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[en] This paper proposes a stress wave monitoring method for monitoring and locating leakage through the impervious layer at a landfill to resolve the “first pollution, then discovery” problem caused by the existing electrical monitoring method. The experimental results show that the linear distance to the geophones from the leak point should be less than 31.5 m to provide a well-defined rupture signal. The amplitudes of the stress wave signals generated during the yield and rupture stages of the high-density polyethylene (HDPE) film are more obvious and easily identified by the geophones; the rupture signal duration is approximately 100 ms, and the bandwidth is distributed within 0 kHz to 1 kHz. By studying the stress wave first arrival times calculated by the picking model, the average error of the picking model is approximately 0.35 ms, and the iteration of the model is ceased when the thresholds of the discriminating indices are 3.5 and 0.9. Experiments reveal that the positioning model should stop iterating when the absolute value of each element in the calibration vector is less than 140. The average positioning error is 0.248 m, and the maximum fiducial errors of the positioning model in the X-axis and Y-axis directions are 0.32% and 0.58%, respectively.
[en] In this study, the efficiency of electrochemical oxidation to treat a sanitary landfill leachate was evaluated by the reduction in physico-chemical parameters and in ecotoxicity. The acute toxicity of the sanitary landfill leachates, before and after treatment, was assessed with the model organism Daphnia magna. Electrochemical oxidation treatment was effective in the removal of organic load and ammonium nitrogen and in the reduction of metal ions concentrations. Furthermore, a reduction of 2.5-fold in the acute toxicity towards D. magna after 36 h of treatment was noticed. Nevertheless, the toxicity of the treated leachate is still very high, and further treatments are necessary in order to obtain a non-toxic effluent to this aquatic organism. Toxicity results were also compared with others described in the literature for different leachate treatments and test organisms.
[en] Nanomaterials (NMs) commercially used for various activities mostly end up in landfills. Reduced biogas productions reported in landfill reactors create a need for more comprehensive research on these greatly-diverse microbial pools. In order to evaluate the impact of one of the most widely-used NMs, namely nano-zinc oxide (nano-ZnO), simulated bioreactor and conventional landfills were operated using real municipal solid waste (MSW) for 300 days with addition nano-ZnO. Leachate samples were taken at different phases and analyzed by 16S rRNA gene amplicon sequencing. The bacterial communities were distinctly characterized by Cloacamonaceae (phylum WWE1), Rhodocyclaceae (phylum Proteobacteria), Porphyromonadaceae (phylum Bacteroidetes), and Synergistaceae (phylum Synergistetes). The bacterial community in the bioreactors shifted at the end of the operation and was dominated by Rhodocyclaceae. There was not a major change in the bacterial community in the conventional reactors. The methanogenic archaeal diversity highly differed between the bioreactors and conventional reactors. The dominance of Methanomicrobiaceae was observed in the bioreactors during the peak methane-production period; however, their prominence shifted to WSA2 in the nano-ZnO-added bioreactor and to Methanocorpusculaceae in the control bioreactor towards the end. Methanocorpusculaceae was the most abundant family in both conventional control and nano-ZnO-containing reactors.
[en] In this study, integrate electrical resistivity tomography (ERT) tests were carried out in a large-scale (5.0 × 4.0 × 7.5 m) MSW landfill cell to investigate the possibility of detecting perched leachate mounds, leachate level, and gas accumulation zones at wet landfills. The resistivity of both bulk waste and waste components at different moisture states were measured and the three-phase volumetric relationships of the waste pile were analyzed to better interpret the ERT test results in the large-scale cell. The following observations were given: (1) The relationship between resistivity and volumetric moisture content (VMC) of waste sample can be reasonably fitted by Archie’s law. The resistivity of waste components at a saturated state was all lower than 21 Ω m. (2) A significant amount of void gas was entrapped in the underwater waste, being 30.4–34.8% of the whole waste pile in volume. (3) Low-resistivity zones (< 5.0 Ω m) were observed in the waste pile being fully drained under a gravity condition, which was believed to be related to a perched leachate. (4) The average VMC values of the waste layer below and above the leachate level were in the ranges of 46.5–53.1% and 28.1–41.3%, respectively. (5) Irregular variations of high-resistivity zones (> 40 Ω m) observed in the underwater waste were associated with the accumulation and dissipation of gas pressure. It was found that the “gas-breaking value” in the gas accumulation zone was up to 10.5 kPa greater than the pore liquid pressure in the stable methanogenesis stage. These findings shone a light on the possibility of using the ERT method as an efficient tool for mapping the gas/leachate distribution and improving operations at wet landfills.
