Treatment Methods for Antibiotic Mycelial Residues: A Review

Abstract

The treatment of antibiotic mycelial residue (AMR) has emerged as a critical challenge hindering the sustainable development of the biopharmaceutical industry. As a representative hazardous solid waste generated during antibiotic manufacturing processes, AMR may pose substantial risks to environmental safety. This review elucidates the properties and hazards of AMR while systematically reviewing current mainstream treatment technologies. Building upon the elucidation of underlying mechanisms, it further examines the application bottlenecks and research progress associated with different techniques. Through a comprehensive understanding of existing research achievements, this paper proposes future development strategies and perspectives for AMR treatment, highlighting that integrated multi-technology treatment approaches may represent the predominant developmental direction in this field.

1. Introduction

Following Alexander Fleming’s landmark discovery of penicillin in 1928, the development and deployment of antibiotics have profoundly reshaped strategies for combating bacterial infections in humans [1]. Beyond therapeutic applications in human medicine, these agents are extensively employed as growth enhancers within agriculture, aquaculture, and livestock production [2]. As the world’s predominant antibiotic manufacturer, Chinese annual output surpasses 248,000 tons, encompassing more than 70 distinct antibiotic varieties and representing approximately 70% of production [3]. Significantly, Chinese facilities supply roughly 75% of the global penicillin industrial salts, 80% of cephalosporins, and an estimated 90% of streptomycin-class antibiotics globally [4].

Antibiotic manufacturing predominantly utilizes microbial fermentation, a process generating substantial quantities of organic solid waste termed antibiotic mycelial residue (AMR). This residue arises during the fermentation of substrates (e.g., starch, corn syrup, inorganic salts) and consists chiefly of spent mycelial biomass from the antibiotic-producing microorganisms, alongside metabolic byproducts, unconsumed nutrients, and residual antibiotic compounds [5]. Estimates based on a production ratio of roughly 10 metric tons of AMR per metric ton of antibiotic indicate that China’s yearly AMR generation exceeds 2 million metric tons [3,6].

Due to its high organic matter and moisture content, AMR is prone to fermentation during storage, producing malodorous gases containing compounds, such as pyridine and pyrrole, which severely impact local air quality [7]. The ecological risks posed by residual antibiotics are particularly critical. Aristilde et al. [8] investigated the ecotoxicological effects and toxicity mechanisms of fluoroquinolone antibiotics on photosynthetic organisms. Their findings demonstrated that fluoroquinolones disrupt energy transfer in chloroplasts of Spinacia oleracea, impairing photosynthesis and significantly inhibiting plant growth. In animal toxicological studies, β-diketone antibiotics have been demonstrated to inhibit superoxide dismutase activity in Danio rerio, resulting in elevated intracellular oxidative stress levels and oxidative damage to biomacromolecules, such as proteins and nucleic acids. This molecular damage progressively accumulates during embryonic zebrafish development, ultimately manifesting as significant teratogenic effects, including developmental abnormalities and morphological malformations [9].

Beyond the inherent chemical pollution from antibiotics, their usage may induce the emergence of antibiotic-resistant bacteria (ARB) and the evolution of antibiotic resistance genes (ARGs), posing latent threats to ecological equilibrium and public health security. The environmental half-lives of antibiotics vary significantly across different classes, ranging from just a few days for chloramphenicol and sulfapyridine to up to 300 days for compounds, like tetracycline [10,11,12]. This substantial variability dictates divergent environmental persistence and behavioral patterns, enabling certain antibiotics to remain biologically active in ecosystems over extended durations.

As a byproduct of antibiotic production and usage, antibiotic residues in AMR may trigger a series of complex biological chain reactions once exposed to the natural environment [13]. Specifically, residual antibiotics could induce selective pressure on bacteria, promoting the development of antibiotic resistance in both non-pathogenic and pathogenic organisms, thereby driving the generation of ARBs. The ARGs carried by these ARBs possess a unique transmission mechanism, capable of horizontal gene transfer and dissemination among bacterial populations through mobile genetic elements [14]. This genetic propagation mechanism transcends traditional vertical inheritance limitations, enabling rapid diffusion of ARGs within bacterial communities. Over time, the continuous accumulation and recombination of diverse ARGs significantly increase the likelihood of developing multidrug-resistant strains, potentially culminating in the emergence of superbugs with exceptional drug resistance [15]. To date, multiple bacterial species exhibiting acquired resistance to one or multiple classes of antibiotics have been identified in environmental settings [16,17]. Genomic sequencing and bioinformatics analyses of river sediments contaminated by antibiotic production effluents reveal distinct microbial community signatures: heightened activity of enzymatic systems mediating horizontal transfer of ARGs, coupled with significantly elevated abundance of resistance plasmids [18].

It is evident that the use of antibiotics and the cascade of complex issues it entails, particularly those related to ARB and ARGs, have emerged as critical challenges demanding urgent resolution. In 2002, China listed AMR in the Catalogue of Drugs Prohibited for Use in Animal Feed and Drinking Water (issued by the Ministry of Agriculture, Ministry of Health, and State Drug Administration) to eliminate potential food chain contamination risks stemming from inappropriate AMR use at the source. In 2008, AMR were formally incorporated into the National Catalogue of Hazardous Wastes (2008 Edition). This designation was further refined in 2016, categorizing them explicitly under the HW02 class (“Medical Waste”) in the updated National Catalogue of Hazardous Wastes (2016 Edition). The current Technical Policy for Pollution Prevention and Control in the Pharmaceutical Industry mandates that “mycelial waste residues from antibiotic and biopharmaceutical production” must undergo hazardous waste management, while stipulating that “antibiotic-containing wastewater with biosafety risks requires pretreatment to disrupt antibiotic molecular structures prior to discharge.” AMR decontamination constitutes a critical safeguard for ecological security [19].

It is noteworthy that AMR is not merely a waste requiring cautious disposal; from a resource utilization perspective, it contains substantial exploitable potential. As a byproduct of fermentation, AMR is rich in biodegradable organic materials, such as proteins and carbohydrates, which typically account for over 80% of its dry weight, and possesses the capacity to be converted into high-value-added products [20]. Thus, AMR possesses dual characteristics as both a solid waste and biomass resource. Achieving its safe and resource-efficient utilization is paramount for environmental protection and resource sustainability.

