Landfill Simulation Tests

Another category of dry, anaerobic biodegradation tests are landfill simulation tests. These tests have primarily been developed in the USA, where biologically active landfills represent a viable waste management option for the future. In Europe however, there is much less interest for biodegradation characteristics in landfills, especially after the adoption in 1999 of the EU landfill directive, which is phasing out the disposal of biodegradable materials in landfills. 

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The concentrations of mercury in the landfill gas were estimated with the aid of a simulation program EandGEM that was developed by the office of Research and Development United States Environmental Protection Agency (US EPA). Land GEM is based on a fust-order decomposition rate equation for quantifying emissions from the decomposition of landfilled waste in municipal solid waste (MSW) landfills. The software provides a relatively simple approach to estimating landfill gas emissions. Model defaults are based on empirical data from US landfills. Field test data can also be used in place of model defaults when available. This software was also useful to forecast the future levels of mercury generation from LEG. 

The blend compositions are currently being exposed to accelerated landfill, simulated marine, and aerobic composting environments to measure the degradability of these blends in more realistic biodegradation tests. 

The ET cover cannot be tested at every landfill site so it is necessary to extrapolate the results from sites of known performance to specific landfill sites. The factors that affect the hydrologic design of ET covers encompass several scientific disciplines and there are numerous interactions between factors. As a consequence, a comprehensive computer model is needed to evaluate the ET cover for a site.48 The model should effectively incorporate soil, plant, and climate variables, and include their interactions and the resultant effect on hydrology and water balance. An important function of the model is to simulate the variability of performance in response to climate variability and to evaluate cover response to extreme events. Because the expected life of the cover is decades, possibly centuries, the model should be capable of estimating long-term performance. In addition to a complete water balance, the model should be capable of estimating long-term plant biomass production, need for fertilizer, wind and water erosion, and possible loss of primary plant nutrients from the ecosystem. 

Column test (described in Dutch standard NEN 7343) is intended to simulate the percolation of (acidic) rainwater through granular materials in a road construction or landfill. The material is placed in a column with a diameter of 5 cm and height of 20 cm, and acidified demineralized water is then passed upwards through it. The eluate is collected in seven fractions at a liquid/solid ratio of between 0.1 and 101 kg-1. The leaching is calculated and expressed in mg kg 1 as a function of time, based on the analysis results. 

TCLP Toxicity Characteristic Leaching Protocol (Procedure ), an EPA-required laboratory test to determine whether harmful amounts of material leach from wastes in simulated landfill disposal conditions. 

The composition of pore waters from contaminated cores 1 and 2 were used to initialize the model (Table 2). Concentrations represent leachate collected from the initial half pore volume of each core. Eluent specified in the transport simulations had the composition of uncontaminated ground water in Table 2. Reactions proposed to describe concentration changes for selected constituents within the cores are based on comparisons between eluent and leachate chemistry and analysis of selected constituents in the core samples. Equilibrium constants and kinetic rates for the reactions were adjusted to give the best fit to leachate concentrations from core 1. The same reactions, equilibrium constants, and kinetic rates were then tested by modeling the concentrations of constituents in leachate from core 2. This geochemical model will be used in the future to simulate evolution of contaminated ground water associated with the Area 4 landfill at the aquifer scale. 

The D20.96 Committee of the American Society of Testing and Materials (ASTM) worked intensively on test methods for water-insoluble polymers and plastic materials [38,39]. Since 1993, five standards for biodegradation of plastic materials in various conditions have been published (Table 2), and other test methods with different environments are nearing completion [39], i.e., anaerobic high-solid digestor and anaerobic accelerated landfill to simulate the fate of a material during solid waste management. Other experimental methods need to be developed for freshwater and simulated marine conditions. 

The situation became even more complicated because of a change in the U.S. hazardous waste management law. In 1990, the U.S. EPA changed its test protocol for determining what wastes should be classified as hazardous. The new toxicity test, called the TCLP test, required that materials be crushed or cut up to a small particle size and exposed to an acetic acid solution. The constituents of the leachate were then measured against standards for (among other elements) cadmium and lead. The idea was to simulate the release of the battery s contents into a landfill environment over a protracted period of time. If excessive quantities of the hazardous constituents of concern were measured, the waste material was to be regulated as hazardous. 

Ress, B.B., Calvert, P.P., Pettigrew, CA., Barlaza, MA., 1998, Testing anaerobic biodegradabiiity of polymers in a laboratoiy-scale simulated landfill. Environ.. redifio/. 32 821-827... 

US-EPA provides two leaching test methods. One is the Toxicity Characteristic Leaching Procedure (EPA SW 846 Method 1311), and is called the TCLP for short. The other is the Synthetic Precipitation Leaching procedure (EPA SW—846 Method 1312), and is called the SPLP. The TCLP is intended to simulate dissolution of waste materials inside a landfill, and is the only leaching test specified by the regulation for characterization of the hazardous waste (40 CFR 261.24 Toxicity Characteristic, waste code D004-D043) under the Resource Conservation and Recovery Act (RCRA). 

D6776-02 Standard test method for determining anaerobic biodegradabihty of radiolabeled plastic materials in a laboratory-scale simulated landfill environment... 

In general, biodegradability of polymers can be tested using Figure 21.9. Screening tests by either enzymatic or aquatic means are inexpensive and fast, but real-life tests can be laborious and expensive. Neither of these two types of processes, however, actually simulates the condition truly present in landfills [50, 51]. 

Other Addition Polymers. There are few studies on other reported polymer and plastic components of landfills. Poly(vinyl chloride) seems to be inert in landfill showing no degradation in real-world tests (23,24) and laboratory simulations (25). In the latter study, plasticizer migration occinred with its subsequent biodegradation. 

ASTM D6776-02, Standard Test Method for Determining Anaerobic Biodegradability of Radiolabeled Plastic Materials in a Laboratory-Scale Simulated Landfill Environment, American Society for Testing and Materials, PA, USA, 2002. (Withdrawn in 2011 ... 

Gu J-D, Gu J-G, Shi HC, li XY (2001b) Simulating anaerobic landfill conditions in bioreactors and testing polymer degradability using poly(P-hydroxybutyrate-co-16 % valerate) and cellulose acetetes (DS 1.7 and 2.5) Water Sci Technol... 

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