PPCPs wet weather mobilization in a combined sewer in NW Spain

Science of the Total Environment 449 (2013) 189–198

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PPCPs wet weather mobilization in a combined sewer in NW Spain Héctor Del Río ⁎, Joaquín Suárez, Jerónimo Puertas, Pablo Ures Group of Water Engineering and Environment, Center of Technological Innovation in Civil Engineering (CITEEC), Campus Elvina, s/n, 15071, Universidade da Coruña, Spain

H I G H L I G H T S ► ► ► ► ►

Hydrographs and pollutographs of sevenwell-known PPCPs have been characterized in a combined sewer in dry and wet weather. Event maximum and mean concentrations were higher than daily dry weather ones in several analyzed PPCPs. A significant mobilization of PPCPs during rain events has been observed. In general, dry weather flow concentrations are similar to extensive literature review. A positive relationship between removal degree in WWTP and wet weather mobilization has been observed.

a r t i c l e

i n f o

Article history: Received 21 September 2012 Received in revised form 14 January 2013 Accepted 14 January 2013 Available online 17 February 2013 Keywords: PPCPs Urban wastewater Urban drainage CSOs

a b s t r a c t An intense campaign was carried out over a 14 month period to characterize concentrations and loads of 7 well-known Pharmaceuticals and Personal Care Products (PPCPs), during dry and wet weather conditions, in an urban combined catchment in the northwest of Spain, a geographical zone with an average annual rainfall over 1500 mm. The main objective was to gather more in-depth knowledge of the mobilization of these “micropollutants” in an urban combined sewer and the possible pressures on water receiving bodies due to combined sewer overflows (CSOs). Hydrographs and pollutographs of these substances in dry weather flows (DWF), on weekdays and weekends, and wet weather flows (WWF) during 10 rain events have been characterized to obtain data that are sufficiently representative for statistical analysis. The research findings show that there is a considerable mobilization of these substances during rain events, mainly in the first part of the hydrographs, especially HHCB galaxolide, ibuprofen and paracetamol with maximum concentrations of 9.76, 8.51 and 5.71 μg/L respectively, whereas these concentrations in dry weather only reached 2.57, 2.11 and 0.72 μg/L respectively. There is a good correlation between the degree of mobilization in wet weather flows and the percentage of dry weather particulate phase of each studied substance, indicating that such mobilization may be associated with adsorption on the sediments deposited on the collectors during the antecedent dry period. These results are in good agreement with removal in conventional WWTP, especially for compounds that tend to adsorb onto sewage sludge. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Urban sanitation systems have developed throughout history, representing a compromise between hygiene needs, human welfare, the state of the environment, technical needs and available resources. In combined sewage, wet weather flow (WWF) due to the contribution from inflow and stormwater runoff in the sewer system, might ultimately lead to an overflow of untreated wastewater from the sewer system. Combined sewer overflows (CSOs) imply a loss of efficiency in the system and a major impact on the aquatic environment owing to the discharge of all types of substances (Butler and Davies, 2000). To become more familiar with the effect of CSO pressures on receiving waters (Adams et al., 1997; Seidl et al., 1998; Even et al., 2007), in recent decades, wet weather flow pollutant loads have ⁎ Corresponding author. Fax: +34 981167170. E-mail address: [email protected] (H. Del Río). 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.01.049

been studied extensively (Chebbo and Saget, 1995; Gupta and Saul, 1996; Veldkamp and Wiggers, 1997; Diaz-Fierros et al., 2002; Suárez and Puertas, 2005; Heinz et al., 2009). Studies on pollutants, in association with rainfall events leading to the mobilization of sediments accumulated in combined sewers during the antecedent dry period, have focused mostly on “conventional” pollutants (COD, BOD, suspended solids, nutrients, etc.) (Ashley et al., 2003; Sakrabani et al., 2009; Gasperi et al., 2010). Nevertheless, these waters also contain a large quantity of chemical substances including pharmaceuticals and personal care products (PPCPs), also called “micropollutants” (according to the order of magnitude of the concentration in wastewater during dry weather, of ppb, ppt or below) or “emerging pollutants”, based on recent studies (Carballa et al., 2005; Conkle et al., 2008; Kasprzyk-Hordern et al., 2009; Rosal et al., 2010). The concept of “micropollutants” includes a wide variety of substances which concentrations are below the range considered normal

