Proceedings of the International Conference on Sustainable Solid Waste Management, 5 - 7 September 2007, Chennai, India. pp.452-459
Fate of Phenol, Diethyl Phthalate and Dibutyl Phthalate in Bioreactor Landfill and Controlled Dump Lysimeters M. Swati and Kurian Joseph Centre for Environmental Studies, Anna University, Chennai-600 025 Email :
[email protected] ABSTRACT Three lysimeters were constructed to simulate controlled dump (A) and bioreactor landfills (B and C). The lysimeters were filled with organic fraction of fresh MSW ( to a height of 1.9m in A and 2.1 m in B and C) over a gravel drainage layer (0.2m) and capped with a composite cover. Phenol was co-disposed in bioreactor lysimeter C, by mixing with leachate at concentrations from 30-800 mg/L. A recirculation system made of perforated interconnected PVC pipes was placed in B and C to enable leachate recirculation. Phenol leached from the lysimeters was quantified every fortnight. The MSW degrading in the lysimeters was subjected to Toxicity Characteristics Leaching Procedure using a Zero Headspace Extractor followed by GC-MS screening to detect phenolics and phthalates occurring initially and after 58 and 96 weeks of operation. The fate of phenol, diethyl and dibutyl phthalate during the course of lysimeter operation was examined. The reduction in leached phenol concentration was faster by two times in the bioreactor landfill than the controlled dump. Enhanced reduction of DEP (54%) and DBP (88%) and complete degradation of the co-disposed phenol were achieved in the bioreactor landfill. Keywords: phenol, phthalate, bioreactor landfill, fate, co-disposal 1.0 INTRODUCTION Hazardous organics such as phthalate compounds, phenolics, pesticides, aliphatic and aromatic hydrocarbons, fatty acids and carboxylic acids, volatile compounds such as benzene, toluene, ethylene and xylene, polyaromatic hydrocarbons and polychlorinated biphenyls have been reported in landfill leachate and gas in developed countries (Oman and Hynning, 1993; Schwarzbauer et al., 2002; Baun et al., 2004). Kjeldsen et al. (2002) found that, even without landfill co-disposal, leachates from MSW are very similar in composition to those from mixed or hazardous landfills. The sources of such compounds have been reported to be hazardous components of household waste deposited into the municipal landfill (Slack et al., 2005). Phenolics and phthalates are the two common hazardous organic compounds reported to occur in highly organic and heterogeneous MSW typical of an urban scenario in a tropical developing country (Swati et al., 2007). The feasibility of degradation of both these types of compound under anaerobic landfill conditions has been established (Ejlertsson et al., 1997; Staples et al., 1997 and Wang and Barlaz, 1998). Knowledge on the fate of these two types of hazardous contaminants in MSW will be useful for realizing the risk from unorganized open dumping of waste, which is a common practice in the developing countries. Many hazardous organic 452
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compounds remain undegraded in a conventional landfill due to lack of enough moisture and biomass. Recirculation of leachate employed in bioreactor landfill is expected to promote attenuation of such refractory organics (Reinhart and Townsend, 1998). This paper presents the findings from lysimeter studies on the fate of three hazardous organics, viz., phenol, di-ethyl phthalate (DEP) and di-butyl phthalate (DBP) in a bioreactor landfill as compared to a conventional controlled dump. Further, fate of a specific organic pollutant, i.e. phenol, when codisposed with the recirculated leachate in the pilot-scale bioreactor landfill was also examined. The studies were carried out by Centre for Environmental Studies, Chennai, India under the Asian Regional Research Programme on “Sustainable Landfill Management in Asia” funded by Swedish International Development Cooperation Agency (Sida). 