WETLANDS, Vol. 24, No. 1, March 2004, pp. 202–206 䉷 2004, The Society of Wetland Scientists
NOTE REMOVAL OF DIBUTYL PHTHALATE BY A STAGED, VERTICAL-FLOW CONSTRUCTED WETLAND Wen Yu Zhao1,2, Zhen Bin Wu1,3, Qiao Hong Zhou1, Shui Ping Cheng1, Gui Ping FU1, and Feng He1 1 State Key Laboratory of Freshwater Ecology and Biotec, Institute of Hydrobiology The Chinese Academy of Sciences Wuhan, 430072, People’s Republic of China Department of Electronic Engineering Guilin University of Electronic Technology Jinji Road 1 Guilin, 541004, People’s Republic of China E-mail:
[email protected] 2
Abstract: Two sets of small scale systems of staged, vertical-flow constructed wetlands (VFCW) were operated in a greenhouse to study the purification of dibutyl phthalate (DBP) in admeasured water. Each system consisted of two chambers in which water flowed downward in chamber 1 and then upward in chamber 2. The systems were intermittently fed with wastewater under a hydraulic load of 420 mm·d⫺1. The measured influent concentrations of DBP in the experimental system were 9.84 mg·l⫺1, while the other system was used as a control and received no DBP. Effluent concentrations of the treated system averaged 5.82 g·l⫺1 and were far below the Chinese DBP discharge standard of ⱕ0.2 mg·l⫺1. These results indicate the potential purification capacity of this new kind of constructed wetland in removing DBP from a polluted water body. Key Words:
DBP, staged vertical-flow constructed wetland, purification
INTRODUCTION
There have been some studies on the purification of PAEs by conventional treatments, for example, granular activated carbon (GAC) (Paune 1998), expandedbed GAC reactor (Narayanan et al. 1993), and acclimated activated sludge (Wang et al. 1997a, 1997b). Only combined UV ozonation treatment is able to destroy all PAEs effectively (Bauer et al. 1998). However, its high cost and possible secondary pollution may make it unsuitable for most developing countries like China. Therefore, there is no economic and reliable treatment available that could remove PAEs from water effectively. There is a need for a new effective treatment system that is less expensive and easier to manage and operate. Constructed wetlands (CWs) can effectively treat domestic wastewater, landfill leachate, stabilization pond effluent, and acid mine drainage (Zachritz and Fuller 1993, Kadlec and Knight 1996, Vrhovsˇek D. et al. 1996). There are more than 650 natural and CW systems in North America and more than 5000 subsurface flow CWs in Europe for wastewater treatment (Kadlec and Knight 1996). There are very few wastewater treatment facilities in most developing countries
Phthalate acid esters (PAEs, phthalates) are manmade organic compounds used in large quantities by present day society. They are mainly used as plasticizers and as constituents in many commercial products such as paper coatings, cosmetic, adhesives, inks, and paints (Giam et al. 1984). Due to their wide application, they have become ubiquitous in the environment. PAEs have been listed as ‘priority pollutants’ by the U.S. EPA (Keith and Telliad 1979) and the Chinese EPA (Chinese Environmental Protection Agency 1989a). Dibutyl phthlate (DBP) is one of the most commonly used PAEs in many countries, including China. In recent years, DBP has been reported to have weak estrogenic effects on many animals (Moore et al. 2000, Patyna et al. 2000) and hydrophytes (Staples et al. 1985). These compounds may affect human reproductive health (Foster 2000). Therefore, it is important to remove the compounds from wastewater before discharging into the environment. 3 Author to whom correspondence should be sent. E-mail:
[email protected]
202
Zhao et al., REMOVAL OF DIBUTYL PHTHALATE BY A CONSTRUCTED WETLAND
Figure 1. Cross-sectional view of the staged vertical-flow constructed wetland (VFCW) system.
