Influence of hydraulic residence time on pesticides ... · Flow rate/Water level Hydraulic...
Transcript of Influence of hydraulic residence time on pesticides ... · Flow rate/Water level Hydraulic...
Influence of hydraulic residence time on pesticides retention in constructed wetlands
Céline Gaullier (LIEC), Sylvie Dousset (LIEC), Nicole Baran (BRGM), David Billet (LIEC)
GFP Nancy – 15-18 of may 2017
� Surface water pollution by pesticidesRunoff, leaching, drainage , spray drift� Limited by grass strip (between crop and river)
� ineffective in case of drained plot
� ‘Free water surface CW’ : mitigation of contaminant concentration transported to the river (30 years)
� Efficiency of CW depends on: • Hydraulic parameters
Flow rate/Water level � Hydraulic residence time (HRT)• Morphology : ratio length/width• Molecules properties : solubility, Kow, Koc• ………
Introduction
From National Engineering HandBook (2002)
� Contradictory results in the
literature
(CW)
Introduction
� Lorraine : drained surface > 16 % cultivated surface (clay +++)� vulnerability of surface water
Frequence of drained surface in Lorraine Vulnerability of pesticides transfert in surface water
LowMediumHigh
Very LowLowMediumHighVery high
Introduction
� 9 CWs set up since 2010/2011
Introduction
� 9 CWs set up since 2010/2011� 2 studied sites during the thesis
3 ponds – 215 m²HRT : 1 h to 16 h
Manoncourt sur Seille (54)
Ville sur Illon (88)
Ditch – 100 m²HRT : 30 min to 3 h
Introduction
Aim: determine hydraulic influence on the efficiency of the CWs
Field80 molecules / 15 metabolites
Pilot-scale4 molecules
� Weekly monitoring: dissolved and particulate� Daily monitoring: dissolved� Br- tracing
� Field = very complex system
� Pilot = under controlled conditions (flow rate, water level, volume etc.)
Stream
Pilot-scale experiment – Questions ?
� Does the HRT influence the effectiveness? � 2 HRT studied
� Do pesticide properties influence his mitigation?
� Does the presence of dead zones/short-circuiting impact the effectiveness?
� What is the fate of pesticides during stagnation?
BSC CYP IPU DMT
Pilot-scale experiment
� Pilot-scale: 1/20° et 1/40° (2.5 m of lenght)� Flow rate/water level representative of the field (1-2 L/s and 8 L/s)
3 ponds Ditch
Manoncourt sur Seille (54)Ville sur Illon (88)
Experimental design
� Example of drainage dynamic in the field
� 4 pesticides + 1 anion (tracer of hydrodynamic) injected at the inlet(charge)
� Alternating of charge (pesticide/anion) and discharge (water) phases
� Automatic sampling in the outlet
StagnationHigh flow
(12 h)Low flow
(36 h)Stagnation
(50 d)
Low HRT High HRT
Results – Concentration at the outlet (3 ponds)
� C/C0 low HRT (high flow) > C/C0 high HRT (low flow)
� [IPU] > [BSC] during charge phase
Results – Effectiveness of the molecules
For the 2 pilots � Low HRT: mitigation of BSC > CYP > IPU and DMT
� in agreement with their Kd (batch)
� High HRT: similar mitigation of the 4 molecules
� Mitigation at high HRT > mitigation at low HRT
� HRT influence the molecule’s mitigation
Low HRT High HRT
Results – Effectiveness of the pilotsLow HRT High HRT
Flow rate (mL/min): 55 7 8 1.8Water level (cm): 3 1.5 1.5 1Volume (L): 9.4 1.7 4.7 1.2
For the 2 HRT� Mitigation ditch > 3 ponds
– Water level, flow rate, and volume ditch < 3 ponds
� Hydraulic parameters influence the pilot effectiveness
Results – The most influencing parameters
� Similar mitigation between ditch and 3 ponds (no significantly different)– flow rate and water level similar– volume ≠ (area and shape ≠)– HRT ≠
� Water level and flow rate are most influencing than HRT
Low HRT High HRT
Flow rate (mL/min): 55 7 8 1.8Water level (cm): 3 1.5 1.5 1Volume (L): 9.4 1.7 4.7 1.2
Results – The most influencing parameters
� The better the mitigation, the lower the flow rate and water level
Low HRT High HRT
Flow rate (mL/min): 55 7 8 1.8Water level (cm): 3 1.5 1.5 1Volume (L): 9.4 1.7 4.7 1.2
Results – Fate of pesticides during stagnation (3 ponds)
1st order kinetict1/2 = 2,3 dt1/2 = 1,4 d
� Fast dissipation from the aqueous phase
� Fate of pesticides ?� Sorption to sediment ? (T50)� Extraction QUECHERS� no quantified (concentration < LOQ)
� Degradation in the water? � Analysed of metabolites from IPU &
DMT
� Metabolites quantified
IPU (2 metabolites): 5% of initial pesticide amountDMT (8 metabolites): 37% of initial pesticide amount
Conclusion
� At pilot-scale the effectiveness is influenced by:• Flow rate and water level � the lower, the better the mitigation• Property of molecules � in case of low HRT (high flow rate), the better
the K d, the better the mitigation• Fast aqueous dissipation � could explained the better mitigation with
high HRT
� Field results: intense monitoring over the 3 years of the thesis– Relation between hydraulic parameters and effectiveness?– Behavior of the molecules ? Different or similar according to
hydraulic?
⇒ Influence of hydraulic will be identical on the effectiveness for the dissolved and the particulate?
Thanks for your attention