Photo credit: Yann H. Contratto, Senior odor expert – Ribe BioGas center a/s (Danemark – July 2014)
By Yann H. Contratto, Senior Odor Expert, President of OlfactoExpert Inc and founder of OlfactoNetwork.
Pressure groups protesting the implementation of biomethanization plants because of potential odors are wrong. Their concepts include deodorizing units, made mandatory by studies based on MDDEFP specifications, which guarantee proper sanitation.
In nearly all these studies, the implementation of a biomethanization project improves the olfactory landscape of the sector in question. From a sample of ten biomethanization plants in North America, odor impact studies show that the frequency and intensity of the odors decreased between 55% and 92% compared with previous conditions.
The odor nuisance reduction rate is even higher when biomethanization projects are implemented within wastewater treatment plants (WWTP) or residual material (RM), and many factors help to effectively improve the quality of life of residents.
The purpose of biomethanization is to convert the biodegradable fraction of various types of RM into biomethane, a biogas which is rich in methane (combustible) but also many odorant chemical components including sulphur with very low olfactory perception thresholds, and nitrogen. All must be efficiently purified.
Consequently, the main influencing factors are the quality and dimensioning of the deodorization procedures. Many chemical and biological technologies are tested to eliminate odors at the source. Sometimes it is an occasion to link other secondary sources, but in every case, it is essential to integrate a guarantee of both chemical and olfactory elimination.
The closed and leaktight design of biomethanization units and related buildings prevents any fugitive or mass emanations while concentrating odors toward their treatment units.
And, depending on the case, a reduction in the amounts of the secondary RM transported is also a notable improvement factor. As for biomethanization projects in conjunction with WWTP, there are many benefits: In addition to improving the environmental report associated with savings in residual matter transportation, this type of cohabitation enables the use of short, leakproof pipelines between sludge production and anaerobic digesters. This change is important because it eliminates many emission sources. These include conveyors, loading and transporting sludge in dump trucks. This pipelines eliminate the need to open doors which are difficult to control as well as the concentrated bursts of odors which cause so many problems. Also eliminated are outdated treatment units, with short chimneys and which, in every case, are so hard to control for WWTP operators.
Finally, these projects put an end to sludge dehydration which at times is a veritable odor generating process. Because the “old” sludge was wet, it had a huge potential to release volatile components as it dried. On the other hand, the digestate extracted from the digesters matures inside the production building and produces nearly dry granules, with a very low odor concentration, often smelling like undergrowth!
In Quebec, each certificate of authorization is carefully examined by the Ministère de l’environnement, which, to the ambient air standards set forth in the “Air Quality Regulations” (Articles 196, 197 and 202 of the AQR – Gazette Officielle, June 2011), has added guidelines adapted to biomethanizatoin and composting activities (2012).
Although the criteria defining the tolerated frequency of odors for the pubic is strictly regulated, the projects that have been evaluated to date show that they not only qualify, but that the frequency and seriousness of olfactory episodes can be greatly decreased.
Biomethanisation requires the involvement of olfactometry experts to monitor the main emission and odor control parameters, including planning the performance of the deodorizing units.
These projects are notable for their significant improvement to the olfactory landscape. It is important, however, not to idealize them because, even though the MDDELCC standards are stringent and even if they are followed, there is no guarantee the unrealistic “zero odor” level will be reached.
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