2.0 MATERIALS AND METHODS Three large-scale lysimeters (3m height and 1.3m dia.) designated as A, B and C were used for simulating controlled dump with fortnightly drainage of leachate, bioreactor landfill with daily recirculation of leachate and bioreactor landfill with daily recirculation of leachate and periodical codisposal of phenol, respectively. The lysimeters were constructed using RCC rings. Coarse gravel drainage medium of 0.2m thickness was introduced at the bottom of the lysimeter. PVC pipes of 100 mm dia. were laid below to collect the leachate. Manually segregated organic fraction of fresh MSW (A: 1750 kg, B: 1825, C: 1870 kg) was loaded over the drainage layer to 1.9m height in A and 2.1 m height in B and C. The MSW was capped with a multiple cover consisting of compost (0.3m), sand (0.1m) and mined MSW (0.3m). A recirculation system made of perforated interconnected PVC pipes was placed over the sand layer in lysimeters B and C for leachate recirculation. The lysimeters were operated for 96 weeks. Phenol leached from the lysimeters was quantified every fortnight. To assess the fate of organics, MSW loaded initially into the lysimeters and thereafter mined from the lysimeter on the 58th and 96th week was subjected to Toxicity Characteristics Leaching Procedure (TCLP) extraction using a Zero Headspace Extractor (ZHE) according to the standard USEPA (1992) method and GC-MS organic screening (as detailed in Swati et al., 2007). 2.1 Co-Disposal of Phenol in Bioreactor Landfill Lysimeter Lysimeter C was dedicated to study the effect of co-disposal of phenol in bioreactor landfill by sequentially spiking at a concentration between 30-800 mg/L into the leachate recirculated. This concentration range was chosen based on the studies of Percival and Senior (1998), which indicated that high concentration of phenol (>1000 mg/L) has a detrimental effect on phenol catabolism. The spiking study was carried out from 18th to 94th week. The concentration of phenol in the leachates was measured a fortnight after every spike during routine sampling of leachate. Successive spiking was initiated after ensuring that the leached phenol concentration fell below detectable levels in atleast two consecutive leachates samples. 2.2 Assessing the Fate of Hazardous Organics in the Landfill Lysimeters Table 1 lists the important properties of the compounds, phenol, DEP and DBP, used along with the primary data from this study to understand their fate in a landfill environment. Phenolics are simpler compounds than phthalates with a relatively much lower molecular weight and simpler molecular formulae.Their high aqueous solubility make them a very potential candidate for co-disposal than phthalates in a system like bioreactor landfill where the recirculated leachate 453
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facilitates biodegradation by carrying the compounds and increasing its contact with the microbes in the MSW mass. Wang and Barlaz (1998) have demonstrated that neutral pH can be beneficial for phenol degradation by anaerobic consortia enriched from decomposing MSW. Volatilization has been reported to be a minor pathway for transport and release of phenolics (< 0.1 % compound loss can be due to volatilisation according to Reinhart and Pohland, 1991) as the Henry’s constant of phenol is very low, i.e., H < 3.97 x 10 -8 atm m3 mole–1 or 0.0040 Pa m3 mole–1 at 25 ºC. Table 1. Important Properties of the Compounds Influencing their Fate in a Landfill
S.No. 1. 2. 3. 4. 5. 6. 7. 8. 9.
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Phenol
CAS Registry No. Molecular weight (g) Molecular formulae Melting point (ºC) Aqueous solubility (mg/L) log Kow pKa Henry’s constant(H), Pa m3/ mol Half life for anaerobic biological transformation, t1/2
108-95-2 94 C6H6O 43 67,000 1.46 9.99 0.0040 1–10 days
Compound Di-ethyl phthalate 84-66-2 222.2 C12H14O4 -40 1,100 2.38 NA 0.0270 40-100 days
Di-butyl phthalate 84-74-2 278.4 C16H22O4 -35 112 4.45 NA 0.0895 100 days
NA : Not Available; Sources: Staples et al., 1997; Wang and Barlaz, 1998; Karlsson et al., 1999; Oman, 2001 3.0 RESULTS AND DISCUSSION The fate of three hazardous organic compounds, viz., phenol, diethyl phthalate and dibutyl phthalate in controlled dump and bioreactor landfill have been discussed in detail below. 3.1 Enhanced Reduction of Phenolics in Leachates from Bioreactor Lysimeters Figure 1 depicts the leaching of the inherent phenolics in MSW in controlled dump and bioreactor. The concentration of phenol in the leachate ranged between 0.100 and 5.248 mg/L in the controlled dump and between 0.309 and 5.862 mg/L in the bioreactor lysimeter. It reduced below detectable levels (BDL) of 0.1 mg/L in bioreactor landfill towards the end of acidogenic phase of MSW degradation in 28 weeks of operation. In the case of controlled dump, the phenol levels reached BDL only after 58 weeks of operation. The pH of the leachates approached near neutral at the same time when the concentration of phenolics in the leachate dropped to below detectable levels. The leaching of phenol was irregular in both cases and no steady declining trend was observed. The decline in the phenol concentrations in leachate was observed to be twice as fast in the bioreactor lysimeters as the controlled dump.
