Quicklime addition to soil at a remediation site was observed to sufficiently reduce TCE levels, but the cause of the removal could not be confirmed with the field data collected. Potential ...mechanisms for CaO treatment of trichloroethylene (TCE) in soil include degradation and volatilization. Since earlier studies found TCE degradation to occur during the hydration of CaO under conditions where volatilization was limited, research was conducted on mechanisms of TCE removal from soil by CaO application under conditions where volatilization was allowed to occur. TCE volatilization in soil treated with 0%, 5%, 10%, and 20% CaO doses was measured in experiments where the degree of volatilization could be tracked. The total TCE removal from soil spiked with TCE at CaO doses from 5% to 20% ranged from 97% to 99% of the initial TCE mass. Volatilization accounted for 64.4–92.5% of the TCE removal, with unrecovered TCE and TCE degradation accounting for the remaining fraction. The greater heat encountered with higher CaO doses helped minimize obstacles to TCE volatilization, such as high soil organic and clay content. Treatment with a 20% CaO dose, however, led to the formation of byproducts such as dichloroacetylene. TCE degradation to dichloroacetylene at the 20% CaO dose ranged from 2.7% to 6.4% of the initial TCE. Volatilization was concluded to be the dominant process for TCE removal from soil during CaO treatment.
The in-situ mitigation of methane (CH4) in landfill gas using landfill cover soil (LCS) is a cost-effective approach, but its efficiency needs to be enhanced. In this study, we incorporated an ...enriched methane-oxidizing bacteria (MOB) consortium into LCS and established four biochar-amended LCS groups with biochar produced at 300 °C (BC300), 400 °C (BC400), 500 °C (BC500), and 600 °C (BC600). The purpose was to evaluate the CH4 oxidation capacity of biochar-amended LCS after inoculation with MOB and to investigate how the physicochemical properties of biochar that are influenced by the pyrolysis temperature affect the performance and microbial activity of biochar-amended LCS. It was found that a 15% volume ratio (representing a mass ratio of 2.49%–2.78%) for biochar amendment in LCS enhanced CH4 removal efficiency, with the highest removal observed to be 46% for BC400-amended LCS compared to 30% for the original LCS. In addition, CH4 adsorption by the biochar was not observed, and a 15% mass ratio for biochar in the LCS had no or a negative impact. Besides improving the water-holding capacity and gas permeability of LCS, other possible advantages of biochar amendment in terms of CH4 oxidization include greater retention of nutrients, electron acceptors, and exchangeable cations, as well as introducing iron ions. It was also found that CH4 oxidation capacity and the methanotroph activity of biochar-amended LCS did not continue to increase with higher pyrolysis temperatures, even though higher micropore volumes and surface areas were obtained at higher pyrolysis temperatures. From this study, BC400 was identified as the optimal choice for the best performance in terms of enhancing both the CH4 oxidation capacity of the amended LCS and the growth of type II methanotroph Methylocystaceae, which can possibly be attributed to having the highest cation exchange capacity of the four biochars.
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•Enriched MOB was inoculated to biochar-amended landfill cover soil (LCS).•In-situ CH4 mitigation of biochar-amended LCS was increased up to 46%.•The cation exchange capacity of biochar peaks at a pyrolysis temperature of 400 °C.•Biochar produced at 400 °C promotes the growth of type II methanotroph most in LCS.
Fast pyrolysis is one of the most promising ways for municipal sewage sludge (MSS) treatment and can generate bio-char as an important and beneficial product. The structure of bio-char determines its ...further utilization. Co-pyrolysis of MSS and wooden waste (WW) was carried out at 800 °C for bio-char preparation with different wet MSS/ WW mixing ratios. Both physical and chemical structural characteristics of the bio-chars were analyzed to reveal the evolution of bio-char structure during the co-pyrolysis. Results showed that the inherent moisture of MSS had gasification effect on the structure of bio-char generated from both MSS itself and WW. With the increase of WW content, the BET surface area of bio-chars increased from 68.49 cm2 g−1 to 119.52 cm2 g−1 due to the high surface area of WW-char (150.59 cm2 g−1). But the average pore sizes of all mixed samples were smaller than 10 nm, which indicated that the MSS-char particles would block the WW-char particles. According to the Raman spectra and XRD results, the inherent moisture was beneficial for the formation of functional groups (mainly carbonyl group) on the bio-char surface. However, the excess moisture led to the additional carbonaceous component consumption and decreased the Raman intensity.
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•Moisture of sludge would not lead to the completely gasification of all samples.•Particles mainly from sludge would block larger pores provided by wooden waste.•Moisture helped increasing the carbonyl group content on the char particle surface.•Excess moisture consumed functional group and decreased the Raman intensity.
