Odor control is a big issue for wastewater managers. Finding cost-effective techniques that don’t create other environmental headaches or disposal problems remains an elusive goal, particularly with respect to sludge processing for class A or B biosolids used as compost for agricultural or other applications. One very promising technique developed by a Canadian company uses ozone to control odors from operations that generate sulfur-based or anaerobic-based odors.
This system has been proven in composting operations that generate anaerobic odors. Although the system was tested in composting operations, any wastewater facility that’s dealing with organic-based odors stands to benefit.
Composting operations turn organic materials into the “soil” used to grow mushrooms. In the composting process, anaerobic and aerobic odors are emitted and various strategies have been used to try to control these odors. These odors include sulfurs, mercaptans, indoles, amines and other problem compounds.
A good example of how problem odors can affect facilities is Greenwood Mushroom Farms in Ashburn, ON, Canada. The company had enjoyed a relatively peaceful existence until urban sprawl from Toronto finally caught up to the operation. While composting was the smell of money to owners Brent and Clay Taylor, their new neighbors did not share their agricultural mindset. Lawsuits ensued and eventually the case reached the Supreme Court of Canada.
Envron Environmental Inc., a Canadian ozone technology company, previously demonstrated an ozone odor control system at the University of British Columbia (UBC) in conjunction with the British Columbia Ministry of Agriculture. UBC researcher Dr. Monty Bruce used an odor panel to test the ozone system and concluded that it had reduced to non-detect levels odors from a mushroom compost operation there. His conclusion:
The untreated samples required dilution rates of between 1,701-3,043 which is typical of odorous substances (A 1-liter sample would be diluted down to 1,701-3,043 liters before being considered non-offensive).The ozone treated samples were diluted to between 209-264, which is typical of non-odorous substances. As well, the treated samples actually smelled like ozone which has an almost antiseptic or sanitary smell.
Envron designed a larger system for Greenwood and installed it on three mushroom composting bunkers. The system uses a computerized controller to coordinate fans that push air into the compost heap and then ventilates the bunker through an ozone contacting system.
Eager to see if there was a solution, the Canadian Mushroom Growers Association in conjunction with Agriculture & Agri-Food Canada and the Ontario Ministry of Agriculture hired AirChem Consulting to provide a report on how well the system performed. AirChem’s conclusion was that the system destroyed the odors from the bunkers. Results in reduction of total sulfur concentrations are noted in Table 1.
Destruct/Retention System - An ozone retention system allows ozone time to react with odorous compounds from the Greenwood composting process.
“We had previously killed odors in hog and poultry barns, septic and sewage systems and other industries,” says Allan Finney, Envron technical directo. “However, it wasn’t until we conducted the tests that people really started to take notice.”
While AirChem measured reductions in total sulfur, Finney says this doesn’t measure the total odor reduction of the system. The UBC study used an odor panel which is a more accurate way of determining odor control. Both studies, though, concluded that odor control was achieved.
Blower/Ozone Generators - Air is forced into the mushroom bunkers with the large fan (left). The ozone system (right) injects ozone into the air exhaust system.
“The penetrating odors are the result of a combination of a number of chemical compounds, not just Sulfur” says Finney. “Ozone is able to quickly break those chemical bonds and kill the associated odors - and it works.”
AirChem Consulting & Research Inc. is based in Bright’s Grove, ON, Canada. Contact: Greg Duns, 519-271-5461 or email@example.com