Key Takeaways & Executive Findings
- •• • At NLR < 1,155 mg·(L·d)−1, PEF (1.5 V, 4 h/cycle) increased TRE by 7.5–17.0%, SAA by 21–71%, and EPS by 54–77% compared to control, indicating enhanced metabolic activity and sludge stability. • • At NLR > 1,320 mg·(L·d)−1, PEF enhancement was negated by nitrite toxicity; increased membrane permeability facilitated toxic influx, leading to reduced performance and microbial richness, revealing a 'double-edged sword' effect. • • PEF enriched Planctomycetes and key anammox genera (Candidatus Brocadia, Candidatus Jettenia) at low-to-moderate NLR, while at high NLR, community diversity and richness declined, indicating load-dependent microbial responses. • • Multivariate analyses (PCA, RDA) identified PEF as the primary driver of community shifts at low NLR, but nitrite concentration became the dominant factor at high NLR, underscoring the need for load-adaptive PEF control strategies.
Abstract
This study investigated the effects of a ring-shaped pulsed electric field (PEF) (1.5 V, 4 h on-time per cycle) on nitrogen removal performance and microbial community structure of anammox granular sludge (AnGS). Two anaerobic sequencing batch reactors (R1 control, R2 with PEF) were operated under stepwise increasing nitrogen loading rates (NLR). At NLR below 1,155 mg·(L·d)−1, R2 exhibited total nitrogen removal efficiency (TRE) 7.5%–17.0% higher than R1, with biomass, specific anammox activity (SAA), and extracellular polymeric substances (EPS) increased by 5%–7%, 21%–71%, and 54%–77%, respectively. However, at NLR above 1,320 mg·(L·d)−1, the toxic effect of nitrite dominated, and PEF enhancement diminished or even reversed to inhibition. Microbial community analysis revealed that at low-to-moderate NLR, PEF increased the relative abundance of Planctomycetes and key anammox bacteria (Candidatus Brocadia and Candidatus Jettenia), along with enhanced community richness (Chao1) and diversity (Shannon/Simpson indices). At high NLR, PEF decreased microbial richness compared to R1. Principal component analysis and redundancy analysis indicated that PEF was the key factor driving community differences at low-to-moderate NLR, whereas nitrite concentration became the dominant factor at high NLR. This study provides theoretical support for enhancing the resilience and engineering application of anammox processes.
1. Introduction
Anammox technology offers a sustainable alternative to conventional nitrification-denitrification for nitrogen removal, with advantages of low energy consumption, no organic carbon requirement, and low sludge production. However, the slow growth rate of anammox bacteria (AnAOB) and their high sensitivity to substrate inhibition, particularly nitrite, limit process stability under fluctuating nitrogen loads. Existing strategies such as reactor optimization, sludge acclimation, and growth factor addition have shown limited success in enhancing resilience to high nitrogen loading rates.
Pulsed electric fields (PEF) have emerged as a promising approach to stimulate microbial activity via electroporation-induced membrane permeability changes. Prior studies have explored PEF effects on AnAOB activity, but systematic understanding of its impact under high nitrogen stress remains lacking. This study addresses this gap by applying a ring-shaped PEF (1.5 V, 4 h/cycle) to anammox granular sludge reactors across a range of nitrogen loading rates, revealing both stimulatory and inhibitory effects depending on NLR, and providing mechanistic insights into microbial community responses.
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WANG Xuzhong, ZHANG Ning, ZHANG Pengyu, MIAO Juan, ZHANG Ruichang, ZHOU Ming, WEI Xuefeng (2026). Pulsed Electric Field Enhancement of Nitrogen Removal Performance and Microbial Community Structure Response in Anammox Granular Sludge. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202507111
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Frequently Asked Questions
What is the optimal voltage and exposure time for PEF to enhance anammox activity without causing cell damage?
This study used 1.5 V with 4 h on-time per cycle (8-h cycle). At NLR below 1,155 mg·(L·d)−1, this enhanced SAA by 21–71% and TRE by 7.5–17%. However, at NLR above 1,320 mg·(L·d)−1, the same PEF conditions led to inhibition, suggesting that optimal parameters depend on loading and nitrite concentration.
How does PEF affect the microbial community structure under different nitrogen loading rates?
At low-to-moderate NLR (<1,155 mg·(L·d)−1), PEF increased the relative abundance of Planctomycetes and key anammox genera (Candidatus Brocadia, Candidatus Jettenia), and enhanced Chao1 and Shannon/Simpson indices. At high NLR (>1,320 mg·(L·d)−1), PEF decreased microbial richness compared to control, indicating a negative impact under nitrite stress.
What is the mechanism behind the 'double-edged sword' effect of PEF at high nitrogen loads?
PEF increases cell membrane permeability, which at low NLR facilitates substrate uptake and EPS secretion, enhancing anammox activity. At high NLR, elevated nitrite concentrations become toxic; increased permeability allows more nitrite to enter cells, exacerbating inhibition and reducing performance and microbial diversity.
Can PEF be applied to full-scale anammox reactors to improve resilience to shock loads?
The study suggests PEF can improve performance at moderate loads, but at high loads it may be detrimental. Therefore, PEF should be dynamically adjusted based on NLR and nitrite levels. Further research is needed to develop control strategies for full-scale application, considering energy costs and electrode fouling.
What are the implications of EPS increase for sludge granulation and stability?
EPS increased by 54–77% under PEF at low NLR, which likely enhances sludge granulation and structural stability, improving settling and resistance to shear stress. This is beneficial for long-term reactor operation, but excessive EPS could also affect mass transfer.
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