## 4 Hybrid Technology  
### Microbial Electrochemical Systems  
Biological electrochemical systems (BESs) effectively degrade antibiotics through the metabolic activities of electroactive microorganisms. The primary mechanisms involvedare extracellular electron transfer (EET) and enzyme-catalyzed pathways. EET is a crucial process for the transfer of electrons between electroactive microorganisms and electrodes, significantly influencing the efficiency of this electron transfer. EET can be categorized into two modes: direct EET and indirect EET [130]. The direct EET mechanism refers to the process by which microorganisms transfer electrons directly to electrodes via cytochromes located on their cell membranes or through conductive nanowires, such as conductive pili. For example, Geobacter sulfur-ducens transfers electrons from inside the cell to the anode through a cytochrome network, oxidizing and degrading tetracycline [131]. At the cathode, Shewanella oneidensis receives electrons through nanowires and reduces the nitro group of chloramphenicol (CAP), achieving a 23% increase in the degradation rate within 24 h [132]. Indirect EET refers to the process where microorganisms secrete or utilize exogenous redox mediators as electron shuttles to accelerate electron transfer. For example, [PERSON] et al. added humic acid (HA) as an electron mediator, increasing the degradation rate of sulfanilamide (SDZ) from 80% to 90% [133]; [PERSON] et al. used biochar as a conductive carrier to promote a long-range electron transfer between microorganisms, increasing the removal rate of sulfamethoxazole (SMX) from 71.58% to 82.44% [134]. In addition, microorganisms can catalyze the breakdown of specific chemical bonds in antibiotics through functional enzymes, leading to their degradation. For example, lacase can bind to the amino structure of tetracycline (TC) and degrade it into smaller molecules via an oxidative pathway [135]. Similarly, nitroreductase gradually reduces the nitro group (-NO\({}_{2}\)) of chloramphenicol (CAP) to an amino group (-NH\({}_{2}\)), with the intermediate product nitroaniline (AMCl\({}_{2}\)) further undergoing dichloromethane [136]. In actual bioelectrochemical systems (BESs), electron transfer (EET) and enzyme catalysis often work in tandem to facilitate antibiotic degradation. For instance, in the BES that degrades chloramphenicol (CAP), a cathodic EET provides electrons, while nitroreductase catalyzes the reduction of the nitro group, ultimately leading to dechlorination [132]. Additionally, the anodic electroactive bacterium Pseudomonas transfers electrons through EET while secreting P450 monooxygenase to oxidize the piperazine ring of ciprofloxacin [137]. Biological electrochemical systems (BESs) can be categorized into two application forms: microbial fuel cells (MFs) and microbial electrolysis cells (MECs). This technology combines the microbial metabolism with electrochemical redox processes, making it an effective approach for treating difficult-to-degrade antibiotics. The main mechanism of MFCs is the conversion of chemical energy into electrical energy through microbial action, where the microorganisms in MFCs can simultaneously generate electricity and degrade pollutants in wastewater [138]. The MFC consists of a biological anode and a non-biological cathode, where antibiotics serve as electron donors and carbon sources at the biological anode. Exoelectrogenic microorganisms and antibiotic-degrading bacteria attach to the anode, forming a biofilm within extracellular polymeric substances, which is responsible for reducing the overpotential of the parent antibiotics and their metabolites [139]. The MEC builds upon the MFC by adding an external power source, and its mechanism involves obtaining certain chemical products through specific reactions in the presence of a small amount of external energy.