76 Questions
What is defined as the presence in water of impurities in such quantity and of such nature as to impair the use of the water for a stated purpose?
Water pollution
What type of wastewater is discharged from residences and from commercial, institutional, and similar facilities?
Domestic (sanitary) wastewater
What is the term for water that enters the sewer system through leaking joints, cracks and breaks, or porous walls?
Infiltration/Inflow
What is runoff resulting from rainfall and snowmelt called?
Storm water
What are the three types of sewer systems mentioned in the text?
Sanitary sewer system, storm sewer system, combined water system
What is the primary aim of secondary wastewater treatment?
Removal of biodegradable organics and suspended solids
Which treatment system involves the removal of large solids to prevent damage to the remainder of the unit operations?
Preliminary wastewater treatment
What is the typical percentage of solids and BOD removed in primary wastewater treatment?
60% of solids and 30% of BOD
What is the main focus of tertiary wastewater treatment?
Polishing of secondary effluent
What is the purpose of screening in preliminary wastewater treatment?
Removing materials that might damage equipment or hinder further treatment
What is the classification of wastewater treatment methods mentioned in the text?
Physical unit operations, chemical unit processes, biological unit processes
What is the primary focus of primary wastewater treatment?
Removal of a portion of suspended solids and organic matter
What does solids treatment and disposal involve?
Collection, stabilization, and subsequent disposal of the solids removed by other processes
What is the primary concern in wastewater treatment regarding contaminants?
Suspended solids
What is the main focus of secondary wastewater treatment?
Removal of biodegradable organics and suspended solids
What does tertiary wastewater treatment primarily involve?
Removing nutrients, toxic compounds, increased amounts of organic material, and suspended solids
What factors affect the rate of biomass production and food utilization in biological wastewater treatment?
Temperature, pH, and salt concentration
What represents the average time in which microorganisms or solids stay in the reactor in biological wastewater treatment?
MCRT/SRT
What does the F/M ratio measure in biological wastewater treatment?
Organic loading and aeration period
What type of biological growth/culture is the activated sludge process an example of in wastewater treatment?
Suspended culture/growth
Which parameter affects treatment efficiency and waste activated sludge production in the activated sludge process?
F/M ratio
What represents the suspended solids in the reactor and is useful in the determination of F/M in biological wastewater treatment?
MLSS
What is the primary focus of the design of biological systems in wastewater treatment?
Biological principles
What type of organisms or culture is required for complete treatment of wastewater?
Mixed culture
What is the term for the microorganisms involved in biological treatment in engineered reactors to optimize organic removal?
Controlled microorganisms
What may irreparably damage microorganisms in biological treatment?
Sudden changes in environmental factors
What are the two types of biological growth/culture used in wastewater treatment?
Suspended culture and attached growth
Which parameter affects the organic loading and aeration period in biological wastewater treatment?
F/M ratio
What is the optimum range of dissolved oxygen (DO) levels for aerobic processes?
1.5 - 2.5 mg/L
What can over-aeration, resulting in DO levels of 5-6, lead to?
Undesirable microorganisms and filamentous bulking in the sludge
What can cause filamentous bulking in secondary clarifiers?
Operational and wastewater characteristic factors
What are the operational causes of non-filamentous organisms?
Over-aeration and the presence of toxic substances
What are the various cures and techniques employed to address wastewater treatment issues?
Adjusting F/M ratio and DO levels, dosing with H2O2, and pre-treating wastewater
What are the two types of aeration techniques mentioned in the text?
Air diffusers and mechanical aerators
What are wastewater ponds often referred to as for natural purification processes?
Aerobic ponds often referred to as polishing or tertiary ponds
Which systems are populated by a variety of organisms and are effective in treating wastewater?
Attached growth systems, such as trickling filters and biotowers
What do trickling filters utilize as a solid medium?
Randomly packed solid medium
What do biotowers use as a medium in a vertical arrangement?
Synthetic media
What is the success of an activated sludge system often dependent on?
The performance of the final clarifier
How is the presence of oxygen primarily provided in ponds?
By photosynthesis
What is the optimum range for Dissolved Oxygen (DO) levels crucial for aerobic processes?
1.5 - 2.5 mg/L
What can lead to undesirable microorganisms and filamentous bulking in the sludge?
Over-aeration, resulting in DO levels of 5-6 mg/L
What can cause filamentous bulking in secondary clarifiers?
Over-aeration
What are the various cures and techniques employed to address wastewater treatment issues?
Adjusting F/M ratio and DO levels
Which technique utilizes randomly packed solid medium and may have odor and clogging problems?
Trickling filters
What distinguishes lagoons from ponds in wastewater treatment?
Lagoons have artificial aeration, ponds rely on photosynthesis
What is the primary focus of attached growth systems like trickling filters and biotowers?
Population of a variety of organisms
What is the primary determinant of the success of an activated sludge system?
Performance of the final clarifier
What type of media do biotowers use in a vertical arrangement?
Synthetic media
What is the primary source of oxygen in ponds?
Photosynthesis
What are wastewater ponds often referred to as?
Polishing ponds
What is the main purpose of lagoons in natural purification processes?
Population of a variety of organisms
Which factor(s) affect(s) the rate of biomass production and food utilization in biological wastewater treatment?
Temperature, pH, and salt concentration
What is the primary purpose of MCRT/SRT in biological wastewater treatment?
To represent the average time in which microorganisms or solids stay in the reactor
What is the role of F/M ratio in the activated sludge process?
Measuring organic loading and affecting aeration period
What type of biological growth/culture is used in the oxidation ditch for wastewater treatment?
Suspended culture/growth
What does MLSS represent in the context of biological wastewater treatment?
