A review of treatment techniques applied for selective removal of emerging pollutant-trimethoprim from aqueous systems

Antibiotics are among the emerging pollutants that pose hazardous effects to the aquatic environment and human health if not properly controlled. Trimethoprim (TMP) is one of the most regularly administered antibiotics whereby its existence in aquatic surroundings has received much concern in recent decades due to its persistent behaviors. In this review, different treatment techniques that have been applied for selective removal of trimethoprim from aqueous systems were discussed in detail. Several studies have reported on the incidence of TMP in water systems including wastewaters, groundwater, river water, surface water and drinking water. The findings from the literature have shown that the advanced oxidation processes (AOPs) have been comprehensively applied for the elimination of trimethoprim from water systems as compared to other treatment techniques. AOPs (particularly ozonation) have showed noteworthy performances on removing TMP followed by membrane processes (nanofiltration and reverse osmosis), combined processes and adsorption process. Effectuation of oxidation processes could be explained due to the structural nature of TMP which contains moieties such as electron-rich aromatic system and deprotonated amine that are highly prone to oxidation attack. However, most of oxidation methods have several limitations that hinder their worldwide applications. A number of oxidation and transformation products are usually formed after treatment of TMP; some of the products are reported to be resistant to further oxidation. Therefore, these products should be carefully examined, and toxicity assessment should be further performed to know the possible toxic effects of transformation and oxidation products, as currently there are limited data available. Lastly, although the adsorption process had been associated with several advantages on removing antibiotics, only limited studies have so far been reported on the removal of TMP via adsorption. Thus, there is a niche for wide range of adsorbents to be investigated for their efficiency for the uptake of TMP from aqueous systems. Therefore, future studies should also focus on synthesizing various adsorbents such as biochars, nanoparticles (carbon nanodots, carbon nanotubes, etc), microporous carbonaceous and polymers that are derived from low-cost agricultural waste materials and examine their adsorption performances toward trimethoprim.