[en] With an increase of service time of landfills, a great amount of old landfills begin to leak and the leachate impairs the surrounding environment severely. Defining the flow of leachate is significant to the monitoring and restoration of the landfill. Field tests and laboratory tests are often used to investigate the leachate flow. However, many uncontrollable factors may affect the accuracy of field tests, and the application of field test results is usually limited. At the same time, it is difficult to simulate and monitor the migration process of leachate in real time in laboratory. To address this problem, a new physical simulating device is created to simulate the leachate migration under flowing conditions, and improved ERT device is designed to monitor the migration in laboratory tests. The results show that the improved ERT could delineate the migration range well in laboratory tests, providing a new method to investigate the leachate migration in laboratory test and providing a reference to the application of ERT in field tests. The relative variation rate of resistivity could reduce the influence of background, and is very suitable for time-lapse ERT. In addition, the effect of flowing rate, leakage rate, and time on the leachate migration is also investigated. The results show that the horizontal migration rate increases with an increase of flowing rate. The leakage rate has a significant influence on the vertical migration, but has limited effect on the horizontal migration. The curvature of migration front increases with an increase of flowing rate and time.
[en] UCOR, an AECOM-led partnership with Jacobs, manages the cleanup of the 2,200-acre East Tennessee Technology Park (ETTP) for its client, the U.S. Department of Energy (DOE), in Oak Ridge, Tennessee. The ETTP site was contaminated with radioactive, hazardous and industrial wastes generated by more than 40 years of national defense and energy missions. Onsite waste disposal is a key component of DoE's cleanup strategy. Less expensive onsite disposal allows remaining funding to be used to accelerate cleanup activities. The initial cover design was intended to be revised and updated as the Environmental Management Waste Management Facility (EMWMF) neared closure. However, accelerating review and modification of the design resulted in additional waste disposal volume that will extend the life of the EMWMF. Two design modifications were implemented: 1) reducing the final cover thickness from 14 ft to 11 ft while maintaining protectiveness, and 2) changing the height of the landfill by reducing the width of the top deck. These two design changes resulted in an additional 130,000 cubic yards of landfill capacity for Oak Ridge Reservation (ORR) demolition and remediation waste and extended the expected life of the EMWMF by approximately 2 years. The addition of more inexpensive onsite waste disposal capacity will continue to facilitate cost-effective cleanup activities at the ORR. (author)
[en] The stabilization of severely As-polluted soil has been a challenge, especially for the extremely toxic As(III) contaminants. In this study, soil with a high As concentration (26084 mg/kg) was availably stabilized by a H2O2 pre-oxidation assisted TMT-15 (Na3S3C3N3 solution with a mass fraction of 15%) and FeCl3·6H2O stabilization method. The results showed that the combination of the two stabilizers (i.e., TMT-15 and FeCl3·6H2O) presented a better stabilization behavior than either stabilizer used individually. The use of the H2O2 pre-oxidation assisted TMT-15 and FeCl3·6H2O stabilization approach not only converted the As(III) to As(V) but also reduced the toxic leaching concentration of As to 1.61 mg/L, which is a safe level, when the additions of TMT-15 and FeCl3·6H2O were 2 mL and 0.20 g, respectively. Thus, using only a simple H2O2 pre-oxidation to combine clean stabilization with non-toxic stabilizers TMT-15 and FeCl3·6H2O could render the severely As-contaminated soil safe for disposal in a landfill.
