Sewage treatment plants need precipitants to remove phosphates from wastewater. Because their production requires a lot of energy, production stagnates. Some federal states now allow higher limits. This becomes a problem in the spring at the latest.

Many sewage treatment plants in Germany no longer have enough iron and aluminum salts to comply with the strict guidelines for phosphates. The so-called precipitating agents, which bind the phosphates and are disposed of with the sewage sludge, are normally a by-product of the production of hydrochloric acid. This production, in turn, falters. There are two reasons for this: Firstly, the production of hydrochloric acid is energy-intensive and therefore very expensive in times of high electricity and gas prices. Second, there is less demand for products that normally use hydrochloric acid to produce them. These are, for example, paints and varnishes.

In September, every fourth sewage treatment plant reported failures in the delivery of precipitants. Around every second sewage treatment plant is expecting problems in October. This is the result of a survey by the German Association for Water Management, Wastewater and Waste (DWA). Delivery problems do not immediately mean that the precipitants are out of stock. Sewage treatment plants usually have a supply that lasts for several weeks or months.

If there is a lack of precipitants, the operators can no longer bind enough phosphates from the wastewater. The concentration of the substances would increase. The treated water is then discharged into rivers. The phosphates are a problem there because they serve as nutrients for algae, for example. They would then sprout out of control, which in turn would deprive other plants and animals in the water of nutrients and oxygen. Some types of algae also excrete toxins into the water that are harmful to flora and fauna there. If too many phosphates get into the sea, algae carpets can form there, which also block sunlight and thus harm other living beings.

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Such dramatic consequences are not to be expected due to the lack of precipitants in Germany. At the same time, authorities are careful not to discharge too much phosphate from sewage treatment plants into rivers. In at least five federal states – Schleswig-Holstein, Lower Saxony, Mecklenburg-Western Pomerania, North Rhine-Westphalia and Saxony-Anhalt – the environment ministries have issued decrees that have temporarily increased the limit values ​​for phosphates. In most cases, however, sewage treatment plants have to prove precisely that the higher concentration is absolutely necessary. Higher phosphate concentrations in rivers are possible in winter because algae hardly grow in the cold season anyway. It would be problematic if the emergency continued in the coming spring or even summer.

In order to be prepared by then, there are several options that need to be determined now, depending on the sewage treatment plant. A simple measure would be a cooperation between regional companies in order to optimally distribute the existing precipitants among themselves. If there are still too few available, there are substitutes. One is biological processes in which microbacteria in the water break down the phosphates. However, these need certain environments in the basin, which not every sewage treatment plant can set up. That is why many plant operators also hope that the state will do more to promote alternative hydrochloric acid production.

Since the problem does not only exist in Germany, the situation could also quickly ease up again. Josef Ortner, who supplies around 400 sewage treatment plants with precipitants with his company from Passau, expects an improvement at the end of November or beginning of December at the earliest, as he told the MDR.

An increased phosphate content in rivers would not be a problem for humans. The substances are also usually nutrients for us, which are required for the development of bones and teeth and for acid regulation in the body. However, if sewage treatment plants have to release more phosphates into the environment, you could feel it on your wallet, because the operators have to pay for every milligram of phosphate and would certainly pass on the higher costs to consumers in the form of higher wastewater fees.

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