|

Industrial Biotrickling Filter Odour Control System

Industrial biotrickling filter system for odour control at a wastewater treatment plant – 15,000 Nm3/h air treatment capacity

Biotrickling Filtration Plant

Technical Summary

Air flow rate: 15,000 Nm³/h
Main pollutants: Reduced sulphur compounds (H₂S)
Treatment technology: Biotrickling filtration
Number of filtration units: 2
Contact time: 24 seconds per filter
Design loading: 150 Nm³/h per m³ of packing


This case study presents an industrial biotrickling filter odour control system designed to treat emissions from a wastewater treatment plant.
The design follows the Best Available Techniques (BAT) described in the BREF for Waste Water and Waste Gas Treatment for biological air treatment systems and VDI 3478 part 1 norm.

Overview

Wastewater treatment plants can generate odorous emissions associated with reduced sulphur compounds, particularly hydrogen sulfide (H₂S).

This project involved the design and installation of an industrial odour control system based on biotrickling filtration technology to treat contaminated air streams at a wastewater treatment facility.

The plant was designed to treat 15,000 Nm³/h of odorous air, ensuring stable removal of sulphur-based odorous compounds through biological oxidation processes.

Engineering Solution

The odour control system consists of two parallel biotrickling filters, each designed to treat 7,500 Nm³/h of contaminated air.

A centrifugal fan installed upstream conveys the polluted air to the filters through a distribution manifold.

Inside the filters, the gas stream passes through a biological packing bed, where microorganisms immobilized on the carrier oxidize hydrogen sulfide and other reduced sulphur compounds into non-odorous forms.

Biotrickling Filter Odour Control Technology

Each filtration unit is built around a polypropylene basin containing the biological packing and irrigation system, designed to ensure proper gas distribution and stable microbial activity.

Play

Main Dimensions

Parameter

Value

Lenght:

10,000 mm

Width:

2,500 mm

Height:

3,300 mm

The filters are constructed entirely in Polypropylene (PP) to ensure resistance against corrosive gases and acidic operating conditions associated with sulphur oxidation processes.

The packing bed is supported by a reinforced polypropylene structural grid capable of supporting loads up to 2,500 kg/m².

Biological Packing Media

The filtration bed is filled with open-cell volcanic lapillus, selected for its suitability in biological filtration applications.

Play

Packing Characteristics

  • Particle size: 14–20 mm
  • Water retention capacity: 6–10 %
  • Available water: 4–7 %
  • Neutral pH
  • High surface area for microbial colonization
  • High mechanical stability

These characteristics promote the formation of a stable microbial biofilm capable of degrading hydrogen sulfide efficiently.

Liquid recirculation system

Each filter includes an independent recirculation tank and irrigation network designed to maintain optimal moisture and nutrient conditions for biological activity.

Main equipment

  • Polypropylene recirculation tank
  • Automatic make-up water valve
  • Visual level indicator
  • Pressure level transmitter (4–20 mA)
  • Automatic purge valve
  • Two AISI 316L submersible pumps (1.1 kW) per filter
  • Nutrient dosing pump
  • Spray irrigation system covering the entire packing surface

This configuration ensures continuous wetting of the biological packing and stable microbial growth.

Air Handling System

Air movement through the treatment system is ensured by a centrifugal fan equipped with inverter control, allowing flow regulation and stable operating conditions.

Fan Specifications

Parameter

Value

Nominal air flow

15,000 Nm³/h

Maximum pressure

250 mm w.c.

Motor power

18.5 kW

Efficiency class

IE3

Noise level

< 81 dB(A)

A standby fan rated at 20,000 Nm³/h was also included to guarantee operational redundancy and maintenance flexibility.

Automation and Control

The system is managed through a PLC-based control panel designed to ensure fully automatic operation.

Control Features

  • PLC control (Siemens S7-1200 or Schneider M221)
  • HMI operator interface
  • pH monitoring
  • Conductivity monitoring
  • Automatic make-up water control
  • Inverter control for the process fan
  • Remote status signals

This architecture ensures reliable operation and simplified plant management.

