Types of Aerobic Treatment Units

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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?

Stabilization ponds Signup and view all the answers

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

Biogas 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?

Higher in anaerobic treatment Signup and view all the answers

What must be considered when implementing methods for groundwater recharge?

Groundwater pollution risks Signup and view all the answers

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

Impoundment Signup and view all the answers

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

Increases effluent treatment costs Signup and view all the answers

For which type of crops is irrigation typically practiced?

Crops for seed production Signup and view all the answers

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

To compensate for scarce natural waters or sparse rainfall Signup and view all the answers

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

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

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

The end products produced Signup and view all the answers

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

The bacteria involved grow at a slower rate Signup and view all the answers

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

UASB type units Signup and view all the answers

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

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

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

To prevent clogging due to solids accumulation Signup and view all the answers

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

~20°C Signup and view all the answers

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

'Upflow Anaerobic Sludge Blanket' Signup and view all the answers

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

To bring more carbon into the anoxic tank Signup and view all the answers

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

To further denitrify nitrates remaining in the liquor Signup and view all the answers

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

Calcium hydroxide Signup and view all the answers

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

Stabilization of sludge solids 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?

Activated sludge plants Signup and view all the answers

What is a common method for sludge dewatering?

Incineration Signup and view all the answers

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

Spreading on eroded land Signup and view all the answers

`Specific gravity` of biological sludge is closest to:

$1.1$ Signup and view all the answers

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

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

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

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

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

Nitrobacter Signup and view all the answers

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

4.6 kg 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?

To prevent the occurrence of algal blooms Signup and view all the answers

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

Combined system Signup and view all the answers

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

Nitrification and Nitrate Conversion Signup and view all the answers

In assimilatory denitrification, what is the role of nitrate?

It is reduced to ammonia for cell synthesis Signup and view all the answers

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

20-30% Signup and view all the answers

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

Nitrate Signup and view all the answers

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

Carbon Signup and view all the answers

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

BOD:N ratio Signup and view all the answers

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

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

What does excessive dosing of methanol in denitrification result in?

Increased oxygen demand Signup and view all the answers

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

>1.2 m/h Signup and view all the answers

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

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

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

To reduce denitrification efficiency Signup and view all the answers

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

$N_2$ (Nitrogen) Signup and view all the answers

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

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

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

$O_2$ (Oxygen) Signup and view all the answers

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

62.5% Signup and view all the answers

What is the purpose of sludge digestion?

To break down organic wastes using anaerobic bacteria Signup and view all the answers

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

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

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

If pH drops, methane formation ceases Signup and view all the answers

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

Standard rate digestion involves heating and mixing Signup and view all the answers

Why is thermophilic range digestion not commonly practiced?

Operational difficulties and odor issues Signup and view all the answers

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

To remove water from sludge through evaporation Signup and view all the answers

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

Methane formation ceases Signup and view all the answers

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

Active methane bacteria Signup and view all the answers

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

Separation of digested solids from supernatant liquor Signup and view all the answers

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

A combination of standard rate and high rate digestion processes Signup and view all the answers

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

Characteristics of the raw wastewater 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?

4.5 to 5.0 m 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?

Hydraulic Retention Time (HRT) 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?

0.5 m/h Signup and view all the answers

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

Uniform flow distribution 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?

To maintain desired effluent quality Signup and view all the answers

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

Facilitating gas collection Signup and view all the answers

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

Assisting in gas-liquid-solid separation Signup and view all the answers

What is the formula to determine digester capacity?

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

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

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

What does the treatment plant layout aim to optimize?

Land requirement, lengths of interconnecting pipes, and pumping heads Signup and view all the answers

Why is siting important in treatment plant development?

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

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

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

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

Difference in water surface elevations in the interceptor and receiving water Signup and view all the answers

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

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

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

~65% Signup and view all the answers

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

'Proper disposal' or reuse requirements Signup and view all the answers

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

'Graphical representation' of the hydraulic grade line through the plant Signup and view all the answers