Recovery of cleaning agents from clean-in-place (CIP) wastewater using nanofiltration (NF) and forward osmosis (FO)

Abstract

This study proposed a Nanofiltration (NF) – Forward Osmosis (FO) membrane system to recover the cleaning agents from model dairy CIP wastewater. The NF steps consist of 4 kDa and 200 Da Nanofiltration (NF) membrane to reduce the lactose and whey protein before the forward osmosis (FO) concentration step. It was found that a series of NF filtration (4 kDa-200 Da) eliminated the lactose under detection level and protein by 96.3 %. The permeates from 4 kDa or 200 Da NF were further treated with FO. Two different FO membranes, cellulose triacetate (CTA) and thin-film composite (TFC). The increase of salts concentration from 0.5 M to 2.0 M increased the water flux from 17.8 LHM to 31.7 LHM when the TFC membrane was used. 4 times increase in the salts concentration did not result in the same magnitude increase in the water flux due to concentration polarization.. In addition, the TFC membrane was found to show an enhanced level of water flux compared to the CTA membrane over the same draw solution concentration due to improved water permeability. The TFC membrane with 2 M of NaCl was selected for further concentrating the NF permeates. Concentration using TFC FO membranes resulted in an increase the active alkali between 0.5% - 0.6%. The cleaning effectiveness of the recovered cleaning agents was assessed using Quartz Crystal Microbalance with Dissipation (QCM-D). The cleaning agents recovered by 4 kDa/200 Da NF and FO were found to present no significant difference as compared to fresh cleaning agents.