Key Outcomes

The installed odour control system provides:

  • Effective removal of hydrogen sulfide and reduced sulphur compounds
  • Reliable odour abatement in wastewater treatment emissions
  • Stable long-term biological operation
  • Low chemical consumption thanks to biological oxidation processes

Biotrickling filtration technology enables continuous treatment of odorous air streams with low operating costs and high process stability.

Related Case Studies

  • |

    Industrial Odour Control System for Dry Pet Food Production

    Technical Summary

    Flow rate: 120,000 m³/h (two parallel lines, 60,000 m³/h each)
    Industry: Pet food production
    Technology: Variable-throat Venturi scrubber + downstream wet scrubbing stages
    Target pollutants: Organic vapours, fatty acids, amines, oil aerosols
    Process air sources: Extrusion, drying, coating and cooling

    120,000 m³/h – Designing for variability, not nominal flow

    Air Pollution and Odour Control in Pet Food Production requires full integration with thermal processes, airflow stability, and emission variability management.

    Air pollution and odour control in pet food production kibble

    Application context – Air emissions in pet food production

    This case study concerns the design of an Air Pollution and Odour Control in Pet Food Production plant, with a total extracted air flow rate of approximately 120,000 m³/h.

    The production process includes:

    • extrusion
    • drying
    • coating
    • cooling

    Air emissions are characterised by:

    • organic vapours
    • fatty acids
    • amines
    • oil aerosols

    In pet food production, emission profiles are not constant. Raw material composition and coating formulations significantly influence contaminant concentration and aerosol load.

    For this reason, air pollution control in pet food plants cannot be designed based on nominal flow rate alone.

    The real engineering constraint: no interference with the drying process

    The odour control system had to be integrated without disturbing:

    • the thermal balance of the oven
    • the internal pressure profile of the dryer
    • the process airflow stability

    Any unstable downstream pressure condition would have:

    • altered the internal oven temperature
    • affected moisture control
    • increased methane consumption
    • reduced product quality consistency

    In pet food production, maintaining thermal stability is directly linked to product performance and energy efficiency.

    The air pollution control system therefore had to adapt to the production process — never the opposite.

    Variable throat Venturi scrubber for emission variability

    Given the fluctuating contaminant load and presence of oil aerosols, a Venturi scrubber with variable throat section was selected as the primary stage of the odour control system.

    The Venturi operates on inertial impaction principles: particle and aerosol removal efficiency is directly related to gas velocity and pressure drop (ΔP).

    The variable throat configuration allows:

    • adjustment of gas velocity according to real operating conditions
    • controlled pressure drop
    • stable capture efficiency across variable loads
    • avoidance of efficiency loss during low-load operation
    • prevention of excessive ΔP during peak conditions

    Unlike fixed-throat systems, the variable geometry maintains the required impact energy while adapting to process variability typical of pet food air emissions.

    The Venturi stage was dimensioned based on required separation efficiency, not solely on nominal air flow rate.

    Controlled fan operation and process stability

    A key design principle of this Air Pollution and Odour Control system was that downstream fans must never interfere with the process fans of the oven.

    The tail-end extraction fans were installed downstream of the treatment plant and equipped with variable frequency drives (VFD).

    Their function is to:

    • continuously adjust rotational speed
    • maintain the required negative pressure
    • compensate for system pressure losses
    • preserve stable depression across the treatment unit

    This ensures that:

    • the internal pressure of the dryer remains unaffected
    • the thermal equilibrium of the oven is preserved
    • process airflow conditions remain stable

    The odour control system behaves as a controlled hydraulic load, not as an active disturbance to the production process.

    Pressure drop and separation efficiency

    In Venturi scrubbers, separation efficiency is directly related to gas velocity and pressure drop. Reducing ΔP in order to minimise energy consumption without understanding the required impact energy inevitably compromises particle and aerosol removal efficiency.

    In this application, the variable throat configuration allows optimisation of ΔP according to real operating conditions, ensuring stable performance without unnecessary energy penalties.

    Energy and quality impact

    Maintaining stable oven conditions in pet food production results in:

    • consistent drying performance
    • stable product temperature profile
    • reduced methane consumption
    • improved product quality consistency

    The air pollution control system therefore contributes not only to emission abatement, but also indirectly to energy optimisation and process reliability.

