CHAPTER: 1 INTRODUCTION
WHAT IS SECONDARY TREATMENT
Secondary treatment is traditionally applied to the liquid portion of sewage after primary treatment has removed settleable solids and floating materials.
It is the portion of the sewage treatment sequence removing dissolved and colloidal compounds measured as biochemical oxygen demand.
1.2 DIFFERENT SECONDARY TREATMENT PROCESSES
Secondary treatment is designed to substantially degrade the biological content of the sewage which is derived from human waste, food waste, soaps and detergent.
The majority of municipal plants treat the settled sewage liquor using aerobic biological processes. To be effective, the biota requires both oxygen and food to live. The bacteria and protozoa consume biodegradable soluble organic contaminant (e.g. sugars, fats, organic short-chain carbon molecules, etc.) and bind much of the less soluble fractions into floc.
Secondary treatment systems are classified as fixed-film or suspended growth systems.
1.2.1 FIXED-FILM OR ATTACHED GROWTH:
It includes trickling filters, bio towers, and rotating biological contactors, where the biomass grows on media and the sewage passes over its surface.
The fixed-film principal has further developed into moving bed bio film reactors (MBBR), and integrated fixed-film activated sludge (IFAS) processes. An MBBR system typically requires smaller footprint than suspended-growth systems.
1.2.2 SUSPENDED-GROWTH SYSTEMS OR ACTIVATED SLUDGE (ASP):
In this processes biomass is mixed with the sewage and can be operated in a smaller space than trickling filters that react the same amount of water.
However, fixed-film systems are more able to cope with drastic changes in the amount of biological material and can provide higher removal rates for organic material and suspended solids than suspended growth systems.
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CHAPTER: 2 ATTACHED GROWTH PROCESS
2.1 INTODUCTION
In fixed growth treatment systems or attached growth systems micro-organisms attach to a surface that is exposed to water. In a fixed growth treatment system, aerobic micro-organisms attach and grow on an inter media.
Waste water flows across a slime layer created by the attached micro-organisms, which extract soluble organic matter from the waste water as a source of carbon and energy.
Fixed growth technologies for fixed growth treatment systems may include the biology of fixed-growth reactors, trickling filter process, and rotating or dual biological processes.
A water treatment system is used to reduce common contaminants in water, such as sediment, calcium, iron, magnesium, sulphate, nitrates, arsenic, or lead.
Water treatment for fixed growth treatment systems can produce cleaner, safer, better tasting, and better smelling water that is better suited for residential, commercial, and industrial use.
The waste water treatment processes follows primary and then secondary treatments. The primary treatments remove settle able and floatable materials. The secondary treatment uses biological or chemical treatment to accomplish substantial removal of dissolved organics and colloidal materials.
Other types of fixed growth treatment system will use grinders (commenter’s), bar screens, and grit channels. Computers may also be used in fixed growth treatment systems to provide stream model software to predict the effects of pollutants entering the waterways.
Biological treatment of wastewater and sewage water used to lower the organic load of solute organic compounds for fixed growth treatment systems.
2.2 MBBR (MOVING BED BIO-FILM REACTOR)
The MBBR is a complete mix, continuous flow through process which combines the benefits of fixed film and suspended growth processes.
The MBBR process uses small plastics carrier elements to provide sites for bacteria attachment in a suspended growth medium.
The carrier allow a higher biomass concentration to be maintained in the reactor compared to a suspended growth process, such as activated sludge. This increases the biological treatment capacity for a given reactor volume.
The carrier elements can be installed in either an anoxic reactor or aeration basin. A screen or sieve assembly with 5 mm slot openings is used to retain the carrier elements in the reactor. The effective open area of the screen is sized to provide less than 2 inches of head loss. However the process does not require backwashing of the retention screens which retain the carriers.
The carrier elements are continuously kept in suspension by either a mixer or an aeration system.
The agitation pattern in the reactor is design to provide an upward movement of the carriers across the surface of the retention screen which creates a scrubbing effect to prevent clogging.
Coarse bubble and jet aeration are typically used to provide oxygen for an aerobic reactor.
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MEMBRANE SEPARATION:-
What is membrane?
The membrane can be defined as a barrier which separates two phases and restricts transport of various chemicals in a selective manner. In other words, a membrane is defined as a structure having lateral dimensions much greater than its thickness, though which mass transfer may occur under variety of driving forces. The membrane can be a selective or a contacting barrier.
Membrane Transport Mechanism:-
Membranes provide absolute barrier to particles greater than their pore size. A membrane process requires two bulk phases physically separated by a third phase, the membrane. The membrane phase interposed between the two-bulk phases controls the exchange of mass between the two bulk phases in a membrane process. The process allows the selective and controlled transfer of a certain species from one bulk phase to another bulk phase separated by the membran
Figure: 3.2 Membrane Transport Mechanisms
Advantages of membrane processes:-
‘ Appreciable energy savings.
