Science - October 16, 2009

Bio air scrubbers do not trap enough ammonia

The European Union should give chemical air scrubbers the status of 'Best Available Technique' in order to reduce ammonia emissions from pig pens. Bio-scrubbers do not deserve this title.

Air scrubbers in a new pig pen.
This is the contention of Wageningen PhD-candidate Roland Melse in last month's Biosystems Engineering. He will be graduating on 26 October.
Air scrubbers were introduced into the Dutch pig farming industry in the past decade to reduce ammonia discharges and combat environmental pollution. While there were 200 air scrubbers located at the back of pig pens in 2004, there were 880 last year, says Melse, of the Wageningen UR Livestock Research unit. Ninety percent of these are chemical air scrubbers, in which an acid removes the ammonia from the air inside the pens. The rest are bio-scrubbers, in which bacteria convert the ammonia into nitrate. The air scrubbers also reduce some of the foul smells and emissions of fine particles. The Dutch government considers both types of scrubbers as 'best available technique' (BAT); but not the European authorities.
High Council
During his research, Melse found that the robust chemical scrubbers often work well, but bio-scrubbers are more erratic. 'The bacteria only work under very exact conditions. If the pig farmer does not know much about these conditions, the performance will be affected.' He therefore advises against placing bio-scrubbers on the BAT list, thus airing his disagreement to the Dutch High Council ruling which considers both the chemical scrubbers and the bio-scrubbers as BAT. Because of this ruling, Melse's advice will not have any practical consequences for Dutch pig farmers. However, it remains to be seen whether the EU will consider one or both air scrubbers as BAT.

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