Author: Site Editor Publish Time: 21-10-2026 Origin: Site
Biochemical effluents generated from pharmaceutical manufacturing, chemical synthesis, and biological experiments contain trace recalcitrant contaminants, such as antibiotic residues, endocrine-disrupting chemicals (EDCs), and highly toxic aromatic chemical intermediates. These substances are ubiquitous in natural water bodies and can easily induce microbial antimicrobial resistance (AMR), disrupt aquatic ecological balance, and threaten drinking water safety, making them a critical hidden danger in current water environment management. Conventional processes, including activated sludge, coagulation-sedimentation, and single chlorination disinfection, exhibit removal efficiencies of less than 50% for these low-concentration trace contaminants and fail to achieve complete mineralization, thus struggling to meet stringent wastewater discharge standards. Advanced oxidation processes (AOPs) are the core technologies for the in-depth treatment of trace contaminants. Among them, the most widely applied UV/H₂O₂ process suffers from drawbacks such as low photon energy utilization, the need for additional quenching of residual oxidants, and high operation and maintenance (O&M) costs [1, 2]. In contrast, the UV/chlorine process can in situ generate multiple highly oxidative radicals to degrade micropollutants, and the residual chlorine can simultaneously disinfect the water body without the need for an oxidant quenching step. This streamlined process offers better economic viability and represents a highly promising alternative technology.
However, the traditional UV/chlorine process relies on mercury lamps as the light source, which presents core technical defects: the fixed emission spectrum of mercury lamps cannot be optimized to match the photolysis characteristics of specific contaminants and chlorine species, resulting in low light utilization efficiency. Furthermore, the risk of mercury pollution and complex equipment maintenance severely restrict the engineering application of this process in decentralized wastewater treatment scenarios for small- and medium-sized pharmaceutical enterprises (SMEs). In recent years, the industrialization of UV-C LED deep ultraviolet light source technology has gradually overcome the technical bottlenecks of traditional mercury lamps, owing to its unique advantages such as precisely tunable wavelengths, mercury-free environmental friendliness, instant on/off switching, and lightweight modules [3, 4]. By precisely matching the UV absorption spectra of aqueous chlorine species and trace contaminants, UV-C LEDs can maximize light utilization efficiency and radical generation efficiency while fundamentally avoiding the risk of heavy metal pollution, thereby meeting the core needs for flexible deployment, greenness, and safety in small- and medium-scale wastewater treatment.
The emergence of UV-C LED-coupled chlorine AOPs has successfully broken the dual bottlenecks of insufficient efficiency and poor engineering adaptability inherent in traditional UV/chlorine processes. It provides a highly efficient, green, and cost-effective novel technical pathway for the in-depth treatment of highly toxic trace contaminants in pharmaceutical and laboratory biochemical effluents, possessing significant scientific research value and engineering promotion significance.
Over the past decade, the industrialization of deep ultraviolet light-emiting diodes (UV-C LEDs, 200–280 nm) has matured, gradually replacing traditional low-pressure (LP) and medium-pressure (MP) mercury UV lamps. They have become the new-generation core light sources for the in-depth treatment of trace hazardous substances in water environments, offering irreplaceable technical advantages and application value in the treatment of effluents from pharmaceutical production, chemical experiments, and biological laboratories.
The AOPs based on UV-C LEDs coupled with oxidants such as persulfate or free chlorine primarily degrade various hazardous substances in biochemical effluents via two pathways: direct photolysis and indirect oxidation. Regarding direct photolysis, the short-wavelength UV light (e.g., 255–295 nm) emitted by UV-C LEDs can be directly absorbed by target contaminant molecules, prompting the cleavage of chemical bonds and subsequent decomposition [5, 6]. In terms of indirect oxidation, UV-C LEDs can be coupled with oxidants like persulfate (PS), hydrogen peroxide (H₂O₂), or free chlorine to in situ generate highly reactive radicals, including sulfate radicals (·SO₄), hydroxyl radicals (·OH), and reactive chlorine species (RCS, such as ·Cl, ·ClO), which efficiently attack contaminant molecules [6]. Depending on the chemical properties of the contaminants, the attack pathways and reaction mechanisms of these radicals vary:
Antibiotics: In the UV-C LED/PS system, ·SO₄ disrupts the characteristic or functional structures of antibiotics via hydrogen abstraction and unsaturated bond addition. Studies have demonstrated that the degradation of ampicillin by ·SO₄ can effectively eliminate its antibacterial activity [7]; In the UV-C LED/PS system, ·SO₄ disrupts the characteristic or functional structures of antibiotics via hydrogen abstraction and unsaturated bond addition. Studies have demonstrated that the degradation of ampicillin by ·SO₄ can effectively eliminate its antibacterial activity [8].
