The Effects of Washing Techniques on Thermal Combustion Properties of Sewage Sludge Chars

Sewage sludge chars were subjected to washing to produce a clean solid fuel of superior quality. First, sewage sludge was converted into chars at different carbonization temperatures (400–700 °C), and then the produced chars were washed with various washing techniques, i.e., water (W), hydrochloric acid (HCl), ethylenediamine tetraacetic acid (EDTA) and ultrasound-assisted water to further reduce ash and heavy metal contents. The washed chars were systematically characterized and their fuel properties were analyzed. The results indicated that all washing techniques decreased ash content of chars and improved their fuel ratio. The washed chars exhibited higher heating values, lower slagging and ash fouling indexes and higher combustion reactivity, indicating the better quality of the derived fuels. Among the washing techniques, HCl washing was the most efficient process as carbon content increased by 20%, while ash content decreased by 50%. The fuel ratio as well as slagging and ash fouling indexes were significantly improved. Furthermore, the combustion reactivity showed similar pattern to coal with high conversion rate suggesting the enhanced thermal stability of the fuel. In conclusion, pyrolysis as a single process seems inefficient to produce high quality chars; however, coupling pyrolysis with washing can yield chars with satisfactory fuel properties. Graphic abstract: [Figure not available: see fulltext.].acceptedVersionPeer reviewe

Graphene-like carbon nanosheets grown over alkali-earth metal oxides : effects of chemical composition and physico-chemical properties

Catalytic effects of alkali-earth metal oxides (MgO, CaO, SrO and BaO) on the growth of graphene-like carbon nanosheets via catalytic chemical vapor deposition of ethanol at 950 °C under atmospheric pressure were investigated. Both commercially available alkali-earth metal oxides as well as three synthetic MgO catalysts were used in this study. Chemical composition and physico-chemical properties, such as morphology, crystal surface geometry and porosity of catalysts were demonstrated to influence the yield and quality of graphene-like carbon nanosheets. Among investigated oxides, the MgO, CaO and SrO displayed different catalytic ability towards the growth of graphene-like carbon nanosheets determined by chemical compositions. The effect of physico-chemical properties was suggested by different properties of carbon products over synthetic MgO. MgO catalysts synthesized with ammonia produced the lowest defect level (ID/IG = 0.26) while MgO synthesized with urea and ethylene glycol produced the highest yield (12.1% per catalyst mass) of graphene-like carbon nanosheets compared to the other catalysts. The lower defect level and higher graphitization degree were attributed to well-defined morphology with uniform oxide crystal particle size and improvement of crystal orientation along (200) lattice plane in the catalyst. The higher yield was related to the higher porosity of catalysts

Carbon dioxide capture from biomass pyrolysis gas as an enabling step of biogenic carbon nanotube synthesis and hydrogen recovery

Utilization of renewable raw materials as feedstock defossilizes industrial manufacturing while subsequent carbon capture reduces carbon footprint. We applied this concept to design a new pyrolysis-based process for synthesis of biogenic multi-walled carbon nanotubes (MWCNTs) and H2 from biomass. It was demonstrated that the conversion of hydrocarbon compounds in pyrolysis gas into MWCNTs and H2 is detrimentally influenced by accompanied CO2 released from biomass decomposition. Capturing CO2 with a calcium sorbent upgraded the pyrolysis gas into a suitable gaseous precursor for downstream production of MWCNTs and H2 -rich gas. Furthermore, the results suggest that CO2 capture with the sorbent has a potential to outperform a liquid alkaline scrubber owing to avoided liquid organic waste generation, sorbent regenerability and higher H2 recovery from biomass pyrolysis gas.National Research Foundation (NRF)Public Utilities Board (PUB)Submitted/Accepted versionThis research/projectis supported by the National Research Foundation, Singapore, and PUB, Singapore’s National Water Agency under its RIE2025 Urban Solutions and Sustainability (USS) (Water) Centre of Excellence (CoE) Programme, awarded to Nanyang Environment & Water Research Institute (NEWRI), Nanyang Technological University, Singapore (NTU)

Support effects on thermocatalytic pyrolysis-reforming of polyethylene over impregnated Ni catalysts

Syngas is a valuable intermediate for sustainable management of waste plastics, which can be converted to new monomers and chemicals. In this work, Ni catalysts were studied for syngas recovery via steam reforming of low-density polyethylene (LDPE) pyrolysis volatiles on various supports, such as Al2O3, MgO, CeO2, Y2O3, TiO2, SiO2 and ZSM-5. Two commercial catalysts (NiAl and NiCaAl) were used for comparison. The supports exhibited distinct effects on the catalytic activity, selectivity and coke formation. Ni/CeO2, Ni/Y2O3, Ni/Al2O3, NiAl and NiCaAl showed high syngas yield but these catalysts were prone to coke formation. Ni/MgO, Ni/TiO2, Ni/SiO2 and Ni/ZSM-5 were the least active. The obtained H2/CO ratios were correlated with CO selectivity, revealing the unique impacts of supports on syngas composition via water-gas shift reaction. Compared with commercial NiAl, our work demonstrated that the prepared Ni catalysts on Al2O3 and MgO were suitable candidates for steam reforming of plastic pyrolysis volatiles.Economic Development Board (EDB)Nanyang Technological UniversityThe authors would like to acknowledge the Nanyang Environment and Water Research Institute, Nanyang Technological University (Singapore) and Economic Development Board (Singapore) for financial support of this research

