This guest column originally appeared in Water & Wastes Digest November 2019 as "Green Odor Control"
Every community produces wastewater. It is not something that we can avoid or change. It is full of bacteria, biomass, and it produces odor. But does it have to stink? Do we have to damage the environment to ensure that our noses are happy? Does choosing sustainable treatment mean that we need to give up effective treatment? You might be surprised to find out that two of the most effective forms of odor control come from thin air.
In recent years, the drive for green technologies has influenced how both communities and manufacturers do business. The water and wastewater industries have been challenged to find environmentally friendly alternatives to standard chemical treatments for odor and corrosion. Traditional methods, such as calcium nitrate, iron salts, pH adjustments and chemical oxidation, are not looked upon as environmentally friendly and sustainable. Mechanical filtration for odor, such as geomembrane systems, filter systems, scrubbers and natural chemicals, have become strong alternatives for odor control but are seen as capital intensive. As sustainable options come to the market place, many people struggle to understand exactly what these treatment do and how they work.
To understand odor control you must understand where and how the odors are generated. The most common source of odor control is the biological degradation of the biomass, caused by sulfide oxidizing bacteria, also known as SOBs. This amazingly resilient bacteria can survive in aerobic, anoxic and anaerobic environments making it a super bug of wastewater. Oxygen-loving at its inception, when there is no more dissolved oxygen left, it will start to feed on nitrogen. Once the nitrogen is no longer present, it makes a metabolic change to sulfate (sulfate reducing bacteria, or SRB), which causes it to produce hydrogen sulfide as a byproduct of its reduction. This hydrogen sulfide is the nuisance and sometimes dangerous odor we smell and what leads to corrosion. However, the bacteria has an Achilles heel; once it has acclimatized to an anaerobic environment, it metabolically changes and no longer can live in an oxygen rich environment. By adding oxygen to the environment, the environment then is uninhabitable for the bacteria, leading to its elimination. This has led to the ultimate sustainable technology, which pulls treatment out of thin air.
There are many methods to produce and administer oxygen into a system, but the chemistry behind the treatment is sound. Add enough oxygen to the environment and the bacteria cannot survive. This works best with purified oxygen methods, most of which are onsite generation or liquid.
Ozone treatment takes oxygen treatment to an additional level. Ozone, though sometimes technically considered a chemical, is a naturally occurring form of elemental oxygen with oxidizing power. It destroys bacteria on contact, losing its electron and breaking down to oxygen. This can raise the dissolved oxygen in the water during treatment. In most cases, raising the dissolved oxygen in a system is beneficial, which supercharges the SOB bacteria, keeping them in a non-odorous state. This can reduce corrosion caused by the bacteria and keeps the systems clean. This treatment method works most effectively in force main systems, where the pressure of the system helps keep the gases in the water. Most ozone systems require a stream of purified oxygen, providing a one-two punch in treatment.
Ozone also has gained popularity in wet wells, where it can effectively keep the vapor space free from odor causing bacteria, killing it on contact. Ozone joins many other forms of mechanical treatment, such as scrubbers and covers, as a way to keep odors from escaping the collection system. Filtered membrane covers also have come to the market, combining the effectiveness of carbon with the ease of a cover. These methods use the movement of air and carbon to filter or “scrub” the odors away.
While the return on investment on each system will be different, the path to sustainable treatment does not need to be lined with dollars and cents. In most cases, the capital outlay of an oxygen or ozone system will be offset by the long-term operating cost savings in chemicals and maintenance. Mechanical or onsite generation methods can require site work and covering.
Oxygen is present in the air we breathe and made from the natural world we live in. With its place as one of the most powerful oxidizers in the world, it is hard to conceive that ozone can be made from this same oxygen. It makes oxygen and ozone the ultimate sustainable green treatment method.