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Figure 1 Leaching of Inherent Phenolics from Controlled Dump and Bioreactor Landfill
3.2 Fate of Phenol Codisposed in the Bioreactor Lysimeter The fate of phenol co-disposed in the bioreactor landfill during the twelve sequential spiking experiments is depicted in Figure 2 (a) and (b). It was observed that in the case of all the twelve spiking experiments, the leached phenol decreased to BDL (< 0.1 mg/L). Phenol reduction was more gradual when the leachate was acidic. As degradation of MSW continued, the leachates became neutral and slightly alkaline. The concentration of phenol spiked was increased above 30 mg/L. During subsequent spiking experiments, the concentration of phenol in the leachate was found to have a sharp initial drop followed by a quick decline to BDL even when the spiked concentration was 500800 mg/L. A drop in pH of the leachate was noticed immediately after the ninth, tenth, eleventh and twelfth spikes. This is because phenol is a weak acid (Elvers et al., 1991). The pH of the leachate, however, recovered to above neutral in a fortnight’s period in the case of all the four spikings. A possibility of inhibition of methanogenic activity due to the depressing pH is thus expected while experimenting with relatively higher phenol concentrations. The maximum permissible limit of phenolic compounds in leachates for safe disposal to inland surface water is 1 mg/L (MoEF, 2000). The final phenol concentration in the leachate produced after a month of the last spiking reached BDL and hence met the disposal limit. No residual phenol was detected in the TCLP extracts of the MSW mined during during the 58th and the 96th week. This was because the influence of partition on the fate of phenolics was minimal as phenol has a low Kow of 1.46. Hence, phenol degradation is enhanced under methanogenic condition prevailing in the lysimeter as loss due to volatilization and sorption is negligeable. Further, pKa value for phenol, which gives the pH value at which half the amount of the compound is dissociated and half is in the neutral form, is 9.99. The maximum pH encountered in the leachate from the bioreactor lysimeter, C, was pH 8.11. Favourable pH for direct abiotic phenol dissociation does not prevail in the present study. Phenolic solutions could be disposed by dissolving in leachate recirculated in a landfill bioreactor during methanogenic stages of landfill operation as acidic pH is favourable for direct leaching rather than biodegradation. It is essential to allow enough standing time for the recirculated leachate in-situ while practicing such codisposal as phenol could otherwise get easily leached away. It is important to control the co-disposed concentrations below 1000 mg/L in leachate.
