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
Two-Stage Packed Column Scrubber – 8,000 m³/h at 80°C
Air Pollution and Odour Control for Category 3 animal by-products processing requires a deep understanding of how emissions are generated during the thermal treatment of protein-rich organic matrices.
In this application, poultry blood classified as Category 3 Animal By-Products (ABP Cat.3) is thermally dehydrated to produce a stable protein powder intended for valorisation.
The exhaust air from the process presents:
high humidity
temperatures up to 80°C
protein-derived aerosols
nitrogen-based odorous compounds
volatile organic compounds (VOCs)
potential ammonia traces
In ABP Category 3 processing, odour generation is not constant but strongly linked to:
raw material freshness
thermal load
protein degradation dynamics
transient operating conditions
Total treated airflow: 8,000 m³/h Maximum gas temperature: 80°C
The project concerned a new Air Pollution and Odour Control system, fully integrated into the Category 3 processing line.
Engineering objective
The objective of this Air Pollution and Odour Control installation was to:
stabilise odour emissions from ABP Cat.3 processing
remove nitrogen-based compounds
control high humidity exhaust streams
ensure chemical stability under variable loads
guarantee long-term operational reliability
In Category 3 animal by-products processing, emissions originate from protein denaturation and partial degradation. This means the system must manage both:
soluble alkaline compounds
oxidisable organic fractions
A purely hydraulic solution would not be sufficient. The treatment architecture had to reflect the chemistry of the emission.
Polypropylene scrubbers are widely used in industrial air pollution control systems due to their excellent chemical resistance and relatively low cost. A Polypropylene scrubber is typically used in wet scrubbing applications where corrosive gases, odours or pollutants must be removed from air streams. However, in real industrial environments, Polypropylene scrubbers are often selected based only on chemical compatibility. This is where most design mistakes begin.
Why Polypropylene Scrubbers Are So Common
The success of scrubbers made in Polypropylene comes from three main factors:
High chemical resistance
Cost-effectiveness compared to stainless steel
Ease of fabrication
For many standard applications, a polypropylene scrubber is a reliable and efficient solution.
But this is only part of the story.
The Real Limit of Polypropylene Scrubbers
The main limitation of scrubbers made in Polyptopylene is not chemical resistance.
It is mechanical behaviour under temperature.
Polypropylene has a high thermal expansion coefficient:
0.15–0.20 mm/m·°C
In industrial scrubbers, this means that even small temperature variations can generate significant structural movement.
Thermal Expansion in Polypropylene Scrubbers
Thermal expansion is often underestimated during design.
In real operation, it leads to:
Misalignment between scrubber and piping
Stress on flanges and connections
Progressive deformation of the structure
Long-term mechanical fatigue
These effects are not immediate, but they become critical over time.
In constrained layouts, like long duct runs with fixed supports, thermal expansion cannot dissipate. It accumulates.
Why Polypropylene Scrubbers Fail in Operation
When scrubbers made in Polypropylene fail, the cause is rarely chemical.
Typical failure mechanisms include:
Rigid piping connected to the scrubber
Lack of expansion compensation
Poor mechanical support design
Temperature fluctuations not considered
In many cases, the problem is attributed to installation errors, while the real issue is design-related.
Polypropylene vs Other Materials
Polypropylene is often compared with other materials such as HDPE or stainless steel.
Each material behaves differently:
Polypropylene scrubbers → excellent chemical resistance, high thermal expansion
HDPE scrubbers → better mechanical resilience, similar expansion issues
Stainless steel scrubbers → low expansion, but limited chemical resistance in aggressive environments
There is no universally “best” material. The correct choice depends on the process conditions.
When Polypropylene Work Well
Polypropylene perform reliably when:
Temperature varies significantly
Large structures are mechanically constrained
The system is rigid and over-constrained
Long-term dimensional stability is critical
In these cases, alternative materials or different design approaches should be considered.
Conclusion: Understanding Polypropylene Scrubbers
Polypropylene scrubbers are not a bad choice. They are often a misunderstood one.
The key is not only to evaluate chemical resistance, but to understand how Polypropylene scrubbers behave under real operating conditions.
In industrial air treatment, material selection is not a chemical decision. It is an engineering decision.
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.
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.
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.
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.
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.
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.
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
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.
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.
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