China has established international leadership in AMR treatment management [21]. While most countries predominantly rely on conventional disposal methods, such as landfilling or incineration, China has achieved large-scale detoxification and resource-directed valorization of AMR through the integrated implementation of technologies, including fermentation and composting [22,23].

Although existing reviews have documented AMR treatment technologies, they predominantly focus on the detoxification efficacy of specific methodologies while lacking comprehensive analysis and critical assessment of the broader technological landscape [24,25]. This review clarifies the compositional characteristics of AMR, systematically categorizes and summarizes current methods in the AMR treatment domain, evaluating the application potential and limitations of each approach. A comprehensive understanding of AMR treatment strategies will advance future research and facilitate the realization of ecological safety in practical applications.

2. Common Properties of AMR

AMR, a solid waste originating from antibiotic manufacturing, is distinguished by its elevated protein levels, considerable calorific value, and the presence of residual antibiotic compounds [4,6]. Freshly produced AMR exhibits high viscosity and moisture content, with water predominantly existing in a bound state within the mycelial matrix, which significantly hinders the efficiency of mechanical dewatering processes [26]. Furthermore, residual antibiotic concentrations in AMR commonly surpass 1000 mg/kg; the material also contains metabolic intermediates, organic solvents, calcium and magnesium ions, and various trace elements [27,28]. The principal characteristics of several prevalent types of AMR are detailed in

Table 1. Main characteristics of common AMR types.

Type		Antibiotic Concentration (mg/kg)	Moisture Content (%)	C/N	References
Beta-lactams	Penicillin	1000~2000	75~82	4.5~7.6	[29,30,31,32]
	Cephalosporin	7860	83~89	5.6~5.9	[33,34]
	Cephalosporin C	810~920	83~92	5.3~6.6	[6,20,35,36,37]
Macrolides	Erythromycin	185~2271	79~90	5.6	[38,39,40,41,42]
	Spiramycin	2110	65~90	4.9	[43,44]
	Avermectin	1208~2653	68~87	-	[26,45]
	Tylosin	15.3~8900	67~68	0.9~8.6	[46,47]
Aminoglycosides	Gentamicin	4500	97	8.48	[48,49]
	Streptomycin	5485	91	-	[50]
	Neomycin	4005~7500	12~50	8.8~9	[51,52]
Tetracyclines	Oxytetracycline	1012~7084	72~86	5.3	[53,54,55,56]
Others	Sulfathiazole	538	92	17.2	[57]
	Lincomycin	2157~14270	51~66	6.4	[58,59,60]

The “-” indicates that the content was not mentioned in the corresponding paper.

.

3. Treatment Methods for AMR

Based on distinct operational mechanisms, the treatment methods of AMR can be categorized into three classes: physical, biochemical, and thermochemical approaches (Figure 1).

• Physical methods focus primarily on modifying the inherent properties of AMR to improve solid–liquid separation efficiency and enhance its compatibility with subsequent processing stages, thereby facilitating more advanced treatment.
• Biochemical methods leverage microbial activity to achieve organic matter stabilization through mineralization, concurrently generating valuable products, such as humic acids or methane.
• Thermochemical methods employ high-temperature conditions to drive the cleavage of chemical bonds and the reorganization of molecular structures. This approach simultaneously achieves thorough contaminant destruction and the targeted conversion of the material into energy carriers, like syngas or bio-oil.

3.1. Physical Methods

3.1.1. Landfill

Within China’s current environmental regulatory framework, AMR is explicitly designated as hazardous waste. Mandated by pertinent legislation, AMR landfill disposal is restricted to facilities specifically engineered for hazardous waste containment. The inherent characteristics of AMR—notably its elevated moisture content and rich organic composition—necessitate pretreatment prior to landfilling. This pretreatment aims to reduce moisture levels and stabilize organic constituents, ensuring adherence to landfill entry standards.

The intricate landfill milieu, coupled with AMR’s distinct chemical properties, hinders its complete post-disposal degradation. Consequently, fermentation-induced secondary pollution occurs, posing latent threats to the soil, groundwater, and broader ecosystems. This scenario also intensifies the technical demands and costs of subsequent leachate management, significantly inflating landfill operational expenditures and sustaining elevated long-term maintenance costs [61]. Moreover, AMR harbors substantial recoverable nutrients. Direct landfill disposal without resource recovery constitutes inefficient utilization and squandering of valuable materials, fundamentally contradicting contemporary principles of circular economy and sustainable development. The significant land footprint required for landfills further compounds the issue, inflicting localized ecological harm and rendering large-scale AMR landfilling unsustainable and irrational over extended periods [3].

Therefore, when evaluated against criteria of technical practicality, environmental impact, resource recovery efficiency, and economic feasibility, landfill technology has not achieved broad acceptance or widespread implementation for AMR management.

3.1.2. Microwave Treatment

Microwave treatment, as a highly efficient physicochemical pretreatment technology, demonstrates significant advantages in enhancing the dewatering performance of AMR and improving the hydrolysis efficiency of biomass waste [68,69]. By generating an alternating electromagnetic field, microwaves induce the realignment of polar molecules within the biomass matrix. During this process, the continuous motion of polar molecules triggers intense intermolecular friction, which is subsequently converted into thermal energy. This thermal effect disrupts the floc structure, thereby increasing the solubility and hydrolysis efficiency of the biomass waste. Compared to conventional thermal methods, microwave pretreatment offers superior penetration depth, rapid heating rates, and higher energy efficiency, achieving enhanced dewatering performance with significantly reduced processing durations [70].

Cai et al. [69] systematically investigated the mechanistic principles and regulatory effects of microwave treatment on AMR dewaterability. Their findings demonstrated that microwaves not only degraded the AMR matrix and altered its particle size distribution but also effectively disrupted micro-floc structures, induced cell wall lysis, and promoted the substantial release of intracellular mucoid polymers (containing proteins, polysaccharides, DNA, etc.), thereby enhancing AMR dehydration performance. Z. Wang et al. [62] employed microwave-assisted wet torrefaction for pretreating avermectin mycelial residue, revealing that this process significantly modified the composition and structure of AMR and achieves 95% avermectin degradation. Post-treatment AMR exhibited a 40% increase in methane yield during anaerobic digestion (AD), reaching 327.9 mL/g volatile solids (VSs). Jiang et al. [48] further investigated the application of microwave-pretreated AMR in AD, exploring its effects on methane production mechanisms and antibiotic degradation processes. Their study indicated that through thermal effects (e.g., hydrogen bond cleavage and weakened van der Waals forces), microwave treatment modified the floc size, increased the soluble protein content, and consequently promoted the methane yield during AD. Additionally, post-microwave AMR demonstrates elevated humic acid-like substances and organic matter levels, suggesting potential as soil amendments [33]. However, even after microwave treatment, AMR may still induce elevated soil pH and electrical conductivity, adversely affecting seed germination [33,71].