Near real-time analysis of para-cresol in wastewater with a laccase-carbon nanotube-based biosensor

Para-Cresol is a water-soluble organic pollutant, which is harmful to organisms even at low concentrations. Therefore, it is important to rapidly detect the p-cresol in wastewater as well as natural water. In this work, a new, simple and stable biosensor was developed for on-site quantitatively determination and near real-time monitoring p-cresol in wastewater. The new biosensor was designed and fabricated using a screen-printed carbon electrode (SPCE) modified by waste-derived carbon nanotubes (CNTs) immobilized with laccase (LAC). The fabrication processes and performance of the biosensors were systematically characterized and optimized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and electrochemical methods. With improved conductivity, the proposed biosensor could provide the direct quantitation of p-cresol. The linear range of the biosensor is 0.2-25 ppm of p-cresol with a detection limit of 0.05 ppm. Additionally, the biosensor exhibited high reproducibility, stability and reusability during the validation. More importantly, the biosensor was successfully applied for the rapid detection of p-cresol in environmental lab wastewater under the interference of metal ions and other organics, and the results were consistent with high-performance liquid chromatography (HPLC). Finally, the biosensor with a portable potentiostat was approved as an easy-to-use, sensitive and inexpensive platform that could provide near real-time monitoring of p-cresol concentration in wastewater during Fenton oxidation treatment process.Nanyang Technological UniversityNational Environmental Agency (NEA)This work was supported by the National Environment Agency (NEA) of Singapore under the Urban Solutions and Sustainability (USS) Integration Fund [Project Reference No.: NEA/ETD/R&DPROJ/ CTWL-2018-4D-03]

Activation of Aspen Wood with Carbon Dioxide and Phosphoric Acid for Removal of Total Organic Carbon from Oil Sands Produced Water: Increasing the Yield with Bio-Oil Recycling

Several samples of activated carbon were prepared by physical (CO2) and chemical (H3PO4) activation of aspen wood and tested for the adsorption of organic compounds from water generated during the recovery of bitumen using steam assisted gravity drainage. Total organic carbon removal by the carbon samples increased proportionally with total pore volume as determined from N2 adsorption isotherms at −196 °C. The activated carbon produced by CO2 activation had similar removal levels for total organic carbon from the water (up to 70%) to those samples activated with H3PO4, but lower yields, due to losses during pyrolysis and activation. A method to increase the yield when using CO2 activation was proposed and consisted of recycling bio-oil produced from previous runs to the aspen wood feed, followed by either KOH addition (0.48%) or air pretreatment (220 °C for 3 h) before pyrolysis and activation. By recycling the bio-oil, the yield of CO2 activated carbon (after air pretreatment of the mixture) was increased by a factor of 1.3. Due to the higher carbon yield, the corresponding total organic carbon removal, per mass of wood feed, increased by a factor of 1.2 thus improving the overall process efficiency.Published versio

Benzene Adsorption from Dry and Humid Air on Activated Carbons from Japanese Cypress Wood Prepared by CO2 and K2CO3 Activation

Activated carbons (ACs) were prepared by physical (CO2) and chemical (K2CO3) activation of wood (Japanese cypress). Porous properties of the ACs, such as BET surface area and micropore volumes Vmic(N2) and Vmic(CO2), were characterized by N2 and CO2 adsorption isotherms. Short activation times caused formation of micropores with sizes smaller than 0.7 nm, which had a restricted access for N2 molecules. As a result, the ACs prepared through short activation time exhibited Vmic(N2) smaller than Vmic(CO2). The ACs were used for benzene adsorption at 5 ppmv concentration and relative humidities (RHs) of 0, 50 and 70 %. The largest benzene adsorption capacities at these RHs were exhibited by the AC prepared with K2CO3 activation at 800 °C. At RH 0 %, the benzene adsorption on the ACs was governed by Vmic(N2), when it was smaller than Vmic(CO2), and by Vmic(CO2), when it was smaller than Vmic(N2). The lower determination coefficients for the relationship between benzene uptake by the ACs and the volume of micropores at RHs 50 and 70 % compared to RH 0 % were attributed to the increased influence of surface chemistry of the ACs in the presence of moisture. In particular, the benzene adsorption at RHs 50 and 70 % was detrimentally affected by larger amounts of ash and surface oxygen groups.Published versio