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(mg/L) by quality analysis procedures (Schwarzenbach et al., 2006). In the case of PPCPs (Pharmaceuticals and Personal Care Products), the concentrations generally found in dry weather flows are in the ppb (μg/L) or ppt (ng/L) order of magnitude. In recent years numerous studies carried out especially in the USA and Europe detected a great number of these compounds in wastewater as well as in ground (aquifers) and surface (rivers and lakes) waters (Benotti and Brownawell, 2007; Buerge et al., 2006; Fono and Sedlak, 2005; Musolff et al., 2009; Spongberg and Witter, 2008; Weyrauch et al., 2010). The reasons for this general concern are based on the following: i) a lot of these substances are designed to produce biological effects (particularly the pharmaceutical compounds); ii) many of them are persistent; iii) they can exert negative environmental effects, even in orders of magnitude of parts per billion or parts per trillion (μg/L or ng/L, respectively) in case of estrogens, especially on aquatic life (Jobling et al., 1998; Luckenbach and Epel, 2005); iv) they may have potential accumulative effects in biota and; v) they may have synergistic effects when used in combination with each other (Fent et al., 2006). PPCP loads discharged from combined sewers may hinder compliance with the requirements of the European Water Framework Directive for the protection of water bodies (EC, 2000). The characterization of organic compounds and PPCPs in both raw wastewater and WWTP effluents is well documented in the literature. Nevertheless, CSOs and urban runoff may be the main sources of these substances in aquatic environments (Phillips and Chalmers, 2009). To date, little documentation exists on PPCP quantities from CSOs and on the environmental pressures of these substances. As a result, there is no legislation governing the parameters of either the spillage or the quality of the receiving waters. In addition, very few studies have been conducted on the behaviour of PPCPs in sewers and on the mobilization of these kinds of pollutants during rain events associated with the flush of sediments in combined sewers. Some important references are Boyd et al. (2004), who sampled two urban runoff channels in the city of New Orleans (USA). These channels receive CSO discharges in rainy weather. Phillips and Chalmers (2009) characterized overflows in wet weather from the Burlington WWTP to Lake Champlain in Vermont (USA). An analysis was performed on the flows from the bypass prior to biological treatment which had been processed through primary treatment and disinfection. By contrast, there are publications that analyse the variation in PPCP concentration in receiving waters depending on the weather, and compare the results obtained in dry weather with those from rainfall events (Benotti and Brownawell, 2007; Buerge et al., 2006; Jonkers et al., 2009; Musolff et al., 2009). Buerge et al. (2006) and Musolff et al. (2009) studied caffeine concentrations in the effluent of a treatment plant and in the aquatic environment. Both studies reported that the main source of caffeine in water bodies comes from the CSOs. In fact, there are sometimes higher concentrations in the aquatic environment than in the WWTP effluent. They conclude that caffeine is a good tracer for overflow discharges from combined sewers in the receiving environment, and is the main source of this substance in this environment. Another similar study was carried out by Fono and Sedlak (2005) in which the drug substance propranolol was used as a tracer to identify anthropogenic discharges to surface waters from CSOs. The study conducted by Benotti and Brownawell (2007) which analysed the concentrations of various micropollutants in Jamaica Bay in New York (USA) under different weather conditions (dry weather and rain events) established a correlation between the change in their concentrations in the waters of the bay and their removal in conventional treatment plants. This correlation shows that substances which, despite the presence of CSOs, tend to decrease their concentration in the water receiving environment in rainy weather have proportionally lower removal rates in the wastewater treatment plant. On the other

hand, micropollutants whose concentrations in the water environment increase during rain episodes, experience a high degree of removal in treatment plants. This phenomenon supports the findings of the previously mentioned study by Phillips and Chalmers (2009) on Lake Champlain in Vermont (USA) as well as the comprehensive work by Weyrauch et al. (2010) on the River Spree in Berlin, which also reported that high concentrations of certain substances found in transient discharges from CSOs may affect aquatic organisms. This article aims to provide a more in-depth understanding of the mobilization of these substances during rain events in urban combined sewers. A suitable characterization of these substances in WWF is necessary to determine whether there is micropollutant mobilization associated with the washout of deposits into the sewage, or if the main source of their presence in water can only be attributed to the dry weather permanent flow circulating through the combined sewer system. In this research paper 7 PPCPs were studied, all of which have been largely characterized in dry weather sewage flows in the literature. These micropollutants were analysed in Ensanche, a combined sewer catchment of the city Santiago de Compostela, located in northwest Spain. In order to determine the degree of mobilization during wet weather, it was necessary to ascertain the concentrations and loads in dry weather daily profiles and in the rain events characterized, for each substance. The PPCPs selected for the study were: HHCB galaxolide and AHTN tonalide (musk fragrances), ibuprofen and diclofenac (anti-inflammatory drugs), carbamazepine (antiepileptic), paracetamol (analgesic) and caffeine (stimulant). These compounds were analysed in both dissolved and solid phase. The knowledge of dissolved and particulate fractions for each substance may help to explain the level of mobilization in wet weather flows due to adsorption to the settled solids into the network during dry weather flows. For this reason, suspended solids have also been characterized. Furthermore, a relationship would be expected to exist between the wet weather level of mobilization of PPCPs and their removal performances in conventional WWTPs. This assumption is proposed on the basis of the adsorption of the substances to the deposits in the sewer. If these substances also have affinity to sludge or grease, they may be removed in the plant processes. The field campaign was extensive enough to get a number of representative results both in dry and in wet weather to perform statistical treatment of the data. A comparison of the results between dry weather and wet weather will allow conclusions to be drawn about the behaviour of each of the substances studied and to establish patterns. The statistical treatment of the data was used to determine maximum and mean concentrations under the two types of weather conditions for each micropollutant and a comparison was made with data from the literature. 2. Materials and methods The Ensanche, located in Santiago de Compostela (Northwest Spain) is the major catchment area of the city's drainage and sewer system (Fig. 1). It has mostly combined sewerage which collects wastewater from a population of 13,000 inhabitants and a catchment area of 20 ha. The urban catchment under study serves mainly residential and commercial areas whose characteristics include high population density and heavy traffic. The percentage of imperviousness in the catchment area is 94.5%. Furthermore, 68% of the area is built, while the rest is distributed among streets and parking zones. Green zones are practically non-existent, so that the Ensanche catchment can be described as predominantly “urban dense”. One of the main characteristics of this catchment is the steep slope of its streets, with an average of 4.2% and a maximum of 13.3%. This is an important fact to bear in mind in terms of the hydrologic–hydraulic

