Anita Turała, Andrzej Wieczorek
West Pomeranian University of Technology, Szczecin, Poland
corresponding author’s e-mail:
Abstract
The study presents a description of both the main problems of biofiltration as well as the new research directions. Discussion of the first subject covered the area of biofiltration applied in purification of exhaust gases. The method traditionally used for the purification of waste gases from biological processes is also suitable for the treatment of hot and dry air, contaminated with substances of high toxic concentrations. According to the literature reports, hydrocarbons belonging to all groups: compounds containing oxygen in the molecule such as aldehydes, ketones and esters, compounds containing nitrogen and sulphur in the molecule like amines, thiols or organic sulphides can all be filtered out. Chlorinated hydrocarbons and some inorganic compounds like ammonia and hydrogen sulphide can also be removed. All these substances can be present individually or in multicomponent mixtures.
The biofilters have been divided into conventional ones provided with a wet bed and the ones fitted with a biotrickling bed. A set of information on the materials used to compose a bed with a division into natural and synthetic has been given. The division of natural beds has been described as biodegradable, like peat, compost, wood chips and non-biodegradable as volcanic rocks. Among the synthetic beds mention are the ones made of mineral types of expanded clay aggregates and other minerals, as well as synthetic organic plastics, for example polyurethane foams.
Factors influencing the biofiltration process, such as gas flow rate, concentration of pollutants, their type and properties, temperature, humidity of gases and sediments, structure a bed, oxygen availability, salinity and pH of the bed, as well as the availability of nutrients not found in treated gases, were presented in the paper.
An extensive chapter was devoted to the microorganisms colonizing the bed of biofilter, which are responsible for the decomposition of filtered out pollutants. They can be introduced to the biofilter as microorganisms that naturally inhabit given building material or placed on a bed in the form of a vaccine. A consortium of microorganisms, formed during the start-up of a biofilter (adaptation), composed of bacteria and fungi, undergoes constant changes caused by the influx of new microorganisms along with purified air and the influence of environmental factors. These changes can be both quantitative and qualitative, manifested by the occurrence of genetic mutations. The microorganisms that colonize the bed belong to many species, such as Pseudomonas, Pseudoxanthomonas, Xanthomonadales, Ralstonia, Mycobacterium, Exophiala i Candidia. They metabolize environmental pollutants. This most often takes place during the catabolic process initiated by enzyme-assisted oxygen attack per molecule. As a result, appropriate alcohols are first formed, which than undergo successive transformations to aldehydes, fatty acids and further down to water and CO2.
The chapter devoted to additives improving the bioavailability of pollutants such as methanol, silicone oils and surfactants, was included in the paper. New products in the field of construction solutions and hybrid systems were explained. Solutions such as rotary biofilters and cylindrical beds aim to reduce problems with even gas flow and excessive flow resistance. Among the hybrid systems, pre-filter solutions with active carbon and a UV pre-treatment module were presented. The idea of a biofilter combining the removal of pollutants with the generation of electric current in microbial fuel cells is also presented.
Keywords
biofiltration, air biofiltration, biofiltration of air pollutants, biofiltration – development trends
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