Neuroactive pharmaceuticals and non-steroidal organic interferents: In the UV-LED/chlorine process, reactive species such as ·OH, ·Cl, and ·ClO act syncergistically to transform their parent structures via hydroxylation, deamination, double-bond addition, and C-N bond cleavage. The dominant radicals vary under different pH conditions—under acidic conditions, ·OH and ·Cl predominate, whereas under alkaline conditions, ·OH and ·ClO become the primary contributors [6].
Aromatic chemical intermediates and chlorinated aromatic compounds: In the UV/PS system, the hydrogen abstraction and electron transfer by ·SO₄ syncrize with the C-Cl bond cleavage via direct UV-C photolysis to achieve efficient degradation. In the UV/chlorine process, RCS and OH⁻ also participate in the degradation of aromatic heterocyclic compounds such as benzotriazole and benzothiazole [9].
Compared with traditional mercury lamps, the core advantages of UV-C LEDs are reflected in the following aspects:
Tunable wavelength and precise light energy utilization: The emission spectrum of mercury lamps is broad and multi-peaked, with a large amount of photon energy concentrated in non-target bands, causing waste. In contrast, UV-C LEDs can be customized to emit specific wavelengths according to the absorption characteristics of target contaminants, achieving highly efficient and targeted light energy utilization [5].
Instant start-up and precise regulation: Mercury lamps require several minutes of preheating to reach stable output, whereas UV-C LEDs enable instant on/off switching and precise electronic regulation of output intensity.
Environmental friendliness: Mercury lamps contain highly toxic heavy metal mercury, and their production, use, and disposal face strict environmental regulary pressures. UV-C LEDs are mercury-free and do not generate ozone during operation, aligning with the development direction of green water treatment technologies.
Long lifespan and low maintenance costs: The service life of LP mercury lamps is generally 8,000–12,000 hours, while UV-C LEDs can exceed 20,000 hours.
As an emerging AOP, the UV-C LED/chlorine process has attracted widespread attention in recent years. By irradiating free chlorine (HOCl/OCl⁻) with UV light, this process in situ generates reactive species such as ·OH, ·Cl, and dichlorine radicals (·Cl₂), efficiently degrading emerging micropollutants like antibiotics, pharmaceutical residues, and EDCs, while simultaneously providing disinfection [10]. Compared to the traditional UV/H₂O₂ process, the UV/chlorine process exhibits superior performance in degrading specific contaminants, maintains residual chlorine in the pipe network, and can be easily upgraded based on existing facilities [10]. Specifically, this process offers the following application advantages in biochemical wastewater treatment:
(1) Green and safe, adaptable to distributed treatment in SMEs
UV-C LEDs are mercury-free and feature lightweight modules that can be integrated and installed modularly. They eliminate the need for complex explosion-proof and leak-proof protective devices required by traditional mercury lamps. This makes them suitable for end-of-pipe in-depth wastewater treatment in small pharmaceutical plants and as multi-stage disinfection barrier units for reclaimed water reuse, thereby avoiding the environmental risk of mercury pollution.
(2) Streamlined process flow and reduced O&M costs
The AOP system can be constructed relying on the residual chlorine already present in the wastewater for disinfection, eliminating the need for the additional storage and dosing of H₂O₂ or PS [10]. Furthermore, the residual chlorine in the treated water does not require the addition of reducing agents for quenching, saving the investment in a complete set of supporting chemicals and equipment, and significantly reducing daily O&M chemical consumption.
(3) Tunable wavelength for on-demand matching of wastewater contaminant compositions
One of the core advantages of UV-LEDs is the flexible adjustment of emission wavelengths (265–310 nm), allowing targeted optimization based on the absorption characteristics of target contaminants and radical generation requirements. Studies have shown that the photolysis efficiencies of HOCl and OCl⁻ in free chlorine differ significantly at different wavelengths—the decomposition rate of ·OCl at 275 nm is higher than that at 254 nm, whereas the opposite is true for HOCl [11]. Therefore, adaptable wavelengths can be selected for different characteristic contaminants in wastewater: for antibiotic contaminants primarily removed via direct photolysis (e.g., sulfamethoxazole), specific absorption bands can be utilized to enhance photolysis efficiency; for chemical intermediates containing aromatic ring structures, longer wavelengths such as 275 nm can be selected to enhance radical oxidation efficiency [12]; for complex composite wastewater, multi-wavelength UV-C LED arrays can be constructed to achieve syncrhetic treatment.
(4) Simultaneous degradation and disinfection to meet discharge regulary requirements
Reactive radicals in the system degrade trace contaminants, while the residual chlorine in the treated water continuously inhibits microbial regrowth, preventing secondary microbial proliferation in the effluent. This simultaneously achieves the dual goals of trace contaminant removal and water disinfection, complying with the microbial limit control standards for pharmaceutical wastewater discharge.
