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Secondary Treatment

Advanced separation and biological processes that remove dissolved and suspended organic matter, nutrients, and contaminants. The core of every wastewater treatment plant where BOD, COD, and nutrient targets are achieved.

The Heart of Wastewater Treatment

Removing dissolved organics, nutrients, and suspended contaminants

Secondary treatment transforms raw effluent into environmentally safe discharge through a combination of physical separation, biological oxidation, and chemical conditioning. Reynolds & Bauhm engineers each secondary stage as part of an integrated treatment train, ensuring that upstream and downstream processes work in harmony to achieve compliance targets consistently.

DAF Flotation

Dissolved air flotation removes fats, oils, grease, and light suspended solids by attaching micro-bubbles to particles and floating them to the surface for skimming.

Biological Reactors

MBBR, SBR, and activated sludge systems use microbial communities to oxidise organic matter, convert ammonia to nitrate, and remove phosphorus through enhanced biological uptake.

Chemical Treatment

Coagulation, flocculation, and chemical precipitation condition wastewater for solids separation and remove specific contaminants such as phosphorus, heavy metals, and colour.

Dissolved Air Flotation Systems

Superior separation for FOG, TSS, and light solids

How DAF Works

Dissolved air flotation generates micro-bubbles by saturating a recycle stream with air under pressure, then releasing it into the influent. These bubbles attach to suspended particles and oil droplets, reducing their effective density and causing them to rise to the surface where they are removed by a skimming mechanism.

CFD-optimised hydraulics for uniform bubble distribution
Adjustable air dissolution for varying influent quality
Integrated chemical dosing for coagulation and flocculation
Automated sludge scraping and collection
Skimmings thickening for reduced disposal requirement
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DAF flotation unit

Standard DAF Units

Rectangular and circular DAF units for flows from 5 to 500 m³/hr. Stainless steel construction with integral chemical mixing, reaction, and separation zones.

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DAF with Lamella Packs

Space-constrained DAF units with integrated inclined plate settlers for enhanced solids removal in a compact footprint. Ideal for retrofit applications.

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High-Rate DAF

High hydraulic loading DAF systems for large flow applications and peak flow management. Designed for municipal and high-volume industrial installations.

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Biological Treatment Systems

MBBR, SBR, and activated sludge for organic and nutrient removal

MBBR Systems

Moving bed biofilm reactors with floating biofilm carriers that provide a high surface area for microbial attachment. No sludge recycle required, compact footprint, and resilient to shock loads. Ideal for industrial applications with variable organic loading.

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SBR Systems

Sequencing batch reactors that perform aeration, settling, and decanting in a single tank. Flexible operation with programmable cycles for fill, react, settle, and draw phases. Excellent for small to medium flow applications with intermittent operation.

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Activated Sludge

Conventional and extended aeration activated sludge systems with clarifier separation and sludge recycle. Proven technology for municipal and industrial applications with steady-state operation and comprehensive nutrient removal capability.

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UASB & EGSB

Upflow anaerobic sludge blanket and expanded granular sludge bed reactors for high-strength industrial effluents. Generate biogas from organic matter while reducing BOD and COD with minimal energy input.

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Nutrient Removal

Enhanced biological phosphorus and nitrogen removal through alternating anaerobic, anoxic, and aerobic zones. Meet stringent total nitrogen and phosphorus discharge limits without excessive chemical dosing.

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Containerised Biological

Pre-engineered containerised biological treatment plants for rapid deployment to remote sites, temporary applications, and phased plant expansions. Plug-and-play design minimises civil works.

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Chemical Treatment

Coagulation, flocculation, pH correction, and precipitation

Chemical Conditioning

Chemical treatment optimises wastewater for physical separation and removes specific contaminants that biological processes cannot address. Reynolds & Bauhm designs chemical dosing systems with precise polymer preparation, inline mixing, and automated control to achieve consistent conditioning at varying flow and load.

pH neutralisation for acid and alkaline effluents
Coagulant dosing for colloidal solids destabilisation
Flocculant addition for particle aggregation
Phosphorus precipitation with metal salts
Heavy metals precipitation and sulphide removal
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Chemical dosing system

Process Fundamentals & Design

This treatment stage is engineered to achieve specific contaminant removal targets while providing stable, predictable performance across variable inlet conditions. Design parameters are calculated from wastewater characterisation data, regulatory requirements, and site-specific constraints including footprint, energy availability, and operator capability.

Process Optimisation

Design validated by CFD modelling and pilot testing to confirm performance guarantees.

Mechanical Reliability

Equipment selected for 20-year design life with minimal wearing parts and easy access.

Chemical Efficiency

Automated dosing and feedback control minimise reagent consumption and sludge production.

Compliance Assurance

Online monitoring and data logging demonstrate continuous consent compliance.

Design Parameters

Design Flow10 – 5,000 m³/h (application specific)
Inlet VariabilityDesigned for 1:3 peak-to-average flow ratio
Removal Efficiency85 – 99% depending on target contaminant
Hydraulic RetentionCalculated from kinetic constants and safety factors
Power Consumption0.5 – 5.0 kWh/100 m³ (process dependent)
Chemical DoseAuto-controlled based on online analysers
Sludge Production0.2 – 1.5 kg DS/kg contaminant removed
MaterialsSS304, SS316L, or carbon steel with coating

Integration with Treatment Train

No treatment stage operates in isolation. This process is designed to receive conditioned influent from upstream stages and deliver effluent quality suitable for downstream processes. Hydraulic and organic loading rates are balanced across the complete treatment train to prevent bottlenecking and ensure overall plant efficiency. Our engineers model the complete flowsheet to optimise Capital expenditure and Operating expenditure across the plant lifecycle.

Upstream Protection

Screening, equalisation, and pre-treatment protect this stage from damage and overload.

Downstream Conditioning

Effluent quality ensures downstream biology, filtration, or disinfection performs optimally.

Recycle Streams

Reject streams, filtrate, and centrate are routed back to appropriate upstream points.

Related Pages & Equipment

Equipment Catalogue

Browse our full range of water treatment equipment and systems.

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DAF Systems

Dissolved air flotation for solids and oil separation.

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Lamella Clarifiers

High-rate settling for primary and secondary clarification.

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Biological Treatment

Activated sludge, MBBR, and SBR systems for organic removal.

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Sludge Dewatering

Belt press, centrifuge, and screw press dewatering.

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Chemical Dosing

Automated coagulant, flocculant, and pH correction systems.

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Pilot Testing

Validate process performance with on-site pilot trials.

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Speak to Our Engineers

Request a consultation or quotation for your project.

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Aeration & Oxygen Transfer

Aeration accounts for 50–70 % of a biological plant’s electrical Operating expenditure — designing it well is the single largest lifetime saving.

Design Your Secondary Treatment Stage

Speak with our process engineers to determine the optimal combination of DAF, biological, and chemical treatment for your effluent profile and discharge requirements.

Industries We Serve

Our expertise spans multiple industries with sector-specific water treatment solutions.