Biological Processes
Biological processes
The biological processes covered by this company's services include conventional processes, BNR reactors, ENR reactors, biofilm reactors, membrane reactors, and other advanced water and wastewater treatment processes.
Biofilm Reactors
H-IFAS System
Types of IFAS Systems
Different types of Hybrid IFAS systems are distinguished by the type of media used, which can be either suspended or fixed-film.
Suspended Media IFAS Systems
Suspended systems use porous sponges or conical-shaped plastic media that float in the activated sludge tank. Each of these systems has its own advantages and disadvantages, but the common feature in all these media is the increased biomass available for treatment without the need to construct additional activated sludge basins.
Fixed-Film Media IFAS Systems
Fixed media are available in blade-like shapes or as rope-like materials. These flexible materials attach to rigid frames or are mounted on modules present in activated sludge tanks.
Lagoon Guard Process
Upgrading and modernizing aerated lagoons is increasingly being applied in multiple areas treating both industrial and municipal wastewater. These systems can effectively remove COD and BOD, but nitrification is not always achievable, resulting in low nitrogen removal efficiency. Since cities with aerated lagoons need to limit the ammonium discharged into receiving waters, they face a difficult choice between building a costly new process or upgrading existing lagoons to achieve nitrification.
Lagoon Guard is a well-designed supplementary MBBR biofilm process installed after the lagoon that can control ammonium while enabling additional COD removal. It is easy to upgrade, cost-effective, compact, and implemented within the lagoon itself, requiring minimal maintenance.
Lagoons can operate year-round, both in summer and winter. In summer, the treatment plant operates as described above. In the cold winter months, when wastewater temperatures drop below 45°F (7°C), only one lagoon is used, followed by Lagoon Guard, which prevents further temperature drops that would otherwise slow down nitrification.
Lagoon Guard is prepared through a two-stage process enabled by two reactors arranged in series. The two-stage LagoonGuard system removes any residual soluble BOD in the wastewater and facilitates ammonium nitrification and nitrite removal. The system requires minimal space and operator attention.
The LagoonGuard process is constructed from thousands of polyethylene carrier elements that provide a habitat for a dense population of activated bacteria capable of treating wastewater. These elements move steadily throughout the wastewater flow with the help of aeration bubbles. Retention screens are also added to keep the media within the reactor.
MBBR Process (Moving Bed Biofilm Reactor)
Microorganism growth on a surface is called biofilm. In a biofilm process, microorganisms are more resilient to disturbances compared to other biological treatment processes. Biofilm wastewater treatment technologies are generally more robust than conventional technologies such as activated sludge. The first biofilm process, the trickling filter, was invented in the late 19th century. While trickling filters can be reliable and stable, they have a major drawback: they easily clog, leading to deterioration even under moderate loading conditions.
In MBBR (Moving Bed Biofilm Reactor) biofilm technology, the biofilm grows on engineered plastic carriers designed to provide a large surface area for biofilm development. These biofilm carriers are suspended and fully mixed with the water phase. This technology works effectively under high loading conditions without clogging and can treat both municipal and industrial wastewater even in a compact space. MBBR biofilm technology is efficient, compact, and easy to operate. It can function as a standalone treatment solution and can also be used to upgrade the treatment potential of existing activated sludge processes.
System Description:
MBBR biofilm technology operates using engineered plastic biofilm carriers or biological carriers that continuously move within a tank or reactor of specified volume. The design of associated aerators, screens, grit removal grids, spray nozzles, and mobile reactor components is critical for system efficiency. When municipal and industrial wastewater enters the MBBR reactor, biofilm grows on the surface of the carriers, breaking down pollutants.
The pollutants removed in this system are nutrients and compounds that also support biofilm growth. Carrier design is critical to ensure adequate mass transfer and oxygen supply to microorganisms, and many research centers worldwide focus on this topic. Excess biofilm is naturally sloughed off.
An aeration grid is installed at the bottom of the reactor to supply oxygen to the biofilm and to provide the energy required to keep the carriers suspended and fully mixed within the reactor. The treated water flows through the grid or screen, keeping the MBBR carriers in the reactor.
