Wastewater Engineering: Decomposition Process

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Questions and Answers

What is the process by which the environment deals with organic materials?

Oxidation

Synthesis

Fermentation

Decomposition (correct)

What is the primary factor that affects the decomposition of organic matter?

pH level of the water

Type of organic matter (correct)

Temperature of the environment

Salinity of the water

What is measured by the biochemical oxygen demand (BOD) test?

The amount of oxygen produced by microorganisms

The amount of nitrogen fixed by microorganisms

The amount of oxygen consumed by microorganisms (correct)

The amount of carbon dioxide produced by microorganisms

What is the purpose of the BOD/COD ratio?

To determine the biodegradability of the waste Signup and view all the answers

What is the result if the BOD/COD ratio is greater than or equal to 0.5?

The waste is easily degradable by biological means Signup and view all the answers

What is the purpose of the standard BOD test?

To measure the oxygen consumed by microorganisms Signup and view all the answers

What is the temperature at which the BOD test is incubated?

20°C Signup and view all the answers

What does the COD test measure?

The oxygen equivalent of organic matter oxidized by a strong chemical oxidant Signup and view all the answers

What is the purpose of measuring dissolved oxygen in wastewater bottles?

To determine the BOD of the wastewater Signup and view all the answers

At what temperature is the standard BOD test conducted?

20 0C Signup and view all the answers

What percentage of organic matter is degraded in 5 days' incubation time?

70% Signup and view all the answers

What is the unit of measurement for BOD?

mg/L Signup and view all the answers

What is the formula to calculate BOD in wastewater?

BOD = DO1 - DO2 Signup and view all the answers

What is the purpose of the equation 𝐵𝑂𝐷𝑡−𝑇 = 𝐿(1 − 𝑒−𝐾1𝑡 )?

To calculate the BOD at a specific time and temperature Signup and view all the answers

What is the unit of measurement for k1?

day-1 Signup and view all the answers

What is the unit of measurement for organic loading?

kg/day Signup and view all the answers

What is the value of BOD5-20 in mg/L?

129.939 Signup and view all the answers

What is the value of K1(25)?

0.289/day Signup and view all the answers

What percentage of water consumption is assumed to reach the sewer?

70-130% Signup and view all the answers

What is the typical range of sewage flow in individual cities?

70-130% of water consumption Signup and view all the answers

What is the formula to calculate the average daily demand?

Average daily demand = (70-130) × of water consumption Signup and view all the answers

What is the typical range of the maximum sewage daily demand?

(1.5-2) × average sewage daily demand Signup and view all the answers

What is the typical range of the minimum sewage daily demand?

(0.5-0.67) × average sewage daily demand Signup and view all the answers

What is the peak flow rate for a small residential area?

225% of the average for that day Signup and view all the answers

What is the formula for Time of Concentration (tc)?

tc = ti + tf Signup and view all the answers

What is the inlet time (ti) in the Time of Concentration formula?

Time required for rainwater to flow from the most remote distance in the catchment area to reach the collecting point Signup and view all the answers

What is the difference between a separate system and a combined system in sewer design?

Separate system has two pipes, combined system has one pipe Signup and view all the answers

What type of sewer carries sanitary sewage and industrial wastes?

Sanitary sewer Signup and view all the answers

What type of sewer is designed to carry surface and storm water?

Storm sewer Signup and view all the answers

What is the flowing time (tf) in the Time of Concentration formula?

Time required for the flowing discharge inside the sewer to reach the collecting point Signup and view all the answers

What is DWF in the context of sewer systems?

Dry weather flow Signup and view all the answers

What is WWF in the context of sewer systems?

Wet weather flow Signup and view all the answers

What is the peak flow of a sewer system serving a city with a normal population and commercial and industrial activities?

150 percent of the daily average Signup and view all the answers

What is the formula used to estimate the maximum rate of domestic sewage flow from small areas?

M = 1 + (14/4 + √P) Signup and view all the answers

What is the minimum flow of sewage flow used in the design of sewage pumping plants?

50 percent of the average Signup and view all the answers

What is the formula used to estimate the runoff discharge?

Q = CiA Signup and view all the answers

What is the term used to describe the time it takes for the runoff to reach the collection point into the desired sewer?

Time of concentration Signup and view all the answers

What is the unit of rainfall intensity in the intensity-duration curves?

mm/hr Signup and view all the answers

What is the purpose of using the minimum rates of sewage flow in design?

To design sewage pumping plants Signup and view all the answers

What is the term used to describe the ratio of the maximum sewage flow to the average sewage flow?

M Signup and view all the answers

Study Notes

Decomposition of Organic Matter

Decomposition occurs through microorganisms, depending on the type of organic matter, dissolved oxygen, microorganism type, and environmental conditions.
There are three methods to determine the concentration of organic matter:
- BOD (Biochemical Oxygen Demand): measures the oxygen utilized by microorganisms to stabilize biodegradable organic matter.
- COD (Chemical Oxygen Demand): measures the oxygen equivalent of organic matter oxidized by a strong chemical oxidant.
- TOC (Total Organic Carbon): measures the organic carbon converted to CO2 by heat, oxygen, ultraviolet radiation, or chemical oxidant.

BOD Test

The standard BOD test involves:
- Incubating a wastewater sample at 20°C for 5 days.
- Measuring the dissolved oxygen (DO) before and after incubation.
- Calculating BOD as the difference between initial and final DO.

Temperature Effects on BOD

The rate of BOD decomposition increases with temperature, according to the formula: K1(T) = K1(20) × 1.047(T-20)
The temperature effect is important for determining the ultimate BOD (BODu) and BOD at different times.

Wastewater Flow

Wastewater flow can be classified into:
- Domestic: 80-90% of water consumption.
- Industrial: includes domestic and process water.
- Public: similar to domestic.
- Runoff or storm sewage: calculated using the rational formula.

Fluctuations in Dry Weather Flow

Fluctuations occur due to variations in water consumption.
The maximum daily demand can be 1.5 to 2 times the average daily demand.
The minimum daily demand can be 0.5 to 0.67 times the average daily demand.

Storm Sewage

The rational formula is used to calculate storm sewage: Q = CiA
The runoff coefficient (C) depends on the surface type and building areas.
The rainfall intensity (i) is calculated using intensity-duration curves.

Time of Concentration

The time of concentration is the runoff time to reach the collection point in the sewer.
It is calculated as the sum of inlet time (ti) and flowing time (tf).

Sewer Systems

There are two types of sewer systems:
- Separate system: uses two pipes for dry weather flow (DWF) and wet weather flow (WWF).
- Combined system: uses one pipe for both DWF and WWF.
Sewer types are classified according to the type of sewage they carry: sanitary sewers and storm sewers.

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Description

This quiz covers the decomposition process of organic matter in wastewater engineering, including factors affecting decomposition and the role of microorganisms. It is a part of Sanitary Engineering Design course at Al Qasim Green University College of Engineering.