47 Questions
What is the definition of water pollution?
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.
What is the predominant component of industrial wastewater?
Industrial wastes
What is the difference between infiltration and inflow in the context of wastewater?
Infiltration is direct water entry, while inflow is indirect water entry.
What is storm water in the context of wastewater?
Runoff resulting from rainfall and snowmelt
Which type of biological growth/culture includes activated sludge and ponds?
Suspended culture
In biological wastewater treatment, what are the phases of microorganism growth?
Lag, log, stationary, endogenous
What is the purpose of engineered reactors in biological wastewater treatment?
To optimize organic removal
Which factors can affect biomass production and food utilization in biological treatment?
Temperature, pH, toxins, salt concentration, oxidants, nutrients deficiency, DO level
What type of process is the activated sludge process in biological treatment?
Suspended-culture process with sludge returns
What are the common variations of the activated sludge process?
Step aeration, tapered aeration, contact stabilization, pure-oxygen activated sludge, oxidation ditch, high rate, extended aeration
What knowledge is required for the design of biological systems in wastewater treatment?
Biological principles, kinetics of metabolism, mass balance, and physical operations
What types of organisms or culture are needed for complete treatment in biological wastewater treatment?
A wide variety of organisms or a mixed culture
How do microorganisms respond to gradual environmental changes?
They can adjust
What are the design and operational parameters in the activated sludge process?
F/M ratio, MLSS, MCRT/SRT, HRT
What are the two types of biological growth/culture mentioned in the text?
Suspended and attached
What can be damaging to microorganisms in biological treatment?
Sudden environmental changes
What is the primary objective of preliminary wastewater treatment?
Removal of large solids to prevent damage to the remainder of the unit operations
Which type of sewer system is designed to handle excess rainwater?
Storm sewer system
What is the main focus of secondary wastewater treatment?
Removal of biodegradable organics and suspended solids
What is the purpose of screening in preliminary treatment?
Removing materials that might damage equipment or hinder further treatment
What does tertiary wastewater treatment primarily involve the removal of?
Nutrients and toxic compounds
Which classification of wastewater treatment methods includes operations such as screening?
Preliminary treatment
What is the main focus of primary wastewater treatment?
Removal of a portion of suspended solids and organic matter by settling or sedimentation
What does solids treatment and disposal involve?
Collection, stabilization, and subsequent disposal of the solids removed by other processes
What are the contaminants of concern in wastewater treatment?
Suspended solids, biodegradable organics, pathogens, nutrients, priority pollutants, refractory organics, heavy metals, and dissolved inorganics
What is the purpose of a storm sewer system?
To handle excess rainwater
What is the main focus of tertiary wastewater treatment?
Polishing of secondary effluent, primarily the removal of nutrients and toxic compounds
What is the optimum level of dissolved oxygen (DO) crucial for aerobic processes?
1.5-2.5 mg/L
What can over-aeration lead to in wastewater treatment?
Undesirable microorganisms and filamentous bulking
What is a critical factor in the success of activated sludge systems?
Filamentous bulking in secondary clarifiers
What are the causes of poor settling due to filamentous bulking?
Operational factors and wastewater characteristics
What impact do aeration techniques have on plug flow and completely mixed reactors?
Impacting oxygen transfer efficiency and maintenance requirements
What do wastewater ponds and lagoons provide for treatment processes?
Natural purification processes
What do attached growth systems like trickling filters and rotating biological contactors utilize to treat wastewater?
Heterotrophic bacteria and algae
What do trickling filters use for wastewater treatment?
Solid medium and intermittent doses of wastewater
What do biotowers use for vertical arrangement and treatment?
Modular synthetic media
What is the result of difficult settling of solids in secondary clarifiers?
Filamentous bulking
What is crucial for the success of wastewater treatment in activated sludge systems?
Adjustments in F/M ratio and DO levels
What is the purpose of aerobic ponds in wastewater treatment?
Additional treatment
What is the purpose of comminution in wastewater treatment?
To shred screenings to approximately 8 mm in size before returning them to the wastewater flow
What is the primary purpose of grit removal in wastewater treatment?
