Biological Odor Control Filter (ESLC Series)

Product Overview

The ESLC series biological odor control filter uses selected high-efficiency microorganisms to treat odorous gases containing hydrogen sulfide, mercaptans, sulfides, ammonia and other odor-causing compounds.

The system can also treat toxic and odorous organic exhaust gases containing volatile organic compounds such as benzene, toluene, chlorobenzene, low-molecular-weight hydrocarbons, alcohols, aldehydes and ketones.

The core technologies of the ESLC system include microorganism selection and cultivation, high-efficiency biofilm formation, biological packing suitable for microbial attachment and growth, and optimized operating conditions for stable biological degradation.

Under suitable temperature, humidity, pH, oxygen and nutrient conditions, microorganisms inside the biological filter use inorganic and organic pollutants in the exhaust gas as carbon sources and energy sources. Through microbial metabolism, odorous pollutants are degraded into water, carbon dioxide and other relatively harmless substances.

Biological filtration is one of the most established and widely used technologies for industrial odor control. Before entering the filter bed, the contaminated gas normally passes through pretreatment processes such as dust removal, humidification or cooling.

The conditioned gas then enters from the lower section of the filter and flows upward through the biological packing. Pollutants transfer from the gas phase into the moisture and biofilm covering the packing material, where they are absorbed and biologically degraded by attached microorganisms.

Biological Degradation Process

Microorganisms use organic pollutants as substrates for growth and reproduction. Through a series of biochemical conversion pathways, large or structurally complex organic molecules are gradually broken down into simpler inorganic substances such as water and carbon dioxide.

During catabolism, microorganisms obtain energy by decomposing pollutants. During assimilation, part of the pollutant material is converted into new microbial biomass. This allows the microbial population to continue growing and maintain its pollutant-degradation capacity.

The removal of pollutants is therefore a combined physical, chemical, physicochemical and biochemical process involving gas absorption, mass transfer, microbial adsorption and biological oxidation.

Working Principle

The ESLC biological filter generally uses a multi-stage biological deodorization process. Compared with a conventional single-stage biological treatment system, the multi-stage configuration provides improved removal efficiency, more stable operation, greater treatment capacity and better resistance to fluctuating pollutant loads.

The system removes harmful gas components through effective contact between the contaminated airflow and the biologically active packing material.

The filter bed uses porous inert packing with a high void ratio, large specific surface area and relatively low airflow resistance. This structure provides sufficient space for microbial attachment and helps remove sulfur-containing odor compounds from the exhaust gas.

The exhaust gas normally requires a relatively long contact time with the biological media. A combination of organic and inorganic packing materials can be used to provide suitable moisture retention, structural stability and microbial growth conditions.

Unlike some continuously irrigated biological systems, the ESLC series generally requires only intermittent spraying during routine operation, subject to the actual humidity and operating conditions.

Treatment Process

Process Stage	Description
1. Exhaust Gas Collection	Odorous gas is collected through extraction hoods or enclosed treatment areas and transported to the biological filter through the duct system.
2. Pretreatment	Dust removal, humidification, cooling or other conditioning processes are used to protect the biological packing and create suitable treatment conditions.
3. Gas Distribution	The gas distribution system delivers contaminated air uniformly across the bottom of the filter bed and prevents short-circuiting or channeling.
4. Pollutant Transfer	Odorous and organic compounds transfer from the gas phase into the moisture layer and biofilm covering the packing material.
5. Microbial Degradation	Selected microorganisms biologically oxidize and decompose the absorbed pollutants.
6. Metabolite Removal	Water-soluble metabolic products such as sulfuric acid and nitrous acid enter the circulating-water system and are removed through drainage or water treatment.
7. Purified Gas Discharge	The treated gas exits the biological filter and is discharged after meeting the applicable odor and emission requirements.

Microbial Treatment Mechanism

The biological purification system can contain several types of functional microorganisms, including anaerobic ammonium-oxidizing bacteria, sulfur-oxidizing bacteria and denitrifying bacteria.

