Sewage Treatment technologies - MBR (Membrane Bioreactor), MBBR (Moving Bed Biofilm Reactor), SBR (Sequencing Batch Reactor), SBBR (Sequencing Batch BiofilmReactors )

MBR, MBBR, SBR & SBBR

 Conventional Activated Sludge Process:

Activated sludge plant involves:

1. Aeration tank in presence of microbes
2. Solid-liquid separation followed by Aeration
3. Discharge of clarified effluent
4. Wasting of excess biomass, and
5. Return of remaining biomass to the aeration tank.

In activated sludge process waste water containing organic matter is aerated in an Aeration tank which micro-organisms degrade the soluble organic matter. Part of organic matter is synthesized into new cells and part is oxidized to CO₂ and water to derive energy. In activated sludge systems the new cells formed in the reaction are removed from the liquid stream in the form of a flocculent sludge in settling tanks. A part of this settled biomass, described as activated sludge is returned to the aeration tank and the remaining forms waste or excess sludge sent to Sludge Drying beds.

Conventional Activated Sludge Process Limitations:

•         MLSS values – 3500 ppm

•         Sludge carry over  in the treated water

•         Media filter efficiency max 100 Microns

•         Colloidal Particles – Poor SDI

•         Difficult to maintain consistent treated water quality

•         Odor  in the Treated effluent

•         Upset in system due to inlet variations

•         Large area and huge civil works required

•         Maximum 70 – 80 % of Bio degradation of BOD/COD.

To overcome the above limitations the following new technologies was innovated for better performance in waste water treatment. They are

 

               Sequencing Batch Reactor (SBR)

---

Definition:

An SBR operates in a batch mode with aeration and sludge settlement both occurring in the same tank.

All the process like Equalization, Aeration and Sedimentation will take place in a single tank. Sequencing batch reactors operate by a cycle of periods consisting of fill, react, settle, decant, and idle. The Influent will enter the tank through bottomdistribution will contact with Microorganisms and Air was supplied for Micro organisms through  Aerator and the Process of Aeration will take place until complete biodegradation of BOD and the Air blower will stop automatically depend upon the BOD load of the Influent and the same tank will act as Settling tank. The clear liquid from the top of the tank will let out after completes settlement and the Extra Bio mass also was sent out through bottom line. During this clarifying period no liquids should enter or leave the tank to avoid turbulence in the supernatant.

The wasted sludge is pumped to an anaerobic digester or sludge drying bed  to reduce the volume of the sludge to be discarded. The frequency of sludge wasting ranges between once each cycle to once every two to three months depending upon system design.

The major differences between SBR and conventional continuous-flow, activated sludge system is that the SBR tank carries out the functions of equalization aeration and sedimentation in a time sequence rather than in the conventional space sequence of continuous-flow systems.

Advantages:

1.       SBR system can be designed with the ability to treat a wide range of influent volumes whereas the continuous system is based upon a fixed influent flow rate. Thus, there is a degree of flexibility associated with working in a time rather than in a space sequence.

2.      SBRs produce sludges with good settling properties providing the influent wastewater is admitted into the aeration in a controlled manner.

3.      Controls range from a simplified float and timer based system with a PLC to a PC based SCADA system with color graphics using either flow proportional aeration or dissolved oxygen controlled aeration to reduce aeration to reduce energy consumption and enhance the selective pressures for BOD, nutrient removal, and control of filaments

4.      . Working with automated control reduces the number of operator skill and attention requirement.

5.      Lesser Foot prints.

6.      . The duration, oxygen concentration, and mixing in these periods could be altered according to the needs of the particular treatment plant.

Disadvantages:

1.      Appropriate aeration and decanting is essential for the correct operations of these plants.

2.      The aerator should make the oxygen readily available to the microorganisms.

3.      The decanter should avoid the intake of floating matter from the tank.

Sequencing Batch Biofilm Reactors (SBBR)

To optimize the operation of traditional SBR’sand reduce the aeration phase with less HRT, a new technology has been developed which  is called as Sequencing Batch Biofilm Reactor (SBBR), a newly developed System in which intelligent controlling system (ICS) has been  adopted to control the SBBR. Stable performance was achieved in the SBBR at a hydraulic retention time (HRT) of 7 h, at which point the removal efficiencies ofNH3-N, TP and COD reached 99%, 100% and 96%, respectively. When compared with conventional SBR, theSBBR controlled by the ICS reduced the HRT and total aeration time by 56% and 50%, respectively, and achieved better performance in removing the COD. In addition, the optimal carbon nitrogen (COD/N) ratio for the Simultaneous removal of nitrogen and COD in the SBBR was found to be 12.5, and no accumulation of NO3—Nor NO2−-N was detected at this ratio, indicating that efficient simultaneous nitrification and denitrification. (SND) was occurring in the reactor. The SND efficiency reached 98%.

