Sustainable Environmental Protection Technologies by Pranas Baltrėnas & Edita Baltrėnaitė

Author:Pranas Baltrėnas & Edita Baltrėnaitė
Language: eng
Format: epub
ISBN: 9783030477257
Publisher: Springer International Publishing

6.4 The Distribution of Temperature, Acidity (pH) and Oxygen in the Packing Material of the Biological Air Treatment Filter

The environmental factors determining the vital activity of microorganisms in low-efficacy biofilters are divided into physical, chemical and biological (Devinny et al. 1999; Iliuta et al. 2005). Physical factors most frequently affecting the growth and proliferation of microorganisms cover humidity, temperature and osmotic pressure (Baltrėnas et al. 2004c). The most important chemical factors having an effect on the vital activity of microorganisms include the composition of the nutrient substrate and its component concentration, hydrogen ion concentration (pH), oxidation-reduction conditions, toxic substances, temperature and oxygen content.

The research carried out under laboratory conditions involved determining the temperature of the medium, pH and oxygen distribution throughout the full volume of the packing material using three different laboratory biofilter benches and three different types of the packing material using straight and wavy lamellar plates and tubes replacing the plates. The studies involved three different types of pollutants. Temperature is the key factor affecting the proliferation rate of microorganisms and the intensity of biochemical reactions. Different groups of microorganisms are adapted to living at different temperatures.

The microorganisms involved in the biodegradation processes of pollutants are classified into psychrophilic, mesophilic and thermophilic. Psychrophilic microorganisms can proliferate at a temperature between 7 °C and 30 °C. The membranes of psychrophilic microorganisms are high in unsaturated fatty acids, and therefore remain semi-liquid in cold. These microorganisms best proliferate at a temperature of 10–20 °C. To decompose volatile organic compounds (VOCs) in small biofilters, mesophilic microorganisms the optimal proliferation temperature of which reaches 20–45 °C are commonly used (Darlington et al. 2001; Yamamoto et al. 2005).

The optimal temperature of thermophilic microorganisms is 45–75 °C (Dhamwichukorn et al. 2001; Kong et al. 2001; Van Liere and Van Groenestijn 2003). US and Canadian researchers found high 99% efficiency of the droplet biofilter removing ethanol and methanol from the air using thermophilic bacteria. The best results were obtained maintaining the temperatures of 53 °C (ethanol decomposition) and 60 °C (methanol decomposition) (Cox et al. 2001; Kong et al. 2001).

Cellular transport mechanisms, reactions and growth rate of microorganisms, the decomposition of substances and the synthesis of materials into new compounds are subject to the acidity of the medium, which is expressed in pH ranging from 0 to 14. The pH of the neutral solution is 7, that of acidic solutions fluctuates from 0 to 7 and that of alkaline solutions varies from 7 to 14 (Biogas… 2013). Generally, the optimal pH for the growth of microorganisms ranges between 6.5 and 7.5. Most microorganisms tolerate pH variations in ±1–2 from the optimal value (Pukalskas 2007). Variations in the reaction of the medium change the activity of heterotrophic enzymes. Neutral, slightly alkaline or acidic media are used for biological air treatment, hydrogen ion concentration in which may fluctuate from 6 to 8 (MacNevin and Barford 2001). Most media applied for decomposing volatile organic compounds have neutral hydrogen ion concentration (pH = 7).

Aerobic microorganisms contribute to the decomposition of volatile organic compounds.

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