This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Wet Air Oxidation & Electrocoagulation”.
1. Wet air oxidation is a form of hydrothermal treatment.
Explanation: Wet oxidation is a form of hydrothermal treatment. It is the oxidation of dissolved or suspended components in water using oxygen as the oxidizer. It is referred to as “Wet Air Oxidation” (WAO) when air is used.
2. The oxidation process occurs above 374˚C.
Explanation: In superheated water at a temperature above the normal boiling point of water (100 °C), but below the critical point (374 °C), the oxidation reactions occur.
3. In a bubble column reactor, fresh water enters from the _________of the column.
d) Top and side
Explanation: Commercial systems typically use a bubble column reactor, where air is bubbled through a vertical column that is liquid full of the hot and pressurized wastewater. Fresh wastewater enters the bottom of the column and oxidized wastewater exits the top.
4. The heat released during the oxidation is_______
a) Released into the atmosphere
b) Cooled using cooling systems
c) Used to maintain operating temperature
d) Used as energy to boil water
Explanation: The heat released during the oxidation is used to maintain the operating temperature. WAO is a liquid phase reaction using dissolved oxygen in water to oxidize wastewater contaminants. The dissolved oxygen is typically supplied using pressurized air, but pure oxygen can also be used.
5. Which form of oxygen is used in the process of wet air oxidation?
a) Molecular oxygen
b) Dissolved oxygen
c) Pure oxygen
d) Atomic oxygen
Explanation: WAO is a liquid phase reaction using dissolved oxygen in water to oxidize wastewater contaminants. The dissolved oxygen is typically supplied using pressurized air, but pure oxygen can also be used.
6. What is the minimum temperature required for WAO?
Explanation: The oxidation reaction generally occurs at moderate temperatures of 150°-320 °C and at pressures from 10 to 220 bars. The process converts organic contaminants to carbon dioxide, water and biodegradable short chain organic acids.
7. What is the percentage of dry solid slurry that can be processed in a WAO system?
Explanation: The thermal conditioning occurs at temperatures of 210 – 240 °C. 4% dry solid slurry can be processed in a WAO system where it is disinfected and the treated effluent can be dewatered to 55% dry solids using a filter press.
8. What is the maximum pressure below which oxidation reactions occur?
a) 110 bar
b) 150 bar
c) 220 bar
d) 250 bar
Explanation: The oxidation reactions occur at temperatures of 150°C to 320°C and at pressures from 10 bars to 220 bars. Higher temperatures require higher pressure to maintain a liquid phase in the system.
9. What is the minimum feed flow rate for industrial applications of WAO?
a) 1 m3/h
b) 5 m3/h
c) 10 m3/h
d) 50 m3/h
Explanation: Higher temperatures require higher pressure to maintain a liquid phase in the system. The feed flow rate must be 1m3/h to 50m3/h for industrial applications for the WAO.
10. Electro-coagulation process removes bacteria.
Explanation: Electrocoagulation process removes emulsified oils, total suspended solids (TSS), heavy metals, emulsified oils, bacteria and other contaminants from water.
11. The cathode material corrodes during the process.
Explanation: An electrocoagulation reactor is made up of an electrolytic cell with one anode and one cathode. The anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation.
12. What is the minimum number of electrodes required for the process?
Explanation: The minimum number of electrodes required for the process of electro-coagulation is 2. Minimum one anode and a cathode are required for the reaction to begin. A series of electrodes are connected for better results.
13. Which among the following corrodes due to oxidation?
c) Anode and cathode
d) Only cathode
Explanation: The anode material will electrochemically corrode due to oxidation, while the cathode will be subjected to passivation when it is connected to an external source.
14. The conductive metal plates are placed in ________
c) Either parallel or perpendicular
d) Neither parallel or perpendicular
Explanation: An EC system essentially consists of pairs of conductive metal plates in parallel, which act as monopolar electrodes. It furthermore requires a direct current power source, a resistance box to regulate the current density and a multimeter to read the current values.
15. _________ results from the oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules.
b) Emulsion breaking
Explanation: The oxygen and hydrogen ions that bond into the water receptor sites of emulsified oil molecules creating a water-insoluble complex separating water from oil, driller’s mud, dyes, inks and fatty acids etc. causes emulsion breaking.
16. What is the common method used for mixing of wastewater in electrocoagulation process?
a) Mechanical mixing
b) Natural mixing
c) Electrical stirrer
d) Magnetic bar stirrer
Explanation: The common method used for mixing of wastewater in electrocoagulation process is through the use of magnetic bar stirrer. This is placed in the bottom of the jar at the centre.
Sanfoundry Global Education & Learning Series – Waste Water Engineering.
To practice all areas of Waste Water Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.