Doctoral dissertation proposal
Abstract
Gaseous pollutants, including volatile organic compounds and aromatic substances, are very harmful and dangerous for the environment and human health. There are many methods such as physical methods, chemical methods and biological methods to remove gaseous pollutants. In the meantime, biological methods are more widely used due to their lower costs. Biofiltration is an effective and economical biological method for removing gaseous pollutants. In a biofilter, gaseous waste is passed through a bed containing microorganisms. This method is especially suitable in cases where the pollutants have a high volume and low concentration. Bacteria and fungi are the two dominant groups of microorganisms used in biofilters. The advantage of bacteria is their rapid substrate consumption and rapid growth. But they have problems in removing hydrophobic compounds. In addition, the operational stability of biofilters is often affected by acidification or drying of the substrate. Mushrooms are more resistant to acidic and dry conditions. In addition, the mycelium structure of mushrooms causes faster absorption of hydrophobic compounds. Mercaptans are major and important impurities among petroleum products. These substances are toxic and produce an unpleasant odor even in very low concentrations. Removing these compounds using an appropriate biological method such as biofiltration is very important.
In this project, the aim of the biodegradation of ethyl mercaptan using a trickling bed biofilter is to investigate the effect of various factors on the performance of the biofilter.
Key words: ethyl mercaptan, biodegradation, biofiltration, loading Discontinuous
1- Introduction
In order to carry out the project defined in this doctoral thesis, the current research topics are presented in two chapters. The first chapter provides a comprehensive definition of volatile sulfur compounds, environmental problems caused by them and different methods of their destruction by reviewing the available sources and documents. The second chapter includes the objectives of the present thesis, research innovations and detailed details for the implementation of this task.
2- Volatile sulfur compounds
The emission of odorous substances is a common environmental problem and can cause serious problems in the neighborhood of the emission site. Among these harmful substances, volatile organic compounds containing sulfur (VOSCs) [1] that are produced from various industries contain a large volume and can cause serious environmental problems that threaten public health. These compounds mainly include dimethyl sulfide, dimethyl disulfide, methane thiol, carbon disulfide, carbonyl sulfide, and ethane thiol [30]. The nature and concentration of molecules detected by olfactory cells differ in different people and in different environmental conditions such as temperature, pressure and humidity. Humans are able to detect very small amounts of scented substances. It is estimated that only 108 or 109 molecules of odorant gases in the nose are enough to detect the smell. Meanwhile, 1 microgram of ethyl mercaptan in the air contains approximately 1016 molecules, which means 107 or 108 times the amount required for detection. The sensitivity of humans to odors makes it necessary to control the amount of odorous wastes closely, if these wastes are produced near human settlements [22].
3- Release of volatile sulfur compounds
Both natural and human sources contribute to the production of organic sulfur compounds and their release in the atmosphere.
3-1- Natural sources [2]
S-methylmethionine[4] and S-methylcysteine[5]. The contribution of methylation reactions, reduction
dimethyl sulfoxide (DMSO) and lignin degradation in the production of Me2S is still unknown. Kelly and Smith [6] (1990), stated the formation of Me2S as a result of oxidation and dimerization of MeSH. About 30% of the COS present in the atmosphere originates from the oxidation of CS2, while the share of oceans and natural soil resources is 28 and 24%. Human activities increase the natural values ??of CS2: the share of chemical industry waste is 58
%. On the other hand, the share of oceans and natural soil resources in the total CS2 in the atmosphere is 4 and 34% [26]. 3-2- Sources related to human activities [7] Volatile sulfur compounds are mainly They are produced in processes where an organic substance is heated or degraded anaerobically. 3-2-1- Anaerobic processes [8]
Hydrogen sulfide is usually known as the most important odorous gas in wastewater treatment industries. However, many researchers recognize volatile organic sulfur compounds close to hydrogen sulfide as the main aromatic substances produced by these industries. Gerrards [9] and his colleagues (1995) measured concentrations of 30 ppmv of Me2S and 4 ppmv of H2S in gaseous wastes from an aerobic wastewater treatment system of a brewery. The emission of volatile sulfur compounds is greatly increased due to the presence of low oxygen areas that encourage the activity of anaerobic (facultative) microorganisms. According to the research conducted by Laplanche [10] and his colleagues (1994), the preliminary stages (pumping, primary treatment, etc.) and the treatment line (concentration, dewatering, etc.), 30 to 65% are involved in the release of odorous substances. Animal breeding sites and compost preparation are also known as the cause of odor production as a result of microbial anaerobic activity. During the production of compost, H2S, COS, MeSH, CS2, Me2S, Me2S2 and dimethyl trisulfide (Me2S3) are the main aromatic compounds produced with concentrations of 24 to 80 ppbv. The total sulfur emitted is about 3.8 mg per kilogram of compost. Conditions
Anaerobic conditions during the composting process, such as the presence of very wet areas or poor mixing of raw materials, encourage the formation of volatile sulfur compounds, while after aeration their emission is greatly reduced [26].
