Photocatalytic degradation of recalcitrant pollutants in batch and membrane reactors

Water pollution caused by recalcitrant pollutants is a major environmental problem because of the incremental consumption of these compounds, which end up in aqueous secondary effluents and are responsible for hazardous consequences to animals and ecosystems. In particular, the mismanagement of pharmaceutical and plastic waste has had a disastrous impact on the aquatic and terrestrial environment. To solve this challenge, heterogeneous photocatalytic processes are preferred for the higher degradation efficiency in mild condition. The combination of photocatalytic process and membrane technology can be very effective in the removal of organic pollutants (particularly recalcitrant compounds) from wastewater. Membrane process can be used in a photocatalytic membrane reactor to improve pollutant mineralization maintaining the pollutants and the photocatalyst in the photoreactor to obtain a good quality treated water but also to recover and concentrate traces of pollutant present in low concentration in real or simulated effluent. Different systems and pollutants photodegradation were studied. The photocatalytic degradation of Gemfibrozil as a model pollutant was performed in batch and membrane photoreactor with a configuration, based on a vertical filter and an external nanofiltration (NF) membrane [1]. The photocatalyst separation and the hydraulic behaviour of the vertical filter, the ability of a nanofiltration membrane to retain gemfibrozil (GEM) and the overall performance of pollutant photodegradation in a batch operation mode have been studied. Another innovative system was used to combines the membrane technology and the photocatalytic process for the recovery and the treatment of polluted effluent with microplastics [2]. The complete recovery of microplastics present in real wastewater from a domestic dryer was performed by using different membrane with the almost complete recovery of the initial performance of the membrane used with a low fouling index. Preliminary photocatalytic experimental tests were carried out on the concentrate effluent coming from the membrane treatment in a batch photoreactor, evidencing the degradation/decomposition of polyester fibers with a weight loss of about 13%. This photocatalytic decomposition was confirmed also by py-GCMS characterization, highlighting the potential of the photocatalytic process to degrade plastic fibers. The obtained results suggested that the photocatalytic process can be tuned to allow the decomposition of micro/nanoplastics avoiding the use of dangerous and costly methods such as the thermal process that can produce toxic by-products. Future work should be direct to combine membrane recovery and photocatalytic membrane reactor to improve wastewater purification.