Large amounts of farmyard manure (animal urine and feces together with contaminated bedding material) and/or slurry (urine, feces, and washing-down water) are generated on livestock farms where animals are housed. Both can be used as an immediate organic matter supplement and fertilizer or kept in manure pits for later use (Velagaleti et al., 2003). Although there is no information on the fate of the degradation products, sulfonamides, aminoglycosides, lactams, and macrolides that have half-lives of 30 days are expected to be considerably degraded during manure/slurry storage. Ivermectin, tetracyclines, and quinolones, on the other hand, have longer half-lives and are therefore probably more persistent (Boxall et al., 2004). On the other hand, enormous amounts of farmyard manure and/or slurry are produced on livestock farms. Typically, this is collected and stored in manure pits for later application or applied to the ground right away. Slurry can be kept for a long time in storage. The time for storage of manure and slurry on an average is usually between 0 and 48 months with an average of 6 months (Gros et al., 2019).

Aerobic soil biodegradation is the primary method by which veterinary drugs are broken down in soils. Different medications degrade at different degrees in soil, and their t ½ can range from days to months. ‌In a study conducted by Topp et al. (2016), the half-life of azithromycin in soil was 12.8 days with the application of azithromycin at concentration 10 mg/kg soil. According to Liu et al. (2015), chlortetracycline was degraded in 4.7 days for 100 mg/kg of soil. A study conducted on soil from wheat field in china by Duan et al. (2017), reported that ofloxacin was degraded 85.6 and 87.3% with 10% compost and 10% compost with 2% of biochar. Oxytetracycline was degraded 86.6, 89.6, 93.7, and 95.4% at concentrations of 1, 3.6, 10, and 30 mg/kg of soil (Ma et al., 2016). Environmental factors that affect the degradation of veterinary medicines include temperature, pH, soil type, soil-organic carbon, nutrient conditions, and the presence of degrading bacteria that have evolved to destroy classes of medicine (Ingerslev et al., 2001). Other modes of chemical breakdown and depletion, such as soil photolysis and hydrolysis, may be significant as well, subject to the nature of the chemical. Since photodegradation is only likely to take place in the top layer of soil, farming practices including the depth and time of any plowing will have an impact on how long photodegradable compounds survive in the environment. In the topsoil layers, breakdown of byproducts of both photolytic and hydrolytic breakdown procedure may go through aerobic biodegradation (Ingerslev et al., 2001). A veterinary drug may deteriorate, leach into groundwater, be transferred to surface waters, or partition to soil particles once it has reached the soil. The weather at the time of application will have an impact on behavior to some extent. The ability of veterinary drugs to bind to soils varies greatly. As a result, there are significant differences in the mobility of several veterinary pharmaceuticals. Variations in soil-organic carbon cannot account for the large differences in distribution of chemical in various soils. In the case of carbadox, the highest known organic-carbon normalized sorption coefficient is around two times higher than the lowest documented value. The fact that several veterinary medications are ionizable around their pKa values while in the natural pH range of soils, helps to explain these significant discrepancies in sorption behavior. Therefore, drugs can exist in the environment as negatively charged, neutrally charged, zwitter ionic charged, and positively charged organisms. Depending on the species, interactions with soil may take the form of hydrophobic interactions, hydrogen bonds at the surface, electrostatic attraction, or surface bridging.

Wastewater treatment plant effluent, are the main sources of contamination by veterinary medicines mostly antibiotic in the environmental compartments mainly surface and underground water (Ezzariai et al., 2018). Due to water shortages driven upon by pollution, urbanization, climate change, and regional droughts, wastewater is frequently utilized to irrigate agricultural land in arid and semi-arid countries. As a result, wastewater is now a useful resource for irrigating agricultural land. Veterinary antibiotics can enter into the ecosystem by way of untreated wastewater discharge into water bodies as lakes and rivers, livestock grazing on land that has been sprayed with manure and slurry, or direct cattle deposition. The pathway of recalcitrant veterinary pharmaceuticals’ entry into environment can be understood with Figure 2. Antibiotics have the potential to build up in soil and then be absorbed by crops when untreated wastewater or animal dung is utilized for agricultural irrigation or fertilization (Pan and Chu, 2017). Monensin concentrations of up to 183 μg/kg have been found in fertilized soils, which could be sources of contamination for surface and groundwater. Antibiotic ionophore values of up to 9 μg/L have also been found in these soils (Delgado et al., 2023). Another route is aquaculture, or fish farming, which often involves the use of antibiotics to prevent or treat bacterial infections in fish populations (Carvalho and Santos, 2016). Antibiotics used in fish farms can enter the surrounding water bodies directly through excretion from treated fish, uneaten medicated feed, or improper disposal of unused medications (de Ilurdoz et al., 2022). Veterinary pharmaceutical residues undergo biotic (biodegradation) or abiotic (hydrolysis or photolysis) processes in water, which can lead to their deterioration and/or transformation. During dry seasons, these degradation mechanisms are more effective because a rise in temperature encourages microbial activity and photolysis (Charuaud et al., 2019). When parent veterinary pharmaceutical compounds degrade, several transformation products may be produced, for example in enrofloxacin and marbofloxacin, photolysis of the fluoroquinolones results in the synthesis of 5 and 2 photo-transformation products, respectively (Sturini et al., 2010).

