Using Ozone to Treat Drinking Water From Dugouts

By Hugh Mack, Alberta Environmental Centre, Vegreville

Many illnesses can be transmitted by surface water. As a result, reducing the risk of illness is the most important consideration when choosing the best water treatment system for you..

Ozone has been used in water treatment for more than 80 years. It is a powerful oxidizing agent that can reduce levels of many impurities in water, including colour, taste and odour. Ozone can also be used as a disinfectant and is a good alternative to chlorine for some applications.

In the summer and fall of 1993, staff from Alberta Environmental Protection conducted field trials on the use of ozone to treat drinking water from farm dugouts.

A trailer-mounted water treatment system was set up at two sites in Alberta's Peace Country. In a series of experiments, ozone was applied to dugout water at and above the rates that are used in most of the home ozone systems currently being marketed in Alberta. Even when ozone was applied at well above typical rates, it failed to disinfect the test waters. This demonstrates that most home ozone systems would be inadequate to disinfect water from similar dugouts, without severe restrictions in the water flow rate.

Comparable laboratory tests on samples collected from Lethbridge area dugouts showed lower ozone requirements than the northern dugout waters. Disinfection of these dugout waters should be possible using controlled water flow rates and available ozone generators.

All of the dugouts used in this study were well-maintained, and of comparable di-mensions. The regional variation is due to differences in filling practice. The southern test dugouts are filled from nearby irrigation systems. The northern test dugouts receive controlled runoff from nearby grass areas or fields.

Variations in dugout water quality limits the use of standard ozone system sizing. The only practical way to ensure a proper dosage is to measure dissolved ozone in the water. Residual ozone has to be present, and should remain in the water several minutes downstream of the ozone injection point to reliably disinfect drinking water.

Here are two examples of ozone treatment on dugout water. Both cases use an ozone generator with a maximum capacity of 0.5 g/hr on air service (considered a "large" model on the local market):

1. A well-maintained farm dugout near Spirit River is filled by controlled runoff from a grass area. More than 15 mg/L of applied ozone is probably required to provide a safe residual ozone level of 0.4 mg/L. To achieve 15 mg/L, the full generator output would have to be dissolved in a water flow of less than 0.5 L/min (1/10 USgal/min).
2. A well-maintained farm dugout in the Lethbridge area is filled with water from southern Alberta's irrigation system. The required ozone dose to achieve the same 0.4 mg/L residual is a fraction of the Peace Country case, at around 3 mg/L. To accomplish this dose, water flow should be limited to 2.8 L/min (3/4 USgal/min).

Ozonation technology boasts a very impressive list of capabilities, however it is not a magic bullet for all situations. Ozone has to be applied at the right dosage and given proper allowance for contact time to achieve disinfection.