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Sewer Processes and Networks France - 2002. V. Rocher, S. Azimi, R. Moilleron, G. Chebbo. Biofilm in combined sewer:  a wet weather pollution source ? and / or  a dry weather pollution indicator ?. Sewer processes and networks - 2002. Presentation plan. 1) What is biofilm ?.

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Sewer Processes and NetworksFrance - 2002

V. Rocher, S. Azimi, R. Moilleron, G. Chebbo

Biofilm in combined sewer:

 a wet weather pollution source ?

and / or

 a dry weather pollution indicator ?


Sewer processes and networks - 2002

Presentation plan

1) What is biofilm ?

1)What is biofilm ?

2) Why study biofilm in sewer ?

3) Description of this research program

4) Main results

5) Conclusions


Waste water

Organic layer (OL):

 brown colour

 high organic content

 2-15 cm thick

Sewer trunk

Gross bed sediment (GBS):

 black and grey colours

 high mineral content

 5-40 cm thick

Sewer processes and networks - 2002

What is biofilm ?

Biofilm:

 brown colour

 high organic content

 1-5 mm thick


Sewer trunk

 fixed to the trunk wall at the mean water level

10-20 cm high

Sewer processes and networks - 2002

  • What is biofilm ?

  • One of the three kinds of sewer deposits


1

2

3

Trunk wall

5 µm

200 µm

40 µm

Organic matter

 Cell layer consists of numerous bacteria compacted together and might be bound by a polysaccharide coat

 Cell morphology of the dominant bacteria is a rod shaped cell of 2 µm diameter and 2-5 µm long

Cell layer

Sewer processes and networks - 2002

  • What is biofilm ?

  • One of the three kinds of sewer deposits

  • Biofilm in the sewer trunk


1

2

Trunk wall

Organic matter

50 µm

100 µm

Cell layer

 This uniform film of bacteria totally covers an organic matrix

 Mineral fragments are embedded in the cell layer

Sewer processes and networks - 2002

  • What is biofilm ?

  • One of the three kinds of sewer deposits

  • Biofilm in the sewer trunk


Organic matrix

Cell layer

Trunk wall

Organic matter

100 µm

 the organic matrix is between the cell layer and the wall

Cell layer

 its thickness is important as it reaches several millimeters

Sewer processes and networks - 2002

  • What is biofilm ?

  • One of the three kinds of sewer deposits

  • Biofilm in the sewer trunk

 it has a fibrous structure: vegetal fibers and organic matter


Sewer processes and networks - 2002

Presentation plan

1) What is biofilm ?

2) Why study biofilm in sewer ?

3) Description of this research program

4) Main results

5) Conclusions


Street and roof runoffs

  • External inputs

  • In-sewer sources

Biofilm erosion

Bed sediment resuspension

Assessment of the biofilm contribution to the wet weather pollution

Sewer processes and networks - 2002

Why study biofilm in sewer ?

  • it could act as a wet weather pollution source

Waste water flow

Two kinds of pollutant sources

  • External inputs

  • In-sewer sources

  • In-sewer sources


Use of biofilm as pollution indicator might make greater scale projects easier, since sampling is easy:

 easily accessible

 do not require specific devices (little metallic scraper)

Sewer processes and networks - 2002

Why study biofilm in sewer ?

  • it could act as a wet weather pollution source


Sewer processes and networks - 2002

Presentation plan

1) What is biofilm ?

2) Why study biofilm in sewer ?

