## 4 Conclusions  
Diclofenac is transformed to different products due to irradiation with UVA light. The absorbance of diclofenac overlaps with the absorbance of phototransformation products, thus transformation is inhibited. Transformation of diclofenac can be increased by adsorbing phototransformation products.  
The addition of PVDF during UVA irradiation increased the transformation of diclofenac from 64.9% (\(SD\) = 0.2%) to 72.3% (\(SD\) = 0.2%) (after 20 min of UVA irradiation), enhanced TOC removal from 17.9% (\(SD\) = 2.7%) to 52.3% (\(SD\) = 1.5%) (after 18 h of treatment) and decreases the toxicity towards _Vibrio fischeri_ from a TU value of 10.2 to 0 (after 18 h of treatment). TOC removal of diclofenac via UV irradiation without PVDF is found to be low in the literature (<10%), but can be raised by the addition of PVDF to over 26%. The PVDF does not need to be irradiated itself during reaction as it only acts as an adsorbing material. The adsorbing capacity can be regenerated by washing PVDF with water or ethanol. As UVA degradation of diclofenac is incomplete, toxicity increases. The addition of PVDF enhances the removal and toxic phototransformation products are removed from the solution.  
This concept of increasing transformation by adsorbing phototransformation products which inhibit the reaction could be enhanced with other adsorbing polymers (e.g., PES, PTFE, PE) having different properties (e.g., surface charge, hydrophilicity, functional groups). As the polymer does not have to be irradiated itself, many different materials can be applied. The concept could be also adopted to other UVA phototransformable pollutants like sulfamethoxazole or ketoprofen. The development of a continuous reactor is required to scale up the process. Further studies will be undertaken to study diclofenac removal in a continuous reactor where diclofenac in water is flowing over PVDF with simultaneous UVA irradiation. Different volume, concentration, flow velocities and surface area will be changed and tested.  
Combining UVA irradiation and adsorption of phototransformation products to a polymer could improve the elimination of many other pollutants from water and decrease its toxicity. Toxic phototransformation products which are generated during UVA irradiation of pollutants are removed via adsorption. The concept is unique, improving different parameters like adsorbing polymer, UVA irradiation and reactor design, could lead to a promising technique to remove UVA phototransformable pollutants and its transformation products from water.  
Conceptualization, K.F. and S.S.; methodology, K.F., S.S., J.G., C.E., I.T., A.A.L. and S.N.; software, S.N.; validation, K.F. and S.N.; formal analysis, K.F. and S.S.; investigation, K.F. and S.S.; writing--original draft preparation, K.F. and S.S.; visualization, K.F. and S.S.; supervision, K.F. and A.S.; project administration, K.F. and A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The authors would like to acknowledge [PERSON] for proof reading the manuscript. The authors declare no conflict of interest.