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Evaluation of three full scale sewage treatment plants for occurrence and removal efficacy of priority phthalates
Journal of Environmental Chemical Engineering 4 (2016) 2628–2636
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Evaluation of three full scale sewage treatment plants for occurrence and removal efficacy of priority phthalates Khalid Muzamil Gani* , Absar Ahmad Kazmi Environmental Engineering Group, Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttrakhand 247667, India
A R T I C L E I N F O
Article history: Received 20 February 2016 Received in revised form 13 April 2016 Accepted 5 May 2016 Available online 7 May 2016 Keywords: Activated sludge process Micropollutants Phthalates Sequencing batch reactor Wastewater treatment plant UASB
A B S T R A C T
The study focuses on evaluation of occurrence of four priority phthalates in sewage and their removal in sequencing batch reactor (SBR), activated sludge process (ASP) and up flow anaerobic sludge blanket (UASB) reactor based full scale sewage treatment plants (STPs). Mean concentration of total four phthalates in raw sewage and secondary sludge was in the range of 35.5–46.1 mg/L and 26.1–71.8 mg/kg respectively. The concentration of phthalates in anaerobic sludge was more (71.8 mg/kg) than aerobic sludge from SBR (26.1 mg/kg) and ASP (48.4 mg/kg). Overall removal of phthalates by biodegradation and adsorption was >75% in all STPs. However, biodegradation was the main removal process. A significant portion of incoming phthalates (18–31%) was removed in primary settling tanks as well. Phthalate removal and conventional performance of STPs showed positive correlation with value of spearman correlation coefficient in the range of 0.443–0.583. The study may act as a contribution to the understanding which is required to improve the removal of phthalates or similar organic micropollutants in wastewater treatment. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Phthalates or phthalic acid esters (PAE) are used as plasticizers in polyvinyl chloride (PVC) products and additives in personnel care products. These compounds are also used in floorings, paints, food packaging, car coatings and wall coverings. Exposure of these compounds have harmful effects such as cancer and endocrine disruption. Other defects such as lethargy, imbalance and respiratory arrest can also occur on their exposure [1,2]. United States Environmental Protection agency (U.S. EPA) classified few phthalates such as Diethyl phthalate (DEP), Dibutyl phthalate (DBP), Benzylbutyl phthalate (BBP) and Diethylhexyl phthalate (DEHP) as priority pollutants for their potential harmful impact in environment [3]. Phthalates get leached from their parent product during manufacturing and during their use or disposal [4]. Past studies have reported the occurrence of phthalates in domestic untreated and treated sewage [5–7]. Gao et al. [8] reported occurrence of six phthalates at three domestic sewage treatment plants in China and
* Corresponding author. E-mail addresses: [email protected] (K.M. Gani), [email protected] (A.A. Kazmi). http://dx.doi.org/10.1016/j.jece.2016.05.006 2213-3437/ã 2016 Elsevier Ltd. All rights reserved.
the concentration reported in influent and effluent samples was 23.28–88.46 mg/L and 6.95–61.49 mg/L respectively. The concentration observed in sludge was in the range of 5.074–28.135 mg/kg with maximum concentration of DEHP. Roslev et al. [9] reported their occurrence at an activated sludge based sewage treatment plant in Denmark and the concentration of four phthalates in influent and effluent was 78.25–193.82 mg/L and 5.90–17.23 mg/L respectively. The mean concentration of four phthalates in sludge was 71.78 mg/kg. Treated effluents from these sewage treatment plants is a major source of phthalates to aquatic sources which if not addressed may have eco toxicological effects on aquatic life [8,10]. Existing sewage treatment plants were designed for organic and nutrient removal or recovery, therefore removal of phthalate like micropollutants is generally poor in such treatment plants [11–13]. Nonetheless advance treatment technologies such as advance oxidation processes, activated carbon and ozonation are effective in removal of phthalates or such toxic compounds [14–16] but the higher costs associated with their implementation make them less preferable. Therefore as an alternative, existing STPs are to be optimized for removal of phthalate like trace organics which require fate investigation of phthalates in full scale STPs. Evaluation of existing STPs may led to generation of real field data and inferences which help in identifying efficient phthalate removal processes. Previous
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studies have shown that removal of phthalates in full scale STPs can vary from 60% to 100% [8,17,18]. Fauser et al. [19] reported that there is approximately 70% and 48% of DEHP and BBP degradation in a full scale STP. Dargnat et al. [6] found DBP, BBP and DEHP are approximately removed by 80%, 97% and 78% respectively in a primary aeration nitrification based plant. Gao et al. [8] found removal of DEP, DMP and DBP as 90–100%, 63–100% and 53–85% respectively in three full scale nutrient removal based STPs. Conventional activated sludge process, sequencing batch reactor (SBR) and up flow anaerobic sludge blanket (UASB) with natural process as post treatment are among commonly adopted sewage treatment technologies [20,21]. Among aerobic suspended growth processes, ASP is the most promising technology designed usually for carbonaceous removal. Cyclic activated sludge process in the form of SBR is a modified form of ASP which operates in a fill and draw manner. Among anaerobic processes of wastewater treatment UASB has been recognized as appropriate technology for its simplicity in construction and operational costs [22]. However, the effluent of UASB reactor usually does not met the discharge standards and are therefore coupled with post treatment of final polishing units [21]. Conventional ASP and SBR based treatment plants exist in developing as well as developed countries while as UASB with polishing units as post treatment is mostly adopted in developing countries like India [23]. These sewage treatment
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technologies have been well studied for organic and nitrogen removal. But little is known about fate of phthalates in these technologies. Therefore the objective of this research was investigation of occurrence level, and removal of phthalates in SBR, ASP and UASB technology based STPs. Samples in between the sewage treatment line were analyzed to determine the removal efficiency of phthalates in various treatment units. Mass balance approach was used to determine the contribution of removal mechanisms involved in removal of phthalates. The phthalates selected for the study were DEP, DBP, BBP and DEHP which are enlisted as priority phthalates by U.S. EPA. Their properties and structures are shown in Table S1. 2. Material and methods 2.1. Chemicals All standard solutions of phthalates were purchased from Sigma Aldrich (Germany) with purity 99.5%. Solvents (N-Hexane, Dichloromethane and acetone) used for the extraction of phthalates were purchased from Merck (Mumbai, India). Distill water from Milli-Q Advantage A10 system (Millipore, USA) was used for cleaning of glassware.
Table 1 Design and operational parameters of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. Parameter 27 MLD SBR Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of primary clarifier (m) Number of primary clarifiers Basin size (m) and number HRT (hours) MLSS of basin (mg L 1) MLVSS of basin (mg L 1) Cycle time (hours) Filling and aeration time Settling time Decanting time Effluent disposal 18 MLD ASP Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of primary clarifier (m) Number of primary clarifier Aeration tank size (m) and number HRT in aeration tank (hours) MLSS of Aeration tank (mg L 1) MLVSS of Aeration tank (mg L 1) Return sludge recycle ratio Dimensions of secondary clarifier Number of secondary clarifier Dimension and number of sludge thickener Number of Sludge digesters Number of Gas collectors Dimensions of sludge drying beds and numbers Sludge Disposal Effluent Disposal 38 MLD UASB Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of UASB and number HRT of UASB (hours) Volume of Polishing pond and number HRT of Pond (hours) Dimensions of sludge drying beds and numbers Disposal of treated sludge Treated effluent disposal
Details 27000 27000 24 Diameter 3 m Depth 2 Area – 39 19.5; Side water depth (SWD) – 4.1 m and 4 in number 11 5205 1807 1641 515 3 1.5 h per cycle 0.75 h per cycle 0.75 h per cycle River Ganga 18000 18000 15 m Diameter and 0.785 m Depth 3 Area – 15 m 15m; SWD – 4.8 m and 3 in number 4.3 3228 276 1516 166 0.5–0.6 Diameter – 19.5 m; Depth – 3.5 m 3 Diameter – 11.4 m; Depth – 3 m and 02 2 4 Area – 35 m 24 m; Depth – 0.25 m and 12 Agricultural land River Ganga 38000 38000 28 m 24 m 6.05 m and 4 numbers 10.2 38000 m3 total and 2 numbers, 24 25 m 14 m each and 20 numbers Agricultural land River Dhamola
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2.2. Sewage treatment plants Three full scale STPs based on SBR, ASP and UASB technology were chosen for this study designed with a treatment capacity of 27000, 18000 and 38000 m3/d. Accordingly the notation adopted in this paper was 27 million litres per day (MLD) SBR, 18 MLD ASP and 38 MLD UASB respectively. Table 1 shows the various operational details of the treatment plants. The raw sewage was pretreated in primary settling tanks (PST) in 18 MLD ASP and 27 MLD SBR. The primary effluent was treated at a hydraulic retention time (HRT) of 11 h and 4.3 h respectively. The operational cycle in the SBR consisted of 90 min of aeration, 45 min of settling and 45 min of decanting and the internal recirculation ratio was 44% of the feed flow. In 18 MLD ASP, returned activated sludge (RAS) was fed at recirculation ratio of 0.5–0.6. These two treatment plants (27 MLD SBR and 18 MLD ASP) were constructed nearby to each other and sludge treatment for both STPs was common. The sludge treatment at the STPs was thickening followed by anaerobic digestion and drying in sludge drying beds. The dried sludge was used by local farmers for agricultural purposes. In 38 MLD UASB, the degritted sewage was treated in UASB reactors at HRT of 10.2 h. The up flow velocity of degritted in UASB was 0.5 m/h. The depth of sludge bed in the UASB reactor was approximately 2 m. The average gas production in the UASB reactors was 773 127 m3/day. UASB effluent was post treated in polishing units having HRT of 24 h. Excess sludge from UASB reactors was removed weekly and dried over sludge drying beds which were 20 in number. The dried sludge was used by local farmers for soil improvement in agricultural fields. 2.3. Sampling Samples of wastewater and sludge were collected for a period of seven months. All sewage samples were collected monthly while as sludge samples were collected bimonthly. Average monthly temperature regime throughout the duration of seven months was15 3 C to 32 4 C. In 27 MLD SBR, sewage samples were collected at inlet, outlet of primary settling tank and outlet of SBR. The sludge samples were collected from aeration basin of SBR. Similarly in 18 MLD ASP, the samples were collected from inlet, primary settling tank outlet and secondary clarifier outlet while as sludge samples were collected from the wastage sludge stream. In