H. Del Río et al. / Science of the Total Environment 449 (2013) 189–198

191

Santiago de Compostela

100 m

Fig. 1. Ensanche catchment aerial view (Santiago de Compostela, NW Spain) and control section location.

sampler and a communication GPRS module, which transmits measured data (level and flow) on-line. Samples were taken over six dry weather days, workdays and weekends in the autumn and summer seasons, and during ten rain events over the four seasons of the year. Precipitation data were obtained from a rain gauge installed in the study area with data recorded at 10 minute intervals. The average dry weather flow measured was 22.4 L/s.

behaviour and pollutant mobilization in rainy weather conditions, with a time of concentration of only 10–15 min. The average annual rainfall in the city ranges between 1600 and 1800 mm (Meteogalicia). A control section was installed in the final part of the combined sewer of the Ensanche catchment between June 2008 and August 2009 (14 months). This section contains a submerged Area/Velocity Sigma 950 Open Channel flowmeter, an automatic Sigma 900 portable Table 1 Characteristics of rain events sampled. Rain events

1st

2nd

3rd

4th

5th

6th

7th

8th

9th

10th

Date Number of samples collected Precipitation data Antecedent dry period (ADP, days) Rainfall duration (hh:mm) Total precipitation (mm) Mean intensity (mm/h) Minutal ten maximum intensity (mm/h) Rain event flows Minimum (L/s) Maximum (L/s) Average (L/s) Max./average dry weather flow Volume Total (m3) Dry weather flow (m3) Runoff (m3) Runoff/total

10/06/08 8

10/21/08 8

01/12/09 8

04/15/09 8

04/25/09 8

05/10/09 8

05/23/09 8

06/04/09 6

06/25/09 6

08/24/09 8

13.6 1:20 1.2 0.9 1.8

4.8 1:30 9.7 6.5 12.6

9.9 3:00 4.4 1.5 4.2

0.8 1:20 2.0 1.5 3.6

6.9 1:00 1.8 1.8 2.4

0.2 1:00 2.6 2.6 7.2

6.3 1:30 4.6 3.1 4.8

0.2 0:20 1.4 4.2 4.8

14.4 0:50 1.1 1.3 3.0

22.9 1:30 4.2 2.8 4.8

35.1 90.6 60.3 4.0

102.1 446.8 183.8 19.9

51.0 133.1 98.4 5.9

28.9 132.6 58.0 5.9

25.2 107.5 64.0 4.8

46.5 91.3 65.1 4.1

75.0 169.5 135.4 7.6

42.6 204.5 105.3 9.1

45.9 106.1 69.7 4.7

36.1 125.0 81.2 5.6

114.7 63.7 51.0 44.4%

784.3 111.2 673.0 85.8%

443.8 135.4 308.4 69.5%

301.0 124.9 176.1 58.5%

273.4 103.9 169.5 62.0%

281.8 116.8 165.0 58.5%

589.6 105.8 483.8 82.1%

235.7 63.3 172.4 73.1%

138.7 71.6 67.0 48.3%

390.7 120.4 270.3 69.2%

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Table 2 Event maximum concentrations (EMACs) and event mean concentrations (EMCs) in the Ensanche catchment. PPCPs EMAC (μg/L) Maximum Minimum Average Std. dev. Median EMC (μg/L) Maximum Minimum Average Std. dev. Median

