Ground waste tire rubber secondary resource
Ground rubber recovered from used tires, containing a crosslinked polymer matrix, fillers and zinc-bearing additives. The selected study used 400-600 micrometre particles from an unnamed waste-tire recycling facility. This secondary resource is distinct from elemental zinc, zinc mineral species, tire combustion ash, pyrolysis char, rubber-manufacturing waste and natural-rubber gloves. Chemical pretreatment does not create a separate material identity, and the feed does not inherit a criticality designation from a constituent element.
Microbial & Biochemical Mechanisms (2)
Culture-associated rubber transformation without demonstrated zinc extraction
other
Microbial
Associated Organisms:
Rhodococcus rhodochrous (NCBITaxon:1829)
Growing Rhodococcus rhodochrous RPK1 cultures were associated with changes in ground-tire-rubber crosslink density, surface structure and reactive-product assays. Chemical pretreatment preceded one culture arm. These laboratory phenotypes provide partial evidence of microbial rubber transformation, without establishing a specific enzyme pathway, complete carbon mineralization or isolated metal recovery. Biological treatment did not demonstrate zinc extraction from the rubber.
Experimental Context & Analytical Limits:
Methods 2.1-2.6 identify RPK1 as DSM 103064 and compare untreated and choline-chloride/urea-DES-pretreated GTR. The chemical preparation is described separately below. The growing whole-cell inoculum was prepared in nutrient broth; 10% v/v culture at OD600 0.8-1.0 was added to 1% w/v GTR in 100 mL mineral salts medium in 250 mL flasks. Initial pH was 7.0 +/- 0.05, with incubation at 30 degrees C and 120 rpm for 28 days. Inoculum washing is not described, so nutrient-broth carryover limits the paper's sole-carbon-source interpretation. Controls include untreated GTR without bacteria and bacteria in medium without GTR. DES-only compositional and swelling data are available, but no DES-pretreated abiotic 28-day arm is shown in the weight-loss or Schiff comparison. Postculture biomass removal and gravimetric drying are not described as clearly as the chemical preparation. This is a laboratory flask study, without a demonstrated industrial rubber- or zinc-recovery process.
Methods 2.1-2.6 identify RPK1 as DSM 103064 and compare untreated and choline-chloride/urea-DES-pretreated GTR. The chemical preparation is described separately below. The growing whole-cell inoculum was prepared in nutrient broth; 10% v/v culture at OD600 0.8-1.0 was added to 1% w/v GTR in 100 mL mineral salts medium in 250 mL flasks. Initial pH was 7.0 +/- 0.05, with incubation at 30 degrees C and 120 rpm for 28 days. Inoculum washing is not described, so nutrient-broth carryover limits the paper's sole-carbon-source interpretation. Controls include untreated GTR without bacteria and bacteria in medium without GTR. DES-only compositional and swelling data are available, but no DES-pretreated abiotic 28-day arm is shown in the weight-loss or Schiff comparison. Postculture biomass removal and gravimetric drying are not described as clearly as the chemical preparation. This is a laboratory flask study, without a demonstrated industrial rubber- or zinc-recovery process.
Curated Evidence Points:
Partial
Source:
shukla2026_tire
Methods 2.7.5, Table 2 and Figure 6 report swelling-derived crosslink densities of 9.61 +/- 0.16 for untreated GTR, 8.09 +/- 0.29 after bacterial treatment, 7.03 +/- 0.25 after DES alone and 5.44 +/- 0.12 after DES plus bacteria, all in units of 10^-5 mol/cm3, mean +/- SD, n = 3. The source reports a 15.81% decrease with bacteria alone. Acetone extraction for 24 h and n-hexane swelling at 25 degrees C for 72 h feed a Flory-Rehner model with assumed interaction parameter 0.45 and rubber density 1.15 g/cm3. Horikx curve interpretation is model-dependent; the printed sol-fraction equation has problematic parentheses. These results do not identify a causal enzyme or prove that chemical pretreatment and biology have a synergistic interaction.
