Ozonation of artificial aquaria seawater: Oxidation kinetics and byproduct formation

Ozone is being extensively used at all major artificial seawater (ASW) aquaria. There is limited information on the chemistry of ozonation in these high total dissolved solids solutions. The purpose of this research was to identify and model the ozone reactions associated with the ozonation of ASW. This model will be used to assist the aquarium industry in understanding the chemical effects of ozonation in their full-scale water treatment processes. The model was developed that accurately predicts ozone decay at an ozone dosage of 1 × 10−5 M (0.5 mg/L) that is typically used on ASW aquaria. The system of 24 differential equations, of which 23 represent inorganic reactions, was solved utilizing a commercially available differential equation solver. The model was validated in both organic-free ASW and three operating aquarium tanks containing organics. This work has shown that direct ozone reactions dominate over indirect (hydroxyl radical mediated reactions). This work has also shown that in the absence of bromide, free chlorine species are formed due to the high concentrations of chloride in the ASW formulations. These free chlorine species may have health effects on the aquarium animal species similar to those caused by free bromine species. This modeling has demonstrated that ammonia removal is achieved through reactions with secondary oxidants following ozonation. Thus ammonia removal via ozonation may impact the design of aquarium water treatment systems. The model also identifies the production of residual oxidants including the free halogens and chloramines. The contribution by this work to the industry includes a more complete understanding of reaction chemistry resulting from ozonation of ASW and a tool to assist in water treatment system design and operations management.