Smart harvesting and in-situ application of piezoelectricity in membrane filtration systems

Fouling remains one of the key challenges in membrane technology. In pressure-driven membrane separations, the vibrational energy induced by hydraulic pumps often dissipates unexploited. We present an innovative concept, in which the hydraulic pressure vibration is converted to electrical energy in the outlet of a filtration pump through an embedded piezoelectric nanogenerator (PENG) ceramic. We found that by increasing the average pressure of the hydraulic pump, the dynamic pressure fluctuation increased. The maximum output voltage of 219.6 V was obtained at 20 psi average pressure. The generated piezoelectricity was directly applied to an electro-assisted membrane cell in either alternating mode or positive/negative rectified form to mitigate membrane fouling. In the first configuration, ultrafiltration (UF) membrane was placed between two metallic electrodes. The optimum fouling resistance was achieved when the positive rectified piezoelectric pole was connected to the electrode. Water flux decline (FD) and water flux recovery ratio (FRR) were improved by 28.6% and 52.1%, respectively, compared to the case where no voltage was applied. In the second configuration, a piece of water-permeable and electro-conductive carbon nanotube (CNT) mat was mounted over the UF membrane and it was connected to the piezoelectric wafer using a wire. The alternating piezoelectricity provided the best antifouling performance in this configuration, with FD of 32.5% and FRR of 78.3%. The generated piezoelectricity was also used as a power source to drive an electro-Fenton (EF) reaction coupled with nanofiltration (NF) for reactive black 5 (RB5) dye separation. The results showed that the highest RB5 degradation rate (8.8%) was achieved when the rectified negative and positive poles were connected to the graphite paper and stainless-steel mesh electrodes, respectively. The proposed piezoelectric energy harvesting can revolutionize the traditional methods of fouling reduction in the electro-membrane processes where an external power should be applied for the oxidation reactions to occur.