Dimethylformamide (DMF) is an important solvent used in the production of polyurethane (PU) synthetic leather. DMF wastewater from leather factories is highly toxic and poorly biodegradable, so DMF recovery is essential.
At present, the main method for DMF recovery from wastewater is two-tower distillation, including atmospheric distillation and vacuum distillation. However, DMF wastewater from PU synthetic leather factories has very high suspended solids content and turbidity. Therefore, pretreatment is very necessary to provide a high-quality feed for further purification in the distillation columns.
In this work, researchers at Changzhou University and Nanjing University of Technology in China used three types of 19-channel ZrO2 microfiltration membranes with different pore sizes for pretreatment of DMF wastewater.
The effects of membrane pore size, crossflow velocity (CFV), and transmembrane pressure (TMP) on ceramic membrane filtration performances were investigated. Experimental results indicated that the optimum membrane pore size is 0.2 μm, optimum CFV is 3 m/s, and optimum TMP is 0.2 MPa. The corresponding liquid turbidity removal rate was 99.62%, and the suspended solids content retention rate was 99.99%.
In addition, the membrane fouling mechanism was analysed using a resistance-in-series model. The main resistance derived from particle adsorption and sedimentation on the membrane surface. The ratio of particle adsorption and sedimentation resistance to total resistance was above 70% for the 0.2 μm membrane.
Backflushing technology was then applied, and the effect of backflushing on the permeate flux was studied. The permeate flux eventually increased by 50% with an optimum backflushing pressure of 0.6 MPa, backflushing time of 5 s, and backflushing interval of 20 min.
Then a combination cleaning method was used to regenerate the ZrO2 microfiltration membrane. The pure water flux recovered to 608.2 L/m2h and the flux recovery rate was 96.8%, which indicates that the combination cleaning method was effective.