The waste-to-energy (WTE) technologies are now recovering energy and materials from over 300 million tonnes of municipal solid wastes worldwide. Extensive studies have investigated substituting natural construction materials with WTE residues to relieve the environmental cost of natural resource depletion. This study examined the beneficial uses of WTE residues in civil engineering applications and the corresponding environmental standards in Europe, the U.S., and China. This review presents the opportunities and challenges for current technical approaches and the environmental standards to be met to stabilize WTE residues. The principal characteristics of WTE residues (bottom ash and fly ash) and the possible solutions for their beneficial use in developed and developing countries are summarized. The leaching procedures and environmental standards for pH, heavy metals, and polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) are compared. The current practice and engineering properties of materials using WTE residues, including mixtures with stone aggregate or sand, cement-based or hot-mix asphalt concrete (pavement), fill material in the embankments, substitute of Portland cement or clinker production, and ceramic-based materials (bricks and lightweight aggregate) are comprehensively reviewed.
Activated carbon (AC) has attracted tremendous research interest as an electrode material for supercapacitors owing to its high specific surface area, high porosity, and low cost. However, AC-based supercapacitors suffer from limited rate performance and low power density, which mainly arise from their inherently low electrical conductivity and sluggish ion dynamics in the micropores. Here, we propose a simple yet effective strategy to address the aforementioned issue by nitrogen/fluorine doping and enlarging the micropore size. During the treatment, the decomposition products of NH4F react with the carbon atoms to dope the AC with nitrogen/fluorine and simultaneously enlarge the pores by etching. The treated AC shows a higher specific surface area of 1826 m2 g−1 (by ~ 15%), more micropores with a diameter around 0.93 nm (by ~ 33%), better wettability (contact angle decreased from 120° to 45°), and excellent electrical conductivity (96 S m−1) compared with untreated AC (39 S m−1). The as-fabricated supercapacitors demonstrate excellent specific capacitance (26 F g−1 at 1 A g−1), significantly reduced electrical resistance (by ~ 50%), and improved rate performance (from 46.21 to 64.39% at current densities of 1 to 20 A g−1). Moreover, the treated AC-based supercapacitor achieves a maximum energy density of 25 Wh kg−1 at 1000 W kg−1 and a maximum power density of 10,875 W kg−1 at 15 Wh kg−1, which clearly outperforms pristine AC-based supercapacitors. This synergistic treatment strategy provides an effective way to improve the rate performance and power density of AC-based supercapacitors.
Forced aeration is one of the promising ways to accelerate landfill reclamation, and understanding the relation between aeration rates and waste properties is the prerequisite to implementing forced aeration under the target of energy saving and carbon reduction. In this work, landfill reclamation processes with forced aeration were simulated using aged refuses (ARs) of 1, 4, 7, 10, and 13 disposal years, and the potential of field application was also investigated based on a field project, to identify the degradation rate of organic components, the O2 consumption efficiency and their correlations to microbes. It was found that the removal rate of organic matter declined from 20.3% (AR1) to 12.6% (AR13), and that biodegradable matter (BDM) decreased from 5.2% to 2.4% at the set aeration rate of 0.12 L O2/kg waste (Dry Matter, DM)/day. A linear relationship between the degradation rate constant (K) of BDM and disposal age (x) was established: K = − 0.0002193x + 0.0091 (R2 = 0.854), suggesting that BDM might be a suitable indicator to reflect the stabilization of ARs. The cellulose/lignin ratio decrease rate for AR1 (18.3%) was much higher than that for AR13 (3.1%), while the corresponding humic-acid/fulvic-acid ratio increased from 1.44 to 2.16. The dominant bacteria shifted from Corynebacterium (9.2%), Acinetobacter (6.6%), and Fermentimonas (6.5%), genes related to the decompose of biodegradable organics, to Stenotrophomonas (10.2%) and Clostridiales (3.7%), which were associated with humification. The aeration efficiencies of lab-scale tests were in the range of 5.4–11.8 g BDM/L O2 for ARs with disposal ages of 1–13 years, and in situ landfill reclamation, ARs with disposal ages of 10–18 years were around 1.9–8.8 g BDM/L O2, as the disposal age decreased. The increased discrepancy was observed in ARs at the lab-scale and field scale, indicating that the forced aeration rate should be adjusted based on ARs and the unit compartment combined, to reduce the operation cost.
