Ozone Disinfection Model Of Drinking Water

Ozone is an excellent disinfectant, which can efficiently inactivate many microorganisms, such as bacteria and viruses; it also has strong inactivation ability on Cryptosporidium and Giardia. The two worms have great hazard on the public health, and are particularly resistant to free chlorine and monochloramine. When the water contains bromide, ozone process maybe generates bromate. Bromate has carcinogenic even at low dosage. China's newly established drinking water standards have making strictly limit to the two worms and bromate concentration. During ozone process in water treatment, the inactivation of two worms requires higher concentration of ozone, leading the possibility of bromate out of limit became higher. Therefore, ozone process is faced with optimization.Firstly, experiments study the characteristics of Escherichia coli. E. coli being one of those non-spores bacteria is highly resistant to ozone. Then experiments study the degree of E. coli. Resistance to ozone and the variation of ozone sterilization effect caused by changing of water quality such as temperature, turbidity, and pH were carried out in experiments. The results found that ozone has a strong sterilization effect on E. coli. With 0.5mg ozone dosing in 400ml water, the disinfection efficiency of more than 4 log values can be achieved. Changes in water quality have no great impact on disinfection efficiency. The disinfection efficiency changes in the small value when turbidity below 6.3NTU. However, with lower temperature and pH, better disinfection was obtained.Then Bacillus subtilis was selected as the ozone inactivation target. When the temperature is high (≥15℃), the B. subtilis spores can be used as a biological indicator of Cryptosporidium in ozone inactivation. B. subtilis spores has a strong resistance to ozone, with CT value as 10min·mg/L, the disinfection efficiency reached only 2.5 log. Changes in water quality have impact on disinfection efficiency. Turbidity of organic matter competes with bacteria to deplete ozone and reduce the disinfection effect. In the turbidity of 12.5NTU, the disinfection effect reduced by about one log value comparing with de-ionized water when the CT was 7.2 min·mg/L.Simulated the ozone bubble column by using FLUENT software and then tests the validity of the simulation result through actual experiments. The ozone gas-liquid mass transfer coefficient Kl was got by using the UDF function of fluent, and then the liquid phase ozone concentration in each grid was obtain. Based on ozone gas-liquid mass transfer coefficient Kl and overall ozone mass, the ozone concentration and CT distribution were finally calculated.Experimental were done to get the actual ozone concentrations distribution and ozone disinfection result of B. subtilis spores at different heights. Experiments results found that the actual ozone concentration distribution generally consistent with the simulation results and the two results shows the same trends on inactivation efficiency. In bubbling ozone column, over 0.86m the simulation result was quite fit with the actual result. Below 0.86m, there was a certain gap between the two results.This paper established the ozone disinfection model which can serve as basic research for the further study. The obtained conclusions are of universal significance making reference valve for ozone contactor optimization.