    Engineering insight

    In dry pet food production, effective Air Pollution and Odour Control requires full integration with process airflow and thermal dynamics.

    Designing only for flow rate leads to instability.

    Designing for:

    • emission variability
    • aerosol load
    • pressure management
    • process integration

    ensures predictable performance.

    Air pollution control in pet food production is not an add-on system.
    It is a process-integrated engineering solution.

  • |

    Air Pollution and Odour Control for Category 3 Animal By-Products Processing

    Technical summary

    Flow rate: 8,000 m³/h
    Industry: Animal by-product ABP transformation
    Technology: 1 Acidic + 1 Alkali/oxidative PC-1 single staged scrubbers
    Target pollutans: Odour, ammonia, VOC
    Process air temperature: 80°C

    Read More “Air Pollution and Odour Control for Category 3 Animal By-Products Processing”
  • |

    Industrial Odour Control System for Meat and Fish Smoking Processes

    Technical Summary

    Flow rate: 500 Nm³/h
    Industry: Meat and smoked fish processing
    Technology: Venturi scrubber + three-stage packed column wet scrubber
    Target pollutants: Organic vapours, fatty acids, amines, H₂S and mercaptans
    Process air temperature: Ambient
    Emission limits @ stack: 300 OU/Nm³ odour, 50 mg/Nm³ TOC, 1 mg/Nm³ H₂S & mercaptans, 3 mg/Nm³ NH₃ & amines

    Industrial Odour Control System for Meat and Fish Smoking Processes

    Industrial air pollution control in meat and fish smoking facilities requires careful integration with production airflow and odour emission characteristics.
    This case study describes the design of an industrial odour control system for smoking emissions from meat and fish processing, based on wet scrubbing technology and multistage chemical treatment.
    This industrial odour control system was designed to treat smoke emissions generated during meat and fish smoking processes.

    Industrial wet scrubber system for odour control from meat and fish smoking processes, featuring multistage packed column scrubber and chemical dosing units.

    Application Context – Air Emissions from Meat and Fish Smoking

    This project concerns the installation of an industrial air pollution and odour control system for a gourmet meat and smoked fish processing facility.
    The extraction system collects air emissions generated during:

    • meat smoking processes
    • fish smoking chambers
    • product cooling stages
    • handling and packaging areas

    Air emissions from smoking operations typically contain:

    • organic vapours generated by thermal degradation of fats
    • fatty acids and condensable smoke compounds
    • amines released from protein processing
    • sticky soot particles generated during meat and fish smoking

    For this reason, the air pollution control system was designed as a controlled hydraulic load rather than an active disturbance to the production process.

    Wet Scrubber Architecture for Odour Abatement

    The installed odour control system combines Venturi pre-scrubbing and multistage packed column wet scrubbing.

    Venturi Scrubber – Aerosol and Smoke Particle Removal

    The first treatment stage is a Venturi scrubber with mobile bed separator, designed to remove:

    • tar droplets from smoke emissions
    • oil aerosols generated during smoking
    • condensable particulate fractions.

    The Venturi stage increases gas velocity to improve inertial impaction efficiency, enhancing the capture of aerosol particles.

    Multistage Packed Column Scrubber (series of 3 single stage)

    Downstream treatment is performed in two vertical packed column scrubbers operating in countercurrent flow configuration.
    The three chemical stages include:

    Acid stage

    • neutralisation of alkaline compounds
    • stabilisation of odour load

    Oxidative stage

    • oxidation of reduced sulphur compounds
    • removal of hydrogen sulphide and mercaptans

    Alkaline stage

    • neutralisation of residual acidic compounds
    • neutralisation of residual oxidative compounds, such as Chlorine.
    • final polishing of odorous emissions.

    Structured liquid distribution systems and demisters ensure stable mass transfer efficiency and droplet separation.

    Chemical Dosing and Process Control

    The system includes automatic chemical dosing units for process control.

