Outflows of waste water containing heavy metals are a serious hazard to nature. They result from numerous industrial processes for example in the cleaning and coating of metal surfaces in the electroplating industry. Their proper disposal calls for specialist expertise. At the same time, these outflows are of considerable commercial value; the metal salts they contain are therefore recovered. ATEC Dr. Mann GmbH in Obrigheim, in collaboration with the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart, has now developed a process that uses bioadsorbers – adsorbers made from natural biological materials – to bind heavy metals.

Both thermal processes and membrane processes are employed today to filter heavy metals from waste water and return them to the production cycle. The most common method at the present time involves precipitation reactions followed by an adsorption process using synthetic-resin ion exchangers. In the ion exchanger, the metal ions are bound to the resin and replaced by hydrogen ions. When the ion exchanger is saturated, it is regenerated with an acid. The result is a highly concentrated acidic salt solution, which can be further condensed – and an ion exchanger which can be reused. One disadvantage of using synthetic resins as ion exchanger is that they are produced from petroleum, a limited resource.

The new process developed by ATEC and the IGB functions in the same way, but has far greater future promise. It uses bioadsorbers – ion exchangers of regenerative raw materials. Residual products of cereal processing are used instead of synthetic resins. “Our patented process,“ explains Dr. Mann, who founded ATEC just three years ago, “involves doping the bran with phosphate groups, enabling it to bind heavy metals.“ After regeneration with acid, they can be reused a number of times – as can be the purified waste water.

Bioadsorbers are of value in various fields of environmental protection, because sustainable raw materials can be modified in numerous ways. ATEC Dr. Mann GmbH and the IGB are now working on adsorbers capable of removing chlorinated hydrocarbons and humic matter from waste water. These commonly seep, for example, from landfill waste-disposal sites. “Moreover, in many countries bioadsorbers could help to turn water into drinking water,“ adds Günter Mann.