Presentation on theme: "CE 370 – Water and Wastewater Engineering"— Presentation transcript:
1 CE 370 – Water and Wastewater Engineering Biological TreatmentCE 370 – Water and Wastewater Engineering
2 Outline Objectives of Biological Treatment Role of Microorganisms in TreatmentTypes of Biological ProcessesSuspended Growth ProcessesActivated sludgeStabilization pondsAttached Growth ProcessesTrickling filtersRotating biological contactorsBiological Kinetics
3 Objectives of Biological Treatment For domestic wastewater, the main objectives are:Transform (oxidize) dissolved and particulate biodegradable constituents into acceptable by-productsCapture and incorporate suspended and nonsettleable colloidal solids into a biological floc or biofilmTransform or remove nutrients, such as nitrogen and phosphorousRemove specific trace organic constituents and compounds
4 Objectives of Biological Treatment For industrial wastewater, the main objectives is:Remove or reduce the concentration of organic and inorganic compoundsPre-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
5 Role of Microorganisms Microorganisms (principally bacteria) oxidize dissolved and particulate carbonaceous organic matter into simple end-productsO2, NH3, and PO43- are required as nutrients for the conversion of organic matter to simple productsMicroorganisms are required to carryout the conversion
6 Role of Microorganisms Ammonia can be oxidized by specific microorganisms (nitrification) to nitrite and nitrateOther bacteria can reduce oxidized nitrogen to gaseous nitrogenBacteria with the ability to take up and store large amounts of inorganic phosphorous
7 Role of Microorganisms Since biomass has a specific gravity that is larger than that of waterIt can be removed from liquid by gravity settling
8 Types of Biological Processes The principle categories of biological processes are:Suspended growth processesAttached growth (bio-film) processesSuccessful design and operation of any process require the knowledge of the following:Types of microorganisms involvedSpecific reactions they performEnvironmental factor that affect their performanceNutritional needs of the microorganismsReaction kinetics of microorganisms
9 Suspended Growth Processes Microorganism are maintained in suspension by appropriate mixing methodsMany of the processes are operated aerobicallyAnaerobic processes are also used treatment of industrial wastewater having high organic content and organic sludgeThe most common process used in domestic wastewater is the activated sludge process
10 Attached Growth Processes Microorganism are attached to an inert packing materialPacking materials include:Rock, Gravel, SandSlagRedwoodWide range of Plastic and other synthetic materialsOperate as aerobic and anaerobic processesThe packing can be submerged completely in liquid or not submergedThe most common process is the trickling filterThe process is followed by settling tank
11 Biological Kinetics 1. Michaelis – Menten Concept (1/X)(ds/dt) = specific rate of substrate utilization(ds/dt) = rate of substrate utilizationKs = maximum rate of substrate utilizationKm = substrate concentration when the rate of utilization is half maximum rateS = substrate concentration
13 If S is very large, Km can be neglected, therefore S cancels out and the reaction is zero order in substrate. K is the rate constant for zero-order reaction.If S is relatively small, it can be neglected in the denominator and the reaction is first-order in substrate. K is the rate constant for the first-order reaction
14 Biological Kinetics 2. The Monod Equation = growth rate constant, time-1max = maximum growth rate constant, time-1S = substrate concentration in solutionKs = substrate concentration when the growth rate constant is half the maximum rate constant.
15 Monod observed that the microbial growth is represented by: dX/dt = rate of cell productionX = number or mass of microbes present = growth rate constant
18 Generalized substrate consumption and biomass growth with time.
19 Effect of Temperature on Growth Rate Arrhenius relationshipkT1 = reaction rate constant at temperature T1kT2 = reaction rate constant at temperature T2 = temperature correction coefficientT1 = temperatureT2 = temperature
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