Nanofiltration of ultrafiltration permeate fom chemical wastewater

Abstract: The aim of this report was to investigate the possibility of further cleaning of the wastewater at Dow in Landskrona. Dow produces water based adhesives from acrylic monomers. The wastewater contains different metal ions, surfactants, residual monomers and polymers. The wastewater at Dow is treated with ultrafiltration (UF) which produces a permeate that is sent to the municipal waste water treatment plant (WWTP). The municipal WWTP is heavily burdened and it might not be long until they start refusing to treat the wastewater from Dow. This study is a proactive investigation of nanofiltration (NF) as a method to produce a permeate clean enough to be reused in the process at Dow. Being proactive in wastewater treatment is getting more and more important, especially with the current water shortage in Sweden and many other places in the world. Five NF and reverse osmosis (RO) membranes were investigated in the initial screening of flat sheet membranes: NF99HF from Alfa Laval, AP from GE, NF270, NF90 and XLE from Dow Filmtec. The UF permeate from Dow was used as feed for the NF. The total organic carbon (TOC) and conductivity was measured in the feed, the UF permeate, and the NF permeates to determine the retention of the membranes. The influence of transmembrane pressure (TMP) and crossflow velocity (CFV) was studied for all membranes to determine the optimal operation conditions. From the studied membranes, NF90 was chosen for further studying in a spiral wound membrane due to the good retention and common use in industrial wastewater treatment. The contents of the UF permeate varies a lot due to the varying production schedule at Dow. That means that the NF membranes must be equipped to handle the worst-case scenario at Dow, if all the NF permeate is to be reused in the process. Despite the varying content of the UF permeate a NF permeate with concentrations of TOC and conductivity lower than that of the city water in Landskrona has been produced on several occasions. This is proof that NF membranes are capable of producing a permeate clean enough to be reused in the process. However, on two occasions the UF permeate from Dow contained high concentrations of TOC, conductivity and inorganic carbon (IC). The concentrations of the produced NF permeate were nowhere near the low concentrations of the city water. Further investigations should be made if this can be avoided if Dow wants to proceed with the NF system. The fouling issue could not be resolved as it seemed that no combinations and concentrations of cleaning detergent could remove the fouling caused by the filtration. The fouling should be of focus in further studies. NF seems to be a promising method to further clean the wastewater but further studies in a larger scale need to be done before deciding on implementing it at Dow.