMWW. For this purpose, a full-factorial design was used to study the effect of different factors involved in coagulation–flocculation. The studied variables were: pH (5–8), coagulant type (ferric chloride; FC and aluminum sulfate; AS), coagulant concentration (250–1000 mg/L) and flocculant (Anionique polyelectrolyte Superfloc A120 PWG) concentration (1–5 mg/L). The results reveal that the use of 250 mg/L FC and 5 mg/L flocculant at an acid pH (around 5) allows for, respectively, a removal of TP and COD of about 10.8% and 31.3%.