38 MLD UASB, sewage samples were collected from inlet, UASB outlet and polishing pond outlet. Sludge samples were taken from wastage flow line UASB reactor. Total 163 grab samples of sewage (untreated, primary treated and treated) and nine samples of sludge were collected during sampling of all three treatment plants. Samples were collected in amber color glass bottles with Teflon cap to avoid photo degradation and contamination of plastic material. Prior to sampling, the sample bottles were rinsed with distill water and acetone. Separate samples were collected for conventional parameters of wastewater and sludge. Collected samples were extracted within 24–48 h of sample collection alongwith preservation at 4 C. 2.4. Sample preparation Sample preparation for the analysis of phthalates was according to the method 606, US EPA [24]. Extraction of 250 ml unfiltered wastewater sample was done by liquid extraction procedure in 25 ml of Hexane/acetone solution (4:1). The extraction was done thrice on a rotary shaker for 15 min followed by separation in a separatory funnel. The extract was passed over 10 g of anhydrous sodium sulphate to remove water content and further concentrated to 2 ml. The concentrated extract was further cleaned up in a chromatographic column (2 cm internal diameter) filled with neutral alumina (10 g) and pre eluted with 20 ml of n-hexane. The sample was eluted with 60 ml acetone/hexane (1:2) solution and concentrated to 5 ml for analysis in GC MS. Sludge samples were dried and one gram of dry sludge was extracted in 80 ml of n hexane/Dichloromethane (60 ml: 20 ml) solution for 12 h on a rotary shaker. The extracted sample was filtered and the filtrate was used for analysis of phthalates in GC MS after concentration and cleanup. The cleanup procedure for sludge extract was same as that of wastewater samples. 2.5. GC MS analysis and quality assurance The concentrated samples were analyzed in a Varian 450 GC coupled to a Varian 240 MS (Agilent Technologies, Avondale, PA, USA) equipped with a capillary column (30 m 0.25 mm ID, 0.25 mm film thickness, Factor Four, Varian Technologies). Helium (99%) was used as carrier gas at a flow rate of 0.8 ml/min. The temperature program for separation was 60 C (hold time of 1.0 min), 250 C (6 C/min, hold time of 1.0 min), and 280 C (hold
Table 2 Concentration of conventional parameters at various treatment stages of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. Parameters
Raw sewage (mg/L) Mean Std. Dev.
Primary/UASB effluent (mg/L) Mean Std. Dev.
Secondary effluent (mg/L) Mean Std. Dev.
27 MLD SBR COD BOD TSS NH4+-N TN
319 148 207 22.8 39.7
77 29 28 6.0 10.0
184 96 101 19.9 35.2
58 9 25 6.4 9.2
36 12 15 0.9 5.1
19 5 7 0.3 0.6
18 MLD ASP COD BOD TSS NH4+-N TN
304 146 204 17.3 33.4
56 31 34 5.4 3.2
164 90 121 13.8 28.6
17 13 38 3.5 2.9
22 12 11 1.1 5.8
10 6 6 0.2 2.1
38 MLD UASB COD BOD TSS NH4+-N TN
374 186 263 31.5 56.3
73 41 80 5.8 3.8
145 63 72 27.3 46.3
23 18 22 5.4 8.0
74 25 53 16.3 22.4
15 8 20 5.2 3.8
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time of 2 min). Five microliters of sample was injected in split less mode with injector temperature of 250 C. The calibration was done with pure standard solution and the spectra obtained was matched with the NIST library and selected as reference in the analysis. The percentage recovery of the analysis method was measured by spiking wastewater samples with known amount of phthalate (Fig. S1, supplementary data). The recoveries obtained were more than 80% for each phthalate (Table S2). The limit of detection of the method was 0.071, 0.13, 0.21and 0.084 mg/L for DEP, DBP, BBP and DEHP respectively. The limit of quantification was 0.210, 0.182, 0.342 and 0.241 mg/L for DEP, DBP, BBP and DEHP respectively.
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performance of the STPs chosen for this study. Based on the physicochemical characteristics, the raw sewage at three STPs can be categorized as medium to high concentrated sewage [29].
2.6. Fate calculations Organic micropollutants are mainly removed by biodegradation, adsorption and volatilization in a sewage treatment plant. Volatilization depends on Henry’s constant (kH) and can occur due to aeration in the biological reactor [25]. Organic micropollutants with kH around 10 7 atm m3/mol have negligible removal by volatilization [26]. The kH of analyzed phthalates is around the same value (Table S1). Therefore the contribution of volatilization to overall removal of phthalates was neglected. The removal of phthalates by biodegradation (Mdeg) was calculated by subtracting the adsorbed flux of phthalates (Msor) from the overall removal (Mi Mo). Mdeg = (Mi
Mdeg = Q (Ci
Mo)
Co)
Msor
(Csor TSwas Qwas)
Where Q is inflow rate of sewage; Ci is the concentration of P PAEs in influent and Co is concentration of PAEs in effluent. Csor P is mean concentration of PAEs in sludge, TSwas is solid content in wasted sludge and Qwas is flow rate of wasted sludge. Multiplication of TSwas and Qwas is the flux of solids wasted from the bioreactor. P
2.7. Data analysis Spearman correlation coefficients were obtained in SPSS, version 20.0 (IBM Corporation). The correlations were considered statistically significant for p < 0.01 and p < 0.05. Remaining data analysis was done in Excel (Microsoft word 2013). 3. Result and discussion 3.1. Sewage characteristics Table 2 shows the average concentration of physicochemical parameters (COD, BOD, TSS, ammonia, total nitrogen and phosphorus) at different stages of treatment in each sewage treatment plant. The source of sewage was domestic at three treatment plants which include wastewater generated in homes, from small scale industries and storm runoff. The average concentration of COD and BOD in raw sewage was 304–374 mg/ L and 146–186 mg/L respectively while as the average concentration of TN was 29.5–56.3 mg/L. Large concentration of COD and low concentration of TN indicate insignificant industrial contribution. in raw sewage at three STPs. Mungray and Kumar [27] also reported comparable characteristics of raw wastewater at 38 MLD UASB with insignificant contribution of industrial wastewater. The average concentration of COD, BOD and TSS was below 150, 30 and 50 mg/L respectively which are standard discharge parameters in India [28]. This indicated the satisfactory operation and
Fig. 1. Percentage removal of conventional parameters in various treatment units of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB.
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3.2. Treatment performance of STPs
3.3. Occurrence of phthalates in raw sewage
Fig. 1 shows the conventional performance of various treatment units of three STPs. During the study period, mean percentage removal of COD and TSS in primary settling tank of 27 MLD SBR was 41.9 13.9% and 48.2 8.3% respectively whereas in primary settling tank of 18 MLD ASP it was 51.0 9.8% and 41.5 13.6% respectively. COD and TSS removal efficiency in primary settling tanks was within the range of 30–60% reported in literature [29]. In bioreactors of these two STPs, carbonaceous and solid removal was 80–90%. There was no significant difference among bioreactors in the removal of these parameters. Both reactors performed well during the study period. Nitrification measured as percentage removal of ammonia was also >90% in both bioreactors. The percentage removal of total nitrogen was 82.4 2.6% in SBR and 84.7 2.1% in whole treatment scheme (Fig. 1). Better nitrogen removal in SBR was obvious but in ASP bioreactor the nitrogen removal was probably due to mixed conditions and surface aeration mechanism [26]. Van Huyssteen et al. [30] reported significant nitrogen loss in aeration basin aerated by surface aerators. They opined about it that as mixed liquor traveled away from surface aerators, the DO get depleted and create conditions favorable for anoxic reactions. Secondly activated sludge floc can contain both aerobic and anoxic zones. Overall both STPs were satisfactory performing in carbonaceous and nitrogen removal during the study period. In UASB reactor, the mean percentage removal of COD, BOD and TSS was 60.5 6.0%, 66.7 6.1% and 61.3 13.3% respectively. The observed organic removal was comparable with the 69% removal as reported by Mungray and Kumar [27] for this STP. The percentage removal of ammonia and total nitrogen in UASB reactor was 59.7 and 30.3% respectively which was lesser compared to 66 and 55% removal in polishing ponds. UASB reactors are not designed for nitrification process however the observed removal may be due to aeration by atmospheric oxygen as the top surface is open to the atmosphere. In addition, anaerobic oxidation of ammonia with nitrite by anammox may have their contribution to the observed nitrification [31]. The pollution parameters were further removed in the final polishing unit and as a result the percentage removal of COD, BOD and TSS was more than 79%, 84% and 83% respectively in the whole treatment plant. Ammonia and TN percentage removal also increased to 62% and 65% respectively. These results confirm proper working of the treatment processes in the STPs and assured that these STPs were appropriate for investigation of fate of phthalates.
