Quality-based drainage of urban rainwater

Potential analysis for the catchment of Hildesheim, GER

Stephan Köster

Maike Beier

Nils-Kristof Kabisch

❖ Since 200 years cities have been built

up including a comprehensive sewer

network

→ > 97% drainage connection rate

→ 580,000 km pipes

→ 60% combined sewer systems

❖ Current focus: adapting the existing

infrastructure to

→ new technical regulations

concerning flow seperation and

water protection

→ heavy rainfall events / climate change

→ Emerging pollutants

German current design background

Brombach & Dettmar 2016

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

Our vision

A modified drainage system in which all polluted wastewater and rainwater is treated at wastewater treatment plants while non-polluted rainwater is available as water resource

WWTP

CSO

decentralised

rainwater treatment

Non-polluted

rainwater

Neighbourhood level Existing „grey“ infrastructure

Quantity

Quality

4´19 – 6´22

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

polluted

rainwater

▪ Local variation

▪ Temporal variations

4

Stormwater Quality (Run off)

LeafLitter

DecomposingStreet Dust

©ISAH 2018

Biocides ?

Microplastic ?

dissolved organic matter ?

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

TSS

Cu

mu

lative

lo

ad

fra

ctio

n [

-]

Duration [h]

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Cu

mu

lative

vo

lum

e f

ractio

n [

-]

0102030405060708090100

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Cumulative Volume [m³]

1

23

40102030405060708090100

0

10

20

30

40

50

60

70

80

90

100

Flo

w [

m³/

h]

▪ Local variation

▪ Temporal variations

5

Rainwater Quality (Run off)

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

4´19 – 6´22

Potential analysis Hildesheim - Method l (Pollution)

▪ Estimation of rainwater pollution via land use Residential (PC I)

Mixed (PC II)

Streets (PC III)

Industry/Commercial (PC III)Regional land use plan of Hildesheim

PC: Pollution Class

628th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

7

Calculated pollution

SA Irina Skripnyuk, 2021

based on 4 different utilisation typesCr

MP

Zn

Cu

Pb

TSS

BOD

COD

▪ Common sealing degrees from literature

▪ 10-year rainfall series with an average of 660.5 mm/a

▪ Average runoff coefficient of 0.7 was applied

▪ Considered Scenarios:

Scenario Industry/Commercial Streets Mixed Residential

S0 current state (sub-catchments with combined sewer systems are connected to WWTP)

S1 connected to WWTP connected to WWTP decoupled from WWTP decoupled from WWTP

S2 connected to WWTP connected to WWTPtemporarily (first 30 min.)

connected to WWTPdecoupled from WWTP

828th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

Potential analysis Hildesheim - Method ll (Flows)

Potential analysis Hildesheim – Results l

Scenario 0: Current State

▪ strong interweaving of the various sub-streams

▪ 475,000 m³/a of Pollution Class I

are not available in the catchment and burdens

the WWTP unnecessarily

▪ 1,120,000 m³/a rainwater of Pollution Class II and

III from areas with a separate sewer system must

be treated by additional treatment facilities

928th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

no optimal

rainwater management

by separated SS2,190,000 m³/a

Scenario 1: no increase of

WWTP inflow

all heavily

polluted

rainwater to

WWTP

available

unpolluted

rainwater

increased by 46 %

Potential analysis Hildesheim – Results ll

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

Scenario 1: no increase of

WWTP inflow

all heavily

polluted

rainwater to

WWTP

available

unpolluted

rainwater

increased by 46 %

Potential analysis Hildesheim – Results ll

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

Scenario 2: spatial and

temporal decoupling

all polluted

rainwater to

WWTP

no extra treatment

available

unpolluted

rainwater

increased by 72 %

Inflow + 20%

Conclusion

28th October | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

The idea of a quality-based rainwater management shows very promising

results:

➢ High utilisation of the existing infrastructure

▪ Major part of polluted rainwater could be treated by existing WWTP

with high efficiency of large and centralised facilities

▪ The need for additional rainwater treatment facilitites can be

reduced by 68% up to zero

→ cost-effective

➢ Increasing water supply in the neighbourhood up to 72 %

→ eco-friendly

13

Thank you for your listening!

Prof. Dr.-Ing. Stephan KösterDr.-Ing. Maike BeierNils-Kristof Kabisch, MSc.

Leibniz University HannoverInstitute of Sanitary Engineering and Waste ManagementWelfengarten 1, 30167 Hanover, Germany

Mail: beier@isah.uni-hannover.deTel: +49 511 - 762 2898

Session 17.4 | Prof. Dr.-Ing. Stephan Köster | Quality-based drainage of urban rainwater

The authors would like to thank

the German Federal Ministry of Education and Research

for funding the TransMiT project within the RES:Z call:

Ressource-optimised city of the future