Surfactant enhances anaerobic fermentative hydrogen sulfide production: Changes in sulfur-containing organics structure and microbial community

Revealing the effect of Al2O3 on sulfur transformation in anaerobic sludge process

Al2O3, one multifunctional adsorbent and dehydrator, was widely recognized as a practical and environmentally friendly additive that enhances fermentation efficiency and facilitates the recovery of resources from waste-activated sludge (WAS). However, its potential harmful effects on WAS fermentation, such as the generation of hydrogen sulfide (H2S), have been previously overlooked. This study found that with the increase of Al2O3 dosage from 0 to 60 mg/g VSS, the maximum production of H2S decreased from 371.60 ± 3.72 × 10-4 to 303.36 ± 3.03 × 10-4 mg/g VSS. The study on the transformation of sulfur-containing compounds has identified that the primary cause for lowering the formation of hydrogen sulfide (H2S) is the inhibitory effect of aluminium oxide (Al2O3) on sulfate reduction. The mechanism analysis discovered that Al2O3 initially stimulated the functional groups and hydrogen bonding networks present in sludge EPS. This resulted in a 2.04 % rise in the content of C-C groups, a 7.78 % increase in the content of C-O-C groups, and a 4.24 % increase in the content of β-turn and α-Helix structures. This resulted in the fracturing of sludge EPS and the release of soluble metal ions such as aluminium, magnesium, and iron. The liberated metal ions facilitated the conversion of H2S gas and dissolved sulfide into metal sulfide, hence contributing significantly to the reduction of H2S gas emissions. Microbial community research revealed that the inclusion of Al2O3 enhanced the performance of methanogens (e.g., Methanothrix), but inhibited sulfate reducing bacteria (e.g., unclassified_c__Deltaproteobacteria). Additional examination of functional genes demonstrated that Al2O3 decreases the amount of functional genes involved in the hydrolysis of organic sulfur (such as MetQ, pepD, CDO1, yhdR, etc.). and sulfate reduction processes (sat, cysC, aprAB, dsrAB, etc.). These findings offer novel perspectives on the treatment of sludge using Al2O3 and could have substantial consequences for sludge treatment.

Enhancing hydrogen sulfide control in urban sewer systems using machine learning models: Development of a new predictive simulation approach by using boosting algorithm

Sewer networks are important urban infrastructure for transporting sewage to treatment plants, yet the generation of hydrogen sulfide within these systems poses significant challenges. This acidic toxic gas not only emits foul odors but also causes corrosion, necessitating effective control measures. Recent studies have introduced a modelling approach to predict and control the formation of hydrogen sulfide in sewer system. However, the conventional and mathematical models have demonstrated limitations in simulating non-linear data. Meanwhile, advanced (boosting) machine learnings are proving to be effective tools for forecasting complex data, making them particularly suitable for simulating of sulfide concentrations. In this work, we aimed to develop a novel approach to predict hydrogen sulfide formation in sewer systems. This work employed 11 machine learning models (4 boosting algorithms and 7 traditional algorithms) for over 700 datasets to analysis the correlations between the key sewer operational parameters (including pH, dissolved oxygen (DO), temperature, weather conditions, sulfate concentration, and ammonia levels) and hydrogen sulfide production. The results showed that eXtreme Gradient Boosting (XGBoost) has the highest prediction efficiency (R=0.97, RMSE=0.177 mg/L), outperformed other boosting and traditional methods. The newly developed boosting-based model successfully predicted sulfide formation in various sewer networks, validated against literature data (R> 0.9, RMSE of 0.24 mg/L), confirming its effectiveness for simulating hydrogen sulfide in sewer tunnels. The optimal conditions for minimizing total sulfide generation were identified by the XGBoost model. These findings have the potential to improve the control and operation of sewer system in the future.

Experimental study on the mechanism of biological hydrogen sulfide generation from organic sulfur-rich coal

Whether of primary or secondary origin, the presence of hydrogen sulfide (H2S) in coalbed methane (CBM) is commonly attributed to sulfate reduction facilitated by sulfate-reducing bacteria (SRB). However, the sulfate content in high-sulfur coal is exceptionally low, insufficient to function as a substrate for sulfate-reducing bacteria (SRB). In this study, an anaerobic digestion experiment was conducted with high-organic-sulfur coal collected from the Late Permian Longtan Formation in Guangxi Province as both the carbon and sulfur sources. The formation mechanism of H2S is revealed from the evolution rules of gas components, liquid organic matter, and microbial communities during the anaerobic digestion process. The findings indicate three distinct mechanisms contributing to the biological formation of H2S in coal seams: firstly, the degradation of readily degradable organic sulfur in coal by microorganisms possessing denitrification capabilities, primarily attributed to the activity of the Wolinella; secondly, The synergistic consortium involving SRB, Pseudomonas spp., and denitrifying Thiobacillus species mediates SO42- reduction and H₂S biogenesis through cross-metabolic interactions; thirdly, Methylotrophic methanogens employ the methyl groups of organic sulfides to produce CH4 and H2S simultaneously. Therefore, biological H2S can be generated under the presence of a sulfur source, appropriate temperature, and conducive environmental conditions. This comprehension will contribute valuable insights to the discourse on the generation and enrichment patterns of H2S in natural coalbed methane. Additionally, it can offer practical avenues for the prevention and control of H2S through technological approaches.

