Study On The Formation And Mechanism Of Chlorinated Disinfection By-products Of Antibiotics In Mariculture System

Chlorination disinfection and antibiotic addition are two universal processes of marine culture.Chlorination disinfection eliminates pathogens,in the meantime,it's unavoidable to react with other organic substances in the water to generate halogenated disinfection by-products(DBFs).Antibiotic residue not only pollutes water but also acts as a precursor that produces new DBFs.Norfloxacin(NOR),Sulfamethoxazole(SMX)and Roxithromycin(ROX)have been repeatedly detected in mariculture waters.The fate of antibiotics in chlorination disinfection,such as the kinetics,reaction centers,products and mechanism were investigated.The results show that:(1)' NOR,SMX and ROX could be oxidized by disinfection agent NaClO,but the oxidation rate was considerably dependent on the type of the disinfected water and followed the trend of sea water>marine culture water>fresh water.The difference was primarily attributed to the promotion role of bromide ions in seawater and marine culture water.The reaction activation energy decreased with increasing concentration of bromide ions,meaning that the reaction should occur more easily and was comparatively faster in the presence of Br'.The total organic halogen analysis showed that the DBPs in marine culture water owned stronger toxicological properties than the DBPs in fresh water.Moreover,the bromide ions could result in the generation of Br-containing DBPs(Br-DBPs).The toxicity increase was attributed to the occurrence of Br-DBPs in the disinfection process of the marine culture water.(2)The main reaction center of NOR with NaClO was N4 atoms on the piperazine ring and C8 in nalidixic ring.Apart from the piperazine ring and C8 atom,the carboxyl group in the quinolone ring has become the primary reaction site with the presence of Cl-1 and Br-1.The main reaction of SMX with NaClO was halogen substitution occurred on the amine moiety rather than the isoxazole ring or sulfonamide nitrogen,however,in the presence of bromide ions,the S-N bond and the S-C bond of the SMX were easily to be cleaved attack by NaClO/Br-and the methyl group on the isoxazole ring was oxidized to yield a carboxylic acid group.The main reaction of ROX with NaClO was halogen substitution reaction followed by cleavage of the N-C bonds on the tertiary amines or loss of the whole desosamine moiety.Therefore,in the presence of Cl-1 and Br-1,the C-O bonds on the cladinose moiety was easily to be cleaved upon attack by chemical oxidation,and then bromine substitution occurred at this breakpoint.Meanwhile,chlorine substitution occurred at the C2,C8 and C10 position.In conclusion,antibiotics is not immediately injected after NaClO disinfection to avoid the formation of more toxic disinfection by-products.At the same time,in the future research should propose a new disinfection process to control the formation of disinfection by-products.