Landfills

Technologies for Onsite Sustainable Leachate Management

As we look toward the future, the ideal leachate management approach will be sustainable, low-cost, site-specific and capable of adaptation to evolving regulations without ignoring the impacts of climate change and population growth.

Daniel E. Meeroff, Ph.D., François Gasnier, Hatsuko Hamaguchi, Swapnil Jain, André McBarnette, and Richard Reichenbach

Municipal landfill leachate is characterized by high concentrations of recalcitrant organic compounds, ammonia, suspended material and heavy metals. As a result, leachate is difficult to manage because conventional forms of biological and chemical treatment are inefficient at dealing with such a diverse and complex waste stream. Because of widely varying practices in solid waste management, an all-inclusive solution to long-term management of landfill leachate is not currently available, such that landfill managers are left with a toolbox of current practices that cannot adequately address inorganics and organics, simultaneously. This result is a major technological need for sustainable, economical options for safe discharge of leachate to the environment.

In this article, futuristic advanced oxidation processes, such as photochemical iron-mediated aeration (PIMA) and TiO2 photocatalytic oxidation are investigated. These processes are able to: 1) convert refractory organics into more biodegradable constituents, 2) remove heavy metals such as Pb, As, Cd, Hg through co-precipitation, adsorption, and redox mechanisms, 3) deal with ammonia through stripping of NH3(g) and also conversion of ammonia to nitrate through aeration, 4) destroy or completely mineralize recalcitrant organics, 5) strip VOCs, 6) achieve high levels of disinfection and 7) address color/odor issues.

The Ideal Approach

As we look toward the future, the ideal leachate management approach will be sustainable, low-cost, site-specific and capable of adaptation to evolving regulations without ignoring the impacts of climate change and population growth. After evaluating 23 different engineering alternatives for long-term leachate management (Meeroff and Teegavarapu, 2010), the results indicated that the most effective and sustainable strategies for the future would involve technologies that can destroy different classes of harmful contaminants all at once, without producing adverse byproducts and residuals. One approach will be to discharge the leachate to the sanitary sewer system after onsite pretreatment, to reduce the toxicity of the leachate. The technology with the most promise includes advanced oxidation that uses the power of ultraviolet radiation from sunlight, which is free and requires no additional energy input. Two such technologies being developed at Florida Atlantic University include photochemical iron-mediated aeration (PIMA) and photocatalytic oxidation using TiO2.

Photochemical Iron-Mediated Aeration (PIMA)

PIMA is a new photochemically-assisted iron-mediated aeration process for oxidizing organics and co-precipitating inorganics in wastewater, which was co-developed by the University of Miami and Florida Atlantic University (Englehardt et al., 2006; Meeroff et al., 2006). The process uses non-toxic materials, generates filterable ferric residuals, and is accelerated by ultraviolet energy, which can be provided by sunlight (see Figure 1). Although the reaction mechanism is not completely understood for PIMA, evidence suggests oxidation via hydroxyl radical and/or ferryl species, implying indiscriminate oxidation of organics. Essentially, the process is thought to begin with a stepwise oxidation of Fe(s) to Fe2+(aq) to Fe3+(aq), enhanced by ultraviolet light. This is then followed by the generation of hydroxyl radical (OH•) similar to the Photo-Fenton reaction (Katsumata et al. 2004; Sirtori et al. 2009). Then the combined action of the oxidative power of the hydroxyl radical, co-precipitation via insoluble ferric precipitates, the stripping power of aeration, and the photolytic effect of ultraviolet energy work to decrease the concentrations of pollutants and impurities.

