Municipal sewage sludge secondary resource
Unincinerated sludge generated by municipal wastewater treatment, represented here by partially dewatered sludge from Kuopio, Finland, and sludge from a municipal treatment plant in Tianjin, China. These heterogeneous processed residues contain organic matter, nutrients and metals; their precise upstream treatment histories and mineral hosts are not fully resolved. This secondary resource is distinct from sewage-sludge incineration ash, untreated wastewater, factory-specific treatment sludge and purified phosphorus or metal products. The selected specimens do not define every municipal sludge.
Microbial & Biochemical Mechanisms (2)
Sulfur-assisted culture-associated acidification and phosphorus mobilization
bioleaching
Microbial
Associated Organisms:
Acidithiobacillus ferrooxidans (NCBITaxon:920), Acidithiobacillus thiooxidans (NCBITaxon:930)
Living acidithiobacilli cultures and indigenous sludge organisms were associated with acidification and increased phosphorus in filtered liquid after elemental sulfur supplementation. This establishes a laboratory solubilization observation, with unresolved phosphorus-source accounting, rather than isolated-product recovery or exclusive causation by either added strain.
Experimental Context & Analytical Limits:
Pradhan et al. used Lehtoniemi WWTP sludge, initially 5.59% total solids, in 250 mL loosely closed bottles containing 10 mL sludge and 90 mL medium or culture. Incubation was at 30 degrees C and 150 rpm. At days 21 and 42, 10 mL incubated mixture was replaced with fresh sludge; nominal 10 g/L elemental sulfur, described as 80% pure, was added at day 42 before continuing to day 63. Added cultures were A. ferrooxidans DSM 29444 and A. thiooxidans DSM 14887, separately or as equal-volume inoculum mixtures. Comparators contained sludge with water or uninoculated growth medium. These were not sterile-sludge controls: indigenous sulfur/iron oxidizers grew in the media. The liquid endpoint was obtained by 0.45 micrometre filtration.
Pradhan et al. used Lehtoniemi WWTP sludge, initially 5.59% total solids, in 250 mL loosely closed bottles containing 10 mL sludge and 90 mL medium or culture. Incubation was at 30 degrees C and 150 rpm. At days 21 and 42, 10 mL incubated mixture was replaced with fresh sludge; nominal 10 g/L elemental sulfur, described as 80% pure, was added at day 42 before continuing to day 63. Added cultures were A. ferrooxidans DSM 29444 and A. thiooxidans DSM 14887, separately or as equal-volume inoculum mixtures. Comparators contained sludge with water or uninoculated growth medium. These were not sterile-sludge controls: indigenous sulfur/iron oxidizers grew in the media. The liquid endpoint was obtained by 0.45 micrometre filtration.
Curated Evidence Points:
Support
Source:
pradhan_2021
Sections 2.4-2.6 and 3.1-3.3, Figures 1-2 and Tables 3-5 support the culture treatments, indigenous growth in controls, acidification after sulfur addition and the increased filtered phosphorus endpoint. Table 5 reports 92% P solubilization at pH 0.9 for T+S in phase 3, compared with 27% in TC+S and 10% in F+S. The preceding T phases report 10% and 5%; the outcome is conditional on the complete sequential treatment.
Partial
Source:
pradhan_2021
Section 2.4 media contain phosphate, iron and trace elements; explicit correction for these inputs and a closed replacement/sampling mass balance are not reported. Thus the reported 92% is not adopted as a verified sludge-derived recovery yield. Table 6 includes apparent elemental percentages exceeding 100%, and some Figure 1 final-pH traces differ from Table 5. The paper's sulfuric-acid concentration inferred directly from pH is not accepted as a measured acid yield. Neither an acidity-matched sterile control, strain-resolved tracking of the indigenous community, isolated phosphate product nor industrial operation was demonstrated.
Context_only
Source:
dsm_29444
The catalogue confirms DSM 29444 as strain R1; it does not establish its individual contribution in sludge.
Context_only
Source:
dsm_14887
The catalogue confirms DSM 14887 as strain 3/TA; species identifiers do not distinguish added cells from indigenous organisms.
Iron-fed indigenous enrichment bioleaching with a separate chemical oxidation extension
bioleaching
Microbial
An unresolved indigenous iron-oxidizing enrichment was used to acidify municipal sludge and mobilize several metals in laboratory flasks. A subsequent hydrogen-peroxide Fenton-like treatment altered extraction and operationally defined metal fractions; that chemical extension is not itself evidence of microbial oxidation or isolated metal recovery.
