Efforts to divert organics away from landfills are viewed by many as an important measure to significantly reduce the climate change impacts of municipal solid waste management. However, the actual greenhouse gas (GHG) impacts of organics diversion from landfills have yet to be thoroughly evaluated and whether such a diversion provides significant environmental benefits in terms of GHG impacts must be answered. This study, using California-specific information, aimed to analyse the GHG impacts of organics diversion through a life-cycle assessment (LCA). This LCA considered all aspects of organics management including transportation, materials handling, GHG emissions, landfill gas capture/utilization, energy impacts, and carbon sequestration. The LCA study evaluated overall GHG impacts of landfilling, and alternative management options such as composting and anaerobic digestion for diverted organic waste. The LCA analysis resulted in net GHG reductions of 0.093, 0.048, 0.065 and 0.073 tonnes carbon equivalent per tonne organic waste for landfilling, windrow composting, aerated static pile composting, and anaerobic digestion, respectively. This study confirms that all three options for organics management result in net reductions of GHG emissions, but it also shows that organics landfilling, when well-managed, generates greater GHG reductions. The LCA provides scientific insight with regards to the environmental impacts of organics management options, which should be considered in decision and policy-making. The study also highlights the importance of how site and case-specific conditions influence project outcomes when considering organic waste management options.
Arsenic Crystallization Technology (ACT) is a potentially eco-friendly, effective technology for stabilization of arsenic-bearing solid residuals (ABSRs). The strategy is to convert ABSRs generated by water treatment facilities into minerals with a high arsenic capacity and long-term stability in mature, municipal solid waste landfills. Candidate minerals considered in this study include scorodite, arsenate hydroxyapatites, ferrous arsenates (symplesite-type minerals), tooeleite, and arsenated-schwertmannite. These minerals were evaluated as to ease of synthesis, applicability to use of iron-based ABSRs as a starting material, and arsenic leachability. The Toxicity Characteristic Leaching Procedure (TCLP) was used for preliminary assessment of candidate mineral leaching. Minerals that passed the TCLP and whose synthesis route was promising were subjected to a more aggressive leaching test using a simulated landfill leachate (SLL) solution. Scorodite and arsenate hydroxyapatites were not considered further because their synthesis conditions were not found to be favorable for general application. Tooeleite and silica-amended tooeleite showed high TCLP arsenic leaching and were also not investigated further. The synthesis process and leaching of ferrous arsenate and arsenated-schwertmannite were promising and of these, arsenated-schwertmannite was most stable during SLL testing. The latter two candidate minerals warrant synthesis optimization and more extensive testing.
Ceria containing slurries are increasingly used in the chemical mechanical polishing of CVD silicon oxide films to obtain STI structures. Unlike silica or alumina, ceria has redox characteristics. Because of this characteristic, removal of ceria particles from planarized surfaces may be possible using chemical reagents that can participate in redox reactions. One such reagent is hydroxylamine, which is already being used in copper CMP. The objective of the work reported in this paper was to characterize the reaction between ceria and hydroxylamine, especially with respect to dissolution of ceria particles. A kinetic study of the dissolution of ceria in hydroxylamine solutions maintained at various pH values has been performed. The extent and kinetics of dissolution of ceria has been determined by ICPMS. Removal of ceria particles from oxide surfaces using hydroxylamine-based chemistries has been investigated.
Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in non-hazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g. the toxicity characteristic leaching procedure, TCLP) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL > RASL > PFA > M1 > HPFA > M2.
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