In carrying antibiotics bioremediation, the bacterial population attains antibiotic resistant genes and some studies have shown positive correlation of antibiotic degradation potential with development of resistant genes (Zad et al., 2018). Bacteria are mostly employed in bioremediation. Bacteria utilized in bioremediation can live in harsh conditions; as they have an intrinsic ability to withstand and grow in adverse conditions (Ünal Turhan et al., 2019). Degradation of ciprofloxacin carried out by the mixture of Bacteroidia and Proteobacteria was proposed as well as dealkylation, deamination and C-F bond cleavage were some of the mechanisms by which ciprofloxacin was biodegraded (Liao et al., 2016; Sodhi and Singh, 2022). Chen and Xie (2018) proposed the microbial degradation of sulfonamide drugs in a sewage treatment plant. Several genera of microorganisms have been isolated from and characterized with efficient potential of sulfonamide drugs (Yang et al., 2021). The reactions by which these sulfonamide antibiotics degraded are oxidation, hydroxylation and acetylation. In a work by Zhang et al. (2020) using a model bacterium Lelliottia aquatilis and amoxicillin as a model β-Lactam antibiotic, improved detoxification of antibiotic wastewater was reported using a novel strategy of co-substrate combined with biological process. They have shown amplified activity of key enzymes, β-Lactamase, amidases, transaminase, and amide hydrolase, resulting in increased removal (95%) of amoxicillin with an increase of 60% from control (Zhang et al., 2020). A Paracoccus spp. isolated from sludge is studied for degradation of Penicillin G. Effective biotransformation of tetracycline by a novel strain Stenotrophomona smaltophilia DT1 (Leng et al., 2016) and Klebsiella sp. SQY5 (Shao et al., 2019) is reported.

In a recent study on bacteria mediated removal of antibiotics from wastewater sludge was studied for seven common antibiotics, namely oxytetracycline, tetracycline, chlortetracycline, amoxicillin, sulfamethazine, sulfamethoxazole andsulfadimethoxine. Twenty-four effective antibiotic degrading genera from both aerobic and anaerobic groups were identified from sludge, which had some well-known groups like Acinetobacter, Bacillus, Burkholderia, Corynebacterium, Klebsiella, Mycobacterium, Pseudomonas. However, they have also reported genera belonging to Achromobacter, Acidovorax, Castellaniella, Comamonas, Dechloromonas, Gordonia, Novosphingobium, Pandoraea, Sphingomonas, Treponema and Xanthobacter and some more as potential antibiotic degraders (Yang et al., 2020; Pathak et al., 2023). Batch fermentation using two different strains was found to be more effective than using a single strain. Additionally, these bacteria not only directly degraded antibiotics but also influenced the microbial community composition in the sludge, enhancing antibiotic degradation capacity (Yang et al., 2020).

The biodegradation of veterinary medicines by fungal laccases enzyme, with the most remarkable outcomes obtained with Trametes laccases. T. versicolor laccases, for example, have been demonstrated to bioremediate the antibiotics tetracycline, chlortetracycline, doxycycline, and oxytetracycline (Suda et al., 2012). Trametes polyzona, another species of the same genus, was also shown to breakdown tetracycline, as well as several β-lactam and quinolone antibiotics (Lueangjaroenkit et al., 2019). In a study by Tormo-Budowski et al. (2021), T. versicolor immobilized on lignocellulosic substrate in a stirred tank bioreactor also substantially eliminated 16 PhACs in synthetic wastewater and those naturally occurring in veterinary hospital wastewater, with removal rates of 95.7 and 85.0%, respectively; however, it increased the general toxicity of wastewater matrices after treatment. The scientists then used a similar set up in a trickled bed bioreactor which led to significant removal of veterinary pharmaceutical compounds and detoxify the wastewater too (Tormo-Budowski et al., 2021). Another white rot fungus, P. chrysosporium, was used in a plate bioreactor and was used in both sequence batch and continuous modes to eradicate carbamazepine at substantial clearance rates ranging from 60 to 80%. The study also found that the bioreactor was successful even after running continuously for over 100 days. Apart from white-rot fungus, Penicillium oxalicum, an ascomycete, was employed for diclofenac biological remediation in a bench bioreactor, with cytochrome P450 enzyme activation playing important roles in its bioremediation endeavor (‌Olicón-Hernández et al., 2017). Similarly, a trickle-bed bioreactor based on various fungal biomass immobilized on rice husks was recently shown to eliminate 88.6 and 89.8% of PhACs in synthetic and real wastewater, respectively, and it was also demonstrated that adsorption was an important physical phenomenon in the trickle-bed bioreactor’s veterinary drug elimination effectiveness (Tormo-Budowski et al., 2021). The study conducted by Lucas et al. (2016), assessed the efficacy of a fungal treatment as a substitute veterinary wastewater treatment method for the removal of 47 veterinary antibiotics that fall into seven categories: β-lactams, trimethoprim, tetracyclines, macrolides, metronidazoles, sulfonamides, and fluoroquinolones. Following the fungal treatment, 77% of antibiotics were eliminated, which is more as compared to traditional treatment methods.

