Antibiotics are used widely in human medicine, veterinary medicine, and agriculture. However, a portion of these compounds is excreted by treated organisms, entering water bodies through hospital effluents, domestic sewage, and agricultural waste. Furthermore, pharmaceutical production and improper disposal contribute to environmental contamination. The presence of antibiotics in the environment can have highly adverse consequences, such as the development and dissemination of bacterial resistance, reducing the effectiveness of antibiotics in treating infections. Several techniques are available for treating antibiotic contamination in water, including physical, chemical, and biological processes. The variety of techniques allows adaptation to the specific conditions of each case, selecting the most effective and cost-effective method considering the available infrastructure.
1. Introduction
Contemporary society faces various environmental challenges related to toxic pollutants and their dissemination in the environment
[1,2][1][2]. Aquatic ecosystems play a crucial role in sustaining life on the planet and represent the primary destination for various contaminants. Furthermore, the availability of potable water is declining, primarily due to human activities
[3]. The rapid advancement of agriculture and industry has significantly contributed to the release of pollutants into aquatic systems, posing threats to marine life and human health
[4]. Projections indicate that by 2030, the planet could face a global water deficit of around 40%, driven by the degradation of the quality and quantity of water resources
[5]. Discharge of industrial effluents and urban wastewater has also exacerbated water pollution, emphasizing reusing these waters as a viable alternative
[1,6][1][6].
Simultaneously, antibiotics in the environment have become a growing concern due to potential impacts on human health and aquatic ecosystems
[7]. Antibiotics are used widely in human medicine, veterinary medicine, and agriculture. However, a portion of these compounds is excreted by treated organisms, entering water bodies through hospital effluents, domestic sewage, and agricultural waste
[8,9][8][9]. Furthermore, pharmaceutical production and improper disposal contribute to environmental contamination. The presence of antibiotics in the environment can have highly adverse consequences, such as the development and dissemination of bacterial resistance
[10], reducing the effectiveness of antibiotics in treating infections
[4,11][4][11]. Besides the financial costs, antibiotics pose a significant risk to humans and other organisms in the environment
[12].
Given these concerns, it is essential to develop remediation strategies to minimize the presence of antibiotics in the environment and ensure water quality
[13]. Several techniques are available for treating antibiotic contamination in water, including physical, chemical, and biological processes
[14,15,16,17,18][14][15][16][17][18]. The variety of techniques allows adaptation to the specific conditions of each case, selecting the most effective and cost-effective method considering the available infrastructure. Additionally, the search for more effective water treatment methods has been a central goal for experts in the field
[19]. Advanced oxidative processes, such as photocatalysis and the Fenton process, have emerged as practical solutions to mitigate the impacts of human activities on water
[20].
2. Antibiotic Classes and Negative Effects on the Environment
Antibiotics are crucial in combating bacterial infections and are categorized based on their mechanisms and specificities
[26][21]. Penicillin and cephalosporins are effective against Gram-positive and some Gram-negative bacteria, while macrolides treat respiratory and soft tissue infections
[27][22]. With a broad spectrum of action, tetracyclines are effective against various bacteria but pose risks like photosensitivity and bacterial resistance
[26][21]. Quinolones, such as ciprofloxacin, are potent but restricted due to safety concerns, while sulfonamides and glycopeptides are used for specific infections
[28][23]. The indiscriminate use and inadequate disposal of antibiotics contribute to environmental pollution, fostering bacterial resistance and posing a significant global health challenge
[7]. In addition, antibiotic residues disrupt ecosystems, impacting wildlife health and facilitating the horizontal transfer of resistance genes
[11]. The environmental impact extends to non-target organisms
[11], affecting aquatic life
[29][24] and soil health, necessitating responsible antibiotic use and effective disposal strategies to minimize these consequences
[30][25].
