& corrosion control
Paul Turgeon and Greg Bock of Anue Water Technologies show how sustainable oxygen and ozone help improve safety and decrease costly equipment damage .
Wastewater systems have
long been subject to issues with odour and corrosion , which is understandable , given the nature of what they convey . Odour is the driving force behind implementing controls in 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 waste that are difficult , if not impossible , to contain or recover .
Corrosion caused by H 2
S
A major contributor to odour and corrosion in industrial systems is hydrogen sulfide ( H 2
S ) and its associated compounds . Some industrial wastewater contains sulfur compounds , which provide the molecular basis for the generation of H 2
S .
H 2
S is a colourless gas that has a characteristic rotten egg odour , 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 . Table 1 shows the effects it can have on humans , at varying concentrations relative to ambient air .
H 2
S arises from the combination of anaerobic conditions and the presence of sulfites and sulfates in conjunction with colonies of microorganisms on the inner walls of all collection systems , referred to as the slime layer . Sulfatereducing bacteria ( SRB ) will use these compounds in the absence of free oxygen ( O 2
) for metabolism . These bacteria do not use the sulfur component , and it is available to react with water , specifically free protons ( H +). This process generates H 2
S , which can then 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 . It also 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 the collection system has easy access to atmospheric oxygen . Bacteria in these areas convert the H 2
S into sulfuric acid , which then begins a destructive reaction with the infrastructure .
56 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981