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Texas Wastewater Class C | Questions with
100% Correct Answers | Verified | Latest
Update 2025
- What is the main purpose of a bar screen in a wastewater treatment plant? A. Remove large debris such as rags and sticks B. Aerate the wastewater C. Remove nitrogen D. Disinfect the effluent Bar screens are used in preliminary treatment to remove large solids that could damage equipment.
- What is the typical detention time in a primary clarifier? A. 15 minutes B. 2 hours C. 6 hours D. 1 day Primary clarifiers generally have a detention time of around 2 hours to allow solids to settle.
- What gas is commonly produced in anaerobic digesters? A. Oxygen
B. Methane C. Carbon monoxide D. Ammonia Methane is produced during the anaerobic digestion of organic matter.
- What laboratory test is commonly used to measure the strength of organic pollutants in wastewater? A. BOD (Biochemical Oxygen Demand) B. DO (Dissolved Oxygen) C. pH D. TSS BOD measures how much oxygen is needed by bacteria to break down organic material.
- What is the ideal pH range for biological activity in activated sludge? A. 4.5โ5. B. 5.0โ6. C. 6.5โ8. D. 8.5โ10. Bacteria in the activated sludge process perform best in a neutral to slightly basic pH range.
- The term โMLSSโ stands for: A. Mixed Liquor Sludge Solids
B. Kill pathogenic organisms C. Add nutrients D. Remove solids Chlorine is used to disinfect treated wastewater before discharge. 10.What is the function of a digester in sludge treatment? A. Aerate the sludge B. Stabilize organic material through microbial activity C. Increase water content D. Chemically treat sludge Digesters reduce pathogens and odors while stabilizing sludge.
11. What is the purpose of a grit chamber in preliminary treatment? A. To remove grease and oil B. To remove sand and heavy inorganic solids C. To neutralize pH D. To settle organic matter Grit chambers remove heavy, inorganic particles like sand and gravel to protect downstream equipment. 12. What is the typical DO (Dissolved Oxygen) level maintained in the aeration tank? A. 0.5 mg/L B. 2.0 mg/L
C. 5.0 mg/L D. 8.0 mg/L Around 2.0 mg/L DO is ideal for biological activity in activated sludge systems.
13. A common cause of bulking sludge is: A. High chlorine residual B. Filamentous bacteria overgrowth C. Low pH D. Excessive grease Bulking sludge occurs when filamentous bacteria dominate, preventing proper settling. 14. The F/M ratio refers to: A. Food to microorganism ratio B. Filtrate to mixed liquor ratio C. Flow to material ratio D. Final to mean concentration ratio F/M ratio measures the balance between available food (BOD) and the microbes available to consume it. 15. The most accurate way to determine sludge age is: A. By smell B. By calculating solids retention time (SRT) C. Using flow meter readings
19. What is the function of a RAS (Return Activated Sludge) line? A. Add chlorine B. Return settled sludge to the aeration basin C. Remove scum D. Provide grit removal RAS sends settled biomass back to the aeration tank to maintain microbial population. 20. What happens if you waste too much sludge? A. Clarifier improves B. Microbial population decreases C. BOD removal increases D. Oxygen demand drops Overwasting reduces the microbial population and can hurt biological treatment. 21. A secondary clarifier is used for: A. Primary solids settling B. Settling of biological floc from the aeration tank C. Grit removal D. Filtration Secondary clarifiers settle biomass from the aeration basin.
22. The term "supernatant" refers to: A. The clear liquid above settled solids B. Sludge at the bottom C. Grit D. Influent Supernatant is the liquid portion that floats above sludge or solids. 23. What condition may result from septic sludge in a clarifier? A. Increased DO B. Odors and gas formation C. Increased nitrification D. Sludge thickening Septic sludge generates gas and foul odors, disrupting operations. 24. What is the primary function of a comminutor? A. Disinfection B. Shred solids into smaller pieces C. Remove chlorine D. Mix chemicals Comminutors grind solids to prevent clogs in downstream units. 25. A plug flow pattern is typical of which unit? A. Clarifier B. Aeration basin
29. The primary cause of foaming in aeration tanks is: A. Chlorine overdose B. Nocardia or filamentous organisms C. Low TSS D. High grit content Nocardia and filaments cause foaming due to their surfactant-like properties. 30. What safety gear is essential when handling chlorine gas? A. Cloth gloves B. SCBA and chemical-resistant gear C. Safety vest D. Flashlight SCBA is required due to the toxic nature of chlorine gas. 31. What does SCADA stand for? A. Safety Control and Discharge Analyzer B. System for Chemical Analysis Data C. Supervisory Control and Data Acquisition D. Sludge Control Automated Device SCADA systems allow operators to monitor and control operations remotely.
