Dr. Born -
Dr. Ermel
Author:
IBE Dr. Born - Dr. Ermel GmbH
Ingenieurbüro für Verfahrenstechnik
Finienweg 7, 28832 Achim
Germany
Telefon: 04202 / 7 58-0
Telefax: 04202 / 7 58-500 www.born-ermel.de
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3.
3.1.
3.2.
3.3.
4.
4.1.
4.2.
5.
1.
2.
2.1.
2.2.
2.3.
6.
Dr. Born -
Dr. Ermel
Initial situation .......................................................................................... 1
Planning parameters ................................................................................ 3
Amount of wastewater ................................................................................ 3
Pollution of wastewater and concentrations ................................................ 3
Legal demands for discharge ..................................................................... 4
Description of process ............................................................................. 5
Mechanical wastewater treatment .............................................................. 5
Biological wastewater treatment ................................................................. 7
Sewage sludge treatment ........................................................................... 9
Layout plan.............................................................................................. 11
Wastewater treatment ............................................................................... 11
Sewage sludge treatment ......................................................................... 13
Effects to the Environment .................................................................... 14
Summary of operational experiences ................................................... 15
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Dr. Ermel
Picture 1: Layout plan of wastewater treatment plant of Dresden-Kaditz before extension ......................................................................................... 2
Picture 2: Main flow chart of inflow area with reconstruction and extension measures ................................................................................................... 6
Picture 3: Main flow chart of aeration facility with reconstruction and extension measures .................................................................................... 8
Picture 4: Main flow chart of sewage sludge treatment with reconstruction and extension measures ........................................................................... 10
Picture 5: Layout plan of extended biological step .................................................... 11
Picture 6: Isometry of new biological step with control room in front (computer simulation) ................................................................................................ 12
Picture 7: Layout plan of extended sewage sludge treatment ................................... 13
Table 1: Inflow of wastewater at wastewater treatment plant Dresden-Kaditz .......... 3
Table 2: Load of wastewater treatment plant of Dresden- Kaditz
(statistical frequency of 85 %) ..................................................................... 4
Table 3: Legal demands for discharge ..................................................................... 4
Table 4: Summary of operational experiences ....................................................... 15
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Dr. Ermel
The wastewater treatment plant Dresden-Kaditz cleans resulting wastewater from Saxon capital
Dresden as well as wastewater from drug factory and some surrounding municipalities. The actual cleaning capacity is 650,000 PT. After connection of another area of drainage with approx.
90,000 PT the wastewater treatment plant of Dresden-Kaditz will reach a capacity of totally
740,000 PT.
The plant is situated north of the Saxon capital city of Dresden at the banks of the river Elbe. The corresponding layout plan of the facility before start of extension is shown in picture 1. Some parts of the plant date from the year 1910 and serve since then for treatment of wastewater of
Dresden. The historical components for mechanical treatment of wastewater are still existing and still are in operation together with some added new technology. This historical complex of machinery was extended by a biological wastewater treatment step as well as a facility for sewage sludge treatment.
Wastewater of the City of Dresden initially passes mechanical cleaning devices as inflow building, coarse screen, mixed-water reduction, fine screen, grid removal and pumping station at construction area A. This inflow group mainly is situated inside the historical part of the wastewater treatment plant where as well other relevant operational and administrative facilities of the City Draining Department of Dresden are located.
The pre-treated wastewater is led by pumping station of primary sedimentation and biological step consisting of aeration and final sedimentation tanks. In the biological step were as well wastewater of drug factory is introduced biological basic treatment of wastewater takes place prior to discharge into the river Elbe.
Treatment of sewage sludge from primary sedimentation and biological step takes place at construction area B. Treatment of sewage sludge comprises static thickening, thickening by machine and subsequent drying of sludge.
The wastewater treatment plant of Dresden-Kaditz actually does not meet the legal requirements of wastewater treatment and therefore needs to be reconstructed as well as extended. In focus of construction measures are new construction of a combined sewage overflow tank for storm water treatment, extension of the biological step as well as new construction of digesters for sewage sludge treatment.
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Dr. Born -
Dr. Ermel
Wastewater treatment plant Dresden-Kaditz
Sewage sludge treatment
Extension of biological step
Extension of control room
Existing biological step
Existing primary sedimentation
Mechanical coarse cleaning within historical area
Entrance area
Picture 1: Layout plan of wastewater treatment plant of Dresden-Kaditz before extension
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Dr. Ermel
2.1. Amount of wastewater
The catchment area of the wastewater treatment plant of Dresden-Kaditz is drained in mixed system. The mixed system is characterized by drain off of wastewater as well as storm water from paved areas in case of rain in a common sewerage system. Inside the wastewater treatment plant the wastewater is cleaned completely in case of dry weather conditions. During rainy conditions wastewater is cleaned up to a defined reduced discharge. Additional amount of combined water is separated in the sewer system as well as inside the wastewater treatment plant.