Figure 1 shows possible transformation and migration pathways for the antibiotics in the water environment and soil. Thus, it is vital to adopt responsible antibiotic use practices in both human and veterinary medicine. In this sense, effective disposal strategies, such as the appropriate treatment of effluents and improving techniques for remediating antibiotics in the ecosystem, are essential to minimize the environmental impact. Therefore, the following topic addresses and discusses the leading technologies for remediating antibiotics in the environment.
Figure 1.
Possible transformation and migration pathways for the antibiotics in the water environment and soil.
3. Antibiotics Remediation Technologies
Figure 2 shows a schematic diagram of the various processes used to treat wastewater contaminated with antibiotics and other emerging pollutants. Physical remediation technologies involve several techniques, such as, adsorption and membrane separation
[14]. Chemical technologies use chemical reactions to degrade antibiotics or convert them to less toxic compounds, for example, ozonation and photocatalysis
[33][26]. Biological processes applied in the remediation of antibiotics involve the use of microorganisms, such as bacteria and fungi, which may metabolize and degrade pollutants
[28][23]. It is important to emphasize that antibiotic remediation technologies must be adapted to the specific characteristics of each contamination scenario, considering factors such as antibiotic concentration, environmental conditions, and technical and economic feasibility
[34][27]. Furthermore, continuous research and development of new technologies are needed to improve the efficiency and sustainability of treatment processes. In this topic, the leading antibiotic remediation technologies, highlighting the process performance, limitations, and recent scientific advances in the area, providing a comprehensive view on the subject, and demonstrating the potential of technologies to mitigate contamination by antibiotics in water, were explored.
Figure 2. A schematic of the various processes used to treat wastewater contaminated with antibiotics and other emerging pollutants.
3.1. Physical Techniques
There are several physical techniques used to remove antibiotics from contaminated water
[15]. The methods aim at the physical separation of antibiotic compounds from the aqueous medium and allow the recovery of treated water with lower concentration or without the contaminant. The main physical techniques reported are filtration, adsorption, sedimentation, flotation, and membranes. Filtration is commonly used to remove solid particles and dissolved substances from water
[35][28]. The process can be performed by filters made of different materials, such as sand. In addition, filtration can be carried out in several stages, applying filters with different porosity to remove other particles of various sizes
[36][29]. Therefore, filtering membranes are used in techniques such as microfiltration, ultrafiltration, and reverse osmosis. Membranes usually have controlled size pores that allow water to pass through but retain larger particles and compounds, including antibiotics
[37][30]. The application of pressure or vacuum can enhance the water flow through the membranes and remove unwanted compounds.
Treatment of water contaminated with several classes of tetracyclines applying the coagulation and filtration process with granular activated carbon has been reported
[15]. Both approaches were suitable for antibiotic removal depending on the type of antibiotic studied. However, filtration with granular activated carbon was relatively more effective with tetracycline, doxycycline hyclate, and chlortetracycline hydrochloride compared to coagulation treatment, which presented greater difficulty in removing these compounds. A filtration matrix made of a new composite based on macroporous metal-polyphenol and melamine foam was tested for tetracycline removal
[16]. The matrix removed virtually 100% of the pollutant in wastewater within 30 min. In addition, the filtration membrane showed an excellent ability to reuse and remove tetracycline in milk and dairy manure wastewater through a dynamic adsorption system.
Adsorption is a process in which compounds present in water adhere to the surface of a material called adsorbent
[9]. Materials such as activated carbon, zeolites, and ion exchange resins are often used to adsorb antibiotics in water
[38][31]. Adsorption is quite effective in removing organic compounds and can be combined with other techniques to improve treatment efficiency. Biochars produced from three raw materials (biosolids, cattle manure, and spent coffee grounds) were applied in low or high concentrations to remove seven antibiotics
[14]. All biochars used, even at low concentrations, efficiently removed more than 70%. Biochars applied at a high dose showed an excellent rate of rapid (5 min) and complete removal of tetracycline, erythromycin, and clarithromycin. However, the application of biochar to remove ofloxacin and sulfamethoxazole was ineffective. Nanostructured biochar produced from pomegranate peels showed promising potential for ciprofloxacin removal
[39][32]. The adsorption capacity of the nanostructured was about 26.85 times higher than bulk pomegranate peels. Furthermore, the study for ciprofloxacin removal from real effluents using batch reactor and fixed bed was 89.94% and 84.74%, respectively.
