Biologycal Treatment of wastewater

Anaerobic biological cleaning of wastewater with UASB process

The RAFA (upflow anaerobic sludge blanket – UASB) reactor method is frequently used for the biological treatment of industrial wastewater. With this process, large amounts of organic substances, such as dissolved sugars, proteins and fats, can also be removed from the wastewater.

These are chemically treated in a special reactor in the absence of atmospheric oxygen by microorganisms, transforming them into biogas. Biogas is a gas mixture that contains mainly methane and carbon dioxide. It can be used as an energy source in production; This generally generates power and heat in a cogeneration plant.

This special version of a biogas plant is mainly used for wastewater treatment in the food and beverage industry, citrus fruit production industry. and in the manufacture of paper and cellulose.

Aerobic biological processes for wastewater treatment

Wastewater cleaning with the MBBR process

The moving bed biofilm reactor (MBBR) process is a technology for the biological treatment of wastewater in which the necessary microorganisms grow as biofilm on a support material.

With the settlement of microorganisms on the surfaces of the filling medium, a large effective surface is generated. The aeration of the reactor ensures that the fluid is permanently mixed and thus sufficient contact of the substances in the waste water with the microorganisms is generated. It is also possible to apply the moving bed process with biofilm anaerobically; in this case, the mixing is carried out with the aid of pumps or with a stirrer.

Both the dominant transverse forces in the bioreactor and the substances in the wastewater influence the thickness and composition of the biofilm on the support material: the higher the content of organic substances in the wastewater, the faster the biofilm will grow.

Advantages of the MBBR process over the activated sludge process

Activated sludge processes have the disadvantage that, by removing the excess sludge, a part of the microorganisms that are in suspension is also removed. Despite the return of the recirculation sludge from the decanter, the microorganisms reach a relatively young age.

In the MBBR process, the microorganisms immobilized on the supports have a substantially longer life. In this way, microorganisms are established in the biofilm that have specialized in difficultly degradable compounds and that have very long generation times. In general, the cleaning process is more stable than activated sludge processes and peak loads can be collected better.

DAS Environmental Expert GmbH uses a support material that has an extremely high specific surface area and thus makes MBBR bioreactors particularly compact. The shape of the filling materials further prevents the support material from blocking, thus achieving a high capacity for continuous space degradation.

Our MBBR plants can be designed as a compact plant or as modular bioreactors. Modular reactors require much less space than conventional activated sludge plants. No excavations or underground works are required. With the corresponding technical process design, our MBBR plant can be built and operated as a denitrification reactor.

Reduced amount of excess sludge in the biofilm process

As in any biological process to degrade organic carbon compounds, an excess of sludge is also generated in the MBBR. In the biofilm process, the quantity is biologically conditioned, but it is clearly lower than in an activated sludge process of equal capacity. However, the already clean wastewater must be separated from the generated sludge after treatment in the MBBR. This can be done for example by sedimentation in a settling tank. In the case of an indirect discharge in another treatment plant, it is possible to evaluate the elimination of a sludge separation, if the capacity and design of the treatment plant allow it and if it can be ruled out that there are unwanted sedimentation processes in the path of transport.

Biological wastewater treatment with the membrane bioreactor (MBR)

The membrane bioreactor (MBR) can also be used for the oxidation and nitrification of organic substances in wastewater. The degradation of toxic substances takes place in this case in a bioventilation tank with a high concentration of sludge.

The separation of the purified water and the activated sludge is carried out by ultrafiltration with the help of the membranes of this reactor. Such a membrane filter module can also be integrated submerged into existing biological treatment phases; however, a separate reactor can be more easily maintained.

The MBR process is ideal for the biological treatment of highly polluted industrial wastewater. In addition, it is often used also for the subsequent clarification of domestic and communal wastewater and for the treatment of gray, rain and surface water.

Due to the small size of the membrane pores, bacteria and viruses cannot pass the membrane filter, so it retains germs. The quality of the water in the purification process thus complies with the EU Bathing Water Directive. Thanks to their compact shape, MBR plants can be designed in a modular way as a container, thus constituting a completely mobile solution. This makes them particularly suitable for limited time use.

Biological cleaning of wastewater with the bacterial bed reactor

In wastewater treatment with a trickle flow reactor (TFR), wastewater is sprayed onto a fixed bed. This consists of a very light fine-grained support material, which after a few days (depending on the respective conditions) grows with a highly active mixed population.

The water flows continuously from top to bottom through the filling material; conversely, the ambient air is supplied to the plant by a fan. Since the load of the support material is not within a closed body of water, little pressure is needed for this. Thus, in the case of TFR technology, a sufficient oxygen supply for microorganisms can be obtained with very little effort. Fully automatic regeneration takes place at regular intervals through which the mixed microbial population is rejuvenated and excess biomass is washed out of the system without causing a loss in yield. Fine sludge can continue to be drained and, depending on site conditions, can be taken to composting or soil conditioning facilities.

Biological wastewater treatment with the SBR process

Sequential biological cleaning (Sequenced Batch Reactor – SBR) is an activated sludge technology for the treatment of wastewater in two separate parts of the plant. A primary settling is first used for the mechanical retention of coarse substances. This also serves as a collecting tank from which the contaminated wastewater is transported to an activation and settling tank called the SBR tank.

There, the incoming wastewater is cleaned in a cyclical process. For this, activated sludge is used, which contains a large number of microorganisms that eliminate organic substances from the wastewater. To ensure good mixing and oxygen supply, the waste water is stirred at regular intervals by supplying air.

This aeration phase is followed by a resting phase without aeration. In this, the activated sludge is deposited on the floor of the facility. On the contrary, in the upper part of the SBR tank a zone of purified water is formed. From this area, the treated wastewater is extracted and led to a drainage channel or an infiltration plant. The excess sludge is removed from the reactor floor by means of pumps. This is sent back to the primary settling. Then the cleaning process starts again.


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