1. 1 CE 548 I Fundamentals of Biological Treatment

2. 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. 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. 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:   O 2, NH 3, and PO 4 3- are required as nutrients for the conversion of organic matter to simple products   Microorganisms are required to carryout the conversion

5. 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. 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. 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. 8 Suspended growth

9. 9

10. 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. 11 Attached Growth Processes

12. 12 Attached Growth Processes

13. 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. 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. 15 Introduction to Microbial Metabolism   Energy Source:

16. 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. 17 Introduction to Microbial Metabolism   Nutrient and growth factor requirements: In biological wastewater treatment process, two types of organisms are important:

18. 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 (2 24 )bacteria after 12 hours.   This rapid change of biomass depends on environmental conditions ; availability of substrate and nutrients.

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

20. 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. 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 C 6 H 12 O 6 (glucose), the following equation (7-3) can be written: The yield based on the glucose consumed cab be obtained as follows:

22. 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. 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. 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. 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; r su = rate of substrate change due to utilization, g/m 3  d k = max. specific substrate utilization rate, g sub/g micro  d X = biomass (microorganisms) concentration S = growth limiting substrate concentration, g/m 3

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

27. 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; µ m = max. bacteria growth rate, g new cells/g cells  d

28. 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. 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. 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