Recently, the sequencing batch biofilm reactor (SBBR) system has attracted a great deal of attention due to its ability to take advantages of both a biofilm reactor and a SBR.

Advantages:

1. SBBR systems showimproved biomass concentration in reactors with corresponding higher specific removal efficiencies, greater volumetric loads, increased process stability toward shock loadings and are capable of covering small areas.

2. SBBR systems canremove nitrogen and phosphorus simultaneously.

3. Presence of an anoxic microzone in the biofilm could result in Simultaneous nitrification and denitrification in the SBBR during the aeration phase.

4.  In such cases, nitrification occurs on the surface of the biofilm, whereas denitrification occurs in the inner layers due to a dissolved oxygen (DO) gradient within the biofilm.

Disadvantages:

1.      Even though we will get good bio degradation of BOD, we will get some Suspended Solids which cannot able to remove by SBBR.

2.      Capital cost is high.

MOVING BED BIO REACTOR (MBBR)

In the MBBR biofilm technology the biofilm grows protected within engineered plastic carriers, which are carefully designed with high internal surface area.   The bio reaction is carried out in controlled environment in this process. The MBBR biofilm technology is based on specially designed plastic biofilm carriers or biocarriers that are suspended and in continuous movement within a tank or reactor of specified volume.  The Bio reactors comprises of a tank, fitted with aeration grid. The bacterial activity needs dissolved oxygen, to synthesize the organic matter. This is supplied by passing air in the form of small bubbles. The air is passed at the bottom of tank, so that complete volume of tank is utilized. Oxygen dissolved in liquid which can now be used by the bacteria. The bacterial population is present on the media, which forms an integral part of the reactor system. The media is made of small plastic elements. Millions of such pieces are kept in the MBBR. The bacteria grow on the plastic media, by using the organic content in the raw sewage and the dissolved oxygen available. Due to constant aeration the media is set in whirling motion, so that continuous mixing takes place. The bacterial layer growth on the media surface increases to a certain extent, and then gets sloughed off after a specific period. This phenomenon is called sloughing. This creates new surface for further bacterial growth. Sloughing takes place only after complete growth and subsequent dyeing – off the bacterial layer.

Diffused aeration involves the introduction of Atmospheric air into the sewage through the submerged diffusers. Part of organic matter is synthesized into new cells and part is oxidized to carbon dioxide and water. The sloughed bio mass must be removed before the treated effluent is taken for downstream treatment. The Sloughed bio mass is drained to sludge drying beds.

Advantages:

1.      It is efficient, compact and easy to operate.

2.      It can be an excellent solution, since it is a standalone process.

Disadvantages:

1.      Continuous monitoring is required.

2.      We may get some dead mass in clear supernatant which increase the filter load.

MEMBRANE BIO REACTOR (MBR)

Definition:

Activated Sludge Process (ASP), an Old technique in waste water treatment is combined with highly efficient membrane filtration to start a sophisticated technique called Membrane Bio Reactor (MBR). Membrane bioreactors (MBRs) combine the use of biological processes and membrane technology to treat wastewater.Within one process unit, a high standard of treatment is achieved, replacing the conventional arrangement of  settling tank and filtration that generally produces what is termed as a tertiary standard effluent. The advent of membranes makes the wastewater treatment easier nowadays. It is an efficient process for maintaining a long solids retention time (SRT) at a relatively short hydraulic retention time (HRT), which is needed for the treatment of waste water.The dependence on disinfection is also reduced, since the membranes with pore openings, generally in the 0.1-0.5µm, range trap a significant proportion of pathogenic organisms. The more common MBR configuration is to have the membrane immersed in the wastewater, although a side stream configuration is also possible, with the wastewater pumped through the membrane module and then returned to the bioreactor. Operating at Mixed liquor suspended solids (MLSS) concentration of up to 12,000 mg/L and a sludge age of 30-60 days

 MBR is favored to all other conventional techniques because the treated water is free from suspended solids and microorganisms, thus making it suitable for reuse. This unique application gives high degradation rates, extremely low sludge production and very compact design.

Advantages:                                                                                       

1. SUPERIOR TREATED WATER QUALITY

1.     Safe rejection of Bio Mass

2.     Enhanced Standard of Hygiene through barrier filtration

3.     Consistent BOD levels of 3-7 ppm

4.     Ultra filtered water free of pathogens.

5.     SDI < 3 achieved consistently

2. PROCESS SUPERIORITY

1. Can  tolerate larger input variations
2. Aeration tank MLSS levels
3. 8000 - 12000 ppm
4. Reduction in aeration tank size
5. Aeration  system can handle higher loads
6. Sludge can be wasted directly to sludge handling equipments.

3. Low SDI in treated water

•          Removes difficult pre treatment for downstream Recycle systems

4. Modular units facilitate easy plant expansion
5. Eliminates filters – No Back wash waste.
6. Disinfection only based on specific requirement