32. The main component of biosolids is: A. Ammonia B. Organic matter C. Chloride D. Oil and grease Biosolids are primarily composed of organic material stabilized during treatment. 33. What is the typical range for TSS in secondary effluent (well-functioning plant)? A. 100โ200 mg/L B. 30โ50 mg/L C. Less than 30 mg/L D. Over 200 mg/L Effluent TSS should be under 30 mg/L to meet discharge permit standards. 34. What is the most common cause of low DO in an aeration tank? A. Low flow B. High alkalinity C. Insufficient aeration or high oxygen demand D. Excessive wasting High oxygen demand or poor aeration causes DO to drop.
C. Decreases D. Oscillates Nitrification consumes alkalinity and causes a drop in pH.
39. The best time to collect a BOD sample is: A. During heavy rainfall B. During normal flow conditions C. At midnight D. After wasting Representative samples are taken during normal operating conditions. 40. What is the meaning of "infiltration"? A. Odor release B. Groundwater entering sewer lines C. Pump failure D. Solids settling Infiltration is unwanted groundwater entering the sewer system. 41. What process follows the secondary clarifier in a typical treatment train? A. Disinfection B. Grit removal C. Equalization D. Influent screening Disinfection occurs after clarification to kill pathogens before discharge.
42. A lift station is used to: A. Mix chlorine B. Aerate wastewater C. Pump wastewater to a higher elevation D. Separate solids Lift stations are pumping units used where gravity flow is not possible. 43. Chlorine gas is: A. Odorless and safe B. Harmless to skin C. Toxic and heavier than air D. Lighter than air and non-reactive Chlorine is toxic and settles in low-lying areas. 44. The presence of filamentous bacteria indicates: A. Good settling B. Potential bulking issues C. Proper F/M ratio D. Strong nitrification Filamentous overgrowth often causes sludge bulking.
C. Seal with plastic D. Light a flare Chlorine leaks require evacuation and use of SCBA.
49. Which parameter must be monitored when using UV disinfection? A. BOD B. DO C. UV intensity and transmittance D. Ammonia UV performance depends on light intensity and water clarity. 50. What is the common unit for measuring flow in wastewater treatment? A. Gallons per pound B. MGD (Million Gallons per Day) C. Liters per gram D. PSI MGD is the standard unit for plant flow capacity and reporting. 51. What does BOD stand for? A. Biological Oxide Demand B. Biochemical Oxygen Demand C. Biological Operation Demand D. Biodegradable Organic Demand BOD measures how much oxygen bacteria need to break down organic matter.
52. What is the typical chlorine contact time required for effective disinfection? A. 1 minute B. 30 minutes C. 2 hours D. 4 hours Most disinfection regulations require at least 30 minutes of chlorine contact time. 53. What is the function of scum baffles in clarifiers? A. Increase flow B. Retain floating material like grease and foam C. Control DO D. Add nutrients Scum baffles prevent floating debris from flowing over the weirs. 54. What color should properly digested sludge be? A. Bright green B. Dark brown or black C. Blue D. Light red Well-digested sludge is dark due to the breakdown of organic matter.
C. DPD colorimeter D. Turbidity meter A DPD colorimeter or comparator measures free and total chlorine residual.
59. What is the first step in the wastewater treatment process? A. Preliminary treatment (screening and grit removal) B. Disinfection C. Secondary clarification D. Sludge digestion Preliminary treatment removes large debris and grit to protect equipment. 60. What is the primary goal of secondary treatment? A. Remove solids B. Biologically remove organic matter (BOD) C. Disinfect D. Remove chlorine Secondary treatment is biological and targets organic pollution. 61. Excessive foaming in the aeration tank may indicate: A. Low pH B. Equipment failure C. Filamentous organism (e.g., Nocardia) D. Grit buildup Filamentous bacteria can cause foamy, stable surface layers.
62. What is a composite sample? A. One-time grab B. Sample collected over time and combined C. Filtered sample D. Random sample Composite samples provide a time-weighted average of water quality. 63. What is the best method to control odors in primary treatment? A. Increase flow B. Decrease pH C. Cover tanks and provide air scrubbing D. Add sludge Covering units and treating off-gas helps reduce odors. 64. A high SVI reading suggests: A. Good sludge settling B. Poor sludge settling or bulking C. High DO D. Low ammonia High SVI means sludge isn't settling properly, often due to bulking.