Suspended solids in the reactor
What are the design parameters/operational parameters in the activated sludge process?
F/M ratio, MLSS, MCRT/SRT, and HRT
What is the primary role of HRT in biological wastewater treatment?
Representing the average time in which the liquid remains in the system
Which type of biological growth/culture is used in ponds and lagoons for wastewater treatment?
Suspended culture/growth
What is the impact of low F/M ratio in the activated sludge process?
High treatment efficiency and little waste activated sludge
What is the primary impact of high F/M ratio in the activated sludge process?
High waste activated sludge and low treatment efficiency
Which factor(s) affect(s) the aeration period in the activated sludge process?
F/M ratio and organic loading
What is the primary role of the activated sludge process in biological wastewater treatment?
Organic removal
What is the primary purpose of grit removal in wastewater treatment?
To separate non-biodegradable solids from organic suspended solids
What is the primary factor affecting sedimentation tank efficiency?
Type of solids and rate of solids flow
What is the main aim of primary treatment in wastewater treatment?
Sedimentation to separate suspended particles from water
What is the typical removal efficiency for settleable solids achieved through sedimentation?
90-95%
What is the primary focus of secondary treatment in wastewater treatment?
Biological conversion of dissolved and colloidal organics into biomass
What is the main purpose of fine screens in preliminary wastewater treatment?
Mechanically cleaning and removing large solids
What is the primary method of disposal for screenings in wastewater treatment?
Hauling to disposal areas
What is the main function of comminution in wastewater treatment?
Shredding screenings to a specific size
What is the purpose of Parshall flumes and Palmer-Bowlus flumes in wastewater treatment?
Flow measurement
What is the primary aim of grit chambers in wastewater treatment?
Protect mechanical equipment and reduce heavy deposits
What is the main purpose of flow distribution in sedimentation tanks?
To evenly distribute the flow and prevent short circuiting
What is the primary function of mechanically-cleaned bar screens in wastewater treatment?
To mechanically clean large solids
Study Notes
Wastewater Treatment Systems and Contaminants: Key Points
- There are three types of sewer systems: sanitary sewer system, storm sewer system, and combined water system.
- Contaminants of concern in wastewater treatment include suspended solids, biodegradable organics, pathogens, nutrients, priority pollutants, refractory organics, heavy metals, and dissolved inorganics.
- The treatment objectives for wastewater treatment are the removal of suspended and floatable material, treatment of biodegradable organics, elimination of pathogenic organisms, removal of toxic compounds, and removal of nutrients.
- Wastewater treatment systems are divided into preliminary, primary, secondary, tertiary, and solids treatment and disposal.
- Preliminary wastewater treatment involves the removal of large solids to prevent damage to the remainder of the unit operations through screening, comminution, grit removal, and flotation.
- Primary wastewater treatment aims to remove a portion of suspended solids and organic matter by settling or sedimentation, typically removing about 60% of solids and 30% of BOD.
- Secondary wastewater treatment is directed principally at the removal of biodegradable organics and suspended solids, including biological treatment by activated sludge, fixed-film reactors, lagoons, and pond systems.
- Tertiary wastewater treatment involves the polishing of secondary effluent, primarily removing nutrients, toxic compounds, increased amounts of organic material, and suspended solids.
- Solids treatment and disposal includes the collection, stabilization, and subsequent disposal of the solids removed by other processes.
- Wastewater treatment methods are classified into physical unit operations, chemical unit processes, and biological unit processes.
- Preliminary treatment includes screening, the first operation performed on incoming wastewater for the purpose of removing materials that might damage equipment or hinder further treatment.
- Screening devices are used to remove coarse solids from wastewater, which consist of sticks, rags, boards, and other large objects that find their way to the wastewater collection systems.
Wastewater Treatment Processes and Equipment
- Fine screens consist of woven wire or cloth perforated plates and should be mechanically cleaned on a continuous basis.
- Mechanically-cleaned bar screens have bar racks 3 to 4 inches apart, while manually-cleaned bar screens require good flow distribution and velocity control.
- Disposal methods for screenings include hauling to disposal areas, burial on the plant site, incineration, disposal with municipal solid wastes, and grinding and returning to the wastewater flow.
- Comminution involves shredding screenings to approximately 8 mm in size using devices like a hammermill or a barminutor.
- Grit removal is essential to separate non-biodegradable solids from organic suspended solids, and it includes channel-type horizontal-flow grit chambers, aerated grit chambers, and vortex-type grit chambers.
- Grit chambers protect mechanical equipment, reduce heavy deposits, and minimize the frequency of digester cleaning.
- Parshall flumes and Palmer-Bowlus flumes are commonly used for flow measurement in wastewater treatment.
- Primary treatment involves sedimentation, which separates suspended particles from water through gravitational settling in sedimentation basins or tanks.
- Factors affecting sedimentation tank efficiency include the type of solids, age of wastewater, rate of solids flow, cleanliness, and mechanical condition of the tank.
- Sedimentation achieves removal efficiency for settleable solids (90-95%), suspended solids (50-65%), BOD (20-35%), and colloidal solids (not removed unless coagulants are added).
- Flow distribution in sedimentation tanks is managed by inlet structures to evenly distribute the flow and prevent short circuiting.
- Secondary treatment involves the biological conversion of dissolved and colloidal organics into biomass, which can be subsequently removed by sedimentation.
Test your knowledge of wastewater treatment systems and contaminants with this quiz. Explore key points such as types of sewer systems, contaminants of concern, treatment objectives, and various wastewater treatment techniques and considerations. From preliminary treatment to biological unit processes, this quiz covers essential information for anyone interested in wastewater management and environmental engineering.
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