It is crucial to underscore that while microwave technology yields promising results in diverse applications, the persistence risks of antibiotic residues and their potential environmental consequences warrant extensive research for thorough assessment. Furthermore, the effects of microwave parameters on different categories of AMR remain insufficiently characterized. To address these gaps, it is imperative to establish a multi-dimensional risk assessment framework grounded in life cycle assessment, which would provide robust theoretical underpinnings and technical safeguards to ensure the sustainable development and safe implementation of this technology [69,72].

3.1.3. Ionizing Radiation

Ionizing radiation technology employs γ-rays or electron beams generated by electron accelerators to treat contaminants, achieving pollutant degradation through dual photophysical and photochemical mechanisms. On one hand, high-energy radiation directly interacts with pollutants, cleaving chemical bonds within contaminant molecules due to its substantial energy deposition. On the other hand, when water molecules are irradiated, highly reactive species, such as hydroxyl radicals (·OH) and hydrated electrons (e_aq⁻), are generated, indirectly degrading pollutants via secondary reactions [73,74]. This technology presents distinct advantages for the detoxification and resource recovery of AMR, offering a viable route for sustainable waste management.

First, extensive studies have demonstrated that ionizing radiation can disrupt the molecular structures of organic compounds in AMR, enabling the efficient degradation of toxic organic pollutants and antibiotics [36,75,76,77,78]. A substantial body of experimental data confirms a clear positive correlation between irradiation dose and degradation efficacy within a rational dose range, where higher doses result in more pronounced degradation effects [57,78,79].

Second, ionizing radiation technology exhibits exceptional performance in eliminating ARGs. Pretreatment experiments utilizing γ-irradiation revealed significant enhancement in AD performance of cephalosporin C mycelial residue. Compared to standalone AD, the combined γ-irradiation and AD process resulted in a 100% enhancement in the removal efficiency of ARGs [20]. Irradiation studies on erythromycin thiocyanate mycelial residue demonstrated that 30 kGy γ-rays dosage eliminates 90~95% of macrolide-associated ARGs and degrades 56% of erythromycin, while not affecting the nutritional composition, such as the protein content, of AMR [57]. This outcome robustly demonstrates the feasibility of irradiated fermentation residues in meeting basic nutritional requirements for fertilizers, providing strong support for their subsequent resource utilization as agricultural amendments.

Third, ionizing radiation technology is capable of disrupting mycelial structures, thereby enhancing the fermentation performance of AMR. Yang and Wang [35] employed a coupled system of γ-irradiation and nanoscale zero-valent iron to enhance antibiotic degradation in deacetoxy cephalosporin C mycelial residue while boosting hydrogen production efficiency. The experimental results demonstrated that γ-irradiation disrupted the complex matrix of AMR, significantly elevating the soluble organic matter content. Concurrently, 98.6% of residual antibiotics were eliminated, mitigating their inhibitory effects on hydrogen-producing bacteria. This synergistic effect resulted in a 139.2% enhancement in hydrogen production yield.

As a highly promising approach, irradiation technology demonstrates exceptional tolerance to complex substrate conditions and inherently avoids secondary pollution risks associated with chemical additives by operating without catalysts. However, the technology is still in its developmental infancy. Key challenges remain unresolved in critical areas, including the elucidation of microscopic interaction mechanisms, optimization of process parameters, and scaling for industrial implementation.

3.2. Biochemical Methods

3.2.1. Aerobic Composting

Aerobic composting represents an established biochemical approach extensively applied for the stabilization and sanitization of organic wastes. During the aerobic composting process, organic matter undergoes gradual degradation through four distinct phases: heating, thermophilic stabilization, cooling/maturation, and humification. This transformation ultimately converts organic waste into humus-like substances, which can be utilized as organic fertilizer or soil conditioner [80,81].

In previous studies, aerobic composting has been recognized as an effective approach for treating AMR. This is attributed not only to its compatibility with the high organic content characteristics inherent in AMR, but also because composting, when integrated with appropriate pretreatment methods, can effectively degrade residual antibiotics within AMR systems [30,32,63,82]. Molecular characterization studies utilizing fluorescence spectroscopy revealed marked transformation features during the co-composting process of penicillin mycelial residue with sewage sludge. Dynamic monitoring data demonstrated that a 99.5% penicillin degradation efficiency was achieved after 12 days of composting treatment [30]. Addressing the resource utilization of tylosin fermentation residue, Yang et al. [46] proposed an integrated treatment strategy involving “high-temperature Coupled with oxidant pretreatment” prior to composting, followed by post-composting thermal treatment. The study demonstrated that under optimal pretreatment conditions, the tylosin concentration in AMR was reduced by 97.1%, with the tylosin content in the composted product falling below the detection limit (less than 1 mg/kg). These findings collectively demonstrate the high removal efficiency of aerobic composting technology for antibiotic contaminants.

Although pretreatment processes can remove the majority of residual antibiotics in raw AMR under most circumstances, the increased abundance of ARGs during composting remains challenging to completely prevent due to the complex interplay of multiple influencing factors. Yang et al. [83] observed a 1.17-fold increase in ARGs quantities compared to initial levels during co-composting of AMR with sewage sludge. Similarly, Gong et al. [54] reported a generalized upward trend of various ARGs subtypes during oxytetracycline fermentation residue composting, with maximum increases of 1548-fold for ARGs and 1449-fold for total integrons at the composting endpoint. These findings signify substantial risks associated with land application of AMR-derived compost, potentially impacting soil ecosystems and crop growth adversely. Furthermore, malodorous emissions generated during composting can deteriorate air quality and pose environmental hazards, including threats to human health and local ecological disruption [84].