Selected microbial strains are immobilized on specially designed biological packing. The packing is supported by a corrosion-resistant FRP grating structure that also helps distribute the airflow evenly through the filter bed.

The high specific surface area of the packing provides a suitable environment for microbial attachment, biofilm formation and pollutant degradation.

The system maintains suitable temperature, humidity and pH conditions and provides sufficient oxygen and nutrients for microbial growth. Organic compounds in the exhaust gas can provide carbon, nitrogen, phosphorus and certain trace elements. When a specific nutrient is insufficient, a suitable supplement can be added according to the operating requirements.

When odorous gas passes through the biological packing, the selected microorganisms oxidize the odor-causing components. Metabolic products generated during degradation, including acidic compounds, enter the circulating-water section and are discharged together with the wastewater.

When operating conditions change, part of the microbial population may become inactive, while the microorganisms best adapted to the new conditions continue to survive and reproduce. This allows the system to develop a dominant microbial population and recover treatment performance after short-term pollutant fluctuations.

Key Features

• Low operating cost compared with many chemical or thermal odor-control technologies
• High degree of automation and stable continuous operation
• Can generally operate with limited manual supervision
• Rapid microbial growth and continuous biological renewal
• Fast restart after temporary shutdown under suitable preservation conditions
• Strong resistance to fluctuating and shock pollutant loads
• Suitable for exhaust gases with varying concentrations
• High-efficiency biological packing with a long service life
• Biological packing service life can exceed ten years under suitable conditions
• Stable packing structure with good mechanical strength
• Relatively low airflow resistance and pressure drop
• Can simultaneously treat several odor-causing and organic pollutants
• No combustion process and relatively low energy consumption
• No secondary solid waste generated during normal biological degradation

Applicable Pollutants

Pollutant Category	Typical Pollutants
Sulfur-Containing Odors	Hydrogen sulfide, mercaptans, sulfides and other reduced sulfur compounds
Nitrogen-Containing Odors	Ammonia and other nitrogen-containing odorous compounds
Aromatic VOCs	Benzene, toluene and chlorobenzene
Hydrocarbons	Low-molecular-weight aliphatic hydrocarbons
Oxygenated VOCs	Alcohols, aldehydes and ketones
Mixed Industrial Odors	Complex odorous gases from wastewater, waste treatment, food and manufacturing processes

Applicable Industries

• Municipal wastewater treatment plants
• Wastewater pumping stations
• Wastewater pretreatment areas
• Sludge treatment and dewatering areas
• Waste transfer and collection stations
• Waste sorting workshops
• Solid-waste treatment facilities
• Paint and coating plants
• Plastic manufacturing
• Rubber production
• Animal feed processing
• Food and beverage production
• Pharmaceutical manufacturing
• Other industrial odor-control applications

Main System Components

Component	Function
Gas Distribution System	Distributes contaminated gas uniformly across the biological filter bed and reduces airflow short-circuiting.
Packing Support Structure	Supports the operating weight of the biological packing, moisture and microbial growth.
Biological Packing	Provides a large surface area for microbial attachment, pollutant adsorption and biofilm development.
Spray and Humidification System	Maintains suitable packing moisture and supports microbial activity.
Circulating-Water System	Collects and transports water-soluble metabolic products and maintains filter-bed humidity.
pH Monitoring and Adjustment System	Monitors and adjusts the biological environment to maintain suitable microbial activity.
Exhaust Fan	Provides the airflow required to transport odorous gas through the treatment system.
Automatic Control System	Controls fans, pumps, spraying, pH adjustment and operating alarms.

Gas Distribution System

The biological filter contains an integrated packing support structure and gas distribution system. These components use a compact design to minimize the space occupied inside the treatment unit.

The packing support system is located above the gas distribution section and supports the operating weight of the biological media.

The support structure is typically manufactured from corrosion-resistant FRP with a thickness of at least 38 mm, subject to the final structural design.

A molded FRP grating panel supports the packing. A filter mesh is placed above the grating to prevent small packing particles from falling into the gas distribution channel.