Quicklime (calcium oxide, CaO) is often used as part of soil cleanup operations to remove contaminants or to create more favorable physical soil conditions for treatment. The extent to which ...quicklime chemically reacts with trichloroethylene (TCE) was evaluated by reacting CaO with a TCE–water mixture in test vessels designed to minimize volatilization loss. The impact of excess water and the presence of air were evaluated. During the hydration of CaO, a fraction of the spiked TCE was destroyed, and several different byproducts were detected (chloride and several organic chemicals). The primary organic byproduct was dichloroacetylene (DCA). In the presence of air, the degradation of DCA resulted in the formation of perchloroethylene (PCE), hexachloro-1,3-butadiene (HCDE), and chloroacetylene (CA). The maximum amount of TCE degradation occurred with a CaO/H
2O ratio of 1:1 in the presence of air. The formation of DCA was hindered by the presence of excess water. In the presence of excess water (a CaO/H
2O ratio of 1:2) the detected byproducts accounted for less than 4% of the total chlorine originally spiked as TCE.
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•Waste compaction could result in either inhibiting methanogens or promoting methane production.•Compaction reduced pore space and increased the contact surface area.•Determining ...timing for compaction in wet waste is critical to control MSW degradation.
This study investigated the impact of compaction and leachate recirculation on anaerobic degradation of municipal solid waste (MSW) at different methane formation phases. Two stainless steel lysimeters, C1 and C2, were constructed by equipping a hydraulic cylinder to apply pressure load (42kPs) on the MSW. When MSW started to produce methane, C1 was compacted, but C2 was compacted when the methane production rate declined from the peak generation rate. Methane production of C1was inhibited by the compaction and resulted in producing a total of 106L methane (44L/kgVS). However, the compaction in C2 promoted MSW degradation resulting in producing a total of 298L methane (125L/kgVS). The concentrations of volatile fatty acids and chemical oxygen demand showed temporary increases, when pressure load was applied. It was considered that the increased substrate accessibility within MSW by compaction could cause either the inhibition or the enhancement of methane production, depending the tolerability of methanogens on the acidic inhibition. Leachate recirculation also gave positive effects on methane generation from wet waste in the decelerated methanogenic phase by increasing mass transfer and the concentrations of volatile fatty acids.
The performance of simulated municipal solid waste (MSW) landfills with two different biogas collection practices – (1) upward and upward-downward biogas flow collection (LT-TB) in sequence and (2) ...simultaneous upward-downward biogas flow collection (LTB) from the beginning of the anaerobic degradation process – was investigated in terms of landfill gas and leachate, enzyme activity, and microbial community structure associated with MSW compression and leachate recirculation. The cumulative methane volume in LTB was 1.5 times higher than that in LT-TB. With MSW compression and leachate recirculation, amylase and lipase activity were enhanced in LTB. In LT-TB, the activities gradually decreased after reaching a peak with compression. The two biogas collection strategies influenced the community structure and activity of bacteria and archaea. The upward and downward gas collection flow with waste compression and leachate recirculation improved the environment for enriching bacterial phyla Firmicutes, Proteobacteria, and Synergistetes and genus Methanosarcina in Archaea.
•The cumulative methane volume in LTB was 1.5 times higher than that in LT-TB.•Amylase and lipase activity was affected by compaction in LTB.•Amylase and lipase activity was affected by leachate recirculation in LTB.•Biogas collection strategies influenced the community structure.
As a byproduct of municipal solid waste incineration (MSWI) plant, fly ash is becoming a challenge for waste management in recent years. In this study, MSWI fly ash (FA) was evaluated for the ...potential capacity of odorous gas H2S removal. Results showed that fly ash demonstrated longer breakthrough time and higher H2S capacities than coal fly ash and sandy soil, due to its high content of alkali oxides of metals including heavy metals. H2S adsorption capacities of FA1 and FA2 were 15.89 and 12.59 mg H2S/g, respectively for 750 ppm H2S. The adsorption of H2S on fly ash led to formation of elemental sulfur and metal sulfide. More importantly, the formation of metal sulfide significantly reduced the leachability of heavy metals, such as Cr, Cu, Cd and Pb as shown by TCLP tests. The adsorption isotherms fit well with Langmuir model with the correlation coefficient over 0.99. The adsorption of H2S on fly ash features simultaneous H2S removal and stabilization and heavy metals found in most MSWI fly ash, making fly ash the potential low cost recycled sorbent material.