Aerobic composting offers robust efficacy for AMR treatment, intrinsically suited to high-organic waste streams by converting them into humus-like fertilizers/amendments, aligning with circular economy goals. Despite partially degrading residual antibiotics, the persistent presence of these compounds in compost products, coupled with elevated abundances of ARGs, poses significant environmental risks of soil contamination when applied to agricultural land. Consequently, future innovation should prioritize: (1) incorporating pretreatment technologies to augment antibiotic and ARG removal, and (2) developing real-time monitoring systems for dynamic control of temperature, moisture, and aeration to optimize composting efficiency and mitigate ARG dissemination.

3.2.2. Anaerobic Digestion

Anaerobic digestion (AD) is a multistep biochemical conversion process wherein facultative bacteria and obligate anaerobes metabolize organic matter into methane, carbon dioxide, and other byproducts under anaerobic conditions [85]. Long recognized as promising for AMR treatment, this technology offers dual benefits: effective elimination of residual antibiotics alongside conversion of low-value AMR into valuable biogas and nutrient-rich digestate, enabling efficient resource recovery and circularity [45,86]. Crucially, akin to composting, AD obviates the need for AMR dewatering pretreatment, conferring significant cost advantages over conventional methods, like incineration and landfilling.

Ren et al. [64] directly utilized untreated erythromycin mycelial residue as a substrate for AD, conducting methanogenic potential and kinetic experiments under varying temperatures. Their results indicate that methane production peaked at 35 °C, with no significant inhibitory effects observed on anaerobic microorganisms—particularly methanogens—demonstrating the feasibility of employing antibiotic-containing erythromycin residue in anaerobic fermentation systems without prior antibiotic removal pretreatment. Yan et al. [49] investigated the anaerobic co-digestion of AMR with corn straw, revealing that the co-digestion system harbored a more diverse and functionally enriched microbial community structure. This attribute enhanced the stability of the methanogenic process while enabling effective degradation of ARGs within AMR. Zhong et al. [87] examined thermo-alkaline pretreatment’s impact on penicillin mycelial residue digestion. They found that it significantly increased soluble chemical oxygen demand (COD), suspended solids solubilization, and biodegradability, thereby enhancing biogas production and providing vital technical insights for process optimization.

However, practical implementation faces challenges. The inherently slow growth of anaerobic microorganisms necessitates protracted retention times, demanding large-scale reactor configurations that increase capital and operational costs while occupying significant space [88]. Furthermore, the process is highly sensitive to parameters, including the organic loading rate, pH, ammonia nitrogen concentration, temperature, and volatile fatty acid levels [89], imposing stringent operational control requirements. Additionally, malodorous hydrogen sulfide emissions during digestion present a notable environmental concern [90].

While technically advantageous for AMR treatment, AD’s large-scale deployment is hampered by its technological complexity and high capital intensity. Future efforts should concentrate on innovations, such as targeted functional microbial consortia acclimation, optimized multiphase reactor design, and intelligent monitoring systems, to surmount barriers to industrial application and enhance market competitiveness.

3.2.3. Biodegradation

Biodegradation treatment utilizes microbial enzymatic catalysis or insect-mediated metabolic pathways to decompose residual antibiotics and organic compounds in AMR, achieving concurrent detoxification and resource valorization. Compared to alternatives, this biological approach offers distinct value for AMR management due to its eco-friendliness and cost-effectiveness [2].

Screening specific environmental microbial strains for antibiotic degradation constitutes a promising avenue, supported by substantial evidence. Wang et al. [65] employed strains isolated from penicillin mycelial dregs to biodegrade penicillin, finding that Klebsiella pneumoniae Z1 exhibited the most superior degradation performance. When treating penicillin residues at a concentration of 300 mg/L, this strain achieved a removal rate exceeding 99% within 24 h. M. Wang et al. [60] isolated Clostridium sp. strain LCM-B from lincomycin mycelial dregs. After 10 days of incubation, the strain degraded 62.03% of lincomycin with an initial concentration of 100 mg/L. L. Zhang et al. [91] screened the yeast strain Galactomyces geotrichum from environmental samples, which exhibited high lincomycin degradation capability. Following 15 days of fermentation, it attained a degradation efficiency of 37% for lincomycin at an initial concentration of 5.012 ppb.

Notably, in addition to microorganisms, certain insect species demonstrate unique processing capabilities in the field of AMR management. Recent studies have revealed that black soldier fly larvae (BSFL), Hermetia illucens L. (Diptera: Stratiomyidae), exhibit tolerance to multiple antibiotics—including sulfonamides, oxytetracycline, and lincomycin—during their ingestion of organic waste [92,93]. Luo et al. [58] conducted an in-depth investigation into the biotransformation process mediated by BSFL, specifically focusing on its feasibility and practical efficacy in nutrient recovery and antibiotic reduction within lincomycin mycelial residues. The findings revealed that the growth and development of BSFL remained unimpaired even when exposed to a lincomycin concentration of 4500 mg/kg in the substrate, demonstrating exceptional tolerance to the antibiotic. Furthermore, after 12 days of biotransformation, an 84.9% degradation rate of residual lincomycin was achieved in the fermentation residues. These results indicate that the BSFL-mediated biotransformation process effectively accelerates lincomycin degradation in mycelial residues, offering a novel perspective and pathway for AMR treatment.

Biodegradation aligns with sustainable development principles, exhibiting minimal ecosystem disruption. Its relatively low cost supports large-scale implementation, showing broad prospects. However, ARG removal efficiency exhibits threshold limitations, and the environmental adaptability of functional strains and ecological risks of insect transformation byproducts merit intensified investigation via metagenomics and life cycle assessment. Future focus should include constructing synthetic microbial consortia, enhancing genetic editing capabilities, and integrating synergistic multi-technologies to overcome safety constraints and advance industrial application in AMR management.

3.3. Thermochemical Methods

3.3.1. Incineration

Current Chinese pollution control standards explicitly prohibit co-incineration of hazardous waste in municipal solid waste incinerators. However, a 2010 proposal addressing municipal solid waste incineration pollutants indicated that, given the thermochemical compatibility between AMR and municipal solid waste, co-processing in municipal solid waste incinerators is feasible under stringent operational controls. Specifically, AMR mass input must be limited to ≤5% of total incinerator capacity to ensure combustion efficiency and emission compliance [94].