HHCB

AHTN

Ibuprofen

Diclofenac

Carbamazepine

Paracetamol

Caffeine

9.760 1.288 3.365 2.473 2.588

2.577 0.150 1.018 0.675 1.038

8.511 0.478 2.954 2.677 1.961

0.3090 0.0101 0.0959 0.0925 0.0770

0.066 0.007 0.033 0.021 0.028

5.71 0.18 1.93 2.63 0.294

32.86 1.30 15.98 11.35 18.063

3.745 0.426 1.395 1.034 1.028

1.735 0.069 0.448 0.494 0.326

5.297 0.110 1.277 1.674 0.600

0.180 0.003 0.055 0.059 0.140

0.029 0.003 0.015 0.009 0.024

4.139 0.100 1.245 1.789 0.140

18.91 0.57 7.72 6.88 8.310

Ibuprofen, diclofenac, carbamazepine, paracetamol and caffeine were analysed with an Agilent 1200 Series liquid chromatographic system, interfaced to an API-3200 triple quadrupole mass spectrometer. A Thermo Fischer Scientific Trace 2000 gas chromatograph, coupled to a Thermo Fischer Scientific Polaris Q ion trap mass spectrometer was used to analyse HHCB galaxolide and AHTN tonalide. A general limit of quantification (LOQ) of 6 ng/L was established for all compounds using the most unfavourable value. Concentration values below LOQ were set at 0 ng/L for the calculations. PPCP concentrations from aliquots with low standard recovery, overlapping peaks in the chromatogram or other problems in the chemical analysis were not considered. Additional method details are provided in the Supporting information. For each sampling campaign hydrograph and pollutographs were plotted. Each rain event presents a great variation in pollutant

For the dry weather methodology 3-L grab samples were taken every 3 h, with a total of eight for each day sampled, including both workdays and weekends. A total of 48 dry weather samples were analysed. In rainy weather, the sampler starts through a signal provided by the flowmeter. This signal is activated immediately when the flow rises over the dry weather maximum, calculated using flowmeter data obtained from the control section operation. The sampler was programmed to take eight 3 L samples, according to the following sampling sequence: 0′, 5′, 10′, 15′, 20′, 30′, 40′ and 60′. This protocol was selected based on the short time of concentration of the catchment. Table 1 shows the characteristics of the ten rain events sampled. Once collected, 200 mL sample aliquots were vacuum filtered through a glass fibre filter. The solid phase was extracted with methanol in an ultrasonic bath. The aqueous phase extraction was carried out with solid phase extraction cartridges, using methanol as an eluent.

Diclofenac, Carbamazepine: EMAC - EMC

0.35

30

0.30

Concentration (µg/L)

Concentration (µg/L)

Caffeine: EMAC - EMC

35

25 20 15 10 5

EMAC EMC

0.25 0.20 0.15 0.10 0.05 0.00

0 EMAC

EMC

Diclofenac

Carbamaze pine

HHCB, AHTN, Ibuprofen, Paracetamol: EMAC - EMC * Outlier

Concentration (µg/L)

10

8

EMAC EMC

Upper extreme

Upper Quartile

6

Mean Median

4 Lower Quartile

2

Lower extreme

0 HHCB Galaxolide AHTN Tonalide

Ibuprofen

Paracetamol

Fig. 2. EMAC and EMC box-whisker plots for PPCPs.

H. Del Río et al. / Science of the Total Environment 449 (2013) 189–198 Table 3 Maximum and average mean obtained for PPCPs in dry and wet weather.

HHCB galaxolide AHTN tonalide Ibuprofen Diclofenac Carbamazepine Paracetamol Caffeine

Statistical analyses of dry and wet weather concentrations were performed by constructing box-whisker plots (MINITAB, 2006).

Maximum concentrations (μg/L)

Mean concentrations (μg/L)

DWF

WWF

WWF/DWF

DWMC

EMC

EMC/DWMC

2.57 1.26 2.11 0.51 0.070 0.72 44.6

9.76 2.58 8.51 0.31 0.066 5.71 32.9

3.8 2.0 4.0 0.6 0.9 7.9 0.7

0.62 0.31 0.25 0.10 0.012 0.16 11.6

1.40 0.45 1.28 0.05 0.015 1.25 7.7

2.3 1.5 5.1 0.5 1.3 7.9 0.7

3. Results 3.1. Wet weather flow concentrations

DWF: dry weather flow. WWF: wet weather flows. DWMC: dry weather mean concentration. EMC: event mean concentration.

concentrations and loads. In order to understand a rain event, it is necessary to know the water flow rate and instantaneous concentration versus time for each substance. Therefore, hydrographs and pollutographs, variations of the pollutant concentrations during an event, are useful analysis tools. Taking into account their huge time variability and different shapes, some authors have suggested working with the event mean concentration (EMC) (Suárez and Puertas, 2005). The EMC is defined as the quotient of the total pollutant mass mobilized during an event and the event total water volume. EMC ¼

