Improving the Operational Reliability of a Biofilter System for Odor Control

This work describes measures which were taken to improve the performance and reliability of a biofilter system for cleaning the ventilation air in a mechanical waste treatment plant. The improvements were required because of the frequent lack of compliance with the emission limits and operational problems of the system. The ventilation air from the whole plant is cleaned in two stages, a scrubber system, which humidifies the ventilation air and removes dust particles and a biofilter for the reduction of volatile organic compounds (VOCs) and odor emissions. In the first step, the design of the scrubber was changed from a packed-bed scrubber into a nozzle scrubber to solve the problem of frequent blockages of the scrubber packing by deposited sludge. In a second step the biofilters were adapted: 1) making appropriate inspection openings in the biofilter casings where the condition of the filter material can be checked periodically; 2) installation of an improved humidification system, which ensures homogeneous moisture distribution in the filter material; and 3) filling the biofilters with new filter material. Afterward, the pressure drop of the whole system was reduced, cutting the power consumption of the main fan by more than 50%. The reduction in odor was in the range of 75–86% and was stable over the following years. The reduction of the VOC concentration was 33–43%. The reason for the reduced efficiency of VOCs is the fraction of low molecular weight alkanes which are odorless and non-biodegradable.