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In hospital wastewater treatment systems, disinfection is a critical step. Different disinfection technologies have their own limitations in terms of microbial inactivation, by-product control, operating cost, and maintenance requirements. For this reason, some hospital wastewater projects consider adopting a multi-barrier treatment approach.
Combining chlorine dioxide with treatment technologies such as ozone and ultraviolet (UV) irradiation can provide complementary functions for different treatment objectives. However, whether such a combination is suitable for a specific project still needs to be evaluated based on actual wastewater quality, target pollutants, treatment requirements, and operating costs.
In actual operation, the key challenge is how to allocate chemicals and energy reasonably so as to achieve an appropriate balance among treatment performance, operational stability, and economics.
Chlorine dioxide has broad oxidation and disinfection capabilities. Compared with conventional free chlorine disinfection, it can generally reduce the formation of some typical halogenated organic by-products, while also oxidizing certain phenolic compounds and other readily oxidizable pollutants.
It should be noted that chlorine dioxide is not a “zero-by-product” technology. Its use also requires attention to transformation products such as chlorite and chlorate.
Therefore, in an integrated treatment process, it is important to clearly define the role of chlorine dioxide and optimize its dosing strategy in order to support downstream treatment performance and overall system stability.
Key optimization points:
Precise dosing: Chlorine dioxide dosing should be adjusted based on a combination of wastewater flow, chlorine dioxide residual, water-quality load, and historical operating data, rather than relying solely on a single parameter such as COD or ammonia nitrogen.
The actual dosage should be determined according to wastewater quality, oxidant demand, target microorganisms, and on-site validation results. A universal fixed dosing range should not be applied.
Reaction condition control: Effective contact time should be determined based on the actual concentration used, target microorganisms, water temperature, wastewater quality, and process validation results.
Chlorine dioxide disinfection performance is relatively less sensitive to pH than that of free chlorine, but actual reaction efficiency can still be affected by water quality, temperature, and the target pollutants. Therefore, “neutral to slightly acidic conditions are always better” should not be used as a universal control principle.
After upstream chlorine dioxide treatment, part of the pathogenic microbial load may already be reduced, but some refractory organic compounds, trace pharmaceuticals, and other pollutants requiring further control may remain in the wastewater.
Depending on the treatment objectives, ozone oxidation or UV disinfection can then be introduced as complementary treatment steps.
Targeted oxidation: Ozone can improve the removal of certain readily oxidizable micropollutants, including some pharmaceuticals and endocrine-disrupting compounds. However, the reactivity of different compounds with ozone varies significantly.
Therefore, ozone dosing should be optimized based on flow rate, conventional water-quality indicators, and periodic monitoring of target pollutants, rather than maintaining a continuously high dose.
Functional complementarity: Ozone and the reactive oxygen species formed under certain conditions can further oxidize some residual organic pollutants, providing functional complementarity with upstream chlorine dioxide treatment. This should not simply be described as a fixed “synergistic reaction.”
Physical disinfection without additional chemical disinfectant dosing: Under appropriate UV dose and water-quality conditions, UV irradiation can provide effective inactivation of certain chlorine-resistant pathogens, including Cryptosporidium and Giardia.
If upstream treatment reduces turbidity, suspended solids, and other substances that interfere with UV transmission, it may improve UV transmittance. However, the UV design dose should still be determined according to target microorganisms, UV transmittance, flow rate, and validation requirements. It should not simply be reduced in proportion to the performance of upstream treatment.
Optimized placement: Under suitable process conditions, UV equipment can be installed near the end of the treatment train as a final supplementary disinfection barrier, helping improve the stability and redundancy of microbial control in the final effluent.
The real improvement in overall system performance comes from clearly defined functions for each treatment unit, properly matched operating parameters, and dynamic control—not simply from adding more treatment equipment.
An automatic feedback control system can be established based on water-quality and operational parameters.
Automatic control may combine online parameters such as flow rate, chlorine dioxide residual, COD or TOC, and UV transmittance. Microbiological indicators are generally more suitable for periodic verification and for checking whether the control strategy remains appropriate.
Based on real-time data, the system can appropriately adjust chlorine dioxide dosing and ozone generator operating intensity.
For UV systems equipped with variable-power control, lamp output can be adjusted according to UV transmittance, flow rate, and the target UV dose, thereby improving operational adaptability.
The key to a multi-barrier treatment process is not that “the more treatment units, the more advanced the system.” The key is that each treatment unit should have a clearly defined treatment objective.
The main wastewater treatment units should be responsible for most of the organic pollutant removal;
chlorine dioxide should primarily be used for disinfection and control of certain readily oxidizable pollutants;
ozone can be used for further treatment of certain refractory micropollutants;
and UV can serve as a final supplementary disinfection step to improve the stability of microbial control.
The order of the treatment units should be validated according to target pollutants, wastewater characteristics, UV transmittance, and by-product control requirements. A fixed sequence such as “chemical treatment first, physical treatment second” or “strong oxidation first, supplementary disinfection afterward” should not be applied mechanically.
Only by clearly defining the role of each treatment step can unnecessary overlap and energy waste be reduced.
When evaluating a combined chlorine dioxide–ozone–UV process, a life-cycle cost analysis should be carried out.
Introducing ozone and UV increases capital investment, electricity consumption, maintenance requirements, and control complexity. At the same time, it may allow the role and dosing strategy of chlorine dioxide to be optimized.
However, whether chlorine dioxide consumption can actually be reduced, by how much, and whether the overall cost is lower must be confirmed through actual operating data.
Economic evaluation should take into account local electricity prices, chemical costs, equipment depreciation, maintenance expenses, testing costs, and by-product monitoring and control costs, so as to find an appropriate balance between treatment performance and total life-cycle cost.
Hospital wastewater characteristics are not constant. Therefore, the performance of each treatment unit and the overall treatment results should be evaluated periodically.
Routine operation should still focus on applicable discharge standards, microbiological control requirements, and key process parameters.
For higher-risk projects or facilities with sufficient technical capability, extended indicators such as biological toxicity, specific micropollutants, and the abundance of antimicrobial resistance genes may be assessed periodically to further evaluate the environmental risk-control performance of advanced treatment.
Based on these evaluation results, the operating intensity of each treatment unit can be adjusted so that the system maintains a reasonable balance among treatment performance, energy consumption, and operational stability.
Remember: simply combining chlorine dioxide, ozone, and UV does not automatically produce better treatment performance. In fact, it may increase capital cost, energy consumption, and process-control complexity.
The real value lies in clearly defining the objective of each treatment unit, minimizing functional overlap, and integrating the technologies rationally according to actual wastewater quality and treatment requirements.
Looking ahead, hospital wastewater treatment projects with reliable online monitoring and automatic control systems may gradually introduce model predictive control or data-driven optimization methods.
Historical and real-time operating data can be used to assist in predicting pollution-load changes and optimizing chlorine dioxide dosing, ozone operation, and the output of variable-power UV systems.
However, such intelligent control depends on reliable online data, proper instrument maintenance, and validated control logic. It should not rely blindly on so-called “AI automatic decision-making.”
The more meaningful direction for intelligent hospital wastewater treatment is to use data to improve operational stability, reduce unnecessary energy consumption, and continuously optimize the balance between treatment performance and cost.
XIUBA will continue to follow developments in related technologies and share more practical application experience and technical insights.
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