Biofilm in combined sewer:  a wet weather pollution source ? and / or  a dry weather pollution indicator ? Sewer Processes and Networks France V. Rocher, S. Azimi, R. Moilleron, G. Chebbo

Presentation plan Sewer processes and networks ) What is biofilm ? 2) Why study biofilm in sewer ? 3) Description of this research program 4) Main results 5) Conclusions 1)What is biofilm ? 1) What is biofilm ?

What is biofilm ? Sewer processes and networks Gross bed sediment (GBS):  black and grey colours  high mineral content  5-40 cm thick Organic layer (OL):  brown colour  high organic content  2-15 cm thickBiofilm:  brown colour  high organic content  1-5 mm thick Waste water Sewer trunk One of the three kinds of sewer deposits  One of the three kinds of sewer deposits

What is biofilm ?  One of the three kinds of sewer deposits Sewer processes and networks Biofilm in the sewer trunk  Biofilm in the sewer trunk Sewer trunk at the mean water level  fixed to the trunk wall at the mean water level cm high  cm high

What is biofilm ?  One of the three kinds of sewer deposits Sewer processes and networks  Biofilm in the sewer trunk Trunk wall Organic matter Cell layer Biofilm architecture (TEM)  Biofilm architecture (TEM) 200 µm 40 µm 5 µm  Cell layer consists of numerous bacteria compacted together and might be bound by a polysaccharide coat 2 µm diameter2-5 µm long  Cell morphology of the dominant bacteria is a rod shaped cell of 2 µm diameter and 2-5 µm long132

Trunk wall Organic matter Cell layer Biofilm architecture (TEM)  Biofilm architecture (TEM) What is biofilm ?  One of the three kinds of sewer deposits Sewer processes and networks  Biofilm in the sewer trunk 100 µm  This uniform film of bacteria totally covers an organic matrix  Mineral fragments are embedded in the cell layer 50 µm 12

What is biofilm ?  One of the three kinds of sewer deposits Sewer processes and networks  Biofilm in the sewer trunk Trunk wall Organic matter Cell layer Biofilm architecture (TEM)  Biofilm architecture (TEM)  it has a fibrous structure: vegetal fibers and organic matter  the organic matrix is between the cell layer and the wall 100 µm Cell layer Organic matrix  its thickness is important as it reaches several millimeters

Presentation plan Sewer processes and networks ) What is biofilm ? 2) Why study biofilm in sewer ? 3) Description of this research program 4) Main results 5) Conclusions

Why study biofilm in sewer ? Sewer processes and networks wet weather pollution source  it could act as a wet weather pollution source  External inputs Waste water flow  In-sewer sources Two kinds of pollutant sources Two kinds of pollutant sources Street and roof runoffs  External inputs Bed sediment resuspension  In-sewer sources Assessment of the biofilm contribution to the wet weather pollution Biofilm erosion  In-sewer sources

Why study biofilm in sewer ? Sewer processes and networks  it could act as a wet weather pollution source  it could be used as a dry weather pollution indicator  do not require specific devices (little metallic scraper) Use of biofilm as pollution indicator might make greater scale projects easier, since sampling is easy:  easily accessible

Presentation plan Sewer processes and networks ) What is biofilm ? 2) Why study biofilm in sewer ? 3) Description of this research program 4) Main results 5) Conclusions

Description of this research program Sewer processes and networks Micro-pollutants measured: hydrocarbons (HC)  Micro-pollutants measured: hydrocarbons (HC)  Aliphatic hydrocarbons (TAH)  Resolved aliphatic hydrocarbons  Unresolved Complex Mixture (UCM) Fluo B[k]F B[b]F APyrP AcylNAcenF B[a]AChryB[a]P D[ah]ABPerIP 16 US-EPA PAHs  Polycyclic Aromatic Hydrocarbons (PAH)  Non-alkylated compounds (2-6 rings)  Alkylated compounds

Description of this research program Sewer processes and networks  Micro-pollutants measured: hydrocarbons (HC) Two different approaches  Two different approaches 1) Quantitative approach2) Qualitative approach HC stock Determination of the HC stock in the 3 kinds of deposits biofilm contribution To assess of the biofilm contribution to the wet weather pollution HC distribution Comparison between the HC distribution in the 3 kinds of deposits indicator To determine whether biofilm could be used as indicator of the HC pollution or not

Sewer network of Paris Seine river Description of this research program Sewer processes and networks Sampling site  Sampling site « 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 Urban surface distribution « Le Marais » network description:  3 main trunks : « Vieille du Temple » and « St Gilles » trunks flow into « Rivoli »  Collector characteristics: St Gilles Vieille du temple Rivoli St Gilles

Description of this research program Sewer processes and networks  Sampling site every 25m it was sampled every 25m from the St Gilles-Rivoli junction up to 600 m upstream top of the st Gilles trunk they were sampled at the top of the st Gilles trunk (600 m upstream Rivoli) Biofilm Bed deposits

Description of this research program Sewer processes and networks  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.

