40 Questions
What is the process by which the environment deals with organic materials?
Decomposition
What is the primary factor that affects the decomposition of organic matter?
Type of organic matter
What is measured by the biochemical oxygen demand (BOD) test?
The amount of oxygen consumed by microorganisms
What is the purpose of the BOD/COD ratio?
To determine the biodegradability of the waste
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
What is the purpose of the standard BOD test?
To measure the oxygen consumed by microorganisms
What is the temperature at which the BOD test is incubated?
20°C
What does the COD test measure?
The oxygen equivalent of organic matter oxidized by a strong chemical oxidant
What is the purpose of measuring dissolved oxygen in wastewater bottles?
To determine the BOD of the wastewater
At what temperature is the standard BOD test conducted?
20 0C
What percentage of organic matter is degraded in 5 days' incubation time?
70%
What is the unit of measurement for BOD?
mg/L
What is the formula to calculate BOD in wastewater?
BOD = DO1 - DO2
What is the purpose of the equation 𝐵𝑂𝐷𝑡−𝑇 = 𝐿(1 − 𝑒−𝐾1𝑡 )?
To calculate the BOD at a specific time and temperature
What is the unit of measurement for k1?
day-1
What is the unit of measurement for organic loading?
kg/day
What is the value of BOD5-20 in mg/L?
129.939
What is the value of K1(25)?
0.289/day
What percentage of water consumption is assumed to reach the sewer?
70-130%
What is the typical range of sewage flow in individual cities?
70-130% of water consumption
What is the formula to calculate the average daily demand?
Average daily demand = (70-130) × of water consumption
What is the typical range of the maximum sewage daily demand?
(1.5-2) × average sewage daily demand
What is the typical range of the minimum sewage daily demand?
(0.5-0.67) × average sewage daily demand
What is the peak flow rate for a small residential area?
225% of the average for that day
What is the formula for Time of Concentration (tc)?
tc = ti + tf
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
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
What type of sewer carries sanitary sewage and industrial wastes?
Sanitary sewer
What type of sewer is designed to carry surface and storm water?
Storm sewer
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
What is DWF in the context of sewer systems?
Dry weather flow
What is WWF in the context of sewer systems?
Wet weather flow
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
What is the formula used to estimate the maximum rate of domestic sewage flow from small areas?
M = 1 + (14/4 + √P)
What is the minimum flow of sewage flow used in the design of sewage pumping plants?
50 percent of the average
What is the formula used to estimate the runoff discharge?
Q = CiA
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
What is the unit of rainfall intensity in the intensity-duration curves?
mm/hr
What is the purpose of using the minimum rates of sewage flow in design?
To design sewage pumping plants
What is the term used to describe the ratio of the maximum sewage flow to the average sewage flow?
M
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.
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.
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