Photocatalytic Oxidation

Photocatalytic oxidation involves the use of ultraviolet (UV) light to excite a semiconductor catalyst, such as TiO2. Irradiation of TiO2 with photons of light energy produce areas of positive charge in the valence band of the semiconductor (“holes”) and free electrons in the conductance band. When the “holes” and free electrons interact with water trapped in the pores of the catalyst, a mixture of indiscriminate oxidants are generated including hydroxyl radical (OH•) and superoxide radical (O2). Hydroxyl radical attack is thought to be the primary mechanism of decomposition, and photocatalytic processes for destruction of organics are well known; however, the destruction of certain nitrogen-containing organic pollutants through a reductive pathway has also been reported (Schmelling et al., 1996) as well as removal of heavy metals (Davis and Green, 1999; Hilmi et al., 1999; Vohra and Davis (2000); Cho et al., 2002). Most of these experiments were conducted on glass plates coated with immobilized TiO2. In those tests, individual metals at concentrations on the order of mg/L were reduced to undetectable levels in less than one hour of treatment. Since suspended TiO2 catalysts enjoy free contact with UV irradiation in a photoreactor (Figure 2), they would be expected to achieve even better removal efficiency than immobilized TiO2 catalysts. However, the separation and reuse of suspended catalyst powders from treated water has limited its application in practice (see Figure 2).

Methods

The constituents of concern for determining process removal efficiencies in this study were analyzed using Standard Methods (APHA, AWWA, and WEF 2005): Pb (SM3120B), BOD5 (SM5210B), COD (SM5220D), and ammonia (EPA Method# 350.1 [SM4500-NH3G] and 350.2). Collection of process performance data was conducted in two phases. The first set of experiments involved initial screening tests with simulated leachates to determine the magnitude of residual generation and oxidation kinetics. Since synthetic leachate provides the substrate for bacteria, but does not contain a significant microbial population, actual field samples of leachate were tested from a variety of landfill sites located in Florida.

Results

For the PIMA process, both individual tests and mixtures of simulated leachate showed promising results: 50 percent COD removal in 24 hours, 50 percent BOD5 removal in 16 hours, and greater than 92 percent Pb removal in four hours and three-log removal in 16 hours. However, ammonia removal was lower than expected (<30 percent), and the reaction was found to be pH-dependent. In terms of reactor kinetics, no additional removal was observed when td > 16 hrs, and no additional removal was achieved when UV intensity exceeded 10 mW/cm2. However, when PIMA was applied to real leachates, the process was found to remove Pb and color effectively, while removing COD and BOD5 slightly less effectively (<50 percent). It was also found that the PIMA process may be capable of removing ammonia with pH adjustment into the alkaline range (pH>10) (see Table 1).

A bacterial analysis was also conducted by Micrim Labs Inc. (Fort Lauderdale, FL) to test the process efficiency of PIMA for disinfection. Bacteria (Bacillus sp., Pseudomonas stutzeri, Pseudomonas fluorescens, Pseudomonas alcaligenes, Micrococcus luteus, and coagulase-negative Staphylococcus) and fungi (Aspergillus niger) were isolated from the raw leachate sample. After 16 hours of PIMA treatment, no sign of viable bacterial or fungal activity was found. This demonstrates the disinfection power of the PIMA process. This finding was not unexpected as UV alone is a well-known disinfectant (Metcalf and Eddy 2003).

The other technology that was evaluated in this study was photocatalytic oxidation with TiO2 particles activated by UV light. For the photocatalytic oxidation process for both simulated and real leachates, it was found that COD removal occurred on the order of minutes instead of hours compared to the PIMA process, and 100 percent mineralization of COD to carbon dioxide and water occurred. The photocatalytic particles could be recovered effectively (80 to 86 percent), with no loss in removal efficiency observed after 4+ uses, and UV without TiO2 was relatively ineffective (Figure 3).

Tests on actual leachate from Broward County, FL Central District Landfill and also from Polk County, FL Landfill were also conducted. For these experiments, COD was the model compound tested for removal efficiency. Even though the starting COD concentrations were considered low for leachate (<400 mg/L), removal exceeded 70 percent after four hours of contact time and the photocatalytic oxidation process performed similarly with leachates from both landfills, as shown in Figure 4. In other tests, with initial COD concentrations on the order of 1000 mg/L, COD was reduced to permissible sewer discharge levels (<800 mg/L) in less than 45 minutes reaction time. Complete mineralization was achieved after 4 hours of contact at UV intensity < 0.07 mW/cm2.