The recently highlighted biomass stabilization system in wastewater treatment is the MBBR (Moving Bed Biofilm Reactor). Its special feature is that biofilm grows on plastic elements that can easily move in the biological reactor. The plastic elements have diameters of about 1–2 cm, with a density very close to water. Only 50–70% of the tank volume is filled with these elements. Compared to other fixed-biomass systems (such as trickling filters or submerged biofilters), this system shows no clogging problems and has low head loss.
Compared to activated sludge systems, MBBR does not have bulking issues and can operate efficiently with multiple reactors in series, even at higher F/M ratios (food to microorganism) and higher biomass in each treatment stage. Moreover, no sludge return is required, simplifying system management. Typically, the extremely large surface area in MBBR systems enhances treatment efficiency. The specific surface area in MBBR plastic carriers is about 160 m² per cubic meter. Compared to activated sludge, this system performs two treatment processes in parallel: organic compound removal and nitrification.
BAS Process
The BAS (Biofilm Activated Sludge) process is a biological treatment method that combines the best features of activated sludge and biofilm technology. The precise design of the activated sludge stages and the MBBR biofilm stage provides resilience against shock loads under high pollution conditions, resulting in increased efficiency in industrial wastewater treatment. The MBBR stage at the beginning of the process enhances resistance to toxic substances and achieves 50–70% BOD reduction while optimizing COD removal. This pre-treatment process increases the capacity by 2 to 3 times compared to conventional activated sludge systems. Additionally, the BAS combined process improves the characteristics of the activated sludge stage, leading to greater sludge stability and easier dewatering of excess sludge.
FBBR Process
The biofilm reactor with a Floating Bed (FBBR) emphasizes the creation of a floating bed that supports the media in the upward flow of wastewater. The media is typically graded stone approximately 1 mm thick, providing a surface for bacterial growth. Oxygen required for the oxidation of organic compounds is supplied from the bottom of the reactor. To minimize the space required, the oxygen concentration must be increased. The proven method is a deep-shaft system capable of producing oxygen at a concentration of 60 grams per liter. The stone/biomass cleaning and separation device removes excess biomass while retaining the media within the reactor. Since the effluent quality is high, a secondary clarifier is not necessary.
The attached-growth nature of this process allows the system to operate under varying flow rates and loads (relative to 50% of the average load for which the system is designed). The influent should have a low concentration of suspended solids. The floating bed is normally flexible, but the maximum pollutant concentration is limited by the maximum dissolved oxygen concentration. The maximum recycle flow that can be pumped to the reactor bottom is also a limiting factor. Floating beds can function as standalone processes.
Biological floating beds are relatively compact and can be adapted to limited spaces in any type of treatment plant. Very little space is required for the floating beds and shaft to dissolve the needed oxygen. This process can be expanded by adding additional floating beds to accommodate increased flow rates.
ENR Process
BABE – Bio-Augmented Batch Process
(BABE (Bio-Augmentation Batch Enhanced)
Bio-augmentation is considered a solution for upgrading water and wastewater treatment plants, and its main application is the treatment of nitrogen-rich streams. The objective of the Bio-Augmentation Batch Enhanced process is to support the development of the nitrifying population by reducing the sludge retention time (SRT) in the reactor. The increased population of nitrifiers in the BABE reactor is used to feed conventional activated sludge systems.
The effect of adding separately cultivated microbial media to the main nitrification reactor has previously been studied, focusing on the treatment of digester supernatant oils. Nitrification capacity can be consistently increased through side-stream treatment of digester supernatant, both by reducing the influent load to the wastewater treatment plant and by increasing nitrifier activity.
Improved effluent quality, creation of additional capacity, and a better ability to handle excessive loadings are also achieved through this process.
Bio-augmentation can be particularly attractive because both nitrifying bacteria and anammox bacteria are added to the wastewater stream.
CANON Process
CANON – Completely Autotrophic Nitrogen Removal Over Nitrite
A new process developed to combine nitrite-removing environments with anaerobic ammonium-oxidizing bacteria (anammox) is called the Completely Autotrophic Nitrogen Removal Over Nitrite (CANON) process.
