Anaerobic Tower / Upflow Anaerobic Sludge Bed
Basic Introduction to Anaerobic Biochemical Method
Anaerobic biochemical method has the following advantages and disadvantages compared to aerobic biochemical method:
Seven Key Advantages
Wide range of applications
Low energy consumption
High load
● Minimal remaining sludge volume
● Nitrogen and phosphorus nutrient requirements are low
The anaerobic treatment process has a certain sterilization effect, capable of killing parasites, viruses, and other pathogens in wastewater and sewage.
Anaerobic active sludge can be stored for long periods, and anaerobic reactors can operate seasonally or intermittently.
Three Areas of Shortcomings
Anaerobic microorganisms have a slow proliferation rate, thus the startup and processing time for anaerobic equipment is greater than aerobic equipment.
● The effluent usually requires further treatment, hence it is generally connected in series with anaerobic treatment followed by aerobic treatment.
● Anaerobic treatment system operation control factors are relatively complex
Application of Anaerobic Biochemical Method
Organic Sludge Treatment
High-concentration organic wastewater
● Organic wastewater with medium and low concentrations
Urban wastewater treatment
Basic Principle of Anaerobic Biochemical Method
Basic Definition: Anaerobic biological treatment of wastewater refers to the conversion of various complex organic molecules in wastewater into other substances under the action of anaerobic microorganisms (including aerobic microorganisms) in the absence of molecular oxygen.MethaneThe process of decomposing substances like carbon dioxide is called anaerobic digestion.
Anaerobic biological treatment of wastewater is a method that utilizes the degrading action of anaerobic microorganisms under anaerobic conditions to purify organic matter in wastewater. Under anaerobic conditions, the anaerobic bacteria in wastewater decompose carbohydrates, proteins, fats, and other organic matter into organic acids, then...MethaneUnder the action of the bacteria, further fermentation formsMethaneCarbon dioxide and hydrogen, among others, are used to purify wastewater. It is one of the effective methods for treating domestic wastewater sludge, high-concentration organic industrial wastewater, and feces.
Anaerobic digestion is divided into three stages.
Phase One: Hydrolysis and Acidification Stage.
Stage Two: Hydrogen and Acetic Acid Production Stage.
Stage Three: ProductionMethaneStage.
Anaerobic Tower (Upflow Anaerobic Compacted Bed Reactor, IC) working principle
Abstract: The Anaerobic Composite Bed Reactor (ACBR) is essentially a combination of the Anaerobic Biofilter (AF) and the Upflow Anaerobic Sludge Bed (UASB), hence also known as an IC Reactor. The lower part of the ACBR consists of a sludge suspension layer, while the upper part is filled with media. It can be considered as a UASB process with a reduced thickness of the media layer in an upflow anaerobic biofilter, leaving space between the bottom irrigation system and the media layer for the growth and accumulation of suspended sludge particles. As a result, it also constitutes a UASB treatment process. As wastewater passes through the suspended sludge layer and the media layer, organic matter comes into contact with the microorganisms on the sludge particles and the biofilm of the media, leading to decomposition.
Operation Principle: Wastewater, after being adjusted for pH and temperature, first enters the mixing zone at the bottom of the reactor, where it is thoroughly mixed with the slurry from the external recycle loop. This mixture then proceeds to the granular sludge expansion bed area for COD biochemical degradation. Here, the COD volume load is high, with most of the incoming COD being degraded, resulting in a large amount of...Biogas. Due toBiogasThe expansion work done on the liquid during the bubble formation process generates a lifting effect, which makesBiogasThe mixture of sludge and water rises, is degraded after passing through the media zone, and then enters the three-phase separator at the top of the reactor.BiogasAfter separation from the mud and water at this location and subsequent export to the treatment system, the mud and water mixture descends along the mudguard to the mixing zone at the bottom of the reactor. After thorough mixing with the incoming water, it is re-introduced into the sludge expansion bed area, forming what is known as the internal circulation. Depending on the varying incoming water COD load and the reactor's construction, the external recirculation flow can reach 0.5 to 10 times the incoming water volume. After treatment in the expanded bed, part of the wastewater is recycled, while the remainder continues to rise, entering the media-filled zone for the remaining COD degradation and production.BiogasThe process enhances and ensures the water quality of the effluent. As most COD has been degraded, the COD load in the media zone is low, resulting in a smaller gas production. The effluent from this area contains:BiogasCollected by a three-phase separator, the effluent is then channeled through the manifold to the treatment system. After passing through the packed section, the wastewater is treated by the separator, with the supernatant discharged from the effluent zone, while the granular sludge is returned to the sludge bed.
Anaerobic Tower Components and Features
IC Composition: The anaerobic tower body is a cylindrical tower made of Q235 carbon steel or 304 stainless steel, without segmented connection flanges. The specific structure consists of the tower body, water distribution system, sludge bed, bio-carrier area, three-phase separator, floating sludge rapid discharge device, and recycle system, etc.