Partial
Source:
shukla2026_tire
Figure 9a and supplementary Table S2 give initial mass 1.00 g and final masses 0.967 g for the untreated abiotic control, 0.951 g for bacteria/GTR and 0.841 g for bacteria/DES-pretreated GTR. Reported gross losses are 3.30 +/- 2.36%, 4.93 +/- 1.15% and 15.84 +/- 8.78%, respectively; the table/caption do not define the replicate count or the plus/minus statistic. Results 3.10's 1.63% and 12.53% subtract the same untreated abiotic loss, as percentage-point differences. Rounded table values instead give 12.54 for the second difference. These are not recovered-product yields or the biological increment above a DES-pretreated abiotic control. The large uncertainties and unresolved biomass/residue preparation constrain quantitative attribution.
Partial
Source:
shukla2026_tire
Figure 9b-e shows pink Schiff staining in both rubber-plus-bacteria cultures, absent from the photographed untreated-GTR abiotic and bacteria/no-GTR controls. Figures 2-4 show spectral and qualitative surface changes, while supplementary Table S1 gives altered carbon and sulfur weight fractions. These observations support a limited transformation phenotype, not a measured CO2 mineralization balance or absolute sulfur-removal yield. Supplementary Table S3/Figure S2 provide tentative LC-MS assignments without a matched abiotic chromatogram or standards-confirmed product identity. The first listed C20H32O2 sodium adduct at m/z 307 is inconsistent with its formula. Lcp, Dsz/4S and other enzyme-pathway explanations are not causally established by the ABTS, total-protein or product assays.
Partial
Source:
shukla2026_tire
Methods 2.7.3 and Results 3.5 report solid-residue ICP-OES Zn fractions of 1.94 +/- 0.06 wt% untreated, 2.25 +/- 0.10 after bacteria, 1.30 +/- 0.17 after DES alone and 1.73 +/- 0.11 after DES plus bacteria. Replicate count and the meaning of plus/minus are not specified for this ICP result. A 0.1 g residue aliquot underwent 24 h room-temperature digestion in 5 mL 68.9% HNO3, dilution to 250 mL in 2% HNO3 and 0.2 micrometre filtration, followed by externally calibrated ICP-OES at 213.857 nm. No aqueous Zn inventory or isolated Zn product is reported. Increased bacterial residue fractions do not demonstrate Zn extraction and also do not prove the source's assertion of exactly unchanged absolute Zn. Surface EDS Table 1 instead gives Zn fractions 3.36, 2.06, 0.80 and 1.06 wt% in those treatment groups, means of two surface measurements. Surface and digest measurements have different sampling bases; neither is a whole-feed metal-recovery yield.
Partial
Source:
shukla2026_tire
Source contradictions limit ancillary mechanistic interpretations. Figure 1b places peak viable counts around 10^12 CFU/mL, whereas Results 3.1 reports values around 10^9; exact counts are unresolved. Figure 1a's pretreated OD trace continues increasing after day 14, contrary to the prose's joint biomass/viability maximum. Figure 10 protein trajectories and its day-28 control differ from the prose, and Figure 8's final char-residue ranking differs from its embedded table. These values are not reconciled or imported as precise mechanism measurements. Qualitative culture-associated changes do not establish a universal or exclusively biological pathway.
Context_only
Source:
dsmz_rpk1
The collection maps RPK 1 to DSM 103064 and R. rhodochrous, agreeing with the main paper and supplementary Table S2. This supports strain-name provenance, not independent verification of the experimental culture or its causal pathway.
Context_only
Source:
ncbi_rhodochrous
NCBI node 1829 supports the species label. Collection identity and experimental strain provenance remain separate from this species CURIE.
Chemical DES pretreatment with reduced solid-residue zinc fraction
other
Choline chloride/urea deep eutectic solvent treatment altered the rubber network and lowered the measured Zn fraction of the remaining solid before bacterial culture. This is a thermochemical preparation stage, not microbial zinc extraction or a demonstrated isolated-metal recovery.
