SBR _ MBR Comparison

8/12/2019 SBR _ MBR Comparison

1/17

ITT Water & WastewaterSBR/MBR ComparisonProject name: General

Date: 20/10/08

ITT Project No. xxxxxxxx

Issue No.1

SBR/MBR Comparison

Project Ref: ******

Client : ******


2/17


Date: 20/10/08

ITT Project No. xxxxxxxx

Issue No.1

Table of Contents

1 Introduction to the ICEAS SBR process.................................................................. 1

2 The ICEAS process................................................................................................. 22.1 History of ABJ and ICEAS process................................................................. 22.2 The ICEAS Process ........................................................................................... 22.3 ICEAS Benefits................................................................................................. 7

3 ICEAS Comparison with MBR................................................................................ 103.1 History of MBR............................................................................................... 103.2 What is an MBR ............................................................................................. 103.3 Performance .................................................................................................. 103.4 Footprint ........................................................................................................ 113.5 Operability ..................................................................................................... 113.6 Cost ................................................................................................................ 123.7 MBR Application ............................................................................................ 133.8 ICEAS SBR suitability .................................................................................... 13


3/17


Date: 20/10/08

ITT Project No. *******

Issue No.1

1

1 Introduction to the ICEAS SBR process

The unit processes of the Sequence Batch Reactor (SBR) and conventional activatedsludge systems are the same. In a conventional activated sludge system, equalization,biological treatment, and secondary clarification would be accomplished by usingseparate tanks. The difference between the two technologies is that the SBR performsthese unit processes in single tank using a time control sequence, meaning the overallfootprint of the plant is significantly smaller thereby reducing construction costs.

The ICEAS (Intermittent Cycle Extended Aeration Cycle) process is a variant of an SBR (sequential batch reactor) system that allows the process to take place in a single basin,whilst constantly filling.

This process is a fully automatic system that responds to flow and load variations, iseasily expanded and produces a high quality effluent. Notably ICEAS requires less landarea and equipment than a conventional Activated Sludge plant and therefore loweroperating and construction costs. In sensitive locations, the ICEAS tanks can be designedto be covered, thereby reducing the environmental impact and minimising noise andodour pollution.

The ICEAS is more cost effective and can produce an equal or better quality of effluentthan conventional activated sludge systems used for treating municipal wastewater(dependant on the incoming effluent parameters the process can also be used onindustrial wastewater). In this compact system, flow equalisation, biological oxidation,secondary sedimentation, and biological nutrient removal occur in a single basin,significantly reducing capital costs. Inherently low energy requirements and O & M costsmake the ICEAS economical to operate. Normal operation providesnitrification/denitrification without costly chemicals and additional equipment. Similarly,efficient phosphorus removal is consistently achieved with the ICEAS process option. The

ITT W&WW ICEAS system are as of today (2008) successfully treating wastewater inover 350 operating plants worldwide, with loads ranging from a few hundred populationequivalent over 1,000,000 population equivalent including projects such as Doha South inQatar and the newly won ASeeb project in Oman.


4/17


5/17


Date: 20/10/08


Issue No.1

3

Figure 1 ICEAS Tank Layout

AERATION REACT

Raw wastewater from screening and grit removal flows into the basin and mixes withthe mixed liquor. The basin is aerated while filling and biological oxidation takes placesimultaneously. The aeration system of choice for municipal projects is fine bubblediffused air due to its oxygen transfer and operational efficiency.

Figure 2 ICEAS aeration phase

Screened InfluentBaffle Wall Decanter

Pre-react Chamber Main Chamber Diffusers


6/17


Date: 20/10/08


Issue No.1

4

During the aeration period, sufficient oxygen is provided to obtain full nitrification whenrequired. The aeration blowers are normally operated continuously in two tank ICEAS

plants unless special nitrogen and phosphorous removal requirements are required.