It was also determined that pre-filtration may not be necessary, particularly for low strength leachates, since we recorded 24 percent COD removal of the pre-filtered leachate after four hours and 29 percent COD removal after four hours unfiltered. In terms of biodegradable organics, we recorded 35 percent removal of BOD5 in four hours (initial BOD5 = 600 mg/L). As for metals, we found 80 percent removal of copper and 40 percent removal of arsenic in just two hours of treatment. With regards to ammonia, the commercially available TiO2 particles (Degussa P25) did not remove ammonia in simulated leachates without pH adjustment, but we recorded 75 percent removal of NH3-N in 4 hours at pH =8.6 (initial concentration = 2,400 mg N/L).

Effective Leachate Management Strategies

Bench scale testing with PIMA and photocatalytic oxidation technologies has been able to achieve: 1) 40 to 50 percent conversion of refractory COD to complete mineralization, 2) >99.9 percent removal of heavy metal contaminants (i.e. Pb, As), 3) 10 to 15 percent removal of ammonia without pH adjustment, 4) effective color removal with detention times less than four hours, 5) complete inactivation of bacterial and fungal fauna present in field samples, and 6) effective treatment with <10 mW/cm2 of UV energy intensity. For the photocatalytic process, the contact times were found to be less than four hours, pre-filtration was not necessary, and testing with actual leachate samples showed 85 percent catalyst recovery efficiency with no loss in performance after multiple (n>4 uses). From these bench scale results, both PIMA and photocatalytic oxidation technologies show promise as an effective leachate management strategy. Determining whether the technology is cost-effective for field application is the next logical step. As a result, a pilot scale system will be tested at one of the landfill facilities. Pilot testing will permit the ability to determine costs for reactor construction and process operation, which is difficult to predict from the bench scale experiments.

Daniel E. Meeroff, Ph.D., is an associate professor in the Department of Civil, Environmental & Geomatics Engineering at Florida Atlantic University (Boca Raton, FL). His area of specialization is Environmental Engineering, specifically focusing on water and wastewater engineering, water quality, environmental microbiology, aquatic chemistry and pollution prevention. He can be reached at [email protected]or visit http://labees.civil.fau.edu.

François Gasnier currently works for Veolia Eau. He has an M.S. from the FAU Department of Civil, Environmental & Geomatics Engineering at Florida Atlantic University. He can be reached at [email protected].

Hatsuko Hamaguchi is an M.S. candidate of the Department of Chemical Engineering at the University of Tokushima, Japan. She can be reached at [email protected].

Swapnil Jain is a B.S. candidate of the Department of Civil Engineering at the Indian Institute of Technology, Bombay. He can be reached at [email protected].

André McBarnette currently works for Geosyntec Consultants. He is an M.S. candidate of the FAU Department of Civil, Environmental & Geomatics Engineering at Florida Atlantic University. He can be reached at [email protected].

Richard Reichenbach is a BS candidate of the FAU Department of Civil, Environmental & Geomatics Engineering at Florida Atlantic University. He can be reached at [email protected].

Acknowledgments: This research was sponsored in part by the William W. “Bill” Hinkley Center for Solid and Hazardous Waste Management and Florida Atlantic University. The researchers would like to thank Joe Lurix, John Booth, Ray Schauer, Shaowei Chen, C.T. Tsai, D.V. Reddy, Richard Meyers, Fred Bloetscher, Manuel Hernandez, Marc Bruner, Matt Zuccaro, Lee Casey, J.P. Listick, Tim Vinson, John Schert, and Bill Forrest for sharing their input as members of the Technical Advisory Group. The following individuals are thanked for their contributions to the research: Deng Yang, William Koseldt, and Jim Englehardt.

