Gravity-driven biomimetic membrane (GDBM): An ecological water treatment technology for water purification in the open natural water system

As an environmental water treatment technology, membrane technology has been prevalent for water purification in the closed membrane reactor system. Can membrane technology be applied as an ecological water treatment technology for water purification in the open natural water system? In this study, the feasibility of water purification in the open natural water system with gravity-driven biomimetic membrane (GDBM) was explored, focusing on the filtration driving force for providing the superior filtration efficiency and stability of long-term operation for improving the practicability. During GDBM preparation process, laccase was immobilized by carrier, then they were filtrated and deposited on microfiltration, thus a biomimetic layer with high permeability was formed. Its filtration process could be driven by the gravity of its own hydrostatic height. Above all, activated carbon, graphene oxide (GO) and carbon nanotube were utilized as carrier materials. Because of more stable immobilization effect for laccase and greater permeable structure, GO-GDBM possessed the better BPA removal rate and higher permeate flux. It even reached 72.1 L m(-2)h(-1) at 12 cm of hydrostatic height, and its fouling rate kept at a low hydrostatic height by the analysis of critical flux theory. Moreover, filtration experiments with BPA micro-polluted water were performed with various carrier dosages, laccase dosages, and BPA concentrations. Under different operating conditions, the filtration performance still kept a desirable degree. With an optimized condition (6 cm of hydrostatic height, 30 g m(-2) of carrier dosage, and 100 g m(-2) of laccase dosage), GO-GDBM sustained above 27 similar to 42 L m(-2)h(-1) of permeate flux and 55 similar to 70% of BPA removal rate during 30 days' operation. In addition, GDBM was proved to be effective to treat real micro-polluted water (natural water body polluted by soy sauce pollutants). Thus, GDBM could obtain sufficient filtration driving force, demonstrate a good capacity of resisting the change of operating conditions, and maintain high stability of long-term operation in the open natural water system. This study demonstrates an example of a niche application, where GDBM is expected to transform membrane technology from environmental water treatment technology to a highly efficient and cost-effective ecological water treatment technology.