Optimization of polymeric nanofiltration performance for olive-oil-washing wastewater phenols recovery and reclamation

Abstract

The core of the present work was to model and optimize an environmentally friendly nanofiltration (NF) treatment process for two-phase olive-oil-washing wastewater (OOWW) valorization throughout the concentration and recovery of its phenolic fraction and the obtention of a purified permeate stream. For this objective, a factorial design was used for the optimization of the process. Results were interpreted by means of the response surface methodology. A statistical multifactorial analysis was performed in order to quantify all the potential complex conjugated effects of the input parameters in the NF process. The process was subsequently modelled by means of a second-grade quadratic fitting model equation. Finally, the parametric quality standards that permit to reuse the purified stream for irrigation, recycling or even discharge in-site reuse purposes were checked. To the author's knowledge, no previous work on the optimization and statistical modelling of membrane processes for OOWW purification and valorization can be found up to the present. The optimized parameters for the proposed OOWW purification process – operating pressure of 26.5 bar, tangential velocity 32.7 m s−1, system temperature 35 °C and pH of 3.7 – ensured high and stable membrane flux (106.2 L h−1 m−2). The obtained optimized data are very relevant for the feasible scale-up of the proposed process in the mills, since the NF membrane (TFC polyamide/polysulfone, MWCO 300 Da) was highly efficient at ambient temperature conditions and raw effluent pH. The optimized conditions provided a permeate stream that could be reused for irrigation purposes and a retantate stream concentrated in volume up to 6.5 times, with a total phenolic content of minimum 1315.7 mg/L.