Adsorption of pyrolysis oil model compound (phenol) with plasma-modified hydro-chars and mechanism exploration.

Phenol is one of the important ingredients of pyrolysis oil, contributing to the high biotoxicity of pyrolysis oil. To promote the degradation and conversion of phenol during anaerobic digestion, cheap hydro-chars with high phenol adsorption capacity were produced. The phenol adsorption capabilities of the plain hydro-char, plasma modified hydro-char at 25 °C (HC-NH3-P-25) and 500 °C (HC-NH3-P-500) were evaluated, and their adsorption kinetics and thermodynamics were explored. Experimental results indicate that the phenol adsorption capability of HC-NH3-P-500 was the highest. The phenol adsorption kinetics of all samples followed the pseudo-second-order equation and interparticle diffusion model, indicating that the adsorption rate of phenol was controlled by interparticle diffusion and chemistry adsorption simultaneously. By DFT calculations, π-π stacking and hydrogen bond are the main interactions for phenol adsorption. It was observed that an enriched graphite N content decreased the average vertical distance between hydro-chars and phenol in π-π stacking complex, from 3.5120 to 3.4532 Å, causing an increase in the negative adsorption energy between phenol and hydro-char from 13.9330 to 23.4181 kJ/mol. For hydrogen bond complex, the average vertical distance decreased from 3.4885 to 3.3386 Å due to the increase in graphite N content; causing the corresponding negative adsorption energy increased from 19.0233 to 19.9517 kJ/mol. Additionally, the presence of graphite N in the hydro-char created a positive diffusion region and enhanced the electron density between hydro-char and phenol. Analyses suggest that enriched graphite N contributed to the adsorption complex stability, resulting in an improved phenol adsorption capacity.

Ecological risk assessment of heavy metals in bottom ashes generated by small-scale thermal treatment furnaces for domestic waste in villages and towns of China.

Small-scale Solid Waste Thermal Treatment (SSWTT) is prevalent in remote Chinese locations. However, the ecological threats associated with heavy metals in resultant bottom ash remain undefined. This research study scrutinized such ash from eight differing sites, assessing heavy metal content, chemical form, and leaching toxicity. Most bottom ash samples met soil contamination standards for development land (GB36600-2018). However, levels of As, Cd, Cr, Cu, Ni, Pb, and Zn in some samples exceeded agricultural land standards GB15618-2018) by 1591%, 64,478%, 1880%, 3886%, 963%, 1110%, and 2011% respectively. Additionally, the As and Cd contents surpassed the construction land control limit value by 383% and 13% respectively. The mean values of the combined oxidizable and residual fraction (F3 + F4) for each heavy metal in all samples exceeded 65%, with Cr, Cu, Ni, and Pb reaching over 95%. All sample leaching concentrations, obtained via the HJ/T 299 procedure, were less than limits set by the identification standards for hazardous wastes (GB5085.3-2007). However, only the leaching concentrations of three samples via the leaching procedure HJ/T 300 met the "Solid Waste Landfill Pollution Control Standard" (GB 16889-2008). The results indicate that the location and type of SSWTT equipment play a crucial role in determining an appropriate solution for bottom ash management.

Preparation of activated carbon from sewage sludge using green activator and its performance on dye wastewater treatment.

The remediation of dyes in wastewater using activated carbon produced from sewage sludge pyrolysis char (PYC) is an environmentally friendly and sustainable process. However, traditional activators can cause corrosion of the processing facility, thereby increasing the costs of waste disposal. Here, activated carbons were prepared from sewage sludge PYC, and the effects of activation conditions (different activators, temperature and time, and char:activator mass ratio) on their specific surface areas and adsorption of iodine and methylene blue (MB; model dye) were studied. The results showed that a value of 952 m2/g could be attained for the specific surface area and values of 882 and 162 mg/g for the adsorption of iodine and MB, respectively, by heating PYC with KHCO3 (PYC- KHCO3: 1:2 w/w) for 60 min at 800 ℃. Compared with activation by KOH, the adsorption of MB using PYC-KHCO3 was slightly lower but the yield was 13.7% higher. Optimization of the activation process using surface response modelling indicated that sensitivity of three key factors to the adsorption of iodine and MB followed the order: Mass ratio > temperature > time. Systematic investigation of the effects of time, pH and temperature on the removal of MB by the activated carbon revealed that adsorption conformed to the Langmuir model and pseudo-second-order kinetics. The proposed mechanisms of MB adsorption involved ion exchange, functional group complexation and physical/π-π interactions. This study provides a basis for the efficient remediation of dyes in wastewater using activated carbon prepared from sustainable sewage sludge PYC and green chemistry.

