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F/M RATIO

EAT303 WASTEWATER ENGINEERING (Part II: Week 7-12) Secondary Treatment: Suspended Growth by Fahmi Muhammad Ridwan. F/M RATIO. The food-to-microorganism ratio (F/M) was developed in the 1950s and 1960s. The “food” is substrate. In equation form, the food-to-microorganism ratio (F/M) is:.

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F/M RATIO

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  1. EAT303WASTEWATER ENGINEERING(Part II: Week 7-12)Secondary Treatment: Suspended GrowthbyFahmi Muhammad Ridwan

  2. F/M RATIO The food-to-microorganism ratio (F/M) was developed in the 1950s and 1960s. The “food” is substrate.In equation form, the food-to-microorganism ratio (F/M) is: where Q = wastewater flow rate into the aeration tank, m3/dSo = influent readily biodegradable soluble COD (rbsCOD), mg/LV = volume of aeration tank, m3X = microorganism concentration (mixed-liquor volatile suspended solids or MLVSS) in the aeration tank, mg/L

  3. SLUDGE VOLUME INDEX (SVI) The sludge volume index (SVI) is the volume of one gram of sludge after 30 minutes of settling.The SVI is determined by placing a mixed liquor sample in a one- to two-liter cylinder and measuring the volume of sludge after 30 minutes. A corresponding sample of the sludge is taken to measure the MLSS concentration. The SVI is calculated as: An SVI of 100 mL/g or less is considered a good settling sludge. An SVI above 150 is typically associated with filamentous growth

  4. EXAMPLES

  5. OXYGEN TRANSFER The rate of mass transfer is given by where KLais the volumetric mass transfer coefficient with units of s1 and Ctis the concentration in the bulk liquid at time t. Integrating Equation 23-46 between the limits C =C0and C = Ct and t = 0 and t = t, where C0 is the initial concentration and Ct is the concentration at time t, yields

  6. Model of the interface mass transfer between gas and liquid

  7. The effects of mixing intensity and tank geometry must be considered in the design process. In most cases aeration devices are rated by manufacturers based on clean water. A correction factor ais used to estimate KLain the actual system: Typical values of a are 0.2 to 0.5 for conventional BOD oxidation, 0.4 to 0.7 for nitrification only, and 0.5 to 0.75 for nitrification-denitrification A second correction factor bis used to correct the oxygen transfer rate for differences in oxygen solubility due to constituents in the water such as salts, particulate matter, and surface active substances: Values of brange from about 0.7 to 0.98. A typical value for wastewater is 0.95

  8. The interrelationship between these factors and temperature, elevation above sea level, and the depth of diffusers is expressed as follows The average dissolved oxygen saturation concentration in clean water (Cavg ) in an aeration tank at temperature T and elevation H is defined as

  9. The atmospheric pressure at elevation H is computed from the ratio of pressure at elevation H divided by the pressure at sea level:

  10. Example 23-5. Estimate the required air flow rate for the new activated sludge plant at Lawrence. Use the following assumptions in preparing the estimate:

  11. OXIDATION DITCH Oxidation ditches, also known as continuous loop reactors (CLRs), are widely used in small to medium-sized communities where flow rates are in the range of 2,000 to 20,000 m3/d.Performance data for 29 plants indicate that they are capable of meeting annual BOD5 and total suspended solids discharge limits of 15 mg/L and 10 mg/L, respectively. In addition, they can achieve nitrification levels of 95 to 99 percent

  12. Typical oxidation ditch plant layout. Typically, the process selected is extended aeration to nitrify and remove carbonaceous BOD. One of the primary reasons for selecting extended aeration is that it minimizes sludge production by providing a long period for endogenous decay of the sludge mass.

  13. Mixed Liquor Suspended Solids (MLSS). The MLSS is typically in the range of 3,000 to 5,000 mg/L (GLUMRB, 2004; Metcalf & Eddy, 2003). Mixed liquor volatile suspended solids (MLVSS) is often assumed to be 70 to 80 percent of MLSS for plants treating primarily domesticwastewater.

  14. Baffle placement and dimensions

  15. NITRIFICATION GROWTH KINETICS Nitrification is the term used to describe the two-step process in which ammonia (NH4 ) is oxidized to nitrite (NO2 ) that is, in turn, oxidized to nitrate (NO3 ). Nitrification may be accomplished byeither suspended growth or attached growth unit processes.

  16. The growth rate of Nitrosomonascontrols the overall conversion reaction. For nitrification systems operated at temperatures below 28oC, ammonia oxidation kinetics arerate limiting. Thus, designs are based on saturation kinetics for ammonia oxidation:

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