Fundamental of Biological Treatment Unit Process Fundamental of Biological Treatment Week 3
Welcome to the 2nd and 3rd Year 2nd Sem: Fundamental of Biological Treatment! Objectives of Biological Treatment Role of Microorganisms Types of Biological Processes
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
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
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
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
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
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
Suspended growth
Suspended growth
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
Attached Growth Processes
Attached Growth Processes
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
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
Introduction to Microbial Metabolism Energy Source:
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
Introduction to Microbial Metabolism Nutrient and growth factor requirements: In biological wastewater treatment process, two types of organisms are important:
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.
Bacterial Growth Bacterial growth pattern in batch reactor; Figure 7-10 shows the growth pattern in batch process.
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:
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:
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:
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
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
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
Microbial Growth Kinetics Rate of utilization of soluble substrate;
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 cellsd
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;
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
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
Let’s Have a Great Sem!