Key Takeaways & Executive Findings
- •• • High C/N (≈28.0:1) with nitrogen-rich wastewater reuse (HRN) cut cumulative N2O emissions by 53.38% and NH3 by 62.15% versus low C/N reuse (LRN), directly mitigating odor and greenhouse gas release in composting operations. • • HRN increased final compost nitrogen content to 4691.27 mg/kg, 3.9% higher than HRW (4514.96 mg/kg), demonstrating enhanced nitrogen conservation and fertilizer value under carbon-sufficient conditions. • • Low C/N (≈20:1) with nitrogen-rich wastewater reuse (LRN) exacerbated NH3 and N2O emissions by 26.43% and 112.99% respectively versus LRW, highlighting carbon limitation as a critical operational threshold for nitrogen recycling. • • All treatments achieved pH (8.17–8.48) and GI (90.85%–122.96%) within national organic fertilizer standards, confirming that nitrogen-rich wastewater reuse does not compromise final compost maturity when C/N is managed.
Abstract
Reducing ammonia emissions and recovering lost nitrogen are critical for enhancing nitrogen content in compost. Biological trickling filters, as end-of-pipe odor control, retain ammonia nitrogen in effluent, offering a reuse pathway. However, the impact of nitrogen-rich wastewater reuse within the optimal C/N range (20.0:1–30.0:1) remains unclear. This study composted biogas residue, sawdust, food waste, and mushroom residue, setting initial C/N as the control variable. Four groups were established: low C/N with nitrogen-rich wastewater (LRN), low C/N with deionized water (LRW), high C/N with nitrogen-rich wastewater (HRN), and high C/N with deionized water (HRW). Simulated wastewater (2000 mg/L NH4+-N and 2000 mg/L NO2−-N) was recycled. Results showed no inhibition of final maturity; pH (8.17–8.48) and seed germination index (GI) (90.85%–122.96%) met organic fertilizer standards. HRN reduced cumulative total greenhouse gases, N2O, and NH3 by 20.32%–30.35%, 0.67%–53.38%, and 52.14%–62.15% compared to LRN and LRW. Although HRN emissions were slightly higher than HRW (total GHGs +4.56%, NH3 +4.99%), HRN final nitrogen content (4691.27 mg/kg) exceeded HRW (4514.96 mg/kg), attributed to sufficient carbon enhancing microbial assimilation. Conversely, low C/N with nitrogen-rich wastewater increased NH3 and N2O emissions (LRN vs LRW: +26.43% and +112.99%) due to carbon limitation. Thus, high initial C/N with nitrogen-rich wastewater reuse effectively reduces gaseous nitrogen loss and greenhouse gas emissions while maintaining compost maturity.
1. Introduction
Composting of organic wastes is often hampered by nitrogen losses through ammonia volatilization and greenhouse gas emissions, reducing fertilizer value and contributing to air pollution. Biological trickling filters effectively capture ammonia from exhaust air, but the resulting nitrogen-rich effluent poses a disposal challenge. Reusing this effluent as a nitrogen source could close the loop, yet its impact on composting performance, particularly within the recommended C/N range of 20:1 to 30:1, has been insufficiently characterized. Prior studies have shown that excessive nitrogen addition can lead to ammonia accumulation and incomplete denitrification, increasing N2O emissions, especially when carbon is limiting.
This study systematically evaluates the effects of nitrogen-rich wastewater reuse on composting under two C/N regimes (low ≈20:1, high ≈28:1). By comparing treatments with recycled nitrogen-rich wastewater versus deionized water, the research isolates the influence of external nitrogen on humification, nitrogen transformation, and greenhouse gas emissions. The findings reveal that high C/N conditions provide sufficient carbon to assimilate added nitrogen, reducing gaseous losses and enhancing nitrogen retention, whereas low C/N conditions exacerbate emissions. These results offer actionable guidance for optimizing nitrogen recycling in composting facilities, balancing odor control, greenhouse gas mitigation, and product quality.
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ZHANG Jingmin, XIE Dong, TANG Shizhao, MA Ruichuan, GAO Ming, WU Chuanfu (2026). Effects of Nitrogen-Rich Wastewater Reuse on Aerobic Fermentation Performance of Substrates with Different Carbon-Nitrogen Ratios. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607014
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Frequently Asked Questions
What is the optimal initial C/N ratio for nitrogen-rich wastewater reuse to minimize N2O and NH3 emissions without compromising compost maturity?
An initial C/N of approximately 28.0:1 (HRN) is optimal. Compared to low C/N (≈20:1) reuse, HRN reduced cumulative N2O and NH3 emissions by 53.38% and 62.15%, respectively, while achieving final pH (8.17–8.48) and GI (90.85%–122.96%) within organic fertilizer standards.
How does nitrogen-rich wastewater reuse affect nitrogen retention in the final compost product?
Under high C/N (HRN), final nitrogen content reached 4691.27 mg/kg, which is 3.9% higher than the control (HRW: 4514.96 mg/kg). This is attributed to sufficient carbon promoting microbial nitrogen assimilation. In contrast, low C/N (LRN) led to nitrogen losses via NH3 and N2O emissions.
What are the trade-offs between greenhouse gas emissions and nitrogen recovery when reusing nitrogen-rich wastewater?
At high C/N, HRN slightly increased total greenhouse gas and NH3 emissions by 4.56% and 4.99% compared to HRW, but this was offset by a 3.9% increase in nitrogen content. At low C/N, emissions increased dramatically (NH3 +26.43%, N2O +112.99%), indicating that carbon availability is a critical factor for balancing emissions and nitrogen recovery.
Does nitrogen-rich wastewater reuse affect compost maturity indicators such as pH and seed germination index?
No. All treatments met national standards: pH ranged from 8.17 to 8.48 (standard 5.5–8.5) and GI ranged from 90.85% to 122.96% (standard >70%). However, low C/N treatments showed a 13.7% decrease in PI and 26.11% decrease in GI compared to controls, suggesting a slight impact on humification kinetics.
What are the implications for scaling up nitrogen-rich wastewater reuse in industrial composting?
Industrial facilities should maintain initial C/N above 25:1 to ensure sufficient carbon for nitrogen assimilation. This strategy can reduce odor and greenhouse gas emissions while increasing fertilizer nitrogen content, potentially lowering the need for synthetic nitrogen supplements. However, careful monitoring of C/N is essential to avoid emission spikes.
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