In recent years, there is a growing concern about the alarming spread of antimicrobial resistance (AMR) in different environments. Increasingly, many species of bacteria, fungi and viruses are becoming immune to the most commonly used pharmaceuticals. One of the causes of the development of the resistance is the persistence of these drugs, excreted by humans, in municipal and hospital wastewater (WW). Consequently, wastewater treatment plants (WWTPs) are a primary source of antimicrobial resistance genes as novel pollutants. This systematic review sought to examine the relevant literature on pharmaceutical residues (PRs) responsible for AMR in municipal and hospital WW in order to propose a classification of the PRs of greatest concern and provide an updated source for AMR management in WWTPs. Among 546 studies collected from four databases, 18 were included in the present review. The internal and external validity of each study was assessed, and the risk of bias was evaluated on a 20-parameter basis. Results were combined in a narrative synthesis discussing influent and effluent PR concentrations at 88 WWTPs, seasonal variations, differences between hospital and municipal WW, environmental risk assessment values of antimicrobial substances and treatment facilities removal efficiencies. Among the 45 PRs responsible for AMR evaluated in this study, the antibiotics ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole and trimethoprim constitute a considerable risk in terms of ubiquitous distribution, worrying concentrations, risk quotient values and resistance to removal treatments. Gaps in knowledge, data and information reported in this review will provide a valuable source for managing AMR in WWTPs.

Microalgae represent an alternative to conventional wastewater treatment, potentially improving antibiotic removal and offering a solution to combat the spread of antimicrobial resistance. Through batch assays, this study investigates the routes for antibiotic removal using three strains (Chlamydomonas acidophila, Auxhenochlorella protothecoides and Tetradesmus obliquus). Using mixtures of ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim at concentrations simulating wastewater composition, it also assesses antibiotic effects on microalgae physiology. The three strains primarily removed antibiotics through rapid biosorption, achieving up to 91.5% removal for specific ones like ciprofloxacin. T. obliquus and C. acidophila showed efficacy, with total removals of 37.2% and 49.3%, respectively. Over time, A. protothecoides demonstrated the highest active removal efficiency, eliminating 22.1% of total antibiotics, with a notable 67.6% removal for sulfamethoxazole. Abiotic degradation through hydrolysis and photolysis contributed to ciprofloxacin, ofloxacin, clarithromycin, and erythromycin removal (34.7% to 96.7%), showing pH-dependent photolysis. However, algae induced a shading effect, reducing the photolytic and hydrolytic degradation of specific antibiotics. T. obliquus and C. acidophila were inhibited by antibiotics, whereas A. protothecoides showed a 30.6% growth rate increase. The stimulatory effect was also observed for the nutrient removal, with A. protothecoides showing a 46.6% increase in ammonium removal and a 44.8% increase in phosphate removal with antibiotics. Additionally, antioxidant activities remained stable, except for a notable increase in peroxidase activity for A. protothecoides and T. obliquus. The study confirms efficient antibiotic removal and stimulatory responses in the three algal strains, indicating their potential for wastewater treatment and combating antimicrobial resistance.

The main objective of this study is to investigate the effect of mixtures of seven widely used human antibiotics (ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim) on the growth, pH, pigment production, and antibiotics removal of three microalgal species (Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas acidophila). Batch assays were conducted with media with antibiotic mixtures at 10, 50, and 100 μg L⁻¹ for each antibiotic. The three microalgae species effectively removed the antibiotics without any growth inhibition, even when exposed to the highest antibiotic concentrations. Biosorption was reported as the primary mechanism for ciprofloxacin, clarithromycin, metronidazole, and ofloxacin, with up to 70% removal, especially in A. protothecoides and C. acidophila. A. protothecoides, a species never investigated for antibiotic removal, was the only microalgae exhibiting bioaccumulation and biodegradation of specific antibiotics, including sulfamethoxazole. Furthermore, in media with the highest antibiotic concentration, all three species exhibited increased chlorophyll (up to 37%) and carotenoid (up to 32%) production, accompanied by a pH decrease of 3 units. Generally, in the present study, it has been observed that physiological responses and the removal of antibiotics by microalgae are interlinked and contingent on the antibiotic levels and types.

In recent years, there is a growing concern about the alarming spread of antimicrobial resistance (AMR) in different environments. Increasingly, many species of bacteria, fungi and viruses are becoming immune to the most commonly used pharmaceuticals. One of the causes of the development of the resistance is the persistence of these drugs, excreted by humans, in municipal and hospital wastewater (WW). Consequently, wastewater treatment plants (WWTPs) are a primary source of antimicrobial resistance genes as novel pollutants. This systematic review sought to examine the relevant literature on pharmaceutical residues (PRs) responsible for AMR in municipal and hospital WW in order to propose a classification of the PRs of greatest concern and provide an updated source for AMR management in WWTPs. Among 546 studies collected from four databases, 18 were included in the present review. The internal and external validity of each study was assessed, and the risk of bias was evaluated on a 20-parameter basis. Results were combined in a narrative synthesis discussing influents and effluents PR concentrations at 88 WWTPs, seasonal variations, differences between hospital and municipal WW, environmental risk assessment values of antimicrobial substances and treatment facilities removal efficiencies. Among the 45 PRs responsible for AMR evaluated in this study, the antibiotics ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole and trimethoprim constitute a considerable risk in terms of ubiquitous distribution, worrying concentrations, risk quotients values, and resistance to removal treatments. Gaps in knowledge, data and information reported in this review provide a valuable source for managing AMR in WWTPs.

The prevalence of antibiotics in wastewater poses risks to human and animal health, contributing to antimicrobial resistance. Although various antibiotic removal methods exist, microalgae-based technology presents a cost-effective and eco-friendly alternative; however, limited research on its long-term integration in semi-continuous wastewater treatment trials hinders our understanding of its potential effectiveness. This investigation explored the antibiotic removal capabilities of the microalga Auxenochlorella protothecoides in photobioreactors with synthetic wastewater under semi-continuous conditions over one month. Additionally, the study assessed the impact of seven commonly used antibiotics (ciprofloxacin, clarithromycin, erythromycin, metronidazole, ofloxacin, sulfamethoxazole, and trimethoprim) on the microalgal system regarding growth, nutrient removal, and biomass productivity. The microalga effectively removed antibiotics, achieving maximum removal efficiencies ranging from 45.8% to 70.1% over 3-4 days of exposure. Remarkably, antibiotics stimulated algal growth, resulting in an 11.0% increase in biomass. Nutrient removal also improved significantly; ammonium removal rose from 78.0% to 86.4%, and phosphate removal increased from 85.1% to 90.3%. Furthermore, the biomass composition showed notable enhancements, with increases in pigments (12.9%), lipids (20.6%), proteins (45.8%), and carbohydrates (50.6%). These findings highlight the potential applicability of A. protothecoides as a valuable addition to conventional wastewater treatment plants. The study emphasises the importance of considering antibiotic presence in microalgae-based wastewater treatment technologies, as these compounds can have a stimulatory effect that enhances both growth and nutrient removal efficiency. Overall, this research contributes to the development of more effective strategies for managing antibiotic pollution in wastewater.