Sewage sludge is waste – but waste with potential. It is produced during the wastewater purification process and contains not only harmful substances but also many valuable nutrients and humic substances. In practice, however, sewage sludge often becomes a problem: approximately 10 million metric tons are produced in Germany each year, and disposal is expensive and requires a great deal of energy. So why dispose of it when we can tap its potential? This is what the Düsseldorf-based company TerraNova Energy asked itself – and developed a method to make the most of sewage sludge. The sludge is heated to 200 degrees in a heat exchanger and then placed in a kind of pressure cooker along with a catalyst. It is then cooled, dewatered in a press, and turned into a coal-like fuel. The process only takes a few hours. In contrast to the fossil fuel coal, the coal produced in this way is regenerative, as it is made from the “renewable” raw material sewage sludge. This reduces CO2 emissions. The separated filtrate, which contains valuable plant nutrients such as phosphorus and nitrogen, also makes a nutrient-rich liquid fertilizer.
Gain energy, use nutrients
Hydrothermal carbonization (HTC) is the name of the process, which chemist Friedrich Bergius experimented with as far back as 1913. He was awarded the 1931 Nobel Prize in Chemistry for his work. Around ten years ago, Professor Markus Antonietti, head of the Max Planck Institute of Colloids and Interfaces, modernized the method and brought about its renaissance. TerraNova Energy has harnessed the potential of HTC to develop a new process. Compared to other technologies for sewage sludge disposal, HTC requires 70% less energy, reduces the operating costs of the sewage treatment plant, and produces a carbon-neutral fuel, as well as recovering the phosphorus contained in the sewage sludge for further use. This idea for the active protection of the environment and resources brought the company the 2015 Innovationspreis der Deutschen Wirtschaft (Innovation Award of German Industry).
(Header image: Marco Becker – Fotolia.com, in the article: antic – Fotolia.com)
