New Evidence for High Sorption Capacity of Hydrochar for Hydrophobic Organic Pollutants

Abstract

This study investigated the sorption potential of hydrochars, produced from hydrothermally carbonizing livestock wastes, toward organic pollutants (OPs) with a wide range of hydrophobicity, and compared their sorption capacity with that of pyrochars obtained from conventional dry pyrolysis from the same feedstock. Results of SEM, Raman, and C NMR demonstrated that organic carbon (OC) of hydrochars mainly consisted of amorphous alkyl and aryl C. Hydrochars exhibited consistently higher log K of both nonpolar and polar OPs than pyrochars. This, combined with the significantly less energy required for the hydrothermal process, suggests that hydrothermal conversion of surplus livestock waste into value-added sorbents could be an alternative manure management strategy. Moreover, the hydrochars log K values were practically unchanged after the removal of amorphous aromatics, implying that amorphous aromatic C played a comparable role in the high sorption capacity of hydrochars compared to amorphous alkyl C. It was thus concluded that the dominant amorphous C associated with both alkyl and aryl moieties within hydrochars explained their high sorption capacity for OPs. This research not only indicates that animal-manure-derived hydrochars are promising sorbents for environmental applications but casts new light on mechanisms underlying the high sorption capacity of hydrochars for both nonpolar and polar OPs.

Hydrothermal Carbonization: Modeling, Final Properties Design and Applications: A Review

“…In contrast to the sorption behavior of heavy metals, the sorption isotherms of organic compounds on hydro-and pyrochars were fit best by the Freundlich model [72,79]. The span of 1/n values for the diverse organic compounds was larger, from highly nonlinear (600 • C pyrochars/estrone 0.22) to approaching linearity (HC/phenanthrene 0.91).…”

“…Some values for sorption of organics with a wide range of hydrophobicity on hydro-and pyrochars are found in Table 4. HCs exhibited higher sorption affinities for organic pollutants with a wide range of hydrophobicity than pyrochars obtained at both low and high temperatures from the same feedstock [72,79]. This was not the case for heavy metal sorption, where HCs showed lower or similar sorption capacities (Table 3).…”

“…Feedstocks for HCs that have been tested for their sorption ability range from woody landscape/forestry residues (sawdust [69]; bamboo sawdust [70]), bioenergy crops (switchgrass [71]) agricultural residues (animal manures [72,73]; wheat straw and corn stalk [69]) to food processing (rice husks [74]; penaut husks [75]; banana peels [76]; orange waste, olive pomace, compost [74]) and domestic wastewater sludges (digested sewage sludge [77]; faecal sludge [78]). …”

“…The environmentally relevant target compounds that have been studied as sorbates span the range from organic agrochemicals, such as pesticides and herbicides (fluridone, norflurazon [79]; isoproturon [80]; atrazine [77]), pharmaceuticals and personal care products (tetracycline [81]; diclofenac, salicylic acid, fluriprofen [82]; triclosan, estrone, acetaminophen, carbamazepine [73]; sulfamethoxazole, carbamazepine, bezafibrate, diclofenac [77]), PAHs, endocrine disrupting chemicals and dyes (phenanthrene [83]; pyrene [72], bisphenol A, 17a-ethinyl estradiol [83]; methylene blue [84][85][86]; Congo red, 2-napthol [70]) to heavy metals Pb (II), Cu (II), Cd (II), Sb (III), Zn (II), As, and phosphate [69,71,[73][74][75]78,[84][85][86][87].…”

“…Furthermore, the sorption of organics has often been found to correlate well with the organic fraction of solids, so K d can be normalized for the organic carbon content of the sorbent (K OC ) and used to compare the relative importance of the other fractions in the system. The log of the OC-normalized distribution coefficient K OC has been used to compare the sorption capacity of various chars for a wide range of hydrophobic organic pollutants [72,79]. The comparison of the logK OC values is made at equivalent sorbate concentrations expressed as a fraction of their water solubility.…”