# Removal of Antibiotics by Biochars: A Critical Review
###### Abstract  
Antibiotics are pharmaceuticals that are used to treat bacterial infections in humans and animals, and they are also used as growth promoters in livestock production. These activities lead to an alarming accumulation of antibiotics in aquatic environments, resulting in selection pressure for antibiotic resistance. Given that it is impractical to completely avoid the use of antibiotics, addressing the removal of antibiotics from the environment has become an important challenge. Adsorption methods and adsorbents have received particular attention because adsorption is highly efficient in the removal of low-concentration chemicals. Among the different adsorbents, biochars have shown promise for antibiotic removal, owing to their low cost and efficiency as well as their potential for modification to further increase their adsorption capacity. This review attempts to analyze the surface properties and ash contents of different biochars and to critically discuss the knowledge gaps in antibiotic adsorption. A total of 184 articles on antibiotic properties, adsorption of antibiotics, and biochar properties were reviewed, with a focus on the last 12 years. Antibiotic adsorption by pristine biochars and modified biochars was critically reviewed. Recommendations are provided for the adsorption of different antibiotic classes by biochars. antibiotics; biochar; tetracycline; surface area; ash content +
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antibiotics [8]. Reports have indicated that global antibiotic consumption increased by 65% between 2000 and 2015 [13] and by 46% between 2000 and 2018 [14]. The global consumption of antibiotics was estimated to be between 100,000 and 200,000 tons 21 years ago [3; 8; 15; 16]. Today, this figure is possibly much higher. It is also likely that, during the COVID-19 pandemic, therapeutic consumption of antibiotics was higher than in previous years [17]. It is expected that by 2030 total antibiotic consumption will increase by 67% for animal use [18] and by up to 200% for total consumption [8]. In recent years, the development of new antibiotics has not kept up with the occurrence rate of antibiotic-resistant bacteria [11]. New antibiotics have mainly been isolated and developed from soil microorganisms, particularly from bacteria of the actinomycte group [19], but this process seems to have faced a hiatus after the years between 1940 and 1960, known as the golden age of antibiotics discovery [19]. Because the discovery rate of new antibiotics has declined, known compounds have started to be rediscovered [5; 19]. New methods of antibiotic development are currently under research, including genome mining and editing of different bacteria [19], as well as the application of artificial intelligence to model antibiotic activity and screen potentially new antibiotics from structurally different molecules [20]. At the same time, measures have been taken worldwide to restrict antibiotic use, particularly in livestock production. However, it is unclear whether they will effectively reduce the concentration of antibiotics in the environment in the short or medium term, particularly in the low- and middle-income countries (LMICs) [21]. Because the world's population has risen exponentially in the last 100 years, global food consumption will likely increase in the foreseeable future, leading to increased use of antibiotics in livestock production if strict measures are not put into effect. The therapeutic use of antibiotics in both human and animal medicine is also a source of concern, because only 10-70% of the administered antibiotics are used by the body, with the rest being excreted and ending up in aquatic environments [8; 22; 23]. Data on the production volume of antibiotics are scarce. However, it has been reported that China alone produces more than 150,000 tons of antibiotics each year [24; 25]. Therefore, it is estimated that huge amounts of antibiotics are released to the environment each year, particularly into the water bodies.