Core Disadvantages of Ultraviolet Disinfection Technology in Sewage Treatment

Core Disadvantages of Ultraviolet Disinfection Technology in Sewage Treatment Although ultraviolet (UV) disinfection technology boasts numerous advantages in sewage treatment, it still has obvious shortcomings restricted by its technical principles and application conditions, which need to be focused on especially under the complex working conditions of sewage treatment: 1.  No sustained bactericidal ability and risk of microbial photoreactivation    UV disinfection is a **physical instantaneous sterilization method, which only damages the DNA structure of microorganisms in water but cannot leave any "residual bacteriostatic components" with sustained antibacterial effect in the water body. If the disinfected sewage is subjected to secondary pollution during pipeline transportation or storage, the residual microorganisms (such as some bacteria and viruses) may repair the damaged DNA and restore their activity through environmental light or dark repair mechanisms (namely the **photoreactivation/dark reactivation phenomenon**), thus reducing the microbial safety of the final effluent. 2.  Significant interference of sewage quality on disinfection effect    Impurities commonly contained in sewage, such as suspended solids, turbidity, chromaticity and organic matter, will seriously affect the penetration ability of ultraviolet rays:    - Suspended solids and colloidal particles will adsorb and wrap microorganisms to form a "protective barrier", preventing ultraviolet rays from effectively irradiating the microbial bodies;    - Colored substances and dissolved organic matter will directly absorb ultraviolet energy, reducing the effective dose actually acting on microorganisms.    Therefore, when the SS (suspended solids) concentration of sewage exceeds 20 mg/L or the turbidity exceeds 5 NTU, additional pretreatment processes (such as coagulation, sedimentation and filtration) are required; otherwise, the disinfection efficiency will drop sharply. 3.  Equipment is prone to contamination and requires frequent maintenance    Calcium and magnesium ions, iron and manganese ions, algae and viscous organic matter in sewage are very easy to form **scales or biofilms** on the surface of quartz sleeves of UV lamps, hindering the transmission of ultraviolet rays. To ensure the disinfection effect, the sleeves need to be cleaned regularly by physical methods (such as mechanical brushing) or chemical methods (such as pickling). The cleaning frequency increases with the deterioration of sewage quality, which not only increases the operation and maintenance workload, but also generates additional cleaning costs.    In addition, UV lamps have a fixed service life (usually 8,000–12,000 hours), which need to be replaced as a whole when expired, and the long-term cost of lamp consumables cannot be ignored. 4.  Limited inactivation effect on specific microorganisms    For some microorganisms with special structures in sewage, the inactivation efficiency of UV disinfection is not as good as that of chemical disinfection:    - For spore-forming bacteria (such as Bacillus subtilis), due to their dense spore shells and stronger DNA protection mechanisms, a higher UV dose is required to achieve effective inactivation;    - For some pathogenic microorganisms deeply wrapped by particles, it is difficult to kill them only by ultraviolet ray penetration. 5.  Dependence on power supply and weak emergency response capability    UV disinfection equipment is completely driven by electricity. In case of power outage or equipment failure in the sewage treatment plant, the disinfection system will fail immediately. Unlike chemical disinfection, it cannot guarantee the basic disinfection effect by emergency dosing of chemicals. For remote areas or scenarios with unstable power supply, standby power supplies need to be equipped, which increases the initial investment and the complexity of operation and maintenance. 6.  Inability to remove chemical pollutants in sewage    Ultraviolet rays only act on the nucleic acid structure of microorganisms, and **have no removal effect on chemical pollutants such as COD, ammonia nitrogen and heavy metal ions in sewage**. If the effluent has requirements for meeting chemical index standards, it is necessary to be combined with other processes such as biochemical treatment and advanced filtration, and it cannot be used alone as the terminal treatment method for sewage purification.