The removal of organic micropollutants (OMPs) in the aquatic environment is crucial to avoid health hazards. Zeolites have been confirmed as a selective adsorbent and can effectively remove target OMPs. To achieve sustainable application of adsorbents, regeneration of zeolites is required.
The objective of this study was to investigate the regeneration performance of dried OMP-loaded granular zeolites through gaseous ozonation process, and the regeneration feasibility in long-term adsorption-regeneration processes. Three types of zeolites (MOR, MFI and BEA) were applied for target OMP (benzotriazole, methyl-benzotriazole, carbamazepine, diclofenac hydrochlorothiazide, sulfamethoxazole, metoprolol, sotalol, trimethoprim, propranolol, and clarithromycin) removal. A sequential process coupling zeolite adsorption and oxidation by gaseous ozone was established in batch mode. To assess the ozone effect on OMP degradation and zeolite itself, ozone bubbling tests and adsorption isotherm experiments were executed as pre-experiments. The relative adsorption capacity obtained through regeneration was used to demonstrate regeneration performance. Operating conditions, adsorption duration and regeneration duration were determined and applied. Ultimately the regeneration performance in long-term adsorption-regeneration processes was investigated.
Experimental results showed that all target OMPs were not resistant to ozonation in the water phase. Gaseous ozone was showed no influence on the adsorption capacities of zeolite granules. 120 hours and 500 mgL-1 zeolite granules were applied in OMP-loading adsorption experiments. Zeolites always showed high adsorption capacities of metoprolol, trimethoprim and sotalol, which regeneration effect was not evidenced. 60 minutes of ozonation was effective and sufficient for regenerating low and medium adsorption OMPs, except for carbamazepine. The regeneration of carbamazepine probably required a longer regeneration duration. In four cycles of adsorption-regeneration experiments, regeneration of sulfamethoxazole could be achieved after four rounds of ozonation. Regarding carbamazepine, diclofenac, benzotriazole, and methyl-benzotriazole, the regeneration performance were significantly reduced after the first cycle of regeneration. The ozonation duration is supposed to be extended above 60 min in long-term regeneration experiments. Intermediates were potentially responsible for the reduction of regeneration performance in ozonation and adsorption processes. Particularly, the effect of intermediates accumulation might be the main factor that hampered the regeneration performance of low and medium adsorption OMPs in long-term operation. ... Read more

Activated carbon (AC) is commonly used in drinking water treatment plants (DWTPs) to remove organic micro-pollutants (OMPs), and it is effective in adsorbing a wide range of OMPs. However, its adsorption efficiency can be affected by natural organic matter (NOM). NOM is a complex matrix and widely exists in water bodies. During the drinking water treatment process, the large size fraction of NOM may block the pore of the granular activated carbon (GAC), and the small size fraction of NOM can compete with OMPs and occupy the sites. The goal of this study is to increase the OMP adsorption efficiency of AC filtration in the drinking water treatment process. The objective was to investigate the feasibility of the competitive NOM removal by zeolite adsorption prior to powdered activated carbon (PAC). Meanwhile, the filtration performance and advantages of nanofiltration (NF) with 1000 Da membranes were found out. Zeolite - AC and NF- Zeolite - AC combined treatments were exterminated. In this study, the properties of zeolites were reviewed and the zeolite with FAU framework was selected as the hydrophobic adsorbent. Batch experiments with FAU and PAC were conducted to examine the adsorption performance of 10 common OMPs in different water samples. Comparative batch tests on UV effluent and NF permeate were carried out with two stages, zeolite pre-treatment and PAC treatment. Ultrapure water and demineralized water were involved as the reference to prove the influence of NOM from adsorption isotherms. Dissolved organic carbon (DOC) measurements were provided by the DWTP. NOM is confirmed to hinder the OMP adsorption on AC according to DOC measurements and adsorption isotherms. NOM smaller than 1000 Da is proved to cause the competition with OMPs. FAU-type zeolite pretreatment was failed to remove the competitive NOM removal. ... Read more