Tannery sludge secondary resource
Chromium-bearing solids from tannery wastewater treatment, represented here by the Xiamen factory sludge tested by Wang et al. (2019). This heterogeneous secondary resource is distinct from untreated tanning liquor, leather shavings, pyrolyzed tannery residue, electroplating sludge and elemental chromium. The experiment does not establish a universal sludge composition or inherit constituent-element criticality.
Microbial & Biochemical Mechanisms (1)
Acidophile-associated acidification and chromium solubilization
bioleaching
Microbial
Associated Organisms:
Acidithiobacillus ferrooxidans (NCBITaxon:920), Acidithiobacillus thiooxidans (NCBITaxon:930)
Acclimatized Acidithiobacillus cultures supplied with ferrous sulfate and elemental sulfur were associated with acidification and aqueous chromium mobilization from one tannery sludge. The combined culture/substrate treatment outperformed the reported comparisons, without isolating species synergy, proving chromium redox transformation or producing an isolated chromium product.
Experimental Context & Analytical Limits:
Wang et al. sampled tannery sludge from a factory in Xiamen, Fujian, China and refrigerated it at 4 °C. Table 1 reports pH 7.10, total solids 12.88% and source-labelled Cr3+ 15.890 g/kg dry weight; ICP-based total chromium analysis does not independently establish that oxidation-state assignment. Source-reported A. ferrooxidans CGMCC NO.0727 and A. thiooxidans CGMCC NO.0759 were cultivated in improved 9K and SM media, then serially acclimatized in sludge to pH 2.0. Batch assays used 250 mL flasks containing 135 mL sludge, acidified initially to pH 6.50 with H2SO4 and conditioned for 12 h, at 28 °C and 180 rpm. Figure captions specify 2% (w/w) sludge. Section 2.3 says 15% volume inoculum, whereas Figures 1–2 say 10% (v/v); the exact inoculum fraction is unresolved. The combined arm used a 1:1 culture mixture and source-stated 4.0 g/L FeSO4 plus 3.0 g/L elemental sulfur. Single-culture arms received their corresponding energy substrate; a mixture without added substrates and uninoculated treatments with and without added substrates were also compared. Treatments and analyses were reported in triplicate. Daily 15 mL samples were centrifuged and filtered through 0.45 micrometre membranes before ICP-OES total-Cr analysis; evaporation loss was replenished, while cumulative sampling corrections are not explained.
Wang et al. sampled tannery sludge from a factory in Xiamen, Fujian, China and refrigerated it at 4 °C. Table 1 reports pH 7.10, total solids 12.88% and source-labelled Cr3+ 15.890 g/kg dry weight; ICP-based total chromium analysis does not independently establish that oxidation-state assignment. Source-reported A. ferrooxidans CGMCC NO.0727 and A. thiooxidans CGMCC NO.0759 were cultivated in improved 9K and SM media, then serially acclimatized in sludge to pH 2.0. Batch assays used 250 mL flasks containing 135 mL sludge, acidified initially to pH 6.50 with H2SO4 and conditioned for 12 h, at 28 °C and 180 rpm. Figure captions specify 2% (w/w) sludge. Section 2.3 says 15% volume inoculum, whereas Figures 1–2 say 10% (v/v); the exact inoculum fraction is unresolved. The combined arm used a 1:1 culture mixture and source-stated 4.0 g/L FeSO4 plus 3.0 g/L elemental sulfur. Single-culture arms received their corresponding energy substrate; a mixture without added substrates and uninoculated treatments with and without added substrates were also compared. Treatments and analyses were reported in triplicate. Daily 15 mL samples were centrifuged and filtered through 0.45 micrometre membranes before ICP-OES total-Cr analysis; evaporation loss was replenished, while cumulative sampling corrections are not explained.
Curated Evidence Points:
Support
Source:
wang2019
Methods 2.2–2.4, Figures 1–3 and Discussion p. 139 support conditional culture-associated solubilization. The combined culture/substrate arm reached source-reported 97.1% after seven days and final pH 1.65. Equation 4 defines efficiency as aqueous Cr quantity divided by initial sludge Cr quantity, multiplied by 100; this is dissolved extraction, not isolated product recovery. Figure 3 shows much smaller release in uninoculated substrate-added sludge and near-zero release in the no-substrate comparisons. The single-culture/substrate arms are lower than the combined treatment under these conditions.
Partial
Source:
wang2019
Uninoculated sludge is not demonstrated sterile; Discussion p. 139 explicitly allows indigenous organisms. Single-culture treatments differ in substrate chemistry from the combined treatment, and no matched-pH acid-only comparison isolates a biological contribution beyond acid generation. Lower pH, higher ORP, falling Fe(II) and increasing sulfate are consistent with the proposed indirect mechanism but do not establish individual species causality, population succession, chromium valence changes or organic-matter breakdown. Figure 4 regressions are associations rather than independent mechanistic proof.
Partial
Source:
wang2019
Source inconsistencies remain unresolved: inoculum 15% in Methods versus 10% in figure captions; acclimatization labels 4 g/L Fe2+ whereas the batch recipe specifies 4 g/L FeSO4. Section 3.2 says sulfate remained unchanged in uninoculated treatments, but Figure 2b shows an increase in the Fe2+ plus sulfur arm and Discussion acknowledges a slight increase. These statements are not silently harmonized or used to reconstruct exact reagent chemistry.
Partial
Source:
wang2019
The reported residual sludge value 531 mg/kg and initial 15.890 g/kg dry weight do not yield 97.1% by simple unchanged-solid-mass subtraction. The paper uses an aqueous-inventory denominator and does not provide a complete solid-mass/sampling balance to reconcile the endpoints. The source-reported values remain separate qualified quantities. Its agricultural/landfill suitability conclusion is not adopted: no independent regulatory applicability check, complete toxicity assessment, isolated product or industrial deployment is established.
Context_only
Source:
ncbi920
The current official entry verifies the species identifier/label, not CGMCC NO.0727 stock identity, culture purity or experimental sequencing.
Context_only
Source:
ncbi930
The current official entry verifies the species identifier/label, not CGMCC NO.0759 stock identity, culture purity or experimental sequencing.
Sources & References
-
wang2019: Wenhao Wang, Jianlei Gao, Yonghong Li and Jingqing Gao (2019). Enhanced Cr bioleaching efficiency from tannery sludge with Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Desalination and Water Treatment 165:134–140. DOI 10.5004/dwt.2019.24500. Complete official seven-page original, Table 1, Figures 1–4 and Equations 1–8 inspected.
https://doi.org/10.5004/dwt.2019.24500 (accessed 2026-10-12) -
ncbi920: NCBI Taxonomy 920: Acidithiobacillus ferrooxidans, species; verifies the species label, not the source-reported CGMCC culture stock.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=920&mode=Info (accessed 2026-10-12) -
ncbi930: NCBI Taxonomy 930: Acidithiobacillus thiooxidans, species; verifies the species label, not the source-reported CGMCC culture stock.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=930&mode=Info (accessed 2026-10-12)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-12T14:02:26.884243Z |
Codex (GPT-6; codex) | CREATE | Created a distinct tannery wastewater-sludge secondary-resource record from the complete Wang2019 primary. Preserved control, inoculum, reagent, sulfate and mass-balance limitations; excluded regulatory suitability, chromium redox and industrial recovery claims. |
Record source: data/records/tannery-sludge.yaml