Mechanisms of iron sulfide-based autotrophic denitrification for removal of nutrients and emerging contaminants from carbon-deficient wastewater
Date
2023-09-19Embargo Date
2025-09-19
Author
Bai, Yang
Metadata
Show full item recordUsage
This item's downloads: 0 (view details)
Abstract
Autotrophic denitrification is a biological nitrogen removal process in which nitrate (NO3
-
) is
reduced to nitrogen gas (N2) by chemoautotrophic denitrifying bacteria in the presence of
inorganic electron donors (i.e. reduced sulfur compounds, hydrogen gas, and iron). Recently,
autotrophic denitrification with iron sulfides as the electron donors has gained increasing
attention. Iron sulfides are a variety of natural minerals and synthetic compounds consisting
of sulfur (S) and iron (Fe) elements. Iron sulfides-based autotrophic denitrification (IAD) has
a unique advantage in terms of simultaneous NO3
- and phosphorus (PO4
3-
) removal with low
operation cost and sludge production. However, the unclear mechanism and slow kinetics of
IAD limit its engineering application in wastewater treatment plants. The objectives of this
PhD research included: (1) study of the NO3
- transformation pathways coupled with sulfur
and iron cycles in the FeS-based autotrophic denitrification process; (2) investigation of
enhanced nutrients removal in an innovative constructed FeS-S0 coupled autotrophic
denitrification (ISAD) system; and (3) exploration of the potential of FeS-based autotrophic
denitrification for emerging contaminants removal.
The results showed that NO3
- can be chemically reduced to ammonium (NH4
+) by FeS under
room temperature and neutral pH conditions. With the inoculation of autotrophic
microorganisms in the IAD biofilter, the nitrogen-transformation network was complex and
consisted of chemical reduction, autotrophic denitrification, dissimilatory NO3
- reduction to
NH4
+ (DNRA) and sulfate reducing NH4
+ oxidation (Sulfammox). Different groups of
functional microorganisms were involved in these biochemical processes and engaged in the
cycles of N, S, and Fe in the IAD biofilter.
The coupled FeS-S0 autotrophic denitrification biofilter showed superior N and P removal
performance; the highest NO3
- removal rate was up to 960 mg/L/d and the PO4
3- removal
efficiency was 100% at 1 hr hydraulic retention time (HRT). Metagenomic sequencing results
revealed that the high-rate NO3
- and PO4
3- removal performance was due to the collaborative
denitrification community formed in the coupled system, which consisted of nitrate-dependent
iron-oxidizing (NDFO) bacteria, sulfur-oxidizing bacteria (SOB), and DNRA bacteria.
When the initial tetracycline concentration was 50 mg/L, higher NO3
- removal efficiency
(>98%) and higher NO3
- removal rate constant (0.54 d-1
) were shown in the IAD system,
compared with Na2S2O3-based system. The ameliorative autotrophic denitrification
performance in the IAD system under high tetracycline stress was due to the effective
removal of TC by FeS through rapid adsorption and reduction. As a result, simultaneous
tetracycline and nutrients (NO3
- and PO4
3-
) removal was achieved in the IAD system.
This PhD research provides fundamental insights into iron sulfides-based autotrophic
denitrification and would make significant contributions to wastewater treatment to meet
more stringent nutrient permits and greatly lower carbon footprints. It will also open new
horizons for removing emerging contaminants from wastewaters.