… an excursion to Stadtentwässerung Dresden.
CIPSEM course participants usually look forward to excursions because they provide more visual and practical learning which goes beyond the theoretical knowledge transfer that happens in the seminar room. However, prior to departure for this excursion to the Wastewater Treatment Plant (WWTP), EM-42 participants had mixed feelings as they feared stench from the plant while also excitedly anticipating the adventure of seeing the WWTP function in real time.
It was one of the beautiful days in Dresden with the sun shining brightly and a warm weather. Some participants dressed up in their least favorite clothes while some took “stench mitigation weapons” like tangerine to protect against the anticipated “sweet smelling” odor of the WWTP. On arrival at Stadtentwässerung Dresden, Mr. Sebastian, Public Relations Officer at the facility, highlighted some of the basic rules of the facility like no touching of barriers, no eating and drinking, wash hands at exit, etc. Additionally, it was learnt that this WWTP began its operation in 1910 and sits on 23 hectares of land. More interestingly, sewers used in the last century, dating back to 1888 were on display and are clearly different with open sewer systems whereas the 1900s had closed sewer systems, perhaps this could be described as evolution of the sewers! Interesting points to note, the plant was automated since 100 years ago and the distance of the sewerage is about 1800 km. The WWTP collects about 160000m3 of wastewater per day in addition to rain water because it is a combined system.
The first step of the facility was shown, that is Neustadter Kanal, where the waste water flows in from the sewerage system of Dresden city. The next step, which is the mechanical treatment involved screening large objects like plastics, tissue towels, etc. in a series rack. At this point, the intensity of the stench was so strong that participants made “eew” sounds, many adopted the weapon of stench mitigation approach, while some covered their nose with one hand and at the same time, took pictures with the other (there was no giving up!). But then, the faeces should not be accused here because as revealed, it is the fats that stink the most! It was really interesting to see the screening bars working and being fully automated, no workers were seen. Furthermore, the channel where dense material such as sand or broken glass settles are removed through suction to prevent wear and tear of mechanical parts of the WWTP and a series of water distribution pumps of varying capacities were also sighted. After that was the primary sedimentation tanks where the suspended materials are removed using gravity. The denser sediments sink while the lighter ones like oils floats on the water. Also, the sludge at bottom of the sedimentation tanks and the floating scum are scraped and pumped into the anaerobic digesters for secondary wastewater treatment.
The next phase of the excursion involved learning about the biological treatment of wastewater through the activated sludge process. The reactors are the first step and here the participants met the Very Important Persons (VIPs) of this process who are also the most hardworking entities. They are called microorganisms! These nice bugs (mostly bacteria) were kept aerated with sufficient oxygen needed to breakdown organic matter (i.e. ammonia) in wastewater to nitrates. This aerobic process called nitrification produces nitrates rich water that could pollute water bodies if discharged without removal of the excess nitrates. Following this step was the denitrification process in which nitrates are reduced to gaseous nitrogen by facultative anaerobes like fungi in anoxic conditions.
From the biological treatment (both aerobic and anaerobic), the treated water is circulated to aeration tanks and then to the clarifier tanks. Remarkably, anaerobic digesters were sighted at a distance in the facility where sludge is channeled for biogas production which feeds into electricity generators. It was very impressive to learn that Stadtentwässerung Dresden generates 80% of its energy demand from renewable resources. Specifically, about 18000 MWh was said to be from the digestion towers. At the final clarifiers, the treated water is discharged into the Elbe river at a rate of 120000 m3 per day where discharging pipe is fitted with turbine that generates about 680 MWh of electricity. The highpoint of the day was the sighting of solar panels in the facility that generates about 160 MWh annually. At this point, participants totally forgot about the oozing stench of fresh wastewater and it was all about different postures for pictures – interessant!
The benefits of a WWTP cannot be overemphasized because, hygiene is very important to every citizen as well as; water resources protection and flood protection. Moreover, discharging untreated waste water into urban lakes or rivers would have detrimental effects, not only on the environment but also on the living organisms. Amidst the fears of odor from the WWTP, the participants gained practical knowledge that could be applied in their home countries. Hence, it was mission accomplished!
The entire EM42-fellows were grateful for the opportunity to visit a WWTP and this appreciation goes to Mr. Sebastian (Stadtentwässerung Dresden), Prof. Dr. P. Krebs (Institute for Urban Water Management, TU-Dresden) Mr. Roman Kiesshauer and all CIPSEM staff team, UNEP, UNESCO & BMU for all the support granted for a successful excursion to the treatment plant. The “sweet smelling odor” was not so bad after all. In fact, it was worth it!
by Ms. Iquo Offiong (Nigeria)
UNEP/UNESCO/BMUV course program 