193

∑Q i ⋅Ci ⋅Δti ∑Q i ⋅Δti

The resulting data analysis of event maximum concentrations (EMAC) and event mean concentrations (EMC) of selected emerging pollutants is presented in Table 2. This analysis shows that the substances can be grouped by concentration ranges as described in the following lines. Higher concentrations of caffeine were found, maximum concentration ranges between 30 and 35 μg/L, with mean EMC values between 5 and 10 μg/L and maximum EMC values of about 20 μg/L (Fig. 2). Concentrations of the fragrance HHCB galaxolide, ibuprofen and paracetamol fall within a similar range showing maximum values between 5 and 10 μg/L, mean EMC values between 1 and 1.5 μg/L and maximum EMC in the vicinity of 3.5–5.5 μg/L. AHTN tonalide had maximum concentrations of around 2.5 μg/L, a mean EMC of 0.5 μg/L and a maximum EMC of 1.7 μg/L. Carbamazepine and diclofenac exhibited lower concentration values with maximum EMACs of about 0.07 and 0.3 μg/L, mean EMCs of 0.015 and 0.06 μg/L and maximum EMC of 0.03 and 0.18 μg/L, respectively. EMAC median of caffeine is approximately one order of magnitude higher with respect to the group of substances made up of HHCB, ibuprofen and AHTN and around 2 orders of magnitude higher than diclofenac and carbamazepine. 3.2. Comparison between dry and wet weather concentrations

Where: The results obtained in the dry weather flow (DWF) and wet weather flow (WWF) campaigns are summarised in Table 3, where maximum values and averaged flow-weighted mean concentrations are shown in both weather flows, DWMC (dry weather mean concentration) and

instantaneous flow instantaneous concentration time period between subsequent samples.

FIFTH EVENT: 04/25/09

FIFTH EVENT: 04/25/09 120

35

HHCB Galaxolide

Flow

80

20 60 15 40 10 20

5 0 17:00

17:30

17:45

18:00

18:15

18:30

18:45

6

19:00

Ibuprofen

60

4 Flow

3

40

2 20

1

0 17:15

3.0

140 120

2.5

100 2.0 80 1.5

60

1.0

40

0.5

20

0.0 18:00

0

HHCB Galaxolide

19:15

19:30

Dissolved HHCB Galaxolide

19:45

Concentration (µg/L)

160

19:00

17:45

18:00

18:15

18:30

18:45

19:00

250

3.0

Flow (L/s)

Concentration (µg/L)

3.5

18:45

17:30

EIGHTH EVENT: 06/04/09 180

18:30

80

Dissolved Ibuprofen

SEVENTH EVENT: 05/23/09 4.0

18:15

100

Dissolved HHCB Galaxolide

5

0 17:00

0 17:15

7

Flow (L/s)

100

Dissolved Caffeine

Concentration (µg/L)

30

Flow (L/s)

Concentration (µg/L)

Caffeine

25

120

8

HHCB Galaxolide

2.5

Dissolved HHCB Galaxolide

200

AHTN Tonalide

2.0

Dissolved AHTN Tonalide

150

Flow

1.5 100 1.0 50

0.5 0.0 21:40

0 21:55

22:10

22:25

Flow

Fig. 3. Total and dissolved PPCP pollutographs during rain events.

22:40

22:55

23:10

23:25

Flow (L/s)

Qi Ci Δti

H. Del Río et al. / Science of the Total Environment 449 (2013) 189–198

Table 4 Suspended solids results. Event maximum concentrations (EMACs) and event mean concentrations (EMCs) in the rain events sampled. Suspended solids (mg/L)

EMAC

EMC

First event Second event Third event Fourth event Fifth event Sixth event Seventh event Eighth event Ninth event Tenth event

437 2240 804 636 1580 568 1668 572 2708 3185

278 362 471 450 555 304 383 263 1447 811

is the slight correlation between the antecedent dry period and event mass flow of HHCB, one of the most highly mobilized PPCPs. In this case the correlation factor was 0.56. 3.3. Phase distribution concentrations

EMC (event mean concentration), for each substance. By comparing the dry and wet weather values obtained, it is clear that both maximum and averaged means for the substances studied in rainy weather flows are higher, or much higher, than in dry weather flows, except for diclofenac and caffeine. Some pollutograph examples (Fig. 3) are given, where significant concentration peaks are observed in the initial part of the rainy weather hydrographs. An overview of the results obtained for suspended solids in the monitored dry weather days present maximum concentrations between 276 and 474 mg/L and flow-weighted mean concentrations of 152–338 mg/L. Nonetheless, if the rainy weather suspension solids are analysed, they reflect much higher maximum concentrations than those of dry weather (Table 4). These high concentrations are registered in the initial part of the rain events (Fig. 4) similar to the results obtained for some PPCPs. It would be reasonable to assume that pollutant peaks are associated with solids washout derived from the antecedent dry weather period. These sediments are a major source of pollution in combined sewers during rain events (Gasperi et al., 2010). A statistical analysis comparing all the concentrations tested in the Ensanche was performed, classifying them into two groups, dry and wet weather (Fig. 5). The PPCPs having the greatest mobilization in rainy weather are, in ascending order, HHCB galaxolide, ibuprofen and paracetamol. Caffeine, diclofenac and carbamazepine concentrations tend to decrease during all period on rain events. However, this does not mean that there is no mobilization during rainfall since the mass flows are higher in rainy weather compared to dry weather for all the substances tested (Table 5). There is a high variability in the results of mobilized loads for any of the specific events sampled. Consequently, no clear relationship between loads and any of the characteristic parameters of each event (antecedent dry period, maximum rain intensity, medium rain intensity…) could be found. The only point worthy of mention

