What are organic micropollutants?
Organic micro-pollutants, also known as trace pollutants (Trace Contaminants), are of various types and exist widely. Common organic pollutants mainly include linear aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), organic pesticides (organophosphorus, organic nitrogen), metal organic compounds, etc. As of December 25, 2017, CAS has recorded over 134.55 million compounds, but only 387,671 compounds have been included in the control, which is less than 0.3%. Any compound and its remnants may evolve and iterate into organic micropollutants.
What are the characteristics of organic micropollutants
1) Low environmental concentration As the name suggests, the concentration of organic micropollutants in the water environment is extremely low, usually <10-6g/L, and at the same time, the types are extremely diverse. As a result, the qualitative and quantitative analysis of specific organic micropollutants The detection work is difficult to carry out.
2) Refractory to biodegradation Due to its stable chemical form and extremely low environmental concentration, it is difficult to effectively treat it using biodegradation methods
3) Existing process lags Existing water/sewage treatment facilities have not been designed for non-pollutants, and conventional water treatment processes are not well suited, and most of them are eventually discharged into ultraviolet water bodies
4) Persistent toxicity Some organic substances are highly toxic persistent organic pollutants or endocrine disrupting substances, which have carcinogenicity, reproductive toxicity, neurotoxicity, endocrine disrupting and other hazards, and have a direct threat to human health.
5) “Three effects” Some organic substances are precursors of disinfection by-products, which can form a variety of halogenated organic compounds in the process of chlorination disinfection, and most substances in halogenated disinfection by-products have been confirmed to have “three effects”. effect, and thus endanger human health
activated carbon adsorption
Activated carbon is a porous substance with a large internal surface area composed of micropores. The removal of organic matter by activated carbon mainly relies on microporous adsorption. The removal rate of activated carbon to trihalomethanes produced by chlorination was 20-30%, and the concentration of trihalomethanes in water and the amount of activated carbon also affected the removal efficiency of trihalomethanes.
Ozone can change the properties of pollutants by destroying the molecular structure of organic pollutants because of its strong oxidizing ability. The effect of ozone on trihalomethane precursors (THMFP) can be divided into two categories. When ozone oxidation is used alone, and the water is chlorinated again, the content of trihalomethanes increases instead of that before oxidation, but if the amount of ozone added can completely convert the organic matter into CO2 and H2O, the trihalomethanes after water chlorination can be avoided. The generation of methane, but this cannot be achieved in the actual water treatment process.
Photocatalytic oxidation is a degradation method in which UV+H2O2/O3 is used in combination. Its outstanding feature is its strong oxidizing ability. The polluted water is irradiated by broadband ultraviolet rays to generate hydroxyl radicals with strong oxidizing ability (∙OH, redox potential 2.78V) to react with the micro-polluted organic matter in the water body to promote its oxidative degradation and decomposition. It is small molecule non-toxic H2O and CO2.