Biological and Chemical Conversion Technologies

1. Chapter 14 Biological and Chemical Conversion Technologies

2. Presentation Outline • Introduction • Properties and Classification of Hazardous Wastes • Sources, Types and Quantity of Hazardous Wastes Found in MSW • Significance of Hazardous Waste in MSW • Physical, Chemical and Biological Transformations of Hazardous Waste Constituents Found in MSW • Management of Hazardous Wastes in MSW

3. Introduction • The purpose of this chapter is to introduce and review the biological and chemical processes that can be used to transform the organic fraction of MSW into gaseous, liquid and solid conversion products • The major focus of this chapter is on the biological process because they have been used most commonly for the transformation of organic waste materials • Biological Processes considered in this chapter include • aerobic composting • low – solid anaerobic digestion • high – solid anaerobic digestion

4. Biological Principal • Nutritional Requirements for Microbial Growth • Carbon and Energy Sources

5. Biological Principal • Nutritional Requirements for Microbial Growth • Nutrient and Growth Factor Requirements • Nutrients may at time be the limiting material for microbial synthesis and growth • The principal inorganic nutrients needed by microorganisms are N, S, P, K, Mg, Ca, Fe, Na, Cl. • Minor nutrients of importance include Zn, Mn, Mo, Se, Co, Cu, Ni and W • The major growth factors (organic nutrients) fall into the following three classes • amino acid • purines • Vitamins

6. Types of Microbial Metabolism • Organisms that generate energy by enzyme – mediated electron transport from an electron transport from an electron donor to an external electron acceptor are said to have a respiratory metabolism • Fermentative metabolism does not involve the participation of an external electron acceptor • Obligate aerobic depends on Oxygen to meet their energetic needs • Anoxic depends on oxidized inorganic compound such as nitrate and sulfate • Facultative anaerobs has the ability to grow in either the presence or the absence of Oxygen

7. Types of Microorganisms • Microorganisms are commonly classified on the basis of cell structure and function • The procaryotic groups are of primary importance in the biological conversion of the organic fraction of solid waste and are generally referred to as bacteria • Eucaryotes important in biological conversion of organic wastes include bacteria, fungi, yeasts, actinomycetes

8. Environmental Requirements • Environmental conditions of temperature and pH have an important effect on the survival and growth of microorganisms. • Table 14-4 presents some typical temperature ranges for various bacteria • The optimum value of pH for bacterial growth lies between 6.5 and 7.5 • Moisture content is another essential environmental requirement for the growth of microorganisms • The moisture content of the organic wastes to be converted must be known, especially if a dry process is to be used.

9. Environmental Requirements

10. Aerobic Biological Transformation • The general aerobic transformation of solid waste can be described by means of the following equation • The amount of oxygen required for aerobic stabilization of the biodegradable organic fraction of MSW can be estimated by the following equation • If complete conversion is accomplished, the corresponding expression is

11. Aerobic Biological Transformation • The amount of oxygen required for the oxidation of ammonia to nitrate can be computed by the following equations • computation of the amount of oxygen required for the stabilization of prepared solid waste is illustrated in example 14-1

12. Aerobic Biological Transformation

13. Anaerobic Biological Transformations • Process Microbiology • The biological conversion of the organic fraction of MSW under anaerobic conditions is thought to occur in three steps • Hydrolysis of higher molecular mass compounds into compounds suitable for use as a source of energy and cell tissue • The bacterial conversion of the compounds resulting from the first step into identifiable lower molecular mass intermediate compounds • The bacterial conversion of the intermediate compounds into simpler end products, principally, methane and carbon dioxide

14. Anaerobic Biological Transformations Insert Figure 14-1

15. Anaerobic Biological Transformations • Biochemical Pathways • It is important to know that methane bacteria can only use a limited number of substrate for the formation of methane.

16. Anaerobic Biological Transformations • Environmental Factors • To maintain an anaerobic treatment system that will stabilize an organic waste efficiently, the rector content should be avoid of dissolved oxygen and free from inhibitory concentrations of free ammonia and heavy metals • The pH should range from 6.5 – 7.5 • Sufficient alkalinity should be present to ensure that the pH will not drop below 6.2, because the methane bacterial can not function below this point • A sufficient amount of nutrients must also be available to ensure proper growth of the biological community • Temperature is also another important environmental parameter

17. Anaerobic Biological Transformations • Gas production • The general anaerobic transformation of solid waste can be described by means of the following equation • For practical purposes, the overall conversion of the organic fraction of solid waste to methane, carbon dioxide and ammonia can be represented with the following equaiton

18. Anaerobic Biological Transformations

19. Biological Process Selection • Aerobic and anaerobic processes both have a place in solid waste management. The relative advantages of aerobic and anaerobic processes are summarized in Table 14-5

20. Biological Process Selection • Aerobic Composting • Aerobic composting is the most commonly used biological process for the conversion of the organic fraction of MSW to a stable humus-like material known as compost • Application of aerobic composting include • yard waste • separated MSW • commingled MSW • co-composting with wastewater sludge

21. Biological Process Selection • Process Description • All aerobic composting process are similar in that they all incorporate there basic steps: 1. preprocessing of the MSW, 2. aerobic decomposition of the organic fraction of the MSW, 3. product preparation and marketing • The three principal methods used for the composting of the organic fraction of MSW are • windrow • aerated static pile • in-vessel

22. Biological Process Selection Design and Operational Consideration

23. Biological Process Selection

24. Biological Process Selection

25. Biological Process Selection • Processing Compost for Market • The economics of compost systems are greatly enhanced if the compost can be sold • To be marketable, compost must be of a consistent size, free from contaminants such as glass, plastics, and metals and free of objectionable odors. • shredding and screening are commonly used to produce a more uniform product • Selection of Aerobic Composting Process • because the performance of properly operating window, aerated static pile and in-vessel composting process is the same, the selection among alternative process is based on capital and operating costs, land availability, operational complexity and potential for nuisance problems.

26. Biological Process Selection

27. Low – Solid Anaerobic Digestion • Low – solids anaerobic digestion is a biological process in which organic waste are fermented at solids concentration equal or less than 4 to 8 percent. • One of the disadvantages of the low-solids anaerobic digestion process is that considerable water must be added to waste to bring the solid contents to the required range of 4-8 percent. • The addition of water results in a very dilute digested sludge which must be dewatered prior to disposal

28. Low – Solid Anaerobic Digestion Process Description

29. Low – Solid Anaerobic Digestion Process Description

30. Low – Solid Anaerobic Digestion Process Design Consideration Important design considerations for the low-solids anaerobic digestion of the organic fraction of MSW

31. High – Solids Anaerobic Digestion • Two important advantages of the high solids anaerobic digestion process are lower requirements and higher gas production per unit volume of the reactor size. • The major disadvantage of this process is that limited full scale operating experience is available • Process Description • The principal difference is at the end of the process, where less efforts is required to dewater and dispose of the digested sludge

32. High – Solids Anaerobic Digestion • Process Design Consideration • Important design considerations for the high-solids anaerobic digestion of the organic fraction of MSW

33. High – Solids Anaerobic Digestion

34. Chemical Transformation Process • Chemical transformation process include a number of hydrolysis process which are used to recover compounds such as glucose and furfural and other chemical compounds • The chemical processes are not used routinely for the transformation of the organic fraction of MSW, because these compounds can also be manufactured from other cellulose – containing waste

35. Chemical Transformation Process Acid Hydrolysis Methanol Production from Methane

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