treatment of polar organic micropollutants in drinking

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Treatment of polar organic micropollutants in drinking water: Investigation of N,N-DMSremoval by activated carbon

Schliemann-Haug, Manuela Anna Maria; Hedegaard, Mathilde Jørgensen; Albrechtsen, Hans-Jørgen

Publication date:2019

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Citation (APA):Schliemann-Haug, M. A. M., Hedegaard, M. J., & Albrechtsen, H-J. (2019). Treatment of polar organicmicropollutants in drinking water: Investigation of N,N-DMS removal by activated carbon. Abstract from ATVVintermøde 2019, Vingsted, Denmark.

https://orbit.dtu.dk/en/publications/f4157aed-cd63-47f0-8acd-53098b43e061

10 ECTS point special course in collaboration with

Treatment of polar organic micropollutants in drinking water:

Investigation of N,N-DMS removal by activated carbonM. Schliemann-Haug*, M. Jørgensen Hedegaard**, H.-J. Albrechtsen*, 2019

*Department of Environmental Engineering, Technical University of Denmark, E-mail: [email protected]; **HOFORGenuchten, M. Th. Van og W.J. Alves. 1982. Analysis solutions of the onedimensional convective-dispersive solute transport equation. U.S. department of agriculture. Technical Bulletin no. 1661.

Lebeau, T., C. Leliévre, D. Wolbert, A. Laplanche, M. Prados og P Coté. (1999). Effect of natural organic matter loading on the Atrazine adsorbtion capacity of an aging powdered activated carbon slurry. Water Research,33:1695-1705.Schmidt, C. K. & Brauch, H. J. (2008). N,N-Dimethylsulfamide as Precursor for N-Nitrosodimethylamine (NDMA) Formation upon Ozonation and its Fate During Drinking Water Treatment. Environmental Science Technology, 42, pg. 6340-6346

INTRODUCTION

Background Objectives• N,N-DMS was detected in Danish drinking water supply in 2018

• Drinking water supply in Denmark is based on groundwater and traditional treatment processes are not designed to remove pesticides and their metabolites

• Litterature on N,N-DMS removal from drinking water is limited

• There are some drinking water treatment plants in Denmark using activated carbon (AC) filtration

The aim of the study was to investigate the removal efficiency of N,N-DMS in drinking water by activated carbon filtration. More specific objectives were:

• To determine the adsorption-isotherm and its magnitude (Full-scale & lab)

• To compare the removal efficiency of two different activated carbon types (lab)

• To document, model and predict N,N-DMS breakthrough in a full-scale activated carbon (AC) filter (Hvidovre DWTP)

METHODS RESULTS: Full-scale

LaboratoryTwo activated carbon types were compared in an adsorption-isotherm investigation (Figure 2). Drinking water was used for more realistic/conser-vative results compared to MilliQ-water.

Figure 2: Set-up of the adsorption-isotherm investigation. Coconut-based AC (AquaSorb CS) was currently used at Hvidovre DWTP. Bitumen-based AC was provided by Silhorko. The activated carbon concentration was kept constant at 400 mg/L based on a Kd-calculation with literature data (Schmidt&Brauch, 2008). The N,N-DMS concentration was 0.5, 2 and 5 µg/L. The experiment lasted 7 days, as sorption typically can be measured after 1-7 days (Lebeau et al., 1999).

Figure 1: Addition of activated carbon stock solution.

Figure 3: Schematic drawing of AC-filter at Hvidovre DWTP. AC type and volume: 14.8 m3 AquaSorb CS. The red area indicates the currently unused volume of activated carbon, as the outlet is above this volume (4 m3).

Figure 4: Breakthrough model and measurements in Level 2 (grey, green) and the outlet (blue)

• Kd-value of 9500 L/kg showed best fit (after top layer)

• 90% breakthrough at the outlet of the filter was predicted to occur after less than 5 months

• Most sensitive model parameters: flowrate, Kd-value and height of activated carbon in the filters

Full-scale• Samples from inlet, Level 1, 2,

3 and outlet (3 months)

• Samples were analyzed by DTU Environment and ALS Denmark using LC-MS/MS.

• Mathematical model was based on analytical breakthrough model by Genuchten & Alves (1982) and calibrated and vali-dated with measurements

• Breakthrough at level 3 was predicted using the best fitting model-scenario for level 2

• 4 m3 of filter volume currently unused

4.40

m

2.60 m

Activated Carbon

0.75

m1.

00 m

Inlet

Outlet

Level 1 sampling tap 0.3 m below coal surface

Level 2 sampling tap 1.3 m below coal surface

Sampling tap level 3 2.1 m below coal surface

Drainage system 0.2 m from bottom

Outlet tap 2.0 m below coal surface0.10 m

1.40 m

RESULTS: Laboratory

CONCLUSIONS

• Adsorption of N,N-DMS by activated carbon is poor compared to other compounds (e.g. highest Kd of N,N-DMS was 170 times lower than for BAM)

• Laboratory Kd-values: 2494-2227 L/kg. Adsorption was linear. Full-scale Kd-value: 9500 L/kg

• No significant difference in the Kd-value of coconut and bitumen based AC

• 90% breakthrough in the full-scale activated carbon filters after less than 5 months