    Reagents used include:

    • sulphuric acid for pH correction
    • sodium hypochlorite for enhanced odour destruction
    • sodium hydroxide for alkaline neutralisation

    Online monitoring ensures process stability through:

    • pH control
    • ORP (redox potential) monitoring

    These parameters allow dynamic adjustment of chemical dosing according to actual emission conditions.

    Air Extraction and Process Stability

    Air extraction is performed through a polypropylene duct system connected to a high-efficiency centrifugal fan.

    Key design characteristics include:

    • corrosion-resistant materials (PP and PVC)
    • controlled airflow at 500 Nm³/h
    • downstream fan installation to maintain negative pressure.

    The fan operates with stable rotational speed to ensure:

    • constant airflow through the scrubber
    • stable pressure conditions in the process ductwork
    • reliable odour capture.

    Emission Performance and Environmental Compliance

    Engineering Insight – Odour Control in Smoking Facilities

    In meat and fish smoking plants, air pollution control cannot be designed based solely on airflow.

    Effective odour control requires understanding:

    • aerosol formation during smoking
    • variability of organic vapours
    • sulphur compound formation
    • interaction between process airflow and treatment units.

    For this reason, industrial odour control systems must be designed as process-integrated solutions rather than simple end-of-pipe equipment.

  • | | |

    Hydrogen Sulfide Removal in Air: Why Caustic Scrubbers Become Unstable

    Hydrogen sulfide removal is not a steady-state problem

    Hydrogen sulfide removal is one of the most common challenges in industrial air treatment.
    In many systems, caustic scrubbers are used as the primary solution to remove H2S.
    On paper, the chemistry is simple.
    In real operation, these systems often become unstable.

    • H2S is absorbed into the liquid phase
    • it reacts with sodium hydroxide (NaOH)
    • it forms soluble sulfide compounds

    On paper, the process is stable.

    In real operation, it is not.

    The chemistry is predictable. The system is not

    The reaction between hydrogen sulfide and caustic soda is well known:

    • H2S + NaOH → NaHS + H2O
    • NaHS + NaOH → Na2S + H2O

    This is not where the problem lies.

    The issue is that industrial air systems do not operate under controlled, steady conditions.

    In real plants:

    • H2S concentration fluctuates
    • emissions occur in peaks, not averages
    • humidity changes continuously
    • aerosols and particulates interfere with mass transfer

    Why hydrogen sulfide removal becomes unstable

    A caustic scrubber is typically designed around average inlet conditions.

    But real systems are defined by variability.

    When peak loads occur:

    • the reaction accelerates locally
    • sulfide concentration in the liquid increases rapidly
    • the recirculation loop changes composition

    Over time:

    • salinity increases
    • mass transfer efficiency drops
    • system response becomes non-linear

    The scrubber still works.

    But it stops working predictably.

    pH control does not guarantee performance

    In many hydrogen sulfide removal systems, pH is used as the primary control parameter.

    The assumption is straightforward:

    high pH ensures effective H2S removal.

    In practice:

    • pH does not reflect sulfide accumulation
    • it does not represent real absorption capacity
    • it does not capture mass transfer limitations

    Operators may observe a stable pH

    while the system performance is deteriorating.

    As a result:

    • caustic consumption increases
    • removal efficiency fluctuates
    • corrective actions become reactive instead of controlled

    pH is an indicator.
    It is not a control strategy.

    Field reality: transient H2S release in industrial processes

    In many industrial processes, hydrogen sulfide is not released at a constant rate.

    A clear example is found in tannery operations during the pickling phase.

    In these conditions:

    • acidic environments react with residual sulfides
    • H2S is released rapidly
    • emissions occur in short, high-intensity peaks

    The key issue is not the average concentration.

    It is the transient load.

    A caustic scrubber exposed directly to these peaks:

    • reacts, but not in a controlled way
    • accumulates reaction products quickly
    • loses operational stability

    Hydrogen sulfide removal becomes a continuous correction process.

    Hydrogen sulfide removal requires load control

    The most critical mistake in H2S treatment design is assuming that the final stage can handle everything.

    In reality, hydrogen sulfide removal requires load management upstream.
    This is where pre-treatment becomes essential.

