Search

Dissolved organic matter (DOM) in landfill leachate impacts the toxicity, bioavailability, and migration of heavy metals. The present study investigated the complexation of heavy metals (Cu2+ and Pb2+) with DOM from two landfill leachate samples, representing an old landfill site containing incineration residues and incombustible waste. The logarithms of the stability constant (log KM) and percentage of complexed fluorophores were calculated using both the Ryan–Weber non-linear model and the modified Stern–Volmer model, yielding good agreement. The log KM values (at pH = 6.0 ± 0.1) calculated using both methods for the two sampling points were 5.02–5.13 and 4.85–5.11 for Cu2+–DOM complexation, and 5.01–5.13 and 4.46–4.87 for Pb2+–DOM complexation, respectively. Log KM was slightly higher for binding of DOM with Cu2+ than Pb2+, and the quenching degree was stronger for complexation with Cu2+ (28.5–30.6% and 38.0–45.9%) than Pb2+ (6.5–7.1% and 10.0–15.4%) in both leachate samples. While log KM values were similar, differences in the contributions of functional groups and molecular composition led to varying degrees of quenching. This study reveals the potential for heavy metal binding by DOM in landfill leachate with a unique solid waste composition and emphasizes variations in fluorescence quenching between Cu2+ and Pb2+ despite similar log KM levels. These findings may be useful for assessing heavy metal behavior in landfill leachate and its impacts on the surrounding environment. [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) influences the bioavailability and behavior of trace metals and other pollutants in landfill leachate. This research characterized fluorescent dissolved organic matter (FDOM) in leachate from an old landfill in Japan during a 13-month investigation. We employed excitation–emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) to deconvolute the FDOM complex mixture into three fluorophores: microbial humic-like (C1), terrestrial humic-like (C2), and tryptophan-like fluorophores (C3). These FDOM components were compared with findings from other studies of leachate in landfills with different waste compositions. The correlations among EEM-PARAFAC components, dissolved organic carbon (DOC) concentration, and ultraviolet–visible and fluorescence indices were evaluated. The FDOM in leachate varied spatially among old and extended leachate collected in the landfill and leachate treatment facility. The FDOM changed temporally and decreased markedly in August 2019, November 2019, and April 2020. The strong positive correlation between HIX and %C2 (r = 0.87, ρ = 0.91, p < 0.001)) implies that HIX may indicate the relative contribution of terrestrial humic-like components in landfill leachate. The Fmax of C1, C2, and C3 and the DOC concentration showed strong correlations among each other (r > 0.72, ρ > 0.78, p < 0.001) and positive correlations with leachate level (r > 0.41, p < 0.001), suggesting the importance of hydrological effects and leachate pump operation on FDOM. [ABSTRACT FROM AUTHOR]

We focused on incineration of solid waste and resource recycling, when clarifying how to achieve carbon neutrality (CN) by 2050; we describe how future municipal solid waste incinerators (MSWIs) should operate. Specifically, eight low-carbon measures were set for four MSWIs located in the Tokyo waterfront area (Chuo, Minato, Shinkoto, and Ariake), and greenhouse gas (GHG) emissions were estimated for each scenario by combining these measures. We concluded that, in addition to MSW reduction and the introduction of biomass plastics, the improvement of power generation efficiency via plant renewal and wide area management of the MSWIs are useful when seeking to achieve CN. If the emission factor of electricity is to achieve CN in the future, the introduction of methanation is desirable in combination with wide area management, but if the emission factor of city-gas is also expected to achieve CN, an expansion of district heat utilization should rather be considered. [ABSTRACT FROM AUTHOR]

Real-time measurement of sewage sludge moisture content renders it possible to optimize the consumption of auxiliary fuel and the thermal treatment. Thus, we explored whether a dielectric soil moisture sensor could be used to measure real-time changes in sludge moisture content. This was possible with the aid of a unified calibration curve. The explanatory variable was the third-order sensor output voltage. The calibration curve well-fitted the data; the mean measurement error was 6.14 wt.%. The use of individual calibration curves for each sludge batch reduced the mean measurement error to 3.09 wt.%. The mean measurement error improves when multiple sensors are simultaneously used. The sensor operates very well when the moisture content is low; the results are minimally affected by the bulk density and Fe level. Considering feed-back to the process, it is ideal to measure sludge moisture content near the outlet of the thermal treatment. [ABSTRACT FROM AUTHOR]

The majority of municipal solid waste in Thailand is organic waste including food and garden waste. Improper waste management has caused negative impacts on the environment. This study aimed to find a hypothetical municipal organic waste management scenario with the lowest environmental impacts using life cycle assessment (LCA). The system boundary of organic waste management includes collection and transportation; treatment, including centralized and on-site treatment technologies; and by-product utilization. The two main waste management systems considered in this study were centralized and on-site waste management systems. The first two scenarios take into account all the amount of the municipal organic waste collected and transported and then treated by centralized waste treatment technologies (composting, anaerobic digestion, and landfill). The remaining three scenarios are integrated between 10% on-site (home composting, food waste processor, and composting bin) and 90% centralized (composting, anaerobic digestion, and incineration) waste treatment technologies; the scenario combining centralized (food waste anaerobic digestion, garden waste composting, and incineration) and on-site (home composting) systems yielded the lowest environmental impacts (except short-term climate change, freshwater, and marine eutrophication). On-site systems can help reduce collection, transportation, and treatment impacts, particularly photochemical oxidant formation, which was proportional to the amount of waste or distance reduced. Benefits from the by-product utilization can offset all impacts in terms of fossil and nuclear energy use and freshwater acidification, and result in a negative impact score or impact reduction. This research can be used as guidance for developing countries with conditions and waste composition similar to Thailand for making initial decisions on environmentally sustainable municipal organic waste management. [ABSTRACT FROM AUTHOR]

Liquefied dimethyl ether (DME) was used to extract lipids from sewage sludge. Factorial experimental analyses were used to evaluate the influence of different variables on raw lipid extraction and sludge drying. The DME method was compared with the Bligh and Dyer (B&D) method for three undigested and two anaerobically digested dewatered sludges. The results indicate that although the raw lipid yield of the B&D method was 5% higher than that of the DME method, the proportion of fatty acid methyl esters (FAMEs) in raw lipids extracted by the DME method was 14.1–33.4%, almost twice that of the B&D method. The FAME composition varied according to sludge type, and the dewatered undigested sludges contained more unsaturated fatty acids (e.g. C18:1, C18:2). The lower heating value (LHV) of product by the DME method ranged from 3.74 to 5.70 MJ/kg compared with 1.21–0.39 MJ/kg for the B&D method. Also, DME could be reused at least five times without significantly reducing the lipid yield and drying efficiency. Finally, an economic analysis of the DME, the conventional solvent extraction, and the heat-drying methods was conducted. [ABSTRACT FROM AUTHOR]