Types of Aerobic Treatment Units
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Questions and Answers

What is the main advantage of anaerobic waste treatment over aerobic treatment?

  • Higher energy input requirements
  • Increased production of excess sludge
  • No production of biogas
  • Lower nutrient requirement (correct)

    • Which type of pond system provides oxygen through mechanical aeration rather than algal photosynthesis?

  • Stabilization ponds
  • Extended aeration ponds
  • Aerated lagoons (correct)
  • Oxidation ditch

    • What is the distinctive feature of an oxidation ditch compared to other activated sludge processes?

  • Short detention period
  • Circular shape
  • Usage of algal photosynthesis
  • Presence of surface rotors (correct)

    • Which type of treatment unit provides long detention periods extending from a few to several days?

    <p>Stabilization ponds</p> Signup and view all the answers

    What does the anaerobic treatment of organic wastes produce as a valuable source of energy?

    <p>Biogas</p> Signup and view all the answers

    In what way does the production of excess sludge per unit mass of substrate differ between aerobic and anaerobic treatment processes?

    <p>Higher in anaerobic treatment</p> Signup and view all the answers

    What must be considered when implementing methods for groundwater recharge?

    <p>Groundwater pollution risks</p> Signup and view all the answers

    Which method is particularly beneficial when the recovery of residues is desired?

    <p>Impoundment</p> Signup and view all the answers

    What implication does direct injection have on effluent treatment and costs?

    <p>Increases effluent treatment costs</p> Signup and view all the answers

    For which type of crops is irrigation typically practiced?

    <p>Crops for seed production</p> Signup and view all the answers

    What is one of the main reasons for practicing irrigation in arid areas?

    <p>To compensate for scarce natural waters or sparse rainfall</p> Signup and view all the answers

    What is the primary purpose of acid fermentation in anaerobic wastewater treatment?

    <p>To form simple organic compounds like short-chain acids and alcohols</p> Signup and view all the answers

    What is a characteristic difference between acid fermentation and methane fermentation?

    <p>The end products produced</p> Signup and view all the answers

    Why is methane fermentation considered the rate-limiting step in anaerobic wastewater treatment?

    <p>The bacteria involved grow at a slower rate</p> Signup and view all the answers

    Which type of anaerobic unit does not require special media and uses sludge granules as 'media'?

    <p>UASB type units</p> Signup and view all the answers

    What is a key advantage of UASB type units in anaerobic wastewater treatment?

    <p>No need for special media like stones or plastic granules</p> Signup and view all the answers

    Why does excess sludge need to be removed from UASB type units?

    <p>To prevent clogging due to solids accumulation</p> Signup and view all the answers

    What temperature range is ideal for the efficient functioning of anaerobic systems like UASB units?

    <p>~20°C</p> Signup and view all the answers

    What does the acronym 'UASB' stand for in the context of anaerobic wastewater treatment?

    <p>'Upflow Anaerobic Sludge Blanket'</p> Signup and view all the answers

    What is the purpose of reversing the relative positions of anoxic and aerobic tanks?

    <p>To bring more carbon into the anoxic tank</p> Signup and view all the answers

    In the Bardenpho arrangement, why is a second anoxic tank used after the first one?

    <p>To further denitrify nitrates remaining in the liquor</p> Signup and view all the answers

    Which chemical is reported to result in approximately 50% increase in surplus sludge during phosphorus precipitation?

    <p>Calcium hydroxide</p> Signup and view all the answers

    What is the objective of residual management in biological waste treatment processes?

    <p>Stabilization of sludge solids</p> Signup and view all the answers

    In which type of plants does the sludge need to be taken to a sludge digester for further demineralization?

    <p>Activated sludge plants</p> Signup and view all the answers

    What is a common method for sludge dewatering?

    <p>Incineration</p> Signup and view all the answers

    Which disposal method involves building up topsoil on eroded or waste land using wet sludge?

    <p>Spreading on eroded land</p> Signup and view all the answers

    Specific gravity of biological sludge is closest to:

    <p>$1.1$</p> Signup and view all the answers

    Aerobic digestion of surplus sludge is commonly done in which waste treatment process?

    <p><code>Extended aeration</code> plants</p> Signup and view all the answers

    What is the range of organic loading on the sludge blanket for domestic sewage?

    <p>1-3 kg COD/m3 day</p> Signup and view all the answers

    Which group of bacteria derives its energy through the oxidation of ammonium to nitrate?

    <p>Nitrobacter</p> Signup and view all the answers

    What is the stoichiometric oxygen requirement for nitrifying 1 kg of nitrogen?

    <p>4.6 kg</p> Signup and view all the answers

    What is one of the main reasons for controlling nitrogen content in effluents that are discharged into lakes or reservoirs?

    <p>To prevent the occurrence of algal blooms</p> Signup and view all the answers

    Which system generally produces a smaller volume of surplus sludge according to the text?

    <p>Combined system</p> Signup and view all the answers

    What is the two-step process involved in biological nitrification/denitrification?

    <p>Nitrification and Nitrate Conversion</p> Signup and view all the answers

    In assimilatory denitrification, what is the role of nitrate?

    <p>It is reduced to ammonia for cell synthesis</p> Signup and view all the answers

    What is the level of nitrogen removal in conventional activated sludge systems according to the text?

    <p>20-30%</p> Signup and view all the answers

    Which component in the effluent does not generally adversely affect stream quality according to the text?

    <p>Nitrate</p> Signup and view all the answers

    What is essential as an electron donor for denitrification to occur?

    <p>Carbon</p> Signup and view all the answers

    Which waste component can be an attractive and economical carbon source for denitrification?