and few studies on the removal of poorly soluble, complex organic contaminant (Zachritz et al. 1996). We studied the removal of DBP from polluted water by a new kind of CW: staged, vertical-flow constructed wetland (VFCW). Analysis of DBP removal provides a baseline of system performance that will allow us to investigate other PAEs and other more complex compounds of environmental concern readily. METHODS AND MATERIALS System Design and Operation. Two pilot-scale wetland systems (Figure 1) were established in a greenhouse located near East Lake in Wuhan, China. Each system consisted of a sequence of two concrete chambers, each measuring 1 ⫻ 1 ⫻ 1 m (L ⫻ W ⫻ H), and installed flush with the ground. The first chamber was filled with 35 cm of sand (0–4mm in diameter) on the top, 20 cm of gravel (4–10mm in diameter) in the middle, and 15 cm of rock (40–55 mm in diameter) on the bottom. The second chamber was identical except for the top layer, which was only 25 cm thick (Figure 1). This design facilitated oxygen replenishment in the surface outflow of the second stage, enhancing aerobic degradation of organic materials. Stainless steel pipes (75 mm in diameter) were used in the entire drainage system to eliminate any possible pollution by plastic water pipes during the transmission of water. The influent was introduced to the firststage chamber through a pipe about 0.5 m in length and was then distributed equally to the chamber surface via scattering pipes with ostioles (5 mm in diameter) on the bottom. Influent infiltrated down through the medium into ‘‘H’’-type collecting pipes, which were placed along the bottom of both chambers.
203
The same piping material was used to collect effluent from the first stage, distribute it to the second stage, and drain the surface of the second chamber. In the first chamber, Canna indica L. was planted, while the more hydrophytic Acorus calamus L. was planted in the second chamber. The systems were maintained with water pumped from East Lake and deposited in a sedimentation tank for pretreatment with a downflow-upflow in the first process (sequence Figure 1). The hydraulic loading was 420 mm·d⫺1, with interim inflow of 140 L every 8 hours. The retention time of the systems was approximately 18 hours according to an earlier hydraulic study. The systems were treated with lake water for four weeks prior to testing to acclimatize the bacterial population to the medium. After the four-week bacterial acclimation period, one system was treated with 9.84 mg·l⫺1 DBP (below the solubility of DBP in water under ambient temperature) in the influent for about 8 months, and the other was treated only with lake water and no DBP as a control. DBP was purchased from Shanghai Solvent Factory, ethyl acetate from Xinxiang 1st Chemical Factory, nhexane from Hangzhou Refinery, and acetone from Shanghai 1st Reagent Factory. They were all analytical grade. A MilliporeR purifying system was used to produce water for the HPLC analysis. Analytical Procedure. Influent and effluent samples were collected to examine the purification of DBP in constructed wetlands. Three replicates were performed for each sample type. Solid-phase extraction (SPE) was used to enrich the analyses. The 10ml octadecyl C18 (10ml⫻500mg, Dalian Institute of Chemical-Physics, Chinese Academy of Sciences) cartridges were preconditioned sequentially using methanol, ethyl acetate, and deionized water (5ml each) prior to use. Water samples (250 ml each) were filtered through a 0.45m disposable membrane filter (Sartorius, Germany) and were drawn through the cartridges at a flow rate of about 15–20 ml min⫺1. The cartridge was then eluted with deionized water and about 10 ml of ethyl acetate. The solution was put through a column filled with anhydrous sodium sulfate to remove water in the solution and then was collected in a 10-ml vial. After concentrating with a rotary evaporator and drying with a stream of N2, the solution volume was adjusted to 0.2 ml with ethyl acetate and stored at 4 ⬚C until analyzed. One-fourth of the tritration of 80 grams sand sampled from the surface medium (0–5 cm in depth) at the end of the experiment was used to determine the adsorption of DBP in the sand media of the two VFCW systems. Three replicates were performed for each sample type. Prior to extraction, the samples were
204
WETLANDS, Volume 24, No. 1, 2004
Figure 2. DBP concentrations in influent and effluent of treatment (A) and control staged vertical-flow constructed wetland (VFCW) systems.