Experimental Context & Analytical Limits:
Qiu et al. used Tianjin municipal sludge adjusted to 4.0% total solids with deionized water. Each 300 mL sludge sample received 5% v/v living enrichment inoculum and 4.00 g/L Fe2+ supplied as FeSO4, followed by shaking at 28 degrees C and 150 rpm for up to 10 days. The inoculum originated from a municipal WWTP thickening tank; no species or strain assignment is justified. Samples of 20 mL were taken every 48 hours. The separate combined arms received 5-15 g/L H2O2 when bioleaching reached pH 4.5, 4.0 or 3.0. Experiments were described as triplicate, with ICP-MS metal analyses and modified BCR sequential extractions.
Qiu et al. used Tianjin municipal sludge adjusted to 4.0% total solids with deionized water. Each 300 mL sludge sample received 5% v/v living enrichment inoculum and 4.00 g/L Fe2+ supplied as FeSO4, followed by shaking at 28 degrees C and 150 rpm for up to 10 days. The inoculum originated from a municipal WWTP thickening tank; no species or strain assignment is justified. Samples of 20 mL were taken every 48 hours. The separate combined arms received 5-15 g/L H2O2 when bioleaching reached pH 4.5, 4.0 or 3.0. Experiments were described as triplicate, with ICP-MS metal analyses and modified BCR sequential extractions.
Curated Evidence Points:
Support
Source:
qiu_2021
Methods pp. 2-3 and Figures 1-3 support progressive acidification and unequal metal mobilization. The single 10-day treatment reports 67.28% Zn and 49.83% Ni solubilization but only 6.32% Cr, with relatively low As and Pb removal. These percentages describe the study's assay, not recovered purified products. Figures 4-5 show that chemical H2O2 addition can increase extraction of several metals while reducing As and Pb removal relative to the single bioleaching endpoint.
Partial
Source:
qiu_2021
No matched sterile Fe-fed or acidity-matched comparison is presented, and community identity and detailed sample pretreatment are not resolved in the main article. BCR fractions are operational extractions, not direct mineral or oxidation-state identification; proposed FeAsO4/PbSO4 formation and hydroxyl-radical pathways remain interpretations. The text varies between 65.81% and 65.19% for a combined-treatment Ni endpoint and gives inconsistent Cu peroxide-dose assignments, so no exact combined optimum is accepted. Neither complete detoxification nor industrial deployment or an isolated metal product was shown.
Sources & References
-
pradhan_2021: Pradhan, Heinonen-Tanski, Veijalainen, Peraniemi and Torvinen (2021). Phosphorus Recovery from Sewage Sludge Using Acidithiobacilli. International Journal of Environmental Research and Public Health 18:7135. DOI 10.3390/ijerph18137135. Complete 13-page original; methods sections 2.1-2.7, Figures 1-2 and Tables 1-6 inspected.
https://doi.org/10.3390/ijerph18137135 (accessed 2026-10-15) -
qiu_2021: Qiu, Xie, Liu, Meng, Wang, Wang and Wang (2021). Removal behavior and chemical speciation distributions of heavy metals in sewage sludge during bioleaching and combined bioleaching/Fenton-like processes. Scientific Reports 11:14879. DOI 10.1038/s41598-021-94216-2. Complete 12-page original, methods pp. 2-3, Figures 1-6 and Table 1 inspected; some enrichment and analytical details are referred to earlier work rather than reproduced in this article.
https://doi.org/10.1038/s41598-021-94216-2 (accessed 2026-10-15) -
dsm_29444: DSMZ catalogue: Acidithiobacillus ferrooxidans DSM 29444, strain R1. Culture identity context; catalogue cultivation conditions do not replace the paper's assay.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-29444 (accessed 2026-10-15) -
dsm_14887: DSMZ catalogue: Acidithiobacillus thiooxidans DSM 14887, strain 3/TA, equivalent to ATCC 19377, NCIMB 8343 and JCM 3867. Culture identity context.
https://www.dsmz.de/collection/catalogue/details/culture/DSM-14887 (accessed 2026-10-15) -
ncbi_920: NCBI Taxonomy 920, Acidithiobacillus ferrooxidans, species; not a strain identifier.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=920 (accessed 2026-10-15) -
ncbi_930: NCBI Taxonomy 930, Acidithiobacillus thiooxidans, species; not a strain identifier.
https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?id=930 (accessed 2026-10-15)
Curation History
| Timestamp | Curator | Action | Summary |
|---|---|---|---|
2026-10-15T02:28:54.524387Z |
Codex (GPT-6; Codex) | CREATE | Created an unincinerated municipal sewage-sludge resource from two original laboratory studies, retaining phosphorus-input uncertainty, indigenous controls, uneven metal mobilization, separate chemical oxidation and unresolved source discrepancies. |
Record source: data/records/municipal-sewage-sludge.yaml