In future the main part of separated combined water should be treated mechanically in the combined sewage overflow tank before being discharged to the river Elbe. Planning parameters for the amount of wastewater are described in following table 1:
Amount of wastewater inflow wastewater treatment plant
Inflow (dry weather conditions)
Inflow (dry weather)
Top inflow (dry weather)
Top inflow (rain weather conditions)
Top inflow combined water
Reduced inflow wastewater treatment
Separated combined water, max.
Q
Q
Q
Q
Q t dt max m ab
Parameter
156,000 m³/d
2.2 m³/s
19.0 m³/s
4.0 m³/s
15.0 m³/s
Table 1: Inflow of wastewater at wastewater treatment plant Dresden-Kaditz
2.2. Pollution of wastewater and concentrations
For determination of real pollution of wastewater at Dresden extended measurements and data investigation have been done. Based on the results a prognosis of future pollution of wastewater was elaborated. Forecasted pollution and concentrations are shown in table 2. A specific CODload per inhabitant of 120 g COD/(inhabitant*day) results in a capacity of 740,000 PT for the wastewater treatment plant of Dresden-Kaditz.
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Dr. Ermel
Parameter Load Concentration *
Inflow primary sedimentation
Chemical Oxygen Demand
Total solids
Total Nitrogen
Total Phosphorous
COD
DS
N tot
P tot
Inflow biological step incl. wastewater of drug factory
Chemical Oxygen Demand COD
88,900 kg/d
53,900 kg/d
8,500 kg/d
1,170 kg/d
570 mg/l
345 mg/l
54 mg/l
7.5 mg/l
75,400 kg/d 483 mg/l
Total solids
Total Nitrogen
**
DS
N tot
24,000 kg/d
8,600 kg/d
Total Phosphorous
**
P tot
1,050 kg/d
*related to Qdt = 156,000 m³/d; ** together with nitrogen reload of sewage sludge treatment
154 mg/l
55 mg/l
6.7 mg/l
Table 2: Load of wastewater treatment plant of Dresden- Kaditz (statistical frequency of 85 %)
2.3. Legal demands for discharge
Legal demands on discharge of wastewater are summarized in table 3. The described future discharge limits have to be met during two hours. Compliance with these limits for nitrogen and phosphorous elimination cannot be ensured with the existing high-performance aeration plant.
That is why the entire biological step needs to be extended respectively reconstructed in all main parts.
Parameter Compliance limits
Chemical Oxygen Demand COD 75 mg /l
Biological Oxygen Demand
Ammonia-Nitrogen
Anorganic Nitrogen, total
BOD
5
NH
4
-N
1) anorg.N
tot
1)
15 mg/l
10 mg N/l
13 mg N/l
Phosphorous, total P tot
1 mg N/l
1)
this limit is valid for wastewater temperature of
12 °C and higher within biological reactor of wastewater treatment plant
Table 3: Legal demands for discharge
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Dr. Ermel
In the following the processing concept of wastewater treatment plant of Dresden-Kaditz is described. Additionally the main calculation parameters and estimated operational data is named.
More information about the intended wastewater treatment plant could be retrieved from main flow charts.
3.1. Mechanical wastewater treatment
Total inflow to the wastewater treatment plant, which consists of Neustädter and Altstädter collector, is passing a four-line coarse screen facility for removal of disturbing substances.
Behind the coarse screen an overfall dam is installed with which inflow to wastewater treatment could be reduced to 4 m³/s. As soon as inflow to wastewater treatment plant exceeds reduced inflow, mixed water is separated up to 9 m³/s into the new constructed combined sewage overflow tank. The combined sewage overflow tank with capacity of 24,000 m³ will be operated as an interim storage of mixed water as well as a continuous flow tank in case of complete filling so that filtrate could be hold back. The interim stored mixed water and the filtrate will be supplied back to inflow of biological step in case of dry weather condition.
Behind mixed water reduction building a three-line fine screen is installed with which fine solid material can be removed. Subsequently the wastewater passes a parallel extended grid removal for elimination of sand.
The water level in the screen grid removal facility is below surface of terrain. Prior to supply to higher lying primary sedimentation wastewater is lifted by six tube propeller pumps. Afterwards wastewater is passing primary sedimentation and aeration facility in free fall.
