Water purification and bioreactor concepts

Biological processes make use of the self-cleaning properties of the ecosystems in which organisms prevail that can break down the existing substrates most efficiently. The precondition for this is that the substrates are, as a matter of principle, biodegradable. By using technical processes for biomass retention, these natural processes can take place highly intensively and in a very small space.

The Fraunhofer IGB has developed various bioreactors for wastewater treatment, for example anaerobic and aerobic loop reactors (gaslift / airlift reactors), membrane bioreactors or a fixed-bed circulation reactor in which the particle bed is periodically recirculated. Fixed-bed reactors are used in anaerobic technology to retain and thus enrich the active biomass that can become immobilized on and between the particles. On the Fraunhofer IGB fixed-bed circulation reactor the fixed bed is partially recirculated at certain times, thus permitting trouble-free operation on a sustained basis.

We select suitable bioreactors and the corresponding process concepts on the basis of the specific wastewater requirements and the intended reutilization, and we adapt them to regional, climatic and cultural conditions.

Anaerobic wastewater purification processes are especially suitable for treating wastewater with a high biological oxygen demand (BOD₅) found, for example, in the food and beverages industries, in slaughterhouses and also at airports (de-icing agents). Larger companies often run their own biological treatment plants. These are usually aerobic and have several disadvantages such as high power requirements for aeration and mixing, a common lack of nutrients (N and P) and the generation of large quantities of sewage sludge, which is expensive to dispose of.

Modern anaerobic technology is much more economical and has already been tested with several partners. The advantages are that the biogas formed can be used energetically and the amount of sludge is reduced by a factor of ten.

A small growth of biomass is characteristic of anaerobic conversion as the majority of the energy contained in the wastewater components can pass straight over into the final product i.e. methane. If turnover rates are to be increased, the active biomass must therefore be retained in the reactor for concentration. Three principal methods are available for this: use of a microbial sludge with good sedimentation properties in appropriate reactors (upflow anaerobic sludge blanket), immobilization of the biomass on a carrier material in a fixed-bed or fluidized-bed reactor (biofilm processes) or mechanical biomass retention in a membrane reactor.

Fraunhofer IGB has various types and sizes of reactors for examining the anaerobic purification of wastewater samples. The first step here is an analysis of the degradability of the specific wastewater based on the procedure in DIN EN ISO 11734 “Complete anaerobic biodegradability in digested sludge” and DIN 38414 “Sludge and sediments”, Part 8 “Determining degradation behavior”. Once a process has been optimized on a semi-technical scale in our biotechnical pilot plant, the scale-up is carried out on-site for our customers.

Fixed-bed circulation reactor for wastewater treatment

A fixed-bed circulation reactor has been developed in which the fixed bed is partially recirculated from time to time. This allows continuous, trouble-free operation.

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Our rotating disk filter efficiently controls the thickness of the particle layer formed during filtration by rotation of its filter disks. Hereby, the filter opens up new applications for membrane filtration such as industrial and municipal wastewater treatment.

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