1. Introduction
Traditional low-pressure mercury UV disinfection systems suffer from several limitations, including mercury contamination risk, warm-up time requirements, single-wavelength emission at 254 nm, and relatively short service life. In contrast, AlGaN-based UV-C LEDs can precisely emit deep ultraviolet light in the 220–280 nm range, making them suitable for mobile, embedded, and compact closed water treatment applications. They comply with mandatory Chinese standards such as GB 28235-2020 Hygienic Requirements for Ultraviolet Disinfection Devices and WS 628-2018 Disinfection Technical Specifications for Medical Institutions .
Water matrix characteristics significantly constrain UVC photon utilization efficiency. Natural organic matter (NOM) and suspended solids reduce disinfection performance through absorption and scattering, creating microbial shielding effects. Water hardness can lead to calcium carbonate scaling on lenses or quartz sleeves under heating and photo-oxidation, continuously reducing irradiation intensity. Meanwhile, different microorganisms—including Gram-negative bacteria, mycobacteria, fungal spores, and viruses—exhibit UV resistance levels that vary by several to tens of times.
There is often a substantial discrepancy between laboratory UV-C LED inactivation results and real-world engineering performance. Laboratory tests may achieve 3–5 log inactivation, while field performance may only reach 1–2 log. Comparative studies show that without pretreatment, turbidity >5 NTU can reduce UV transmittance at 265 nm by more than 40%, while high humic acid concentrations can decrease disinfection efficiency by 50% under the same power conditions.
This paper categorizes water quality into different levels, analyzes key interference factors, and proposes matched configurations of light source parameters, reactor design, pretreatment processes, and minimum required UV doses. The goal is to establish a graded and adaptive UV-C LED disinfection system framework.
2. UV-C LED Disinfection Strategies for Five Typical Water Sources
2.1 Municipal Tap Water (Point-of-Use / Secondary Supply)
Water quality characteristics:
Turbidity <1 NTU, SS <3 mg/L, humic acid <2 mg/L; pH 6.8–7.8; total hardness 50–200 mg/L. Background microorganisms mainly include Escherichia coli and Legionella pneumophila , with no highly resistant spores or mycobacteria. Residual chlorine is 0.2–0.8 mg/L, UVT >85%, indicating minimal optical interference.
UV-C LED solution:
Light source: Single wavelength at 270 nm.
Dose: 8 mJ/cm² achieves >5 log inactivation of E. coli and 4.2 log for Legionella , meeting GB 5749-2022 drinking water standards .
Reactor: Small-diameter tubular reactors for 1–20 L/min; modular parallel “tower-type” reactors for higher flow rates to avoid hydraulic short-circuiting.
Pretreatment: 5 μm filtration only; no coagulation or activated carbon required.
2.2 Shallow Groundwater (Wells, Spring Water)
Water quality varies significantly.
Deep groundwater (turbidity <1 NTU):
Shallow groundwater (turbidity 2–8 NTU):
Light source: Primary 265 nm with supplementary 275 nm to reduce NOM absorption losses.
Pretreatment: Aeration for iron/manganese removal → 10 μm filtration → 5 μm filtration; add activated carbon if humic acid is high.
Dose: Increased by a factor of 1.8–2.2, reaching 20–25 mJ/cm².
Reactor: Extended chamber with turbulence-inducing structures to reduce particle shielding.
Anti-scaling: Automatic acid cleaning every 7 days.
Validation: Without pretreatment, 6 mJ/cm² achieved only 2.1 log inactivation; with filtration, performance improved to 5.3 log under the same power.
2.3 Surface Water (Rivers, Lakes, Reservoirs)
Water quality characteristics:
High interference: turbidity 5–20 NTU (peaks >30 NTU), humic acid 5–15 mg/L, high suspended solids and algae content. Microbial populations include fungi, mycobacteria, viruses, and protozoa with high UV resistance. UVT is typically 20%–50%.
Solution:
Single UV-C LED treatment is insufficient; a combined system is required.
Pretreatment: Coagulation–sedimentation → sand filtration → activated carbon → 5 μm filtration.
Light source: High-density flip-chip 265 nm LED arrays.
Dose: ≥40 mJ/cm² for bacteria and viruses; 65–75 mJ/cm² for protozoa.
Reactor: Multi-stage baffled design to accumulate dose and compensate for attenuation.
Advanced oxidation: UV/H₂O₂ (5–15 mg/L), improving efficiency by ~35%.
Validation: Without pretreatment, 80 mJ/cm² achieved only 1.2 log inactivation of Cryptosporidium; with full pretreatment, 4.7 log was achieved .
2.4 Reclaimed Greywater (Domestic Wastewater Reuse)
Characteristics:
Turbidity 3–12 NTU; high surfactants and suspended solids; fluctuating quality; contains bacteria, fungi, and viruses.
Solutions:
Toilet flushing reuse: Disc filtration + 5 μm filtration; 265 nm LEDs; 22 mJ/cm² dose for ≥3 log E. coli removal.
Landscape reuse: Biofilm pretreatment to reduce COD; 45 mJ/cm²; external sleeve reactor for easy cleaning.
Control strategy: Online turbidity monitoring; reduce flow rate when turbidity >10 NTU.
2.5 Aquaculture Water (Recirculating Systems)
Characteristics:
High ammonia, nitrite, and organic load; SS 4–15 mg/L; pathogens include Vibrio, fungal spores, and Flavobacterium. Water temperature 22–30°C accelerates scaling. Chlorine is prohibited.
Solution:
Wavelength: 265 nm (primary) + small proportion of 275 nm to protect nitrifying bacteria.
Dose control: 15–25 mJ/cm² in circulation loop; ≤12 mJ/cm² for larvae.
Reactor: Low-velocity, large cross-section design; self-cleaning scraper system.
Pretreatment: 60-mesh filtration to remove large particles.
Validation: At 20 mJ/cm², Vibrio parahaemolyticus achieved 5 log inactivation, while nitrifying bacteria retained ≥65% viability .
3. Conclusion
UV-C LED water disinfection does not have a universal standardized module; water matrix characteristics are the core constraint in system design. Low-interference water sources such as municipal tap water and deep groundwater can be effectively treated using compact 265 nm single-wavelength systems with minimal pretreatment. Medium-interference waters (e.g., shallow groundwater, reclaimed water, aquaculture systems) require increased UV dose, enhanced filtration, and anti-scaling measures. High-interference waters such as surface water and medical wastewater require integrated systems combining physicochemical pretreatment, high-density UV-C LED arrays, and high safety dose margins.
In terms of wavelength selection, 265 nm is the optimal primary disinfection wavelength across scenarios, while 275 nm serves as an auxiliary wavelength in high organic content waters. Engineering design should incorporate a water quality-based amplification factor rather than directly applying laboratory UV dose values. This graded adaptation strategy enables compliance with disinfection standards while optimizing system cost, energy consumption, and lifespan, providing a scalable framework for decentralized water supply, water reuse, healthcare, and aquaculture applications.
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