A pilot-scale study on biofilters for controlling animal rendering process odours.

Heating of animal tissue during the process of rendering liberates a variety of odorous compounds. The performance of biofiltration in removing these odours was investigated using pilot-scale biofilters containing different media (sand, finely and coarsely crushed wood bark, and bark/soil mixture). Odour-removal performance of the biofilters was determined using olfactometry. Biofilter odour removal efficiencies of between 29.7% and 99.9% were measured at influent odour concentrations of between 143,100 and 890,000 odour units m(-3), and various air loading rates (0.074-0.592 m(-3) air m(-3) medium min(-1)). Biofilters with bark or bark/soil media and low air loading rates gave the best odour removal. The bark and sand biofilters generally maintained good odour reduction for about three years at an air loading rate of 0.148 m(-3) air m(-3) medium min(-1). Drainage from the biofilters contained significant concentrations of nitrogenous and organic compounds, suggesting that controlled leaching has the potential to remove accumulated substances in biofilter media from rendering gas emissions and increase the longevity of a biofilter system. High pressure drop across biofilter media can adversely affect the odour removal performance. Sand and fine bark, due to their small particle size, caused high pressure drops. Coarse bark showed negligible pressure drop at several examined air loading rates. Pressure drop also increased with moisture content, particularly in sand and fine bark biofilters. Overall pressure drop characteristics of the biofilters described in this paper were maintained without significant change over the three year operation.