Aerobic biological processes

Activated Sludge Tank:

Aerobic wastewater treatment in an activated sludge tank is the most widely used method in wastewater purification and has been a proven technology for decades.

In this process, organic and chemical pollutants in the wastewater (such as BOD, COD, nitrogen, and phosphorus) are broken down through aerobic biological processes. Various microorganisms—which require elemental or chemically bound oxygen for their oxidative metabolism—aggregate into sludge flocs, converting the unwanted pollutants in the water into CO₂ and additional biomass.

The benefits for our customers include:

• high process reliability,
• simple, low-maintenance process engineering,
• low investment and operating costs,
• precise control and adjustment of the purification process to accommodate fluctuating influent values.

 

SBR (Sequencing Batch Reactor):

An SBR is an activated sludge tank that is filled on a discontinuous (batch) basis. All biological purification processes—such as aeration, mixing, and secondary clarification—take place within a single tank.

The process can be divided into five sequential stages:

• Filling: The reactor is filled with wastewater and the substrate to be broken down. Aeration/mixing may already take place during this phase.
• Aeration/Mixing: The biomass present in the reactor breaks down the wastewater constituents, primarily organic matter. Carbon and nitrogen removal can occur through mixing alone. If necessary, iron salts are added to precipitate phosphorus.
• Settling: The biomass is separated from the wastewater through sedimentation within the same tank. An additional secondary clarifier is not required.
• Effluent withdrawal: The treated wastewater, which collects at the surface, is drawn off to create capacity for the next filling cycle.
• Idle/Sludge removal: There may be periods of inactivity, particularly when multiple SBRs (Sequencing Batch Reactors) are connected in series. During these intervals, excess sludge, for example, can be removed from the tank.

This is a robust, stable, and easy-to-operate process.

 

Biological Phosphorus Removal:

Phosphorus is an essential element for cell growth. Phosphorus accounts for approximately one percent of the dry mass of bacteria. Certain microorganisms are capable of storing phosphorus within their cells in the form of polyphosphates, allowing them to reach a phosphorus content of up to 7% of their dry mass. By utilizing a system that promotes the growth of these "polyphosphate-accumulating organisms" (PAOs), a significant portion of the phosphorus present in the wastewater can be removed.

 

Nitrification and Denitrification:

Like phosphorus, nitrogen is required by all living organisms for cell growth. In nature, the nitrogen available to organisms is often a limiting factor. To prevent over-fertilization (eutrophication) and the associated uncontrolled algal growth in the receiving water body, specific nitrogen concentration limits must be maintained in the treated wastewater. Under high loading conditions, targeted biological nitrogen removal can be advantageous. This process consists of two separate biological stages: nitrification and denitrification.

Most of the nitrogen present in wastewater enters the treatment plant either as ammonium (NH₄⁺) or bound within organic matter. During nitrification, this nitrogen is converted into nitrate (NO₃) under aerobic conditions. The nitrate produced during nitrification can then be converted into gaseous nitrogen (N₂) through an anoxic process (in the absence of dissolved oxygen).

Nitrogen is removed from the wastewater either via excess sludge or as a gas, enabling compliance with even stringent requirements for the treated effluent.

Over the years, many different methods have been developed to combine these two treatment stages. Biological nitrogen reduction can be carried out in one or more activated sludge tanks or SBR (sequencing batch reactor) units.

 

MBBR (Moving Bed Biofilm Reactor):

In the MBBR (Moving Bed Biofilm Reactor) process, active biomass adheres to plastic carrier elements (media) located within the bioreactor. The high specific surface area of ​​these plastic elements—ranging from 300 to 5,500 m²/m³—allows for a high density of active biomass, which in turn enables smaller tank volumes. The plastic carriers are kept in suspension using aerators or agitators to ensure optimal contact between the biomass and the substrate. The long sludge age facilitates targeted nitrogen removal. The resulting excess sludge is discharged from the bioreactor.