References

  • APHA, AWWA, and WEF (2005). Standard Methods for the Examination of Water and Wastewater, 21st Edition. American Public Health Association, American Water Works Association and Water Environment Federation, Washington, DC.

  • Cho, S.P., Hong, S.C., Hong, S.I. (2002). “Photocatalytic degradation of the landfill leachate containing refractory matters and nitrogen compounds.” Applied Catalysis B: Environmental, Vol. 39, pp. 125-133.

  • Davis, A.P. and Green, D.L. (1999). “Photocatalytic oxidation of cadmium-EDTA with titanium dioxide.” Environmental Science and Technology, Vol. 33(4), pp. 609-617.

  • Englehardt, J.D., Meeroff, D.E., Echegoyen, L.A., Raymo, F., and Shibata, T. (2006). “Oxidation of aqueous EDTA and associated organics and coprecipitation of inorganics by ambient iron-mediated aeration.” Environmental Science and Technology, Vol. 41(1), pp. 270-276.

  • Hilmi, A., Luong, J.H., and Nguyen, A.L. (1999). “Utilization of TiO2deposited on glass plates for removal of metals from aqueous wastes.” Chemosphere, Vol. 38(4), pp. 865-74.

  • Katsumata, H., Kawabe, S., Kaneco, S., Suzuki, T., and Kiyohisa, O. (2004). “Degradation of bisphenol A in water by the photo-Fenton reaction.” J Photochem Photobiol A,Vol. 162, pp. 297–305.

  • Meeroff, D.E., Englehardt, J.D., Echegoyen, L.A., Woolever, C.A., and Shibata, T. (2006). “Development of an energy-assisted iron-mediated aeration process for in situ groundwater applications.” Journal of Environmental Engineering. Vol. 132(7), pp. 747-757

  • Meeroff, D.E., Gasnier, F. and Tsai, C.T. (2008). “Investigation of Energized Options for Leachate Management: Year Two Tests of Advanced Oxidation Processes for Treatment of Landfill Leachate.” Final Report Year 2 for the William W. “Bill” Hinkley Center for Solid and Hazardous Waste Management, Gainesville, FL. Report # 0632018.

  • Meeroff, D.E. and Teegavarapu, R. (2010). “Interactive Decision Support Tool for Leachate Management.” Final Report for the William W. “Bill” Hinkley Center for Solid and Hazardous Waste Management, Gainesville, FL. Report # 0832028.

  • Metcalf and Eddy, Inc. (2003). Wastewater engineering: treatment and reuse (4th ed.), revised by Tchobanoglous, G., Burton, F.L., and Stensel, H.D. McGraw-Hill, New York.

  • Schmelling D.C., Gray, K.A. and Kamat, P.V. (1996). “Role of reduction in the photocatalytic degradation of TNT.” Environmental Science and Technology, Vol. 30, pp. 2547– 2555.

  • Sirtori, C., Zapata, A., Oller, I.. Gernjak, W. Agüera, A. and Malato, S. (2009). “Solar Photo-Fenton as Finishing Step for Biological Treatment of a Pharmaceutical Wastewater.” Environmental Science and Technology, Vol. 43(4), pp. 1185-1191.

  • Vohra, M.S. and Davis, A.P. (2000). TiO2-Assisted photocatalysis of lead–EDTA. Water Research, Vol. 34(3), pp. 952-964.

Figure 1

Figure 1Leachated

Schematic diagram of PIMA laboratory reactor.

Figure 2

Figure 2Leachates

Schematic diagram of photocatalytic oxidation laboratory reactor.

Figure 3

Figure 3 Leachates

Photocatalytic oxidation tests with simulated leachate for COD removal (initial COD concentration was 1060 mg/L.

Figure 4

Figure 4 Leachates

Photocatalytic oxidation tests with real leachate for COD removal.

Table 1

Table 1 Leachates

Summary of lead removal testing with PIMA, IMA (no UV), and UV (no iron) on real leachate from Broward County, FL.

Figures/Table courtesy of Daniel Meeroff.

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