Research article Continuous measurements of ammonia, nitrous oxide and methane from air scrubbers at pig housing facilities C. Van der Heyden a, b , E. Brusselman b , E.I.P. Volcke a , P. Demeyer b, * a Department of Biosystems Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium b ILVO, Institute for Agricultural and Fisheries Research, Technologyand Food Unit, Burgemeester Van Gansberghelaan 115, Bus 1, 9820 Merelbeke, Belgium article info Article history: Received 21 April 2016 Received in revised form 1 June 2016 Accepted 4 June 2016 Keywords: Air scrubber Ammonia Nitrous oxide Methane Removal efficiency abstract Ammonia, largely emitted by agriculture, involves a great risk for eutrophication and acidification leading to biodiversity loss. Air scrubbers are widely applied to reduce ammonia emission from pig and poultry housing facilities, but it is not always clear whether their performance meets the requirements. Besides, there is a growing international concern for the livestock related greenhouse gases methane and nitrous oxide but hardly any data concerning their fate in air scrubbers are available. This contribution presents the results from measurement campaigns conducted at a chemical, a biological and a two-stage biological air scrubber installed at pig housing facilities in Flanders. Ammonia, nitrous oxide and methane at the inlet and outlet of the air scrubbers were monitored on-line during one week using a photoacoustic gas monitor, which allowed to investigate diurnal fluctuations in the removal performance of air scrubbers. Additionally, the homogeneity of the air scrubbers, normally checked by gas detection tubes, was investigated in more detail using the continuous data. The biological air scrubber with extra nitrification tank performed well in terms of ammonia removal (86 ± 6%), while the two-stage air scrubber suffered from nitrifying bacteria inhibition. In the chemical air scrubber the pH was not kept constant, lowering the ammonia removal efficiency. A lower ammonia removal efficiency was found during the day, when the ventilation rate was the highest. Nitrous oxide was produced inside the bio- logical and two-stage scrubber, resulting in an increased outlet concentration of more than 200%. Methane could not be removed in the different air scrubbers because of its low water solubility. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Ammonia can harm the environment as it involves a risk for eutrophication and acidification leading to biodiversity loss (Oenema et al., 2012). As 94% of the ammonia emissions originates from agricultural activities (UNECE/LRTAP, 2012), this sector has a great effort to make. Since 2004, newly built pig housing facilities in Flanders are legally obligated to implement low ammonia emission techniques. This can be achieved e.g. by applying air scrubbers that remove ammonia from the outgoing ventilation air through ab- sorption in water, followed by chemical and/or biological conver- sions and removal of the end products. Intense contact between the gas and liquid phase ensures mass transfer of water soluble pollutants (e.g. ammonia) from the air to the washing water, where a chemical equilibrium is established, e.g. with ammonium: NH 3ðgÞ þ H 2 O ðlÞ 4NH 3ðlÞ þ H 2 O ðlÞ 4NH þ 4ðlÞ þ OH  ðlÞ (1) The washing water is recirculated to reduce water consumption. Eventually, the concentration of accumulating contaminants in the washing liquid becomes too high and discharge of the washing water becomes necessary. Fresh water must be added to compen- sate the water loss due to discharge and to evaporation. In a chemical air scrubber an acid is added to the washing water to decrease the pH and thereby increasing the driving force as more ammonia is converted into ammonium. In biological air scrubbers, ammonium captured in the washing water is oxidized by nitrifying bacteria to nitrite (NO 2  ) and subsequently to nitrate (NO 3  ). In a combined air scrubber, two or more scrubbing stages are placed in series. These can involve a water stage, mostly followed by a chemical or a biological scrubbing stage. More details on the operating principles of biological, chemical and two-stage air * Corresponding author. E-mail addresses: caroline.vanderheyden@ugent.be (C. Van der Heyden), Peter. Demeyer@ilvo.vlaanderen.be (P. Demeyer). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.06.006 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management 181 (2016) 163e171