Equipment Design Features Required for SBR Systems/اسس تصميم واختيار معدات المعالجة بنظام الاس بى ار

Equipment Design Features Required for SBR Systems:
1.
Flow Equalization Basins
Designs must include an evaluation of the cost and benefits of an influent flow equalization basin to equalize diurnal flow and facilitate operation while one SBR basin is off-line for necessary repairs and maintenance.

2.
Screens
Designs must include an appropriate method of removing grit, rags, floatables, and other solid waste. Designers should give preference to screens over comminutors. Designs not incorporating preliminary treatment must include an acceptable justification.
3.
Scum Control
Designs must provide scum removal features. Where designs employ scum troughs, they may either be fixed or floating (such as attached to the decant boom). Designs may specify manual scum removal if it is not needed more than every third day.
4.
Foam Control
Designs should include spray bars supplied with chlorinated non-potable water for foam suppression and to facilitate scum collection.
5.
Mixing Equipment
Designs for mixing equipment must include the capacity for anoxic mixing (without supplying air). Designs must provide for complete mixing of the contents of the basin so that solids concentrations vary less than 10% after the first five minutes.
6.
Diffuser Anti-Clogging Features
Designs must specify whether the aerators chosen require continuous positive pressure to avoid clogging, and if so, how the system will meet this requirement.
7.
Alkalinity Addition Systems
Designs must include an evaluation of the potential need to add alkalinity to maintain a neutral effluent pH and residual alkalinity of 50 mg/l. The analysis must presume that the SBR system will achieve complete nitrification (whether required or not). Designs must show an accessible location for an alkalinity addition system. Where alkalinity addition is anticipated, designers should give preference to an alkalinity source or mix of chemicals which supplies carbonate ions.
8.
Tank Maintenance
Designs must include provisions for cleaning such as a sloped bottoms and sumps, ladders, and features to facilitate the removal of waste activated sludge. Designers should give preference to systems which use pumps to positively control the rate of removal of waste solids rather than decanting waste solids by gravity. Designs must provide a means for the operator to transfer activated sludge from one SBR to the other(s) to bring a tank online after cleaning or to recover after an upset.
9.
Decanting Equipment
Designs for decanters must include an evaluation of their ability to pass the peak-day flow in the allocated decant time without re-
suspending settled mixed liquor or decanting scum. Decant mechanisms should draw the treated effluent along a horizontal plane below the scum level. Designs for decanting equipment should also keep solids from accumulating in the decanting mechanisms during the react phase. Decanting equipment must require at least two independent control signals or valves to open for decanting to occur (one may be a manual valve).
10.
Disinfection Equipment
Designs must ensure disinfection systems will meet permit limits and meet the disinfection criteria at the flow rates and conditions which occur at the start of a decant cycle. Follow-on processes (pipes, filters, or effluent pumps and diffusers) must not cause a backup at these rates. Designs should include a comparative life cycle cost analysis of post treatment equalization basins, their amortized cost weighed against the higher power and larger disinfection system needed without it.
11.
Valve Positioning
Designs must show valves are positioned in easily serviceable locations, avoiding areas subject to flooding or freezing (unless protected). Designs must protect electronics from electrical power surges. Plans and O&M manuals must reinforce the need to maintain spare valve actuators for each size of automatic valve used.
12.
Blower Turndown Features
Designs must show that blowers can meet air demands at the anticipated range of flows and loadings without significant loss of efficiency.
13.
Sampling Equipment
Designs must specify flow-paced composite samplers for the effluent because effluent flows are not continuous. Samplers must draw sample aliquots at the beginning and end of decant cycles on a representative basis. Designs must show sampling ports at the locations relevant for process control.
14.
Freeze Thaw Protection
Designs must include features to protect exposed components and pipes from freezing in areas where freezing might be reasonably anticipated. Designs must anticipate that exposed pipes of SBR systems are at greater risk of freezing than flow through systems.
F.
Reliability Requirements for SBR Systems
1.
Diffuser Features
Designs must provide for retrievable aeration equipment, or an alternate method of cleaning or backflushing the diffusers. In systems with only two reactor tanks, designers must configure diffusers in multiple banks that can be independently isolated and repaired. Reactor basins must
provide sufficient aeration with a diffuser section or jet aerator out of service.
2.
Motor Operated Valve Features
Designs must include automatically controlled, motor-operated (or hydraulic cylinder-operated) valves for influent, decant, and air control valves. All motor-operated valves should have the ability to be manually operated should the electronics fail, or the design must include a manual backup valve. Influent valves must pass solids.
3.
Blowers
Engineers must size air blowers for SBR systems, as with other conventional secondary treatment systems, to supply the design oxygen requirements with the largest unit out of service. Where this requires valves to divert air from one tank to another, the valves must be electronically switchable.
4.
Backup Power Systems
Designs must supply an uninterruptible power supply with electrical surge protection for each Programmable Logic Controller (PLC) or computer in computer controlled systems. The system must retain program memory in event of a power loss or fluctuation (e.g. the process control program, last-known set points, valve positions, cycle state, and equipment run hours and status.).
5.
Sensitive Discharge Area Protection
Where the facility must meet category 1 reliability standards, or where discharges to shellfish beds, designs must provide online TSS meters on the decant lines from each SBR tank. Designs must integrate these meters into the plant’s control system. Excessive TSS values must cause an alarm that triggers prompt operator attention or halts the discharge until the operator corrects the problem.
G.
Control System Requirements for SBR Systems:
1.
General Control Functions
The control system must monitor key information and control routine operations of the SBR process. Key information includes system status, valve positions, tank levels, monitoring probe values, and equipment status. Routine operations include valve operation, aeration, mixing, decanting, sludge wasting, and disinfection. Designs may base operation on the tank’s fill level (flow-based) or a fixed schedule (time-based) with level overrides. Both must allow operator adjustment of the cycle structure.
2.
Load Equalization
Designs should give flow-based operation priority over time-based schemes to give more consistent loadings and better use capacity. When time based cycles are used, the cycle times must be staggered so alternating basins accept peak daily loads.