Dissolved and particulate distribution in dry and wet weather conditions, for all of the PPCPs studied, have been analysed in order to compare the two conditions. Fig. 6 presents a summary of the average values obtained. The most important observations of the analysis of this figure are described below. All substances are found mostly in dissolved form in both weather conditions. However, it is important to note that the particulate fraction is reduced during rainfall except in the case of carbamazepine whose value is identical in both weather cases. The percentage of particulate fraction for the group of fragrances (HHCB and AHTN), ibuprofen, caffeine and paracetamol ranged between 20% and 40% in dry weather, with this value being reduced by almost half in wet weather (15%–20%). This phenomenon also occurs with diclofenac, but with lower particulate fraction values, ranging from 10% (dry weather) to 5% in wet weather flows. The substances with lower rates of particulate fraction in the two weather cases, diclofenac and carbamazepine, have a lower mobilization during rain events with regard to the rest of the PPCPs, except caffeine. The studied Kd values for the events sampled, based on EMC of dissolved and particulate forms of the PPCPs ranged between 0.15 and 1 L/g for ibuprofen, paracetamol, caffeine and the fragrances HHCB galaxolide and AHTN tonalide. However, for substances with lower mobilization, diclofenac and carbamazepine, the maximum values did not exceed 0.45 L/g. 3.4. Comparison with the literature A review of the literature is presented as a broad summary (Table 6) which includes a comparison of the 7 selected PPCP concentration ranges obtained in the Ensanche catchment, in both weather conditions, with those presented in numerous publications where these substances have been analysed in raw sewage from different cities around the world of diverse population sizes. The results obtained in the above references by Boyd et al. (2004) and Phillips and Chalmers (2009) have also been added to Table 6. The concentration ranges of the PPCPs studied in the Ensanche catchment are similar to those found in the literature. It should also be noted that there are several references to concentration results with higher orders of magnitude, especially those presented by Gómez et al. (2007) who analysed PPCPs in the WWTP influent in Almeria (Spain) which receives wastewater from a nearby hospital.

SEVENTH EVENT: 05/23/09

FIFTH EVENT: 04/25/09 1800 100

Flow 80

1200 60

1000 800

40

600 400

20

200 0 17:00

0 17:15

17:30

17:45

18:00

18:15

18:30

18:45

19:00

Concentration (mg/L)

1400

SS

Flow (L/s)

Concentration (mg/L)

1800 1600

180

2000

120

2000

1600

SS

160

Flow

140

1400

120

1200

100

1000 80

800

60

600 400

40

200

20

0 18:00

0 18:15

18:30

Fig. 4. Suspended solid pollutographs during two rain events.

18:45

19:00

19:15

19:30

19:45

Flow (L/s)

194

H. Del Río et al. / Science of the Total Environment 449 (2013) 189–198

DWF vs WWF - Caffeine

DWF vs WWF - Diclofenac - Carbamazepine

50

0.4

Concentration (µg/L)

Concentration (µg/L)

195

40 30 20 10

DWF WWF

0.3 0.2 0.1 0.0

0 DWF

Diclofenac

WWF

Carbamazepine

DWF vs WWF - HHCB, AHTN, Ibuprof., Parac. 6 5

Concentration (µg/L)

* Outlier

DWF WWF

Upper extreme

Upper Quartile

4 Mean

3

Median

2 Lower Quartile

1

Lower extreme

0 HHCB Galaxolide AHTN Tonalide

Ibuprofen

Paracetamol

Fig. 5. PPCP box-whisker plots for DWF and WWF concentrations.

The PPCP concentrations in the Ensanche catchment during rainfall events indicate that there is no dilution effect for these substances. The concentration values obtained always remain within the same order of magnitude as those of dry weather wastewater. The literature reviewed here includes only one reference that can be used in a comparison with the casuistry of the Ensanche catchment. As discussed earlier, this paper shows that wet weather PPCP concentrations do not obey the “dilution effect”, rather the opposite is assumed to occur at the beginning of rain events. The concentrations are generally higher as compared to those found in dry weather flows. This implies that the mass flow proportions of wet weather pollutants are even greater than those of the dry weather flows generated in the catchment. This reference work was published by Musolff et al. (2009), who characterized a PPCP group in an urban catchment in Leipzig (Germany). The concentrations of a pair of micropollutants, one of which was carbamazepine, were found to be higher in the CSO discharges with respect to dry weather wastewater. The rest of the micropollutants studied decreased in concentration during rain events but were always higher than the theoretical values, when only the dilution factor was taken into account. Musolff et al. (2009) attribute these results to several possible factors: the high temporal variability of the PPCP concentrations in wastewater, the low temporal representativeness of the manual Table 5 Average mass flow in dry and wet weather. PPCPs

