Feasibility of membrane processes for Volatile Fatty Acids (VFAs) concentration:data elaboration, modelling and design

The need for recovery and concentrate a Volatile Fatty Acids (VFAs) effluent resulting from a biological fermentation step, has aimed a feasibility study on pressure-driven membrane separation processing. A previous experimental campaign, carried out at LABIC-DICAM for the NoAW (No-Agricultural Waste) EU project, involving total recirculation and concentration trials on RO and NF modules, was the starting point for subsequent elaboration, modelling, simulation and preliminary design. The presented mass transfer-solution modelling allowed the estimation of both VFAs and Na+ real rejections for all investigated total recirculation trials. The modelling ability to assess the system’s osmotic pressure and polarization magnitude was successfully tested accounting for the validity of the osmotic-pressure model. Total recirculation trials calculated real rejections trends were interpolated using the Mason&Lonsdale and solution-diffusion transport models, providing a set of adjustable parameters. The interpolated RReal (Jv) curves were used in the simulation of the experimental concentration trials, proving our capability to fairly faithfully reproduce the experimental trends. The accomplishment encouraged the simulation of further concentration trials whose experimental evidence was not available. The simulations aimed at investigating the modules performances for different applied pressures with the final objective of identifying a few design best cases. Two possible process alternatives were proposed: pure RO process and an integrated process RO + NF. Subsequent comparison of the alternatives’ preliminary design best-cases showed the two to be competitive.