Sedimentation is a gravity-based process that effectively separates solid particles and dissolved compounds from water. It is widely used in wastewater treatment plants where contaminated effluent can settle, allowing the particles and compounds to naturally separate and accumulate within the tank. Finally, the clarified water can be easily separated from the top. The combined process of polyferric sulfate coagulation, Fenton, and sedimentation was applied to treat non-degradable antibiotic fermentation wastewater
[40][33]. The sedimentation process was crucial for removing pollutants right after treatment with the Fenton process at neutral pH. Overall color removal, chemical oxygen demand, and suspended solids reached 97.3%, 96.9%, and 86.7%, respectively. Therefore, applying combined processes may be a suitable way to treat wastewater from different fields, for example, the pharmaceutical industry. The application of the flocculation process may be an interesting strategy for the removal of antibiotics from water. However, most conventional flocculants are not effective. Therefore, scientific efforts have been applied to produce new flocculants. Fabrication of a flocculant based on a thermosensitive and cationic organic polymer was employed to remove antibiotics. The removal of levofloxacin and tetracycline using the developed flocculant was 68.71% and 66.83%, respectively
[41][34].
Flotation is a technique in which microbubbles of air or other gas are applied to the water so that adsorbed particles or compounds attach to the bubbles and float to the surface where they can be separated. Flotation is particularly efficient at removing organic compounds, e.g., antibiotics. The application of a new system consisting of modified dissolved air flotation and self-excited oscillating pulsed cavitation-impinging processes was tested for removing antibiotics, microplastics, and antibiotic resistance genes
[2,42][2][35]. The treatment application with only self-excited oscillating pulsed cavitation impinging promoted the removal of more than 97% and 100% of antibiotics and antibiotic resistance genes, respectively. The combined system removed virtually all antibiotics, 99.2%. Some physical techniques commonly used to remove antibiotics from water have been discussed in this topic. It is important to emphasize that the appropriate approach depends on the specific characteristics of the contaminated water, the concentrations of antibiotics, and the required performance. Furthermore, the combination of different physical techniques has been adopted to maximize the efficiency of the removal process.
3.2. Chemical Techniques
Several chemical techniques may be used to remove antibiotics from water
[34,43][27][36]. The methods involve chemical reactions that aim at the degradation, transformation, or removal of compounds present in the aqueous matrix. The main chemical techniques used to treat wastewater containing antibiotics are advanced oxidative processes, chlorination, and chemical precipitation
[43][36]. Advanced oxidation techniques involve the application of strong oxidants, for example, hydrogen peroxide, ozone, or potassium persulfate, to oxidize and degrade the compounds
[44,45][37][38]. The presence of oxidants leads to the production of highly reactive free radicals, which attack and break the chemical bonds of pollutants, transforming them into less toxic or completely inactive products. However, the ideal form of an advanced oxidative process is the conversion of pollutants into water and carbon dioxide
[22][39].
Additionally, chemical reduction processes can reduce some antibiotics to be less toxic. The addition of reducing agents, such as sodium bisulfite and zero-valent iron, may reduce inactive or less harmful forms of antibiotics from reacting with pollutants
[46][40]. The presence of two oxidants, hydrogen peroxide, and peroxydisulfate, in a photocatalytic treatment based on metal–organic structures using Basolite F300 was investigated in the degradation of lincomycin
[17]. The presence of both oxidants demonstrated that the process was highly effective, with potentiation possibly occurring through heterogeneous Fenton-type reactions. The use of a zeolitic iron molybdate-based octahedral metal oxide for the degradation of ciprofloxacin together with hydrogen peroxide was reported
[47][41]. Treatment with metal oxide and hydrogen peroxide resulted in the removal of the antibiotic in neutral and weakly alkaline water matrices (78%; 5 h).
