Biosystems Engineering (2006) 95 (1), 69–82 doi:10.1016/j.biosystemseng.2006.05.006 SE—Structures and Environment Size Reduction of Ammonia Scrubbers for Pig and Poultry Houses: Use of Conditional Bypass Vent at High Air Loading Rates R.W. Melse; A.V. van Wagenberg; J. Mosquera Wageningen University and Research centre (WUR), Animal Sciences Group, PO Box 65, 8200 AB Lelystad, Netherlands; e-mail of corresponding author: roland@melse.info (Received 21 June 2005; accepted in revised form 9 May 2006; published online 24 July 2006) In The Netherlands, both acid and biological air scrubbers are used for removal of ammonia from exhaust air at pig and poultry houses. Current regulations require that scrubbers are dimensioned for treating the maximum airflow rate that may occur, so on average these systems are overdimensioned and underloaded. A new approach is introduced that is based on bypassing airflow peaks untreated. As a result, the air loading rate in m 3 [air] m À3 [scrubber] h À1 and ammonia loading rate in kg [NH 3 ]m À3 [scrubber] h À1 of the scrubber are more constant in time and average loading rates increase. By model calculations and analyses of measurement datasets it was demonstrated that the application of such a scrubber significantly decreases the required scrubber size while ammonia emission levels are only slightly increased (e.g. where the bypass is operated at 50% of the maximum ventilation rate and the scrubber volume is reduced by 50%, the bypass venting systems only allows 10–20% of the total ammonia load to be vented untreated). As a result, both the efficiency of scrubber utilisation in kg [NH 3 removal] m À3 [scrubber volume] and the cost-effectiveness of air scrubbing for ammonia removal in kg [NH 3 removal] h À1 are increased. r 2006 IAgrE. All rights reserved Published by Elsevier Ltd 1. Introduction 1.1. Animal husbandry and ammonia abatement Pig and poultry production contributes substantially to the economies of many Western European countries in terms of employment and export of products. Pig production in Western Europe is concentrated in several regions characterised by large-scale intensive farms. The Netherlands, with 16 million inhabitants and a popula- tion density of about 400 inhabitants per km 2 , houses 11 million pigs at approximately 10 000 farms (CBS, 2004). From the 1980s onwards, the emission of ammonia (NH 3 ) from livestock farming has become a major environmental concern because ammonia emission is one of the three main sources of soil acidification and eutrophication of natural soils in The Netherlands (Heij & Erisman, 1995, 1997). Therefore considerable efforts have been put into the development of ammonia abatement techniques in animal operations. This focus on ammonia abatement has resulted in the development of a variety of low-emission livestock housing systems that are applied today. These systems include end-of- pipe systems for treatment of the exhaust air from pig and poultry houses, viz. acid scrubbers and bioscrubbers or biotrickling filters. However, investment and opera- tional costs of scrubber systems are generally considered as high. 1.2. Working principle of ammonia scrubbers An air scrubber, or trickling filter, is a reactor that has been packed with an inert packing material. The packing material usually has a large porosity, or void volume, and a large specific area. The packed bed is wetted by spraying water on top. Exhaust air from an animal house, containing ammonia, is introduced either in a cross-current or counter-current direction which results in intensive contact between air and water ARTICLE IN PRESS 1537-5110/$32.00 69 r 2006 IAgrE. All rights reserved Published by Elsevier Ltd