Wastewater


Ozone for Water Treatment and Disinfection

Waste WaterWastewater 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.

Scientific Publications
Gas Ozone
Reduction of Antibiotic Resistant Bacteria During Conventional and Advanced Wastewater Treatment, and the Disseminated Loads Released to the Environment
Foam fractionation and ozonation in freshwater recirculation aquaculture systems
Use of Ozone and Oxygen in Advanced Wastewater Treatment
Wastewater Technology Fact Sheet Ozone Disinfection

 

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What are other benefits of using ozone for wastewater?

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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.

Water/Well Remediation with Ozone

wellwater-ozone.pngOzone has a greater ability to disinfect water of bacteria and viruses compared to chlorination. To properly disinfect water with chlorine or ozone there must be enough residual of the chlorine or ozone in mg/L (same as saying parts per million or PPM) in the water, AND enough minutes of contact time for disinfection to occur. Water chemistry is also very important.  The pH of the water (how acid or alkaline it is) along with the turbidity and other contaminants all play a role in how effective chlorine or ozone will be at disinfecting your well water of bacteria. Ozone is faster at killing bacteria and oxidizing iron and manganese compared to chlorine or peroxide. For example, the CT value (Concentrate of the oxidizer multiplied by the Time in minutes) for disinfecting water of viruses is 6. 6 minutes at 1 PPM chlorine concentration. Whereas for ozone the CT value is less than 1 (1 PPM with 1 minute of contact time) so disinfection and oxidation occur faster than chlorine or peroxide.

The treatment of well water with ozone is one of the most cost-effective and reliable options available.  The ozone will revert to oxygen and will be perfectly safe to drink without adding any chemicals or salts. An ozone well water treatment system can be developed to provide well water treatment for small to medium sized residential and agricultural systems. Chemicals or salt are not necessary to solve most water quality issues. 

Using an ozone system, it is simplest to eradicate iron, sulfur, and manganese from water. Ozone’s oxidative power makes this possible. As part of the ozone oxidation process, the system must be sized based on the amount of iron, sulfur, and manganese in the water, the well pump’s gallons per minute (gpm), and the quantity of water consumed per day (gpd). In addition to these, there are a number of other factors to consider.

  • Are there contaminants in the water?
  • What is the flow rate?
  • How much water is being used?

It is critical to first understand what oxidation means before you can understand how ozone accomplishes its task. By combining with or adding oxygen, oxides change their form, and electrons are lost, increasing the valence of an element.  

By oxidizing the organic material in bacteria’s membranes, oxygen kills bacteria by causing cell walls to weaken and rupture. As a result, the organism is exposed to the external environment, leading to the death of its cells almost immediately.

The Process of Well Water Ozonation

  • Injection of ozone
  • Aeration
  • Filtration

 

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Additional information provided from the EPA: https://www3.epa.gov/npdes/pubs/ozon.pdf