CE 548 I Fundamentals of Biological Treatment

1. CE 548 I Fundamentals of Biological Treatment

2. Overview of Biological Treatment • Objectives of Biological Treatment: • For domestic wastewater, the main objectives are: • Transform (oxidize) dissolved and particulate biodegradable constituents into acceptable by-products • Capture and incorporate suspended and nonsettleable colloidal solids into a biological floc or biofilm • Transform or remove nutrients, such as nitrogen and phosphorous • Remove specific trace organic constituents and compounds

3. Overview of Biological Treatment • Objectives of Biological Treatment: • For industrial wastewater, the main objectives are: • Remove or reduce the concentration of organic and inorganic compounds • Pre-treatment of industrial wastewater may be required due to presence of toxicants before being discharged to sewer line. • For agricultural wastewater, the main objective is: • Remove nutrients, such as N and P, that stimulate the growth of aquatic life

4. Overview of Biological Treatment • Role of Microorganisms (MOs) in Wastewater Treatment: • Microorganisms (principally bacteria) oxidize dissolved and particulate carbonaceous organic matter into simple end-products: • O2, NH3, and PO43- are required as nutrients for the conversion of organic matter to simple products • Microorganisms are required to carryout the conversion

5. Overview of Biological Treatment • Role of Microorganisms (MOs) in Wastewater Treatment: • Ammonia can be oxidized by specific microorganisms (nitrification) to nitrite (NO2-) and nitrate (NO3-) • Other bacteria can reduce oxidized nitrogen to gaseous nitrogen • Since biomass (Bacteria flocs) has a specific gravity that is larger than that of water, It can be removed from liquid by gravity settling

6. Types of Biological Processes • The principle categories of biological processes are: • Suspended growth processes • Attached growth (bio-film) processes • Successful design and operation of any process require the knowledge of the following: • Types of microorganisms involved • Specific reactions they perform • Environmental factor that affect their performance • Nutritional needs of the microorganisms • Reaction kinetics of microorganisms

7. Suspended Growth Processes • Microorganism are maintained in suspension by appropriate mixing methods • Many of the processes are operated aerobically • Anaerobic processes are also used for treatment of industrial wastewater having high organic content and organic sludge • The most common process used in domestic wastewater is the activated sludge process

8. Suspended growth

9. Suspended growth

10. Attached Growth Processes • Microorganism are attached to an inert packing material • Packing materials include: • Rock, Gravel, Sand • Slag • Redwood • Wide range of Plastic and other synthetic materials • Operate as aerobic and anaerobic processes • The packing can be submerged completely in liquid or not submerged • The most common process is the trickling filter • The process is followed by settling tank

11. Attached Growth Processes

12. Attached Growth Processes

13. Introduction to Microbial Metabolism • Understanding of microbial metabolism (biochemical activities) is important to design and selection of biological treatment. • Table 7-6 shows the classification of microorganisms by electron donor, electron acceptor, carbon source, and end products. • Organisms require the following for growth: • Source of energy • Carbon for cell synthesis • Nutrients

14. Introduction to Microbial Metabolism • Carbon source: Microorganisms obtain their carbon for cell growth from either: • organic matter (heterotrophs) • or from carbon dioxide (autotrophs). • autotrophs have lower growth rate than heterotrophs

15. Introduction to Microbial Metabolism • Energy Source:

16. Introduction to Microbial Metabolism • Nutrient and growth factor requirements: Nutrients: The principal inorganic nutrients needed: • N, S, P, K, Mg, Ca, Fe, Na, and Cl • Growth factor: Organic nutrients required by some organisms include: • amino acids • purines and pyrimidines • vitamins

17. Introduction to Microbial Metabolism • Nutrient and growth factor requirements: In biological wastewater treatment process, two types of organisms are important:

18. Bacterial Growth • Bacterial reproduction; • The primary mechanism of reproduction is binary fission. • One cell becomes two new cells. • The time required for each division (generation time) can vary from days to less than 20 minutes • If generation time is 30 min, one bacterium would yield about 16 million (224)bacteria after 12 hours. • This rapid change of biomass depends on environmental conditions ; availability of substrate and nutrients.

19. Bacterial Growth • Bacterial growth pattern in batch reactor; • Figure 7-10 shows the growth pattern in batch process.

20. Bacterial Growth • Biomass Yield; • Biomass yield is defined as the ratio of the amount of biomass produced to the amount of substrate consumed: Since wastewater contains a large number of organic compounds, the yield is expressed in terms of measurable parameters such as COD or BOD. Thus the yield would be:

21. Bacterial Growth • Estimating biomass yield and oxygen requirements; A stoichiometric relationship exists between the substrate removal, the amount of oxygen consumed, and the observed biomass yield. Assuming organic matter can be represented as C6H12O6 (glucose), the following equation (7-3) can be written: The yield based on the glucose consumed cab be obtained as follows:

22. Bacterial Growth • Estimating biomass yield and oxygen requirements; To express the yield in COD bases, the COD of glucose must be determined: The theoretical yield expressed in terms of COD is given by:

23. Bacterial Growth • Estimating biomass yield and oxygen requirements; The amount of oxygen required can be obtained based on the stoichiometry as defined by equation (7-3) in which 8 moles of oxygen are required for 3 moles of glucose. Study Example 7-1

24. Microbial Growth Kinetics • Microbial growth kinetic terminology; • bCOD: biodegradable COD; since wastewater contains numerous substrates, the concentration of organic compounds is defined by biodegradable COD. bCOD comprise soluble, colloidal, and particulate components. • bsCOD: biodegradable soluble COD. • TSS (total suspended solids) and VSS (volatile suspended solids): represents the biomass solids in the bioreactor. • MLSS (mixed liquor suspended solids) and MLVSS (mixed liquor volatile suspended solids): the mixture of solids resulting from combining recycled sludge with influent wastewater in the bioreactor. • nbVSS: non-biodegradable volatile suspended solids • iTSS: inert inorganic total suspended solids

25. Microbial Growth Kinetics • Rate of utilization of soluble substrate; The substrate utilization rate in biological system can be modeled with the following expression: Where; rsu= rate of substrate change due to utilization, g/m3  d k= max. specific substrate utilization rate, g sub/g micro  d X = biomass (microorganisms) concentration S = growth limiting substrate concentration, g/m3

26. Microbial Growth Kinetics • Rate of utilization of soluble substrate;

27. Microbial Growth Kinetics • Rate of utilization of soluble substrate; The maximum growth rate of bacteria is related to the maximum specific substrate utilization rate as follows: Where; µm= max. bacteria growth rate, g new cells/g cellsd

28. Microbial Growth Kinetics • Rate of biomass growth with soluble substrate; The relationship between cell growth rate and substrate utilization rate is given by: (not all subs. is converted to cells) But bacteria experience loss in growth rate due to decay and predation, this is termed endogenous decay: Therefore;

29. Microbial Growth Kinetics • Rate of biomass growth with soluble substrate; If both sides of Eq. (7-22) are divided by the biomass concentration X, the specific growth rate is defined as: Where; µ = specific biomass growth rate, g VSS/g VSS d

30. Microbial Growth Kinetics • Kinetic Coefficients, Oxygen Uptake and Temperature • Typical kinetic coefficients are given in T7-9. • The rate of oxygen uptake is given by: • Effects of temperature on reaction rate:  varies from 1.02 to 1.25 in biological systems