Wastewater treatment has become a focus for states and municipalities across the United States. In order to meet the effluent guidelines and EPA regulatory standards for discharge into the natural environment, many governments are evaluating their current systems for safety and effectiveness.
The generation of wastewater can come from various industrial sources, including textiles, paper manufacturing, oil & gas, iron and steel, food industry, pharmaceutical industry, and others. Wastewater contains a wide range of COD, BOD, and TSS levels, as well as contaminants such as pharmaceuticals, aldehydes, glycol, amines, alcohols, complex proteins. In addition, there are other contaminants found in wastewater; biodegradable organic compounds, volatile organic compounds, xenobiotics, metal ions, suspended solids, nutrients such as phosphorous, nitrogen, microbial pathogens and parasites.
However, the challenge isn’t limited to water disinfection. Some water contaminants may be released into the surrounding air, generating odors. Odor problems are common for wastewater treatment plants due to the abundance of sulfur compounds (H2S and mercaptans), ammonia and those other organic substances.
While each stage in the wastewater treatment process is essential, the EPA says disinfection is considered the primary mechanism to prevent the spread of waterborne diseases to downstream users and the environment. In essence, ineffective wastewater treatment can have damaging environmental consequences.
What is ozone’s role in disinfecting wastewater?
In municipal applications, chlorination, ultraviolet light, and chloramines are primary methods of wastewater disinfection. Ozone disinfection is the least used method in the U.S., although this technology has been widely accepted in Europe for decades. It is generally used at medium to large-sized plants after a secondary or later treatment. Since organic material is naturally present in water, and chlorine can react with these organic materials to form harmful by-products, many municipalities seek other disinfection methods. Ozone treatment has the ability to achieve higher levels of disinfection than either chlorine or UV. It can destroy harmful substances, colors, odors, and microorganisms directly without harmful by-products or the creation of chemical residue.
When ozone decomposes in water, the free radicals, hydrogen peroxy (HO2) and hydroxyl (OH) that are formed have the great oxidizing capacity and play an active role in the disinfection process. This oxidation destroys bacteria through cell wall disintegration (cell lysis). Ozone will also help remove tensides, phenols, and cyanides from wastewater.
What are other benefits of using ozone for wastewater?
Ozone is the most powerful, safest, and environmentally friendly disinfectant available for water decontamination and eliminating odors. But those aren’t the only benefits for wastewater. Another benefit of ozonation is the removal of iron and manganese. While these two elements cause little to no health issues, their removal reduces the discoloration of discharge water. Ozonation will also be beneficial in limiting the build-up of iron and manganese on pipes, fixtures, and other components, helping to reduce overall maintenance costs. Some other benefits of ozone include:
- Ozone requires a short contact time
- Ozone leaves no harmful residuals that need to be removed after ozonation
- Ozone eliminates regrowth of microorganisms, except for those protected by the particulates in the wastewater stream
- Ozone eliminates the costs, storage requirements and logistical uncertainty of chemicals
- Ozone can eliminate the need for re-aeration and raise the level of Dissolved Oxygen DO concentration
- Requires less space and less equipment than many chemical treatment/storage systems
- Ozone will remove some BOD, COD, and other contaminants in the wastewater stream
- Filtration will not be necessary after ozone disinfection
- Fewer secondary by-products like Trihalomethanes (THM) are formed with the use of ozone
- Odor control may be completed during the disinfection process.
Why isn’t ozone used more?
Even though ozone is more effective than other disinfectant options, and it is widely accepted in Europe, it is only slowly gaining acceptance by municipalities in the US. While it has long been used for commercial disinfection of drinking water, EPA guidelines and initial costs are the primary roadblocks to wider ozone implementation.
Ozone generally comes with higher initial capital expenditure – something municipalities are often hesitant about. However, those costs are offset in the long-term by reducing maintenance, eliminating the need for residual removal, and reducing or eliminating chemical purchase and storage expenses. The use of Dissolved Ozone Flotation (DOF) also allows Dissolved Air Flotation (DAF) and Dissolved Gas Flotation (DGF) systems to be more efficient for wastewater treatment. And by consulting with Ozone Solutions design and engineering team, we can help ensure the most efficient and effective system.
Additional information provided from the EPA: https://www3.epa.gov/npdes/pubs/ozon.pdf