Insight into the shaping of microbial communities in element sulfur-based denitrification at different temperatures

A novel dynamic membrane-equipped element sulfur-based denitrification reactor for efficient and easily maintainable treatment of high-nitrate wastewater

Using powdered sulfur (S0) with high specific surface area enables high efficiency in an elemental sulfur-based denitrification (ESDeN) reactor but faces challenges with S0 retention. While integrating the ESDeN process with microfiltration membranes (MM) has been shown to effectively reject S0 powder, severe membrane fouling and high membrane costs restrict its practical application. This study, for the first time, reports a dynamic membrane-equipped ESDeN (ESDeN-DM) reactor. The DM was formed by in-situ pre-coating a solid mixture (particle size: 0.4 μm to 110 μm) of S0 powder and denitrifying sludge onto inexpensive nylon fabrics. Initially, we optimized the DM formation conditions, determining that a nylon fabric pore size of 25 μm and a pre-coating flux of 300 L m-² h-1 resulted in permeate turbidity lower than 5 NTU within 60 mins. Subsequently, we identified the duration (12.5 days) of a transmembrane pressure (TMP)-dependent run (≤30 KPa) for the reactor and found that the TMP increase was related to the thickening and densification of the cake layer. Finally, we conducted a comparative examination of the ESDeN-DM reactor and the conventional ESDeN-MM reactor during long-term operation. The results demonstrated that the ESDeN-DM reactor achieved a comparable denitrification rate to the ESDeN-MM reactor (both with the maximum value more than 3 kg N m⁻3 d⁻¹) but exhibited significantly better membrane fouling tolerance (56 % longer TMP-dependent run time), easier regeneration of specific flux (online backwash versus offline chemical cleaning), and exceptional cost-effectiveness (over 90 % total cost reduction). This study presents a highly efficient and easily maintained membrane-equipped ESDeN process with great potential for treating high-nitrate industrial wastewater.

Unraveling nitrogen removal performance during increasing loading rates in simultaneous nitrification and autotrophic denitrification: A functional and ecological analysis approach

Nitrogen contamination of water sources poses significant environmental and health risks. The sulfur-driven simultaneous nitrification and autotrophic denitrification (SNAD) process offers a cost-effective solution, as it operates in a single reactor, requires no organic carbon addition, and produces minimal sludge. However, this process remains underexplored, with microbial population dynamics, their interactions, and their implications for process efficiency not yet fully understood. To address this gap, this study analyzed microbial populations in a 0.8 L fluidized bed reactor performing sulfur-driven SNAD under increasing nitrogen loading rates (NLR), ranging from 11 to 105 g N/m3 d. The process achieved 93.5 % total nitrogen and 95.1 % ammonium removal at a hydraulic residence time (HRT) of 1.8 days. However, when the HRT was reduced to 0.96 days, nitrate removal instability occurred, reducing the nitrate removal efficiency to 42 %. Although increasing the HRT improved performance, two additional instability events were observed in subsequent stages at HRTs of 1.2 and 1.03 days, where nitrate removal efficiencies dropped to 11 % and 39 %, respectively. Functional analysis showed that NLR negatively impacted the proportion of sulfur-oxidizing bacteria, which was correlated with high nitrate levels in the effluent, although ammonium oxidation remained stable. Ecological network analysis revealed positive interactions between ammonia-oxidizing and heterotrophic bacteria, supporting nitrification stability. However, it also uncovered negative interactions between heterotrophic bacteria and sulfur-oxidizing denitrifiers, such as Dyella and Thiobacillus, suggesting these negative interactions contributed to temporary nitrogen removal problems in the system. This study highlights the importance of functional microbial and ecological network analyses over traditional metataxonomic approaches in understanding SNAD processes.

Optimized start-up strategies for elemental sulfur packing bioreactor achieving effective autotrophic denitrification

The start-up efficiency of the elemental sulfur packing bioreactor (S0PB) is constrained by the slow growth kinetics of autotrophic microorganisms, which is essentially optimized. This study aims to optimize start-up procedures and offer scientific guidance for the practical applications of S0PB. Through comparing the start-up efficiencies under various conditions related to inoculation, backwashing, and EBCT, it was found that these conditions did not significantly influence start-up time, but they did impact denitrification performance in detail. Using activated sludge as the inoculum was not recommended as the 2.5 ± 0.2 mg-N/L higher nitrite accumulation and 26.0 ± 5.1 % lower TN removal rate, compared to self-enrichment. Starting with a long-to-short EBCT (1 → 0.33 h) achieved higher nitrate removal of 11.5 ± 0.6 mg-N/L and eliminated nitrite accumulation compared to constantly short EBCT (0.33 h) conditions. Daily and postponed backwashing were suggested for long-to-short EBCT and constantly short EBCT start-up, respectively. Enrichment of Sulfurimonas was beneficial for the effective nitrite reduction process.

Synergistic between autotrophic and heterotrophic microorganisms for denitrification using bio-S as electron donor

In recent years, biological sulfur (bio-S) was employed in sulfur autotrophic denitrification (SAD) in which autotrophic Thiobacillus denitrificans and heterotrophic Stenotrophomonas maltophilia played a key role. The growth pattern of T.denitrificans and S.maltophilia exhibited a linear relationship between OD₆₀₀ and CFU when OD₆₀₀ < 0.06 and <0.1, respectively. When S.maltophilia has applied alone, the NorBC and NosZ were undetected, and denitrification was incomplete. The DsrA of S.maltophilia could produce sulfide as an alternative electron donor for T.denitrificans. Even though T.denitrificans had complete denitrification genes, its efficiency was low when used alone. The interaction of T.denitrificans and S.maltophilia reduced nitrite accumulation, leading to complete denitrification. A sufficient quantity of S.maltophilia may trigger the autotrophic denitrification activity of T.denitrificans. When the colony-forming units (CFU) ratio of S.maltophilia to T.denitrificans was reached at 2:1, the highest denitrification performance was achieved at 2.56 and 12.59 times higher than applied alone. This research provides a good understanding of the optimal microbial matching for the future application of bio-S.