‘ Clean Technology with operational case
‘ Replaces the conventional processes
‘ Recovery of high value products
‘ Greater flexibility in designing systems
‘ Hybrid process development
Disadvantages of membrane processes:-
‘ Membrane fouling
‘ Upper solid limits
‘ Expensive
Energy use in membranes:-
Membrane processes use a significant amount of energy. Even low pressure membranes use approximately 100 kHz per million gallons (3.785 million liters) of water produced. The development of new composite membranes has reduced the operating pressures considerably. Lower pressure operation means lower energy consumption. Whereas 400 pounds per square inch (psi) (2,760 kPa) pressure was considered normal for RO as recently as ten years ago, today’s ultralow pressure RO membranes function efficiently at pressures as low as 125 psi (862 kPa); the norm for brackish water desalination is 225 psi (1,550 kPa).A comparison of energy consumption per 1,000 gallons (3,785liters) of water produced and various types of pressure driven membranes.
Classification of Membrane Processes:-
Membranes can be classified as follows:
Pressure driven membrane process:
‘ Reverse Osmosis (RO)
‘ Nano filtration (NF)
‘ Ultra filtration (UF)
‘ Microfiltration (MF)
‘ Membrane gas separation
‘ Membrane extraction
‘ Electro dialysis (ED)
Figure3.3 Component separations during pressure driven membrane process
Apart from the above processes, there are other membrane processes such as:
‘ Facilitated or carrier mediated membrane transport
‘ Liquid membrane separation
‘ Membrane contactors
‘ Membrane reactors
‘ Charge mosaic membranes
‘ Synthetic membranes
Application:-
Membrane Processes are no longer bound in the domains of laboratory but have found their way into the industries as viable separation techniques.
Major areas of application of membrane technology are:
‘ Chemical Industry
‘ Pharmaceutical industry
‘ Food and Dairy Industry
‘ Biotechnology Industry
Figure: 3.4:- Application of Membrane Separation Processes
HAPTER 3 EXPECTED OUTCOME
3.1 MBBR
From theoretical data it can be observed that for maximum reduction in BOD among all the biological treatments can be achieved by MBBR (Moving Bed Bio-film reactor) efficiently and cost-effectively.
3.1.2 INTRODUCTION
The MBBR is a complete mix, continuous flow through process which combines the benefits of fixed film and suspended growth processes.
The MBBR process uses small plastics carrier elements to provide sites for bacteria attachment in a suspended growth medium.
The carrier elements allow a higher biomass concentration to be maintained in the reactor compared to a suspended growth process, such as activated sludge. This increases the biological treatment capacity for a given reactor volume.
This carrier Elements can be installed in either an anoxic reactor or aeration basin. A screen or sieve assembly with 5 mm slot openings is used to retain the carrier elements in the reactor. The effective open area of the screen is sized to provide less than 2 inches. However, the process does not require backwashing of the retention screen which retain the carriers.
The carrier elements are continuously kept in suspension by either a mixer or an aeration system.
The agitation pattern in the reactor is designed to provide an upward movement of the carriers across the surface of the retention screen which creates a scrubbing effect to prevent clogging.
Coarse bubble and jet aeration are typically used provide oxygen for an aerobic reactor. A report using fine bubble aeration in an MBBR system indicates the media cause the bubble to coalesce, thereby reducing oxygen transfer efficiency.
Jet aeration is recommended for new installation due to its intense mixing and improved oxygen transfer efficiency when compared to coarse bubble aeration. Ideal depths for the jet aeration system range between 16 to 24 feet. figure 1 shows a photograph of a jet aeration piping within the MBBR reactor.
3.1.3 BIO-CARRIER
There are different sizes and designs of carrier elements used in the MBBR process. The type K1 carriers by Anoxkaldnes were used for the talecris WWTP.
There carriers are cylinders constructed of high density polyethylene which are 10 mm in diameter with a height of 7 mm. The carrier elements have a specific gravity of 0.96 g/m3 and provide an effective surface area for bio film growth of 500 m2/m3.
The carrier elements have a cross in the middle and longitudinal fins on the outside to maximize the available surface area, as shown in figure 2 below.
3.1.4 WORKING
The aeration provided at the base moves the whole waste water in circular direction which provides excess amount of dissolved oxygen for the microbial growth therefore more number of bacterial growth can be achieved, which affects the treatment of waste water.
Aeration pipelines are placed most likely that maximum DO can be generated. Also media particles with large amount of surface area are used for maximum biological growth.
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MOVING BED BIOFILM REACTOR
Introduction
Limited water resources and increasing urbanization require a more advanced technology to preserve water quality. One of the important factors affecting water quality is the enrichment of nutrients in water bodies. Wastewater with high levels of organic matter (COD) Phosphorus (P) and Nitrogen (N) cause several problems, such as eutrophication, oxygen consumption and toxicity, when discharged to the environment. It is, therefore, necessary to remove these substances from wastewaters for reducing their harm to environments. Biological processes are a cost-effective and environmentally sound alternative to the chemical treatment of wastewater.
Biological treatment processes are systems that use microorganisms to degrade organic contaminants from wastewater. In wastewater treatment, natural biodegradation processes have been contained and accelerated in systems to remove organic material and nutrients. Excess microbial growth is removed from the treated wastewater by physical processes.
