Principle
Secondary treatment (mostly biological wastewater treatment) is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option. A "primary treatment" step often precedes secondary treatment, whereby physical phase separation is used to remove settleable solids. During secondary treatment, biological processes are used to remove dissolved and suspended organic matter measured as biochemical oxygen demand (BOD). These processes are performed by microorganisms in a managed aerobic or anaerobic process depending on the treatment technology.
Bacteria and protozoa consume biodegradable soluble organic contaminants (e.g. sugars, fats, and organic short-chain carbon molecules from human waste, food waste, soaps and detergent) while reproducing to form cells of biological solids. Secondary treatment is widely used in sewage treatment and industrial wastewaters. Secondary treatment systems are classified as fixed-film or suspended-growth systems, and as aerobic versus anaerobic. The fixed-film principle has further developed into moving bed biofilm reactors (MBBR) and Integrated Fixed-Film Activated Sludge (IFAS) processes. Surgended growth systems include activated sludge, which is an aerobic treatment system, based on the maintenance and recirculation of a complex biomass composed of micro-organisms (bacteria and protozoa) able to absorb and adsorb the organic matter carried in the wastewater. Fixed-film systems are better 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.
Integrated fixed film activated sludge (IFAS) is an innovative wastewater treatment technology that offers several advantages over conventional activated sludge technologies. IFAS involves adding an attached growth media to an activated sludge tank to facilitate biomass growth and strengthen the treatment process.
Difference Between MBBR and IFAS
The difference between IFAS and MBBR is that in the IFAS system, the activated sludge from the sludge recirculation is additionally used. IFAS is a combination of activated sludge and MBBR media is used in the same reaction tank volume. This means carrier-fixed biofilms and activated sludge are both used in one reaction tank.
Both IFAS and MBBR use some type of media, as a platform for biofilm growth. The difference is that the MBBR has no return sludge. IFAS does have return sludge, MBBR usually has a higher fill % than IFAS,
Design Parameters of IFAS system
The size of the IFAS tanks and the related carrier media filling rate are determined based on the pollutant loads (COD mg/l and flow rate m³/h) and in consideration of specific product factors of the carrier media.
Crucial factors for designing of IFAS system
Wastewater Temperature
In order to obtain the appropriate design for IFAS plants, it is necessary to determine the minimum and maximum design temperatures. At higher operating temperatures, the removal rates will be higher than ambient operating temperature of 25°C. Hence the carrier media requirement and reaction tank glume will be low than what is required at ambient temperature. For lower than ambient temperatures, the tank size and carrier media quantity requirement will be higher. But this may not be possible because the admissible maximum media filling rate is between 50-70%. Hence an optimization of investment in civil costs vs MBBR media that can offer higher surface than the normal media has to be worked upon for effective management of temperature differences throughout the year.
Oxygen Demand
In order to obtain the appropriate design for IFAS plants, it is necessary to determine the minimum and maximum design temperatures. At higher operating temperatures, the removal rates will be higher than ambient operating temperature of 25°C. Hence the carrier media requirement and reaction tank glume will be low than what is required at ambient temperature. For lower than ambient temperatures, the tank size and carrier media quantity requirement will be higher. But this may not be possible because the admissible maximum media filling rate is between 50-70%. Hence an optimization of investment in civil costs vs MBBR media that can offer higher surface than the normal media has to be worked upon for effective management of temperature differences throughout the year.
The components include packings with a high surface area (typically MBBR media), as well as aerators or agitators and a mounting frame. The aerators are customized to meet carbon and nitrogen removal requirements. For denitrification, the system includes an agitator to move the water through the anoxic system. The difference between IFAS and MBBR is that in the IFAS system, the activated sludge from the sludge recirculation is additionally used, which means that the combination of activated sludge and carrier- fixed biofilms is used in the same reaction tank volume.
IFAS (Integrated Fixed Film Activated Sludge) process is becoming more popular due to its hybrid configuration and specific benefits the process provides to the wastewater treatment plants. Though originally developed for the upgradation of existing activated sludge plants, the hybrid process configuration can be applied for the new plants as well.
Workiing of IFAS
IFAS process (Integrated Fixed Film Activated Sludge) combines two technologies in one aeration tank
- Activated sludge process
- MBBR technology
MBBR media is added in the activated sludge tank containing MLSS to increase growth area for additional biomass. This combination allows a much higher biomass concentration and sludge age compared to conventional activated sludge processes.
As a consequence, the following general rule applies
- The lower temperature is considered for calculating the required tank and carrier media volume.
- The higher temperature ↑ is considered for the calculation of the oxygen supply.
- The yield: The yield for considering the bacterial growth usually differs according to the type of wastewater. It is determined based on lab trials and expertise in the field.