DWF (mg/h)

Rain event (mg/h)

HHCB galaxolide AHTN tonalide Ibuprofen Diclofenac Carbamazepine Paracetamol Caffeine

50.0 ± 16.4 25.0 ± 5.9 20.2 ± 15.2 8.1 ± 7.8 1.0 ± 0.4 12.9 ± 5.8 935.4 ± 497.5

504.0 ± 253.3 162.0 ± 128.3 460.8 ± 410.7 18.0 ± 17.2 5.4 ± 3.5 450.0 ± 410.7 2772.0 ± 1887.7

samples and the recognition of specific “first flush” effects in the catchment. It was therefore concluded that discharges from CSOs represent short spills in terms of duration in time but with high loads of PPCPs. However, it is not easy to obtain a comprehension of the behaviour of micropollutants in the sewerage since the particularities of each substance in terms of their physico-chemical properties increase the complexity of the phenomena that occur when they flow through miles of collectors that form the combined sewer system. In any case, it would seem evident that the best CSO tracers are the PPCPs which have a high rate of removal in wastewater treatment plants, such as caffeine and ibuprofen (Buerge et al., 2006; Buser et al., 1999, cited by Fono and Sedlak, 2005). In the literature there are numerous references to the removal efficiencies of the 7 PPCPs studied in the Ensanche catchment in conventional WWTPs (Table 7). Carballa et al. (2005) studied the removal efficiency of several PPCPs in the wastewater treatment plant of Santiago de Compostela, including tonalide, galaxolide and ibuprofen. The results showed high removal rates, especially for the fragrances, with values ranging between 70% and 90%. This behaviour was attributed mainly to the adsorption capacity of these fragrances on solid particles. Paracetamol concentrations decrease almost entirely in WWTPs, with removal ranging from 92% to 100% in two wastewater treatment plants in Wales (Kasprzyk-Hordern et al., 2009). These results corroborate those reported by Jones et al. (2007). A similar behaviour was observed with ibuprofen at WWTP removal efficiencies of 96% (Bendz et al., 2010), 78%–100% (Lindqvist et al., 2005) and 87% (Yu et al., 2006). These removal values were consistent with the results of Nakada et al. (2006). By contrast, the findings in the literature indicate that diclofenac shows, generally, low removal rates in conventional treatment plants (Kasprzyk-Hordern et al., 2009; Lishman et al., 2006; Spongberg and Witter, 2008; Yu et al., 2006). Paracetamol, ibuprofen and diclofenac WWTP performances are also in keeping with the studies of Gómez et al. (2007) and Terzic et al. (2008).

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Particulate phase

PPCPs Particulate Fractions: DWF vs WWF

50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0%

DWF

WWF

Fig. 6. Average particulate fraction of each PPCP studied in dry and wet weather flows.

The antiepileptic carbamazepine behaves in the same way as diclofenac and they both also have a low removal rate in conventional wastewater treatment plants according to Kasprzyk-Hordern et al. (2009) and Lindqvist et al. (2005). However, Benotti and Brownawell (2007) obtained a removal performance of 37% for this substance. Caffeine is one of the most widely studied PPCPs and all of the references would indicate that its removal in WWTPs is very high,

ranging from 85% to 100% (Bendz et al., 2010; Buerge et al., 2006; Conkle et al., 2008; Gómez et al., 2007; Lin et al., 2009). An analysis of the WWTP removal efficiency values found in the literature and the variation in DWF and WWF concentrations for each PPCP studied in the Ensanche catchment, indicated a strong agreement between them. The greater the increase between DWF and WWF concentrations, the higher the removal rate in WWTPs, which was probably due to solids and biofilm adsorption affinity of each substance. This phenomenon may explain the conclusions of Benotti and Brownawell (2007) and Phillips and Chalmers (2009) in their studies on the water quality of Jamaica Bay and Lake Champlain, respectively. Table 7 shows a good agreement between the degree of mobilization during rain events and sewage treatment plant removal efficiency in each micropollutant studied, except caffeine. The correlation factor between the ratio average EMC/average DWMC and mean removal in WWTPs is 0.56. This represents only a weak positive relation. If caffeine is taken out, the correlation factor improves to 0.74. This result supports the assumption, previously suggested in the introduction section, that the substances with higher removal rate in the WWTPs, are sensitive to adsorption on solid phase phenomena. Hence, they suffer a higher degree of mobilization in wet weather associated with the washout of sediments and biofilms in combined sewers. The different behaviour of the caffeine is probably due to degradation processes instead of adsorption. This explanation is in agreement with Buerge et al. (2006) and Sui et al. (2010); as they state that caffeine is highly removed in secondary treatment but not removed to a significant extent during primary clarification.