    <p>BOD:N ratio</p> Signup and view all the answers

    What is the range of BOD/COD removal efficiency for sewage as mentioned in the text?

    <p>75-85% for BOD, 74-78% for COD</p> Signup and view all the answers

    What does excessive dosing of methanol in denitrification result in?

    <p>Increased oxygen demand</p> Signup and view all the answers

    What is the upflow velocity at peak flow as per the text?

    <p>&gt;1.2 m/h</p> Signup and view all the answers

    How many inlet points are required per floor area according to the text?

    <p>Minimum 1 point per 3.7-4.0 m2 floor area.</p> Signup and view all the answers

    Why should the use of methanol or artificial carbon sources be avoided in denitrification processes?

    <p>To reduce denitrification efficiency</p> Signup and view all the answers

    What does biological denitrification release as an inert gas to the atmosphere?

    <p>$N_2$ (Nitrogen)</p> Signup and view all the answers

    What is the theoretical gas production per kg of COD removed?

    <p>0.38 m3/kg COD removed.</p> Signup and view all the answers

    In dissimilatory denitrification, what does nitrate serve as in energy metabolism?

    <p>$O_2$ (Oxygen)</p> Signup and view all the answers

    What percentage of oxygen used in nitrification is released back during denitrification?

    <p>62.5%</p> Signup and view all the answers

    What is the purpose of sludge digestion?

    <p>To break down organic wastes using anaerobic bacteria</p> Signup and view all the answers

    What is the primary outcome of the first stage of sludge digestion?

    <p>Production of short-chain (volatile) acids and alcohols</p> Signup and view all the answers

    Why is methane fermentation considered a rate-limiting step in anaerobic wastewater treatment?

    <p>If pH drops, methane formation ceases</p> Signup and view all the answers

    What is the key difference between standard rate digestion and high rate digestion?

    <p>Standard rate digestion involves heating and mixing</p> Signup and view all the answers

    Why is thermophilic range digestion not commonly practiced?

    <p>Operational difficulties and odor issues</p> Signup and view all the answers

    What is the primary function of sand beds in sludge drying?

    <p>To remove water from sludge through evaporation</p> Signup and view all the answers

    What happens if the pH drops below 6.0 during sludge digestion?

    <p>Methane formation ceases</p> Signup and view all the answers

    What is a key characteristic of mesophilic conditions for anaerobic digestion?

    <p>Active methane bacteria</p> Signup and view all the answers

    What is the primary role of the second stage digester in anaerobic wastewater treatment?

    <p>Separation of digested solids from supernatant liquor</p> Signup and view all the answers

    What is a distinguishing feature of two-stage digestion in anaerobic digesters?

    <p>A combination of standard rate and high rate digestion processes</p> Signup and view all the answers

    What is the main factor that determines the amount of sludge produced daily in a UASB reactor?

    <p>Characteristics of the raw wastewater</p> Signup and view all the answers

    In a UASB reactor treating low BOD municipal sewage, what is the typical depth range for the full depth of the reactor?

    <p>4.5 to 5.0 m</p> Signup and view all the answers

    What is the parameter used to ensure that the desired Sludge Retention Time (SRT) is achieved in a UASB reactor?

    <p>Hydraulic Retention Time (HRT)</p> Signup and view all the answers

    What is the recommended upflow velocity in a UASB reactor at average flow to retain flocculent sludge and prevent solids carry over?

    <p>0.5 m/h</p> Signup and view all the answers

    What is one way to design the feed inlet system in a UASB reactor?

    <p>Uniform flow distribution</p> Signup and view all the answers

    In treating high BOD wastes in a UASB reactor, why might the depth of both the sludge blanket and the reactor need to be increased?

    <p>To maintain desired effluent quality</p> Signup and view all the answers

    What role does the Gas-Liquid-Solid-Separator (GLSS) play in a UASB reactor?

    <p>Facilitating gas collection</p> Signup and view all the answers

    What is the primary function of the deflector beam in a UASB reactor?

    <p>Assisting in gas-liquid-solid separation</p> Signup and view all the answers

    What is the formula to determine digester capacity?

    <p>V = [Vf-2/3 (Vf - Vd)]t1 + Vdt2</p> Signup and view all the answers

    What is the composition of sludge gas produced in a treatment plant?

    <p>65% methane, 30% carbondioxide, 5% nitrogen and other inert gases</p> Signup and view all the answers

    What does the treatment plant layout aim to optimize?

    <p>Land requirement, lengths of interconnecting pipes, and pumping heads</p> Signup and view all the answers

    Why is siting important in treatment plant development?

    <p>To take advantage of existing site topography and facilitate gravity flow</p> Signup and view all the answers

    What factors are considered when preparing hydraulic profiles through a treatment plant?

    <p>Peak and average design flows, main paths of flow, and head losses</p> Signup and view all the answers

    In the hydraulic profile of a treatment plant, what does the total available head represent?

    <p>Difference in water surface elevations in the interceptor and receiving water</p> Signup and view all the answers

    What is the purpose of natural evaporation in treating effluent from a plant?

    <p>Involves large impoundments with no discharge depending on climatic conditions</p> Signup and view all the answers

    'Gas Collection' at a treatment plant typically consists of what percentage of methane in the sludge gas?

    <p>~65%</p> Signup and view all the answers

    'Treated Effluent Disposal' is crucial for what aspect of planning wastewater treatment facilities?

    <p>'Proper disposal' or reuse requirements</p> Signup and view all the answers

    'Hydraulic Profile' in a treatment plant represents what aspect graphically?

    <p>'Graphical representation' of the hydraulic grade line through the plant</p> Signup and view all the answers

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