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Book ChapterDOI

Modelling of Organic Acid Transport in Unsaturated Subsurface System

TL;DR: In this article, a one-dimensional numerical model has been developed to understand and forecast the transport of organic acids in unsaturated soil using a finite difference technique, where the Richards equation was used to simulate the water content in the unsaturated soils and advection-dispersion equation was also used to predict the transportation of organic acid.
Abstract: Leachate from municipal solid waste landfill contains a variety of contaminants including organic acids. The subsequent vertical movement of organic acids from the landfill may reach and pollute the groundwater. Hence, the prediction of vertical movement in the unsaturated sub-surface system is essential to monitor the groundwater contamination. To achieve this, a one-dimensional numerical model has been developed to understand and forecast the transport of organic acids in unsaturated soil using a finite difference technique. This study considers acetic acid as a representative organic compound in the landfill leachate. The Richards equation is used to simulate the water content in the unsaturated soil and advection–dispersion equation is used to predict the transport of organic acid. Moreover, first-order decay coefficient is also considered during the migration of organic acid. The numerical results suggest that the transport of organic acid is strongly influenced by water content variation in the unsaturated subsurface. Further, it is also observed that the soil distribution coefficient was found to be one of the most influencing parameters, which is significantly affecting the organic acid concentration profile in the unsaturated soil. Moreover, the decay coefficient is also affecting the distribution of organic acid in the vadose zone. Overall, the numerical results show that the higher simulation time allows the concentration of organic acid to reach larger depth. Hence, there is a high probability of groundwater contamination by organic acid concentration.
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Journal ArticleDOI
TL;DR: In this paper, the long-term behavior of landfills with respect to changes in oxidation-reduction status is discussed based on theory and model simulations, and it seems that the somewhere postulated enhanced release of accumulated heavy metals would not take place within the time frames of thousands of years.
Abstract: The major potential environmental impacts related to landfill leachate are pollution of groundwater and surface waters. Landfill leachate contains pollutants that can be categorized into four groups (dissolved organic matter, inorganic macrocomponents, heavy metals, and xenobiotic organic compounds). Existing data show high leachate concentrations of all components in the early acid phase due to strong decomposition and leaching. In the long methanogenic phase a more stable leachate, with lower concentrations and a low BOD/COD-ratio, is observed. Generally, very low concentrations of heavy metals are observed. In contrast, the concentration of ammonia does not decrease, and often constitutes a major long-term pollutant in leachate. A broad range of xenobiotic organic compounds is observed in landfill leachate. The long-term behavior of landfills with respect to changes in oxidation-reduction status is discussed based on theory and model simulations. It seems that the somewhere postulated enhanced release of accumulated heavy metals would not take place within the time frames of thousands of years. This is supported by a few laboratory investigations. The existing data and model evaluations indicate that the xenobiotic organic compounds in most cases do not constitute a major long-term problem. This may suggest that ammonia will be of most concern in the long run.

2,122 citations

Journal ArticleDOI
TL;DR: Three mathematical models proposed to describe the effects of sorption of both bacteria and the herbicide (2,4-dichlorophenoxy)acetic acid on the biological degradation rates of 2, 4-D in soils indicated that sorbed 2,3-D is completely protected from degradation and that both sorbed and solution bacteria are capable of degrading 2,4,D in solution.
Abstract: Three mathematical models were proposed to describe the effects of sorption of both bacteria and the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D) on the biological degradation rates of 2,4-D in soils. Model 1 assumed that sorbed 2,4-D is not degraded, that only bacteria in solution are capable of degrading 2,4-D in solution, and that sorbed bacteria are not capable of degrading either sorbed or solution 2,4-D. Model 2 stated that only bacteria in the solution phase degrade 2,4-D in solution and that only sorbed bacteria degrade sorbed 2,4-D. Model 3 proposed that sorbed 2,4-D is completely protected from degradation and that both sorbed and solution bacteria are capable of degrading 2,4-D in solution. These models were tested by a series of controlled laboratory experiments. Models 1 and 2 did not describe the data satisfactorily and were rejected. Model 3 described the experimental results quite well, indicating that sorbed 2,4-D was completely protected from biological degradation and that sorbed- and solution-phase bacteria degraded solution-phase 2,4-D with almost equal efficiencies.

460 citations

Journal ArticleDOI
TL;DR: In this paper, the results of physico-chemical analyses of leachate confirmed that its characteristics were highly variable with severe contamination of organics, salts and heavy metals, and the BOD5/COD ratio (0.69) indicated that the leachates was biodegradable and un-stabilized.

197 citations

Journal ArticleDOI
TL;DR: This review is an attempt to understand the dynamics and dimensions of landfill and dumpsite rehabilitation in many developed and developing countries.

129 citations

Journal ArticleDOI
TL;DR: Simulation of the carbon isotope geochemistry independently supported the proposed reaction network and demonstrated the relevance and impact of various secondary geochemical processes on leachate plume evolution.

96 citations