Water Treatment

Sustainable odour and corrosion prevention in wastewater systems
2nd July 2018

By Michael Smith

Ozone and oxygen quickly and effectively remove the H2S leading to odour and corrosion in collection systems. We look at ozone

Anue-Force-FCS-System (2) Photo.pngOzone and oxygen quickly and effectively remove the H2S leading to odour and corrosion in collection systems. We look at ozone technology, an ultimate solution for sustainable, green wastewater treatment.

 

Odour and corrosion
A major contributor to odour and corrosion in wastewater collection systems is hydrogen sulfide (H2S) and associated compounds, which arise following a growth of sulfate reducing bacteria in  anaerobic conditions. As well as having environmental effects, including an extremely unpleasant odour, H2S is a corrosion risk when in contact with moist concrete or metals, in the presence of oxygen.

Historically, H2S was controlled by directly treating the wastewater inside the collection system, for example by drip-dosing oxidizing, sulfide-scavenging or pH-adjusting chemicals, to prevent the formation or release of harmful compounds. However, these solutions require bulk storage of hazardous chemicals, and they do nothing to address a major source of these compounds, namely microorganisms such as sulfate-reducing bacteria.
 

An ideal solution
Ozone is a naturally-occurring form of atmospheric oxygen – O3. The third oxygen atom makes it a highly reactive molecule, with very high oxidation potential. Ozone can be generated by exciting a flow of oxygen, forcing some ‘normal’ oxygen molecules (O2) to split and combine with others. This is a natural process that can also be applied in wastewater settings, simply using the oxygen in the surrounding air as a source material.

Ozone has been shown to be an effective treatment for the destruction of volatile organic compounds. In fresh water, the half-life of ozone is typically 10-20 minutes, but in wastewater ozone is entirely consumed in under 10 seconds, due to the high levels of potential reactants that are present, including H2S.1 Infusing wastewater with ozone can prevent sulfide production, and eliminate any sulfides already present, but presents no additional hazard to life or the environment, and does no harm to the collection system. It would appear to be an ultimate solution for sustainable, green wastewater treatment.
 

Technical application
Ozone treatment reduces H2S vapour and sulfide levels by oxidizing sulfur-containing organic compounds so that they exist in a form that is no longer malodorous, corrosive or otherwise detrimental to the system and environmental health.  These sulfur-containing compounds, particularly H2S, are typically associated with the anaerobic bacteria ‘slime layer’ found in the parts of the system that have low to zero oxygen present at any given time, such as the inner walls of piping.

Ozone infusion, along with oxygen, into wastewater increases dissolved oxygen (DO) levels.  Increased DO levels will cut through the slime layer and convert the environment into an aerobic layer that is uninhabitable for the bacteria. By eliminating the bacteria and impeding the creation of H2S through oxidation, the technology is able to significantly decrease these negative effects. Compared with conventional drip-dosing techniques, which create technical and financial compromises (e.g. chemical storage and maintenance, infrastructure corrosion, clogging, and even facilitating the sulfide-producing anaerobic slime layer), ozone and oxygen technology provides significant advances in effectiveness and decreases ongoing costs.
 
The technology is useful for industrial wastewater as well as municipal waste. Wastewater from the manufacture and use of organic materials, such as solvents, paints, pharmaceuticals, pesticides, products from coke production, and others, can be difficult to treat. Oxidation may provide a novel solution for many industrial settings, reducing corrosion and contributing to reuse and recycling efforts that are increasingly important as the strain on water sources increases, leading all users to work towards water conservation.
 

Ozone in action
Anue Water Technology has designed and manufactures a range of ‘FORSe Series’ systems (pictured above) that use oxygen and ozone for sustainable and cost-effective treatment of odour and corrosion in wastewater collection systems. This involves a proprietary process of direct treatment into the force main, coupled with treatment in the wet well of the lift station. Furthermore, Anue has developed a system that generates ozone on-site, when and where it is needed. The technology simply takes air, separates out the oxygen, and processes it into ozone. The ozone reverts to oxygen when it reacts, so the system is highly sustainable and very efficient.

Several case studies demonstrate the utility and effectiveness of ozone technology, providing interesting insights into the efficacy of this approach.

Case study 1: For example, one customer in Tennessee approached Anue with an odour problem that was not being sufficiently controlled by the addition of chemicals. The system was dealing with around 175,000 gallons per day. Anue proposed a demonstration of its FORSe 5 Odor & Corrosion system, with the goal of reducing H2S from 120 ppm to ≤50 ppm. The system was installed, and ozone and oxygen were pumped into the collection system at the lift station and force main. Within 3 days, the average H2S level had dropped to 20–30 ppm (Figure 1). A couple of months later, a constant H2S average of 1 ppm was recorded. The ozone technology removed the H2S problem and saved the city thousands of dollars per year in chemical expenses.
 
Similar results have been reported at other sites, always showing immediate results and eventual removal of the H2S problem.
 
Case study 2: An interesting test case was performed at a lift station in Alberta, Canada. Following installation of the oxygen technology for three days, the system was stopped for 2 days, and then re-started four days later. Clear and immediate responses in H2S and DO levels were observed in response to the test system starting, stopping and re-starting again. The average H2S level before oxygen treatment was 59 ppm, dropping to 2.4 ppm after 2 days of treatment. When treatment was stopped for 2 days, H2S levels increased slowly to an average of 34 ppm on Day 2, and then slowly reduced again to 1.17 ppm a few days later.  
 

Conclusions
Oxygen and ozone have been around since the beginning of time … literally. It has only been in the past few years, however, that the injection, monitoring and control technology has become cost-efficient enough for industrial and municipal water treatment professionals to use. Effects can be clearly seen in less than 24 hours, and there are no undesirable side effects.

Another driver in the increased use of ozone and oxygen has been regulatory, public and worker safely concerns over the transportation and continued use of potentially harmful chemicals.
 
Together, the technology improvements in ozone and oxygen injection, with the regulatory and consumer demands to replace certain chemicals, are making ozone and oxygen, two of the world’s oldest elements, the newest wave in wastewater treatment.
 
Reference
  1. Terry PA. Int J Chem Engin 2010; article ID 250235.
Contact
Tonya Chandler , Vice President of Sales and Marketing  of Anue Water Technologies, 5123 S Royal Atlanta Drive, Tucker, GA 30084, USA
T: +1 760 213 7739
E: info@anuewater.com



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