The mean concentrations of individual compounds in raw sewage and treated sewage is shown in Table 3 and the sum of P phthalates ( PAEs) at various stages of treatment scheme of the wastewater treatment plants is shown in Table 4. PAE concentration in raw sewage was almost same at 27 MLD SBR and 18 MLD ASP (45.571 mg/L and 46.107 mg/L respectively) which may be due to their common sewerage system. The concentration at 38 MLD UASB was slightly lower with mean concentration as 35.508 mg/L and varied over a wide range of 1.014–155.939 mg/L. The wide variation was obvious because of the inconsistency in the sources of these compounds. The sources of phthalates in domestic sewage may be toilet water, personnel care products, leachates from solid waste dumping sites and urban runoff [32]. There are no norms in Indian standards for phthalates. However, comparison with international regulations showed that DEHP in treated effluents of investigated STPs exceeded its environmental quality standard (EQS) of 1.3 mg/L (Table S4, supplementary information). The relation between phthalate concentration and the corresponding conventional parameters (COD, BOD and TSS) was analyzed by spearman correlation coefficient. The obtained correlation was significant for all three parameters as shown in Table S3 (p < 0.01; n = 63). The value of coefficient was around 0.5 for all parameters which showed positive relation between phthalates and conventional parameters (COD, BOD and TSS). Positive correlation of phthalate concentration with COD may be due to organic nature of phthalates and COD measures the degradable and non-degradable organic content in the wastewater. Positive correlation between phthalates and TSS may be due to high octanol water coefficient of phthalates such as BBP and DEHP for which these compounds are adsorbed to organic suspended solids. 3.4. Occurrence of phthalates in sludge Table 3 shows the concentration of phthalates in the secondary sludge of STPs. All four phthalates were present in the secondary sludge of each treatment plant. The mean concentration in secondary sludge of 18 MLD ASP and 27 MLD SBR was 26.1 mg/ kg and 48.4 mg/kg respectively. Whereas the phthalate concentration in sludge of 38 MLD UASB was 71.8 mg/kg which was larger than that observed in 18 MLD ASP and 27 MLD SBR. The presence of phthalates in sludge is a consequence of their adsorption to biosolids [20]. An evaluation survey of hazardous chemicals in sludge has showed that mean concentrations of phthalates in
Table 3 Concentration of individual phthalates in raw sewage and treated sewage alongwith their removal in investigated treatment plants. Phthalates
Raw sewage
Treated sewage
Removal (%)
Range
Mean SD
Range
Mean SD
Mean SD
27 MLD SBR DEP DBP BBP DEHP
n.d.–7.376 n.d.–30.390 n.d.–6.893 1.354–124.357
5.417 4.149 11.175 9.977 1.968 2.280 27.011 14.341
n.d.–3.076 n.d.–5.417 n.d.–1.175 n.d.–16.451
0.737 0.410 2.188 1.847 0.259 0.043 4.253 2.521
86 24 80 13 87 28 84 31
18 MLD ASP DEP DBP BBP DEHP
n.d.–13.363 1.740–90.360 n.d.–19.807 n.d.–26.021
5.319 3.407 19.153 9.310 3.845 0.618 17.790 7.693
n.d.–3.298 0.661–10.718 n.d.–4.732 n.d.–8.062
0.879 0.117 3.263 2.366 0.907 0.612 2.923 1.257
84 16 83 24 76 18 84 21
38 MLD UASB DEP DBP BBP DEHP
n.d.–5.331 0.813–12.228 n.d.–6.479 n.d.–132.441
3.095 2.084 5.471 4.393 2.772 1.818 24.169 14.673
n.d.–1.328 n.d.–2.675 n.d.–2.633 n.d.–32.549
0.509 0.311 1.027 0.755 0.715 0.238 6.932 1.055
84 21 81 23 74 13 71 8
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Table 4 Concentration of total phthalates in wastewater and sludge of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. STP
Raw sewage (mg/L) Min
Max
27 MLD SBR 18 MLD ASP 38 MLD UASB
16.794 14.467 1.014
130.997 123.711 155.939
Primary effluent/UASB effluent (mg/L)
Secondary effluent (mg/L)
Mean concentrations in sludge (mg/kg)
Mean
Min
Max
Mean
Min
Max
Mean
Excess sludge
UASB sludge
45.571 46.107 35.508
6.324 2.534 1.317
110.544 84.908 54.407
37.524 30.283 16.690
0.998 0.878 2.127
20.446 18.040 35.224
7.437 7.973 9.148
26.051 9.34 48.385 17.89 –
– – 71.765 8.44
secondary sludge due to sorption was 26.1 9.3 mg/kg which cause 11% of influent phthalates removal. The adsorption of analyzed phthalates was consistent with their large octanol water partition coefficient especially of BBP and DEHP which constitute 50% of analyzed phthalates. However, a difference was observed in adsorption to primary and secondary sludge. The removal of phthalates via adsorption to secondary sludge was less than primary sludge (11% versus 18% respectively). This may be either degradation of phthalates during sorption to secondary sludge or less flux of solids in the wasted sludge from the SBR. In addition, it may also happen that there was desorption of phthalates from biosolids in the SBR which decreased sorbed phthalates in secondary sludge and so their removal via adsorption. Removal of phthalates in the SBR by biodegradation was obtained as 681 g/d which was 55% of influent phthalate loading. However, the net biodegradation efficiency of the bioreactor calculated on the basis of primary effluent flux was 67.2%. The overall percentage removal of phthalates was comparable to previous study by Fauser et al. [19] in which 60–70% removal of PAEs was observed in a nitrogen removal based activated sludge plant. Martinnen et al. [17] reported biodegraded percentage removal of only 29% in a SBR but the calculations were done for DEHP only which is more stable towards biodegradation compared to DEP, DBP and BBP. In another mass balance study reported by Clara et al. [7], the average removal P of PAEs was 56%, which was comparable to our results.
sludge ranged from 11.7–1250 mg/kg of dry sludge [33]. More concentration of phthalates observed in anaerobic sludge was probably be due to more retention time of sludge in the UASB reactors as compared to aerobic reactors of 18 MLD ASP and 27 MLD SBR. The sludge retention time in a UASB reactor is approximately 52 days [29]. It may also happen that there is intra molecular diffusion of phthalates inside the anaerobic sludge granules with time which increased their concentration in the anaerobic sludge. Alvarino et al. [34] observed maximum concentration of organic micropollutants in anaerobic sludge granules and the concentration in anaerobic sludge also increased with time. The presence of phthalates in sludge was larger than reported by Dargnat et al. [6] and Gao et al. [8]. However the concentration of phthalates in sludge observed in this study was in between the range of 11–140 mg/kg reported by Cai et al. [35] in the sludge samples from 11 STPs in China. 3.5. Fate of phthalates in 27 MLD SBR Fig. 2 shows the fate of phthalates in the wastewater treatment stream of 27 MLD SBR. The operational wastewater flow rate was 27000 m3/d and the average concentration of sum of phthalates P P ( PAEs) in raw wastewater was 45.6 mg/L. Average flux of PAEs at inlet of PST was 1230 g/d which reduced to 1013 g/d in the P primary effluent. The percentage removal of PAEs in the primary settling tank was 18%. The removal of suspended solids and organic content (COD) in the primary settling tank was 51% and 42% respectively. Other than settling, there is no other removal process in PST, therefore the removal of phthalates in it can be associated to settling of suspended solids. This was also confirmed by significant spearman correlations obtained between TSS removal and phthalate removal. This association of phthalate removal with solid removal also suggest that better solid separation might improve removal of phthalates in the primary settling tanks. The flux of phthalates in primary effluent decreased to 201 g/d in effluent of SBR. Percentage removal of phthalates in SBR was 66% of influent flux and 80.1% of primary effluent flux. Observed concentration of phthalates in sludge reveal adsorption as a removal mechanism also. The mean concentration of phthalates in
3.6. Fate of phthalates in 18 MLD ASP The mass flux diagram of phthalates in 18 MLD ASP treatment plant is shown in Fig. 3. Mean phthalate flux to the primary settling P tank was 830 g/d assumed as 100% and the removal of PAEs in the primary settling tank was 31%. The phthalate loadings to the P aeration tank was 575 g/d and the flux of PAEs in the effluent of ASP was 144 g/d which constituted 16% of influent loading. The mass flux of phthalates released with secondary sludge was observed as 68 g/d which constituted 8% of the influent phthalate loading. Though the carbonaceous and nitrogen removal was comparable in both SBR and ASP reactors (Fig. 1) but the phthalate degradation was different. The biodegraded percentage of influent
681g/d Degraded 55% 1230g/d 100%
1013g/d 82% Primary settling tank
201g/d 16% Bio selector
Aeration Basin Effluent
Influent 217g/d 18% Wastewater sample Sludge sample
Excess sludge Primary sludge
132g/d 11% Sludge Treatment
Agricultural land
Fig. 2. Phthalate flux and mass balance analysis in 27 MLD SBR. (Bold values indicate calculated flux and regular values indicate measured flux).