Chlorination is a process in which chlorine is added to water for disinfection and removal of contaminants
[48][42]. Chlorine reacts with compounds in the water, oxidizing them and inactivating antimicrobial activity. However, chlorination may form highly undesirable by-products, such as trihalomethanes, which may pose risks to human health. A study investigated the chlorine degradation of two typical macrolide antibiotics, erythromycin and roxithromycin, and identified the transformation products formed
[49][43]. The chlorinated by-products of erythromycin and the reduced hydroxylation products of roxithromycin exhibited greater ecotoxicity than the respective parent compounds. However, algal growth inhibition assays showed that the overall ecotoxicity of the chlorinated mixture of erythromycin or roxithromycin was lower than that of the antibiotics before chlorination. The chlorination process must be thoroughly evaluated before being implemented in real wastewater treatment plants, as harmful substances may be formed for the ecosystem.
Heterogeneous photocatalysis is a widely applied process that uses light energy to trigger chemical reactions
[26][21]. In heterogeneous photocatalysis, a catalyst such as titanium dioxide is added to water contaminated with antibiotics. Once the catalyst is activated by light, reactive oxygen species are generated to oxidize and degrade the substances. Hafnium oxide nanohybrids with separate incorporation of ruthenium and platinum nanoparticles were applied in the photocatalytic treatment of nitrofurantoin and ciprofloxacin
[50][44]. Both nanohybrids showed complete removal of the two antibiotics in a short time.
Furthermore, the degradation achieved in the photocatalytic process was predominantly governed by hydroxyl radicals through oxidation. The preparation of carbon nitride modified by nitrogen vacancies and oxygen replacement was applied in the degradation of tetracycline, ciprofloxacin, and sulfadiazine under visible light irradiation
[51][45]. The modified carbon nitride showed the degradation activity of all studied antibiotics compared to the unmodified material, demonstrating great potential for application in real conditions.
Perovskite LaNiO
3 co-substituted by Ce and Cu elements with enhanced photocatalytic performance for the degradation of the norfloxacin was reported
[52][46]. The photodegradation capacity and the TOC removal efficiency were almost two times higher than that of pure LaNiO
3. As per the authors, incorporating Ce and Cu as partial substitutes for La and Ni in perovskite materials proves to be a straightforward method for enhancing the photocatalytic performance in water treatment, particularly in the degradation of antibiotics.
A novel catalyst composed by ultrathin aurivillius perovskite Bi
4Ti
3O
12 nanosheets and typical perovskite LaCoO
3 particles was developed
[53][47]. The authors assert that this novel composite catalyst has demonstrated remarkable catalytic activity and impressive stability in the degradation of tetracycline, achieving an efficiency of 87.8%. Furthermore, even after undergoing four cycles, the catalyst’ss activity remained considerable at 78.4%.
Table 1 shows other reported works that applied perovskite oxides in the degradation of antibiotics.
Table 1.
Some reported work on the application of perovskite oxide for antibiotic degradation via the photocatalytic process.
]. Also, another promising approach is the catalytic oxidation of antibiotics utilizing hybrids composed of perovskite oxide-based materials and biological enzymes. Perovskite oxides, known for their unique structural and catalytic properties, are integrated with biological enzymes to create synergistic hybrid systems capable of efficiently degrading antibiotics. This interdisciplinary strategy harnesses the catalytic prowess of perovskite oxide materials and the specificity of biological enzymes, enhancing the overall efficacy of antibiotic oxidation processes. This novel avenue holds great potential for addressing antibiotic pollution, offering a sustainable and tailored solution to mitigate the environmental impact of these pharmaceutical compounds. To date, few studies have explored this approach
[59,60,61][53][54][55]. Exploring such hybrid systems contributes to advancing
ourthe understanding of catalytic oxidation mechanisms. It paves the way for the development of environmentally friendly technologies in the realm of wastewater treatment and antibiotic remediation. Finally, it is essential to consider that the appropriate chemical technique depends on the properties of the antibiotics present in the water, the environmental conditions, and the quality of the treated water which should be achieved by ecological regulations. It is also important to evaluate and control the possible by-products or residues generated by chemical processes to ensure the safety and sustainability of treatment of wastewater contaminated with pharmaceuticals.
