At present, disinfection is commonly adopted in recirculating mariculture system (RMS) to control marine animal diseases and improve water quality. The chemistry associated with the disinfection of aquarium seawater is more complicated than that of freshwater, therefore limited information is available on the formation and speciation of disinfection byproduct (DBPs) in marine aquaria. The accumulating character in recirculating seawater treatment makes it more urgent to control the DBPs formation during disinfection in RMS.
      First, this study investigated various DBPs concentrations and speciations under different water qualities and disinfection processes in Beijign Aquarium. It was found that the adopted disinfection processes were highly effective in controlling marine heterotrophic bacteria, but emerging concerns were raised on the formation of various kinds of DBPs including the secondary oxidants, inorganic oxyanions, and organic species. Free chlorine and free bromine were generated from ozonation with health-relevant concentrations. High concentrations of BrO3– and ClO3– were formed in mammal tanks, which exceeded the USEPA-regulated maximum contaminant level (MCL) for drinking water by 19–25 and 52–54 times, respectively. Extremely high concentrations of NO3– were detected in mammal tanks, which greatly exceeded the MCL regulated by the Sea Water Quality Standard of China for mariculture industry (Class II) by about 1100 times. Undoubtedly, the presence of various DBPs posed serious health threats to aquarium animals.
      Second, the effects of organic precursor, bromide (Br–) and pre-ozonation on the formation and speciation of several typical classes of DBPs, including trihalomethanes (THM4), haloacetic acids (HAAs), iodinated trihalomethanes (I-THMs), and haloacetamides (HAcAms), were investigated during the chlorination/chloramination of aquarium seawater. Results indicate that with an increase in dissolved organic carbon concentration from 4.5 to 9.4 mg/L, the concentrations of THM4 and HAAs increased by 3.2–7.8 times under chlorination and by 1.1–2.3 times under chloramination. An increase in Br– concentration from 3 to 68 mg/L generally enhanced the formation of THM4, I-THMs and HAcAms and increased the bromine substitution factors of all studied DBPs as well, whereas it impacted insignificantly on the yield of HAAs. Pre-ozonation with 1 mg/L O3 dose substantially reduced the formation of all studied DBPs in the subsequent chlorination and I-THMs in the subsequent chloramination. Because chloramination produces much less DBPs than chlorination, it tends to be more suitable for disinfection of aquarium seawater.
      As last, an ozone-bioactivated carbon (O3-BAC) system was designed and operated in an attempt to remove the DBPs precursor and control their formation upon chlorination or chloramination in the RAS. The DOC removal efficiency of the activated carbon column dropped from initial value of approximately 35% to less than 5% in 1500 bed volume operation time. For now, the adsorption capacity of the activated carbon became saturated and GAC filter functioned primarily as a BAC filter, and the DOC removal efficiency kept around 5%.
      Based on the investigation of concentration and speciation of DBPs formed in the RMS of Beijing Aquarium, the influencing factors on DBPs formation upon chlorination/chloramination  and organic precursor removal efficiency via O3-BAC pilot tests were evaluated, which provides theoretical basis for controlling DBPs in RMS.