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(b) Figure 2 Fate of Phenol Co-Disposed in the Bioreactor Landfill
3.3 Fate of Diethyl Phthalate and Dibutyl Phthalate in the Landfill Lysimeters Figure 3 (a) and (b) illustrate the fate curves for DEP and DBP in the lysimeters. The initial concentrations of DEP and DBP in the fresh MSW were 1714.70 and 491.46 mg/kg, respectively. Enhanced reduction of both the phthalates could be observed in the bioreactor lysimeters as compared to the controlled dump. The reduction of DEP in the MSW in 58 weeks of operation of A, B and C were 24, 31 and 41 %, respectively. After 96 weeks of operation, the DEP concentration decreased by 47.44, 53.74 and 55.82 %, respectively at the end of 96 weeks. The reduction of DBP in the MSW in 58 weeks of operation of A, B and C were 37, 84 and 80 %, respectively. After 96 weeks of operation, the DBP concentration decreased by 43, 91 and 86 %, respectively. 456
Fate of Phenol, Diethyl Phthalate and Dibutyl Phthalate in Bioreactor Landfill and Controlled Dump Lysimeters 600
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Figure 3 Fate of Diethyl Phthalate and Dibutyl Phthalate in MSW
Despite the fact that the molecular weight of DBP (278.4 g) is higher than DEP (222.2 g) and the alkyl chain length of DBP is twice that of DEP, higher ultimate loss was noted for DBP than DEP in all the lysimeters. This was because the initial concentration of DBP was 3.5 times lesser than DEP in the during loading. Jobling et al. (1995) reported that DBP is estrogenic with a cumulative action. Gray et al. (1999) revealed that male reproductive development is acutely sensitive to DBP. Van Wezel et al. (2000) have established an environmental risk limit (ERL) of 0.7 g/kg of fresh weight for DBP, for fresh soils with atleast 10% organics, exceeding which it would cause endocrine disruptive effects. The concentration of DBP (0.491 g/kg) was below the ERL even during the commencement of the studies. External addition of phthalate containing components might lead to levels exceeding the above mentioned threshold. Therefore, co-disposal of phthalates is not recommended. Losses of the compounds from landfills through leachates are partially a function of the aqueous solubility (Staples et al., 1997). The aqueous solubility of DEP (1100 mg/L) is almost 100 times that of DBP. Thus, the probability of leaching via an aqueous medium is relatively higher for DEP than DBP. Nevertheless, in a complex matrix like MSW, the leachability of a compound cannot be assessed from its aqueous solubility alone. A favourable pH and poor sorption to waste also give the compound an opportunity to leach easily. The high Kow values of DBP (Table 1) rule out the possibility of its appearance in the landfill leachate. Hence, its loss could be exclusively attributed to enhanced degradation of MSW in the bioreactor lysimeters. In general, the dominant removal mechanism for compounds in bioreactors is biodegradation while in the controlled dump, it is leaching. The ultimate loss of DEP in the bioreactors was 1.15 times that in controlled dump. In the case of DBP, the ultimate loss in the bioreactors was 2.07 times that in controlled dump. Clearly, higher aqueous solubility and moderate absorbability of DEP has lead to losses due to leaching of this compound in A. This in turn has led to almost comparable ultimate losses of this compound in the three lysimeters. DBP, on the other hand, is sparingly soluble, and is leached in lesser amounts from the controlled dump. Volatile losses of both DEP and DBP are highly unlikely (H: 0.0270 Pa.m3 /mol for DEP and 0.0895 Pa.m3 /mol for DBP). The present results confirm the enhanced biodegradation of DEP and DBP in bioreactor landfills. The result is supported by reported laboratory observations that landfill derived microbes could degrade di-ester phthalates (Staples et al., 1997) and ultimate degradation of these phthalates to methane and carbon-di-oxide is feasible (Ejlertsson et al., 1997; Mersiowsky et al., 2001).
