Biofilters versus bioscrubbers and biotrickling filters: state-of-the-art biological air treatment

Methods for biotreatment of polluted air streams can be classified into four main categories, namely ones using biofilters, biotrickling filters, bioscrubbers, and other bioreactor types. An important advantage of these air treatment methods over competing physical and chemical technologies is that biological processes can be conducted at moderate temperatures (10°C–40°C) and atmospheric pressure. Moreover, microbial degradation processes are generally oxidative in nature and produce compounds such as carbon dioxide, water, sulfate, and nitrate that are ecologically safe. Applications of air biotreatment date back to 1950s. Initially, simple biofilters with soil beds have been employed and later, the use of other bed materials in more advanced filter structures has been reported and more sophisticated types of filtration equipment such as biotrickling filters and bioscrubbers have been developed. On the basis of accumulated experience, some more process options and equipment types for the application of biotreatment emerged in recent years. An overview of the state of the art is provided by outlining process principles and characteristics including the use of various microorganisms and nutrients, variations in equipment design, and application ranges of the different technologies of air biotreatment.