Incineration, a high-temperature thermochemical conversion process, achieves AMR mineralization and detoxification via oxidative decomposition. Operating temperatures typically exceed 850 °C, ensuring complete decomposition of organic components and presumed elimination of antibiotics and ARGs [95]. This technology offers significant engineering advantages, including rapid processing rates and substantial volume reduction (>95% mass reduction) [3]. Residual ash undergoes final disposal via sanitary landfill [96].

Additionally, the heat generated during incineration can be recovered for electricity generation or district heating, enabling resource recycling. Du et al. [97] conducted an in-depth investigation into the co-combustion characteristics of coal blended with varying proportions of bio-fermentation residue, performing kinetic analysis. Their findings revealed that BR contains combustion-favorable components. Compared to coal, BR exhibits enhanced ignition properties but reduced burnout performance. Based on these results, the optimal blending ratios for BR in coal-fired systems are recommended as: 10.1~42.2% for grate furnaces, 90.7~100% for fluidized beds, and 3.1~86.3% for pulverized coal combustion. Complementing this, Hong et al. [66] demonstrated that increasing AMR blending ratios significantly improves the ignition characteristics, burnout performance, and comprehensive combustion characteristic index of mixed fuels. These findings conclusively validate the positive effects of AMR addition on coal combustion processes.

Current incineration technology faces two primary constraints in practical applications. First, the generally high moisture content of AMR necessitates pre-treatment dehydration prior to incineration. However, the inherent bio-colloids or mycelial structures in raw AMR exhibit strong water-binding properties, rendering conventional mechanical dewatering methods (e.g., centrifugation, compression) ineffective [34]. Consequently, advanced dehydration techniques, such as hydrothermal treatment or microwave processing, are typically required, significantly increasing operational costs [34,68]. Second, similar to most industrial biomass feedstocks, AMR contains elevated nitrogen and sulfur content. This necessitates stringent control of nitrogen oxides (NO_x) and sulfur dioxide (SO₂) emissions from flue gases during combustion. Zhang et al. [98] investigated gaseous pollutant emission profiles during AMR incineration using fluidized bed reactors. Their study revealed that concentrations of nitrogen and sulfur oxides in combustion byproducts increase proportionally with elevated incineration temperatures and higher excess air ratios.

Although incineration technology demonstrates relative maturity with distinct advantages in volume reduction and detoxification efficiency, its practical implementation faces critical bottlenecks including high operational costs, low resource recovery rates, and energy-intensive dehydration pretreatment requirements. Amid heightened environmental and energy sustainability concerns, conventional incineration systems may no longer represent the optimal solution for AMR management. Future advancements should prioritize intelligent combustion parameter modulation, integration of multi-pollutant synergistic control systems, and optimization of policy subsidy frameworks to enhance the environmental-economic sustainability of this technology.

3.3.2. Pyrolysis Gasification

Pyrolysis, also termed destructive distillation, refers to the thermochemical decomposition of organic materials under high-temperature, oxygen-free conditions (typically >300 °C), resulting in irreversible changes to their chemical composition and physical state [99]. As an emerging thermochemical conversion technology, pyrolysis could generate a range of products applicable to renewable energy and other sectors, such as bio-oil, biochar, and syngas [99,100]. Currently, pyrolysis and gasification technologies have been deployed for treating biomass wastes, including municipal sludge, urban solid waste, and crop straws, demonstrating notable environmental-energy synergies [101,102,103,104].

Chen et al. [25] performed a life cycle assessment and safety analysis of four AMR treatment strategies: incineration, pyrolysis/gasification, AD coupled with landfilling, and AD coupled with incineration. Their findings identified pyrolysis/gasification as the optimal approach for AMR treatment, exhibiting the lowest environmental impact and highest resource recovery efficiency. Adopting this technology to treat AMR can not only effectively eliminate persistent organic pollutants, such as antibiotics, but also yields high-value products, thereby alleviating environmental burdens and enabling energy-efficient valorization of solid waste [105,106,107].

Specifically, the solid-phase product of AMR pyrolysis is biochar; the liquid phase comprises aqueous and bio-oil fractions, while the gaseous phase consists predominantly of CO₂, CO, H₂, CH₄, and C₂~C₅ hydrocarbons [107,108,109]. AMR-derived biochar exhibits exceptional performance in environmental and energy applications, demonstrating high adsorption efficiency for aqueous antibiotics, recyclability, and superior stability, thus showcasing significant practical potential [105,106,110]. Liquid-phase products are dominated by oxygenated compounds, nitrogen-containing species, and hydrocarbons, with abundant nitrogen content but negligible phosphorus [108,111,112]. The composition of gaseous products varies systematically with pyrolysis temperature: CO₂ predominates at lower temperatures, while H₂ and CH₄ concentrations increase steadily with rising temperatures, accompanied by a marked decline in CO₂ levels. This phenomenon likely arises from secondary cracking reactions of primary volatiles under high-temperature conditions [107,109].

However, practical implementation requires pretreatment steps, such as dehydration, drying, and pulverization, of raw AMR prior to pyrolysis, introducing challenges analogous to incineration—notably high dehydration costs and wastewater treatment expenses (including pyrolysis liquid byproducts) [31,108,109]. Furthermore, secondary pollution during pyrolysis gas incineration needs to be stringently controlled due to the presence of sulfur and nitrogen [108,109].

Pyrolysis gasification technology demonstrates robust antibiotic removal efficiency, achieving waste reduction, detoxification, and resource recovery. However, even though pyrolysis has more resource products to compensate for the cost consumption compared with incineration, the operating cost is still high, and there are fewer reports on the application of the pyrolysis treatment of pristine AMR in practical engineering. Future progress hinges on enhancing feedstock adaptability, developing modular reactors, and advancing high-value product utilization technologies for large-scale AMR management.