3) Description of this research program

4) Main results

5) Conclusions


N

Acen

Acyl

F

 Aliphatic hydrocarbons (TAH)

Resolved aliphatic hydrocarbons

 Unresolved Complex Mixture (UCM)

 Polycyclic Aromatic Hydrocarbons (PAH)

 Non-alkylated compounds (2-6 rings)

 Alkylated compounds

P

A

Fluo

Pyr

16 US-EPA PAHs

B[a]A

Chry

B[a]P

B[k]F

B[b]F

D[ah]A

BPer

IP

Sewer processes and networks - 2002

Description of this research program

  • Micro-pollutants measured: hydrocarbons (HC)


1) Quantitative approach

2) Qualitative approach

Determination of the HC stock in the 3 kinds of deposits

Comparison between the HC distribution in the 3 kinds of deposits

To assess of the biofilm contribution to the wet weather pollution

To determine whether biofilm could be used as indicator of the HC pollution or not

Sewer processes and networks - 2002

Description of this research program

  • Micro-pollutants measured: hydrocarbons (HC)


« Le Marais » network description:

3 main trunks : « Vieille du Temple » and « St Gilles » trunks flow into « Rivoli »

Collector characteristics:

« Le Marais » catchment description:

located in central Paris

 densely populated (295 inhabitants. ha-1)

 covers an area of 42 ha in an old residential district

 impervious at 90% and divided into 3 kinds of urban surfaces

Sewer network of Paris

Vieille du temple

Seine river

Urban surface distribution

St Gilles

Rivoli

St Gilles

Sewer processes and networks - 2002

Description of this research program

  • Sampling site


Biofilm

it was sampled every 25m from the St Gilles-Rivoli junction up to 600 m upstream

Bed deposits

they were sampled at the top of the st Gilles trunk (600 m upstream Rivoli)

Sewer processes and networks - 2002

Description of this research program

  • Sampling site


Sewer processes and networks - 2002

Description of this research program

  • Sampling site

  • Bed deposit sampling procedures

 Gross Bed Sediment: sampled with an adapted shovel that isolates the sediment during sampling and traps the fine particles of this sediment.


Sewer processes and networks - 2002

Description of this research program

  • Sampling site

  • Bed deposit sampling procedures

 Organic layer: sampled with a PVC box (85x30x50) (Ahyerre et al, 1999). It was inserted in the GBS during 10 dry weather days, then OL was scraped.


Sewer processes and networks - 2002

Presentation plan

1) What is biofilm ?

2) Why study biofilm in sewer ?

3) Description of this research program

4) Main results

4.1) Quantitative approach

4.2) Qualitative approach

5) Conclusions


Waste water

GBSi fraction below 400 µm

GBSs fraction above 400 µm

 Biofilm PAH content was 4 to 8 times smaller than other deposit ones

 Biofilm TAH content was 3 to 5 times greater than other deposit ones

Sewer processes and networks - 2002

Results: quantitative approach

  • PAH and TAH contents (µg/g dw) in the 3 deposits

PAH contents

TAH contents

Biofilm

4 +/- 6

196 +/- 59

OL

14 +/- 19

68 +/- 18

31 +/- 39

42 +/- 21

GBSi

GBSs

22 +/- 18

68 +/- 80


Deposit masses (kg)

PAH stocks (g)

TAH stocks (g)

393

1052

22

1200

2800

13700

4

81

117

935

Biofilm (n=14)

OL (n=4)

GBSi (n=5)

GBSs (n=5)

0.1

16

86

307

0.1

4

 PAHs and TAHs stored in the biofilm only reached 0.1 and 4 g, respectively

 PAHs and TAHs were mainly stored in the GBS

Sewer processes and networks - 2002

Results: quantitative approach

  • PAH and TAH contents (µg/g dw) in the 3 deposits


Sewer processes and networks - 2002

Results: quantitative approach

  • PAH and TAH contents (µg/g dw) in the 3 deposits

  • PAH and TAH stocks in the 3 deposits

  • Biofilm contribution to the wet weather HC pollution

To assess the biofilm contribution to the wet weather HC pollution, we assumed that:

Waste water

1) The GBS was not resuspended

2) The OL was entirely resuspended

3) The biofilm was entirely eroded


Biofilm 1%

Biofilm 5%

PAH

TAH

OL 99%

OL 95%

Sewer processes and networks - 2002

Results: quantitative approach

  • PAH and TAH contents (µg/g dw) in the 3 deposits

  • PAH and TAH stocks in the 3 deposits

  • Biofilm contribution to the wet weather HC pollution

Conclusion 1: Low values emphasised that biofilm was not an important in-sewer source of wet weather pollution and can be disregarded


Sewer processes and networks - 2002

Presentation plan

1) What is biofilm ?

