AIR POLLUTION CONTROL BY BIOLOGICAL TREATMENT

AIR POLLUTION CONTROL BY BIOLOGICAL TREATMENT

Introduction

Industrial air emissions are generally contaminated with one or more of the air pollutants namely dust, fumes, gas, mist and vapor. There has also been increasing concern over the emission of hazardous air pollutants (HAPs), smog pre- cursors and odors from industrial facilities. Contaminants are commonly removed from industrial waste air by thermal treatment, activated carbon adsorption, or scrubbers. Thermal treatment includes direct flaring or catalytic oxidation. This is effective at high concentration of the organic pollutant. However, it becomes too costly when concentrations are low because a secondary fuel has to provide the majority of the energy required to oxidize the contaminant. In activated carbon adsorption, compounds are adsorbed on to the surface of the carbon, producing a very clean effluent. However, the amount adsorbed per unit mass of carbon is related to the concentration of the contaminant in the air. Low concentrations cause a low adsorption rate; therefore, the amount of carbon required per unit mass of contaminant becomes too large as concentrations decrease. Scrubbers are effective for removing many odors and other highly soluble compounds, but suffer from very high operational costs and the production of a secondary waste stream – compounds are transferred but not destroyed. In recent years, research into the accessibility and transferability of best available control technologies (BATs), specifically environmentally sound technologies (ESTs), has expanded rapidly (OECD 1995; UNEP 1997; SCAQMD 1999).Biological treatment systems, classified as ESTs, provide ecologically sensitive as well as cost effective options because they have intensive operation and maintenance, and reduce or eliminate the need for additional treatment of end products. They also meet the need for an economical method for treating low concentrations of contaminants. A need has therefore been felt to prepare a state of paper on biological treatment of polluted air. The present paper
(i) briefly summarizes the conventional approaches to control air pollution and
(ii) provides concept along with salient features and recent developments in biological waste gas purification.