While sizing and selecting an ozone generator is a simple process for many applications with consistent source waters, however, it is not as straightforward for every case or treatment objective.
Consistent Source Water Sizing
Groundwater that does not have surface water influence and water sources that use significant pretreatment processes are typically consistent feedwater. The flow ozone generator sizing equation is used to size these water sources with level ozone demands:
Ideally, bottled water should have a residual ozone residual of 0.1 to 0.2 after 2 to 4 minutes of detention time. This will disinfect and eliminate odor from the area.
Sizing of Variable Source Water
A high degree of variability in monitored quality parameters and ozone demand will be observed in surface water, groundwater influenced by surface water, industrially contaminated groundwater, and industrial and municipal wastewater.
Drinking water treatment plants and commercial-industrial customers experience larger organic load variations during spring snow melt, summer downpours, algae blooms, and autumnal turnover. During challenging seasonal conditions, municipal treatment plants with flocculation, sedimentation, and filtration systems may experience operational difficulties.
They can provide safe drinking water in compliance with federal and state standards, but elevated TOC levels can use up all the ozone in the bottled water ozone system sized without safety factors. This leads to a low residual content in the bottles.
The public has become increasingly aware of endocrine disrupting compounds (EDCs), personal pharmaceutical care products (PPCPs), and other emerging contaminants. Industrial waste treatment processes and municipal wastewater treatment processes bring these substances into our water at low levels.
Water Quality & Ozone Demand
As a result of the fact that spring or groundwater contain more ozone than reverse osmosis (RO) permeate, which has already removed most dissolved ionic and organic materials with which ozone may react, the suggested 1 mg/L dose for RO permeate and 1.6 mg/L dose for spring water is based on the premise that spring or groundwater have more ozone demand. A source water analysis may be used to estimate ozone demand based on elements measured in the treated or untreated source water, such as iron, manganese, sulfide ions or hydrogen sulfide (H2S), total organic carbon (TOC), and microorganism load.
It is possible for an ozone generator supplier to assist with the standard ozone reaction doses for these materials. For example, a good stoichiometric dose for sulfide ion/H2S is 4 mg/L ozone for 1 mg/L sulfide ion.
The oxygen in the gas stream participates in the ozone oxidation process, resulting in a reduction in the amount of ozone required in the real world compared to the chemical reaction. Gas-to-liquid mass transfer systems can have a significant impact on how much ozone is actually needed from air-fed and enriched oxygen sources. As a result of low capital and operating costs, oxygen-fed ozone generators are currently the most common system designs.
Example of Bottled Water Sizing
If 20,000 gallons of purified water are bottled each day from reverse osmosis (RO) treatment, a 0.5 parts per billion (ppb) ozone generator would be needed to produce 1.0 mg/L of ozone at a rate of 9 gph from reverse osmosis (RO). In order to bottle 20,000 gallons of natural spring water per day, a 0.8 parts per billion (ppb) ozone generator would be required, assuming 1.6 mg/L dose of ozone.
Typical ozone generators have flow rates of 10, 20 or 30 gallons per hour. It is therefore important to choose the generator size based on the source water. If you use RO permeate, you will need a 10-gph unit, while if you use spring water, you will need a 20-gph unit. Purchasing at least a 15-gph ozone generator is required for a bottled water business that offers both purified and spring water to its customers and runs two consecutive eight-hour shifts. It is possible to expand up to 25% with a 30-gph system if both bottling lines are to be operated over the eight-hour period.
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