Robustness of the synergistic partial-denitrification, anammox, and fermentation process for treating domestic and nitrate wastewaters under fluctuating C/N ratios.

The synergistic partial-denitrification, anammox, and fermentation (SPDAF) process presents a promising solution to treat domestic and nitrate wastewaters. However, its capability to handle fluctuating C/N ratios (the ratios of COD to total inorganic nitrogen) in practical applications remains uncertain. In this study, the SPDAF process was operated for 236 days with C/N ratios of 0.7-3.5, and a high and stable efficiency of nitrogen removal (84.9 ± 7.8%) was achieved. The denitrification and anammox contributions were 6.1 ± 7.1% and 93.9 ± 7.1%, respectively. Batch tests highlighted the pivotal role of in situ fermentation at low biodegradable chemical oxygen demand (BCOD)/NO3- ratios. As the BCOD/NO3- ratios increased from 0 to 6, the NH4+ and NO3- removal rates increased, while the anammox contribution decreased from 100% to 80.1% but remained the primary pathway of nitrogen removal. The cooperation and balanced growth of denitrifying bacteria, anammox bacteria, and fermentation bacteria contributed to the system's robustness under fluctuating C/N ratios.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment.

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Insight into the potentiality of nano zero-valent iron on enhancing the nitrite accumulation and phosphorus removal performance of endogenous partial denitrification systems.

Endogenous partial denitrification (EPD) has drawn a lot of interest due to its abundant nitrite (NO2--N) accumulation capacity. However, the poor phosphate (PO43--P) removal rate of EPD restricts its promotion and application. In this study, the potentiality of various nano zero-valent iron (nZVI) concentrations (0, 20, 40, and 80 mg/L) on NO2--N accumulation and PO43--P removal in EPD systems had been investigated. Results showed that nZVI improved NO2--N accumulation and PO43--P removal, with the greatest nitrate-to-nitrite transformation ratio (NTR) and PO43--P removal rate of 97.74 % and 64.76 % respectively at the optimum nZVI level (80 mg/L). Microbial community analysis also proved that nZVI had a remarkable influence on the microbial community of EPD. Candidatus_Competibacter was contribute to NO2--N accumulation which was enriched from 24.74 % to 40.02 %. The enrichment of Thauera, Rhodobacteraceae, Pseudomonas were contributed to PO43--P removal. The chemistry of nZVI not only compensated for the deficiency of biological PO43--P removal, but also enhanced NO2--N enrichment. Therefore, nZVI had the huge potentiality to improve the operational performance of the EPD system.