Water Treatment


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Ozone and oxygen for sustainable odour and corrosion control


Paul Turgeon, CEO and Tonya Chandler, VP Sales & Marketing at Anue Water Technologies explain how sustainable oxygen and ozone help improve safety and decrease costly equipment damage in wastewater systems.


W


astewater systems have long been subject to issues with odour and corrosion,


which is understandable given the nature of what they convey. The odour is the driving force behind implementing controls these systems. Corrosion, however, is the issue with the greatest potential for environmental harm and real systemic and economic damage. This damage can arise in the form of burst pipes and other equipment and system failures. Failures of this type require the repair and replacement of system materials and equipment, and they have the potential to expose the environment to unpredictable releases of hazardous wastes that are difficult, if not impossible, to contain or recover.


Corrosion caused by hydrogen sulfide


A major contributor to odour and corrosion in industrial systems is hydrogen sulfide (H2


S) and its


associated compounds. Some industrial wastewater contains sulfur compounds, which provide the molecular basis for the generation of H2


S, which arises


from the combination of anaerobic conditions and the presence of sulfites and sulfates in conjunction with colonies of microorganisms present on the inner walls of all collection systems, referred to as the slime layer. Sulfate-reducing bacteria (SRB) will use these compounds in the absence of free oxygen (O2


) for their metabolism.


These bacteria do not use the sulfur component, and it is available to react with water, specifically free protons (H+ which results in the generation


), 50


S is a colourless gas that has a characteristic rotten egg odor, is highly toxic and is corrosive to certain metals. It is heavier than air, meaning it can accumulate in wells, manholes and other similar locations that do not have much ventilation.


H2 of H2 H2 S.


Following its generation, S can be released into the


atmosphere and find its way to receptors through junctions of the atmosphere and collection system, at which point it is an odour concern. H2


the collection system has easy access to atmospheric oxygen. Bacteria in these areas convert the H2


sulfur from the cycle entirely. S into sulfuric acid, which S is a colourless


gas that has a characteristic rotten egg odor, is highly toxic and is corrosive to certain metals. It is heavier than air, meaning it can accumulate in wells, manholes and other similar locations that do not have much ventilation. The effect it can have on humans, at varying concentrations relative to ambient air, is shown in Table1. H2


S becomes a corrosion issue when it contacts moist concrete or steel, among other metals, in the presence of oxygen, even at very low gaseous concentrations. Conditions such as these are common in the headspace of some pipes and other areas where


then begins a destructive reaction with the infrastructure. Historically, control of odour and/or corrosion has been implemented through either vapour-phase techniques, where the headspace of a system is treated, or liquid-phase techniques, where treatments target the liquid flow. Vapour phase treatments like scrubbers do not provide corrosion control. Some of the liquid phase techniques offer corrosion control. The most common method of inducing liquid-phase treatment, or directly treating the wastewater inside the collection system, has been by dosing chemicals into these systems. A constant and continuous dose of chemical is fed into the collection system from a large reservoir with a small pump, typically at a manhole or pump station. These chemicals are meant to react with the odour- causing compounds present in the wastewater or stop their formation and/or release from solution.


Conventional control options


The conventional classes of reactions used to control H2


S are:


• Oxidation – Chemical oxidation of H2


S is accomplished through the use of an oxidant such as hydrogen peroxide or sodium hypochlorite (bleach).


• Sulfide scavengers (iron salts) –Chemicals that interact with H2


S and sequester, or


scavenge, the sulfur into a relatively insoluble form, such as ferric chloride and ferrous chloride, can be used to remove


• pH adjustment – Because of the waythat its ions dissociate in the aqueous phase, the release of H2


S from wastewater will not occur if the pH is at 9 or above.


Alternate oxygen source/ sulfate substitute In an anaerobic environment, the microbiology in a collection system will use oxygen from a nitrate (NO3


a sulfate (SO4


result, benign nitrogen is released rather than H2


S. Chemicals such


as calcium or sodium nitrate are commercially available and can be used for this purpose. They can be expensive, however, and they feed and grow the SRB layer, potentially requiring a higher volume for treatment over time. Upon cessation of treatment, the amount of H2


S can be even


higher than before. Excess wet well build-up requiring increased clean-out cycles because of the addition of the waxes used to stabilize the nitrate molecules can be encountered downstream in the collection system. In addition, emerging federal and state regulations are beginning to include nitrate concentrations on discharge limitations. Real-time, active monitoring of wastewater H2


carried out, so enough chemical to control peak H2


S levels is seldom S values is


typically added on a constant basis. By treating for peak values with chemicals such as these, the likelihood is very high that excess nitrate will be present and actively added to the wastewater, requiring additional denitrification processes or fines, both of which can be very expensive.


Summer 2020


) group more readily than from ) group and, as a


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