This set of Waste Water Engineering written test Questions & Answers focuses on “Sequential Batch Reactor & BOD Removal Methods”.
1. SBR is a type of ________
a) Aerobic process
b) Activated sludge process
c) Anaerobic process
d) Chemical process
Explanation: Sequencing batch reactors (SBR) or sequential batch reactors are a type of activated sludge process for the treatment of wastewater. SBR reactors treat wastewater such as sewage or output from anaerobic digesters or mechanical biological treatment facilities in batches.
2. The one tank is aerating and filling while the other one is decant.
Explanation: The tanks have a “flow through” system, with raw wastewater (influent) coming in at one end and treated water (effluent) flowing out of the other. One tank is in settle/decant mode the other is aerating and filling in multiple tank systems.
3. Bio-selectors direct the flow.
Explanation: In some systems, tanks contain a section known as the bio-selector, which consists of a series of walls or baffles which direct the flow either from side to side of the tank or under and over consecutive baffles.
4. ___________ helps to mix the incoming influent and the returned activated sludge.
Explanation: This helps to mix the incoming Influent and the returned activated sludge (RAS), beginning the biological digestion process before the liquor enters the main part of the tank.
5. How is mixing done in SBR?
c) Air stripping
d) Agitation by air
Explanation: The inlet valve opens and the tank is being filled in, while mixing is provided by mechanical means (no air). This stage is also called the anoxic stage.
6. In which stage of the SBR is aeration performed?
Explanation: The fixed or floating mechanical pumps are used or air is transferred into fine bubble diffusers fixed to the floor of the tank during the second stage aeration of the mixed liquor.
7. In which stage are the aeration and mixing avoided?
Explanation: No aeration or mixing is provided in the third stage and the settling of suspended solids starts. During the fourth stage, the outlet valve opens and the “clean” supernatant liquor exits the tank.
8. The multiplication of _________ is encouraged by the addition of oxygen.
b) Aerobic bacteria
c) Anaerobic bacteria
Explanation: Aeration times vary according to the plant size and the composition/quantity of the incoming liquor, but are typically 60 to 90 minutes. The multiplication of aerobic bacteria is encouraged by the addition of oxygen.
9. ______ is used to remove phosphorus compounds from the liquor.
a) Aluminium nitrate
b) Aluminium phosphate
c) Aluminium sulphate
d) Sodium nitrate
Explanation: To remove phosphorus compounds from the liquor, aluminium sulphate (alum) is often added during this period. It reacts to form non-soluble compounds, which settle into the sludge in the next stage.
10. The _________ is usually the same length in time as the aeration.
a) Screening stage
b) Mixing stage
c) Clarification stage
d) Settling stage
Explanation: The settling stage is usually the same length in time as the aeration and during this stage the sludge formed by the bacteria is allowed to settle to the bottom of the tank.
11. Which part of the tank is suitable for anaerobic bacteria to flourish?
d) Middle zone
Explanation: The aerobic bacterium multiplies until the dissolved oxygen is all used up. The bottom conditions are more suited for the anaerobic bacteria to flourish.
12. ______ is removed by Anammox.
a) Nitric oxides
Explanation: An anaerobic process uses anoxic methods to remove ammonia, such as the removal of ammonia via Anammox or the study of slow-growing micro-organisms.
13. How many types of BOD are present?
Explanation: BOD can be used as a gauge of the effectiveness of wastewater treatment plants. It is listed as a conventional pollutant in the U.S. Clean Water Act. The two major types of BOD are soluble BOD and insoluble BOD.
14. BOD is a physical procedure for determining DO needed for aerobic biological organisms.
Explanation: BOD is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material.
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