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 - Variability of the wastewater stream

Purpose of using equalization for industrial treatment facilities Dampening of organic fluctuations  prevent shock loading of biological systems pH control  Minimize chemical requirements for neutralization Minimize flow surges to physical – chemical treatment. Permit chemical feed rates compatible with feeding equipment

Purpose of using equalization for industrial treatment facilities Provide continuous feed to biological system (even when the factory is not operating) Controlled discharge of wastes to municipal system. Distribute waste loads evenly. Prevent high concentrations of toxic materials from entering the biological treatment plant.

Mixing Requirements for Equaliztaion Tanks Mixing is required for: - Adequate equalization - Prevent settlement of solids - Oxidation of reducing compounds - Reduction of BOD by air stripping (limited)

Mixing Methods 1.Distribution of inlet flow and baffling 2.Turbine Mixing 3.Diffused air aeration 4.Mechanical aeration

Mixing Methods Most common method  Submerged mixers For readily biodegradable wastes use surface aerators  – kW /m 3 Air requirement for diffused air aeration: 3.5 – 4.0 m 3 air / m 3 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.

Equalization basin equalize - Flow or - Concentration or - Both

Flow equalization Plot cumulative flow versus time Determine maximum volume with respect to constant discharge line

Concentration Equalization Equalization basin may be sized to restrict the dischatge to a maximum concentration

Equalization volume Volume of completely mixed basins used in treatment can be considered as part of equalization basin (e.g. Activated sludge) Example: Total time required for equalization: 16h Aeration basin: ? 8h Required equalization: 8 h

Patterson and Menez Method Used to calculate equalization volume when both the flow and the strength vary randomly Based on material balance C i QT + C o V = C 2 QT + C 2 V

Construction details for equalization basins 1.Influent should be given to the equalization basin close to the mixing device to prevent short circuiting 2.Cleaning system for grease and scum which can accumulate on the walls should be considered 3.An overflow weir should be installed to discharge wastewater in case of failure of pumps 4.Spray nozzles should be installed to break the foams

Factors effecting need for equalization 1. Cost of construction and implementing effective equalization 2. Cost saving by reducing the effects on downstream treatment systems

Flow Equalization Processes 1.ALTERNATING FLOW: 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

Flow Equalization Processes 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: - volume - variance of the diverted water  to reduce downstream effect

Flow Equalization Processes 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.

Flow Equalization Processes 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.