The gas distribution section can include supporting members and a structural frame to provide sufficient rigidity, strength and corrosion resistance.

The design should account for the additional loads generated by microbial growth, spray-water retention, wet packing weight and natural settlement during operation.

Odorous gas may otherwise flow unevenly inside the filter and reduce treatment performance. The ESLC system can therefore be equipped with air-distribution pipes, channels and equalization devices to reduce short-circuiting and channeling.

Biological Packing

The ESLC series uses composite biological media designed to provide suitable conditions for microbial attachment and odor degradation.

The packing includes pH-buffering characteristics that help reduce acidification. Under normal operating conditions, additional pH-adjustment solution may not be required continuously.

The media provides good permeability, structural stability, pollutant adsorption capacity and a suitable environment for microbial growth.

The packing is suitable for treating exhaust gas at temperatures from approximately 5°C to 40°C. It is resistant to biological decay and maintains good adsorption and attachment performance.

Before the biological filter is commissioned, the packing is treated or inoculated with a solution containing selected microbial strains.

Advantages of the Composite Biological Packing

• Low pressure loss
• High structural stability
• Good resistance to acidic and alkaline environments
• Resistance to compaction and settlement
• Suitable surface structure for microbial attachment
• Low risk of hardening and aging
• Supports automatic or monitored pH adjustment
• Initial pressure loss generally below 1,000 Pa at the designed empty-bed gas velocity
• Non-toxic to operators under normal use
• Does not generate significant secondary pollution

Microbial Strains

The biological degradation of odor pollutants depends strongly on the quality and suitability of the microbial strains. Microbial selection, biofilm formation and acclimatization are therefore key technologies in biological deodorization.

Microorganisms used for treating odorous gas from municipal wastewater generally perform well within a pH range of approximately 4–8.

Because acidic metabolic products may be generated during pollutant degradation, long-term operation can gradually lower the pH of the filter bed. Excessive acidification may inhibit microbial growth and reduce odor-removal performance.

The ESLC system can therefore be equipped with pH monitoring and automatic adjustment functions to help maintain the biological environment within the required range.

The selected microbial strains are suitable for the climatic and operating conditions of the project. Under normal operation, the odor-treatment process may not require continuous addition of nutrient solution when the exhaust gas and system conditions provide sufficient nutrients.

The composite microbial community can maintain treatment performance over a relatively wide temperature range of approximately 5–40°C. Biological activity is generally strongest between approximately 10°C and 35°C.

Microbial Adaptability and Self-Renewal

Microorganisms continuously reproduce and renew their population. Because individual microbial life cycles are relatively short, the microbial community can gradually adapt to changing operating conditions.

Microorganisms that are well adapted to the pollutant environment reproduce more rapidly, while less suitable organisms gradually decline. Over time, the dominant pollutant-degrading population increases and the treatment capacity improves.

Different microorganisms coexist as a biological community. Because many pollutants can be degraded by corresponding microbial species found in nature, a properly selected mixed culture can simultaneously treat several types of contaminants.

When environmental conditions or pollutant concentrations change, some microorganisms may become inactive or die. The surviving microorganisms can reproduce within a relatively short period and develop into a new dominant population, allowing the system to recover after shock loading.

Operating Conditions

Operating Factor	Recommended Condition
Exhaust Gas Temperature	Approximately 5–40°C
Preferred Biological Activity Range	Approximately 10–35°C
pH Range	Approximately 4–8
Filter-Bed Moisture	Maintained through intermittent spraying or humidification
Oxygen Supply	Sufficient oxygen for the selected aerobic biological process
Nutrients	Provided by the exhaust gas where possible, with selective supplementation when required
Initial Packing Pressure Loss	Generally not more than 1,000 Pa at the design empty-bed gas velocity

Resistance to Shock Loads

The ESLC biological filter provides strong resistance to fluctuations in pollutant concentration and airflow.

When the pollutant concentration suddenly increases, the treatment efficiency may temporarily decrease. However, microorganisms that adapt to the higher pollutant loading can rapidly reproduce and restore the system’s performance.