Mechanistic insights into Fe3O4-mediated inhibition of H2S gas production in sludge anaerobic digestion

The addition of iron-based conductive materials has been extensively validated as a highly effective approach to augment methane generation from anaerobic digestion (AD) process. In this work, it was additionally discovered that Fe3O4 notably suppressed the production of hazardous H2S gas during sludge AD. As the addition of Fe3O4 increased from 0 to 20 g/L, the accumulative H2S yields decreased by 89.2 % while the content of element sulfur and acid volatile sulfide (AVS) respectively increased by 55.0 % and 30.4 %. Mechanism analyses showed that the added Fe3O4 facilitated sludge conductive capacity, and boosted the efficiency of extracellular electron transfer, which accelerated the bioprocess of sulfide oxidation. Although Fe3O4 can chemically oxidize sulfide to elemental sulfur, microbial oxidation plays a major role in reducing H2S accumulation. Moreover, the released iron ions reacted with soluble sulfide, which promoted the chemical equilibrium of sulfide species from H2S to metal sulfide. Microbial analysis showed that some SRBs (i.e., Desulfomicrobium and Defluviicoccus) and SOB (i.e., Sulfuritalea) changed into keystone taxa (i.e., connectors and module hubs) in the reactor with Fe3O4 addition, showing that the functions of sulfate reduction and sulfur oxidation may play important roles in Fe3O4-present system. Fe3O4 presence also increased the content of functional genes encoding sulfide quinone reductase and flavocytochrome c sulfidedehydrogenase (e.g., Sqr and Fcc) that could oxidize sulfide to sulfur. The impact of other iron-based conductive material (i.e., zero-valent iron) was also verified, and the results showed that it could also significantly reduce H2S production. These findings provide new insights into the effect of iron-based conductive materials on anaerobic process, especially sulfur conversion.

How Does Triclocarban Affect Sulfur Transformation in Anaerobic Systems?

Triclocarban (TCC), as a typical antimicrobial agent, accumulates at substantial levels in natural environments and engineered systems. This work investigated the impact of TCC on anaerobic sulfur transformation, especially toxic H2S production. Experimental findings revealed that TCC facilitated sulfur flow from the sludge solid phase to liquid phase, promoted sulfate reduction and sulfur-containing amino acid degradation, and largely improved anaerobic H2S production, i.e., 50-600 mg/kg total suspended solids (TSS) TCC increased the cumulative H2S yields by 24.76-478.12%. Although TCC can be partially biodegraded in anaerobic systems, the increase in H2S production can be mainly attributed to the effect of TCC rather than its degradation products. TCC was spontaneously adsorbed by protein-like substances contained in microbe extracellular polymers (EPSs), and the adsorbed TCC increased the direct electron transfer ability of EPSs, possibly due to the increase in the content of electroactive polymer protein in EPSs, the polarization of the amide group C═O bond, and the increase of the α-helical peptide dipole moment, which might be one important reason for promoting sulfur bioconversion processes. Microbial analysis showed that the presence of TCC enriched the organic substrate-degrading bacteria and sulfate-reducing bacteria and increased the abundances of functional genes encoding sulfate transport and dissimilatory sulfate reduction.

Performance of volatile fatty acids production from food waste at the presence of alkyl ethoxy polyglycosides and sodium dodecyl sulfate

In the current context of technological and industrial development, strategies for sustainable development and resource utilization have become increasingly important. FW anaerobic fermentation (Fermentation of Wastes) is a process that utilizes organic waste for biotransformation and is widely used for the production of volatile fatty acids (VFAs). Volatile fatty acids (VFAs) are a kind of high value-added product generated from anaerobic fermentation process, and has extensive applications in chemical synthesis and electricity generation. This study investigated the performance of VFAs production from food waste at the presence of alkyl ethoxy polyglycosides (AEG) and sodium dodecyl sulfate (SDS). The highest yield of VFAs was obtained at 0.1 g AEG/g TS (14.53 g COD/L), which increased by 25.80% than the Blank. But inhibited phenomenon was observed at other reactors with relatively low yield and delayed fermentation time. The inhibition of lactate's production and bioconversion delayed the fermentation time, and SDS has changed the acidogenic fermentation type from lactate-butyrate fermentation to acetate fermentation. In addition, more organic matter dissolved in the fermentation liquor with the addition of AEG and SDS, but the hydrolysis and acidification of polysaccharide were inhibited to some extent. Microbial community analysis showed that the abundance of key bacteria Clostridium has significantly decreased from 82.71% (Blank) to 33.54% (AEG) and 23.72% (SDS), leading to low VFAs production performance.