BIOFILTRATION OF WWTP SLUDGE COMPOSTING EMISSIONS AT CONTACT TIMES OF 2 TO 8 SECONDS Antonio D. Dorado*, David Gabriel ** and Xavier Gamisans* *Department of Mining Engineering and Natural Resources, Universitat Politècnica de Catalunya, Bases de Manresa 61-73, 08240 Manresa, Spain **Department of Chemical Engineering, Universitat Autònoma de Barcelona, Edifici C, 08193 Bellaterra, Barcelona, Spain E-mail: dorado@emrn.upc.edu ABSTRACT The performance of a biotrickling filter for the abatement of composting emissions was evaluated at short contact times of 2 to 8 seconds. The effect of EBRT, pH control and water renovation rate were evaluated. The average elimination capacity was 13 and 3.3 g N/C m -3 h -1 for ammonia and VOCs, respectively, and the maximum EC obtained during a doping process were 40 and 20 g N/C m -3 h -1 . Biotrickling filters appear as a better alternative than biofilters due to their controllability. However, water renovation becomes a critical parameter to avoid substrate inhibition by nitrite and ammonia accumulation. Not only ammonia absorption is negatively affected at low renovation rate but it is also affected the biological process. A decrease of 40 % was detected in the nitrification step when the hydraulic residence time increased from 2 to 5 hours. Results presented herein demonstrate that high removal efficiencies can be achieved for composting emissions in a biotrickling filter operated at short contact times which entails a substantial reduction of operational and investment costs in comparison to traditional techniques. INTRODUCTION Emissions from waste water treatment plants (WWTP) sludge composting are characterized by high flow rates and low concentrations of several compounds, mainly ammonia and volatile organic compounds (VOCs). The ammonia emission is the consequence of the undesirable nitrogen losses from composting material and the amount emitted is determined by the ammonia/ammonium balance, which depends on the temperature, pH and moisture content. While the ammonia concentration in a composting process of the organic fraction of municipal solid wastes varies between 18 and 150 g NH 3 Mg −1 waste, concentrations up to 700 mg NH 3 m −3 have been reported in exhaust gases from sludge composting (Haug, 1993). Even though these relatively low concentrations in the off gases, they can commonly be perceived even at very long distances from the source, due to their relatively low odour thresholds (Prado et al., 2009). Several physical and chemical processes have been traditionally used to abate ammonia and VOCs from waste gas, including activated carbon adsorption, wet-scrubbing, incineration and air stripping. However, high costs associated to these technologies and the possibility of secondary pollutants emissions make them uncompetitive (Chung et al., 1997). The suitability of either biofilters (BF) or biotrickling filters (BTF) have been successfully tested for the abatement of ammonia and a wide range of volatile organic compounds and conditions in lab-scale studies (Pagans et al., 2007; Baquerizo et al.,