ENVE 420 Industrial Pollution Control. EQUALIZATION Dr. Aslıhan Kerç. Objective of Using Equalization Basins. Minimize or control fluctuations in wastewater characteristics and flowrate. Size and type of equalization basin varies with: - Quantity of waste
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Dr. Aslıhan Kerç
- Variability of the wastewater stream
- Adequate equalization
- Prevent settlement of solids
- Oxidation of reducing compounds
- Reduction of BOD by air stripping (limited)
Most common method Submerged mixers
For readily biodegradable wastes use surface aerators 0.003 – 0.004 kW /m3
Air requirement for diffused air aeration:
3.5 – 4.0 m3air / m3 waste
Variable volume in the equalization tank provide a constant effluent flow
Program effluent pumping rate Discharge maximum quantity of waste during periods of low flow
Organic loading of treatment plant is maintained constant for 24-h.
Plot cumulative flow versus time
Determine maximum volume with respect to constant discharge line
Equalization basin may be sized to restrict the dischatge to a maximum concentration
Example: Total time required for equalization: 16h
Aeration basin: ?
Required equalization: 8 h
Based on material balance
CiQT + CoV = C2QT + C2V
1. Cost of construction and implementing effective equalization
2. Cost saving by reducing the effects on downstream treatment systems
Collects total flow of the effluent for a given period of time (normally 24 hours) while a second basin is discharging. Alternative between filling-discharging. High degree of equalization by leveling all discharge parameters.
Disadvantage high construction cost
2. INTERMITTENT FLOW DIVERSION:
Allows any significant variance in stream parameters to be diverted to an equalization basin for short durations. Diverted flow is then bled back into the stream at a controlled rate. Rate at which the diverted flow is fed back into main stream depends on:
- variance of the diverted water to reduce downstream effect
3. COMPLETELY MIXED COMBINED FLOW:
Complete mixing of multiple flows combined at the front end of the facility. Reduce variance in each stream by thorough mixing with other flows.
4. COMPLETELY FIXED FLOW:
A large completely mixed holding basin before wastewater treatment facility. Levels variations of influent stream parameters and provides a constant discharge.