NH₃ + 0.85 O₂ → 0.11 NO₃⁻ + 0.44 N₂ + 0.14 H⁺ + 1.43 H₂O
This process is based on the concept of simultaneous nitrification and denitrification (SND) within a single reactor under stable operating conditions. With the discovery of anammox bacteria (anaerobic ammonium-oxidizing bacteria), the CANON process was proposed, utilizing anaerobic ammonium oxidizers as nitrate reducers (denitrifiers). Creating conditions with limited oxygen is essential to facilitate cooperation between aerobic and obligate anaerobic bacteria. Sequencing batch reactors (SBRs) are used to develop the CANON process. Unlike the anammox process, CANON can directly feed ammonium-rich influent at a suitable loading rate. In a reactor, nitrite oxidizers prevail due to competition with denitrifying bacteria (nitrifiers).
In a biofilm bacterial environment, simultaneous accumulation of nitrite in the aerobic biofilm layer and the anammox reaction in the anaerobic inner layer of the biofilm, along with cooperation between bacterial layers, is possible. A coordinated and balanced reaction between the two bacterial groups has been observed. Nitrosomonas can supply nitrite to Brocadia (anammox bacteria) at the oxic/anoxic biofilm interface, acting as an oxidizer. This cooperation is possible despite the natural competition for the ammonium nutrient. Nitrosomonas limits the anammox process in the CANON reactor due to its inhibitory role in oxygen diffusion to lower layers and its provision of nitrite for anammox bacteria. However, based on Gibbs free energy calculations, anammox bacteria are more efficient than nitrosomonas.
HF-MBfR Process
The Hollow-Fiber Membrane-Biofilm Reactor (HF-MBfR) provides a suitable environment for bringing together oxidized contaminants, bacteria, and H₂ as an electron donor. It was developed for the removal of nitrate from contaminated drinking water using molecular hydrogen as a clean electron donor substrate. The hollow fibers are sealed at one end and pressurized with hydrogen at the other end.
In the HF-MBfR, H₂ gas diffuses through the composite membrane wall to the naturally occurring autotrophic biofilm on the outside of the membrane, where the electrons are transferred to pollutant-oxidizing bacteria (e.g., NO₃⁻ or ClO₄⁻) dispersed in the water. Hydrogen pressure in the hollow fibers is a key control parameter that can be adjusted quickly and easily. For denitrification, partial nitrate removal is often acceptable, and the hydrogen pressure can be kept low to minimize H₂ supply costs and H₂ concentration in the effluent.
INNITRI Process
Explanation and Process Features:
A new process for nitrification, the side-stream process, proposes Mixing & Mass Transfer (M²T) technologies, which enable nitrification to occur in a smaller aeration tank than typically designed, even at short sludge retention times and low winter temperatures.
The InNitri process is designed as a cost-effective solution for treatment plants in cold climates that require air heating or pure oxygen-activated sludge processes for nitrogen removal throughout the year. In general, InNitri nitrifiers are continuously added to the main activated sludge process to replace nitrifiers lost from the activated sludge.
InNitri Structure:
Supplementary nitrifiers grow in a small, separate side-stream aeration tank using ammonium from dewatered digested sludge and commercial ammonium. Conventional secondary treatment plants consist of a primary sedimentation tank, an aeration tank, a secondary clarifier, and a sludge thickener, complemented with anaerobic digestion and complete sludge dewatering. Upgrading such a plant to provide year-round nitrification using the InNitri process (short SRT nitrification) requires adding a small aeration tank and clarifier for nitrifier growth.
In this process, the warm dewatered liquid (typically 30–35°C) containing high ammonium concentrations (300–900 mg/L) is mixed with a small portion of primary effluent (for temperature adjustment and organic carbon supply) and denitrified in the side-stream nitrification aeration tank. A portion of the resulting biological sludge, containing a high percentage of nitrifiers, is discharged to the main aeration tank, providing support nitrifiers for the main activated sludge process. This eliminates the need for a digester. In this way, commercial ammonia nitrification is maintained year-round. The process can also be applied similarly in other treatment plants.
