Effects of salinity on nitrite and elemental sulfur accumulation in a double short-cut sulfur autotrophic denitrification process

Sulfide-based autotrophic denitrification process with efficient nitrogen removal under high salinity stress: Threshold behaviors and recovery enhanced via glutamate supplementation

The sulfide-based autotrophic denitrification (SAD) has become one of the hotspots in the wastewater treatment due to the urgent requirement for carbon emission reduction. However, it faces a great challenge from the high salinity of nitrogenous wastewaters. In this study, a SAD system was investigated to treat the nitrogenous wastewater under high salinity stress, achieving 99.82 % nitrogen removal at 2.57 % salinity. With the further salinity elevation, the SAD system suffered collapse at the salinity of 5.14 %wt, while it was partially reversed by 1 mmol/L glutamate dosing. The good adaptation of SAD system to the high salinity stress was ascribed to the enrichment of salinity-tolerant microbial populations, as well as limited Na+ accumulation and the antioxidant metabolic compensation. Proteobacteria and Campilobacterota were identified as the dominant phyla, and the relative abundance of Proteobacteria were observed to increase with the whole salinity elevation. The high salinity stress on SAD system was ascribed to the combined effect of osmotic stress and ionic toxicity, and the ionic toxicity was inferred as the primary contributor to the performance collapse by inducing the sharp increase of intracellular reactive oxygen species and cellular rupture. Glutamate supplementation mitigated reactive oxygen species -induced oxidative stress and DNA damage, resulting in partial recovery of denitrification performance (60.56 ± 2.64 %). The microbial network analysis and community assembly supported above conclusions. The information of this study is helpful for the innovation and application of SAD processes, even other bioprocesses under the high salinity stress.

A critical review of sulfur autotrophic denitrification coupled with anammox

Anaerobic ammonium oxidation (anammox) is an environmentally sustainable process with high nitrogen removal efficiency; however, nitrite serves as the limiting factor in this process. Sulfur autotrophic denitrification (SADN) employs sulfide as an electron donor to reduce nitrate to nitrite. Therefore, coupling SADN and anammox (SDA) can improve the nitrogen removal efficiency. This review analyzes the coupling mechanisms of three common SDA systems: S0-SDA, S2--SDA, and S2O32--SDA, as well as the dominant genera in the SDA process. This paper summarizes the influence of key operating parameters, including influent nitrogen loading, pH, and the N/S ratio, on the nitrogen removal efficiency of the SDA process and the effect of S2O32- addition on microbial structure in anammox. The application of the SDA process in real wastewater treatment is analyzed in detail. Overall, this overview of the SDA process plays an important role in the direction of the SDA development.

Performance and microbial mechanism in sulfide-driven autotrophic denitrification by different inoculation sources in face of various sulfide and sulfate stress

To develop a reliable sulfide (S2-) autotrophic denitrification (SAD) process under S2- and SO42- salinity stresses, the biofilm performance and microbial mechanisms were comparatively studied using different inocula of activated sludge (AS) and intertidal sediment (IS). Biofilm IS enriched more denitrification genes (0.34 %) and S2- oxidation genes (0.29 %) than those with AS. Higher denitrification performance was obtained under S2- (100 mg/L) and SO42- (5-15 g/L Na2SO4) stresses, but no significantly differences were observed under levels of 0-200 mg/L S2- and 30 g/L Na2SO4. Notably, biofilm samples in SAD systems with IS still had more S2- oxidation genes at high S2- levels of 100-200 mg/L and Na2SO4 level of 30 g/L. The key functional genus Thiobacillus accumulated well at 30 g/L Na2SO4, but was strongly inhibited at 200 mg/L S2-. The findings were advantage to SAD application under sulfide and salinity stresses.

Effects of O2 on accumulation of nitrous and elemental sulfur and microbial community structure in double short-cut sulfur autotrophic denitrification system

Understanding the effect of O2 on the accumulation characteristics of NO2--N and S0 in the sulfur autotrophic denitrification (DSSADN) system is crucial for enhancing the denitrification efficiency of partial nitrification-anammox using DSSADN. The results revealed that in an environment without O2 entry, the NO2--N accumulation efficiency (NiAE) and S0 accumulation efficiency (S0AE) of the DSSADN system reached 89.40 % and 93.41 %, respectively. Once system entered O2, ORP value kept increasing. When ORP increased to -59.9 mV (DO = 0.1 mg/L), soxB and nirK gene expression rose and as well NiAE and S0AE continuously decreased to 48.13 % and 29.35 %. When ORP was above 30.9 mV (DO >0.2 mg/L) but below 81.0 mV (DO<0.4 mg/L), narG gene expression reduced and the relatively high sqr gene expression allowed NiAE and S0AE remained at 45.08 % and 33.31 %. O2 promoted the synergistic effect of Thiobacillus and Azoarcus without the proliferation of nitrite oxidizing bacteria.