3.3.3. Hydrothermal Technology

Hydrothermal treatment (HT) refers to a process conducted under high-temperature and pressure conditions, utilizing water as the reaction medium. By exploiting the unique properties of water in subcritical/supercritical states, this method achieves the detoxification of hazardous compounds and the decomposition of macromolecular organic substances [113,114]. As a mainstream technology, HT not only disintegrates colloidal structures and biomass matrices to release soluble organic matter into the liquid phase but also eliminates antibiotics in aqueous matrices at subcritical temperatures [38,53,114,115,116]. For high-moisture feedstocks, like AMR, HT eliminates dehydration pretreatment, reduces energy consumption, enhances conversion efficiency, and mitigates pollutant release associated with conventional dewatering [113,117].

Currently, HT is predominantly applied in municipal sludge treatment. Under moderate operational conditions, this method effectively processes urban sludge with high moisture content and pollutant concentrations, achieving significant volume reduction and enabling energy recovery [118]. Both AMR and municipal sludge undergo a fermentation process and both contain mycelium, which is similar in composition. This commonality establishes the feasibility of applying hydrothermal technology to AMR management, supported by substantial research evidence [37]. M. Wang et al. [59] employed HT to process lincomycin mycelial residues. Their results demonstrated effective removal of ARGs and mobile genetic elements, alongside heavy metal immobilization, confirming the capacity of the technology to mitigate environmental risks. Zhang et al. [37] conducted systematic investigations on HT for AMR, revealing that the process nearly completely decomposed residual antibiotics while substantially enhancing the dewaterability of AMR solids. Additionally, HT successfully recovered 42.5% of high-calorific solid fuel and reduced the nitrogen content in solid products to 5.8%. Furthermore, Hong et al. [29] and Zhuang et al. [67] successfully produced high-energy-density bio-oil from AMR via hydrothermal liquefaction. These studies collectively validate that hydrothermal technology not only achieves secure AMR treatment but also enables effective production of clean bioenergy.

HT can also serve as a pretreatment method for other disposal technologies to enhance the processability of AMR. C. Li et al. [5] demonstrated that hydrothermal pretreatment not only effectively degrades residual antibiotics but also breaks down organic particulates in AMR into soluble low-molecular-weight substances, significantly improving its anaerobic digestibility. Following HT, the methane yield of AMR increased markedly from 100 mL/g-VS to 290 mL/g-VS, representing a 190% enhancement in methane production. These results indicate that HT substantially improves the anaerobic digestive performance of AMR.

HT, as an emerging thermochemical treatment method, has demonstrated multiple advantages in the AMR treatment process. It not only enables deep removal of pollutants to alleviate environmental pressures caused by AMR but also facilitates the production of high-quality fuels and realizes energy recovery from AMR, providing novel insights for achieving reduction, harmlessness, and resource-oriented utilization of AMR. However, industrial-scale application is constrained by challenges: high costs of high-pressure reactors, corrosive media damaging alloy materials, and underdeveloped continuous feeding systems. Future advancements should focus on establishing subcritical catalytic systems, optimizing waste heat cascade utilization, and innovating equipment materials to overcome economic feasibility barriers in large-scale AMR treatment.

3.4. Multi-Technology Coupling

AMR safe disposal confronts multifaceted challenges: high moisture, antibiotic residues, and ARG contamination. Single-technology approaches often suffer from high costs, significant secondary pollution risks, and low resource conversion efficiency. Multi-technology coupling integrates diverse processes to achieve efficient antibiotic degradation while enhancing product value and mitigating environmental risks [5]. This strategy leverages complementary effects between optimized technologies based on AMR composition, enabling simultaneous pollution control and resource recovery.

3.4.1. Incineration Coupled with Advanced Dehydration Technologies

Incineration technology requires pretreatment dehydration processes, yet AMR typically exhibits high moisture content, necessitating dehydration prior to incineration. Native AMR contains tightly bound biogels or mycelium–water complexes, rendering conventional mechanical dehydration methods (e.g., centrifugation, compression) ineffective [34,37]. Extensive research confirms that advanced pretreatment technologies—such as microwave irradiation or HT—significantly enhance AMR dewaterability.

For biomass wastes, like AMR, microwave irradiation degrades the matrix, modifies particle size distribution, and disrupts microfloc structures through cell wall lysis, thereby releasing intracellular mucoid polymers (containing proteins, polysaccharides, DNA, etc.) and improving dehydration efficiency [69]. Compared to conventional heating, microwave pretreatment offers superior penetration depth, rapid heating rates, energy efficiency, and non-contact operation, achieving enhanced dewatering performance with a reduced processing time [70,119].

HT induces more pronounced phase transformations than microwave processing. Under conditions of 180~200 °C for 30 min, HT reduces the AMR moisture content from more than 80 wt% to less than 50 wt%, achieving 40% solid recovery [37]. Hydrolysis-condensation converts volatile nitrogen (amino acids, ammonia) to gaseous N for removal, lowering solid product N-content to <6.0 wt%, enabling 20~30% NO_x reduction during subsequent incineration [95]. Coupling with air-staged combustion further reduces NO_x by 45% versus conventional combustion, with enhanced efficacy at higher temperatures, demonstrating synergistic pollution control and effective nitrogen management.

3.4.2. Physicochemical Technologies for Enhanced AD

The synergistic integration of AD with physicochemical technologies demonstrates significant advantages in current technical frameworks. While AD is cost-effective, limitations include operational inefficiency, incomplete antibiotic degradation, and ARG horizontal transfer risk.

AD efficiency is constrained by kinetic equilibria in multi-stage biochemical reactions, with the initial hydrolysis phase universally recognized as the rate-limiting step due to substrate recalcitrance [120,121,122]. Ionizing radiation technology leverages direct ionization effects and indirect free radical oxidation mechanisms characteristic of high-energy radiation to simultaneously dissociate biomass flocs and disrupt microbial cell walls, releasing extracellular polymeric substances and intracellular organics. This process significantly elevates soluble chemical oxygen demand (SCOD), carbohydrates, and protein concentrations in the liquid phase, thereby enhancing biodegradability [123,124,125].

Notably, γ-irradiation induces marked shifts in microbial community richness and diversity. Post-treatment with 50 kGy radiation significantly increases the relative abundance of methanogenesis-facilitating microbes, like Arcobacter, fostering microbial consortia conducive to subsequent acidogenesis and methanogenesis [20]. This directional regulation is amplified when combined with nano zero-valent iron (nZVI). The coupled irradiation-nZVI-AD system, despite reducing microbial diversity, enriches specific functional taxa (e.g., Clostridium sensu stricto), boosting hydrogen yield from 8.55 mL/g-VS to 10.9 mL/g-VS and increasing volatile fatty acid (VFA) metabolic flux by 122.7%, with acetate accounting for 73.5~83.8% of the total VFAs [35].

