Olive mill wastewater valorisation through phenolic compounds adsorption in a continuous flow column

A continuous-flow adsorption/desorption process for the recovery of phenolic compounds (PCs) from olive mill wastewaters (OMWs) was developed in a 0.53 m packed column, using a previously selected resin (Amberlite XAD16) and an actual OMW. The main goals of the study were (i) to evaluate the PC adsorption/desorption performances of XAD16 by means of adsorption isotherms and adsorption/desorption breakthrough tests, and (ii) to develop a reliable model of the process. A combination of centrifugation and microfiltration resulted necessary to attain a high suspended solid removal (98.5%) and thus avoid clogging of the packed bed. The quality of two packing procedures was evaluated by means of frontal analysis tests. XAD16 performed well in terms of both adsorption yield at 20% breakthrough (87-88%) and PC/COD selectivity (PC/COD adsorption constant = 7-9). The desorption solvent (acidified ethanol) was effectively regenerated by vacuum distillation. The adsorption breakthrough curves were successfully simulated with a 1-D convection/dispersion model with mass-transfer (R2 = 0.95-0.99; kLa = 0.8-2.5 · 10−3 1/s), whereas an equilibrium adsorption model with dispersion failed to predict the experimental data. In the perspective of a process scale-up, the simulation of the best-performing operational condition was used to evaluate the process performances for different column lengths (0.5-10 m). A precise and automated HPLC method for total PC measurement was developed and compared to the traditional Folin-Ciocalteu methodology. Further research is needed to optimize the desorption step, to scale up the process and to evaluate the long-term resin performances.