MSW pyrolysis volatiles' reforming by incineration fly ash for both pyrolysis products upgrading and fly ash stabilization.

The effective disposal of municipal solid wastes (MSW) and its incineration-derived fly ash (IFA), which contains large amounts of heavy metals (HMs) and chlorine (Cl), is an urgent task. In this study, IFA was used to reform MSW pyrolysis volatiles within 500-800 °C. The changes of reformed pyrolysis products, the migration characteristics of HMs and Cl between IFA and pyrolysis products were investigated. The results indicated that the O- and Cl-containing compounds in pyrolysis oil tended to decrease, light hydrocarbons and its calorific value increased accordingly after reforming; more CH4 and H2 gases were produced concurrently. The increase in reforming temperature enhanced these trends. The IFA absorbed Cl from volatiles during reforming, which reduced HCl in the gas product. The toxicity equivalent (TEQ) of PCDD/Fs in IFA decreased dramatically from 0.47 µg/kg to 0.0055 µg/kg after reforming at 500 °C, and it decreased with increasing reforming temperature. Some of the HMs' concentrations in the used IFAs increased, but their leaching capacity all decreased significantly at 800 °C except for Cr. The used IFA at 800 °C (IFA-800) corresponded to the lowest HMs leaching concentrations and could meet the landfill requirements; while the used IFA at 500 °C (IFA-500) corresponded to the maximum carbon deposition of 14.63 wt%, providing the energy source for its melting. Therefore 800 °C was recommended for harmless disposal of IFA, and 500 °C was better for a further melting of IFA., The contamination of pyrolysis liquid caused by inorganic Cl-containing compounds at 500 and 800 °C with much lower levels than the original. This study showed the hazardous properties of IFA can be dampened after interacting with MSW pyrolysis volatiles within the tested temperature range, and provided a good chance for the simultaneous disposal of IFA and recovery of high-quality MSW pyrolysis products.

Upgrading gas and oil products of the municipal solid waste pyrolysis process by exploiting in-situ interactions between the volatile compounds and the char.

The gas and oil product derived from municipal solid waste (MSW) pyrolysis was upgraded by utilizing the interaction between the volatile compounds and the char and the mechanism involved is explored. The influences of operation parameters, including interaction temperature, char/volatiles mass ratio (C/V) and gas hourly space velocity (GHSV) of the volatiles on the distribution and property of the upgraded products were investigated. The results showed that the higher interaction temperature, higher C/V and lower GHSV favored the conversion of condensable volatiles into gas products, thus increasing the gas yield in the outlet stream. The highest gas yield (44.14 wt%) was obtained at 700 °C with the natural C/V ratio (0.8) and GHSV, which was twice of the gas yield in the volatiles. The chemical energy portion of gas increased to 8065 kJ/kgMSW from 3209 kJ/kgMSW at this condition. Syngas with H2/CO molar ratio of around 2 can be obtained at 700 °C with C/V ratio of 0.8 or at 600 °C with higher C/V ratios (C/V = 1.5-2.2). Oxygenates and acidity of the reformed oil products decreased; but monoaromatics and light polyaromatics concentration increased greatly. Heavy polycyclic aromatic hydrocarbons (PAHs) in the liquid products were degraded after volatiles/hot char interaction. Suitable conditions can be varied and recommended for obtaining different desired high-quality products based on this process.