Alkaline pretreatment is another established AMR treatment method. By establishing a strongly alkaline environment, this technology multi-dimensionally optimizes AD of biomass waste. Its mechanisms include [126,127,128,129,130]:

• Disrupting AMR cell wall/membrane structures to release endogenous organics;
• Catalyzing hydrolysis of macromolecular organics to improve substrate bioaccessibility;
• Degrading residual antibiotics via alkali-catalyzed reactions to alleviate metabolic inhibition;
• Inducing DNA hydrolysis to reduce ARGs abundance.

Additionally, alkaline conditions promote targeted enrichment of functional microbial consortia, synergistically enhancing hydrogen and methane yields for high-efficiency energy recovery. Q. Zhang et al. [131] enhanced the AD performance of rifamycin fermentation residue by alkaline heat pretreatment at 140 °C, pH 12, and a residence time of 3 h. The experimental results showed that the SCOD increased from 32.6% to 58.5%, the rifamycin removal efficiency increased from 34.2% to 59.2%, and the cumulative methane production increased by 86.4%, reaching 444 mL/g-VS after the alkaline heat treatment. This indicated that the alkaline heat treatment increased the organic matter solubility, significantly improved the removal efficiency of antibiotics, and markedly promoted the AD performance. Notably, when the concentration of ammonia exceeds 1670 mg/L, it inhibits the AD process of methanogenic bacteria [132]. In Zhang’s experiment, ammonia nitrogen concentrations peaked at 600~1100 mg/L by day 10 before stabilizing at 550~800 mg/L, remaining below inhibitory thresholds for methanogens. This indicates effective mitigation of ammonia-induced microbial inhibition. Furthermore, increased microbial diversity post-pretreatment enhanced the digestion efficiency and system resilience to environmental stressors, like antibiotics.

HT similarly enhances AMR digestion efficiency, particularly in boosting methane and biogas production. Under high-temperature and high-pressure conditions, organic particulates undergo hydrolytic chain scission, generating soluble low-molecular-weight compounds that promote the enrichment of carbon and nitrogen in the liquid phase [133,134]. Post-HT, the increased solubility of organic matter renders residual components more accessible for microbial degradation, thereby optimizing subsequent AD efficiency [56,135]. Furthermore, HT effectively removes antibiotics from fermentation residues and markedly reduces the abundance of ARGs, thereby mitigating antibiotic-induced inhibition. Notably, the removal efficiencies of antibiotics and ARGs exhibit a positive correlation with HT temperature [41,55,136].

Y. Wang et al. [137] experimentally demonstrated that hydrothermal pretreatment can converts 40.2% of solid organic matter in AMR into dissolved forms, with 75% of organic compounds in the filtrate being converted into biogas during AD, achieving 8~11 times higher methane production compared to untreated residue. HT exhibits broad applicability, showing efficacy across 10 AMR types spanning 5 antibiotic classes, including β-lactams, aminoglycosides, and macrolides. Researchers have further proposed a systematic solution involving an integrated hydrothermal–pyrolysis–AD system [50]. HT at 180 °C enhances biodegradability and dewaterability of antibiotic fermentation residues, reducing filter cake moisture content to 39% and decreasing ARGs’ absolute abundance by 2.4~5.2 logs. Subsequent pyrolysis and upflow anaerobic sludge blanket processes facilitate resource recovery from filter cakes and filtrate, achieving a total mass reduction rate of 97.7% and organic utilization efficiency of 80.2%. Energy balance analysis confirms that byproduct biogas and pyrolysis gas meet system energy demands, enabling energy self-sufficiency. However, excessive treatment may elevate ammonia levels and trigger Maillard reaction-driven organic repolymerization, counteracting digestion efficiency [55,138].

Innovatively, Hui et al. [139] employed tea polyphenols to pretreat kanamycin residue. Quinones generated through polyphenol oxidation polymerize with amino groups present in kanamycin, achieving high-efficiency antibiotic removal while enhancing the compost humification index and nitrogen retention rates. This breakthrough provides novel pathways for producing high-activity biostimulants.

3.4.3. Other Coupling Techniques

Thermochemical technology coupled with other approaches represents a widely adopted strategy. Beyond conventional hydrothermal methods, calcination processes integrated with activation techniques can overcome the application bottlenecks of single-technology systems. Research indicates that calcination effectively removes moisture from biomass and reduces the oxygen-to-carbon (O/C) ratio, significantly enhancing its physicochemical properties [140]. When applied to AMR treatment, this method efficiently eliminates residual antibiotics and improves thermal stability, yielding structurally stable biochar [141]. However, biochar produced via calcination typically exhibits a low specific surface area, limiting its material-oriented applications [142]. By coupling chemical activation technologies and introducing chemical activating agents, such as KOH/ZnCl₂, pore structure development can be induced. The resulting biochar not only demonstrates enhanced specific surface area and porosity but also forms abundant defect sites and diverse oxygen-containing functional groups. These augmented physicochemical characteristics broaden its application prospects in fields such as materials science and carbon-based technologies [143].

Currently, multi-technology coupling provides a comprehensive solution for AMR treatment, yet its large-scale implementation still faces significant challenges. The primary constraint lies in the stringent requirements for cross-system parameter collaborative optimization and equipment compatibility design, leading to a concurrent escalation in system operational complexity and costs. Secondly, uncertainties persist regarding the ecological safety of resource-oriented products. For instance, the environmental residual effects of biochar and similar outputs necessitate systematic toxicological studies and long-term environmental behavior monitoring to establish a scientifically robust risk assessment framework. Future research should prioritize low energy consumption-coupled processes, utilizing intelligent control algorithms to optimize reaction parameters and reduce costs. Concurrently, advancing life cycle assessments and refining environmental health risk frameworks are critical for transitioning AMR treatment toward green, low-carbon, circular models.

