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Biofilters a natural way to control hog barn odour

Odour mitigation is an important question for the future of Manitoba’s growing hog industry

A new research project at the University of Manitoba is taking aim at hog manure odours the natural way.

PhD student Desmond Essien is investigating the potential of using biofilters as an odour mitigation technology for use in swine barns in Manitoba.

Essien spoke about his research at the New and Emerging Research sessions at last month’s Prairie Livestock Expo.

A biofilter, Essien explained, is essentially a layer of organic material (typically mixture of 30 per cent compost and 30 per cent wood chips) that supports a microbial population. Odourous air is forced through this material and is converted by the microbes to carbon dioxide and water.

Research first began in North America in 1999 when Dick Nicoli, a professor at University of Minnesota started to explore the concept.

Nicoli began by building a 750-sow facility and placed a biofilter on it. He then invited guests to a series of lunches at the facility. When not a single complaint about smell was received, Nicoli realized he was on to something and the research on biofilters gained traction.

A biofilter built on the side of a curtain-side finishing building in the U.S. state of Iowa.
photo: Iowa State University

Essien did a literature review of the science since that time and found the research is encouraging.

Studies reported:

  • A reduction of ammonia of 45-75 per cent;
  • A reduction of hydrogen sulphide of 80-95 per cent;
  • A reduction of odour of 70-95 per cent;
  • A reduction of particulate matter of 80 per cent; and
  • A reduction of volatile organic compounds (VOC) of 76-93 per cent.

The wide range in the results was largely because the effectiveness is seasonally dependent.

Moisture content is the most critical part for the efficient operation of a biofilter. Generally a sprinkler system on automated timers is used to maintain optimum moisture content (50-60 per cent humidity). But Essien points out that achieving the optimum levels is a fairly tricky process because it’s difficult for farmers to determine what that moisture level exists at in the biofilter.

The most accurate measurement is known as a gravimetric method which involves taking a sample of the medium and putting it in your oven to determine the moisture content. The problem with this method is that it’s impossible to get real-time results.

To get real-time results, other methods have been used: a “load-cell” method (measures the change in weight of the material); a time domaine reflectometry (TDR) method (passes energy through the system and produces a waveform reading that is analyzed to determine moisture); and soil and hay moisture probe method. But none of these methods are as accurate as the gravimetric method.

Essien says he is working on combining these methods.

“I want to use the gravimetric method and calibrate them to the load-cell method, the TDR and the soil and hay moisture probes,” he said.

The optimal operating temperature of a biofilter is between 30-35 C. In winter it is a huge challenge to reach these temperatures. However, Essien said that research from Minnesota was showing that the air exhaust from the barns has shown to be warm enough to keep the biofilter operational in winter.

The final factor affecting the efficiency of a biofilter is the empty bed contact time (EBCT). This refers to the amount of time the air has to be in contact with the biofilter. Early tests were using 20 seconds or more contact time, but it’s been determined that a 70 per cent reduction in odour can be achieved with an EBCT of just three seconds.

Construction costs including materials and labour, typically run between $80 and $270 per 1,000 cfm. Operating and maintenance costs are estimated at between $5-$15 per 1000 cfm annually.

During the opening remarks of the Emerging Research session Andrew Dickson, Manitoba Pork’s general manager, noted that there is a desperate need for more hog barns to make sure that production facilities run at full capacity.

With this projected growth, and odour being one of the big complaints of people living nearby hog barns, Essien is convinced odour mitigation will be an important consideration for the industry’s future.

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