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363g/d Degraded 44% 830g/d 100%
Primary settling tank
575g/d 69%
Secondary settling tank
Aeration tank
Influent
144g/d 17%
Effluent
Excess Sludge Wastewater sample Sludge sample
255g/d 31%
68g/d 8% Primary Sludge
Sludge treatment
Agricultural land
Fig. 3. Phthalate flux and their mass balance analysis in 18 MLD ASP. (Bold values indicate calculated flux and regular values indicate measured flux).
460g/d Degraded 34% 1349g/d 100%
634g/d 47%
UASB Reactor
285g/d removed 21%
349g/d 26%
Polishing Pond
Influent
Effluent
UASB sludge
255g/d 19%
Wastewater sample Sludge sample
Sludge Drying Beds
Agricultural land
Fig. 4. Flux and mass balance analysis of phthalates in 38 MLD UASB sewage treatment plant with post treatment of polishing ponds.
phthalates in the ASP bioreactor was 44% (363 g/d). The degradation efficiency of ASP reactor calculated on the basis of concentration of phthalates in primary effluent was 63% which was lesser than the percentage of phthalates degraded in SBR (67%). The less degradation of phthalates in ASP reactor may be a consequence of absence of various environmental conditions as available in SBR bioreactor. Different treatment conditions in the form of anoxic and oxic zones facilitate the presence of diverse microbial communities which may be capable of the degradation of organic micropollutants [36]. Another factor for more degradation in SBR might be large SRT (13–18 days in SBR as compared to 7–8 days in ASP) which facilitates the growth of slow growing bacterial communities capable of degrading micropollutants [37]. Nevertheless the results of two treatment plants showed that the primary settling tanks may be the first step for optimization of the phthalate removal in wastewater treatment (18–31% removal) which may be improved by enhanced solid removal. Secondly the degradation of phthalates depends on different environmental conditions of treatment and two sludge system in the form of
anoxic oxic environment such as in SBR may cause their more degradation. 3.7. Fate of phthalates in 38 MLD UASB Fig. 4 represents the fate of four phthalates in 38 MLD UASB treatment plant. The mean concentration of phthalates in raw sewage was 35.508 mg/L (Table 3) and flux of phthalates into the UASB reactors was 1349 g/d (Fig. 4). The mean concentration of P PAEs in the UASB sludge was 71.765 8.44 mg/kg and with P wastage rate of solids as 3551 kg/d, the flux of PAEs in wasted sludge was 255 g/d (19% of influent loading). Mass balance P calculations showed that the overall removal efficiency of PAEs in the UASB reactor was 53% and the amount of phthalates degraded was 460 g/d (34% of influent loading). The removal efficiency of UASB was lower than aerobic reactors of 27 MLD SBR and 18 MLD ASP which may be due to lower efficiency of oxidizers present in UASB reactor. The oxidizers present in UASB reactor such as sulphate have less oxidation potential than oxygen present in
Table 5 Comparison of observed performance with other full scale technologies reported in literature. Treatment technology
Phthalates
Total influent concentration (mg/L)
Average Removal (%)
Reference
Activated sludge Primary settler + aeration + nitrification UASB + Constructed wetland Membrane Bioreactor Sequencing Batch reactor (nutrient removal type) Activated sludge process UASB + polishing pond
DBP, BBP, DEHP DEP,DBP, BBP, DEHP DEP, DBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP
131 33 6.4; 12.2 136 46 46 36
87 87 >83; >80 85 86 83 74
Roslev et al. (2007) Dargnat et al. (2009) Reyes-Contreras et al. (2011) Boonyaroj et al. (2012) This study This study This study
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Table 6 Spearman correlation coefficient matrix of percentage removal of phthalates and conventional parameters. P PAE removal COD removal BOD removal TSS removal TN removal TP removal
P PAE removal
COD removal
BOD removal
TSS removal
TN removal
TP removal
1.000 0.443** 0.482** 0.545** 0.583** 0.070
1.000 0.837** 0.830** 0.745** 0.503**
1.000 0.777** 0.791** 0.412**
1.000 0.716** 0.432**
1.000 0.554**
1.000
Bold values are coefficients of interest. ** Correlation is significant at the 0.01 level (2-tailed).
aerobic reactor. The removal by degradation was less than the 90% as reported by Liang et al. [38] in a lab scale UASB reactor. The variation in results may be the synthetic sewage feed used by Liang et al. [38] that contained only phthalates and phenol, making them more bioavailable while as the bioavailability get reduced in real wastewater due to low concentration of the phthalates. The phthalate loadings in the effluent of UASB to the polishing ponds were 634 g/d (47% of influent loading). The concentration of phthalates in the effluent of polishing pond was 9.148 mg/L (26% of influent flux) and the removal of phthalates in the ponds was 285 g/d (21% of influent loading). Based on the phthalate flux from the UASB reactors the removal efficiency of ponds was 50%. It was not feasible to differentiate the contribution of adsorption and biodegradation to overall removal in polishing ponds because of unknown solid flux from the ponds. Overall removal of sum of four phthalates in UASB + pond combination was 74%. The removal was lower than those reported for other full scale wastewater treatment technologies. Reyes-Contreras et al. [39] reported 80– 83% removal of three phthalates (DEP, DBP, DEHP) in UASB post treated by constructed wetland (Table 5). Low removal efficiencies of phthalates in the pond might not be the inefficiency of this treatment technology but a consequence of operating factors. The HRT in the pond was only 24 h as it was provided as post treatment while as the usual HRT in pond based wastewater treatment systems range upto 15- 30 days [40]. However, together with UASB, the overall removal of phthalates in the STP was 1000 g/d (74%) and the fate of phthalates was that 745 g/d was degraded (55%), 255 g/d (19%) was adsorbed to UASB sludge and 349 g/d (26%) was discharged with effluent. The difference during anaerobic degradation in UASB and aerobic degradation in ASP and SBR might be due to difference in the availability and specificity of emulsifiers released by anaerobic and aerobic bacteria. Aerobic bacteria are able to release solubilizers that increase the concentration of dissolved phthalates particularly higher molecular weight ones which have low aqueous solubility and are more adsorbed to biosolids. While as anaerobic degraders behave differently with regard to solubilization compared to aerobes. They might not release solubilizers or the threshold concentration for release of solubilizers is more in case of anaerobic bacteria [41]. However, the validation of the differences was not clear due to huge dynamics of processes at a fullscale wastewater treatment plant. Therefore further investigations in terms of release, specificity of emulsifiers and increase in concentration of dissolved phthalates are required. 3.8. Relation between conventional and phthalate removal The quality of effluent of the sewage treatment plant depends on its treatment efficacy which in turn is characterized by percentage removal of contaminants such as COD, BOD, TN and TP. Phthalates are also one of contaminants therefore the correlation between removal of phthalates and conventional contaminants was examined. Spearman correlation coefficient shown in Table 6 were obtained between percentage removal of
P phthalates ( PAE) and percentage removal of COD, BOD, TSS, TN and TP. The correlation was significant for percentage removal of COD, BOD, TSS and TN (p < 0.01; n = 63). The value of correlation coefficient for these parameters was in the range of 0.443 to 0.583. The positive correlation of phthalate removal and organic removal (COD and BOD) may be due the organic nature of phthalates. A significant amount of phthalates bind with organic matter which is then reduced in the treatment process, characterized by COD, BOD and TSS removal. Consequently, a significant relation between COD, BOD and TSS removal was probable. Significant relation between phthalates and TN in raw wastewater might be a consequence of larger SRT that favors the removal of total nitrogen as well as removal of micropollutants [37]. 4. Conclusion This study evaluated the occurrence of four priority phthalates in wastewater and sludge at different treatment stages of three full scale sewage treatment plants. All compounds were present in wastewater and sludge. DEHP in treated effluents was more than the recommended EQS value of 1.3 mg/L. The concentration of phthalates in anaerobic sludge was more than the aerobic sludge. The concentration of phthalates reported in the study can be used as reference in future monitoring programs and risk assessment studies. The fate and removal of these compounds investigated by mass balance analysis revealed their removal efficiency of primary settling tanks, SBR, ASP, UASB reactor and polishing ponds. The study showed that a substantial portion of phthalates (18–31%) is removed in primary settling tanks which can reduce loadings to secondary treatment units and can be first point to optimize the efficient removal of phthalates in a sewage treatment plant. Among SBR and ASP, SBR technology was more efficient in degradation of phthalates than ASP. The outcomes of the study will add to the understanding of removal of phthalates in full scale sewage treatment plants. Acknowledgement Corresponding author is thankful to Ministry of Human Resource Department, India for financial assistantship during the study. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jece.2016.05.006. References [1] D. Calley, J. Autian, W.L. Guess, Toxicology of a series of phthalate esters, J. Pharmacol. Sci. 55 (1966) 158–162. [2] S. Oishi, K. Hiraga, Testicular atrophy induced by phthalic acid monoesters: Effects of zinc and testosterone concentrations, Toxicology 15 (1980) 197–202. [3] U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS): Dibutyl phthalate, (1990) http://www.epa.gov/iris/subst/0038.html.
