The Study on Nitrogen Removal Enhancement from Secondary Biochemical Effluent by Sulfur Autotrophic Denitrification Composite Filler

Yi Rong; Hua Fang

doi:10.30560/sdr.v7n2p71

Yi Rong School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China
Hua Fang School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China

DOI: https://doi.org/10.30560/sdr.v7n2p71

Keywords: sulfur-iron-based filler, synergistic denitrification, microbial community structure

Abstract

Experiments were conducted using simulated secondary effluent from wastewater treatment plants. A composite filler was prepared by mixing sulfur and pyrite (FeS₂) as electron donors for microorganisms to evaluate the nitrate removal efficiency under different filler compositions. Three iron-carbon-based composite sulfur autotrophic denitrification fillers were synthesized with varying pyrite-to-sulfur mass ratios (2:1, 1:1, and 1:2, labeled as FS1, FS2, and FS3, respectively). A synergistic autotrophic-heterotrophic denitrification biofilter system was established to compare the operational conditions and nitrogen removal performance among mixed autotrophic-heterotrophic, heterotrophic, and autotrophic denitrification processes. The results showed that the FS2 system (FeS₂:S = 1:1) achieved the shortest start-up time (7 days), 33% and 50% faster than FS1 (FeS₂:S = 2:1) and FS3 (FeS₂:S = 1:2), respectively. During the start-up phase, FS2 exhibited the highest NO₃⁻-N removal rate (1.82 mg/(L·h)), significantly outperforming FS1 (1.25 mg/(L·h)) and FS3 (0.98 mg/(L·h)). The optimal HRT for pyrite-based systems was 24 h, with FS2 achieving the highest NO₃⁻-N removal efficiency (94.2%), followed by FS3 (84.2%) and the pure sulfur system (80%). When HRT was reduced to 12 h, FS2 maintained a removal efficiency of 81.3%, while FS1 and FS3 declined to 78.5% and 65.2%, respectively. Within pH 6.5–8. 0, FS2 demonstrated stable NO₃⁻-N removal (95%–98%) with minimal effluent pH fluctuation (±0.3 from initial pH 7.0), whereas FS1 and FS3 exhibited larger pH variations (±1.2 and ±1.8, respectively), indicating inferior buffering capacity. The FS2 filler (FeS₂:S = 1:1) exhibited superior denitrification efficiency, rapid system start-up, and robust pH stability, making it a promising candidate for enhancing nitrogen removal in secondary effluent treatment.

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