Study On The Effect Of Dissolved Organic Matter(DOM) To Photodegradation Of Typical Antibiotics-Metronidazole

With the rapid development of social economy, science and technology, the application of pharmaceuticals and personal care products(PPCPs) are increasing sharply. As a kind of emerging environmental pollutants, PPCPs were continuously detected in various environmental media(such as surface water, groundwater, drinking water, sewage treatment plant, sediments, etc.) in recent years, mostly in levels of ng/L~μg/L. But due to most of this kind of materials were hard to biodegrade, and activated sludge process of sewage treatment plant couldn’t remove them completely, causing many drugs and their metabolites were introduced to all kinds of water environment with the drainage of sewage treatment plant for a long time, which could adverse impact on human health and ecosystems. In numerous of PPCPs processing, Semiconductor photocatalysis oxidation technology is highly appreciated because of its distinguished merits such as high efficiency, low selectivity, no secondary pollution, broad-spectrum property, etc. And nanometer materials showed excellent ability on the degradation of various environmental pollutants, which has attracted much attention because of its low price, high stability and high photocatalysis activity.As a kind of environmental organic matter, Dissolved organic matter(DOM), which has been found in any water environment at any time(Dissolved organic matter in natural water is humic acid and fulvic acid). There is a huge amount of such organisms around water contaminants or particles objectively. Therefore, any water pollutants interact with the DOM inevitably, or must interact with the DOM first, while interacting with particles or sediment. The structure of humic acid and fulvic acid contain large numbers of phenolic hydroxyl groups and carbanyl groups, which can interact with oxide, metal ions and organic compounds including toxic and harmful substances, thus affecting environmental chemical behavior of these materials, such as chemical degradation, photolysis, biological absorption, migration and volatilization of organics and so on.Taking metronidazole as the target pollutant, this text mainly studied the effects of the dissolved organic matter(DOM) on photodegradation of metronidazole. The experimental results are as follows:(1) when illumination intensity was 3360 W/m2, the p H of the solution was 6.55, and the dosing quantity of Ti O2 was 20 mg, the degradation of 20 mg/L metronidazole were best within 60 min, which can reach 100%.(2) Adsorption experiments showed that dissolved organic matter(DOM) had no obvious characteristics of direct action with metronidazole.(3) Under the presence of DOM, the photodegradation and photocatalytic degradation process of metronidazole were both inhibited, the inhibition strengthened with the increase of concentration of DOM. And there were differences between the inhibitory effect. In photodegradation process, the inhibition rate of 50 mg/L humic acid to metronidazole within 60 min was 13.3%, however, fulvic acid was only 5.6%. In photocatalytic degradation process, the inhibition rate of 50 mg/L humic acid to metronidazole within 60 min was 83.6%, nevertheless, fulvic acid could reach 89.7%.(4) Through Characterizing the humic acid extracted from the jiulong river estuary sediments and humic acid of goods, found that although there were some differences in element contents of the humic acid extracted from the jiulong river estuary sediments and humic acid of goods, but they had similar structures and functional groups, and the humic acid extracted from the jiulong river estuary sediments had stronger inhibitory effect than humic acid of goods in both photodegradation and photocatalytic degradation process of metronidazole.