Within the six lines of primary sedimentation facility with useable volume of 4,800 m³ mechanical pre-cleaning of wastewater is achieved by sedimentation of material. It concerns a short time primary sedimentation which enables good desludging. Main part of carbon compounds (COD) remains in the wastewater to achieve good conditions for denitrification of nitrogen and biological elimination of phosphorous in the subsequent aeration. Primary sludge of primary sedimentation is supplied to sewage sludge treatment on construction area B.
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Dr. Ermel
Picture 2: Main flow chart of inflow area with reconstruction and extension measures
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Dr. Ermel
3.2. Biological wastewater treatment
After primary sedimentation mechanically cleaned wastewater together with wastewater from drug factory flows to the biological step which is laid out as a weak loaded aeration facility.
The aeration facility consists of the main components aeration and final sedimentation tanks. In the aeration tank extended contact of wastewater ingredients with aerated sludge takes place which results in reduction of organic load (BOD
5
/COD) as well as nitrification/denitrification. In addition biological elimination of phosphorous occurs there (bio-p) which is completed by chemical precipitation of phosphorous.
In the final sedimentation tanks aerated sludge and cleaned wastewater are separated. Cleaned wastewater is discharged into the river Elbe, aerated sludge is goes back to the aeration tank by return sludge pumping station after separation of excess sludge.
Calculation of the aeration facility mainly is based on results of technical experiments which are performed by the University of Dresden between 1995 and 1997. Results are evaluated and specified by dynamical computer simulation.
Calculation of aeration tanks results in the fact that for secure compliance with legal demands for quality of discharge an aeration volume of approx. 125,000 m³ will be necessary. From this
96,000 m³ have to be ventilated during winter season to ensure complete nitrification. For biological elimination of phosphorous an anaerobic volume of 10,000 m³ is intended.
In the aeration facility a sludge age of 10 to 12 days will be set regarding sludge load up to 0.19 kg COD/(kg DS d). To secure flexible division of nitrification (aerated) and denitrification (not aerated) volume parts of denitrification volume could be varied between 25 and 50 % by switch off of aeration gates. With this processing conception an all-season complete nitrification could be achieved. Performance of denitrification is around 70 % and could be improved by addition of external substrate like ethanol.
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Dr. Ermel
Picture 3: Main flow chart of aeration facility with reconstruction and extension measures
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Dr. Ermel
Maximum oxygen demand of aeration facility is about 3,700 kg O
2
/h in aerated zones under operational conditions and concentration of oxygen of 2 mg O
2
/l . Supply of oxygen is realized by introduction of max. 48,000 Nm³/h of process air by compressors taking into account a depth of 7.5 m of aeration tanks.
Final sedimentation tanks are calculated for maximum inflow of mixed water to biological step during rainy conditions. Sludge index of 120 ml/g results in depth of 4.54 m of final sedimentation tanks with a surface of 10,900 m².
The technical solution is to reuse the existing aeration facility for purpose of biological phosphorous elimination with inserted denitrification
The aerated tanks for nitrification and simultaneous denitrification as well as the six round final sedimentation tanks and central machinery station with switch gear, return sludge and excess sludge pumping station and compressor for production of process air have to be new constructed.
3.3. Sewage sludge treatment
Excess sludge from aeration facility and primary sludge will be thickened by static thickener.
Thickened and mixed sludge together with bio-waste from other sources will be stabilized in digesters, which are operated in mesophile temperature range. It is intended to set up three digesters with total volume of 24,000 m³.
Subsequently stabilzed sludge will be dewatered by machines and afterwards dried thermally.
The dried sewage sludge then will be used as fertilizer for agricultural purposes.
For production of necessary energy for thermal drying of sludge bio-gas is used which is generated during digestion of sludge. Heat from drying facility is used for warming up of sludge prior to digestion and dewatering. All processes of sewage sludge treatment in this way could be operated in an optimized energetic way.
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Dr. Ermel
Picture 4: Main flow chart of sewage sludge treatment with reconstruction and extension measures
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Dr. Ermel
4.1. Wastewater treatment
The arrangement of parts of plant of biological step is shown in the layout plan in picture 5 as well as in the computer animated view in picture 6.
All new parts of the biological step will be erected in the area of the free construction area between existing biological step and dike of the river Elbe. With this conception new construction could be done without any interference of running operation. Chosen arrangement of aeration and final sedimentation tanks is result of optimization of direction of flow. The existing aeration facility will be used as inserted denitrification, distribution and anaerobic step.