Design Guidelines / Technical Information:
Conventional nitrification typically consists of a fully mixed aeration tank with a 6-hour hydraulic retention time (HRT) operating at 10°C, with an influent containing 25 mg/L total nitrogen (TKN), of which 25% is in the side-stream dewatered liquid. To demonstrate the difference between conventional nitrification and nitrification with supplementary nitrifiers (InNitri process), researcher KOS provided an equation and modeling results for a typical wastewater treatment plant.
Mathematical modeling showed that for conventional nitrification at 10°C, as SRT decreases, the concentration of nitrifiers also decreases, while ammonium in the effluent increases. The results indicated that in the InNitri method, nitrifiers dominate the main aeration tank at any retention time. Nitrifiers cannot be washed out of the aeration tank even at low HRTs, allowing nitrification to occur at very short SRTs. In other words, the InNitri process has no minimum SRT below which nitrification cannot occur, making the process more stable and not requiring the safety factors of conventional nitrification.
Modeling repeated at 7.5–20°C showed that effluent quality in InNitri, even at short SRT, was similar to conventional nitrification in terms of ammonium concentration. When the effluent ammonium concentration was designed at 2 mg/L, the minimum SRT for InNitri was 60% of that required for conventional nitrification. Comparing SRTs for InNitri and conventional nitrification demonstrates lower costs for using InNitri.
Research at the University of Manitoba showed that transferring nitrified sludge from the warm side-stream reactor to a cold main reactor poses no problems. Evaluation of the process for upgrading existing facilities also indicated significant cost savings compared to conventional systems.
Sharon-Anammox Process
Sharon – Separate Reactor for High-Activity Ammonia Removal Over Nitrite
Sharon, or the single reactor for high-activity ammonia removal over nitrite, is a process that occurs in a fully mixed reactor without biomass retention. This process has been developed for treating very strong side streams resulting from sludge digestion. The conventional method of converting ammonia to nitrogen gas uses nitrification/denitrification processes. In the Sharon process, ammonia is directly converted to nitrite (unlike conventional methods where it is converted to nitrate) and then directly to nitrogen gas. The conversion of ammonium to nitrite can be expressed by the following formula:
NH₄⁺ + 1.5 O₂ ⇒ NO₂⁻ + H₂O + 2 H⁺
Ammonium oxidation in the nitrite stage using the Sharon process stops at elevated temperatures. At high temperatures, ammonia-oxidizing bacteria grow faster than nitrite-oxidizing bacteria. In this process, the hydraulic retention time (HRT) equals the solids retention time (SRT). Therefore, slow-growing nitrite oxidizers are washed out of the system, and ammonium oxidation in the nitrite stage ceases. This is a thermophilic process that occurs at temperatures between 30 to 40°C (86 to 104°F).
Depending on the ammonia concentration in the side stream to be treated and limitations regarding the effluent, the hydraulic retention time can range between 1 to 2 days. The side stream temperature of the digester can be between 25 to 30°C. Thermophilic microbial activity in the Sharon reactor produces a temperature increase of approximately 5 to 8°C. Depending on the local climate, additional heating may be required during winter. Nitrogen balances in wastewater treatment plants show a significant internal nitrogen load in the return water from the sludge digester to the main wastewater stream. By treating this return water separately, the nitrogen load in the activated sludge process can be significantly reduced. The Sharon-Anammox process is a nitrogen removal system for return water from sludge dewatering facilities and other ammonia-rich wastewater streams. This combined process involves two technologies that were independently developed. Anammox, in fact, means anaerobic ammonium oxidation. Sharon is an acronym derived from “Single reactor for High-activity Ammonia Removal Over Nitrite.”
Process Description and Features
The Sharon/Anammox process is a system in which nitrogen removal occurs through the combination of two separate stages: partial nitrification (Sharon) followed by anaerobic ammonium oxidation (Anammox). The figure below illustrates the treatment sequence of the Sharon/Anammox process.
Sharon/Anammox – process scheme
Sharon Process:
The Sharon process is used to produce a combination of ammonium-nitrite in which only 50% of ammonium is converted to nitrite.