Experimental Context & Analytical Limits:
Methods 2.3-2.4 describe choline chloride and urea at 1:2 molar ratio, mixed at 70 degrees C. GTR was washed three times with 70% ethanol and vacuum-dried at 45 degrees C to constant weight. Rubber and DES at 1:40 w/w were left to swell for 24 h at room temperature, sonicated at 37 kHz for 2 h and stirred at 180 degrees C for 45 min. Treated particles were ethanol-washed, filtered and dried at 50 degrees C to constant weight. This preparation is distinct from the separate isothermal TGA, whose Methods 2.5 says a 60 min hold whereas Figure 7 marks 45 min. The study does not demonstrate an industrial solvent cycle, recovered-Zn product, closed mass balance or lifecycle benefit.
Methods 2.3-2.4 describe choline chloride and urea at 1:2 molar ratio, mixed at 70 degrees C. GTR was washed three times with 70% ethanol and vacuum-dried at 45 degrees C to constant weight. Rubber and DES at 1:40 w/w were left to swell for 24 h at room temperature, sonicated at 37 kHz for 2 h and stirred at 180 degrees C for 45 min. Treated particles were ethanol-washed, filtered and dried at 50 degrees C to constant weight. This preparation is distinct from the separate isothermal TGA, whose Methods 2.5 says a 60 min hold whereas Figure 7 marks 45 min. The study does not demonstrate an industrial solvent cycle, recovered-Zn product, closed mass balance or lifecycle benefit.
Curated Evidence Points:
Partial
Source:
shukla2026_tire
Results 3.5 assigns the fall from 1.94 +/- 0.06 to 1.30 +/- 0.17 wt% solid Zn to DES alone and calls it 33% removal. This is a relative residue-concentration decrease, not an independently measured fraction of feed Zn recovered in a product. Subsequent bacterial culture raises the residual fraction to 1.73 +/- 0.11 wt%, so the initial decrease cannot be attributed to microbial action. Table 2's DES-only swelling result and supplementary Table S1's carbon/sulfur fractions provide chemical-treatment context; they do not resolve a DES-matched abiotic incubation or validate the source's broad detoxification/mineralization language. Disc diffusion and residual growth readings likewise do not establish general solvent nontoxicity.
Sources & References
-
shukla2026_tire: Shukla, Roy and Bhand (2026). Deep eutectic solvent-assisted bacterial devulcanization, detoxification, and degradation of waste tyre rubber. RSC Advances 16(28):26205-26221. DOI 10.1039/d6ra01664b; published 18 May 2026; PMCID PMC13185686.1. Complete primary XML, Tables 1-4, original Figures 1-11, and complete supplementary PDF Tables S1-S3 and Figures S1-S2 inspected through Europe PMC. The publisher's main PDF was not acquired; the original supplementary images were also extracted to inspect the overlapping layout on its page 3.
https://doi.org/10.1039/d6ra01664b (accessed 2026-10-11) -
dsmz_rpk1: DSMZ catalogue DSM 103064, Rhodococcus rhodochrous, strain designation RPK 1. Current collection identity independently matches the paper's reported RPK1 culture; this is not authentication of the experimental stock.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-103064 (accessed 2026-10-11) -
ncbi_rhodochrous: NCBI Taxonomy 1829, Rhodococcus rhodochrous, species-level taxonomic context. The species identifier does not identify strain DSM 103064.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=1829 (accessed 2026-10-11)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-11T17:06:09.837914Z |
Codex (GPT-6; Codex) | CREATE | Curated a distinct ground waste tire rubber resource from complete primary XML, original figures and supplement. Kept partial culture-associated transformation separate from chemical DES pretreatment, with no demonstrated microbial Zn extraction, residue-fraction and mass-loss basis limits, unmatched controls and unresolved graphic/text discrepancies. |
Record source: data/records/ground-waste-tire-rubber.yaml