Treatment of cauliflower processing wastewater by nanofiltration and reverse osmosis in view of recycling

Abstract

The vegetable industry is a large consumer of drinking water. This paper investigates the possibilities of Reverse Osmosis (RO) or tight Nanofiltration (NF) for the treatment of cauliflower blanching wastewater with a view to recycling within the production unit. Ultrafiltration at 100 000 g mol −1 molecular weight cut-off was necessary to decrease turbidity below 1 NTU as required before NF or RO. Three NF (DK, NF270 and SRD3) and one RO (ESPA4) membranes were tested at bench-scale in a crossflow filtration mode. Only RO allowed to reach the desired quality for a reuse purpose, with an acceptable residual COD content of 225 mg O 2 L −1 . The Solution-Diffusion model was validated for the transfer of glucose and fructose, for NF270, DK and ESPA4 membranes and their permeability coefficients calculated. • Ultrafiltration followed by reverse osmosis allows to consider recycling of cauliflower wastewater. • ESPA4 membrane at 19 bar leads to 70 L h −1 . m −2 permeate flux and 95% COD rejection. • Solution-diffusion model considering concentration polarization was successfully applied. • DK, NF270 and ESPA4 permeabilities for fructose and glucose were determined. • Nanofiltration with 150–300 g mol −1 molecular weight cut-off is not suitable, due to the transfer of small metabolites.