[en] Ammoniacal nitrogen is considered as one of the major pollutants of the leachate generated from the landfill site and has the potential to deteriorate the environment as well as health. Considering this, locally available agricultural waste, i.e., sugarcane bagasse ash, was employed as an adsorbent for the removal of ammoniacal nitrogen from landfill leachate. Batch-mode experiments were conducted to see the effect of dose (2–60 g L−1), pH (2–12), and temperature (20–60 °C) on ammoniacal nitrogen adsorption. Application of sugarcane bagasse ash showed 60% removal of ammoniacal nitrogen (50 mg L−1 strength) at an optimum dose of 20 g L−1 and 180 min of contact time with an adsorption capacity of 0.31 mg g−1. The Langmuir adsorption model was found to be best fit at 40 °C with R2 = 0.944, depicting a monolayer coverage of ammoniacal nitrogen onto sugarcane bagasse ash. According to the result, solute uptake rate could be well described by the pseudo-second-order model (R2 = 0.928), whereas the intraparticle diffusion model and Boyd plot indicated that the overall adsorption rate is governed by the external mass transfer. Thermodynamic studies revealed that adsorption is feasible, spontaneous, and endothermic in nature. Hence, the study shows that sugarcane bagasse ash could turn out to be a cost-effective adsorbent for the removal of ammoniacal nitrogen from leachate
[en] The objective of this paper was to study the pore-size distribution of municipal solid waste (MSW) and provide a basis for understanding the mechanism of preferential flow in MSW. Two methods were used to investigate the pore-size distribution in MSW. The first was an indirect method based on the soil-water characteristic curve (SWCC) and the second was a direct method using nuclear magnetic resonance (NMR). Samples taken from different depths of a landfill were used. In the SWCC method, SWCCs of the matrix region were obtained by a pressure plate extractor and SWCCs of the macropore region were determined by water breakthrough tests. A SWCC equation is proposed by modifying the Van Genuchten equation to consider the dual-porosity feature of MSW and the pore-size distribution was obtained based on the Young–Laplace equation. In the NMR method, the pore-size distribution of MSW was obtained by analyzing the T2 curves. The results of the two methods were qualitatively similar and both showed a dual-porosity characteristic of MSW. The average macropore radii of shallow, middle, and deep MSWs obtained from the SWCC method are 0.193, 0.184, and 0.173 mm, and those obtained from the NMR method are 0.213, 0.138, and 0.145 mm, respectively. The proportion of macropores decreases with depth. The average micropore radii given by the SWCC method are 0.022, 0.011, and 0.008 mm, and those given by the NMR method are 0.013, 0.011, and 0.008 mm, respectively. As the depth and fill age increase, the average micropore size becomes smaller and the proportion of micropores increases. The volume ratios of macropores obtained by the two methods are quantitatively quite different. The discrepancy is mainly caused by the different test principles adopted by the two methods.
[en] To study the impact of leachate recirculation frequency on the transformation of carbon and nitrogen pollutants in a semi-aerobic bioreactor landfill (SABL), three laboratory-scale SABLs were investigated, each using a different leachate recirculation frequency (daily, once each 3 days, and once each 5 days). Results showed that degradation of total nitrogen (TN), ammonium nitrogen (NH4+-N), chemical oxygen demand (COD), and total organic carbon (TOC) could be described using a quadratic polynomial-compound index model. Degradation rates of TN, NH4+-N, COD, and TOC slightly increased from 0.01795, 0.01814, 0.01451, and 0.01166 day−1 to 0.02054, 0.01903, 0.01488, and 0.01203 day−1, respectively, when the recirculation frequency increased from once per 5 days to once per 3 days. When recirculation frequency was increased to daily, degradation rates of TN, NH4+-N, COD, and TOC significantly increased to 0.03698, 0.02718, 0.02479, and 0.02872 day−1, respectively. Moreover, when recirculation frequency increased from once per 5 days to once per 3 days, the gasification rate of nitrogenous and carbonaceous pollutants was enhanced between 20.38 and 8.17%, respectively. When the leachate recirculation rate further increased to daily, only a small amount of carbonaceous and nitrogenous pollutants was transformed to the liquid phase. Thus, increasing the leachate recirculation frequency in an SABL benefits the removal of carbonaceous and nitrogenous pollutants from the reactor. In addition, the greater is the recirculation frequency, the lower is the residual carbon and nitrogen in the solid phase, and the higher is the gasification rate. A proper recirculation frequency promotes the stabilization of landfill leachate. This study provides a theoretical reference and experimental evidence for accelerating the stabilization of MSW and contributes to the macro-control of landfills.