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4.0 CONCLUSION The reduction of leached phenol concentration was two times faster in the bioreactor landfill than the controlled dump lysimeter. In the case of phenol codisposal in the bioreactor landfill, the leached phenol dropped to below detectable levels quite rapidly in alkaline leachates. Therefore, codisposal of phenol is recommended during the methanogenic phase of MSW stabilization. Enhanced reduction of the hazardous organic phthalates, DEP (54 %) and DBP (88 %) and a complete degradation of codisposed phenol could be achieved in the bioreactor landfill. ACKOWLEDGEMENT The authors wish to acknowledge the support provided by the Swedish International Cooperation Development Agency (Sida) for the realization of this study. REFERENCES Baun A., Ledin A., Reitzel L.A., Bjerg P.L. and Christensen T.H., Xenobiotic organic compounds in leachates from ten Danish MSW landfills – chemical analysis and toxicity tests, Water Research, 38, 3845-3858 (2004). Ejlertsson J., Alnervik M. and Svensson B.H., Influence of water solubility, side chain degradability and side chain configuration on the degradation of phthalic acid esters under methanogenic conditions, Environmental Science and Technology, 31, 2761-2764 (1997). Elvers B., Hawkins S. and Schulz G., Ulman’s Encyclopedia of Industrial Chemistry, Fifth Edition, ISBN 3-527-20119-X, Weinheim, Federal Republic of Germany (1991). Gray L.E., Wolf C., Lambright C., Mann P., Price M., Cupper R.L. and Ostby J., Administration of potentially antiandrogenic pesticides (procymidone, linuron, iprodione, chlozolinate, p,p`-DDE and ketoconazole) and toxic metabolites (DBP and DEHP, PCB 169 and ethane dimethane sulphonate) during sexual differentiation produces diverse profiles of reproductive malformations in the male rat, Toxicology and Industrial Health, 15, 94-118 (1999). Jobling S., Reynolds T., White R., Parker M.G. and Sumpter J.P., A variety of environmentally persistent chemicals, including some phthalate plasticizers, are weakly estrogenic, Environment Health Perspectives, 103, 582-587 (1995). Karlsson A., Ejlertsson J., Nezirevic D. and Svensson B.H., Degradation of phenol under meso- and thermophilic, anaerobic conditions, Anaerobe, 5, 25-35 (1999). Kjeldsen P., Barlaz M.A., Rooker A.P., Baun A., Ledin A. and Christensen T.H., Present and longterm composition of MSW landfill leachate: a review’, Critical Reviews on Environmental Science and Technology, 32, 297-336 (2002). Mersiowsky I., Weller M. and Ejlertsson J., Fate of plasticised PVC products under landfill conditions: A laboratory-scale landfill simulation reactor study, Water Research, 35, 30633070 (2001). MoEF, Municipal solid waste (Management and Handling) Rules, 2000, in MoEF notification, New Delhi, the 25th September (2000) : Oman C. and Hynning P., Identification of organic compounds in municipal landfill leachates’, Environmental Pollution, 80, 265-271 (1993). Oman C., Comparison between the Predicted Fate of Organic Compounds in Landfills and the Actual Emissions, Environmental Science and Technology, 35, 232-239 (2001). 458
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Percival L.J. and Senior E., An assessment of the effects of the dual co-disposal of phenol and waste activated sewage sludge with refuse on the refuse anaerobic fermentation and leachate quality, Water SA, 24, 57-70 (1998). Reinhart D.R. and Pohland F.G., The assimilation of organic hazardous wastes codisposed with municipal refuse, Journal of Industrial Microbiology, 8, 193-200 (1991). Reinhart D.R. and Townsend T.G., Landfill Bioreactor Design and Operation, Lewis Publishers: New York, ISBN: 1-56670-259-3 (1998). Schwarzbauer J., Heim S., Brinker S. and Littke R., Occurrence and alteration of organic contaminants in seepage and leakage water from a waste deposit landfill, Water Research, 36, 2275-2287 (2002). Slack R.J., Gronow J.R. and Voulvoulis N., Household hazardous waste in municipal landfills contaminants in leachate, Science of the Total Environment, 337, 119-137 (2005). Staples C.A., Peterson D.R., Parkerton T. F. and Adams W.J., The environmental fate of phthalate esters: A literature Review, Chemosphere, 35, 667-749 (1997). Swati M., Rema T. and Kurian J., Hazardous organic pollutants in municipal solid waste: Qualitative screening and batch studies on co-disposal, Proceedings of International Conference on Cleaner Technologies and Environmental Management, Pondicherry, India, 04-06 January (2007). USEPA, Toxicity Characteristics Leaching Procedure, SW 846, Chapter 8, Method 1311, (1992). Van Wezel A.P , Van Vlaardingen P., Posthumus R., Crommentuijn G.H. and Sijm D.T., Environmental risk limits for two phthalates, with special emphasis on endocrine disruptive properties, Ecotoxicology Environmental Safety, 46, 305-321 (2000). Wang Y.S. and Barlaz M.A., Anaerobic biodegradability of alkylbenzenes and phenol by landfill derived microorganisms, FEMS Microbiology Ecology, 25, 405-418 (1998).
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