2) Why study biofilm in sewer ?

3) Description of this research program

4) Main results

4.1) Quantitative approach

4.2) Qualitative approach

5) Conclusions


C27

C29

%

C17-18

Biofilm

C29

Carbon number

%

C27

OL

C17-18

Carbon number

 Biofilm and OL showed the same aliphatic distribution pattern

Sewer processes and networks - 2002

Results: qualitative approach

  • HC distribution (%) in the 3 deposits: TAH


C27 to C29

C17-C18

Biofilm-OL

Predominance of heavy compounds

%

C18

Predominance of light compounds

GBS

Carbon number

 Aliphatic distributions of GBSi and GBSs contrasted significantly with the biofilm and OL distributions

Sewer processes and networks - 2002

Results: qualitative approach

  • HC distribution (%) in the 3 deposits: TAH

GBSi and GBSs exhibited almost the same aliphatic distribution


In all the deposits, the same PAHs were observed

The 3 major PAHs were the same in all the deposits

40%

GBSs

GBSi

15%

OL

Biofilm

PAH distributions were almost similar in OL, GBSs and GBSi, whereasthe biofilm showed more Pand less Fluo than other deposits.

Fluo

Pyr

P

Sewer processes and networks - 2002

Results: qualitative approach

  • HC distribution (%) in the 3 deposits: PAH


TAH Fingerprint

PAH Fingerprint

Biofilm

Biofilm

OL

GBS

OL

GBS

Biofilm and OL fingerprints were found to be similar, while GBS showed a fingerprint significantly different

Biofilm fingerprint was slightly different than other deposit ones, even if the major PAHs were the same in all the deposits.

Sewer processes and networks - 2002

Results: qualitative approach

  • Biofilm as a pollution indicator?

Conclusion 2:Biofilm is an indicator of the aliphatic pollution of the OL

Biofilm is not an indicator of the aromatic pollution of the bed deposits, but it could be used to estimate the main PAHs present in the OL and the GBS


Sewer processes and networks - 2002

Conclusions: a wet weather pollution source and/or a dry weather pollution indicator?

Answer 1

Biofilm does not contribute significantly to the wet weather HC pollution

Answer 2

Biofilm is a reliable indicator of the aliphatic pollution

Biofilm is not a reliable indicator of the aromatic pollution

Thank you for your attention


Step 1: box installation

 The unit was inserted into the GBS, in the direction of the flow.

 Samples were taken after each 5 to 10 dry weather day period.

Step 2: pumping

Waste water

Pump

GBS

 Two panels were lowered.

 The water in the box was pumped out.

Step 3: scraping

 When all the water was pumped, OL was scraped until reaching the GBS.

Sewer processes and networks - 2002

Description of this research program

  • Sampling site

  • Bed deposit sampling procedures

 Organic layer: sampled with the assistance of a PVC box (85x30x50) opened on two sides so that water can flow through it.


OL 4%

OL 4%

Biofilm 0.02%

OL 7%

OL 7%

Biofilm 0.4%

GBSi 10%

GBSi 21%

GBSi 10%

GBSi 21%

GBSi 10%

GBSi 21%

GBSs 75%

GBSs 83%

GBSs 75%

GBSs 83%

GBSs 75%

GBSs 83%

Sewer processes and networks - 2002

Results: quantitative approach

  • PAH and TAH contents (µg/g dw) in the 3 deposits

  • PAH and TAH stocks in the 3 deposits

PAH

TAH

 HC were mainly stored in the GBS

 Remaining HC were mainly stored in the OL

 HC stock in the biofilm wasa lot smallerthan the OL and GBS ones


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