Comparison of nitrification performance in SBR and SBBR with response to NaCl salinity shock: Microbial structure and functional genes

Ammonia removal by nitrifiers at the extremely high salinity poses a great challenge for saline wastewater treatment. Sequencing batch reactor (SBR) was conducted with a stepwise increase of salinity from 10 to 40 g-NaCl·L-1, while sequencing batch biofilm reactor (SBBR) with one-step salinity enhancement, their nitrification performance, microbial structure and interaction were evaluated. Both SBR and SBBR can achieve high-efficiency nitrification (98% ammonia removal) at 40 g-NaCl·L-1. However, SBBR showed more stable nitrification performance than SBR at 40 g-NaCl·L-1 after a shorter adaptation period of 4-15 d compared to previous studies. High-throughput sequencing and metagenomic analysis demonstrated that the abundance and capability of conventional ammonia-oxidizing bacteria (Nitrosomonas) were suppressed in SBBR relative to SBR. Gelidibacter, Anaerolineales were the predominant genus in SBBR, which were not found in SBR. NorB and nosZ responsible for reducing NO to N2O and reducing N2O to N2 respectively had s strong synergistic effect in SBBR. This study will provide a valuable reference for the startup of nitrification process within a short period of time under the extremely high NaCl salinity.

Salt stimulates sulfide-driven autotrophic denitrification: Microbial network and metagenomics analyses

Sulfur autotrophic denitrification (SADN) is a promising biological wastewater treatment technology for nitrogen removal, and its performance highly relies on the collective activities of the microbial community. However, the effect of salt (a prevailing characteristic of some nitrogen-containing industrial wastewaters) on the microbial community of SADN is still unclear. In this study, the response of the sulfide-SADN process to different salinities (i.e., 1.5 % salinity, 0.5 % salinity, and without salinity) as well as the involved microbial mechanisms were investigated by molecular ecological network and metagenomics analyses. Results showed that the satisfactory nitrogen removal efficiency (>97 %) was achieved in the sulfide-SADN process (S/N molar ratio of 0.88) with 1.5 % salinity. In salinity scenarios, the genus Thiobacillus significantly proliferated and was detected as the dominant sulfur-oxidizing bacteria in the sulfide-SADN system, occupying a relative abundance of 29.4 %. Network analysis further elucidated that 1.5 % salinity had enabled the microbial community to form a more densely clustered network, which intensified the interactions between microorganisms and effectively improved the nitrogen removal performance of the sulfide-SADN. Metagenomics sequencing revealed that the abundance of functional genes encoding for key enzymes involved in SADN, dissimilatory nitrate reduction to ammonium, and nitrification was up-regulated in the 1.5 % salinity scenario compared to that without salinity, stimulating the occurrence of multiple nitrogen transformation pathways. These multi-paths contributed to a robust SADN process (i.e., nitrogen removal efficiency >97 %, effluent nitrogen <2.5 mg N/L). This study deepens our understanding of the effect of salt on the SADN system at the community and functional level, and favors to advance the application of this sustainable bioprocess in saline wastewater treatment.

Salinity stress results in ammonium and nitrite accumulation during the elemental sulfur-driven autotrophic denitrification process

In this study, we investigated the effects of salinity on elemental sulfur-driven autotrophic denitrification (SAD) efficiency, and microbial communities. The results revealed that when the salinity was ≤6 g/L, the nitrate removal efficiency in SAD increased with the increasing salinity reaching 95.53% at 6 g/L salinity. Above this salt concentration, the performance of SAD gradually decreased, and the nitrate removal efficiency decreased to 33.63% at 25 g/L salinity. Approximately 5 mg/L of the hazardous nitrite was detectable at 15 g/L salinity, but decreased at 25 g/L salinity, accompanied by the generation of ammonium. When the salinity was ≥15 g/L, the abundance of the salt-tolerant microorganisms, Thiobacillus and Sulfurimonas, increased, while that of other microbial species decreased. This study provides support for the practical application of elemental sulfur-driven autotrophic denitrification in saline nitrate wastewater.

