On March 15, 2022, the national "Hygienic Standard for Drinking Water" GB5749-2022 was released, replacing the original GB5749-2006. The new national standard has adjusted the indicators from the original 106 to 97 items, with 4 new indicators added: geosmin (10ng/L), 2-methylisoborneol (10ng/L), acetochlor (0.02 mg/L), and chlorate (0.7 mg/L).
Process Flow Example
Hazards of Micro-pollutants
Geosmin (GSM), also known as methyl mercaptan, is a common odor-causing substance that is usually produced along with the growth of bacteria and plankton, especially cyanobacteria. It can cause irritation to the respiratory tract and skin, and long-term exposure can pose serious health risks.
2-Methylisoborneol (2-MIB) is also a common odor-causing substance that coexists with geosmin in bacteria and plankton. It has a vinegar-like pungent odor. Long-term exposure can harm the central nervous system, causing symptoms such as dizziness and nausea, and in severe cases, it can damage the liver and kidneys.
Urban Water Supply Treatment Process Flow Description
(1) Raw Water Intake and Pre-treatment
Raw water: sourced from surface water (rivers, lakes, reservoirs) or groundwater.
Pre-treatment:
Pre-chlorination (Pre-chlorine addition): A small amount of chlorine (Cl2 or sodium hypochlorite) is added to inhibit the growth of algae and microorganisms, reducing the load on subsequent processes.
Pre-ozone (Pre-ozone addition): Ozone (O3) is added to oxidize and decompose organic matter, remove color and taste, and enhance coagulation effects.
(2) Coagulation - Sedimentation - Filtration
Coagulation: Coagulants (such as PAC, aluminum sulfate) are added to destabilize colloidal particles.
Sedimentation: Flocs are removed in sedimentation tanks (such as horizontal flow tanks, lamellar tanks).
Filtration: Suspended solids and some microorganisms are further removed through sand filters or activated carbon filters.
(3) Advanced Oxidation Treatment
Primary ozone oxidation (Post-ozone): O3 is added in the ozone contact tank to efficiently degrade refractory organic substances such as pesticides and antibiotics and inactivate viruses. This is usually accompanied by a biological activated carbon (BAC) filter to utilize microorganisms to degrade ozone by-products (such as small molecular organic substances).
UV/H2O2 advanced oxidation: Ultraviolet light (UV) activates H2O2 to generate hydroxyl radicals (·OH), oxidizing pollutants non-selectively. This is suitable for the removal of trace pollutants (such as 2-methylisoborneol, geosmin, etc.).
UV/O3 advanced oxidation: UV and O3 work synergistically to generate ·OH, with higher oxidation efficiency than ozone alone. This is suitable for the removal of trace pollutants (such as 2-methylisoborneol, geosmin, etc.).
(4) Disinfection (Post-chlorination)
Chlorine disinfection: Liquid chlorine or sodium hypochlorite is added to ensure a residual chlorine level of 0.05~0.3mg/L at the end of the distribution network, preventing secondary pollution.
(5) Clear Water Tank and Water Supply
Clear water tank: Stores disinfected water to regulate water supply flow.
Secondary chlorination: Chlorine is added before leaving the plant to ensure the residual chlorine level in the distribution network meets the standard.
Distribution network: Water is supplied to users, with continuous monitoring of residual chlorine and microbial indicators during this period.
Core Technologies
Dual-effect Catalytic Oxidation System (DUET-Ox)
The Crown DUET-Ox advanced oxidation process is based on UV/H2O2 and UV/TiO2 and has the following advantages:
(1) Complementary dual oxidation pathways
TiO2 photocatalysis: Generates long-lasting reactive species such as ·OH and ·O2−, suitable for the ring-opening reactions of micro-pollutants; UV/H2O2: Directly cleaves H2O2 to generate high concentrations of ·OH, rapidly attacking unsaturated bonds; Synergistic effect: H2O2 adsorbed on the surface of TiO2 can be reduced to ·OH by conduction band electrons (electron transfer efficiency increased by 40%).
(2) Technical and economic advantages
Efficient use of oxidants: H2O2 dosage reduced by 30-50% (TiO2 catalysis enables H2O2 to cycle and activate);
Improved UV energy efficiency: 254nm UV simultaneously excites TiO2 (bandgap 3.2eV) and cleaves H2O2 (ε=19.6 L/mol·cm).
Strong anti-interference ability: Wide pH adaptability (pH 3-9), with acidic conditions enhancing the UV/H2O2 pathway and neutral/alkaline conditions leveraging the surface hydroxylation activity of TiO2; high tolerance to water quality fluctuations (quenching effects of Cl−, HCO3− reduced by 60%).
(3) Engineering application advantages
Flexible modular design;
Intelligent control support, with dynamic H2O2 dosing algorithms based on ORP/pH linkage; light intensity self-adaptive adjustment (to prevent electron-hole recombination in TiO2).