NH₄⁺ + HCO₃⁻ + 0.75 O₂ ⇒ 0.5 NO₂⁻ + 0.5 NH₄⁺ + CO₂ + 1.5 H₂O
Conversion occurs in a single, fully mixed reactor without biomass at temperatures between 30 to 40°C and retention times between 1 to 2 days, resulting in only 50% of ammonium being converted to nitrite. Oxygen availability in this process is limited.
The Sharon reactor can operate intermittently under aerobic and anoxic conditions or continuously under limited oxygen. In the latter case, oxygen consumption by nitrifying organisms produces the anoxic conditions required for the second treatment stage – Anammox.
Anammox Process:
In this stage, the ammonium-nitrite mixture produced in the Sharon reactor is converted to nitrogen gas under anoxic conditions, where ammonium acts as the electron donor. The conversion of ammonium and nitrite to nitrogen gas is expressed as:
N₂ + 2 H₂ ⇒ NO₂⁻ + NH₄⁺
The bacteria catalyzing this reaction are autotrophic, facilitating conversion without the use of COD or an external carbon source. Bacteria capable of catalyzing the Anammox reaction can be sourced from conventional sludge. However, these bacteria have relatively slow growth rates, with a doubling time of 10 days at 30°C. Therefore, the Anammox reactor must be designed with sufficient biomass to prevent the washout of slow-growing Anammox bacteria. In pilot designs, sequencing batch reactors (SBR) have been used. Due to the good granule-producing capacity of the bacteria, gas-lift-loop reactors are recommended to ensure effective mass transfer, mixing, and compact biomass retention.
OLAND Process
OLAND – Oxygen Limited Autotrophic Nitrification Plus Denitrification
OLAND is a biological nitrogen removal process that combines nitrification with anaerobic ammonium oxidation (Anammox). In this process, unlike the CANON process, ammonium-oxidizing bacteria are capable of converting ammonium to nitrogen gas in a reactor under oxygen-limited conditions. Nitrosomonas species, due to limited electron acceptors, can utilize the nitrite produced.
NH₄⁺ + 0.75 O₂ → 0.5 N₂ + H⁺ + 1.5 H₂O
Aeration of autotrophic nitrifiers enriched with controlled pH can stimulate bacteria to consume nitrite.
| Anammox | CANON / OLAND | |
|---|---|---|
| Required influent (g COD/g N removed) | 0.00 | 0.00 |
| Oxygen required (g O2/g N removed) | 0.00 | 2.50 |
| Alkalinity consumed (g CaCO3/g N removed) | 0.22 | 0.55 |
| Biomass formation (g COD biomass/g N removed) | 0.08 | 0.17 |
For practical purposes, the OLAND process can be easily implemented due to the simplicity of producing nitrifier inoculum from activated sludge. This system does not require direct nitrite supply, and ammonium-rich influent can be treated directly. However, the capacity of current systems remains limited.
Anaerobic Processes
ABR Process
ABR – Anaerobic Baffled Reactor
The ABR reactor is a type of reactor with multiple baffles, in which wastewater containing organic pollutants is forced to flow up and down (or through) the baffles between the system’s inlet and outlet. The bacteria inside the reactor slowly settle due to the flow characteristics and gas production, moving downward at a slow rate. However, to improve reactor performance, several flow modifiers are also installed.
The main driving force in this process is the reactor design, which increases the solids retention capacity.
The reactor is made up of a series of compartments through which wastewater flows from upstream. The influent wastewater mixes with sludge, so that the bacteria that degrade pollutants enter the wastewater flow.
Degradation occurs progressively within the reactor compartments.
The BOD removal rate is 90%, and pathogen reduction ranges from 40 to 75%.
The baffled reactor is resistant to shock loads and changes in influent flow. It is easy to operate and maintain, and because of its buried structure, it does not require extra space.
Due to the reactor’s partitioning, it has the potential for modification. For example, by adding an aerobic stage in the penultimate compartment, part of the COD resistant to degradation and excess sulfide from the anaerobic stage can be oxidized, resulting in nitrification—especially when using immobilized cells.
Because of the long solids retention time in the reactor, the overall cellular yield is about 0.03 g of cells per gram of wastewater compounds, so only a small amount of sludge is produced for disposal.
Due to the very slow downward movement of cells in the reactor, it is possible to use selected or genetically modified cells that can remain in the reactor for months.
