Slope stability analysis of a landfill subjected to leachate recirculation and aeration considering bio-hydro coupled processes

During the operation of landfills, leachate recirculation and aeration are widely applied to accelerate the waste stabilization process. However, these strategies may induce high pore pressures in waste, thereby affecting the stability of the landfill slope. Therefore, a three-dimensional numerical analysis for landfill slope stability during leachate recirculation and aeration is performed in this study using strength reduction method. The bio-hydro coupled processes of waste are simulated by a previously reported landfill coupled model programmed on the open-source platform OpenFOAM and then incorporated into the slope stability analysis. The results show that both increasing the injection pressure for leachate recirculation and maximum anaerobic biodegradation rate will reduce the factor of safety (FS) of the landfill slope maximally by 0.32 and 0.62, respectively, due to increased pore pressures. The ignorance of both waste biodegradation and gas flow will overestimate the slope stability of an anaerobic bioreactor landfill by about 20–50%, especially when the landfilled waste is easily degradable. The FS value of an aerobic bioreactor landfill slope will show a significant reduction (maximally by 53% in this study) when the aeration pressure exceeds a critical value and this value is termed as the safe aeration pressure. This study then proposes a relationship between the safe aeration pressure and the location of the air injection screen (i.e., the horizontal distance between the top of the injection screen and the slope surface) to avoid landfill slope failure during aeration. The findings of this study can provide insights for engineers to have a better understanding of the slope stability of a bioreactor landfill and to design and control the leachate recirculation and aeration systems in landfills.

A review of anaerobic landfill bioreactor using leachate recirculation to increase methane gas recovery

Municipal Solid Waste (MSW) treatment with anaerobic landfill bioreactor utilizes landfill as a place of biodegradation and produces methane gas which can be used as renewable alternative energy source. Anaerobic landfill bioreactor technology is a landfill development method that can increase waste degradation and increase biogas production. The increase of biogas and the removal of pollutants from leachate needs to pay attention to the factors that influence the success of anaerobic landfill bioreactor, including pH value, temperature, water content, and COD concentration after recirculation, and methane production. The relationship between these factors was discussed in depth in this paper. The method used is a narrative review where metadata is obtained from Google Scholar and Web of Science. This study explains the development of an anaerobic landfill bioreactor and conducts a synthesis for future research development plans by leachate recirculation.

Application of leachate recirculation on the concentration of landfill gases

Leachate is the product of the biodegradation process in the landfill. On-site treatment of leachate using leachate recirculation is one of the alternative methods to reduce the hazard. The operation of leachate recirculation provides benefits such as speeding up biodegradation, lowering pollutant concentrations, and increasing gas production. This study aims to evaluate the application of leachate recirculation on the concentration of CO2 and CH4 produced. Experiments were performed in a laboratory using 20 lysimeters, with 1 L in volume for 365 days. The lysimeter was divided into two groups, with 10 reactors, each group arranged in series. Leachate recirculation will be given to the second reactor until the tenth reactor, using a high leachate concentration for the first group and a low concentration of leachate for the second. The addition of leachate in the two reactor treatment groups significantly increased the organic content in the leachate. Leachate recirculation does not cause a significant escalation in CO2 and CH4 concentration compared to reactors without leachate recirculation. In the reactor group with high leachate concentrations, reactors with leachate recirculation produced a more stable gas concentration than those without leachate recirculation which produced more volatile CH4 concentration.

Effect of leachate recirculation and bulking agent on leachate quality

The purpose of leachate processing is to reduce pollutants in leachate without using equipment that requires high investment and complicated maintenance. This research aims to determine the impact of leachate recirculation and bulking agents on leachate quality. Fresh solid waste recirculated using artificial leachate with a continuous flow of 1 L/h. The study is conducting for 14 days on a laboratory scale. On the 14th day, combination recirculation and bulking accelerate the increased pH value. Leachate recirculation increases the potential for contact between methanogenic bacteria and dissolved organic matter and contributes to buffering pH during the hydrolysis process. R3 produces a higher Electric Conductivity (EC) value than other reactors since the 7th day. This increase is probably due to the addition of dissolved salts from solid waste decomposition. The role of the bulking agent may not be too significant for changes in the EC value. On day 14, TDS at R1 was 11,748 mg/L, R2 was 12.144 mg/L, and R3 was 14.916 mg/L.

Numerical Model of Leachate Recirculation in Bioreactor Landfills with High Kitchen Waste Content

Surface spraying, horizontal trenches, and vertical wells are the most common leachate recirculation system used at landfills in engineering practice. In order to quantify the efficiency of the three aforementioned recirculation systems, a hydro–biochem–mechanical-coupled model was developed in the present work, which can describe hydrodynamic and biochemical behaviors in food-waste-rich landfills. A typical landfill cell was modeled in COMSOL. The results indicate that leachate recirculation can accelerate the decomposition of municipal solid waste (MSW) with food-rich waste content, relieving acidification, improving gas generation efficiency, and consequently, increasing the early settlement in landfills.