3.
Control System Redundancy
Designs must provide both an automatic programmable logic controller (PLC) or computer-based control system and a manual interface in case the automated system is inoperable. Designs must provide a redundant control system, and incorporate reasonable redundant control features (e.g. having computer based control systems loaded on multiple computers).
4.
Process Optimization and Efficiency Features
Designs should employ telemetry from probes continuously monitoring levels of dissolved oxygen, oxidation reduction potential, pH, and alkalinity (when alkalinity addition is needed). Control logic should use this information to control aerator output and cycle times. Systems should vary blower run time, output, or the number of blowers operating to keep oxygen levels within a range determined by control logic or the operator.
5.
Alternative Operation for High Flows
Designs must address the operational strategy for high flow situations. For time-based operation, the control system should automatically and progressively adjust cycle times when influent flows exceed what “normal” cycle times can handle. The control strategy for flow-based operation should adjust to faster fill rates with shorter cycles, greater decant volumes, and/or higher high-water levels, with control settings adjusted in turn. Designs must include a level-based high water alarm and cycle structure override. Control logic must always provide at least 20 minutes between react and decant phases.
6.
Manual Override Features
Designs must include both automatic and manual controls to allow independent operation of each tank. Manual controls should also prevent decant with less than 20 minutes of settling unless emergency bypass procedures are employed.
7.
Sludge Wasting Features
Designs must use waste activated sludge pumps rather than wasting by gravity unless the flow of waste sludge is metered. The volume of sludge flowing by gravity in a given time is otherwise too great for good process control. Designs must describe how to determine the volume and frequency of settled sludge to waste to ensure the stability of the system. Designs should automate sludge wasting as needed for stable performance considering weekend staffing levels.
8.
Valve Telemetry
Electronic controls must include feedback to ensure confirmation of proper valve operation. Critical valve failures must cause an alarm traceable to the specific valve. The control logic should make a record of each valve’s operating history.

9.
Alarm and Backup Features
Alarm features must provide audible alarms to immediately alert the operator to any critical fault, and provide a visual signal until the fault is corrected. After hours alarms must trigger an auto-dialer to call a sequential list of staff with an alarm message. The control system must display the status of the process and equipment (ideally both numerically and graphically). The control system should maintain an operational history of the facility and regularly and automatically store this in non-volatile format. This information should allow restoring the system, estimating when services are due, and allow for warranty claims.

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» التصميم العام لخزانات الاس بى ار للمعالجة البيولوجية General Design Standards for SBRs