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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece
Evaluation of three full scale sewage treatment plants for occurrence and removal efficacy of priority phthalates Khalid Muzamil Gani* , Absar Ahmad Kazmi Environmental Engineering Group, Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttrakhand 247667, India
A R T I C L E I N F O
Article history: Received 20 February 2016 Received in revised form 13 April 2016 Accepted 5 May 2016 Available online 7 May 2016 Keywords: Activated sludge process Micropollutants Phthalates Sequencing batch reactor Wastewater treatment plant UASB
A B S T R A C T
The study focuses on evaluation of occurrence of four priority phthalates in sewage and their removal in sequencing batch reactor (SBR), activated sludge process (ASP) and up flow anaerobic sludge blanket (UASB) reactor based full scale sewage treatment plants (STPs). Mean concentration of total four phthalates in raw sewage and secondary sludge was in the range of 35.5–46.1 mg/L and 26.1–71.8 mg/kg respectively. The concentration of phthalates in anaerobic sludge was more (71.8 mg/kg) than aerobic sludge from SBR (26.1 mg/kg) and ASP (48.4 mg/kg). Overall removal of phthalates by biodegradation and adsorption was >75% in all STPs. However, biodegradation was the main removal process. A significant portion of incoming phthalates (18–31%) was removed in primary settling tanks as well. Phthalate removal and conventional performance of STPs showed positive correlation with value of spearman correlation coefficient in the range of 0.443–0.583. The study may act as a contribution to the understanding which is required to improve the removal of phthalates or similar organic micropollutants in wastewater treatment. ã 2016 Elsevier Ltd. All rights reserved.
1. Introduction Phthalates or phthalic acid esters (PAE) are used as plasticizers in polyvinyl chloride (PVC) products and additives in personnel care products. These compounds are also used in floorings, paints, food packaging, car coatings and wall coverings. Exposure of these compounds have harmful effects such as cancer and endocrine disruption. Other defects such as lethargy, imbalance and respiratory arrest can also occur on their exposure [1,2]. United States Environmental Protection agency (U.S. EPA) classified few phthalates such as Diethyl phthalate (DEP), Dibutyl phthalate (DBP), Benzylbutyl phthalate (BBP) and Diethylhexyl phthalate (DEHP) as priority pollutants for their potential harmful impact in environment [3]. Phthalates get leached from their parent product during manufacturing and during their use or disposal [4]. Past studies have reported the occurrence of phthalates in domestic untreated and treated sewage [5–7]. Gao et al. [8] reported occurrence of six phthalates at three domestic sewage treatment plants in China and
* Corresponding author. E-mail addresses: [email protected] (K.M. Gani), [email protected] (A.A. Kazmi). http://dx.doi.org/10.1016/j.jece.2016.05.006 2213-3437/ã 2016 Elsevier Ltd. All rights reserved.
the concentration reported in influent and effluent samples was 23.28–88.46 mg/L and 6.95–61.49 mg/L respectively. The concentration observed in sludge was in the range of 5.074–28.135 mg/kg with maximum concentration of DEHP. Roslev et al. [9] reported their occurrence at an activated sludge based sewage treatment plant in Denmark and the concentration of four phthalates in influent and effluent was 78.25–193.82 mg/L and 5.90–17.23 mg/L respectively. The mean concentration of four phthalates in sludge was 71.78 mg/kg. Treated effluents from these sewage treatment plants is a major source of phthalates to aquatic sources which if not addressed may have eco toxicological effects on aquatic life [8,10]. Existing sewage treatment plants were designed for organic and nutrient removal or recovery, therefore removal of phthalate like micropollutants is generally poor in such treatment plants [11–13]. Nonetheless advance treatment technologies such as advance oxidation processes, activated carbon and ozonation are effective in removal of phthalates or such toxic compounds [14–16] but the higher costs associated with their implementation make them less preferable. Therefore as an alternative, existing STPs are to be optimized for removal of phthalate like trace organics which require fate investigation of phthalates in full scale STPs. Evaluation of existing STPs may led to generation of real field data and inferences which help in identifying efficient phthalate removal processes. Previous
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studies have shown that removal of phthalates in full scale STPs can vary from 60% to 100% [8,17,18]. Fauser et al. [19] reported that there is approximately 70% and 48% of DEHP and BBP degradation in a full scale STP. Dargnat et al. [6] found DBP, BBP and DEHP are approximately removed by 80%, 97% and 78% respectively in a primary aeration nitrification based plant. Gao et al. [8] found removal of DEP, DMP and DBP as 90–100%, 63–100% and 53–85% respectively in three full scale nutrient removal based STPs. Conventional activated sludge process, sequencing batch reactor (SBR) and up flow anaerobic sludge blanket (UASB) with natural process as post treatment are among commonly adopted sewage treatment technologies [20,21]. Among aerobic suspended growth processes, ASP is the most promising technology designed usually for carbonaceous removal. Cyclic activated sludge process in the form of SBR is a modified form of ASP which operates in a fill and draw manner. Among anaerobic processes of wastewater treatment UASB has been recognized as appropriate technology for its simplicity in construction and operational costs [22]. However, the effluent of UASB reactor usually does not met the discharge standards and are therefore coupled with post treatment of final polishing units [21]. Conventional ASP and SBR based treatment plants exist in developing as well as developed countries while as UASB with polishing units as post treatment is mostly adopted in developing countries like India [23]. These sewage treatment
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technologies have been well studied for organic and nitrogen removal. But little is known about fate of phthalates in these technologies. Therefore the objective of this research was investigation of occurrence level, and removal of phthalates in SBR, ASP and UASB technology based STPs. Samples in between the sewage treatment line were analyzed to determine the removal efficiency of phthalates in various treatment units. Mass balance approach was used to determine the contribution of removal mechanisms involved in removal of phthalates. The phthalates selected for the study were DEP, DBP, BBP and DEHP which are enlisted as priority phthalates by U.S. EPA. Their properties and structures are shown in Table S1. 2. Material and methods 2.1. Chemicals All standard solutions of phthalates were purchased from Sigma Aldrich (Germany) with purity 99.5%. Solvents (N-Hexane, Dichloromethane and acetone) used for the extraction of phthalates were purchased from Merck (Mumbai, India). Distill water from Milli-Q Advantage A10 system (Millipore, USA) was used for cleaning of glassware.
Table 1 Design and operational parameters of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. Parameter 27 MLD SBR Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of primary clarifier (m) Number of primary clarifiers Basin size (m) and number HRT (hours) MLSS of basin (mg L 1) MLVSS of basin (mg L 1) Cycle time (hours) Filling and aeration time Settling time Decanting time Effluent disposal 18 MLD ASP Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of primary clarifier (m) Number of primary clarifier Aeration tank size (m) and number HRT in aeration tank (hours) MLSS of Aeration tank (mg L 1) MLVSS of Aeration tank (mg L 1) Return sludge recycle ratio Dimensions of secondary clarifier Number of secondary clarifier Dimension and number of sludge thickener Number of Sludge digesters Number of Gas collectors Dimensions of sludge drying beds and numbers Sludge Disposal Effluent Disposal 38 MLD UASB Design capacity (m3 d 1) Operating capacity (m3 d 1) Dimensions of UASB and number HRT of UASB (hours) Volume of Polishing pond and number HRT of Pond (hours) Dimensions of sludge drying beds and numbers Disposal of treated sludge Treated effluent disposal
Details 27000 27000 24 Diameter 3 m Depth 2 Area – 39 19.5; Side water depth (SWD) – 4.1 m and 4 in number 11 5205 1807 1641 515 3 1.5 h per cycle 0.75 h per cycle 0.75 h per cycle River Ganga 18000 18000 15 m Diameter and 0.785 m Depth 3 Area – 15 m 15m; SWD – 4.8 m and 3 in number 4.3 3228 276 1516 166 0.5–0.6 Diameter – 19.5 m; Depth – 3.5 m 3 Diameter – 11.4 m; Depth – 3 m and 02 2 4 Area – 35 m 24 m; Depth – 0.25 m and 12 Agricultural land River Ganga 38000 38000 28 m 24 m 6.05 m and 4 numbers 10.2 38000 m3 total and 2 numbers, 24 25 m 14 m each and 20 numbers Agricultural land River Dhamola
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2.2. Sewage treatment plants Three full scale STPs based on SBR, ASP and UASB technology were chosen for this study designed with a treatment capacity of 27000, 18000 and 38000 m3/d. Accordingly the notation adopted in this paper was 27 million litres per day (MLD) SBR, 18 MLD ASP and 38 MLD UASB respectively. Table 1 shows the various operational details of the treatment plants. The raw sewage was pretreated in primary settling tanks (PST) in 18 MLD ASP and 27 MLD SBR. The primary effluent was treated at a hydraulic retention time (HRT) of 11 h and 4.3 h respectively. The operational cycle in the SBR consisted of 90 min of aeration, 45 min of settling and 45 min of decanting and the internal recirculation ratio was 44% of the feed flow. In 18 MLD ASP, returned activated sludge (RAS) was fed at recirculation ratio of 0.5–0.6. These two treatment plants (27 MLD SBR and 18 MLD ASP) were constructed nearby to each other and sludge treatment for both STPs was common. The sludge treatment at the STPs was thickening followed by anaerobic digestion and drying in sludge drying beds. The dried sludge was used by local farmers for agricultural purposes. In 38 MLD UASB, the degritted sewage was treated in UASB reactors at HRT of 10.2 h. The up flow velocity of degritted in UASB was 0.5 m/h. The depth of sludge bed in the UASB reactor was approximately 2 m. The average gas production in the UASB reactors was 773 127 m3/day. UASB effluent was post treated in polishing units having HRT of 24 h. Excess sludge from UASB reactors was removed weekly and dried over sludge drying beds which were 20 in number. The dried sludge was used by local farmers for soil improvement in agricultural fields. 2.3. Sampling Samples of wastewater and sludge were collected for a period of seven months. All sewage samples were collected monthly while as sludge samples were collected bimonthly. Average monthly temperature regime throughout the duration of seven months was15 3 C to 32 4 C. In 27 MLD SBR, sewage samples were collected at inlet, outlet of primary settling tank and outlet of SBR. The sludge samples were collected from aeration basin of SBR. Similarly in 18 MLD ASP, the samples were collected from inlet, primary settling tank outlet and secondary clarifier outlet while as sludge samples were collected from the wastage sludge stream. In