3.3. Biological Techniques
Biological techniques have been widely used to remove antibiotics from contaminated water, mainly taking advantage of the ability of microorganisms to degrade and metabolize the compounds
[62][56]. Some of the main biological techniques employed are bioremediation, phytoremediation, and biofiltration
[63][57]. Bioremediation is a process that uses microorganisms, such as bacteria, fungi, and microalgae to degrade the antibiotics in water. Microorganisms have enzymes capable of breaking the chemical bonds of antibiotics and converting them into products with less or no toxicity
[63][57]. Bioremediation can be carried out in biological reactors or treatment ponds, where microorganisms can be cultivated and maintained under suitable conditions to optimize the degradation of antibiotics. The activated sludge process is another biological technique widely used in wastewater treatment
[62][56], including effluents contaminated with antibiotics. In this process, microorganisms are mixed with contaminated water in an aerobic reactor, where they feed on the organic compounds present and degrade them through metabolic processes, eventually leading to the separation of the sludge from the treated water, which removes the pollutants
[64][58].
Removal of oxytetracycline through a bioremediation system has recently been reported
[65][59]. The bioremediation system contained an organism isolated from oxytetracycline-enriched activated sludge,
Achromobacter sp., which showed the ability to remove the studied antibiotic via co-metabolic biotransformation. The microorganism was isolated in alginate, and the developed system showed significant removal of more than 60% of the pollutant with a hydraulic retention time of 10 h. Bioremediation mediated by microalgae and a microalgae–bacteria consortium for ciprofloxacin treatment was also evaluated
[63][57]. The maximum ciprofloxacin removal efficiencies by the pure microalgae and the consortium were 87.5% and 96.1%, respectively. The presence of symbiotic bacteria in the consortium improved ciprofloxacin biodegradation by reducing microalgae cell damage and accelerated the rate of antibiotic elimination by secreting fulvic acid-like compounds. Also, nitrogen-fixing bacteria in the microalgae–bacteria consortium suggested that improved biodegradation may be associated with nitrogen co-metabolism.
Phytoremediation involves using plants to remove compounds from a polluted system, such as water contaminated with antibiotics
[66,67][60][61]. Some plant species may absorb and metabolize drugs through root systems. The acting plants act as “living filters”, where the plants capture and degrade antibiotics
[68][62]. Phytoremediation may be used in systems such as built-up wetlands or agricultural areas to treat water contaminated with antibiotics. Phytoremediation may generally be categorized into phytoextraction, phytostabilization, phytovolatilization, phytofiltration, and phytotransformation
[68][62].
Figure 3 illustrates a scheme with the main types of reported phytoremediation.
Figure 3. Scheme with the main types of reported phytoremediation.
Substrate-free hydroponic microcosms of
Myriophyllum aquaticum were used to evaluate the phytoremediation potential of water contaminated with antibiotics and copper
[28][23]. Efficient antibiotic removal was achieved by the hydroponic microcosm of 88–99%, 83–99%, and 99% for tetracycline, oxytetracycline, and chlortetracycline, respectively. The uptake and metabolism of clarithromycin and sulfadiazine in lettuce under controlled hydroponic conditions were also reported
[69][63]. Concentrations of clarithromycin and sulfadiazine reached 1629 g·kg
−1 and 683 g·kg
−1 in lettuce leaves, respectively, and 4977 g·kg
−1 and 24,599 g·kg
−1 in lettuce roots, respectively. Phytoremediation has been used widely for removing pollutants from soil and water, offering significant environmental benefits. However, it is vital to consider some potential hazards associated with phytoremediation, particularly concerning human exposure. The main hazards reported may be related to the accumulation of pollutants in plants and the release of toxic by-products into the environment.