Autotrophic denitrification based on sulfur-iron minerals: advanced wastewater treatment technology with simultaneous nitrogen and phosphorus removal

Autotrophic denitrification technology has many advantages, including no external carbon source addition, low sludge production, high operating cost efficiency, prevention of secondary sewage pollution, and stable treatment efficiency. At present, the main research on autotrophic denitrification electron donors mainly includes sulfur, iron, and hydrogen. In these autotrophic denitrification systems, pyrite has received attention due to its advantages of easy availability of raw materials, low cost, and pH stability. When pyrite is used as a substrate for autotropic denitrification, sulfide (S2-) and ferrous ion (Fe2+) in the substrate will provide electrons to convert nitrate (NO3-) in sewage first to nitrite (NO2-), then to nitrogen (N2), and finally to discharge the system. At the same time, sulfide (S2-) loses electrons to sulfate (SO42-) and ferrous ion (Fe2+) loses electrons to ferric iron (Fe3+). Phosphates (PO43-) in wastewater are chemically combined with ferric iron (Fe3+) to form ferric phosphate (FePO4) precipitate. This paper aims to provide a detailed and comprehensive overview of the dynamic changes of nitrogen (N), phosphorus (P), and other substances in the process of sulfur autotrophic denitrification using iron sulfide, and to summarize the factors that affect wastewater treatment in the system. This work will provide a relevant research direction and theoretical basis for the field of sulfur autotrophic denitrification, especially for the related experiments of the reaction conversion of various substances in the system.

Sulfur autotrophic denitrification as an efficient nitrogen removals method for wastewater treatment towards lower organic requirement: A review

The sulfur autotrophic denitrification (SADN) process is an organic-free denitrification process that utilizes reduced inorganic sulfur compounds (RISCs) as the electron donor for nitrate reduction. It has been proven to be a cost-effective and environment-friendly approach to achieving carbon neutrality in wastewater treatment plants. However, there is no consensus on whether SADN can become a dominant denitrification process to treat domestic wastewater or industrial wastewater if organic carbon is desired to be saved. Through a comprehensive summary of the SADN process and extensive discussion of state-of-the-art SADN-based technologies, this review provides a systematic overview of the potential of the SADN process as a sustainable alternative for the heterotrophic denitrification (HD) process (organic carbons as electron donor). First, we introduce the mechanism of the SADN process that is different from the HD process, including its transformation pathways based on different RISCs as well as functional bacteria and key enzymes. The SADN process has unique theoretical advantages (e.g., economy and carbon-free, less greenhouse gas emissions, and a great potential for coupling with novel autotrophic processes), even if there are still some potential issues (e.g., S intermediates undesired production, and relatively slow growth rate of sulfur-oxidizing bacteria [SOB]) for wastewater treatment. Then we present the current representative SADN-based technologies, and propose the outlooks for future research in regards to SADN process, including implement of coupling of SADN with other nitrogen removal processes (e.g., HD, and sulfate-dependent anaerobic ammonium oxidation), and formation of SOB-enriched biofilm. This review will provide guidance for the future applications of the SADN process to ensure a robust-performance and chemical-saving denitrification for wastewater treatment.

Effect of salinity stress on nitrogen and sulfur removal performance of short-cut sulfur autotrophic denitrification and anammox coupling system

The effects of salinity on anaerobic nitrogen and sulfide removal were investigated in a coupled anammox and short-cut sulfur autotrophic denitrification (SSADN) system. The results revealed that salinity had significant nonlinear effects on the nitrogen and sulfur transformations in the coupled system. When the salinity was <2 %, the anammox and SSADN activities increased with increasing salinity, and the total nitrogen removal rate, S⁰ production rate, and nitrite production rate were 0.41 kg/(m³·d), 0.37 kg/(m³·d), and 0.28 kg/(m³·d), respectively. With continuous increase of salinity, the performances of the anammox and SSADN gradually decreased, and the three indicators decreased to 0.14 kg/(m³·d), 0.22 kg/(m³·d), and 0.14 kg/(m³·d) at 5 % salinity, respectively. When the salinity reached 5 %, the nitrogen removal contribution of anammox decreased to 68.4 %, while the contribution of the sulfur autotrophic denitrification increased to 31.6 %. The coupled system recovered in a short time after alleviation of the salinity stress, and the SSADN activity recovery was faster than anammox. The microbial community structure and functional microbial abundance in the coupled system changed significantly with increasing salinity, and the functional microbial abundance after recovery was considerably different from the initial state.