In this context, a wide range of fungal enzymes, including laccases, peroxidases, cytochrome P450 mixed function oxidases, lipases, and esterases, have been identified for their functions in degrading veterinary medicines. Fungal enzymes have been characterized as having extraordinary potential in the degradation of veterinary active compounds found in a variety of waste streams under different conditions. As a result, they provide a more cost-effective and ecologically friendly alternative to traditional treatment procedures (Vaksmaa et al., 2023). This amazing capacity has been attributed to their resilience, which enables them to breakdown complicated chemical structures into simpler and less hazardous compounds that may be digested further by other microbes (Rathore et al., 2022). The fungal enzymes have been found to aid in the biodegradation of nonpolar and poorly soluble pharmaceutically active veterinary compounds and other xenobiotics in organic solvents (Espinosa-Ortiz et al., 2021). These enzymes alter and detoxify medicines by reduction, oxidation, hydroxylation, dehalogenation, dehydrogenation, deamination, formylation, and other processes (Ferrando-Climent et al., 2015; Narayanan et al., 2022).

Aquatic environments are the principal producers of algae. Because of their short development cycle, high sensitivity to aquatic pollutants, and ability to begin stress response mechanisms, they can be employed as ecological indicators to eliminate pharmaceutical pollutants (Rodríguez Sánchez et al., 2015). Recently, algae-based techniques have been widely used for the treatment of antibiotic-containing wastewater, providing numerous benefits such as efficient CO₂ fixation, low environmental impact, solar energy-driven activity, and the production of a potential raw material for the generation of biofuel or other high-value by-products (Xiong et al., 2021). For example, Nannochloris can entirely eliminate triclosan from water after 7 days of culture (Bai and Acharya, 2016), and it can efficiently digest diphenhydramine, memantine, and trihexyphenidyl, with average degradation rates of 88, 59, and 83%, respectively (Gojkovic et al., 2019). Organic pharmaceutical pollutants such as pesticides and antibiotics might be removed from groundwater using microalgae-mediated technology (up to 65%) (Ferrando and Matamoros, 2020). Similarly, Wang et al. (2021) introduced green alga Scenedesmus obliquus into wastewater to examine the erythromycin degradation routes. After 5 days of cultivation, the main mechanisms of erythromycin degradation in the microalgae-mediated system were biodegradation (including bioadsorption), hydrolysis, and photolysis, with biodegradation responsible for the highest proportion of removal (57.87%), followed by hydrolysis (34.13%), and photolysis (5%). It has previously been reported that Chlamydomonas sp. Tai-03 can entirely remove ciprofloxacin, with biodegradation accounting for up to 65.05% of clearance (Xie et al., 2020). According to Sutherland and Ralph, algae from the genera Scenedesmus, Chlorella, and Chlamydomonas are the species most explored and widely used for antibiotic bioremediation. Microalgae exhibit three primary pathways, bioadsorption, bio-uptake, and biodegradation for the bioremediation of pharmaceutical compounds, through which complex compounds undergo catalytic metabolic degradation. Furthermore, because microalgal cells are negatively charged and hydrophilic, lipophilic cationic chemicals show strong bioadsorption affinity with microalgae (Sutherland and Ralph, 2019). Ndlela et al. (2021) have demonstrated that Chlorella protothecoides and Chlorella vulgaris are effective in removing sulfamethoxazole (77.3 and 46.5%) and ofloxacin (43.5 and 55.1%) from samples containing 10 and 100 ppb concentrations, respectively.

Enzyme-mediated bioremediation is the process of cleaning polluted locations by using naturally existing enzymes found in microorganisms or plants to break down or eliminate harmful, unwanted, and resistant environmental contaminants (Karigar and Rao, 2011). Enzyme mediated bioremediation plays a significant part in the breakdown of antibiotics, which is crucial for the development of antibacterial resistance mechanisms. A correlation exists between the development of antibiotic-degraded enzymes, antibiotic-resistant genes, and antibiotic-resistant microorganisms. Study by Wencewicz (2019) shows that antibiotic resistance genes that express beta-lactamase enzymes and modify aminoglycosides existed long before the environment was exposed to synthetic antibiotics for medicinal purposes (Wang et al., 2020).