38 MLD UASB, sewage samples were collected from inlet, UASB outlet and polishing pond outlet. Sludge samples were taken from wastage flow line UASB reactor. Total 163 grab samples of sewage (untreated, primary treated and treated) and nine samples of sludge were collected during sampling of all three treatment plants. Samples were collected in amber color glass bottles with Teflon cap to avoid photo degradation and contamination of plastic material. Prior to sampling, the sample bottles were rinsed with distill water and acetone. Separate samples were collected for conventional parameters of wastewater and sludge. Collected samples were extracted within 24–48 h of sample collection alongwith preservation at 4 C. 2.4. Sample preparation Sample preparation for the analysis of phthalates was according to the method 606, US EPA [24]. Extraction of 250 ml unfiltered wastewater sample was done by liquid extraction procedure in 25 ml of Hexane/acetone solution (4:1). The extraction was done thrice on a rotary shaker for 15 min followed by separation in a separatory funnel. The extract was passed over 10 g of anhydrous sodium sulphate to remove water content and further concentrated to 2 ml. The concentrated extract was further cleaned up in a chromatographic column (2 cm internal diameter) filled with neutral alumina (10 g) and pre eluted with 20 ml of n-hexane. The sample was eluted with 60 ml acetone/hexane (1:2) solution and concentrated to 5 ml for analysis in GC MS. Sludge samples were dried and one gram of dry sludge was extracted in 80 ml of n hexane/Dichloromethane (60 ml: 20 ml) solution for 12 h on a rotary shaker. The extracted sample was filtered and the filtrate was used for analysis of phthalates in GC MS after concentration and cleanup. The cleanup procedure for sludge extract was same as that of wastewater samples. 2.5. GC MS analysis and quality assurance The concentrated samples were analyzed in a Varian 450 GC coupled to a Varian 240 MS (Agilent Technologies, Avondale, PA, USA) equipped with a capillary column (30 m 0.25 mm ID, 0.25 mm film thickness, Factor Four, Varian Technologies). Helium (99%) was used as carrier gas at a flow rate of 0.8 ml/min. The temperature program for separation was 60 C (hold time of 1.0 min), 250 C (6 C/min, hold time of 1.0 min), and 280 C (hold
Table 2 Concentration of conventional parameters at various treatment stages of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. Parameters
Raw sewage (mg/L) Mean Std. Dev.
Primary/UASB effluent (mg/L) Mean Std. Dev.
Secondary effluent (mg/L) Mean Std. Dev.
27 MLD SBR COD BOD TSS NH4+-N TN
319 148 207 22.8 39.7
77 29 28 6.0 10.0
184 96 101 19.9 35.2
58 9 25 6.4 9.2
36 12 15 0.9 5.1
19 5 7 0.3 0.6
18 MLD ASP COD BOD TSS NH4+-N TN
304 146 204 17.3 33.4
56 31 34 5.4 3.2
164 90 121 13.8 28.6
17 13 38 3.5 2.9
22 12 11 1.1 5.8
10 6 6 0.2 2.1
38 MLD UASB COD BOD TSS NH4+-N TN
374 186 263 31.5 56.3
73 41 80 5.8 3.8
145 63 72 27.3 46.3
23 18 22 5.4 8.0
74 25 53 16.3 22.4
15 8 20 5.2 3.8
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time of 2 min). Five microliters of sample was injected in split less mode with injector temperature of 250 C. The calibration was done with pure standard solution and the spectra obtained was matched with the NIST library and selected as reference in the analysis. The percentage recovery of the analysis method was measured by spiking wastewater samples with known amount of phthalate (Fig. S1, supplementary data). The recoveries obtained were more than 80% for each phthalate (Table S2). The limit of detection of the method was 0.071, 0.13, 0.21and 0.084 mg/L for DEP, DBP, BBP and DEHP respectively. The limit of quantification was 0.210, 0.182, 0.342 and 0.241 mg/L for DEP, DBP, BBP and DEHP respectively.
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performance of the STPs chosen for this study. Based on the physicochemical characteristics, the raw sewage at three STPs can be categorized as medium to high concentrated sewage [29].
2.6. Fate calculations Organic micropollutants are mainly removed by biodegradation, adsorption and volatilization in a sewage treatment plant. Volatilization depends on Henry’s constant (kH) and can occur due to aeration in the biological reactor [25]. Organic micropollutants with kH around 10 7 atm m3/mol have negligible removal by volatilization [26]. The kH of analyzed phthalates is around the same value (Table S1). Therefore the contribution of volatilization to overall removal of phthalates was neglected. The removal of phthalates by biodegradation (Mdeg) was calculated by subtracting the adsorbed flux of phthalates (Msor) from the overall removal (Mi Mo). Mdeg = (Mi
Mdeg = Q (Ci
Mo)
Co)
Msor
(Csor TSwas Qwas)
Where Q is inflow rate of sewage; Ci is the concentration of P PAEs in influent and Co is concentration of PAEs in effluent. Csor P is mean concentration of PAEs in sludge, TSwas is solid content in wasted sludge and Qwas is flow rate of wasted sludge. Multiplication of TSwas and Qwas is the flux of solids wasted from the bioreactor. P
2.7. Data analysis Spearman correlation coefficients were obtained in SPSS, version 20.0 (IBM Corporation). The correlations were considered statistically significant for p < 0.01 and p < 0.05. Remaining data analysis was done in Excel (Microsoft word 2013). 3. Result and discussion 3.1. Sewage characteristics Table 2 shows the average concentration of physicochemical parameters (COD, BOD, TSS, ammonia, total nitrogen and phosphorus) at different stages of treatment in each sewage treatment plant. The source of sewage was domestic at three treatment plants which include wastewater generated in homes, from small scale industries and storm runoff. The average concentration of COD and BOD in raw sewage was 304–374 mg/ L and 146–186 mg/L respectively while as the average concentration of TN was 29.5–56.3 mg/L. Large concentration of COD and low concentration of TN indicate insignificant industrial contribution. in raw sewage at three STPs. Mungray and Kumar [27] also reported comparable characteristics of raw wastewater at 38 MLD UASB with insignificant contribution of industrial wastewater. The average concentration of COD, BOD and TSS was below 150, 30 and 50 mg/L respectively which are standard discharge parameters in India [28]. This indicated the satisfactory operation and
Fig. 1. Percentage removal of conventional parameters in various treatment units of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB.
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3.2. Treatment performance of STPs
3.3. Occurrence of phthalates in raw sewage
Fig. 1 shows the conventional performance of various treatment units of three STPs. During the study period, mean percentage removal of COD and TSS in primary settling tank of 27 MLD SBR was 41.9 13.9% and 48.2 8.3% respectively whereas in primary settling tank of 18 MLD ASP it was 51.0 9.8% and 41.5 13.6% respectively. COD and TSS removal efficiency in primary settling tanks was within the range of 30–60% reported in literature [29]. In bioreactors of these two STPs, carbonaceous and solid removal was 80–90%. There was no significant difference among bioreactors in the removal of these parameters. Both reactors performed well during the study period. Nitrification measured as percentage removal of ammonia was also >90% in both bioreactors. The percentage removal of total nitrogen was 82.4 2.6% in SBR and 84.7 2.1% in whole treatment scheme (Fig. 1). Better nitrogen removal in SBR was obvious but in ASP bioreactor the nitrogen removal was probably due to mixed conditions and surface aeration mechanism [26]. Van Huyssteen et al. [30] reported significant nitrogen loss in aeration basin aerated by surface aerators. They opined about it that as mixed liquor traveled away from surface aerators, the DO get depleted and create conditions favorable for anoxic reactions. Secondly activated sludge floc can contain both aerobic and anoxic zones. Overall both STPs were satisfactory performing in carbonaceous and nitrogen removal during the study period. In UASB reactor, the mean percentage removal of COD, BOD and TSS was 60.5 6.0%, 66.7 6.1% and 61.3 13.3% respectively. The observed organic removal was comparable with the 69% removal as reported by Mungray and Kumar [27] for this STP. The percentage removal of ammonia and total nitrogen in UASB reactor was 59.7 and 30.3% respectively which was lesser compared to 66 and 55% removal in polishing ponds. UASB reactors are not designed for nitrification process however the observed removal may be due to aeration by atmospheric oxygen as the top surface is open to the atmosphere. In addition, anaerobic oxidation of ammonia with nitrite by anammox may have their contribution to the observed nitrification [31]. The pollution parameters were further removed in the final polishing unit and as a result the percentage removal of COD, BOD and TSS was more than 79%, 84% and 83% respectively in the whole treatment plant. Ammonia and TN percentage removal also increased to 62% and 65% respectively. These results confirm proper working of the treatment processes in the STPs and assured that these STPs were appropriate for investigation of fate of phthalates.