There are already many different Bio-film systems in use, such as trickling filters, Rotating Biological Contactors (RBCs), fixed media submerged bio-filters, granular media bio-filters, fluidized bed reactors, etc. They all have advantages and disadvantages. Two technologies are commonly used for biological treatment of sewage: activated sludge and trickling filters. A moving bed biological reactor (MBBR) is a compilation of these two technologies.
The biomass in the MBBR exists in two forms: suspended flocs and a bio-film attached to carriers. It can be operated at high organic loads and it is less sensitive to hydraulic overloading.
At the core of the technology are specially designed polyethylene carriers that provide a large protected surface area for the microorganisms (that eat the waste) to grow and multiply. This allows a higher concentration of active biomass to be maintained in the reactor for biological treatment without increasing the reactor size. The result is more treatment capacity in a smaller area which saves you valuable space, money and allows you to install in tighter spaces. Besides offering an overall footprint reduction compared to an equivalent SBR system, the MBBR process also offers a buffer against shock loads.
BASIC TREATMENT PROCESS
The idea of the MBBR is to combine the two different processes (attached and suspended biomass) by adding bio-film small High Density Polyethylene (HDPE) carrier elements into the tank and bio-film attachment and the growth has been proposed. The kind of system is usually referred as IFAS (Integrated Fixed-film Activated Sludge) process. In these systems the biomass grows both as suspended flocs and as attached bio-film. In this way, the carrier elements allow a higher biomass concentration to be maintained in the reactor compared to a suspended growth process, such as activated sludge. This increases the biological treatment capacity for a given reactor volume.
Figure shows the anaerobic, aerobic reactors and the bio-film carrier used for MBBR process.
Figure: The principle of Moving Bed Bio-film Reactor and the shape of bio-film carrier
The agitation pattern in the reactor is designed to provide an upward movement of the carrier across the surface of the retention screen which creates a scrubbing effect to prevent clogging, so that the whole reactor volume is biologically active resulting in higher biomass activity.
The foremost difference between the MBBR and IFAS system is the presence of a return activated sludge stream that remains central to the IFAS process. In the MBBR process, biomass is remained in the bioreactor through attachment to suspended carrier material using sieves.
The majority of carbon input to wastewater treatment plants constitutes particulate organic matter in the form of slowly biodegradable organic matter. Particles entering a MBBR are either degraded by microorganisms in the bio-film or pass straight through the process. The particles may be completely degraded and taken up by microorganisms but they could also be partially degraded and then released back into the bulk liquid. A fraction of partially degraded particles will join under graded particles that pass straight through the process, most of the partially degraded particles are however likely to come in contact with bio-film again for further degradation.
Figure: Development of Bio film on carrier
Completely degraded substrate is transported through the bacterial membrane, where it is used for respiration and production of new biomass. Almost 50% of the energy in the substrate is bound in new biomass. Biomass eventually detaches from the carrier surface mainly due to shear forces and degradation in the interior bio-film. Thus, to some extent, biodegradation transforms organic matter in influent water to particles of biomass.
EXPERIMENTAL
Collection of wastewater sample
The sewage wastewater sample was collected from GNFC Township sewage treatment plant, Bharuch, Gujarat
The three sewage samples were taken on different days. The reactor was made up of acrylic having the volume of 0.064 m3. 15 lit samples of sewage wastewater were put in the reactor where packing media was provided. The characteristics of barrier used are shown in the following table. Two submerged pipe aerators of capacity 180 lit/hr were provided in the tank to supply air. The samples were allowed to treat for 30 minutes. Then 4 hours settling was provided. The samples were analysed for COD and BOD before and after treatment.
CONCLUSION
In this research, an experimental study to evaluate the application of MBBR system for COD and BOD removal from sewage wastewater is described.
The lab-scale MBBR system was a very effective treatment to remove COD and BOD with removal efficiencies 60-64% and 80-85% respectively, with 20 minutes HRT and 4 hours settling time.
According to the results of lab-scale experiments and literature review, we can suggest that the moving bed bio-film process could be used as an efficient and effective treatment for BOD and COD removal from sewage wastewater.
Methodology
We need to know the inlet parameters first. What is BOD, COD, TSS, oil & grease, carbonaceous compounds, nitrogenous compounds at inlet. Also, We need to know for what utilization we are treating this. Rest single formula, there will be designing of each and of each and every tank, equipments, pumps, blowers, etc.
Advantage of Moving Bed Bio-film Processes
The MBBR is a complete mix, continuous flow through process which combines the advantage of fixed film and suspended growth processes, this advantage include
1. Compact units with small size.
2. Increased treatment capacity.
3. Complete solids removal.
4. Improved settling characteristics.
5. Operation at higher suspended biomass
6. Concentrations resulting in long sludge retention times.
7. Enhanced process stability.
8. Low head loss.
9. No filter channeling.
10. No need of periodic backwashing.
11. Reduced sludge production and no problems with
12. Sludge bulking.
Disadvantages of MBBR:
Upstream fine screening
Medium/ coarse bubble aeration
Media retention screen assemblies
Limited degree of process control
Less common process
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FUTURE WORK
Design Modification
Generation of Bio film
Application work
Experimental setup
Result and conclusion