Iron-Rich Biochar to Adsorb Volatile Organic Compounds Emitted from Asphalt-Surfaced Areas

Abstract

This study introduces iron-rich biochar to selectively adsorb some volatile organic compounds (VOCs) emitted from asphalt-surfaced areas. Adsorption and retention of VOCs can improve the air quality while reducing asphalt’s mass loss which compromises asphalt’s durability. The iron-rich biochar was made from a hybrid feedstock of Cyanidioschyzon merolae (CM) algae and swine manure (SM) with a blend of 20:80 CM/SM, showing the highest biochar yield of 27 wt % and the highest metal content of Fe (21.8 g kg–1). Comparison of VOC adsorption of iron-rich biochar and low-iron biochar shows the significant role of Fe content in adsorption of VOCs. When the iron-rich biochar was introduced to asphalt, a total emission reduction of 76% was observed; this number was only 59% when low-iron biochar was used. The superiority of iron-rich biochar over low-iron biochar in adsorbing volatiles is observed for some specific volatiles such as non-polar aromatics in our experiment. The dominant contribution of lightweight cyclic aromatics and alkanes in bitumen emissions indicates that minimizing the VOC emissions from saturate and aromatic fractions of bitumen could be a key factor in reducing the VOCs from asphalt. The hybrid biomass feedstock used here is also a nitrogen-rich substance containing abundant N sites to coordinate with Fe to form −C–N–Fe bonds. To understand the role of N–Fe functionals in the higher efficacy of Fe-rich biochar, density functional theory (DFT) calculations were performed on three O-containing compounds (benzoic acid, benzofuran, and hexanal) and three S-containing compounds (dibenzothiophene, 3-pentylthiophene, and hexanethiol). Based on DFT results, the adsorption energies of VOCs on active sites of Fe–biochar (containing −N–Fe functionals) are 8 to 10 times higher than those for pristine biochar (containing just N groups). It was also found that the presence of iron stimulates the catalytic performance of biochar, as evidenced by our DFT results, indicating degradation of dibenzothiophene and hexanethiol on the N–Fe active zones of iron-rich biochar. Application of iron-rich biochar can suppress the volatiles emitted from asphalt-surfaced areas; this in turn can improve the air quality and extend the service life of roadway infrastructures. Therefore, the study outcomes can promote built environment’ sustainability and public health.

Suppressing Actions of Inorganic Flame Retardants on the Pyrolysis Behavior of Asphalt

“…From Figure b, some alkane gases and a small amount of CO and CO 2 are still generated in the FR asphalt pyrolysis process . No new substances are generated, indicating that CFR is not involved in chemical reactions within asphalt .…”

“…From Figure 3b, some alkane gases and a small amount of CO and CO 2 are still generated in the FR asphalt pyrolysis process. 20 No new substances are generated, indicating that CFR is not involved in chemical reactions within asphalt. 21 Comparing Figure 3a,b, the concentrations of gaseous products generated from asphalt are higher than those of FR asphalt.…”

Bio‐Carbon as a Means of Carbon Management in Roads

“…[95] It has been documented that introduction of select biochar can not only reduce this number, but also retain emission of volatile organic compounds (VOCs) which otherwise emits from asphalt during its service life. [29,96] It should be noted that VOCs contain significant amounts of carbon; for instance, hexadecane (C 16 H 34 ) which is typically emitted from asphalt-surfaced areas during construction and service life contains 0.847 g carbon per mole, and its release into the atmosphere contributes to air pollution and negative health impacts. [97] When biochar is added to asphalt latter loss can be reduced by as much as 76%.…”

“…[97] When biochar is added to asphalt latter loss can be reduced by as much as 76%. [96] If only 1% biochar is added in paving mixture, ≈22 tons of biochar would be used in every lane-mile (3.7 m wide and 15.2 cm thick). [49] Since biochar contains 33-48% carbon, this would sequester 7-10 tons of CO 2 per lane-mile of road.…”

Long-Term Lead Immobilization in River Sediment by Ca(OH)2-Modified Rice Straw Biochar

“…Biochar (BC), produced via pyrolysis of waste biomass, has been received increasing attention for its environmentally friendly and cost-effective superiority. , Especially, after further modification, BC has been widely accepted as a low-cost sorbent for the removal of various inorganic and organic pollutants, owing to its adequate chemical and physical stability, high surface area, and functional groups. , Among the various of biochar-modified chemicals, the alkalis can alter pore structures, crystallinity, and surface area of the biomass. , Ca­(OH) 2 , as a mineral prevalently existing in the terrestrial environment, has been found to have superiority for heavy-metal immobilization in the river sediment . Besides, Ca­(OH) 2 can also capture CO 2 generated during biomass pyrolysis processes with the potential to form CaCO 3 and was also reported to have the ability to enrich oxygen-containing functional groups on the biochar surface .…”