separated from residual plant and root material. We extracted the DBP from the medium with hexane/acetone (2:1, v/v). The samples were dried as above, treated with 0.2 ml hexane, and stored at 4 ⬚C until analyzed. DBP concentration in the samples was determined by high-performance liquid chromatography (HPLC) using a Waters System HPLC equipped with a 4.6⫻150mm ODS, 5m C18 reverse-phase column. Isopropyl alcohol/water (70:30) was used as the mobile phase, with a flow rate of 0.7ml min⫺1 and 224 nm detection unit. DBP standards were run prior to each sample run to obtain a calibration curve and to update the response factors. The recovery of DBP between 2 and 1000 ng averaged 141.2% for water samples and 101.5% for sand samples based on the DBP added during the pretreatment process. Water temperatures, pH, and ORP (oxidation-reduction potential) were also measured by instruments according to the standard methods set by the Chinese EPA (Chinese Environmental Protection Agency 1989b). The VFCWs were housed in a greenhouse so that rainfall events did not affect the systems. In order to compare the replicate results of the DBP concentrations in the samples, standard deviation values were calculated. T-tests were used to compare the differences of general parameters between treatment and control system. RESULTS Monitored reactor water temperatures varied between 14 and 30⬚ C, with an average of 21.1⬚ C during
the test period. Measured pH values suggested that both systems were slightly acidic (mean values of both systems were 6.7), and there was no significant difference between them during the experimental period (p ⫽ 0.95). Effluent ORP values of both systems were negative (⫺83 to ⫺104 mv), with positive influent values (10 to 95 mv) indicating strong reducing conditions in the chambers. DBP concentrations of the influent and effluent of the treated system are shown in Figure 2, and the general performance data of the VFCWs are summarized in Table 1. DBP removal in the treatment system exceeded 99.9%. The system performed well at influent DBP concentrations of 9.84 mg·l⫺1, with effluent concentrations averaging 5.82 g·l⫺1 and far below the DBP discharge standard of 0.2 mg·l⫺1 set by the Chinese EPA (Chinese Environmental Protection Agency 1989a). In the control system, influent DBP concentration averaged 3.94 g·l⫺1, with effluent concentration averaging 0.76 g·l⫺1, and the average removal of DBP was approximately 80.1%. DBP concentrations in the sand media of the two reactors ranged from 0.036 to 0.366 g·g⫺1 (Figure 3). The DBP concentrations of the sand media were about 75% greater in the treated system than those in the control system, suggesting that absorption contributed to the removal of DBP in the VFCWs. It could be assumed that sand media play a role in the removal of DBP through adsorption. However, three kinds of medium were used in the systems, which supply different sizes and types of materials for the physical and chemical process of DBP. So, more work is needed to determine whether there is any absorbent or other process of DBP in the other layers. DISCUSSION In the treated system, DBP concentrations in the sand media of the upflow chamber were about five times those in the downflow chamber, which indicated that the absorption of DBP in the upflow chamber might be more intensive than in the downflow chamber, or maybe in the downflow chamber, the absorbed DBP was more inclined to be efficiently degraded by microorganisms. However, more research should be done on the differences between the running conditions, including ORP and DO between the upflow
Table 1. System parameters for staged vertical-flow constructed wetland (VFCW).
System
DBP loading (g·m⫺3 day⫺1)
Mean influent (g·1⫺1)
Mean effluent (g·1⫺1)
Removal (%)
treated control
3.18 0.0010
9840.82 3.82
5.82 0.76
99.94 80.14
Zhao et al., REMOVAL OF DIBUTYL PHTHALATE BY A CONSTRUCTED WETLAND
205
staged vertical-flow chambers. However, to prove the validity of this system design, the circulation of DBP in the system through the probable chemical and biological mechanism should be studied in later work. Given the limited studies on using CW to treat complex organic compounds (Machate et al. 1997), more research is necessary to identify specific removal mechanisms. ACKNOWLEDGMENTS The authors thank Dr. Stephen P. Faulkner for his advice and encouragement during the writing and revising of the manuscript and for the patient reviewing of it. The authors are also very grateful to Dr. Douglas A. Wilcox for his valuable advice. In addition, the authors are grateful to the groups of the Environmental Biology in Institute of Hydrobiology, the Chinese Academy of Sciences for their support. The work was supported by the National Prominent Youth Foundation of China (39925007), the State High-Tech (863) Project of China (2002AA601021), the Knowledge Innovation Project of the Chinese Academy of Sciences (KSCX-SW-102), the Youth Foundation of Guangxi Chuang Autonomous Region in China (0339038), and the Foundation of Guilin University of Electronic Technology (Z20210). LITERATURE CITED
Figure 3. DBP concentrations in the sand media of the VFCW systems.
