Results 1 - 10 of 63
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[en] This study investigates the hydraulic performance and the fouling characteristics of a bench-scale membrane sequencing batch reactor (MSBR), treating mature landfill leachate under various time-based operating conditions. The MSBR system operated initially under a high-flux condition (Period 1) which resulted in a rapid trans-membrane pressure (TMP) rise due to intense fouling. Following the characterization of Period 1 as super-critical, the system was subsequently operated under a near-critical condition (Period 2). The overall filtration resistance analysis showed that cake layer formation was the dominant fouling mechanism during Period 1, contributing to 85.5% of the total resistance. However, regarding the MSBR operation during Period 2, adsorption was found to also be a dominant fouling mechanism (Days 1 to 47), contributing to 29.1% of the total resistance. Additionally, the irregular total resistance variation, which was observed during the subsequent operation (Days 48 to 75), and the respective filtration resistance analysis suggested also the formation of an initial sludge cake layer on the membrane surface, contributing to the 47.7% of the total resistance.
[en] Household wastes may constitute a vector of environmental contamination when buried, in particular through degradation and production of leachates containing significant trace metal (TM) concentrations that may constitute a serious risk to biota. The objectives of this study were to assess the bioavailability and transfer potential of various TMs present in water and sediments in a reservoir receiving landfill leachates. An active biomonitoring approach was adopted consisting of exposing naive laboratory organisms in cages deployed in the field. Aquatic insects such as Chironomus riparius larvae are good candidates since they represent key organisms in the trophic functioning of aquatic ecosystems. The results show that water, suspended particles, and sediments were significantly contaminated by various TMs (As, Cd, Cu, Ni, Pb, and Zn). Their contribution to the transfer of TMs depends, however, on the specific element considered, e.g., Cd in sediments or Pb in both suspended particles and sediments. The internal fate of TMs was investigated according to their fractionation between an insoluble and a cytosolic fraction. This approach revealed different detoxification strategies capable of preventing the induction of deleterious effects at the individual scale. However, the accumulation of several TMs in C. riparius larvae tissues may also represent a significant load potentially transferable to higher trophic levels.
[en] The article presents the analysis of standard approaches to degassing of landfills. The need of comprehensive work on the degassing of the landfill body is identified. The author's task decomposition of the landfill degassing is formulated. The analysis of existing methods of work on degassing of landfills is presented. The author's approach is including implements of series of parallel studies in the framework of achieving a common goal to reduce the anthropogenic pressure on the ecosystem of the region due to the need for disposal of solid waste. An action plan for the development of the target problem-oriented management techniques of the landfill with the following development of the effective energy complex is formulated. (paper)
[en] Highlights: • Thermal desorption tubes and methanol impingers prove to be accurate and reliable. • Tedlar® bags and SUMMA canisters yield significantly lower D5 recovery rates. • Adsorption of D5 within the containers is the primary cause of reduced recovery. • Storage temperature has no influence on the D5 recovery from Tedlar® bags. - Abstract: Biogas from landfills and wastewater treatment facilities typically contain siloxane contaminants that can cause severe operational problems in engines and boilers when biogas is used as fuel. Likely due to their relatively low volatility, reliable siloxane sampling and analysis has proven challenging, and no standard sampling technique for gas-phase siloxanes exists, leading to high variability in analytical results. This study evaluates four techniques commonly used for sampling gas-phase siloxanes. Samples of a reference gas containing decamethylcyclopentasiloxane (D5) were taken using these techniques and measured D5 concentrations were compared to the reference gas D5 concentration. Methanol impingers and thermal desorption tubes proved to be most accurate and reliable, whereas Tedlar® bags and SUMMA canisters yielded lower D5 recovery rates due to adsorption to container surfaces. Based on these results, the methanol impinger and thermal desorption tube sampling methods appear to be more suitable for the quantitative analysis of gas-phase siloxanes in biogas.
[en] Landfills are an important anaerobic microbial ecosystem, primarily due to their methane generation potential and carbon sequestration capacity. However, the mechanism by which methane production begins in refuse is poorly understood. Methane initiation typically occurs under low pH, high volatile fatty acid (VFA) conditions that are generally considered inhibitory. One theory is that sub- populations of methanogenic Archaea are acid tolerant and consume VFAs until methanogens more suited to pH- neutral conditions are established. Another theory is that spatially isolated areas of neutral pH exist, even though bulk pH is acidic, and these localized regions of neutral pH act as initiation centers for methanogenesis. In this study, methanogen acid tolerance and spatial differences in pH were assessed in decomposing refuse during methane initiation. Results of quantitative PCR and 16S rRNA gene clone libraries show methanogenesis under low pH, high VFA conditions is catalyzed by acid tolerant Methanosarcina species that promote the development of a pH neutral reaction front which advances through the waste. In a second study, succession of microbial communities in response to changing conditions was monitored in a laboratory-scale simulated landfill. 16S rRNA gene sequences retrieved at separate stages of decomposition showed significant succession in both Bacteria and methanogenic Archaea. Correspondence analysis showed bacterial population shifts were attributed to carboxylic acid concentration and solids hydrolysis, while archaeal populations were affected more by pH. Terminal restriction fragment length polymorphism (T-RFLP) analysis showed specific taxonomic groups responded differently and exhibited unique responses during decomposition, suggesting that species composition and abundance within Bacteria and Archaea are highly dynamic. This study shows landfill microbial demographics are highly variable across both spatial and temporal transects. The implications of these results to methane capture and landfill operation will be discussed. (author)
[en] A dual-permeability hydro-biodegradation model is developed to describe the leachate flow in municipal solid waste (MSW) and predict the long-term settlement induced by biodegradation in bioreactor landfills. The model is verified against Hydrus-1D and a recirculation experiment conducted in a full-scale landfill. Preferential flow and mass transfer between fissure and matrix can be reasonably modeled by the proposed model. A higher recirculation flow rate can speed up the stabilization process of landfill. However, too much recirculation leachate is not economical and environmental friendly. A stabilization speed index and a leachate utilization index are adopted to evaluate the stabilization speed of bioreactor landfill and utilization rate of leachate, respectively, and the optimal recirculation flow rate is estimated. A flow rate of q = 5 × 10−5–5 × 10−4 m/h (equivalent to recirculation intensity of Q = 15–150 L/tonwaste/year) is recommended for recirculation, which has been verified by the field data in numerous bioreactor landfills.