•MSWI fly ash was evaluated as a potential alternative adsorption material for H2S removal.•The main sorption mechanisms of MSWI fly ash for H2S removal include physisorption and chemisorption.•After H2S adsorption, the heavy metal leachability in fly ash significantly reduced.•The H2S sorption capacity of fly ash increased with the increase of inlet H2S concentrations.•The adsorption isotherms fitted well with Langmuir model.
Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is commonly used for BA management. However, BA co-disposal may cause clogging of geotextiles in MSW landfills. This study ...investigated the effect of different BA co-disposal ratios on geotextile clogging, including MSW, low ash co-disposed (BA_L), high ash co-disposed (BA_H) landfills, and BA mono-fill. Results showed that the BA_L group increased the geotextile clogging by 0.1–0.6 times, compared to that in the MSW landfill. In contrast, the geotextile clogging of the BA_H and BA groups was reduced than that in the MSW landfill. The clogging was in a dynamic process during the experimental period in all the conditions, including chemical clogging and bio-clogging. Moreover, bio-clogging was the main contributor to the geotextile clogging, accounting for 64–83% of the total clogging mass. The BA co-disposal affected the leachate characteristics, such as pH, calcium concentration, and alkalinity, resulting in chemical clogging. When pH was above 7.0, calcium concentration and alkalinity were limiting factors for the calcium carbonate formation. In terms of the bio-clogging, the microbial analysis indicated that different BA co-disposal ratios influenced the diversity and structure of microbial community. These findings could help clarify the effect of BA co-disposal on geotextile clogging, thus useful to landfill operation in practice.
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•Geotextile clogging was studied at different bottom ash (BA) co-disposal landfills.•BA co-disposal changes the characteristics of leachate and microbial activities.•The clogging consisted of calcium carbonate precipitation and bio-clogging.•BA mono-fill was suggested to eliminate the clogging in landfills.
Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is a common way for BA management. However, BA co-disposal in MSW landfills may accelerate geotextile clogging and reduce ...the performance of leachate collection system. This study compared geotextile clogging in a simulated MSW landfill leachate (MSWL) and a BA co-disposed landfill leachate (BAL) at different landfill stages. Geotextile clogging test was conducted using the MSWL and BAL taken from the simulated landfills on the 10th, 80th, 140th and 200th day, respectively. The results demonstrated that geotextile clogging varied with landfill age, due to the change of leachate characteristics. The mass of clogging material in geotextiles with BAL increased from 0.45 g to 2.74 g, which was 43.87%–63.73% greater than those with MSWL. The formation of biofilm was the main contributor for the geotextile clogging. At the same stage, the amount of biofilm formed on geotextile in different leachate was comparable. However, the amounts of CaCO3 precipitation on geotextile in BAL were 3.85–10.44 times of those in MSW leachate. The pH of leachate played a critical role in CaCO3 precipitation. The microbial analysis revealed that the co-disposal of the BA greatly influenced the microbial community diversity and structure.
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•The study investigated geotextile clogging at different stages of landfills.•The formation of biofilm was the main contributor for the geotextile clogging.•The behavior of geotextile clogging was different as landfill aged.•Bottom ash co-disposal accelerates geotextile clogging chemically and biologically.
Methane (CH4) mitigation of biocovers or biofilters for landfills is influenced by the bed material and oxygen availability. The improvement of active aeration for the CH4 oxidation efficiency of ...biochar-amended landfill soil cover was investigated over a period of 101 days. There were column 1 as the control group, column 2 with biochar amending the soil cover, and column 3 with daily active aeration besides the same biochar amendment. All groups were inoculated with enriched methane oxidation bacteria (MOB). The average CH4 removal efficiency was up to 78.6%, 85.2% and 90.6% for column 1, 2, and 3, respectively. The depth profiles of CH4 oxidation efficiencies over the whole period also showed that the stimulation of CH4 oxidation by biochar amendment was apparent in the top 35 cm but became very faint after two months. This probably was due to the rapid depletion of nitrogen nutrition caused by enhanced methanotrophic activities. While through aeration, CH4 oxidation efficiency was further improved for column 3 than column 2. This enhancement also lasted for the whole period with a reduced decline of CH4 oxidation. Finally, the major MOB Methylocystis, commonly found in the three columns, were most abundant in the top 35 cm for column 3. A more balanced ratio of MOB and more homogeneous microbial community structures across different soil depths were also the results of active aeration.
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•Active aeration was operated for biochar-amended landfill soil cover (LSC).•Average CH4 removal efficiency was 90.6% for biochar-amended and aerated LSC.•Active aeration enhanced and prolonged the stimulation of biochar amendment.•Active aeration resulted in more abundant and balanced MOB in the top 35 cm.