Description of this research program Sewer processes and networks  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.

Presentation plan Sewer processes and networks ) What is biofilm ? 2) Why study biofilm in sewer ? 3) Description of this research program 4) Main results 5) Conclusions 4.1) Quantitative approach 4.2) Qualitative approach

3 to 5 times greater  Biofilm TAH content was 3 to 5 times greater than other deposit ones 4 to 8 times smaller  Biofilm PAH content was 4 to 8 times smaller than other deposit ones Results: quantitative approach Sewer processes and networks  PAH and TAH contents (µg/g dw) in the 3 deposits Waste water 4 +/ / /- 39 PAH contents TAH contents Biofilm OL GBSi GBSs 22 +/ / / / /- 80 GBSi fraction below 400 µm GBSs fraction above 400 µm

Results: quantitative approach Sewer processes and networks   PAH and TAH contents (µg/g dw) in the 3 deposits  PAH and TAH stocks in the 3 deposits Deposit masses (kg) Biofilm (n=14) OL (n=4) GBSi (n=5) GBSs (n=5) PAH stocks (g) TAH stocks (g) only reached 0.1 and 4 g  PAHs and TAHs stored in the biofilm only reached 0.1 and 4 g, respectively0.14 mainly stored in the GBS  PAHs and TAHs were mainly stored in the GBS

Results: quantitative approach Sewer processes and networks   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 Waste water we assumed that: To assess the biofilm contribution to the wet weather HC pollution, we assumed that: 1) The GBS was not resuspended  2) The OL was entirely resuspended 3) The biofilm was entirely eroded

Results: quantitative approach Sewer processes and networks   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 TAHPAH OL 99% Biofilm 1% OL 95% Biofilm 5% Conclusion 1:ow values emphasised that biofilm was not an important in-sewer source of wet weather pollution and can be disregarded Conclusion 1: Low values emphasised that biofilm was not an important in-sewer source of wet weather pollution and can be disregarded

Presentation plan Sewer processes and networks ) What is biofilm ? 2) Why study biofilm in sewer ? 3) Description of this research program 4) Main results 5) Conclusions 4.1) Quantitative approach 4.2) Qualitative approach

Results: qualitative approach Sewer processes and networks  HC distribution (%) in the 3 deposits: TAH %Carbon number % Biofilm OL same aliphatic distribution pattern  Biofilm and OL showed the same aliphatic distribution pattern C29 C29 C17-18 C27 C17-18C27

Results: qualitative approach Sewer processes and networks  HC distribution (%) in the 3 deposits: TAH % Carbon number GBS the same aliphatic distribution GBSi and GBSs exhibited almost the same aliphatic distribution  C18 Biofilm-OL C17-C18 C27 to C29 Predominance of light compounds Predominance of heavy compounds contrasted significantly with the biofilm and OL distributions  Aliphatic distributions of GBSi and GBSs contrasted significantly with the biofilm and OL distributions

Biofilm GBSs OL GBSi Results: qualitative approach Sewer processes and networks  HC distribution (%) in the 3 deposits: PAH same PAHs were observed In all the deposits, the same PAHs were observed 40% 15%, more Pand less Fluo than other deposits. PAH distributions were almost similar in OL, GBSs and GBSi, whereas the biofilm showed more P and less Fluo than other deposits. P Pyr Fluo 3 major PAHs The 3 major PAHs were the same in all the deposits

was slightly different Biofilm fingerprint was slightly different than other deposit ones, even if the major PAHs were the same in all the deposits. Biofilm and OL fingerprints be similar Biofilm and OL fingerprints were found to be similar, while GBS showed a fingerprint significantly different Results: qualitative approach Sewer processes and networks  Biofilm as a pollution indicator? Biofilm OLGBS TAH Fingerprint   PAH Fingerprint  Biofilm OLGBS  Conclusion 2:Biofilm is an indicator of the aliphatic pollution of the OL 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

Conclusions: a wet weather pollution source and/or a dry weather pollution indicator? Sewer processes and networks 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 3: scraping  When all the water was pumped, OL was scraped until reaching the GBS.  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. GBS Waste water Step 1: box installation Description of this research program Sewer processes and networks  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. Pump  Two panels were lowered.  The water in the box was pumped out. Step 2: pumping

Results: quantitative approach Sewer processes and networks   PAH and TAH contents (µg/g dw) in the 3 deposits  PAH and TAH stocks in the 3 deposits  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  HC stock in the biofilm was a lot smaller than the OL and GBS ones TAHPAH GBSs 75% GBSi 21% OL 4% GBSs 83% GBSi 10% OL 7% GBSs 83% GBSi 10% GBSs 75% GBSi 21% GBSs 83% GBSi 10% OL 7% Biofilm 0.4% Biofilm 0.02% GBSs 75% GBSi 21% OL 4%