500 mL outlet water from filter of Sjælsø Plant 2400 mg/L activated carbon

Coconut-based AC Bitumen-based AC

2 ug/L 5 ug/L

0.5 ug/L 2 ug/L

5 ug/L

0.5 ug/L

90% Breakthrough

50% Breakthrough

Calibration & validation // Level 2Kd: 4993 L/kg (calculated from literature)Kd: 2494 L/kg (laboratory)Kd: 9500 L/kg (fitted)

Measurements:DTU - level 2 (light green: below detection)ALS - level 2 (light green: below detection)

Validation & prediction // OutletKd: 9500 L/kg (fitted at level 2)

Measurements:DTU - outlet ALS - outlet (light blue: below detection)

Coconut-based AC

2494 L/kg (STD 227)

Bitumen-based AC

2227 L/kg (STD 312)

0.85

m

Figure 6: AC filters at Hvidovre DWTP

Figure 5: Adsorption in all batches over time

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5.3 Results and DiscussionIn this section, the results of the adsorption isotherm investigation are presented and discussed. All calculations are provided in Appendix 1d.

5.3.1 Adsorption kineticsIn each batch, adsorption was measured over time (Figure 10). Sorption equilibrium was achieved after 1-7 days (Figure 10). This indicates that the initial calculations and assumptions to design the experiment were valid enough to attain sorption processes in a detectable range within the observation period.

The sorption kinetics of both activated carbon types do not show major differences (Figure 10). Assuming linear sorption, as in the initial calculations (section 5.1), the average adsorption was calculated for each activated carbon type after 1 and 7 days. The adsorption of N,N-DMS by AquaSorb CS amounted to 54% [51 ; 57]95% after 1 day and 50% [46 ; 53]95% after 7 days. The sorption by the AC from Silhorko was determined to 41% [37 ; 46]95% after 1 day and 44% [36 ; 52]95% after 7 days (Figure 10). Adsorption of N,N-DMS was less efficient than assumed in the initial calculations prior to the experiment (section 3.3).

The batches with 0.5 µg/L and 2 µg/L N,N-DMS and Silhorko AC reached a stable equilibrium after 1 day (same concentration in water after 1 and 7 days). The batch with 0.5 µg/L N,N-DMS and AquaSorb CS reached as well equilibrium after 1 day (same concentration in water after 1 and 7 days).

The batches with 2 µg/L and 5 µg/L N,N-DMS and AquaSorb CS showed a declining sorption from day 1 to day 7. This might be related to uncertainties in the mixing of the batches and the sampling procedure.

The batch with 5 µg/L N,N-DMS and Silhorko AC demonstrated an increase in sorption from day 1 to day 7. This might also be related to uncertainties in the sampling procedure and the mixing of the batches. It could however indicate that sorption did not reach equilibrium in this batch in the observed period.

5.3.2 Adsorption-isothermsThe adsorbed concentrations (Cs) after 1 and 7 days were calculated for each batch using a mass balance equation (digital Appendix 1d):

The adsorbed N,N-DMS concentration (Cs) as a function of the concentration in the water (Cw) indicated opposite trends at high concentrations for AquaSorb CS and Silhorko AC (Appendix 2). For AquaSorb CS Cw was higher than Cs, while Cs was higher than Cw for Silhorko AC (Appendix 2). Due to the uncertainties at high concentrations, an average Cs and Cw of day 1 and day 7 was determined (digital Appendix 1d).

Figure 10: Adsorption in all batches as a function of time

17

The batch with 5 µg/L N,N-DMS and Silhorko AC demonstrated an increase in sorption from day 1 to day 7.

This might also be related to uncertainties in the sampling procedure and the mixing of the batches. It could

however indicate that sorption did not reach equilibrium in this batch in the observed period.

Figure 10: Adsorption in all batches as a function of time.

5.3.2 Adsorption-isotherms The adsorbed concentrations (Cs) after 1 and 7 days were calculated for each batch using a mass balance

equation (digital Appendix 1d):

𝑀𝑀𝑀𝑀mno_8287[(µμg) = 𝑀𝑀𝑀𝑀\](mg) ∗ 𝐶𝐶𝐶𝐶" tµμgmgu+ 𝐶𝐶𝐶𝐶( v

µμgL x ∗ 𝑉𝑉𝑉𝑉( (𝐿𝐿𝐿𝐿) → 𝐶𝐶𝐶𝐶" =

𝑀𝑀𝑀𝑀mno_8287[ − (𝐶𝐶𝐶𝐶( ∗ 𝑉𝑉𝑉𝑉()𝑀𝑀𝑀𝑀\]

The adsorbed N,N-DMS concentration (Cs) as a function of the concentration in the water (Cw) indicated

opposite trends at high concentrations for AquaSorb CS and Silhorko AC (Appendix 2). For AquaSorb CS Cw

was higher than Cs, while Cs was higher than Cw for Silhorko AC (Appendix 2). Due to the uncertainties at high

concentrations, an average Cs and Cw of day 1 and day 7 was determined (digital Appendix 1d).

17














17














• Sorption equilibrium after 1 to 7 days

• Linear sorption isotherm for both AC types

• Kd-values for the two AC types:

• Kd-values of the two AC types were not significantly different (confidence level 95%)

Coconut 0.5 ug DMS/LCoconut 2 ug DMS/LCoconut 5 ug DMS/LBitumen 0.5 ug DMS/LBitumen 2 ug DMS/LBitumen 5 ug DMS/L

treatment of polar organic micropollutants in drinking

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