## 1 Introduction  
Odour abatement from industrial activities, in particular from wastewater or waste management activities, still represents a significant concern to plant operators due to the gradual encroachment of cities on industrial park and the ever stricter environmental regulations [1]. Despite odorant prevention strategies are applied at source, the implementation of active end-of-the-pipe technologies is often needed to mitigate odour nuisance. In this context, physical-chemical technologies such as incineration, activated carbon adsorption or chemical scrubbing exhibit high operating costs and environmental impacts, which has recently paved the way to odour-treatment biotechnologies [2]. Biotechnologies are based on the biocatalytic action of fungi and bacteria to oxidize, at ambient pressure and temperature, the malodorous compounds present in industrial emissions at significantly lower operating costs and environmental impacts than their physical-chemical counterparts. Bioscrubbers, biofilters and biotrickling filters rank among the most popular biotechnologiesfor odour abatement, although biotrickling filters (BTFs) are increasingly implemented due to their lower footprint, reduced operating cost and high efficiency [3]. However, the high removal performance recorded in BTFs is commonly limited to the highly soluble VOC fraction of the polluted emission, while the abatement of the hydrophobic odorants is commonly restricted due to their low mass transfer rates from the gas to the microbial-containing aqueous phase as a result of their low aqueous solubility [4]. In this context, the addition of a non-aqueous phase to conventional biotrickling filters (i.e., two-phase partitioning bioreactors or TPPB) may boost the removal of the hydrophobic fraction of the odorous emission by enhancing the transport of these compounds from the gas to the microbial degrading community [4]. Despite the significant advances in biological odour removal technologies in the past 20 years, packing material selection still represents the most uncertain and critical design variable in biofilm systems. This is paradoxical since packing material ultimately determines odorant removal efficiency and process operating costs (i.e., pressure drop across the bed and frequency of packing replacement) [5]. In this context, packing materials should meet certain design specifications in order to ensure the most suitable environment for microbial growth and foster gas-liquid mass transfer: high specific surface area and porosity, near-uniform particle size to enhance gas-biofilm exchange and gas distribution throughout the bed, good water retention capacity to avoid biofilter desiccation, significant pH-buffering capacity, high nutrients content, diverse microflora, etc. Additionally, low cost, market availability and good structural properties (to avoid compaction of the bed) are of utmost importance [5; 6]. A compilation of data from full-scale installations revealed that approximately 87% of the biofilters were operated with organic packing materials, wood chips and compost from primary sources such as bark, wood residue, yard trash or agricultural waste being the most popular supports [7; 8]. Compost offers a high specific surface area and porosity, high nutrients content, high microbial diversity, good water holding capacity, easy availability and low cost [6]. Thus, compost-based biofilters have been implemented for the abatement of numerous volatile organic and inorganic compounds (VOCs and VICs) present in gaseous emissions within a wide range of concentrations (from trace levels up to several g m\({}^{-3}\)) [6; 9]. However, compost also lacks from structural stability and compacts easily, resulting in high pressure drops across the packed bed and therefore high energy consumptions. The pressure drop also limits the height of the compost-based biofilter to about 1.5 m, resulting in significant area requirements. In addition, as reported by [PERSON] et al.