In each pairs of basins, the two basins operate completely out of phase with each otherat all times. One basin is aerating while the other basin is in an anoxic settling phase. Ina four basin operation the two pairs are staggered by one quarter of a cycle. In thisoperation effluent decanting periods will be near continuous with few non-decantingperiods. In the storm operation, the cycles are reduced to increase the hydraulicthrough put of the ICEAS, while still maintaining the overall aeration period.

ANOXIC REACT

Denitrification of the effluent occurs naturally in the settling and decant phases. Sincedenitrification occurs on a regular basis the level of nitrate in the system is low and risingsludge is not a problem. However, the settle and decant modes may not provide sufficientanoxic periods to provide the required level of denitrification and nitrogen removal fortight consent requirements. In such cases, an anoxic period can be added to the reactperiod as shown in Figure 3. If anoxic react periods are required, mixers must be addedto the tank to provide contact between the nitrate and the bacteria.

Figure 3 Anoxic operation

SETTLE

At the end of the react phase, aeration is stopped and the solids settle to the bottom of the basin leaving clear water on top. The settling period allows solids separation to occurproviding a clarified supernatant to be discharged as an effluent. The settling processmay vary from twenty (20) to sixty (60) minutes so that the sludge blanket remainsbelow the basin bottom water level during the draw or decant period.


7/17


Date: 20/10/08


Issue No.1

5

Figure 4 Settlement phase

The basin continuously receives the influent, even during the settle phase, but theprereact zone filters the incoming sewage through the sludge blanket at the far endfrom the decanters. This improves biological take-up of the BOD and minimisesdisturbance to the sludge blanket.

DECANT

At the end of the settle phase, the decanter arm is driven through the treated effluent tothe bottom water level. The clear water is discharged from the top of the basin,while the basin continuously receives the influent. Typically, sludge is wasted duringthis phase of the cycle.

Figure 5 Decant Phase


8/17


9/17


Date: 20/10/08


Issue No.1

7

The decanting period may vary from 15 minutes to one hour. A surface-skimmingdecanter designed to prevent floating material from being entrained in the dischargeremoves effluent.

STORM FLOWSHydraulically stable, even a single tank ICEAS system is capable of accommodating flowvariations of up to 7 times average dry weather flow (ADWF). To accommodate stormflow, a storm cycle sequence is activated when it is predicted that the liquid level will risein excess of the top water level (TWL). A float switch triggers a sequence of abbreviatedprocess times of aeration, settlement and effluent decanting during the storm flows. The

system will then automatically revert to the original treatment sequence once flows havereduced.

2.3 ICEAS Benefits

The USEPA undertook an analysis of the ICEAS system in 1999 1. Advantages of a SBR wastewater treatment system they found were as follows:

Minimal footprint Equalization, primary clarification (in most cases), biological treatment, and

secondary clarification can be achieved in a single reactor vessel Operating flexibility and control Potential capital cost saving by eliminating clarifiers and other equipment

ITT believe this difference in system configuration gives the SBR system severaladvantages over the conventional activated sludge process including:

Lower Capital Cost: Requires smaller footprint No primary or secondary clarifiers and accompanying pumping systems are needed Simpler and faster installation Lower construction costs

Enhanced Biological Performance: Low sludge volume Enhanced nutrient removal Quick response to changing influent conditions No washout of activated sludge during peak storm flows

Lower Operating Cost: Reduced power


10/17


Date: 20/10/08


Issue No.1

8

Reduced maintenance Nutrient removal without costly chemicals

Design Flexibility: Easily expandable Hydraulic peaks easily accommodated Handles shock loads without degradation of final effluent quality Control system provides high flexibility

Some of the principal features and significant benefits of ICEAS are:

2.3.1 Simplicity of Operation

ICEAS cycles are timed based, rather than level based. The operator can modify thecontrol system simply by entering process event timings through the Display ScreenControls. Level controlled processes often require more complicated control programrevisions to adapt to changing process conditions. Air output is easily adjusted throughblower run timers in the PLC controls for optimum basin Dissolved Oxygen (D.O.) levels.