    The role of pre-treatment in hydrogen sulfide removal

    Iron-based media systems (CIF) are often used as a pre-treatment stage.

    clean catalytic iron media used in CIF systems for hydrogen sulfide removal before sulfur formation
    severe sulfur fouling on pall rings in H2S removal system reducing airflow and efficiency

    They are not designed to remove all hydrogen sulfide.

    Their function is to:

    • reduce peak concentrations
    • stabilize inlet conditions
    • protect downstream scrubbers

    When pre-treatment is correctly applied:

    • transient peaks are dampened
    • load becomes more uniform
    • the caustic scrubber operates within a manageable range

    This changes the system from reactive to controlled.

    Designing hydrogen sulfide removal for real conditions

    Effective hydrogen sulfide removal systems are not designed around average values.

    They are designed around:

    • variability
    • peak loads
    • real process behavior

    A caustic scrubber without pre-treatment is forced to absorb all fluctuations.

    And no single stage can do that reliably.

    A necessary distinction in hydrogen sulfide removal

    Hydrogen sulfide removal in industrial air systems must be treated as a specific engineering problem.

    Air treatment systems are characterized by:

    • low but highly variable concentrations
    • intermittent emissions
    • complex mixtures of contaminants

    Design approaches taken from other processes
    do not apply directly.

    Each system must be designed based on its actual operating conditions.

    Hydrogen sulfide removal does not fail because the chemistry is wrong.
    It fails because the system is designed for average conditions
    instead of real variability.

    Evaluate whether your hydrogen sulfide removal system is designed as a machine or as a process

  • | | |

    Scrubber foam problem: root causes

    Scrubber foam problem: context

    In many industrial wet scrubbing systems, foam formation is often dismissed as a secondary or cosmetic issue. In reality, persistent foam is almost always the visible symptom of a deeper process inconsistency.
    This insight originates from real operational evidence: a recirculation tank completely filled with stable foam, generated during normal plant operation.

    What foam really indicates

    Foam inside a scrubber is not random. It is the result of a combination of physical and chemical conditions:

    • Presence of surfactants or organic compounds
    • High gas velocities and turbulence
    • Unstable liquid chemistry (pH, oxidation state, salinity)
    • Accumulation of reaction by-products

    When these factors align, foam transitions from transient to persistent.
    At that point, it stops being a nuisance and becomes a process variable.

    Why Foam Is a Problem

    The consequences are rarely limited to aesthetics:

    • Loss of effective liquid–gas contact
    • Carryover of droplets and contaminants
    • Unstable pressure drop
    • Reduced mass transfer efficiency
    • Risk of downstream fouling
    • Cavitation of recirculation pump

    In extreme cases, the scrubber continues to operate, but no longer performs its intended function.

    The Typical Reaction (and Why It Fails)

    The most common response is the addition of antifoam agents.
    This approach is appealing because it is immediate and simple.
    However, it rarely addresses the root cause.
    Antifoam acts on the symptom, not on the mechanism that generates foam. As a result:

    • Consumption increases over time
    • Performance becomes inconsistent
    • Operating costs rise without solving the instability

    Engineering Perspective: Treat the Cause, Not the Symptom

    Foam must be interpreted within the broader process context.
    The correct approach requires asking fundamental questions:

    • What compounds are actually present in the gas phase?
    • Is the chemical regime (acid/base/oxidative) coherent with those compounds?
    • Is the liquid recirculation accumulating by-products?
    • Is the hydraulic design promoting local imbalances?

    Only by reconnecting the scrubber to the upstream process can the issue be solved.

    Design Implications

    Persistent foam often reveals deeper design limitations:

    • Systems designed for steady-state conditions operating under variable loads
    • Lack of pollutant speciation during the design phase
    • Oversimplified assumptions about liquid chemistry
    • Inadequate purge and make-up strategies

    In other words, the problem is not the foam itself.
    The problem is that the system was never designed to handle the real process conditions.

    Key Takeway

    A scrubber does not fail when foam appears.

    It fails when foam is treated as an isolated issue.

    Understanding and controlling the origin of the emission is the only way to restore performance.