[en] Different types of NORM residues are generated in many industries and most of them require appropriate management. The paper discusses the classification of the materials, especially the differences between ‘NORM residue’ and ‘NORM waste’ and between relevant management strategies. Several practical examples are also provided. The management of NORM residues may involve immediate removal or alternatively long term storage, prior to reprocessing. The management of NORM waste may involve long term storage prior to disposal. There are three optional strategies for disposal: (i) concentrate and contain, (ii) delay and decay, or (iii) dilute and disperse. Additional information is also provided for the dilute and disperse management option, as in many cases it is selected as the preferred one, both for NORM residues (that are blended with other materials in the process of their use) and for NORM waste (as no radiologically contaminated legacy sites are created after blended material is disposed of in mining voids and landfills). (author)
[en] The objectives of this study were to characterize the heavy metal contamination status of surface soils sampled at two dredged sediment land disposal sites (the Baimao and Kongwan landfills) in Meiliang Bay, Lake Taihu, China, as well as to investigate the effect on their leaching behaviors due to acid rain. Among all the metals, only the nickel content in the Baimao landfill was higher than the Chinese reference value, and all metal contents were below the limit values for agricultural soils. The fraction distribution of metals by sequential extraction was similar at both sites. Cadmium had a relatively high proportion of exchangeable-carbonate fractions, while the other metals were mainly classified as residue fractions. The metals released from soils by simulated rainwater comprised less than 1% of the total soil metal content, and the effect of acid rain on heavy metal release from dredged sediments in land disposal sites was found to be negligible at both sites. All results indicate no environmental concern for the land disposal of dredged sediments and support the feasibility of beneficially reusing dredged sediment soils as a supplement to agricultural soils.
[en] Landfill is known as a potential source of atmospheric Hg and an important component of the local or regional atmospheric Hg budget. This study investigated the gaseous elemental Hg surface–air fluxes under differing conditions at a typical municipal solid waste landfill site, highlighting the interactive effects of plant coverage and meteorological conditions. The results indicated that Hg fluxes exhibited a feature represented by diel variation. In particular, Hg deposition was observed under a condition of Kochia sieversiana coverage, whereas emission that occurred after K. sieversiana was removed. Hg emission was the dominant mode under conditions of Setaria viridis coverage and its removal; however, the average Hg emission flux with the S. viridis coverage was nearly four times lower than after its removal. These findings verified that the plant coverage should be a key factor influencing the Hg emission from landfills. In addition, Hg fluxes were correlated positively with solar radiation and air/soil temperature and correlated inversely with relative humidity under all conditions, except K. sieversiana coverage. This suggested that the interactive effects of meteorological conditions and plant coverage played a jointly significant role in the Hg emission from landfills. It was established that K. sieversiana can inhibit Hg emission efficiently, and therefore, it could potentially be suitable for use as a plant-based method to control Hg pollution from landfills.
[en] Highlights: • Hydrate-based acidic gases capture with synergic additives was investigated. • Synergic additives was comprised by TMS and TBAB. • CO2 and H2S could be synchronously captured. • Synergic additives enhance the dissolution and diffusion of acidic gases. • Synergic additives promoted hydrate-based capture process. - Abstract: The widespread need for carbon dioxide (CO2) and hydrogen sulfide (H2S) removal from potential gaseous fuel processes associated with upgrading of natural gas, biogas and landfill gas has led to a continuing interest in developing acid gas capture technologies. This work experimentally investigated the hydrate-based acidic gases (CO2 and H2S) capture for clean methane (CH4) fuel from biogas or natural gas with new synergic additives, which comprised physical gas solvent (TMS) and traditional hydrate promoter (TBAB). The results show that, with the synergic additives, the equilibrium hydrate formation pressures were moderated by about 90% relative to pure water, the selectivity of CO2 over CH4 and the selectivity of H2S over CH4 could achieve 18.56 and 11.38, respectively. Compared with TBAB, the synergic additives could improve the hydrate formation rate and the gas storage capacity by 149% and 84%, respectively. Furthermore, the promotion effect could be enhanced when with the help of H2S. It has been shown that CO2 and H2S could be synchronously captured through the hydrate formation process. It will be of importance to the fundamental study of enhancing gas hydrate formation process, and of practical significance for the hydrate-based application industry.