The “sweet smelling” odor of the waste water treatment plant …

… 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.

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Anaerobic digesters sighted in Stadtentwässerung Dresden, WWTP (photo by Ms. Haili Zhou)

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!

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The excursion guide, Mr. Sebastian (left), Mr. Roman Kiesshauer (back) with EM42-Participants at the Stadtentwässerung Dresden WWTP (photo by Ms. Sreymoch Bun)

by Ms. Iquo Offiong (Nigeria)

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(Less than) 50 Shades of Brown

Most likely, this morning some of us went to the bathroom, brushed our teeth, took a bath, and did our things in the toilet, maybe followed by washing the dishes that have been sitting on the sink since last night dinner. Little did we know, the water (or better we call it wastewater) that we used is flushed and drained to a collection pipe. In the case of EM-41 class, our wastewater is collected by sewer pipes in Dresden which has a total length of 1700 km with diameter of up to 2 meters.

These pipes are laying under the roads of Dresden and deliver our wastewater to a specific plant in Kaditz, an area northwest of Dresden. Occupying an area as large as 25 football fields, the plant was constructed in 1910 to treat the wastewater produced by Dresden’s population. Currently, everyday approximately 120.000 m3 of wastewater coming from 700.000 people is reaching the treatment plant. Since Dresden’s wastewater system applies a combined system, the incoming wastewater is collected together with rainwater and treated together in the wastewater treatment plant (WWTP).

To give you some illustration about the smell that we inhaled that afternoon, here is a picture of raw wastewater which just arrived in the WWTP; a dark-brown water.

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Dirty, hence the dark color. Full of organic materials, which could lead to oxygen depletion in the aquatic ecosystems.  Full of microorganisms, which some are harmful to humans, and of course smelly. And these are the shades of brownish colors of the same wastewater during the treatment processes:

More or less 24 hours later, we will receive this not-even-close-to brown water, which is the treated water from the WWTP.

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Almost like clear water, it is still not safe for drinking, but is now safe to be discharged into receiving water bodies, in this case the famous Elbe River. With only 5 mg/l of Biochemical Oxygen Demand (BOD5), and 41 mg/l of Chemical Oxygen Demand (COD), NH4-N of 0,7 mg/l, N total of ±13 mg/l, and P Total of 1 mg/l, this water won’t be a harm to humans and neither to the environment once it is discharged into the river.

How could the wastewater be turned into clear water? The answer is because of several physical, biological, and chemical processes that were taking place in the plant. At first, the wastewater was treated with physical and mechanical treatment with bar screens and grit chamber to remove the trash and to remove sand subsequently from the wastewater. The water then underwent a sedimentation process in which its floating and settle-able solids sink to the bottom of the tank. Afterwards, the water was transported to aeration tanks. In these tanks, air bubbles were introduced to the water to be used by the microorganisms which “eat” the organics. The water then again settled in secondary sedimentation tanks, from which it can then be safely discharged to receiving water bodies.

The sludge coming from the primary and secondary sedimentation tanks was also treated in a series of sludge treatment units. Unfortunately, we did not have the chance to visit all the units, but we could see from afar the two giant egg-shaped anaerobic digestion tanks.

We had fun during the visit, especially since the weather was rather nice today. And since 81% of the energy used is produced by the plant (mainly from anaerobic sludge treatment units and small amount produced by solar systems), we proudly took a picture in between the solar panel systems.

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by Vika Ekalestari (Indonesia)

special credit to Tamara Karp (CIPSEM) for the title idea 😉

Visiting the wastewater treatment plant Dresden-Kaditz

By Liu Haibo, China

Today we visited the wastewater treatment plant Dresden-Kaditz. Although the weather conditions were not beautiful with wind and rain, the EM40 course participants still happily visited the unit. This unit, as the only municipal sewage treatment plant in the area, has a long history but is maintained well and orderly. Although conventional sewage treatment technology is used, the plant is unique in its design / operation and management. Moreover the processing indicators can meet the management requirements.

Photos: T. Karp / Liu Haibo

Mr. Lucke, the head of the environmental analysis laboratory at the wastewater treatment plant, guided us along the treatment process, and explained the different treatment steps from inflow to coarse and fine screens to the different clarification tanks and sludge treatment. Seeing the huge groundwater pipes, we could feel our gap with Germany not only on the ground, more perhaps we can not see the place. During the visit, the participants were able to ask questions about the treatment process, the rainwater impact,and so on.