Table 6 Comparison of the PPCP concentrations in the Ensanche catchment with the literature. Concentration (μg/L) Ensanche DWF Carballa et al. (2005)a Kasprzyk-Hordern et al. (2009)a Fent et al. (2006)a Gibson et al. (2007)a Gros et al. (2006)a Gros et al. (2009)a Lajeunesse and Gagnon (2007)a Roberts and Thomas (2006)a Yu et al. (2006)a Zorita et al. (2009)a Nakada et al. (2006)a Lin et al. (2009)a Conkle et al. (2008)a Vieno et al. (2007)a Rosal et al. (2010)a Buerge et al. (2006)a Sui et al. (2010)a Takao et al. (2008)a Lishman et al. (2006)a Terzic et al. (2008)a

Range DWMC range DWMC average

Range Average

HHCB galaxolide

AHTN tonalide

Ibuprofen

Diclofenac

Carbamazepine

Paracetamol

Caffeine

0.01–2.57 0.08–0.83 0.62 2.1–3.4

bLOQ–1.26 0.001–0.43 0.31 0.9–1.7

0.01–2.11 0.08 –0.31 0.25 2.6–5.7 1.68/2.29 0.54–38.7 4.38/5.09 bLOQ–0.9 13.2 0.83–1.17 0.027–7.74 1.9 6.9 0.381–1.13 0.71–17.9 9.92

bLOQ–0.51 0.004–0.14 0.10 bLOQ 0.069/0.26 0.35–5 1.72/6.36 0.05–0.54 0.73 0.020–0.216 0.90–1.04 0.11 0.23

bLOQ–0.070 0.001–0.021 0.012 bLOQ

bLOQ–0.72 0.05 –0.51 0.16

bLOQ–44.6 0.02–16.2 11.6

bLOQ–1.93 0.95

bLOQ–4.1 2.7

bLOQ–0.56 0.23

5.2 2.03 0.03–2.67 0.63

2.0 0.80 0.052–0.86 0.25 1.9–4.7

0.006–1.07 0.147 16.5 8.45 bLOQ–11.9 3.20 0.16 –1.1

0.07–9.76 0.43–3.75 1.40 0.37–0.43

bLOQ–2.58 0.07–1.74 0.45 bLOQ–0.11

bLOQ–25.0 10.0

0.32 Range Average Maximum Average Range Average

Simonich et al. (2000)a, Bester (2004)a Ensanche WWF Phillips and Chalmers (2009)b Boyd et al. (2004)c

0.003–0.437

Range EMC range EMC average

bLOQ: lower than the limit of quantification. a WWTP Influent Dry Weather. b Bypass WWTP wet weather prior to biological (primary treatment + disinfection). c Urban runoff flow with CSO discharges.

bLOQ–0.674 0.01–8.51 0.11 –5.30 1.28

0.7/1.5 bLOQ–0.95 0.157 0.044–0.701

211.4/178.1 6.9 0.13 –26.1 10.9 0.069–6.92 0.96

0.015–0.27 0.082–0.357 0.057 0.16–0.82 0.106–0.173 0.13

39.3

5.01–65.6 22.9 7.0–73.0 3.4–6.6

0.113 bLOQ–0.35 0.062

1.01 0.204 0.050–4.20 0.859

0.12–1.55 0.419

bLOQ–0.31 0.003–0.180 0.055

bLOQ–0.066 0.003–0.029 0.015

5.2–17.5 25.6

0.04 –5.71 0.10 –4.14 1.25

bLOQ–32.9 0.57–18.91 7.72 11–12

H. Del Río et al. / Science of the Total Environment 449 (2013) 189–198 Table 7 Range and mean concentration values in dry and wet weather flows in the Ensanche catchment and WWTP removal efficiency values obtained in the literature for each of the PPCPs studied. PPCPs (μg/L)

DWF

WWF

Removal efficiency in WWTPa

HHCB galaxolide

0.01–2.57 0.62 bLOQ–1.26 0.31 0.01–2.11 0.25 bLOQ–0.51 0.10 bLOQ–0.070 0.012 bLOQ–0.72 0.16 bLOQ–44.6 11.6

0.07–9.76 1.40 bLOQ–2.58 0.45 0.01–8.51 1.28 bLOQ–0.31 0.055 bLOQ–0.066 0.015 0.04–5.71 1.25 bLOQ–32.9 7.72

70%–90%

AHTN tonalide Ibuprofen Diclofenac Carbamazepine Paracetamol Caffeine

70%–90% 78%–100% 0%–18% 0%–37% 98%–100% 85%–100%

a Bendz et al. (2010), Benotti and Brownawell (2007), Buerge et al. (2006), Carballa et al. (2005), Conkle et al. (2008), Gómez et al. (2007), Kasprzyk-Hordern et al. (2009), Lin et al. (2009), Lindqvist et al. (2005), Lishman et al. (2006), Spongberg and Witter (2008), Terzic et al. (2008) and Yu et al. (2006).

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