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 Moreover, the pH exhibits a deeper influence than the T, according to the p-values withdrawn from the analysis, and the squared effects are significant too, but more significant in the case of the pH.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. © 2015 Elsevier B.V. All rights reserved.

In this research work, a simple and cost-effective pretreatment upstream an UF membrane operation for the purification of the main olive mill effluent streams (OME) of olive oil factories is examined. The raw wastewater was processed by a pH-temperature (T) flocculation process formerly studied at lab scale in previous work by the Authors. In the present paper, optimization and modelization of the pretreatment process is addressed at pilot scale. Statistical multifactorial analysis showed that 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 Moreover, the pH exhibits a deeper influence than the T, according to the p-values withdrawn from the analysis, and the squared effects are significant too, but more significant in case of the pH. Moreover, the second-grade quadratic fitting equation proposed for the modelization of the pretreatment process was found to present a significant relationship at the 95.0% confidence level (p-value of 0.0001 for the model). Contour plots and response surface support the previous results, and the optimized parameters were found to be a temperature of 21.4 °C and a pH equal to 2.2, yielding 98.4–98.6% TSS reduction and a recovery of up to 90.5% v/v of clarified water. In view of the results, the proposed pH-T flocculation process may be successfully operated at ambient temperature conditions, posing an economic alternative to current coagulation–flocculation processes with commercial flocculants for the removal of the TSS load in olive mill effluents, which are based on polyelectrolytes and are quite more expensive than the flocculation proposed herein proposed. 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 steady-state performance and the cost-efficiency of the integral process.