- Removal rates (removal efficiency) of the MBBR media: This is largely dependent on the type of MBBR media that is used in the system. MBBR media substantially contribute to the efficiency of pollutant removal. Transcend cleantec's design team has expertise and vast experience with Transchip MBBR media. Many lab trials, small and large scale project execution over the years give an upper edge to our team while designing the system. The unique parabolic structure of Transchip MBBR media, very high surface area leading to deposition of high amount of active biomass on the transchip, increased diffusion depth, non abrasive material of construction leading to minimum wear and tear make Transchip the best choice of use in IFAS systems.
ADVANTAGES OF IFAS OVER MBBR
- IFAS technology uses the existing industrial waste water plants and increases treatment capacity upto 100%
Reduces footprint of new plants since more treatment media is accommodated in the same aeration tank size.
Due to presence of biomass both on MBBR media and in the MLSS present in suspension, IFAS process
provides higher volumetric reduction which reduces the wastewater treatment plant foot print significantly.
Significant reduction of secondary clarifier load. Since use of MBBR media reduce the MLSS requirement.
- Ease of operation. IFAS uses the same instrumentation and process flowchart as conventional activated sludge process. Thus no special training is required for the plant operators.
Variations in input concentrations of flow are better managed with IFAS systems. IFAS process allows retention of biomass both in suspension as well as on IFAS media, thus fluctuation in parameters can be easily and quickly controlled
- Provides development of diverse microbial community structure which improves the process performance enhancing toxic and shock load response of the process.
Because of its hybrid nature, IFAS process allows development of a diverse community of microbes responsible for the degradation of a wide range of organic pollutants present in different wastewater generating from both industries as well as municipalities. Due to biofilm formation on attached growth IFAS media, retention of poorly flocculating biomass in the biological reactor is feasible which allows for improved reduction efficiencies. Under toxic shock load conditions, the diversity of microbial community allows speedy process recovery and thus IFAS process has much better toxic shock load response compared to conventional technologies
The conventional sludge dewatering systems like centrifuges, Belt press, Filter press (Plate & Frame type) have many draw backs. The drawbacks include-
- Large foot print
- High power consumption
- High Operational cost / consumables
- Frequent breakdown
- Non-continuous (batch) operation
- High maintenance requirement
- Multiple Pretreatment
- High labor
As the Multi-Disc Screw Press can take the load directly from the oxidation ditch, considerable capital cost, construction costs and maintenance cost can be avoided
DIRECT DEWATERING FROM OXIDATION DITCH
Feed sludge directly from the oxidation ditch / aeration tank. This eliminates the need to construct settling tanks, sludge thickener or sludge feed tanks. This advantage leads to a good reduction in CAPEX as well as OPEX.
CLOG FREE DESIGN
The series of heavy duty finely machined fixed and rotating rings placed alternately provides efficient filtration that remains clog free due to the continuous movement of the rings. This eliminates the need for consumables like filter cloth etc
FULLY AUTOMATIC
The system can be fully automatic with PLC controls. Option of variable frequency drive (VFD) is available to control the dosing and the screw speed to automatically adjust to the varying loads of the effluent. The system can run continously, unmanned.
LOW CAPEX
The system can take sludge directly. This eliminates the need to build sludge thickening tank and sludge storage tank, thereby saving on space and civil construction costs.
ODOURLESS PROCESS
Since both the sludge thickening tank and the sludge storage tank is eliminated and as sludge is not stored for long periods of time, there is no anaerobic process happening. This eliminates the possibility of unpleasant odour.
HANDLES OILY SLUDGE
Due to the rotation of the helical axis, the moving rings detach from the fixed rings while continuous- ly cleaning itself. As a result clogging is avoided. Therefore it can easily handle oily sludge.
LOW OPEX
The system works on its internal pressure. It saves energy due to its low running speeds (2-4 rpm). The average power consumption is only 0.01 – 0.1 kw/h which is 12% of a belt press and 5% of a centrifuge
SMALLEST FOOTPRINT
The Transcend Cleantec Screw Press takes the least space among other technologies. Its approximately 45% less space than Centrifuge, 62% less space than Belt Press and 78% less space than Filter Press of conventional design.
CAPACITY & SCALABILITY
Transcend Cleantec Multi Disc Screw Press is designed to cater to various capacities. Systems are available from 0.2 m3/hr – 133.5 m3/hr (@0.2%sludge conc.) Due to its modular design and compact construction, the capacities can be easily scaled up by running systems in parallel to cater to almost any capacity as required and as and when required. We can also optimize the design for cost and efficiency based on your custom requirement using the standard models.
INSTALLATION, SERVICE SUPPORT & TRAINING
Our experienced and trained team of engineers help you with the installation and operator training. Our systems are designed to be a work horse and run for years without needing any service. But there are odd chances that you may need service support. Our trained technicians are an email or call away. With adequate training and spares at their disposal, they will ensure the system is up and running in a very short time.