Enzymes are smaller than microbial cells, which makes it easier for them to come into touch with pollutants (Sharma et al., 2018). This helps with faster movement, more interaction with pollutants, and more focused, rapid, and efficient degradation or reduction to an acceptable or less dangerous form. The involvement of several enzymes (oxygenase, laccases, peroxidases, haloalkane dehalogenases, carboxylesterases, phosphodiesterase, lipases, and cellulases) in the breakdown routes of different pollutants is extensively described by Mansour et al. (2012). More operational condition flexibility is available when enzymes are applied rather than microorganisms or plants. They can be used in more severe environmental settings that are unsuitable for microbial populations, such as pollutant concentration, pH, temperature, and salinity (Cho et al., 2015). Compared to microbial or whole cell therapy, mass transfer limitation is significantly decreased with enzymatic treatment. Furthermore, enzymatic processes are simpler to manage than microbial remediation. Using enzymes for bioremediation is faster, less expensive, more accessible, and more focused than using plants or microorganisms. For microbial entire cells to develop at their best, air and nutrients must be introduced. Solvents and/or surfactants can improve bioavailability and immobilization (Demarche et al., 2012). From an enzymatic standpoint, it is also more practical than using whole cells. Additionally, compared to chemical and some forms of microbial remediation, enzyme-mediated biodegradation greatly minimizes the creation of hazardous byproducts. A further advancement in the miniaturization of analytical equipment with higher qualitative and quantitative quantification of chemicals of interest at site has been made by enzyme-based biosensors (Rocchitta et al., 2016).

Microbial electrochemical technologies stand out among cutting-edge water treatment methods as an effective and environmentally safe way to remove pharmaceutical pollutants in wastewater (Morris and Jin, 2007; McCormick et al., 2013). The advantageous features of microbiology, electrochemistry, and material science are combined in microbial electrochemical technologies, which offer viable methods for a variety of environmental engineering applications, such as resource recovery, wastewater treatment, bioremediation, and environmental monitoring. Microbial electrochemical technologies are often used in the bio-electro-Fenton process, microbial fuel cell, microbial electrolysis cells, and microbial desalination cell. METs have shown promise in recent years for the removal of stubborn pollutants and the rehabilitation of the environment because of their sustainable, effective, and energy-efficient characteristics (Xu et al., 2022). Microbial fuel cells (MFCs) harness the remarkable power of microbial communities to transform organic or inorganic compound oxidation into electricity through bio-electrochemical processes. This technology essentially taps into the natural metabolic activities of microbes, converting their energy-generating capabilities into a sustainable source of electric current (Gul et al., 2021; Nawaz et al., 2022). The primary source of METs, electrochemical active bacteria, can oxidize a variety of organic and inorganic materials found in sewage, organic waste, and wastewater used for dyeing. METs are a potential method for getting rid of drugs. Proteobacteria, Bacteroidetes, and Firmicutesemerge as the predominant organisms in mostmicrobial bioelectrochemical reactors (Hassan et al., 2021). Pseudomonas and Klebsiella are also a dominant genus in biocathodes for nitrofurazon degradation (Kong et al., 2017).

The first report on the use of METs for the removal of pharmaceutical pollutants, specifically antibiotics, has been reported by Wen et al. (2011). A specially designed two chambered microbial fuel cell was used for metronidazole degradation in wastewater treatment, and 85% removal of antibiotic was achieved within 24 h (Song et al., 2013). Still, several issues require attention. The main emphasis of future studies should be to support the environmentally friendly growth of METs during the treatment of pharmaceutical wastewater like constructing modeling tools to assess bio electrochemical systems. Other major concerns are to forecast treatment efficiencies of wastewaters containing pharmaceuticals under various operating conditions (Ortiz-Martínez et al., 2015) or combining METs with additional technologies, like a moving bed biofilm reactor (MBBR), to enhance the efficiency of pharmaceutical degradation (Chen F. et al., 2020; Chen M. et al., 2020). As pharmaceutical compounds can be highly variable in terms of their complex structure, continued research to determine their removal limits across different operational conditions becomes important. Some experimental electrochemical systems have shown promise of almost complete mineralization of antibiotic substances, e.g., microbial fuel cell coupled wetland constructs and microbial electrolytic cells and microbial fuel cell systems (Hassan et al., 2021). While significant progress has been made in understanding the antibiotic removal capacity of microbial electrochemical systems, it is still not enough considering the fast-growing environmental pollution.