(5) Long-wavelength UV-C LEDs reduce disinfection by-products (DBPs) and effluent toxicity
Studies on the degradation of iodinated contrast media by multi-wavelength UV-C LEDs have confirmed that longer UV wavelengths result in lower DBP formation and a synchronous decrease in the effluent cytotoxicity index. Compared to short-wavelength light sources at 254 nm, 275 nm UV-C LEDs reduce the ecotoxicological risk of the effluent while ensuring treatment efficiency, balancing treatment performance with aquatic environmental safety [10].
The UV-C LED-coupled chlorine AOP integrates the wavelength tunability and mercury-free safety of deep UV light sources with the continuous bactriostatic capability of chlorine disinfection, providing a feasible pathway that balances technical efficacy and engineering economics for the in-depth treatment of biochemical wastewater in small- and medium-sized pharmaceutical enterprises. Compared with the traditional mercury lamp/H₂O₂ process, this technology not only eliminates the steps of external oxidant storage, dosing, and residual oxidant quenching, greatly streamlining the water treatment process, but also leverages the mercury-free, lightweight, and instant on/off characteristics of UV-C LEDs to achieve flexible modular deployment within limited plant spaces.
With the continuous improvement of the wall-plug efficiency (WPE) of UV-C LED chips, the year-by-year decline in unit costs, and the continuous enhancement of the standardization and intelligence levels of complete water treatment equipment, the UV-C LED-coupled chlorine AOP is expected to become one of the mainstream technologies for in-depth wastewater treatment and reuse in small- and medium-sized pharmaceutical enterprises. Driven by the "Dual Carbon" goals (carbon peaking and carbon neutrality) and increasingly stringent pharmaceutical wastewater discharge standards, it will propel water pollution control in the pharmaceutical industry towards a green, low-carbon, and intelligent direction.
Xu MY, Z.C., et al., Wavelength dependency and photosensitizer effects in UV-LED photodegradation of iohexol. Water Res, 2024. 255:121477.
Farzanehsa, M.V.L.C. and A.K.S.J. Zamyadi, Comparison of UV-Cl and UV-H2O2 advanced oxidation processes in the degradation of contaminants from water and wastewater: A review. 2023. 37(4): p. 633–643.
Würtele MA, K.T.L.M., Application of GaN-based ultraviolet-C light emitting diodes--UV LEDs--for water disinfection. Water Res, 2011(45(3):1481-9).
Song K, T.F.M.M., Microorganisms inactivation by wavelength combinations of ultraviolet light-emitting diodes (UV-LEDs). Sci Total Environ, 2019: p. 665:1103-1110.
Bennett JL, M.S., R.M.F.R. Li J and G.G. Stoddart AK, Photolysis at the Speed of Light: Chemical-Free Degradation of Trace Organic Contaminants by Bespoke Photolysis Using High-Intensity Ultraviolet C Light-Emitting Diodes. ACS ES T Water, 2025. 5(11): p. 6375-6387.
Qi Fu, Z.Z.Y.L., et al., Mechanisms of radical regulation during carbamazepine degradation by UV-LED/chlorine process with different wavelengths in water. Journal of Environmental Chemical Engineering, 2025. 12(6): p. 6375-6387.
Laxman G. Raikar, J.G. and H.P. K. V. K. Gupta, Degradation of Ampicillin with antibiotic activity removal using persulfate and submersible UVC LED: Kinetics, mechanism, electrical energy and cost analysis. Chemosphere, 2024. 349.
Ye JS, L.J.O.H. and W. LL, Degradation of ciprofloxacin by 280 nm ultraviolet-activated persulfate: Degradation pathway and intermediate impact on proteome of Escherichia coli. Chemosphere, 2016. 165: p. 311-319.
Nunes RF, R.J., D.D. Carvalho-Silva VH and T. ACSC, UVC/Sulfite coupled to persulfate for removing chlorinated compounds under oxic conditions: effects of process variables, transformation products and toxicity. Environ Technol, 2025. 46(24): p. 5011-5026.
BAI T Q, Y.Y. and L. X, Research progress on UV/chlorine advanced oxidation process for treating emerging contaminants. Journal of Environmental Engineering Technology, 2026. 16(1): p. 230-241.
Kwon M, Y.Y., J.Y. Kim S and K. Hwang TM, JW. Removal of sulfamethoxazole, ibuprofen and nitrobenzene by UV and UV/chlorine processes: A comparative evaluation of 275 nm LED-UV and 254 nm LP-UV. Sci Total Environ, 2018: p. 637-638.
Gao ZC, L.Y., et al., Effect of UV wavelength on humic acid degradation and disinfection by-product formation during the UV/chlorine process. Water Res, 2019. 154: p. 199-209.