The mean concentrations of individual compounds in raw sewage and treated sewage is shown in Table 3 and the sum of P phthalates ( PAEs) at various stages of treatment scheme of the wastewater treatment plants is shown in Table 4. PAE concentration in raw sewage was almost same at 27 MLD SBR and 18 MLD ASP (45.571 mg/L and 46.107 mg/L respectively) which may be due to their common sewerage system. The concentration at 38 MLD UASB was slightly lower with mean concentration as 35.508 mg/L and varied over a wide range of 1.014–155.939 mg/L. The wide variation was obvious because of the inconsistency in the sources of these compounds. The sources of phthalates in domestic sewage may be toilet water, personnel care products, leachates from solid waste dumping sites and urban runoff [32]. There are no norms in Indian standards for phthalates. However, comparison with international regulations showed that DEHP in treated effluents of investigated STPs exceeded its environmental quality standard (EQS) of 1.3 mg/L (Table S4, supplementary information). The relation between phthalate concentration and the corresponding conventional parameters (COD, BOD and TSS) was analyzed by spearman correlation coefficient. The obtained correlation was significant for all three parameters as shown in Table S3 (p < 0.01; n = 63). The value of coefficient was around 0.5 for all parameters which showed positive relation between phthalates and conventional parameters (COD, BOD and TSS). Positive correlation of phthalate concentration with COD may be due to organic nature of phthalates and COD measures the degradable and non-degradable organic content in the wastewater. Positive correlation between phthalates and TSS may be due to high octanol water coefficient of phthalates such as BBP and DEHP for which these compounds are adsorbed to organic suspended solids. 3.4. Occurrence of phthalates in sludge Table 3 shows the concentration of phthalates in the secondary sludge of STPs. All four phthalates were present in the secondary sludge of each treatment plant. The mean concentration in secondary sludge of 18 MLD ASP and 27 MLD SBR was 26.1 mg/ kg and 48.4 mg/kg respectively. Whereas the phthalate concentration in sludge of 38 MLD UASB was 71.8 mg/kg which was larger than that observed in 18 MLD ASP and 27 MLD SBR. The presence of phthalates in sludge is a consequence of their adsorption to biosolids [20]. An evaluation survey of hazardous chemicals in sludge has showed that mean concentrations of phthalates in
Table 3 Concentration of individual phthalates in raw sewage and treated sewage alongwith their removal in investigated treatment plants. Phthalates
Raw sewage
Treated sewage
Removal (%)
Range
Mean SD
Range
Mean SD
Mean SD
27 MLD SBR DEP DBP BBP DEHP
n.d.–7.376 n.d.–30.390 n.d.–6.893 1.354–124.357
5.417 4.149 11.175 9.977 1.968 2.280 27.011 14.341
n.d.–3.076 n.d.–5.417 n.d.–1.175 n.d.–16.451
0.737 0.410 2.188 1.847 0.259 0.043 4.253 2.521
86 24 80 13 87 28 84 31
18 MLD ASP DEP DBP BBP DEHP
n.d.–13.363 1.740–90.360 n.d.–19.807 n.d.–26.021
5.319 3.407 19.153 9.310 3.845 0.618 17.790 7.693
n.d.–3.298 0.661–10.718 n.d.–4.732 n.d.–8.062
0.879 0.117 3.263 2.366 0.907 0.612 2.923 1.257
84 16 83 24 76 18 84 21
38 MLD UASB DEP DBP BBP DEHP
n.d.–5.331 0.813–12.228 n.d.–6.479 n.d.–132.441
3.095 2.084 5.471 4.393 2.772 1.818 24.169 14.673
n.d.–1.328 n.d.–2.675 n.d.–2.633 n.d.–32.549
0.509 0.311 1.027 0.755 0.715 0.238 6.932 1.055
84 21 81 23 74 13 71 8
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Table 4 Concentration of total phthalates in wastewater and sludge of 27 MLD SBR, 18 MLD ASP and 38 MLD UASB. STP
Raw sewage (mg/L) Min
Max
27 MLD SBR 18 MLD ASP 38 MLD UASB
16.794 14.467 1.014
130.997 123.711 155.939
Primary effluent/UASB effluent (mg/L)
Secondary effluent (mg/L)
Mean concentrations in sludge (mg/kg)
Mean
Min
Max
Mean
Min
Max
Mean
Excess sludge
UASB sludge
45.571 46.107 35.508
6.324 2.534 1.317
110.544 84.908 54.407
37.524 30.283 16.690
0.998 0.878 2.127
20.446 18.040 35.224
7.437 7.973 9.148
26.051 9.34 48.385 17.89 –
– – 71.765 8.44
secondary sludge due to sorption was 26.1 9.3 mg/kg which cause 11% of influent phthalates removal. The adsorption of analyzed phthalates was consistent with their large octanol water partition coefficient especially of BBP and DEHP which constitute 50% of analyzed phthalates. However, a difference was observed in adsorption to primary and secondary sludge. The removal of phthalates via adsorption to secondary sludge was less than primary sludge (11% versus 18% respectively). This may be either degradation of phthalates during sorption to secondary sludge or less flux of solids in the wasted sludge from the SBR. In addition, it may also happen that there was desorption of phthalates from biosolids in the SBR which decreased sorbed phthalates in secondary sludge and so their removal via adsorption. Removal of phthalates in the SBR by biodegradation was obtained as 681 g/d which was 55% of influent phthalate loading. However, the net biodegradation efficiency of the bioreactor calculated on the basis of primary effluent flux was 67.2%. The overall percentage removal of phthalates was comparable to previous study by Fauser et al. [19] in which 60–70% removal of PAEs was observed in a nitrogen removal based activated sludge plant. Martinnen et al. [17] reported biodegraded percentage removal of only 29% in a SBR but the calculations were done for DEHP only which is more stable towards biodegradation compared to DEP, DBP and BBP. In another mass balance study reported by Clara et al. [7], the average removal P of PAEs was 56%, which was comparable to our results.
sludge ranged from 11.7–1250 mg/kg of dry sludge [33]. More concentration of phthalates observed in anaerobic sludge was probably be due to more retention time of sludge in the UASB reactors as compared to aerobic reactors of 18 MLD ASP and 27 MLD SBR. The sludge retention time in a UASB reactor is approximately 52 days [29]. It may also happen that there is intra molecular diffusion of phthalates inside the anaerobic sludge granules with time which increased their concentration in the anaerobic sludge. Alvarino et al. [34] observed maximum concentration of organic micropollutants in anaerobic sludge granules and the concentration in anaerobic sludge also increased with time. The presence of phthalates in sludge was larger than reported by Dargnat et al. [6] and Gao et al. [8]. However the concentration of phthalates in sludge observed in this study was in between the range of 11–140 mg/kg reported by Cai et al. [35] in the sludge samples from 11 STPs in China. 3.5. Fate of phthalates in 27 MLD SBR Fig. 2 shows the fate of phthalates in the wastewater treatment stream of 27 MLD SBR. The operational wastewater flow rate was 27000 m3/d and the average concentration of sum of phthalates P P ( PAEs) in raw wastewater was 45.6 mg/L. Average flux of PAEs at inlet of PST was 1230 g/d which reduced to 1013 g/d in the P primary effluent. The percentage removal of PAEs in the primary settling tank was 18%. The removal of suspended solids and organic content (COD) in the primary settling tank was 51% and 42% respectively. Other than settling, there is no other removal process in PST, therefore the removal of phthalates in it can be associated to settling of suspended solids. This was also confirmed by significant spearman correlations obtained between TSS removal and phthalate removal. This association of phthalate removal with solid removal also suggest that better solid separation might improve removal of phthalates in the primary settling tanks. The flux of phthalates in primary effluent decreased to 201 g/d in effluent of SBR. Percentage removal of phthalates in SBR was 66% of influent flux and 80.1% of primary effluent flux. Observed concentration of phthalates in sludge reveal adsorption as a removal mechanism also. The mean concentration of phthalates in
3.6. Fate of phthalates in 18 MLD ASP The mass flux diagram of phthalates in 18 MLD ASP treatment plant is shown in Fig. 3. Mean phthalate flux to the primary settling P tank was 830 g/d assumed as 100% and the removal of PAEs in the primary settling tank was 31%. The phthalate loadings to the P aeration tank was 575 g/d and the flux of PAEs in the effluent of ASP was 144 g/d which constituted 16% of influent loading. The mass flux of phthalates released with secondary sludge was observed as 68 g/d which constituted 8% of the influent phthalate loading. Though the carbonaceous and nitrogen removal was comparable in both SBR and ASP reactors (Fig. 1) but the phthalate degradation was different. The biodegraded percentage of influent
681g/d Degraded 55% 1230g/d 100%
1013g/d 82% Primary settling tank
201g/d 16% Bio selector
Aeration Basin Effluent
Influent 217g/d 18% Wastewater sample Sludge sample
Excess sludge Primary sludge
132g/d 11% Sludge Treatment
Agricultural land
Fig. 2. Phthalate flux and mass balance analysis in 27 MLD SBR. (Bold values indicate calculated flux and regular values indicate measured flux).
