Management of clean-in-place wastewater using a hybrid membrane process (nanofiltration–forward osmosis–DCMD): Influence of operating conditions

This study proposed Nanofiltration (NF) – Forward Osmosis (FO) – Direct Contact Membrane Distillation (DCMD) to recover the cleaning agents and freshwater from the clean-in-place wastewater. As a prefiltration step, NF (4 kDa then 200 Da) removed lactose to non-detectable levels and reduced protein content by 94 %. The NF permeate was further concentrated with FO and DCMD at various temperatures (20–60 °C) and flow rates (500–1500 mL/min). At 1500 mL/min, water flux for both FO and DCMD increased by up to 35 %, and raising the feed/draw temperatures boosted FO flux from 43.7 to 63.1 LHM. Mass and heat transfer models showed close agreement with experiments, although fouling under high-temperature conditions reduced the accuracy of FO predictions. Despite this challenge, the integrated FO–DCMD produced high-quality water with minimal ionic content. The recovered cleaning agents exhibited cleaning efficacy comparable to fresh solutions, as confirmed by Quartz Crystal Microbalance with Dissipation monitoring. Overall, these findings highlight the potential of NF–FO–DCMD for sustainable CIP wastewater management, enabling both chemical and water reuse with possible cost savings and minimized environmental impact.