On the optimization of a flocculation process as fouling inhibiting pretreatment on an ultrafiltration membrane during olive mill effluents treatment

In this work, a simple and cost-effective pretreatment upstream an UF membrane operation for the purification of the main olive mill effluent streams (OME) is examined. The raw wastewater was processed by a pH-temperature (T) flocculation process formerly studied at lab scale in previous work. In the present paper, modelization and optimization of the pretreatment process are addressed at pilot scale. Statistical multifactorial analysis showed both pH and T remarkably influence the suspended solids concentration removal efficiency (p-value practically equal to zero), confirming a statistically significant relationship between the variables considered at 95% confidence level. Moreover, the pH exhibits a deeper influence than the T, according to the p-values withdrawn from the analysis, and the squared effects are significant too, but more significant in the case of the pH. Contour plots and response surface support the previous results, and the optimized parameters were 21.4 °C and pH equal to 2.2, yielding 98.4 − 98.6% TSS reduction and 90.5% v/v recovery of clarified water. Finally, a boundary flux value of 9.7 L/hm2 and a significant reduction of the fouling index (3.4·10− 2 min− 1) were ensured, and a permeate stream reusable for irrigation, boosting the cost-efficiency of the integral process.