Ozonation for Reuse of Gold Mine Service Water

Gold mine service water is primarily intended for cooling and dust suppression. Faecal pollution makes disinfection imperative as the workers prefer this chilled water to potable water. Ammonia and nitrite formed by the partial biological oxidation of ammonia lead to an excessive disinfectant demand. Ozo-nation on a 3.6 Mi/d scale proved successful in oxidizing nitrite with simultaneous good disinfection. Ozone transfer efficiencies of more than 96% could be achieved within a deep U-tube compared with 80-90% using a bubble column and 73-80% using an in-line mixer. A unit process capable of introducing 7 mg/ℓ ozone on a 50 Mℓ/d scale would cost US $1.5 million and US $75 000 per year to operate compared with an estimated cost of $1 million per annum for either chlorine or chlorine dioxide.