Oil-based drill cuttings (OBDCs) are hazardous wastes generated during shale gas exploration, and the rapid, efficient and safe disposal methods for OBDCs have attracted the attention of many researchers. Plasma pyrolysis technology is widely used in solid waste treatment due to its extremely high temperature and reaction activity. A laboratory-scale thermal plasma pyrolysis system was built to investigate the plasma pyrolysis mechanism of simulated OBDCs. The thermal decomposition characteristics of OBDCs were studied by thermogravimetric-derivative thermo gravimetric-differential scanning calorimetry (TG-DTG-DSC) analysis in the range of 50–1300 °C. The thermal decomposition process of OBDCs was divided into the following four stages: evaporation of water and light oil, evaporation and decomposition of heavy oil, carbonate decomposition, and phase change reaction from solid to liquid. The effects of the oil ratio, water content, and water/oil (W/O) ratio of OBDCs on the composition and gas selectivity of pyrolytic gas were investigated. The results show that thermal plasma can crack the mineral oil in the OBDCs into clean gases such as H2, CO and C2H2, while water can promote the decomposition of the heavy oil molecules and enhance the H2 production. The energy consumption model calculation for the pyrolysis and melting of OBDCs shows that the highest energy utilization and the lowest molar energy consumption of H2 were achieved at a W/O ratio of 1:4. Based on the thermal plasma pyrolysis system used in this study, the commercial application prospects and economic benefits of the plasma pyrolysis of OBDCs were discussed.
Extensive use of fossil fuel has led to an increase in solid and gaseous particulates in the environment, which in turn necessitated newer, effective, and economical control strategies to abate pollutants, particularly gaseous pollutants. In the current research work, focus has been placed on utilizing industry wastes to adsorb nitrogen oxides present in diesel engine exhaust, which is pre-treated by plasma. Sampled exhaust from a 5 kW diesel generator is exposed to discharge plasma where the oxidation of nitric oxide to nitrogen dioxide occurs, which is then made to flow through another reactor filled with industry wastes drawn from agriculture, foundry, utility, marine industry, etc., comprising mulberry waste, rice husk, wheat husk, areca nut husk, sugarcane bagasse, coffee husk, foundry sand, lignite ash, red mud, and oyster shells. While the adsorption of nitrogen dioxide was observed in all the wastes, reduction of nitric oxide was observed in metallic compound-based industry wastes. At about 184 J/L, specific energy plasma cascaded industrial waste red mud yielded 98% NOx removal efficiency, and that with agriculture rice husk waste yielded 53% NOx removal. TiO2/Fe2O3 present in industry wastes might have exhibited photo-catalysis in visible light resulting in the possible reduction of NO. A new pathway for recycling the waste can be expected through nitrogen dioxide adsorption, and the results are further discussed with respect to plasma-alone and cascaded plasma adsorbent systems.
The present research work aims to explore the potency of piranha solutions at the best-optimized concentrations, i.e., 40% and 30% to reduce the recalcitrant and heterogeneous structure of wheat straw, and the treated wheat straw was denoted as WS40 and WS30. The effect of pretreatment on wheat straw was determined by anaerobic digestion (AD) in a batch mode, followed by the analysis of soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFAs). After pretreatment, the surface fibers shattered and detached, showing a distorted surface of wheat straw. An increase in the crystallinity of wheat straw after pretreatment was also observed due to the removal of amorphous cellulose and lignin. Enhancement in methane yield was obtained on the 9th day, which was 103±6.92 and 99.33±0.57 mL/d for WS40 and WS30, respectively. Displaced water measurement revealed that the pretreatment of wheat straw minimized the hydrolysis period by 14 days. It also improved the methane yield by 2.65 (WS40) and 2.45 (WS30) fold in comparison with the control which yielded 35.66 mL/d methane on the 23rd day. The modified Gompertz model (MGM), logistic function model (LFM) and transference function model (TFM) adequately described the degradation process and explained the kinetic behavior of the cumulative methane yield. Among the three models, MGM was found to fit best for the methane yield of WS40 and WS30.
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