Environmental technology: Sewer filters allow Hockenheimer to breathe a sigh of relief

Located in the Upper Rhine lowlands, Hockenheim is worth a visit not only because of the racetrack and fantastic nature. But residents looked down their noses recently because the smell of sewers dampened their mood. The city took the initiative: A solution was found within a very short time.

The civil engineering department drew attention to the situation early on: The dirt in municipal and commercial wastewater led to unpleasant vapors from the sewage system, especially during warm months. When residents also complained to the municipal council parliamentary group, the measure was full. “We had to act,” remembers Reiner Lenz.

Service life and heat

His civil engineering department knew the cause of the disaster. “Organic compounds with sulfur, nitrogen, oxygen and hydrocarbons form a cocktail that leads to emissions after just a short stay in the sewer,” says Lenz. The temperature in the channel is relevant: the higher, the greater the effect. Inorganic substances such as ammonia and hydrogen sulphide would be particularly noticeable. “They give off the typical sewage smell.”

It was known from other municipalities that they had already experimented with activated carbon filters in the shaft inlets. There are differences in nature and effectiveness depending on the technical approach. Lenz and his colleagues became knowledgeable early on. “For necessary reasons, but also for testing, we purchased several COLASI filters four years ago,” says Lenz. They were used in the shaft inlets and side road entrances on Landauer Straße. “We have had good experiences with this.” Since then, there have been no more complaints.

mats with organic organisms

For the current problem in the larger area around Karlsruher Straße, a need of around 60 assignments has been identified. Coasli was used again not only because of the good filter effect. Ulrich Bethge from the manufacturer explains what makes the system so special.

“The highlight is the natural microorganisms,” Bethge reveals. “They metabolize the most common odour generators.” The cultures come from our own laboratory. “They eat up the stench.” As a result, these filters work biologically, but not exclusively: Two additional stages are installed, which filter mechanically and chemically. The activated carbon insert is important. The porous, fine-pored carbon acts catalytically and thus neutralizes many odorous components. “With these filters, we achieve virtually complete odour retention.”

The manufacturer calls its approach triple hybrid filtering. The process is also used in large plants such as municipal sewage treatment plants or in industry.

“Preventive maintenance”

Lenz and his colleagues carry out the installation in the sewer themselves. The estimated time is around ten minutes per piece. It is even faster to change the filter mats once they have reached their lifespan. “We expect downtimes of up to three years,” says Bethge, referring to the individual operating conditions. The filters are neither human, plant nor animal pathogens and are therefore harmless to health. Filter mats are easier to handle than tablets such as in other systems. “On top of that, warehousing is easier,” adds Lenz.

The department also sees filters as a contribution to cost savings. Depending on the type, odorous substances can permanently damage sewer structures and technical systems. The reason for this is microbacterially induced corrosion (MIC) caused by hydrogen sulphide, which often requires expensive renovations. The filters therefore not only act as an odour killer, but also as a comparatively inexpensive measure for preventive maintenance.

Info box:

Complaints about bad odors from sewers should not “blow the wind” to authorities and companies. People quickly feel annoyed by stench. At state offices, stench is by far one of the most common reasons for complaint. As a rule, the complainants do not come to terms with the situation. Because an unpleasant smell is a warning sign that causes anxiety, anger and stress. This is deeply rooted in human evolution. Thus, anyone who causes stench is the immediate focus of criticism. Not every smell is a problem. In open land, for example, the reasonable threshold is higher than in residential areas. The hours of smell per year are considered. 15 percent can be considered tolerable. Individual reports are decisive. Smell is usually a mixture of gaseous substances. These are caused, for example, by heating, rotting, and fermentation. Only highly volatile, water-soluble and fat-soluble substances register human odour cells. Interactions are problematic, also depending on temperature, air pressure and light. According to current knowledge, most odors are not considered harmful to health.

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