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363g/d Degraded 44% 830g/d 100%
Primary settling tank
575g/d 69%
Secondary settling tank
Aeration tank
Influent
144g/d 17%
Effluent
Excess Sludge Wastewater sample Sludge sample
255g/d 31%
68g/d 8% Primary Sludge
Sludge treatment
Agricultural land
Fig. 3. Phthalate flux and their mass balance analysis in 18 MLD ASP. (Bold values indicate calculated flux and regular values indicate measured flux).
460g/d Degraded 34% 1349g/d 100%
634g/d 47%
UASB Reactor
285g/d removed 21%
349g/d 26%
Polishing Pond
Influent
Effluent
UASB sludge
255g/d 19%
Wastewater sample Sludge sample
Sludge Drying Beds
Agricultural land
Fig. 4. Flux and mass balance analysis of phthalates in 38 MLD UASB sewage treatment plant with post treatment of polishing ponds.
phthalates in the ASP bioreactor was 44% (363 g/d). The degradation efficiency of ASP reactor calculated on the basis of concentration of phthalates in primary effluent was 63% which was lesser than the percentage of phthalates degraded in SBR (67%). The less degradation of phthalates in ASP reactor may be a consequence of absence of various environmental conditions as available in SBR bioreactor. Different treatment conditions in the form of anoxic and oxic zones facilitate the presence of diverse microbial communities which may be capable of the degradation of organic micropollutants [36]. Another factor for more degradation in SBR might be large SRT (13–18 days in SBR as compared to 7–8 days in ASP) which facilitates the growth of slow growing bacterial communities capable of degrading micropollutants [37]. Nevertheless the results of two treatment plants showed that the primary settling tanks may be the first step for optimization of the phthalate removal in wastewater treatment (18–31% removal) which may be improved by enhanced solid removal. Secondly the degradation of phthalates depends on different environmental conditions of treatment and two sludge system in the form of
anoxic oxic environment such as in SBR may cause their more degradation. 3.7. Fate of phthalates in 38 MLD UASB Fig. 4 represents the fate of four phthalates in 38 MLD UASB treatment plant. The mean concentration of phthalates in raw sewage was 35.508 mg/L (Table 3) and flux of phthalates into the UASB reactors was 1349 g/d (Fig. 4). The mean concentration of P PAEs in the UASB sludge was 71.765 8.44 mg/kg and with P wastage rate of solids as 3551 kg/d, the flux of PAEs in wasted sludge was 255 g/d (19% of influent loading). Mass balance P calculations showed that the overall removal efficiency of PAEs in the UASB reactor was 53% and the amount of phthalates degraded was 460 g/d (34% of influent loading). The removal efficiency of UASB was lower than aerobic reactors of 27 MLD SBR and 18 MLD ASP which may be due to lower efficiency of oxidizers present in UASB reactor. The oxidizers present in UASB reactor such as sulphate have less oxidation potential than oxygen present in
Table 5 Comparison of observed performance with other full scale technologies reported in literature. Treatment technology
Phthalates
Total influent concentration (mg/L)
Average Removal (%)
Reference
Activated sludge Primary settler + aeration + nitrification UASB + Constructed wetland Membrane Bioreactor Sequencing Batch reactor (nutrient removal type) Activated sludge process UASB + polishing pond
DBP, BBP, DEHP DEP,DBP, BBP, DEHP DEP, DBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP DEP, DBP, BBP, DEHP
131 33 6.4; 12.2 136 46 46 36
87 87 >83; >80 85 86 83 74
Roslev et al. (2007) Dargnat et al. (2009) Reyes-Contreras et al. (2011) Boonyaroj et al. (2012) This study This study This study
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Table 6 Spearman correlation coefficient matrix of percentage removal of phthalates and conventional parameters. P PAE removal COD removal BOD removal TSS removal TN removal TP removal
P PAE removal
COD removal
BOD removal
TSS removal
TN removal
TP removal
1.000 0.443** 0.482** 0.545** 0.583** 0.070
1.000 0.837** 0.830** 0.745** 0.503**
1.000 0.777** 0.791** 0.412**
1.000 0.716** 0.432**
1.000 0.554**
1.000
Bold values are coefficients of interest. ** Correlation is significant at the 0.01 level (2-tailed).
aerobic reactor. The removal by degradation was less than the 90% as reported by Liang et al. [38] in a lab scale UASB reactor. The variation in results may be the synthetic sewage feed used by Liang et al. [38] that contained only phthalates and phenol, making them more bioavailable while as the bioavailability get reduced in real wastewater due to low concentration of the phthalates. The phthalate loadings in the effluent of UASB to the polishing ponds were 634 g/d (47% of influent loading). The concentration of phthalates in the effluent of polishing pond was 9.148 mg/L (26% of influent flux) and the removal of phthalates in the ponds was 285 g/d (21% of influent loading). Based on the phthalate flux from the UASB reactors the removal efficiency of ponds was 50%. It was not feasible to differentiate the contribution of adsorption and biodegradation to overall removal in polishing ponds because of unknown solid flux from the ponds. Overall removal of sum of four phthalates in UASB + pond combination was 74%. The removal was lower than those reported for other full scale wastewater treatment technologies. Reyes-Contreras et al. [39] reported 80– 83% removal of three phthalates (DEP, DBP, DEHP) in UASB post treated by constructed wetland (Table 5). Low removal efficiencies of phthalates in the pond might not be the inefficiency of this treatment technology but a consequence of operating factors. The HRT in the pond was only 24 h as it was provided as post treatment while as the usual HRT in pond based wastewater treatment systems range upto 15- 30 days [40]. However, together with UASB, the overall removal of phthalates in the STP was 1000 g/d (74%) and the fate of phthalates was that 745 g/d was degraded (55%), 255 g/d (19%) was adsorbed to UASB sludge and 349 g/d (26%) was discharged with effluent. The difference during anaerobic degradation in UASB and aerobic degradation in ASP and SBR might be due to difference in the availability and specificity of emulsifiers released by anaerobic and aerobic bacteria. Aerobic bacteria are able to release solubilizers that increase the concentration of dissolved phthalates particularly higher molecular weight ones which have low aqueous solubility and are more adsorbed to biosolids. While as anaerobic degraders behave differently with regard to solubilization compared to aerobes. They might not release solubilizers or the threshold concentration for release of solubilizers is more in case of anaerobic bacteria [41]. However, the validation of the differences was not clear due to huge dynamics of processes at a fullscale wastewater treatment plant. Therefore further investigations in terms of release, specificity of emulsifiers and increase in concentration of dissolved phthalates are required. 3.8. Relation between conventional and phthalate removal The quality of effluent of the sewage treatment plant depends on its treatment efficacy which in turn is characterized by percentage removal of contaminants such as COD, BOD, TN and TP. Phthalates are also one of contaminants therefore the correlation between removal of phthalates and conventional contaminants was examined. Spearman correlation coefficient shown in Table 6 were obtained between percentage removal of
P phthalates ( PAE) and percentage removal of COD, BOD, TSS, TN and TP. The correlation was significant for percentage removal of COD, BOD, TSS and TN (p < 0.01; n = 63). The value of correlation coefficient for these parameters was in the range of 0.443 to 0.583. The positive correlation of phthalate removal and organic removal (COD and BOD) may be due the organic nature of phthalates. A significant amount of phthalates bind with organic matter which is then reduced in the treatment process, characterized by COD, BOD and TSS removal. Consequently, a significant relation between COD, BOD and TSS removal was probable. Significant relation between phthalates and TN in raw wastewater might be a consequence of larger SRT that favors the removal of total nitrogen as well as removal of micropollutants [37]. 4. Conclusion This study evaluated the occurrence of four priority phthalates in wastewater and sludge at different treatment stages of three full scale sewage treatment plants. All compounds were present in wastewater and sludge. DEHP in treated effluents was more than the recommended EQS value of 1.3 mg/L. The concentration of phthalates in anaerobic sludge was more than the aerobic sludge. The concentration of phthalates reported in the study can be used as reference in future monitoring programs and risk assessment studies. The fate and removal of these compounds investigated by mass balance analysis revealed their removal efficiency of primary settling tanks, SBR, ASP, UASB reactor and polishing ponds. The study showed that a substantial portion of phthalates (18–31%) is removed in primary settling tanks which can reduce loadings to secondary treatment units and can be first point to optimize the efficient removal of phthalates in a sewage treatment plant. Among SBR and ASP, SBR technology was more efficient in degradation of phthalates than ASP. The outcomes of the study will add to the understanding of removal of phthalates in full scale sewage treatment plants. Acknowledgement Corresponding author is thankful to Ministry of Human Resource Department, India for financial assistantship during the study. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jece.2016.05.006. References [1] D. Calley, J. Autian, W.L. Guess, Toxicology of a series of phthalate esters, J. Pharmacol. Sci. 55 (1966) 158–162. [2] S. Oishi, K. Hiraga, Testicular atrophy induced by phthalic acid monoesters: Effects of zinc and testosterone concentrations, Toxicology 15 (1980) 197–202. [3] U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS): Dibutyl phthalate, (1990) http://www.epa.gov/iris/subst/0038.html.
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