3-2-2- High temperature processes[11]
In slaughterhouses, waste and dead animals are turned into valuable products such as glue, non-edible greases and fat (pi). During cooking (T>105?C), harmful aromatic substances are produced, which are mainly related to the presence of volatile sulfur compounds, amines, acids, alcohols and aldehydes. Chalo and Namink [12] (1984), measured the average concentration of H2S and MeSH at 30 ppmv in the exhaust gases collected from the cooking units of slaughterhouses. According to the research conducted by Lekamate [13] and his colleagues (1995), 10 to 1000 grams of sulfur and nitrogen compounds are produced per ton of materials and per hour in a slaughterhouse, the main of which are: H2S, MeSH, ethane thiol and NH3. In thermal sludge treatment industries, methyl sulfides, pyrazines, thiopenes, and indole are the cause of the smell caused by these industries.
Contents & References of Biodegradation of ethyl mercaptan using stabilized microbial system
List:
Chapter 1- An overview of the topic
1- Introduction 1
2- Volatile sulfur compounds 1
3- Publication of volatile sulfur compounds 1
3-1- Natural resources 2 3-2- Sources related to human activities 3-2-1- Anaerobic processes 3-2-2- High-temperature processes 4-3-2-3- Industrial uses 4 3-2-4- Chemical processes 4- Characteristics of volatile sulfur compounds 5- 4-1- Odor threshold 5- 4-2- Toxicity 6- 4-2-1- Toxicity to humans 6- 4-2-2- Toxicity for microorganisms 7- 4-3- Corrosive effect 7- 5- Ethyl mercaptan and its properties 8- 6- Degradation methods of volatile sulfur compounds. 10 6-1-Physicochemical methods 10 6-1-1 Thermal oxidation 10 6-1-2 Catalytic combustion 12 6-1-3 Scrubbing 14 6-1-4- Adsorption on solid surface 15 6-2- Biological methods 17 6-2-1- Bioscrubbing 17 6-2-2- Trickling bed biofiltration 18
6-2-3- Biofiltration 21
7- Terminology related to biofilters 24
7-1- Empty bed residence time and actual residence time 24
7-2- Inlet mass load 24 7-3- Removal efficiency and removal capacity 25 8- Parameters affecting the operation of biofilters 25 8-1 Biofilter substrate 25 8-2 Amount 28
8-3- Porosity 28
8-4- Pressure drop 29
8-5- Specific substrate surface 29
8-6- pH 30
8-7- Flow rate 31 8-8- Pollutant concentration 31 8-9 Gas phase humidity 32 8-10 Liquid phase 32 8-11 Temperature 33 12-8- Microorganisms 33 9- Enzyme system of the fungus Phanrochaete chrysosporium 36 9-1- Ligninolytic enzymes 36 9-2- Kinetics Oxidation of environmental pollutants by ligninolytic enzymes 37
9-2-1- Catalytic cycle of peroxidases 37
9-2-2- Manganese peroxidase reactions 38
9-2-3- Lignin peroxidase reactions 39 9-3- Cytochrome P 450 42 9-3-1 Structure and reaction mechanism 42 10 Research done in Iran 44 Chapter Two - Objectives, innovations and detailed work details
1- Objectives and stages of the project 47
2- Project innovations 52
3- Project schedule 53
References
Source:
1- Taginejad Namini, Masoud, using trickle biofiltration for Removal of hydrogen sulfide from synthetic gases, Master's thesis, Faculty of Chemical Engineering, Amirkabir University of Technology, 2016.
[3] An, T., Wan, Sh., Li, G., Sun, L., Guo, B., 2010. Comparison of the removal of ethanethiol in twin-biotrickling filters inoculated with strain RG-1 and B350 mixed microorganisms. J. Hazard. Mater. 183, 372-380. [4] Busca, G., Pistarino, Ch., 2003. Technologies for the abatement of sulphide compounds from gaseous streams: a comparative overview. J. Loss Prevention in the Process Industries. 16, 363-371.
[5] Cho, K., Ryu, H. W., Lee, N. Y., 2000. Biological Deodorization of Hydrogen Sulfide Using Porous Lava as a Carrier of Thiobacillus thiooxidans. J. Biosci. Bioeng. 90(1), 25-31.
[6] Devinny, J. S., Deshusses, M. A., Webster, T. S., 1999. Biofiltration for air pollution control. Boca Raton, FL: Lewis Publishers, CRC Press LLC.
[7] Guo-ying, Z., Jun-xin, L., 2004. Investigation of factors on a fungal biofilter to treat waste gas with ethyl marcaptan. J. Environ. Sci. 16(6), 898-900. [8] Harvey, P. J.