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

General Design Standards for SBRs
1.
Basis of Design
a.
General Design Basis
All designs must clearly identify the design loadings and appropriate flow and loading criteria based on peaking factors .

Designs must identify the following parameters: SVI, F:M ratio, MLVSS:MLSS ratio, decanter depth, high and low water levels, mean cell residence time, cycle times at various flow conditions, decant volume, and tank dimensions .

Project proponents must evaluate proprietary system designs and document how they meet the criteria of this section

. This analysis must include the calculations needed to support any performance claims.

b
.
Guarantees

Major SBR equipment manufacturers sometimes provide design calculations along with performance “guarantees”. While guarantees may provide some important insurance to a community, Ecology’s obligation to safeguard the environment prohibits accepting manufacturer guarantees in lieu of the engineering basis for the design
.
c
.
General Reliability

Designs for SBR systems must provide the same reliability of treatment required for continuous flow through designs

. Since each SBR reactor serves several functions, it must meet the most stringent of the reliability criteria for the various components it replaces (e.g.: primary
clarifier, aeration basin, aerators, backup power, control logic, etc).

d
.
Comparison of Alternatives

Designers comparing the SBR option to other alternatives should do so on the basis of their comparative life cycle costs. The analysis must use a common cost basis comparison to determine which system most reliably and economically provides an effluent that will meet all anticipated requirements for discharge, disposal, or reuse over the useful service life of the project.

e
.
Solicitation Methods

Individual SBR equipment manufacturers often provide proprietary control system and process components. They will also specify optimum tank configurations that are unique for their process.

As a result, early identification of a preferred SBR system may be necessary for efficient plant design. Proponents must ensure that any pre-selection or prequalification of a SBR system follows the current federal and state procurement laws.
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2
.
Required Number of Basins
•
Designers must provide for more than two reactor vessels (basins) unless Ecology approves the system as a continuous flow-through system.
•
Designers may request Ecology approve a two basin system if all other requirements for sizing are met and if design features ensure uninterrupted treatment with a malfunction in one tank. Designs for such systems must show how the operator can isolate, replace, or service a malfunctioning component with little or no reduction in treatment capacity. Such functionality typically requires an equalization basin(s) or removable components (diffuser grids, mixers, etc.). The design must provide a backup for all major assemblies, including motors, pumps, valves, blowers, and control logic. Plans for any two basin system must also show the location of a future third SBR basin. Plans should also provide for “stub outs” for a third basin if growth projections predict the need within twenty years.

3
.
Sizing Aeration Tanks

a
.
Basis for sizing

Engineers must size aeration tanks based on rational calculations which ensure compliance with anticipated permit limits.

b
.
Oxic Sludge Age

Designs must provide sufficient tank volume to operate at an “oxic” sludge age of 8 to 15 days (minimum). The oxic sludge age equals the mean cell residence time (MCRT) multiplied by the
proportion of time the tank is in the react phase.

The “oxic sludge age” for an SBR is the corollary to “sludge age” in a conventional activated sludge system.

Designs must assess the need for longer sludge ages if reactors will operate below 15ºC
.
c
.
Separation at end of Decant Cycle

Designs must provide an adequate zone of separation between the sludge blanket and the decanter(s) throughout the decant phase. Designers must estimate the clear water depth at the end of the decant cycle based upon a reasonable worst case Sludge Volume Index (SVI).

Designers should use operating data from an existing SBR system with loading characteristics and operating goals similar to the proposed facility to estimate the facility’s design SVI. If comparable site specific data is not available, designers should use a default SVI of 250 ml/g.

d
.
Minimum Decantable Volume

Designs must have a decantable volume (Vd) and decanter capacity that, with the largest basin out of service, will pass 75% or more of the design maximum day flow (Qd) without altering cycle time (ct, hours). Formula: Vd > (.75*Qd*(ct/24))/(n-1) where ‘n’ is the total number of SBR tanks.

Designs also may not specify a decantable volume of more than 1/3 of the total tank volume (Vt) per cycle (Vt > Vd * 3).

e. Maximum F:M Ratio

Designs must provide adequate tank volume to meet a nutrient loading rate limit.

This limit is a food to micro-organism (F/M) ratio of 0.10 lb BOD5/day/lb MLVSS at the design maximum monthly average loading rate.

The ratio of volatile suspended solids to total suspended solids within the mixed liquor (MLVSS:MLSS) should be based on rational calculations or data from similar facilities. Designers must provide operating examples to support design MLSS concentrations above 4,000 mg/l at full tank volume.

f. Mass Loading Rate

Designs must provide adequate tank volume to limit the mass loading rate to 15 lb BOD5/d/1000 ft3 [0.24 kg BOD5/d/m3].

Designers should evaluate this criteria using the tank volume at the normal low-water level and using the maximum monthly average loading for BOD5.

4
.
Sizing the Air Delivery System

a

.
General Process

Designs must supply the air needed for biological treatment under the range of anticipated conditions to maintain the proper mix of healthy biota. Designers must incorporate the following factors in their analysis:
•
Peak loadings rates (carbonaceous and nitrogenous) at critical conditions (lower water depth, higher temperature)

•
Diffuser specific oxygen transfer rates
•
Specific motor and blower efficiency and pressure (head) losses through the air delivery system

Standard Oxygen Transfer Efficiency

Designers must provide the diffuser manufacturer’s estimated oxygen transfer efficiencies.

Ecology encourages designers to verify such claims with an oxygen transfer test conducted in accordance with ASCE Procedures (ANSI/ASCE 2-19, Measurement of Oxygen Transfer in Clean Water).

Ecology may require such verification for unfamiliar system, or atypical claims.
c
.
Adjustment Factors

Designers must typically multiply the standard oxygen transfer values (for clean water) for a diffuser by three separate factors to obtain oxygen transfer rates for a specific site.

The factors include the alpha (oxygen mass transfer coefficient ratio from clean to wastewater), beta (salinity-surface tension correction factor), and fouling factors (diffuser specific decrease in efficiency over a specified period).

Designers must provide the basis for selected factors, ideally using site specific data.

Absent better data, designers should use alpha values of 0.5 for fine bubble diffusers, 0.75 for jet aerators, and 0.85 for coarse bubble diffusers
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d
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Considering Nutrient Removal

SBR designs can achieve excellent conversion of ammonia to nitrates, and good removal of total nitrogen.

SBR designs may also achieve phosphorus removal by creating alternating aerobic and anoxic reactor environments during the “react” phase of the process. Several sources report good total overall nitrogen removal with typical SBR cycle times of 6 -10 hours.

If the system must achieve low effluent total nitrogen levels, the designer may need to employ additional treatment steps.

» مبادئ تصميم خزانات الترسيب للمعالجة البيولوجية الثانوية بطريقة الحماه النشطة/General design guidelines for secondary sedimentation as a part of the activated sludge process
» General Design Considerations FOR Continuous Flow ofActivated Sludge procesess/lfمبادئ تصميم خزانات المعالجة البيولوجية باسلوب الحماة النشطة
» Batch Treatment (Sequencing Batch Reactor design/مبادئ تصميم وحدات المعالجة البيولوجية بنظام الاس.بى.ار
» مبادئ تصميم خزانات المعالجة البيولوجية بنظام الرياكتور/the principal biological reactor design
» مبادئ تصميم وحدة التهوية الطويلة للمعالجة البيولوجية/Extended Aeration