Effectiveness of Exogenous Fe2+ on Nutrient Removal in Gravel-Based Constructed Wetlands

Liping Tian; Baixing Yan; Yang Ou; Huiping Liu; Lei Cheng; Peng Jiao

doi:10.3390/ijerph19031475

Effectiveness of Exogenous Fe²⁺ on Nutrient Removal in Gravel-Based Constructed Wetlands

Int J Environ Res Public Health. 2022 Jan 28;19(3):1475. doi: 10.3390/ijerph19031475.

Authors

Liping Tian^{1

2}, Baixing Yan^{1

3}, Yang Ou^{1

3}, Huiping Liu⁴, Lei Cheng⁴, Peng Jiao⁵

Affiliations

¹ Key Laboratory of Wetland Ecology and Environment, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130102, China.
² University of Chinese Academy of Sciences, Beijing 100049, China.
³ Jilin Provincial Engineering Center of CWs Design in Cold Region & Beautiful Country Construction, Changchun 130102, China.
⁴ College of Plant Protection, Jilin Agricultural University, Changchun 130118, China.
⁵ College of Resources and Environment, Jilin Agricultural University, Changchun 130118, China.

Abstract

A group of microcosm-scale unplanted constructed wetlands (CWs) were established to evaluate the effectiveness of exogenous Fe²⁺ addition on ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and total phosphorus (TP) removal. The addition of Fe²⁺ concentrations were 5 mg/L (CW-Fe5), 10 mg/L (CW-Fe10), 20 mg/L (CW-Fe20), 30 mg/L (CW-Fe30), and 0 mg/L (CW-CK). The microbial community in CWs was also analyzed to reveal the enhancement mechanism of pollutant removal. The results showed that the addition of Fe²⁺ could significantly (p < 0.05) reduce the NO₃^--N concentration in the CWs. When 10 mg/L Fe²⁺ was added and the hydraulic retention time (HRT) was 8 h, the highest removal rate of NO₃^--N was 88.66%. For NH₄⁺-N, when the HRT was 8-24 h, the removal rate of CW-Fe5 was the highest (35.23% at 8 h and 59.24% at 24 h). When the HRT was 48-72 h, the removal rate of NH₄⁺-N in CWs with 10 mg/L Fe²⁺ addition was the highest (85.19% at 48 h and 88.66% and 72 h). The removal rate of TP in all CWs was higher than 57.06%, compared with CW-CK, it increased 0.63-31.62% in CWs with Fe²⁺ addition; the final effluent TP concentration in CW-Fe5 (0.13 mg/L) and CW-Fe10 (0.16 mg/L) met the class III water standards in Surface Water Environmental Quality Standards of China (GB3838-2002). Microbical diversity indexes, including Shannon and Chao1, were significantly lower (p < 0.05) in Fe²⁺ amended treatment than that in CW-CK treatment. Furthermore, phylum Firmicutes, family Carnobacteriaceae, and genus Trichococcus in Fe²⁺ amended treatments was significantly (p < 0.05) higher than that in CW-CK treatment. Fe³⁺ reducing bacteria, such as Trichococcus genus, belonging to the Carnobacteriaceae in family-level, and Lactobacillales order affiliated to Firmicutes in the phylum-level, can reduce the oxidized Fe³⁺ to Fe²⁺ and continue to provide electrons for nitrate. It is recommended to consider adding an appropriate amount of iron into the water to strengthen its purifying capacity effect for constructed artificial wetlands in the future.

Keywords: Sanjiang Plain; constructed wetlands; ferrous iron; nitrogen removal; phosphorus removal.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Ammonium Compounds*
Nitrogen / analysis
Nutrients
Waste Disposal, Fluid / methods
Wastewater
Wetlands*

Substances

Ammonium Compounds
Waste Water
Nitrogen