2.3.2 Simplified Installation

In the simplest installations the fixed floor grid, membrane disc fine bubble or coarsebubble aeration system eliminates the need for any mechanical mixers and hoists, jetaspirators and motive pumps or retrievable diffuser frames. The small sludge pumps ineach basin discharge directly to a sludge tank without the need for sludge recirculationpiping, dry pit pumps and associated galleries.

2.3.3 Sludge Stability

The ICEAS process dispenses with return sludge recirculation lines and controls.

Research conducted at ABJs pilot plant, and previous experience at operational plantshas confirmed that sludge recirculation to bio sorption and/or pre-react zones do little toenhance treatment. Published data gathered over the last eight years from largeoperational ABJ treatment plants without sludge return provide evidence of the efficacy of the ICEAS process, even when located in severe winter locations such as the mountainsof the Northeast U.S.A or the northern plains of the Midwest U.S.A.

The sludge generated by the ICEAS process is well stabilised, since the process operatesin an extended aeration mode with a high solids retention time, normally over 12 days.The biomass experiences anoxic and anaerobic conditions during the settle and decantphases of each operating cycle, using the continuous influent as a carbon source for NO 3 -


11/17


Date: 20/10/08


Issue No.1

9

conversion. Sludge stability in the ABJ basins is also enhanced as a result of the repeatedaerated/non-aerated condition of the sludge.

2.3.4 Nutrient Removal

The ICEAS process has been refined over the years to meet increasingly stringenteffluent quality standards for nutrient removal. The alternating aerobic and anoxicconditions during aeration and settling/decanting periods of each operating cycleencourage nitrification and denitrification. A phosphate removal option called ICEAS DNPis available. Several papers regarding treatment obtained at operating plants have beenpublished.

2.3.5 Expansion Potential

The ICEAS process design lends itself to simplified expansion since each basin forms amodular treatment unit. Continuous influent allows additional flows to be distributed toall basins simultaneously. No motorised influent valves or piping, level controls ormodified process controls are required. The standard ABJ 4-hour process cycle isdesigned for operating up to four basins without overlapping aeration periods, whileusing two duty blowers to supply both pairs of basins. Doubling the system capacitywould only require the addition of four basins with fixtures (decanters, air control valves,

aeration system, and sludge pumps), additional blowers and an expanded control system.


12/17


Date: 20/10/08


Issue No.1

10

3 ICEAS Comparison with MBR

3.1 History of MBR

MBR, in comparison with SBR is a new technology and is still very much in thedevelopment and optimisation phase. ITT has constructed/is constructing a number of MBR wastewater treatment plants on municipal and industrial waste.

MBR was developed initially in Japan where many small installations have been madeover the last 20 years mainly using plate and frame module construction. During thelast decade hollow fibre immersed membranes have become prevalent and largerinstallations have been built using this geometry.

In recent years pressurised or side stream tubular MBR has been successful and isoffering an external alternative to the immersed membrane technology.

MBR is under constant development with new technologies and geometries are beingdeveloped and tested all the time. The main difference between MBR and SBR in thedevelopment cycle is that SBR is in the system optimisation phase, whereas MBR is in themuch earlier membrane development phase.

3.2 What is an MBR An MBR is an activated sludge system that utilises suspended growth bacteria to remove

pollutants from a waste stream. In this sense it is exactly the same as an ICEAS SBR. Thedifference is the means of separating the bacteria from the cleaned effluent. An ICEASSBR uses gravity to separate the solids from the cleaned effluent but an MBR usesmembrane filters to separate the solids.

A comparison of the two technologies is detailed below

3.3 PerformanceMBR

An MBR will produce effluent of exceptional quality.

The plant will usually produce anaverage effluent of 5:5:1 BOD:SS:NH 4,suitable for discharge to a long seaoutfall or irrigation without furthertreatment, though residual disinfectionmay be required.

