How Rainer Schuhmann and Anke Ehbrecht reclaim an indispensable finite resource.
What do milk, wine and sausage have in common with fertilizer and sewage sludge? Among others, they share one thing: phosphorus. The chemical element P is a finite resource, much like petroleum. If it runs out, the consequences could be even worse than when oil wells dry up. Since phosphorus is essential to plant, animal and human organisms, and there are no alternative ways to replace it, the end of resources would potentially not only lead to wars - ultimately, it could bring life on Earth to a halt.
"We can't create new deposits, and we can't create phosphorus in the lab. Our chance is recycling," says Schuhmann, a KIT researcher. Phosphorus, mainly in the form of phosphates, is found in many products. "Large amounts of phosphate are found in foods such as dairy products, wine, meat products, but especially in field products," explains geoecologist Anke Ehbrecht. People take in this phosphate through food intake, but do not utilize the complete proportion in the organism.
"Innovation is about making a small contribution to saving the world."
The rest ends up where no one even considers recycling: in the wastewater treatment plant. "Wastewater contains lots of phosphorus, which we can recover and use as fertilizer. At the moment, a large part of it is lost," says Schuhmann.
Germany imports 100 percent of the raw phosphate it needs because there are no usable resources in the country. In total, this amounts to more than 100,000 metric tons per year, the majority of which is used in fertilizers. The price of raw phosphates has already risen many times over in the past ten years. "The less phosphorus there will be, the more we will feel the dependence on phosphorus exporting countries, such as China," Schuhmann points out.
Since 2007, he and his colleague have been working on the further development of a technology to recover phosphorus from wastewater which would allow about ten percent of the phosphorus imported into Germany to be reused. Calcium silicate hydrates (CSH) separate phosphates dissolved in wastewater in an intermediate reaction step. CSH is mainly used for the production of building materials - a comparatively inexpensive mass product. When this mineral material is brought into contact with wastewater, the dissolved P crystallizes as a phosphate mineralam CSH. The end product can be used as a fertilizer without further treatment.
In 2011, plant manufacturer Alltech GmbH from Weingarten in Baden-Württemberg recognized the potential of KIT's patented technology. KIT and the medium-sized company are now jointly developing systems that can be installed in existing wastewater treatment plants. The project offers municipalities the chance to make an economical start in phosphorus recovery.
The city Neuburg an der Donau has seized the opportunity. Paul Leikam, head of the Neuburg Wastewater Disposal and Flood Control Department, explains why: "The sewage sludge from our plant is incinerated in the cement plant, with thermal and material recycling taking place in accordance with the principles of closed-loop recycling management. The non-combustible, mineral components of the sewage sludge are needed for cement production and are firmly integrated into the cement clinker. The phosphorus it contains is not needed for this purpose, but is thus lost forever. This gave rise to the idea of setting up a phosphorus recycling project together with a scientific partner. The results so far give us hope that we will be able to integrate a recovery plant permanently into the plant in the future and thus create a new source of income. If these good results are confirmed, large-scale implementation would be conceivable from mid-2014."
The prototype process works, and now the task is to develop plants for a wide range of applications and focus on broad use: "There are not only different wastewater qualities - from municipal to agricultural wastewater - from which phosphorus can be recovered. The production processes for many foodstuffs also produce quantities of phosphate that make recycling worthwhile," say Rainer Schuhmann and Anke Ehbrecht. The two have made rethinking this a personal mission: "Phosphorus recycling is vital for generations to come. That's why our research should not remain gray theory, but in its implementation make a contribution to preserving the basis of life for future generations."