    Final note

    Visible phenomena in industrial systems are rarely superficial.
    They are signals.
    Ignoring them — or masking them with quick fixes — only delays the real engineering work.

  • |

    Two-Stage Packed Column Scrubber for Pet Food Air Pollution Control

    Technical Summary

    Flow rate: 30,000 m³/h
    Industry: Pet food production
    Technology: PC-2 Two-stage packed column wet scrubber (acid stage + caustic-oxidative stage)
    Target pollutants: Amines, organic vapours, fatty acids, oil aerosols
    Process air characteristics: Emissions from extrusion, drying, coating and cooling phases

    Acid and caustic-oxidative stages designed around operational maintenance windows

    Air Pollution Control for Pet Food Production requires alignment between scrubber architecture and factory operating schedule.

    Air Pollution Control for Pet Food Production – two-stage packed column scrubber 30,000 m³/h
    Two-stage packed column scrubber installed for pet food air pollution control. Designed for 30,000 m³/h with maintenance-based operation strategy.

    Application context

    This Air Pollution and Odour Control system was designed to treat up to 30,000 m³/h of process air generated by a dry pet food production line operating on a single 8-hour shift.

    Air is extracted from the complete production cycle:

    • Extrusion
    • Drying
    • Coating
    • Cooling

    The emission profile includes:

    • Amines
    • Organic vapours
    • Fatty acids
    • Oil aerosols from coating phases

    Although airflow is relatively stable, contaminant concentration varies according to recipe formulation and coating intensity.

    Why a packed-only solution was selected

    Packed column scrubbers are often considered structurally limited in pet food applications because of oil mist deposition on the first stage packing.

    However, this limitation becomes critical only when production schedules do not allow regular maintenance.

    In this specific case, the production line operates on a single daily shift, providing predictable downtime. This makes it possible to:

    • Schedule periodic inspection
    • Perform cleaning when required
    • Manage progressive packing fouling as part of normal operation

    The engineering decision was therefore based on operational rhythm, not on catalogue standardisation.
    In this case, Air Pollution Control for Pet Food Production is based on predictable maintenance cycles rather than continuous elastic operation.

    System architecture

    The installed configuration consists of two separate packed columns, operating sequentially:

    First stage – Acid

    Designed to neutralise amines and stabilise odour load.

    Second stage – Caustic-oxidative scrubber

    Designed to complete neutralisation and improve robustness against residual organic compounds.

    The physical separation between stages allows:

    • Independent hydraulic and aeraulic control
    • Clear chemical segregation
    • Targeted maintenance planning

    This architecture remains structurally simple while ensuring staged treatment.

    This configuration was selected as a structured Air Pollution Control for Pet Food Production strategy aligned with the plant’s operating rhythm.

    Operational reality: fouling as a managed parameter

    In pet food production, oil aerosols generated during coating inevitably deposit on internal surfaces.

    In packed towers, the first stage becomes the primary deposition surface.

    Consequences over time may include:

    • Gradual pressure drop increase
    • Reduced mass transfer efficiency
    • Risk of channel formation
    • Foam generation

    In this installation, these effects are not treated as unexpected faults but as predictable phenomena integrated into the maintenance strategy.

    Because the factory does not operate continuously, the system remains viable and economically rational.

    Engineering positioning

    A two-stage packed column system can be an effective Air Pollution and Odour Control solution for pet food production up to 30,000 m³/h — provided that:

    • The plant does not operate continuously
    • Maintenance intervals are structurally available
    • Operational discipline is maintained

    Where these conditions exist, a packed-only architecture remains technically sound.

    Where production shifts increase or variability intensifies, reaction dynamics and fouling management require a different approach — which led to a more efficient evolution.

    When to choose a two-stage packed column scrubber

    Air Pollution Control for Pet Food Production can effectively rely on a two-stage packed column architecture when production operates on limited daily shifts and structured maintenance windows are available. In these conditions, oil mist deposition on the first stage packing can be managed through scheduled cleaning without compromising long-term stability. Where continuous three-shift production is required, reaction dynamics and fouling accumulation demand more elastic configurations.