To separate non-biodegradable grit from organic suspended solids to prevent accelerated wear on equipment
What is the purpose of Parshall flumes and Palmer-Bowlus flumes in wastewater treatment?
To measure flow in wastewater treatment as open channel venturi meters
What is the primary purpose of primary treatment in wastewater treatment?
To separate suspended particles from water by gravitational settling
What are the factors affecting sedimentation efficiency in primary treatment?
Types of solids, age of wastewater, rate of solids flow, cleanliness, and mechanical condition of the tank
What is the primary focus of secondary treatment in wastewater treatment?
Biological conversion of dissolved and colloidal organics into biomass for subsequent removal by sedimentation
What is the purpose of grit chambers in wastewater treatment?
To protect mechanical equipment from abrasion and reduce heavy deposits
What is the primary function of Parshall flumes and Palmer-Bowlus flumes in wastewater treatment?
To measure flow in wastewater treatment as open channel venturi meters
Study Notes
Wastewater Treatment Techniques and Considerations
- Dissolved oxygen (DO) is crucial for aerobic processes; the optimum level is 1.5-2.5 mg/L, with over-aeration leading to undesirable microorganisms and filamentous bulking at levels of 5-6 mg/L.
- Filamentous bulking in secondary clarifiers results from difficult settling of solids and is often a critical factor in the success of activated sludge systems.
- Causes of poor settling due to filamentous bulking include operational factors and wastewater characteristics, requiring adjustments in F/M ratio, DO levels, and pre-treatment of wastewater.
- Aeration techniques such as air diffusers (fine and coarse bubble) and mechanical aerators are used in plug flow and completely mixed reactors, impacting oxygen transfer efficiency and maintenance requirements.
- Wastewater ponds and lagoons provide natural purification processes for treatment, with aerobic ponds used for additional treatment and anaerobic ponds requiring subsequent aerobic treatment.
- Attached growth systems like trickling filters and rotating biological contactors utilize organisms such as heterotrophic bacteria and algae to treat wastewater, with the biomass growing into dense films that decompose organic matter.
- Trickling filters use solid medium and intermittent doses of wastewater, requiring primary clarifiers to prevent clogging and pre-treatment to address odor and vector issues.
- Biotowers use modular synthetic media for vertical arrangement and treatment, offering advantages in height and weight, but still requiring pre-treatment and addressing potential clogging problems.
Wastewater Treatment Processes
- Fine screens are used to filter out particles from wastewater and should be mechanically cleaned on a continuous basis.
- Bar screens with varying distances between bars are used for filtering out larger and smaller particles, and they should be cleaned to ensure good flow distribution.
- Screenings, coated with objectionable organic material, are disposed of through methods such as landfilling, burial, incineration, or grinding and returning to the wastewater flow.
- Inefficient screening can lead to septic shock loading and the production of H2S due to backflow of influent wastewater.
- Comminution involves shredding screenings to approximately 8 mm in size before returning them to the wastewater flow.
- Grit removal is essential to separate non-biodegradable grit from organic suspended solids to prevent accelerated wear on equipment.
- Grit removal facilities include channel-type horizontal-flow grit chambers, aerated grit chambers, and vortex-type grit chambers.
- Grit chambers protect mechanical equipment from abrasion, reduce heavy deposits, and minimize the frequency of digester cleaning.
- Flow measurement in wastewater treatment commonly uses Parshall flumes and Palmer-Bowlus flumes as open channel venturi meters.
- Primary treatment involves sedimentation to separate suspended particles from water by gravitational settling.
- Factors affecting sedimentation efficiency include types of solids, age of wastewater, rate of solids flow, cleanliness, and mechanical condition of the tank.
- Secondary treatment typically involves the biological conversion of dissolved and colloidal organics into biomass for subsequent removal by sedimentation.
Test your knowledge of wastewater treatment techniques and processes with this quiz. Explore topics such as dissolved oxygen levels, filamentous bulking, aeration techniques, wastewater ponds, attached growth systems, and various treatment processes such as screening, grit removal, and sedimentation.
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