Characteristics of the IC reactor can be summarized as:
(1) The IC reactor features a compact structure, integrating an anaerobic biofilter (AF), an upflow anaerobic sludge blanket (UASB), and sedimentation.
(2) The IC reactor's distinctive feature is its ability to form granular sludge within the reactor, resulting in an average sludge concentration of 30-40g/L and a bottom sludge concentration as high as 60-80g/L.
(3) The IC reactor has a high volumetric loading, typically ranging from 10 to 20 kgCODCr/(m³·d), with the maximum reaching up to 30 kgCODcr/(m³·d). Additionally, it features a short hydraulic retention time, commonly utilizing mesophilic anaerobic digestion, and can sometimes operate at ambient temperatures.
(4) The reactor is equipped with a three-phase separator, allowing sludge separated in the sedimentation zone to automatically return to the reaction zone. Additionally, a reflux device has been added. It also utilizes its own generatedBiogasAnd with the inflow of water current to achieve mixing, no mixing equipment is required. Thus, the process is simplified, reducing the system's process equipment, and maintenance and operation are relatively straightforward.
(5) The IC reactor is equipped with a bio-carrier zone, which is an anaerobic digestion method that utilizes both suspended growth and attached growth. Compared to the anaerobic biofilter, the IC anaerobic composite bed reactor reduces the height of the filling layer, thereby minimizing the risk of clogging. In contrast to the UASB process, the filling layer not only serves as a carrier for anaerobic microorganisms but also traps suspended anaerobic activated sludge fragments in the water flow. This enables the anaerobic reactor to maintain a high microbial quantity and ensures the quality of the effluent.
The anaerobic hybrid bed reactor combines the advantages of anaerobic biofilter and upflow anaerobic sludge blanket reactor, overcoming their shortcomings. It not only increases the biomass but also enhances the volumetric utilization rate of the reaction zone. The total height of the reactor can exceed 10 meters, thereby reducing the land area required and significantly improving the processing capacity.
The reactor is made of fiberglass, formed through a single whole-wound process, offering ease of manufacturing, high strength, minimal land occupation, high processing efficiency, excellent results, corrosion resistance, aging resistance, and a long service life.
The reactor is equipped with a control system consisting of an on-line analyzer, pH controller, differential pressure transmitter, pressure sensor, flow sensor, conductivity meter, level controller, solenoid valve, variable-frequency drive, and control cabinet, etc. All control conditions are displayed in digital form on the monitor interface, making it easy for managers to understand at a glance, and with fault alarms for convenient management and maintenance.
Anaerobic reactor operation and management
1. Key considerations for the operation and management of anaerobic biological treatment facilities:
(1) When the treated wastewater concentration is high (CODCr value over 5000 mg/L), a recycling operation mode must be adopted. The recycling ratio is determined based on the specific conditions. Effective recycling not only reduces the incoming water concentration but also increases the incoming water volume, ensuring uniform flow distribution within the treatment facility and preventing short-circuiting. Recycling also prevents drastic fluctuations in the incoming water concentration and the pH value within the anaerobic reactor, ensuring a stable anaerobic reaction. This means it can reduce the demand for alkalinity in the anaerobic reaction, thereby lowering operating costs. Anaerobic reaction is a productive process, with the effluent temperature higher than the incoming water. Therefore, during low winter temperatures, the reactor temperature remains constant, and it is advisable to maintain the anaerobic microorganisms at their optimal temperature for activity.
(2) Generally, the temperature of industrial wastewater is difficult to reach 35°C and requires heating (especially in winter). Therefore, to conserve the energy needed for heating, one should pay attention to insulation (including measures like increasing recirculation flow), to prevent as much heat loss from the reactor as possible. Additionally, take advantage of the higher sludge concentration within the reactor to maximize sludge concentration inside and mitigate the impact of temperature on anaerobic reactions.
（3）BiogasTo be timely and effectively discharged. Anaerobic digestion processes are inevitably accompanied byBiogasThe emergence,BiogasIt serves as a stirrer and promotes the mixing and contact between wastewater and sludge, which is one of its advantages. At the same time,BiogasThe presence also serves a similar function as scum.BiogasWhen overflowing, it brings part of the sludge to the liquid surface, causing the formation of scum and an increase in suspended solids in the effluent, as well as a deterioration in water quality. Therefore, it is necessary to set up gas baffles and gas collection hoods.BiogasExtracted from the anaerobic digestion unit, a sufficient sedimentation area is left near the effluent weir to ensure the quality of the discharged water.
(4) The sludge load should be appropriate. To maintain the balance of the three stages in the anaerobic digestion process, ensure the generation and consumption of intermediate products like volatile fatty acids are balanced, and prevent acid accumulation from causing a drop in pH, the organic load of the incoming water should not be too high, generally not exceeding 0.5 kg CODcr/(kg MLSS·d). Higher sludge concentration within the reactor can be achieved while maintaining a relatively low sludge load, thereby obtaining a higher volume load. Generally, the volume load of anaerobic digestion units is above 5 kg CODcr/(m³·d), sometimes reaching up to 50 kg CODcr/(m³·d).
