73 Questions
What distinguishes aerated lagoons from stabilization ponds?
Oxygen is provided through mechanical aeration in aerated lagoons.
What is a characteristic of the oxidation ditch in the treatment of sewage?
It has two surface rotors placed across the channel.
Why is anaerobic waste treatment preferred over aerobic treatment in some cases?
It requires a lower energy input as no oxygenation is needed.
What advantage does the production of biogas in anaerobic treatment provide?
It serves as a valuable source of energy.
What characteristic is common to both stabilization ponds and aerated lagoons?
They are both open flow through basins.
In anaerobic treatment, what does the degradation of organic wastes lead to?
Production of carbon dioxide and methane.
What are some considerations that must be given in groundwater recharge methods?
Net evaporation and possible percolation
Which crops are typically irrigated by effluent according to the text?
Cotton and sugar beets
What is a challenge associated with direct injection in groundwater recharge methods?
High costs of treating effluent
Why is irrigation primarily practiced in arid areas according to the text?
To substitute for scarce natural waters or sparse rainfall
What makes recovery of residues desirable in certain disposal methods according to the text?
For disposal of brines
What is the primary outcome of the first stage of anaerobic wastewater treatment?
Conversion to simple organic compounds
Which acids are primarily produced during acid fermentation in anaerobic wastewater treatment?
Acetic and butyric acid
What is the rate-limiting step in anaerobic wastewater treatment?
Methane fermentation
Why are fixed film anaerobic filters likely to face problems?
They accumulate solids in the interstices
In UASB units, what serves as the 'media' to support biological growths?
Sludge granules
'Gas collection and conversion or conveyance' is a stage commonly found in which type of anaerobic reactor unit?
UASB type unit
'Screening and degritting' is a typical process that occurs in which stage of a UASB treatment plant for municipal sewage?
Main UASB reactor
'No mixers or aerators are required' is a notable feature of which type of anaerobic reactor units?
'UASB type units'
'Excess sludge is removed from time to time through a separate pipe and sent to a simple sand bed for drying' - which aspect of anaerobic wastewater treatment does this statement refer to?
'Design Approach'
'At equilibrium condition, sludge withdrawn has to be equal to sludge produced daily' - this statement is related to which specific element of UASB design?
'Size of Reactor'
What is the primary factor that determines the amount of sludge produced daily?
Amount of VSS in the raw wastewater
What is a parameter used to control sludge retention time in a UASB reactor?
Hydraulic Retention Time (HRT)
What might happen if the upflow velocity in the UASB reactor exceeds recommended values?
Deterioration in effluent quality
How is the settling compartment in a UASB reactor typically formed?
Sloping hoods for gas collection
What is the primary function of the Gas-Liquid-Solid Separator (GLSS) in a UASB reactor?
Separating gas, liquid, and solid components
What is the impact of increasing the depth of both the sludge blanket and the reactor for high BOD wastes?
Keeps organic loading on solids within prescribed range
Why should the upflow velocity in a UASB reactor not exceed certain limits?
To prevent carry over of solids and maintain effluent quality
Which group of bacteria obtains energy through the oxidation of nitrite to nitrate?
Nitrobacter
What is the stoichiometric oxygen requirement for nitrifying 1 kg of nitrogen?
$4.6$ kg
What is the organic loading on the sludge blanket for agro-industrial wastes?
$0.3-1.0$ kg COD/kg VSS day
What is the BOD/COD removal efficiency for sewage?
75-85%
What determines the rate-limiting step for the conversion of ammonium to nitrate in nitrification?
Nitrosomonas
In which system is the first tank smaller in size due to a higher F/M ratio?
Separate system
What is the range of nitrogen removal using the nitrification-denitrification method?
$70-90$%
How many groups of chemoautotrophic bacteria are associated with nitrification?
$2$ groups
What is the average upflow velocity during peak flow conditions?
$1.2$ m/h
What is the primary means by which nitrogen removal is achieved in the biological nitrification/denitrification process?
Dissimilatory denitrification
What is the first step in the biological nitrification/denitrification process?
Nitrification
What is the importance of a carbon source in denitrification?
To reduce oxygen input needed into the system
Which process involves nitrate conversion to various gaseous end products, mainly molecular nitrogen?
Dissimilatory denitrification
Why should the use of methanol or any other artificial carbon source be avoided in denitrification?
To avoid introducing unnecessary BOD in the effluent
What is the effect of using a raw waste bypass in the biological nitrification/denitrification process?
Reduces sizes of tanks
Which step involves the reduction of nitrate to ammonia to serve as a nitrogen source for cell synthesis?
Assimilatory denitrification
What is released as an inert gas to the atmosphere during denitrification?
Molecular nitrogen
What is the purpose of break point chlorination in wastewater treatment?
To control nitrogen content in effluent
Which process involves a carbon source as an essential electron donor?
Biological nitrification/denitrification
What is the formula to determine the capacity of a digester?
V = Vf - 2/3 (Vf - Vd)t1 + Vdt2
What percentage of sludge gas is composed of methane?
65%
What is the calorific value range of sludge gas per cubic meter?
5400 to 5850 kcal/m3
What does plant layout in a treatment plant focus on optimizing?
Land requirement and pipe lengths
What is an important principle to consider in siting a treatment plant?
Site on a side-hill to facilitate gravity flow
What is the purpose of preparing hydraulic profiles through the treatment plant?
To graphically represent hydraulic grade line through the plant
What is included in the head losses through the treatment unit?
Miscellaneous and free fall surface allowance
What is the purpose of sludge digestion?
To treat concentrated organic wastes with anaerobic bacteria
What is the primary function of acid fermentation in sludge digestion?
Hydrolysis of complex waste components
What is the outcome of the methane fermentation stage in sludge digestion?
Generation of methane and carbon dioxide
Why is the thermophilic range for methane bacteria not commonly used?
To avoid operational difficulties and odour issues
What are the two types of anaerobic digesters mentioned in the text?
Standard rate and high rate digesters
What is typically done in the second stage digester in a two-stage digestion process?
The digested solids are separated from the supernatant liquor
What is the primary role of a thickener in dewatering extended aeration sludge?
To remove bulk water from the sludge
In sludge digestion, what happens if the pH drops below 6.0?
Acid fermentation ceases abruptly
What is not a reason why thermophilic range is not commonly used in sludge digestion?
Reduction in short-chain acids generation rates
What is the purpose of reversing the relative positions of anoxic and aerobic tanks?
To increase the oxygen requirement of the waste in the anoxic state.
How can more complete nitrification-denitrification be achieved in wastewater treatment?
By employing a Bardenpho arrangement.
What is the advantage of having a second anoxic tank in the wastewater treatment process?
It allows for more efficient nitrification-denitrification.
Which chemical is more expensive and generates extra sludge in wastewater treatment?
Alum
What is a feasible time for reaeration of the flow from the anoxic tank?
10-15 minutes
How does adding iron salts help in wastewater treatment?
Aids in achieving high removal of total phosphorus
In which type of waste treatment are surplus sludge solids stabilized within the unit itself?
Facultative type aerated lagoons
Which method is NOT commonly used for sludge dewatering?
Ionization
What is one common method for final disposal of sludge?
Land application as fertilizer
Why is it essential to know the characteristics of sludges for designing sludge drying systems?
To determine dewatering properties and moisture content
Test your knowledge on the stages of waste degradation, including acid fermentation and subsequent metabolic processes. Explore how complex waste components are broken down into simple organic compounds by bacteria.
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