Wastewater & Sewage Treatment

Waste and biomass processing plants generate complex air emissions associated with organic material handling, thermal treatment and biological degradation processes. These emissions often contain odorous compounds, ammonia, hydrogen sulphide and organic vapours whose concentration can vary significantly depending on feedstock composition and process conditions.

The case studies in this category present industrial air pollution and odour control systems designed for waste treatment facilities, biomass processing plants and organic material valorisation processes. Each project illustrates how scrubber architecture and gas treatment technologies must be adapted to highly variable emission profiles typical of these applications.

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    Industrial Biotrickling Filter Odour Control System

    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.

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    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.

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    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.

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    Air Treatment System for Sludge Dryer Emissions – WWTP Application

    Technical Summary

    Application: Sludge drying
    Industrial sector: Wastewater treatment
    Air flow rate: 6,000 Nm³/h
    Air characteristics:     humid process air
    Main pollutants: H₂S, ammonia, sulfur compounds, VOCs
    Treatment lines: 2

    This sludge dryer odour control system is designed for wastewater treatment plants handling complex industrial emissions.

    Project Overview

    Sludge drying processes used in wastewater treatment plants generate complex gaseous emissions containing hydrogen sulfide, ammonia and various odorous organic compounds released during thermal treatment of sewage sludge.
    For the sludge drying units, two dedicated air treatment systems were engineered and installed to ensure reliable odour abatement.
    Each system was designed to treat process air extracted directly from the sludge dryer and combines multiple treatment stages to address the complex chemical composition of the emission stream.

    Engineering Challenges


    Air emissions generated by sludge dryers present several challenges for air pollution control systems:

    • variable pollutant composition
    • high humidity and condensable vapours
    • presence of aerosols and fine droplets
    • coexistence of sulfur compounds, nitrogen compounds, VOCs and dust

    These conditions require a multi-technology treatment approach, capable of handling different pollutant classes within the same emission stream.

    Sludge dryer odour control System Configuration

    Each treatment line integrates several sequential technologies.

    Venturi Scrubber + Packed Column

    The first treatment stage consists of a wet scrubber system composed of a Venturi section followed by a packed column.
    The Venturi section improves gas–liquid contact and promotes removal of dust and soluble compounds.
    The packed column increases gas–liquid contact time and allows efficient absorption of odorous pollutants.
    Main design parameters:

    • Air flow rate: 6,000 Nm³/h
    • Pressure drop: < 1,500 Pa
    • Contact time: 2 s
    • Column diameter: up to 2,000 mm
    • Column height: up to 7.5 m
    • Construction material: polypropylene
    industrial sludge dryer odour control system in wastewater treatment plant

    Biofiltration Stage

    Downstream of the chemical scrubber, the air stream is treated through a biofilter designed to biologically oxidize residual odorous compounds.
    The biofilter uses wood chips as filtering media, providing a suitable environment for microbial populations capable of degrading sulfur compounds.

    Main characteristics:

    • Filter media volume: 75 m³
    • Media type: wood chips
    • Moisture range: 55–85 %
    Biofiltration stage used for odour control of sludge dryer emissions in a wastewater treatment plant.

    Air Conditioning System

    To maintain optimal operating conditions for the biofilter, the system includes an air conditioning section with electric heating.
    This stage stabilizes temperature and humidity before biological treatment.

    Air conditioning stage installed upstream of the biofilter for treatment of sludge dryer emissions in a wastewater treatment plant.

    Activated Carbon Polishing Filters

    The final stage consists of activated carbon adsorption filters designed to remove trace pollutants remaining after biological treatment.
    Each filter contains approximately 2,500 kg of activated carbon, complemented by impregnated alumina for enhanced removal of sulfur compounds.

    Results

    The sludge dryer odour control system ensures stable performance and reliable odour abatement over time.

    The installed systems provide stable treatment of emissions generated by sludge drying operations, ensuring reliable odour abatement and compliance with environmental regulations.

    The integration of chemical scrubbing, biofiltration and adsorption allows progressive removal of pollutants with different chemical properties, increasing operational robustness.