(5) When the concentration of suspended solids in the wastewater to be treated is high (usually above 1000 mg/L), appropriate pretreatment such as sedimentation, filtration, or flotation should be performed to reduce the suspended solids content of the incoming water and prevent clogging of the media bed. Typically, the incoming suspended solids for an AF system do not exceed 200 mg/L. However, if the suspended solids are biodegradable and evenly distributed in the wastewater, they have little adverse effect on the AF process.
(6) Ensure a sufficient anaerobic environment. Anaerobic conditions are a prerequisite for the normal activity of anaerobic microorganisms.MethaneMicroorganisms only function under absolute anaerobic conditions. To minimize contact with air, efforts should be made to avoid splashing and turbulence during the flow of wastewater into anaerobic digestion units and during the return of effluent. Covers should be installed on regulating and return pools, and air-lift pumps should not be used for wastewater lifting. The anaerobic reaction structures have passed airtightness tests to ensure they are tightly sealed with no leaks.
2. Anaerobic bioreactor control indicators:
(1) Redox Potential: Utilizing the method of determining redox potential to assess whether the multiple redox component systems within an anaerobic reactor are in a balanced state. Although this method has poor reliability, due to the simplicity of redox potential measurement, when combined with other monitoring indicators, it holds certain guiding significance.
(2) Propionate to Acetate Ratio: If the organic load in the anaerobic reactor exceeds the normal range, the ratio of propionate to acetate concentrations will increase immediately before any other operating parameters change. Therefore, the ratio of propionate to acetate concentrations can be used as a sensitive and reliable warning indicator for abnormal operation caused by overloading of the anaerobic reactor.
(3) Volatile Fatty Acids (VFA): Abnormal elevation of volatile fatty acids is indicative of anaerobic reactor production issues.MethaneEffective indicator for inhibition of microbial metabolism.
(4) Phenylacetic Acid: Phenylacetic acid is an intermediate product generated from the degradation of aromatic amino acids and lignin, among other large molecular organic compounds. When treating wastewater containing such pollutants, the concentration of phenylacetic acid in the anaerobic treatment effluent is a sensitive indicator reflecting the operational status of the anaerobic reactor.
（5）Methyl Mercaptan：Methyl MercaptanThe scent is distinctive, detectable by smell even at very low concentrations.Methyl MercaptanA sudden increase in content (or the appearance or intensification of odor) often indicates a sudden increase in toxic chlorinated hydrocarbons in the incoming water.
（6）Carbon DioxideCO : The generation of COMethaneThe production is closely related; CO is poorly soluble in water and can be monitored online. There is a good correlation between the concentration of CO in the gas phase and the concentration of acetates in the liquid phase. The variation in CO content is also related to the inhibitory effects caused by heavy metals and organic toxicity.
3. Basic conditions for maintaining high efficiency in anaerobic bioreactors:
(1) Appropriate pH Level: To ensure anaerobic operation proceeds smoothly, the pH value in the reactor must be maintained between 6.5 and 8.2.
(2) Sufficient Regular Nutrition: The concentration of nitrogen within the reactor must be maintained between 40-70 mg/L to meet requirements, while lower concentrations of phosphorus and sulfur are sufficient.MethaneMicroorganisms have specific requirements for sulfides and phosphorus, and their concentrations must be ensured within the reactor. Sometimes, it is necessary to add phosphate fertilizers and sulfates to the incoming water.
(3) Essential trace-specific nutrients: forMethaneSpecific nutrients with activating effects on microorganisms include iron, cobalt, nickel, zinc, manganese, molybdenum, copper, and even selenium, boron, and many more. The deficiency of any one of these can severely impact the entire biological treatment process.
(4) Suitable Temperature: Anaerobic reactions typically operate under moderate temperatures of 30-37°C.
(5) Toxicity Adaptability: Must complete acclimatization for anaerobic microorganisms to toxic substances.
(6) Sufficient Metabolic Time: Ensure both the Anaerobic Biological Treatment's Hydraulic Retention Time (HRT) and Solid Retention Time (SRT) are adequate.
(7) Appropriate Carbon Source: The organic matter from the influent water should satisfy the heterotrophic organismsMethaneMicroorganisms serve as carbon sources for biological synthesis, and the dissolved CO2 within the reactor must meet the requirements for autotrophic organisms.MethaneCarbon source required for the bacteria.
(8) Good mass transfer from pollutants to microorganisms: The granular sludge in the anaerobic bioreactor has good mass transfer capacity in the fluidized state. However, excessive accumulation of biomass or excessively thick biofilm when using the anaerobic biofilm method may cause mass transfer issues. It is necessary to regularly discharge excess biological sludge or increase the recycle ratio to reduce some mass transfer resistance.
