Removal of herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) from saline industrial wastewater by reverse osmosis and nanofiltration

Conventional reverse osmosis (RO), a novel temperature-swing RO (TSRO), and tailored nanofiltration (NF), were investigated to target the removal of the chlorophenoxy broad-leaf herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) from saline (HCl-rich) wastewater at pH between 1 and 2. Batch concentration by RO at 17.5 bar using BW30 and SW30 membranes showed similar performance, where BW30 showed rejections of 95.3% for MCPA and 25.9% for acid, but initial flux of 13 L.m−2.h−1 declined by 82% upon reaching 80% volume recovery. For the novel TSRO using BW30 and swing temperature from 24°C to 45 °C based on MCPA solubility tests, practical higher overall flux was achieved while showing similar MCPA rejection, but with slightly higher acid rejection of 37%. Pilot scale NF using NF270 and NF90 membranes showed decreased rejections of both MCPA and acid. The NF270 showed rejections of 71.3% for MCPA and 16.8% for acid. But despite lower MCPA rejection, its high flux up to 80% volume recovery could be used with RO or other treatments to meet MCPA discharge requirements. RO and NF are therefore suitable for MCPA removal from saline (HCl-rich) wastewaters, but novel temperature swing RO process offers potential to achieve higher MCPA rejection simultaneously to higher overall flux at practical volume recoveries.