EGSB Process
Expanded Granular Sludge Bed (EGSB) is another type of anaerobic UASB digestion for wastewater treatment. A distinctive feature of this system is the high upward flow velocity, which forces wastewater to pass through the sludge bed.
The advantages of this system include increased wastewater contact with the granular sludge, improved interaction between wastewater and sludge, and enhanced separation of small suspended particles from the sludge bed. The increased flow velocity is achieved using tall reactors, by recycling effluent, or both.
EGSB is designed for soluble wastewater with a low load (less than 1–2 g soluble COD/L) or for wastewater containing biodegradable suspended solids that are stagnant or weak, which should not be allowed to accumulate in the sludge bed.
IC Process
The Internal Circulation (IC) reactor is a type of anaerobic digester primarily designed for wastewater treatment. The IC reactor is an evolved form of UASB and EGSB digestion systems. The digester typically produces biogas with a high methane concentration (≈80%). The IC reactor is essentially designed to improve digestion rates and gas yield.
The IC reactor is usually part of a two-stage anaerobic digestion system, including an acidification and hydrolysis tank. The effluent from the IC reactor often requires aerobic treatment to reduce BOD and COD and meet discharge standards.
UASB Process
UASB – Upflow Anaerobic Sludge Bed
In the UASB reactor, four anaerobic digestion phases exist:
- Hydrolysis: This phase involves converting complex, heavy, and insoluble compounds (proteins, carbohydrates, fats) into lighter substances (such as amino acids, sugars, alcohols) through bacterial fermentation, releasing enzymes.
- Acidogenesis: A stage where soluble compounds are transformed into simpler compounds (e.g., volatile fatty acids, alcohol, lactic acid, CO₂, H₂, NH₃, H₂S, and new cellular material).
- Acetogenesis: A phase in which digested products are converted into acetate, CO₂, H₂, and new cellular material.
- Methanogenesis: A phase where acetate, hydrogen, and carbonates, formate, or methanol are converted into CH₄, CO₂, and new cellular compounds.
UASB Reactor Features
Granular Sludge:
In a UASB reactor, anaerobic sludge develops good settling characteristics and is mechanically mixed by the upflow of incoming wastewater, producing gas bubbles in the reactor. Therefore, mechanical mixing can be eliminated, reducing maintenance and capital costs. This mixing process leads to the formation of granular sludge, which has many advantages over conventional floc sludge:
- Dense biofilm formation
- High settling capacity (30–80 m/h)
- Balanced microbial community
- High methanogenic activity (0.5 to 2 g COD/g VSS·d)
- Resistant to toxic shocks
Figure 1: Main parts of a UASB reactor
UASB Design
- If the influent COD is between 5000–15000 mg/L or higher, design should be based on organic load.
- If influent COD is below 5000 mg/L, design should be based on hydraulic loading rate.
| Influent COD | Sludge Height |
|---|---|
| <300 mg/L | 3–5 m |
| >300 mg/L | 5–7 m |
Note: Sludge layer is taller than the bed layer.
If the installation zone height is ≥2.5 m, the UASB tank area in m² is calculated as: A = HRT × Q / H
HRT: Hydraulic Retention Time
Operation:
- Suitable pH range: 6.6–7.6
- Wastewater temperature should not drop below 5°C as low temperatures reduce phase 1 hydrolysis and methanogen activity. Therefore, in winter, methane gas may be needed to heat wastewater entering the reactor.
- COD:N:P ratio should always remain 350:5:1. If any nutrient deficiency exists, supplements must be added to keep microorganisms alive. Common nutrients include: (NH₄)₂CO₃, KH₂PO₄, NH₄, H₂PO₄
Effects of Suspended Solids on Anaerobic Process:
- Formation of scum and foam due to insoluble compounds with buoyancy, such as oils and fats.
- Delayed or complete prevention of granular sludge formation.
- Adsorption of granular sludge in a layer of insoluble materials and sometimes decomposition of granular sludge.
- Sudden and nearly complete washout of sludge from the reactor.
- Decrease in overall methanogenic activity of sludge due to accumulation of suspended solids.