Connected are the new aerated tanks of aeration facility.
Final sedimentation tanks (new)
Aeration tanks
(new)
Distributor (new)
Central machinery house (new)
Dosing station
(new)
Discharge building
(new)
Central control room (extension, exisiting)
Picture 5: Layout plan of extended biological step
Aeration tanks
(existing)
Distributor
(reconstruction, exisiting)
Preliminary sedimentation
(exisiting)
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Dr. Ermel
The last step of the wastewater treatment, final sedimentation, will be constructed near the dike of the river Elbe. With this arrangement a clear and obvious main flow direction is defined in direction to the discharge into the river Elbe.
In the centre of the new equipment a machinery house will be arranged. Here all relevant supply installations and pumping stations will be placed for optimal operation. The central location enables in addition optimized short and economical pipelines and flow paths.
Picture 6: Computer animated view of new biological step with control room in front
The centralized control room at existing transformer station 1 will be extended functionally and constructive. Between historical parts of the plant and new biological step all relevant machinery parts of the wastewater plant could be served. In addition the control room will be in the focus as communication, supervision and command centre for wastewater treatment, sewage sludge treatment and sewer system.
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Dr. Ermel
4.2. Sewage sludge treatment
Facilities for extension of sewage sludge treatment will be erected on construction area B north east of the existing sludge treatment complex. The space-saving compact arrangement of new buildings connected free areas in north west and north east direction will be conserved. These will be useable for reception of bio-waste and extension areas for future extension of the plant.
The digesters will be erected in oval shape. Oval tanks combine pleasing optical architecture with operational advantages because of ideal flow design.
Picture 7: Layout plan of extended sewage sludge treatment
Machinery for biowaste (new)
Machinery for fluid sludge (new)
Digester (new)
Machinery for digestion (new)
Storage for dewatering concentrate (new)
Dewatering building
(exisiting)
Primary sludge thickener
(exisiting)
Excess sludge thickener
(exisiting)
Seeping tank (new)
Gas torch and gas processing facility (new)
Mixing tanks (new)
Gas storage (new)
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Dr. Ermel
By putting into operation of the reconstructed and extended aeration facility a noticeable improvement of discharge quality will be achieved. The organic load (BOD
5
, COD) will be eliminated almost totally. The all-season complete nitrification of ammonia-nitrogen will reduce significantly the pollution of the river Elbe with oxygen demanding material.
Denitrification of nitrate to molecular nitrogen which will escape from wastewater and by elimination of phosphorous from wastewater another load of the river water will be reduced significantly.
Wastewater treatment plants are technical installations which might have negative impact to the environment. These may be stress by noise, odour or aerosol. Because of the direct neighbourhood of residential and commercial areas to the plant, manifold measures will be taken to reduce any impact of the above named impact. That is why odour intensive parts of the plant like mechanical and sludge treatment will be enclosed. Exhaust air from sludge treatment will be captured and treated in bio-filters.
In addition turbulent flow paths and hydraulic dams will be enclosed as well to reduce generation of aerosol. Noise intensive machinery like compressors will equipped with specific noise reduction installations and placed in solid buildings.
In this way the wastewater treatment plant of Dresden-Kaditz will contribute significantly to improvement of the environmental quality of the river Elbe. Stress in the direct surrounding of the plant will be reduced to a inevitable minimum.
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Dr. Ermel
The following table summarizes exemplary data of the Wastewater Treatment Plant Dresden-
Kaditz being in operation:
No Topic
1 Availability
Unit Parameter
1.1 Operating time
1.2 Time for revisions
1.3 Overall availability hours/year hours/year
%
8,760 none, redundant system
100
2 Quantities
2.1 Overall influx
2.2 COD
2.3 N tot
2.4 P tot m³/year
Mg/year
Mg/year
Mg/year
55 million
25,000
2,600
350
3 Quality
3.1 Chemical Oxygen Demand
(COD)
3.2 Biological Oxygen Demand
(BOD
5
)
3.3 Ammonia-Nitrogen
(NH
4
-N)
3.4 Anorganic Nitrogen, total
(anorg.N
tot)
3.5 Phosphorous, total
(P tot)
4 Investment Costs
4.1 Overall investment
4.2 Mechanical waste water treatment
4.3 Biological waste water treatment
4.4 Sewage sludge treatment
4.5 Others mg/litres mg/litres mg N/litres mg N/litres mg N/litres
Euro (€), net
Euro (€), net
Euro (€), net
Euro (€), net
Euro (€), net
110 million
21 million
60 million
25 million
4 million
2
8
0.6
55
10
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