Biofiltration is another biological technique that uses a biologically active filter medium to remove pollutants from the water that must be treated. The filter medium is colonized by microorganisms capable of degrading antibiotic compounds
[35][28]. Contaminated water passes through the filter medium, in which the microorganisms adhered to the medium carry out the degradation of the pollutants. Biofiltration is considered efficient in removing organic compounds and has been successfully applied in the treatment of water contaminated with antibiotics
[70][64]. Furthermore, biological oxidation is another process that combines microorganisms and chemical oxidation to degrade antibiotics. Microorganisms are used to metabolize antibiotics, while complementary chemical reactions contribute to the degradation of the compounds
[65][59]. Biological oxidation is an approach that combines the benefits of biological and chemical techniques, improving the efficiency of antibiotic removal in the aqueous medium. Biological techniques offer numerous advantages, such as the use of natural processes, the reduction of unwanted by-products, and the efficiency of removing antibiotics from contaminated water
[71][65]. However, the need for proper control of operating conditions and careful selection of microorganisms and plants to ensure the efficiency and safety of the remediation process is critical to achieve satisfactory process performance. In general, the excellent choice of technique for the type of effluent to be treated and the conditions needed to reach the concentration of the pollutant are vital for the success of the treatment.
Table 2 shows the performance comparison of several techniques reported for treating drug-contaminated systems. Thus, studying the treatment and knowing about the risks it also poses to the ecosystem, for example, the generation of by-products more toxic than the original, becomes a prerequisite for implementing any remediation process.
Table 2.
Performance of different techniques applied in the drugs removal.
Chemical precipitation involves adding specific chemicals to contaminated water to form insoluble compounds. Insoluble compounds may include complexes with antibiotics, which precipitate and can be removed by sedimentation or filtration. Chemical precipitation is often combined with other treatments to increase removal efficiency. The application of portlandite aqueous carbonation in removing amoxicillin, ceftriaxone, and cefazoline was recently reported
[57][51]. The treatment showed the best removal rate for amoxicillin, followed by cefazoline and ceftriaxone. Another study prepared a series of two-dimensional catalysts (LFCO/Ti
3C
2−x) by dispersing perovskite on layered Ti
3C
2 for a microwave-combined peroxymonosulfate-catalyzed degradation of ciprofloxacin
[58][52
While antibiotic remediation technologies are pivotal in addressing antibiotic contamination in water, pursuing more effective and sustainable methods remains a top priority. The escalating use of antibiotics in various sectors, including human medicine, veterinary medicine, and agriculture, has heightened their presence in our aquatic ecosystems, giving rise to concerns regarding their impacts on human health
[30,77][25][71]. Despite observing remarkable advances in water treatment techniques, many of these approaches encounter significant challenges, such as prohibitive costs and adverse environmental repercussions. Consequently, the scientific community has increasingly focused on discovering more efficient and sustainable strategies to grapple with this intricate issue.
In this context, the application of perovskite-based materials has emerged as a promising prospect
[24,78][72][73]. As
wthe researche
rs delve into the intricacies of antibiotic remediation,
wethe researchers shift
ourthe attention toward the transformative potential offered by these materials. Perovskites are renowned for their distinctive crystal structure and catalytic properties, rendering them ideal candidates for purifying water contaminated with emerging pollutants
[79][74]. The crystalline structure allows for the incorporation of metal ions and the presence of chemical defects, enhancing their catalytic prowess. Moreover, perovskites exhibit robust thermal and chemical stability, rendering them highly appealing for deployment in demanding water treatment environments
[80][75]. By exploring this topic,
wthe researche
rs will present how perovskites promise to revolutionize the treatment of antibiotic-contaminated water and other emerging pollutants, highlighting a new era of unparalleled efficiency and sustainability.