4. Discussion

In the current landscape of environmental science and resource management, the treatment of AMR undeniably stands as a critical and highly prominent issue. AMR exhibits extreme compositional complexity, encompassing not only residual antibiotics of diverse classes but also substantial amounts of mycelium and persistent impurities resistant to separation. This inherent complexity renders AMR treatment exceptionally challenging, while distinct advantages and limitations arise across treatment technologies due to variations in operational parameters and underlying mechanisms, as detailed in

Table 2. Processing conditions and effects of different technologies.

Technology	Condition	Antibiotic Removal Rate	ARGs Removal Rate	References
Microwave Treatment	200 °C, 30 min	95%	-	[62]
Ionizing Radiation	30~50 kGy of gamma rays	56~99%	90~95%	[35,57]
Aerobic Composting	12~42 d	>99%	increased abundance	[30,54]
Anaerobic Digestion	20~30 d	>80%	58%ARGs	[49,64]
Biodegradation	Bacteria, fungi, insects, 8~15 d	37~85%	-	[58,60,91]
Incineration	>800 °C	-	-	[144]
Pyrolysis Gasification	600 °C, 30 min	100%	100%	[106]
Hydrothermal Treatment	160~180 °C, 30 min	>99%	>99%	[37,59]

The “-” indicates that the content was not mentioned in the corresponding paper.

and

Table 3. Advantages and disadvantages of various AMR treatment technologies.

Technology		Advantages	Disadvantages
physical methods	Landfill	Simple operation; Mature technology	Residual antibiotics and ARGs risks; Low resource recovery rate; Secondary pollution risks; High land occupation
	Microwave Treatment	High efficiency; Significant effectiveness	Residue antibiotic risks; High capital and operational costs
	Ionizing Radiation	High efficiency; Mild conditions; Strong adaptability; No secondary pollution	Immature technology; High capital and operational costs
biochemical methods	Aerobic Composting	Mature technology; Large-scale treatment capacity; Resource recovery potential	Residue ARG risks; Limited technical universality
	Anaerobic Digestion	Significant effectiveness; Resource recovery potential	Stringent technical requirements; High treatment cost; Secondary pollution risks
	Biodegradation	Low treatment cost; Environmentally friendly; Supports resource recovery	Residue antibiotic risks; Limited biological adaptability
thermochemical methods	Incineration	Mature technology; Significant volume reduction and detoxification	High treatment cost; Low resource recovery rate
	Pyrolysis Gasification	Significant volume reduction and detoxification; Resource recovery potential; Strong adaptability; No secondary pollution	Technically complex; High capital and operational costs
	Hydrothermal Treatment	Remarkably improved dewatering performance; Significant volume reduction and detoxification; Resource recovery potential	Harsh reaction conditions; High capital and operational costs

.

AMR treatment currently faces three major challenges:

• Economic constraints. As AMR is classified as hazardous waste, its treatment—whether through physical, biochemical, or thermochemical methods—involves multiple complex stages, each requiring substantial resource inputs and technical specifications;
• The diverse sources and compositional complexity of AMR necessitate customized treatment schemes for different feedstocks, further complicating cost control. Second, limitations of existing technologies. While numerous AMR treatment methods have been explored and proposed in prior studies, these approaches exhibit significant drawbacks. For instance, landfill and incineration require costly dewatering pretreatment. Aerobic composting and AD eliminate the need for dewatering but demand stringent reaction conditions and pose environmental risks. Ionizing radiation, pyrolysis/gasification, and HT entail high capital and operational costs, limiting their large-scale adoption. These shortcomings render existing technologies inadequate to meet stringent environmental standards, efficient resource utilization demands, and escalating public health safety requirements;
• The absence of standardized regulations. The lack of unified and authoritative guidelines—including pollutant emission standards, safety assessment protocols, and environmental technology specifications—leaves pharmaceutical enterprises without clear frameworks for designing economically viable and environmentally compliant AMR treatment processes. This regulatory gap hinders the advancement of AMR treatment practices. The Waste Framework Directive issued by the European Union provides detailed provisions governing the definition, classification, collection, transportation, treatment, and disposal of hazardous waste but lacks specific disposal requirements for AMR [145]. Furthermore, the inherently ambiguous definitions and discretionary features within European directives risk generating contradictory rulings by the European Court of Justice. This legal ambiguity, coupled with the decentralized transposition of amended directive obligations into national legislation, may result in divergent interpretations and regulatory frameworks across Member States during implementation [146].

Despite confronting multidimensional challenges across technological, economic, and regulatory spheres, AMR governance retains considerable scientific merit and industrial promise. Within the biotechnology domain, the rational engineering of microbial consortia and targeted isolation of high-efficiency degrading strains facilitate the precise breakdown and bioconversion of hazardous AMR constituents—notably residual antibiotics and ARGs. This transformation yields either ecologically harmless substances or high-value bio-based products. Emerging physical techniques, exemplified by ionizing radiation, offer breakthrough capabilities for cleaving refractory antibiotic molecules and inactivating ARGs, leveraging their robust oxidative potential, absence of chemical additives, and mild operational conditions. Consequently, these technologies emerge as pivotal enablers for next-generation environmentally sustainable AMR treatment. Additionally, cutting-edge technologies, such as CRISPR editing, have great potential in ARG treatment [147].

Critically, singular technologies are inadequate for comprehensively resolving the intricate challenges embedded within the AMR pollution continuum. Future advancement will prioritize developing integrated treatment platforms founded on multi-technology synergies. Through spatiotemporal optimization, such systems can achieve synergistic outcomes encompassing stratified pollutant abatement and closed-loop resource management.

5. Conclusions

The treatment of AMR represents a critical challenge for the sustainable development of the biopharmaceutical industry. This review systematically consolidates current AMR treatment technologies, encompassing physical, biochemical, and thermochemical methodologies, and provides a comprehensive evaluation of their respective advantages and limitations. While significant progress has been made, persistent challenges include high operational costs, inadequate removal efficiencies for residual antibiotics and ARGs, and suboptimal resource recovery efficiency. Future research must prioritize innovative multi-technology coupling strategies to achieve efficient AMR treatment and maximized resource valorization, while addressing critical barriers, including restricted economic viability, managing microbial hazards during valorization, and the persistent removal inefficiencies of residual antibiotics and ARGs. Concurrently, establishing standardized protocols and regulatory frameworks is essential for facilitating the scalability and practical implementation of these technologies.