Odour is a challenging aspect of wastewater treatment. It impacts employee satisfaction and health, in turnover and succession planning, and simply just getting people excited about the industry.
Odour makes itself present in rinse water, solid waste/sludge, collection systems, holding tanks, secondary biological systems, and incinerators. In the anaerobic state, microbes present in wastewater have no dissolved oxygen available, which allows sulfate-reducing bacteria to thrive. These bacteria respire utilizing sulfate ions present in wastewater, resulting in hydrogen sulfide - a strong corrosive agent, as well as a strongly odorous one.
Other organic compounds can often cause odour problems in the industry - mercaptans and amines, in addition to hydrogen sulfide.
It’s an overt problem for many who work in the industry. How do we control industrial odour?
Masking has a bit of a bad name. While it’s important in households, (what would we do without Febreeze?) in industrial sizes it doesn’t really meet the scale of the hydrogen sulfide problem. While it may help with citizen and local complaints, it’s doesn’t eliminate the problem. It just covers it up.
Still, it has its uses in industrial settings.
The city of Charlottetown, PEI, found masking to be a good interim odour solution. When citizens were complaining about a new sewage facility and the odours expelled, engineers said the plant simply had to get up to capacity in order to mitigate the smells. But citizens weren’t too happy.
Their temporary solution was vanilla. Charlotte ordered industrial spray to mask the offensive odour while they looked for a more permanent solution and to buy time for the facility and operators to work out the kinks before trying a more permanent solution.
The masking agent only cost the facility $200, which is easily the cheapest option on the market for temporary industrial odour abatement.
When odours are the result of harmful chemicals in the air, then masking isn’t an option. Neutralizing, instead, removes chemicals from the air without (or with the assistance of) filtration.
Hydrogen sulfide, for example, is responsible for most of the odour problems associated with brewery and food processing wastewater treatment. Heavier than air, colorless, corrosive and extremely toxic, its raises serious workplace health and safety concerns. It also can threaten the integrity of processing equipment, and impact employee productivity.
In air treatment, vapour-phase technologies filter from the source, such as wet walls, headworks, and more. The system maintains negative pressure in affected areas, which prevents leakage of odorous air from vents. Air only has one route - through the ventilation system - and so it’s effective for medium- to large-scale odour abatement and removal of non-corrosive materials, as well as particulate matter.
A type of filtration system, wet scrubbing is a system that forces pollutants in contact with water or other solutions, which are then filtered out.
It’s extremely effective for both gaseous materials and particulate matter. Particles are captured (either absorbed or dissolved) in liquid droplets, which are then treated before being reused by the facility or disposed of.
Wet scrubbing is highly effective, and scales with power usage. It also neutralizes many corrosive gases. On the other hand, some chemicals can become corrosive acids when mixed with scrubbing agents, and so wet scrubbing is a solution for very specific odour and chemical problems like hydrogen sulfide, organic wastewater odours, and ammonia.
When multiple odours or agents are present, a two-stage scrubbing system can be put in place. Hydrogen sulfide is best neutralized with sodium hydroxide, while other compounds are treated with sodium hypochlorite in a second stage. This increases efficiency of the system and decreases the amount of each treatment chemical needed for the space,
Hydroxyl-generating machines use multi-frequency UV rays to create reactive, compound-neutralizing molecules. They’re probably the best solution for occupied spaces, since hydroxyls are safe to breathe (unlike scrubbing or ozone generators).
Generators can be used in both closed and open areas, because it’s safe to breathe. The area can be occupied while the generators are running.
A variable speed fan blows contaminated air through the machine’s chamber, where UV rays and ambient humidity oxidise to create hydroxyl radicals. Quartz optics may also deodorize airflow and eradicate other bacteria.
Purified air exits the chamber, and carries the newly-generated hydroxyl radicals. They react (oxidise) extremely easily with hydrogen sulfide and other industrial wastewater compounds, removing them from the air, from surfaces and from contents. When these chemicals oxidise, the result is water and organic radicals.
Not all contaminated air has to pass through the chamber to be effective. In fact, it’s probably the most reliable system for open-air deodorizing.