Real time control strategies for a biological chemical wastewater treatment plant - Demonstrations in Oslo

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Candace Wilkerson
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1 Real time control strategies for a biological chemical wastewater treatment plant - Demonstrations in Oslo Ragnar Storhaug, Bjarne Paulsrud, Aquateam COWI AS Rashid Abdi Elmi, Oslo Water and Sewerage Works 1

2 Agenda Tunnels and wastewater treatment plants in Oslo Changes in operational modes of the treatment plant Examples Conclusions 2

3 City of Oslo main sewer system Bekkelaget WWTP VEAS WWTP 3

4 Bekkelaget WWTP Design capacity: pe The plant is overloaded and treats wastewater from pe living in the eastern and south eastern parts of Oslo Average daily flow: m 3 Maximum daily flow m 3 Wastewater processes: mechanical, chemical and biological treatment, including nitrogen removal (predenitrification), simultaneous precipitation with ferrous salts and additional filtering of wastewater before it is discharged at - 50 m depth in the Oslofjord 4

5 Bekkelaget WWTP The sludge treatment consists of mechanical thickening, thermophilic digestion and dewatering before final disposal on agricultural land. The biogas is upgraded to vehicle fuel. 5

6 Bekkkelaget WWTP The plant is built in rock caverns, except for storage tanks for chemicals and biogas 6

7 The tunnel storage volume 7

8 Bekkelaget WWTP Process flow sheet 8

9 Modes of operation 1. Dry weather flow mode (Q<1,9 m 3 /s) : All incoming wastewater undergoes mechanical and biological/ chemical treatment. 2. Medium flow mode (1,9 m 3 /s<q< 3,0m 3 /s): Approximately % of the incoming wastewater undergoes mechanical and biological/ chemical treatment, while % of the wastewater is only treated by chemical precipitation. 3. Maximum flow mode (3,0 m 3 /s<q<4,0m 3 /s): Approximately 50 % of the incoming wastewater undergoes mechanical and biological/ chemical treatment, while 50 % of the wastewater undergoes only chemical precipitation. 9

10 Operational mode 1: Dry weather flow Q < 1,9 m³/s Primary settling in both Block 1 and Block 2 10

11 Operational mode 2 Medium flow 1,9 m³/s < Q < 3,0 m³/s Primary settling in Block 1 and chemical precipitation in Block2 11

12 Operational mode 3: Maximum flow 3,0 m³/s < Q < 4,0 m³/s Chemical precipitation in both Block 1 and Block2 12

13 Operational mode regulation 13

14 Flow regulation example Flow and operational modes 13/4/ /4/

15 Accumulated flow Flow and operational modes 18/9/ /11/

16 Removal efficiency Average removal efficiency for 6 demonstration periods 16

17 Conclusions 1. Due to an expected increased frequency of heavy rain falls in the future, the risk of pollution from discharges via storm water overflow weirs will increase. Consequently, a major goal should be to utilize the treatment capacity of the wastewater treatment plants as far as possible. 2. Turning a part of the normal wastewater treatment process into a simpler process for particle removal (e.g. chemical precipitation) with direct discharge to the recipient, will be an option for achieving the goal. 17

18 Conclusions 3. Real time data from the sewer network can control which treatment mode to be used at any time. 4. For existing wastewater treatment plants with primary settling tanks, and for planning of new wastewater treatment plants, the option of turning a part of the normal treatment process into a simpler process for particle removal (e.g. chemical precipitation) with direct discharge to the recipient, should be considered. During high flow events, the overall removal efficiency of the plant will be reduced, but discharges via storm water overflow weirs will be reduced. 18

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