Photocatalytic nanofiltration reactor for agricultural wastewater purification and reuse

In recent years, the Agrofood industry utilizes pesticides for improving the agricultural production. Nevertheless, the presence of pesticide residues in agricultural wastewater can cause adverse impact on water resources and have harmful effects on human health. Consequently, intensive actions are required for their degradation. Conventional wastewater treatment methods are inefficient to confront pesticides, as most of them are recalcitrant organic molecules. The novel technology of photocatalytic nanofiltration integrates in one reactor module the most effective water treatment technologies against micropollutants. Photocatalysis and nanofiltration are combined synergistically to achieve augmented efficiency. Photocatalysis leads to the oxidative micropollutant degradation by radicalary mechanisms, while simultaneously, the retention of micropollutants is achieved by nanoporous membranes. Thus, based on a previous engineering study, which materialized a patented photocatalytic membrane reactor concept, a novel pilot-scale photocatalytic nanofiltration reactor (PNFR) was fabricated for the demands of agricultural wastewater purification and reuse. The PNFR pilot unit consists of twelve seven-channeled photocatalytic nanofiltration monoliths, prepared via a wash-coating technique. The smart design of the reactor’s internals endows the process with additional flow channels, which in addition to the monoliths host 240 polyvinylidene fluoride porous hollow fibers with stabilized TiO2 photocatalyst nanoparticles into their matrix. Irradiation is achieved both on the shell side of monoliths and photocatalytic fibers and on the lumen side of the monoliths. The reactor encloses 1.5 m2 of photocatalytically active surface and has a clean water production capacity up to 1.2 m3/day. Experimental campaigns were performed involving different feed flow rates (2.3-3.3 L/min) and transmembrane pressures (3-4.5 bar) and employing various concentrations (6-55 ppb) of Acetamiprid (ACT) and Thiabendazole (TBZ), which are frequently detected in the fruit-industry wastewater. In about 3 h, 95% of the wastewater was recovered, while the amount of ACT and TBZ was reduced by 25 and 42%, respectively.