ICEAS SBR

An ICEAS SBR will produce effluent of very good quality.

The plant will usually produce anaverage effluent of 10:10:1 BOD:SS:NH 4,suitable for discharge to a long seaoutfall or irrigation without furthertreatment, though residual disinfectionmay be required. The low turbidity of theSBR effluent makes it ideal fordisinfection by UV


13/17


Date: 20/10/08


Issue No.1

11

3.4 FootprintMBR

The MBR basin has an aeration zone andmembrane zone. These combined have avery low foot print.

The MBR will also need blower andadministration buildings.

The MBR will need inlet works with fine(6mm perforated) and very fine (1-3mm perforated) screens grit removaland fat oil and grease removal.

The MBR will need sludge storage.

The works will require storm tanks.

ICEAS SBR

The ICEAS SBR basin combines theaeration zone and settlement zones.These combined have a low foot print

The ICEAS SBR will also need blower andadministration buildings,

The ICEAS SBR will need inlet workswith fine (6mm perforated) screens onlyand grit removal.

The ICEAS SBR will need sludge storage.

The works will require storm tanks.

The footprints of the two plants will be similar once all the ancillary units and equipmentis added to the site.

3.5 Operability

MBR

The MBR is a highly sophisticated systemwith significant process monitoring andcontrol systems.

The MBR system requires regularmaintenance of the fine screens and gritremoval to ensure protection of the

delicate membranes.

The MBR has pressure monitoring on allunits and regular backwashing of themembrane modules.

The MBR membranes will slowly block until normal backwashing no longerprovides sufficient cleaning. At his point

the membranes require lifting out andchemical cleaning. See Figure 7.ICEAS SBR

The ICEAS SBR is a time controlledsystem and requires minimal monitoringand control systems.

The 6mm screens are standard waste

water industry equipment. The ICEASSBR can cope with high levels of grit,screenings and fats without affecting theprocess in the short to medium term.


14/17


Date: 20/10/08


Issue No.1

12

Figure 7: Hollow Fibre Immersed MBR Membranes being removed for cleaning.

3.6 CostMBR

MBRs are a high tech solution that issized on the flow restrictions of themembrane units. They are usuallyutilised in low flow applications due tothe high cost of the membranes.

The very high solids design of the MBR basin means aeration efficiency isinefficient and so expensive to operate.

The high cost hollow fibre membranesrequire replacing approximately every 7years.

ICEAS SBR

The ICEAS SBR has no high costmembranes.

The solids concentration is standard foractivated sludge processes.

There are no high cost hollow fibremembrane replacement costs.


15/17


Date: 20/10/08


Issue No.1

13

3.7 MBR Application

With higher capital and operating costs, more complex operation and the overriding risk of managing the membrane condition and operating life, one would only select MBR where thereis a specific need that cannot be achieved by other technology. The greatest use of such MBR technology is where the effluent is required to be treated to a higher standard for reuse aswater for further processing for potable consumption; or to satisfy the needs of a sensitivedischarge point.

3.8 ICEAS SBR suitability

The MBR produces an extremely high quality effluent, far better than that usuallyrequired for discharge to a long sea outfall or irrigation needs. It is very low foot print,but this is achieved by a highly increased technological complexity, capital and operatingcost.

The SBR produces a good quality effluent suitable for discharge to a long sea outfall andused for irrigation system (though may require some disinfection). Primarily, it is a simplerobust, proven technology with low footprint.


16/17


17/17

ITT Water & Wastewater Aerobic DigestersProject name: Sulaibiya WwTW

Date: June 6 th 2008


I N 1

15

References

1. USEPA Wastewater (1999) Technology Fact Sheet, Sequencing Batch Reactor, EPA 832-F-99-073

SBR _ MBR Comparison

Documents

Transcript of SBR _ MBR Comparison