chamber and the downflow chamber. More chemical precipitation and adsorption to remove the pollutant in water may have occurred in the upflow chamber than in the downflow chamber. In conclusion, the staged VFCW effectively removed DBP at both high and low concentrations (Table 1). There are often multiple mechanisms affecting pollutant removal in CWs, including sedimentation, filtration, precipitation, adsorption, microbial degradation, and uptake by vegetation (Watson et al. 1989). The presence of an effective absorbent in the upper layer of the sand filling was assumed in the study, and more work is needed to determine whether there is any absorbent in the other layers. Double-stage (upflowdownflow), planted constructed wetlands may be a good combination of treatment components for excellent pollutant removal at high and low loading rates (Zachritz et al. 1996). The rather good performance in this study might owe to the specific design of the two-
Badkoubi, A., H. Ganjidoust, A. Ghaderi, and A. Rajabu. 1998. Performance of subsurface wetland in Iran. Water Science Technology 38:345–350. Bastian, R. K., P. E. Shanaghan, and B. P. Thompson. 1989. Use of wetlands for municipal wastewater treatment and disposal-Regulatory issues and E.P.A. policies. p. 265–278. In D. A. Hammer (ed.) Constructed Wetlands for Wastewater Treatment-Municipal. Industrial and Agricultural. Lewis Publishers, Chelsea, MI, USA. Bauer, M. J., R. Herrmann, A. Martin, and H. Zellmann. 1998. Chemodynamics, transport behaviour and treatment of phthalic acid esters in municipal landfill leachates. Water Science Technology 38:185–192. Chinese Environmental Protection Agency (ed.). 1989a. Environmental Priority Pollutants. Chinese Environmental Publisher, Beijing, China. Chinese Environmental Protection Agency (ed.). 1989b. Standard determination Methods of Water and Wastewater, third edition. Chinese Environmental Publisher, Beijing, China. Foster, P. M. D., R. C. Cattley, and E. Mylchreest. 2000. Effects of di-n-butyl phthalate (DBP) on male reproductive development in the rat: implications for human risk assessment. Food and Chemical Toxicology 38:97–99. Giam, C. S., A. Atlas, J. M. A. Powers, and J. E. Leonard (ed.). 1984. Phthalic acid esters. p. 67–140. In O. Hutzinger (ed.) Handbook of Environmental Chemistry-Anthropogenic Compounds. Springer Verlag, NewYork, NY, USA. Kadlec, R. H. and R. L. Knight. 1996. Treatment Wetlands. Lewis Publishers, Boca Raton, FL, USA. Keith, L. H. and W. A. Telliard. 1979. Priority pollutants. Environmental Science Technology 13:416–419. Machate, T., H. Noll, H. Behrens, and A. Kettrup. 1997. Degradation of phenanthrene and hydraulic characteristics in a constructed wetland. Water Research 31:554–560.
206 Moore, N. P. 2000. The oestrogenic potential of the phthalate esters. Reproductive Toxicology 14:183–192. Narayanan, B., M. T. Suidan, A. B. Gelderloos, and R. C. Brenner. 1993. Treatment of semivolatile compounds in high strength wastes using an anaerobic expanded-bed GAC reactor. Water Research WATRAG 27:171–180. Patyna, P. and K. R. Cooper. 2000. Multigeneration reproductive effects of three phthalate esters in Japanese medaka (Oryzias latipes). Marine Environmental Research 50:191–199. Paune, F., J. Caixach, I. Espadaler, J. Om, and J. Rivera. 1998. Assessment on the removal of organic chemicals from raw and drinking water at a Llobregat River water works plant using GAC. Water Research 32:3313–3324. Staples, C. A., A. F. Werner, and T. J. Hoogheem. 1985. Assessment of priority pollutant concentrations in the United States using STORET database. Environmental Toxicology and Chemistry 4: 131–142. Vrhovsˇek, D., V. Kukamja, and T. Bulc. 1996. Constructed wetland (CW) for industrial waste water treatment. Water Research 30: 2287–2292.
WETLANDS, Volume 24, No. 1, 2004 Wang, J. L., P. Liu, and Y. Qian. 1997a. Biodegradation of phthalic acid esters by immobilized microbial cells. Environment International 23:775–782. Wang, J. L., P. Liu, H. Ch. Shi, and Y. Qian. 1997b. Kinetics of phthalic acid ester degradation by acclimated activated sludge. Process Biochemistry 32:567–571. Watson, J. T., S. C. Sherwood, R. H. Kadlec, R. I. Knight, and A. E. Whitehouse. 1989. Performance expectatipns and loading rates for constructed wetlands. p. 319–351. In DA. Hammer (ed.) Constructed Wetlands for Wastewater Treatment: Municipal, Industrial and Agricultural. Lewis Publishers, Chelsea, MI, USA. Zachritz II, W. H. and W. J. Fuller. 1993. Performance of an artificial wetlands filter treating facultative lagoon effluent at Carville. Louisiana. Water Environmental Research 65:46–52. Zachritz II, W. H., L. L. Lundie, and H. Wang. 1996. Benzoic acid degradation by small, pilot-scale artificial wetlands filter (AWF) systems. Ecological Engineering 7:105–116. Manuscript received 25 April 2002; revisions received 10 January 2003 and 5 September 2003; accepted 11 November 2003.