The actual recovery time depends on pollutant type, concentration, temperature, humidity, pH, oxygen availability and the condition of the microbial community.

Automatic Control

The ESLC system can use PLC-based automatic control to coordinate the fan, circulating-water pump, spraying system, pH adjustment and operating alarms.

• Automatic intermittent spraying
• Circulating-water level monitoring
• pH monitoring and adjustment
• Fan and pump interlock control
• Temperature monitoring
• Pressure-drop monitoring
• Fault alarm and equipment protection
• Automatic or manual operating modes

Selection Considerations

• Exhaust gas airflow
• Pollutant composition and concentration
• Odor intensity and required removal efficiency
• Exhaust gas temperature and humidity
• Dust, oil mist and particulate content
• Required gas residence time
• Available installation space
• Local climate and winter operating conditions
• Circulating-water and drainage requirements
• Local odor and emission standards

Pretreatment Requirements

Pretreatment may be required when the incoming gas contains dust, excessive temperature, insufficient humidity, oil mist or other substances that could inhibit microbial activity or block the packing.

Available pretreatment options include:

• Dust filters
• Spray humidification
• Gas cooling
• Oil mist separation
• Acid or alkaline pre-scrubbing
• Condensate removal

Why Choose ES Air ESLC Series?

• Suitable for sulfur-containing, nitrogen-containing and mixed industrial odors
• Can also treat selected low-concentration VOCs
• Multi-stage biological deodorization provides stable operation
• Selected microorganisms and high-efficiency biological packing
• Low operating energy consumption
• Strong resistance to fluctuating pollutant loads
• Long-life packing with relatively low pressure loss
• Automatic pH, humidity and equipment control available
• Suitable for municipal and industrial odor-control projects
• Customized design according to actual exhaust gas conditions

Frequently Asked Questions

What is a biological odor control filter?

A biological odor control filter is an air-treatment system that uses microorganisms attached to packing material to absorb and degrade odor-causing compounds and selected organic pollutants.

What pollutants can the ESLC series treat?

The ESLC series can treat hydrogen sulfide, mercaptans, sulfides, ammonia and selected VOCs such as benzene, toluene, chlorobenzene, alcohols, aldehydes and ketones.

Does the system require chemical reagents?

The main treatment process relies on microbial degradation. Chemicals may only be required for pH adjustment, nutrient supplementation or pretreatment under specific operating conditions.

Does the biological packing need to be replaced?

The high-efficiency biological packing has a long service life and may operate for more than ten years under suitable conditions. Replacement depends on structural condition, blockage, pressure loss and actual treatment performance.

What temperature range is suitable?

The biological packing is generally suitable for gas temperatures from approximately 5°C to 40°C, with optimum microbial activity commonly occurring between 10°C and 35°C.

Can the system handle fluctuating odor concentrations?

Yes. The microbial community can adapt to changing pollutant loads, although a sudden increase may cause a temporary reduction in treatment efficiency before the dominant microorganisms recover.

Is continuous spraying required?

Continuous spraying is not always necessary. The system generally uses intermittent spraying to maintain suitable packing moisture, depending on the actual humidity and operating conditions.

Can ES Air customize the biological filter?

Yes. ES Air can design the system according to airflow, pollutant composition, odor concentration, temperature, humidity, residence time, installation space and local emission requirements.

Customized Biological Odor Treatment Solutions

ES Air provides biological filters and integrated industrial odor-control systems for municipal wastewater, sludge treatment, waste processing, food, pharmaceutical, rubber, plastics and other industrial applications.

Contact ES Air for exhaust gas evaluation, microbial process selection, biological packing design and customized odor-control solutions.

SEO Brief: The ES Air ESLC Series Biological Odor Control Filter uses selected microorganisms and high-efficiency biological packing to remove hydrogen sulfide, mercaptans, sulfides, ammonia and selected VOCs from municipal and industrial exhaust gas. The system features low operating costs, strong resistance to shock loads, long-life packing and automatic humidity and pH control for wastewater treatment, waste processing, food, pharmaceutical, rubber and plastics applications.