Upstream Natural Pulsed Ventilation: A simple measure to control the sulfide and methane production in gravity sewer

Enhancing sewer low-loss transportation by food waste microencapsulation treatment: Dual suppression of organic leaching and biofilm architecture-function for mitigating hazardous gases and blockage risks

Food waste management posed a critical global sustainability challenge, with significant environmental, economic, and social impacts. The installation of food waste disposers emerged as a primary strategy for source-separated food waste transfer to wastewater treatment systems through municipal pipelines. However, this approach accelerated the transformation of sewer systems into bioreactors and induced sewer pipe deterioration. Therefore, a novel microencapsulation method was developed and optimized to rapidly immobilize comminuted food waste particles. The stability of FW-encapsulated microcapsules was evaluated for their capacity to suppress organic leaching, destabilize functional biofilm architectures, and mitigate hazardous gas emissions and pipeline blockages in sewer systems during sewage conveyance. Results showed that FW-loaded microcapsules exhibited physicochemical stability against hydrodynamic shear and microbial degradation during sewer transport. It suppressed 33.62 mg/L organic matter release based on COD, reduced fluorescent substance accumulation/degradation, and limited macromolecular organics leakage. Microencapsulation destabilized sewer biofilm integrity via EPS reduction, disrupted humic acid stabilization, altered microbial dominance, and induced protein conformational loosening, impairing biofilm resilience. The technology mitigated sewer risks by curbing 3078.3 ppm VOC. It eliminating 100 % and 98.80 % increments of CH4 and CO compared to crushed FW discharge increments(2.55 mg/L and 0.09 mg/L), suppressing 0.80 mg/L sulfide conversion increments, and minimizing sedimentation through particle size and suspended solids control. Integration with food waste disposers enhanced source-segregated organic collection, optimized hydro-transport to alleviate pipe deterioration, reduced 0.915 MtCO2-eq transport-related carbon emissions, and improved treatment efficiency of wastewater treatment plants. This microencapsulation strategy provided a sustainable solution for FW management, combining infrastructure preservation, emission control, and resource recovery.

Enhancing sulfide mitigation via the synergistic dosing of calcium peroxide and ferrous ions in gravity sewers: Efficiency and mechanism

Chemical dosing constitutes an effective strategy for sulfide control in sewers; however, its efficacy requires further optimization and enhancement. In this study, a novel dosing strategy using the synergistic dosing of calcium peroxide (CaO2) and ferrous ions (Fe2+) for sulfide control was proposed, and its efficacy in controlling sulfides was evaluated using a long-term laboratory-scale reactor. The results showed that adding CaO2-Fe2+ improves the effect of sulfide control. When the ratio of the agent to the sewage (w/v) was 0.30 %, the RT50 of sulfide production rate was 8.34 days. The analysis of microbial communities in sewage biofilm revealed that the relative abundances of sulfate-reducing bacteria (SRB) and sulfide-oxidizing bacteria (SOB) demonstrated an overall downward tendency, suggesting that the potent oxidizing •OH generated by the synergism of CaO2 and Fe2+ could indiscriminately restrain the growth of microorganisms. Additionally, intracellular metabolic pathways, along with enzyme activities and the relative abundances of genes associated with sulfide metabolism, were significantly impaired. The cost of CaO2-Fe2+ synergistic dosing is 31.3 % of CaO2 and 63.4 % of Fe2+ alone addition. It can be reasonably proposed that the addition of CaO2-Fe2+ may provide an efficacious and cost-effective method for the mitigation of sulfide in sewer systems.

Methanogenic Potential of Sewer Microbiomes and Its Implications for Methane Emission

The sewer system, despite being a significant source of methane emissions, has often been overlooked in current greenhouse gas inventories due to the limited availability of quantitative data. Direct monitoring in sewers can be expensive or biased due to access limitations and internal heterogeneity of sewer networks. Fortunately, since methane is almost exclusively biogenic in sewers, we demonstrate in this study that the methanogenic potential can be estimated using known sewer microbiome data. By combining data mining techniques and bioinformatics databases, we developed the first data-driven method to analyze methanogenic potentials using a data set containing 633 observations of 53 variables obtained from literature mining. The methanogenic potential in the sewer sediment was around 250-870% higher than that in the wet biofilm on the pipe and sewage water. Additionally, k-means clustering and principal component analysis linked higher methane emission rates (9.72 ± 51.3 kgCO2 eq m-3 d-1) with smaller pipe size, higher water level, and higher potentials of sulfate reduction in the wetted pipe biofilm. These findings exhibit the possibility of connecting microbiome data with biogenic greenhouse gases, further offering insights into new approaches for understanding greenhouse gas emissions from understudied sources.

In-situ advanced oxidation of sediment iron for sulfide control in sewers

Sulfide control is a significant problem in urban sewer management. Although in-sewer dosing of chemicals has been widely applied, it is prone to high chemical consumption and cost. A new approach is proposed in this study for effective sulfide control in sewers. It involves advanced oxidation of ferrous sulfide (FeS) in sewer sediment, to produce hydroxyl radical (·OH) in-situ, leading to simultaneous sulfide oxidation and reduction of microbial sulfate-reducing activity. Long-term operation of three laboratory sewer sediment reactors was used to test the effectiveness of sulfide control. The experimental reactor with the proposed in-situ advanced FeS oxidation substantially reduced sulfide concentration to 3.1 ± 1.8 mg S/L. This compares to 9.2 ± 2.7 mg S/L in a control reactor with sole oxygen supply, and 14.1 ± 4.2 mg S/L in the other control reactor without either iron or oxygen. Mechanistic investigations illustrated the critical role of ·OH, produced from the oxidation of sediment iron, in regulating microbial communities and the chemical sulfide oxidation reaction. Together these results demonstrate that incorporating the advanced FeS oxidation process in sewer sediment enable superior performance of sulfide control at a much lower iron dosage, thereby largely saving chemical use.

Trace antibiotics increase the risk of antibiotic resistance genes transmission by regulating the biofilm extracellular polymeric substances and microbial community in the sewer

Sewer is considered a potential hotspot for antibiotic resistance, but the occurrence and proliferation of antibiotic resistance genes (ARGs) under trace antibiotics exposure have received little attention. This work evaluated the effects of tetracycline (TC) and sulfamethoxazole (SMX) individually and in combination in the sewer system and revealed the related mechanisms of ARG proliferation. The relative abundance of tetA and sul1 increased the most under TC and SMX stress, respectively, whereas sul1 increased the most under combined stress. Intl1 was abundant in both the liquid phase and the biofilm, and redundancy analysis confirmed that horizontal gene transfer was the main reason for the proliferation of ARGs. The increase in extracellular polymeric substances (EPS) secretion and the enhancement of the main hydrophobic functional groups facilitated the accumulation of biofilms, which promoted the proliferation of ARGs in biofilms. The relative abundance of most ARGs in the liquid phase was significantly correlated with EPS, protein and tryptophan-like substances. Furthermore, the microbial community structure and diversity affected the proliferation and spread of ARGs in the sewer. These findings contribute to our further understanding of the proliferation and development of ARGs in the sewer and lay the foundation for the front-end control of ARGs.

Enhancing sulfide mitigation via the sustainable supply of oxygen from air-nanobubbles in gravity sewers

Traditional air or oxygen injection is an effective and economical mitigation strategy for sulfide control in pressure sewers, but it is not suitable for gravity sewers due to the low solubility of oxygen in water under normal atmospheric conditions. Herein, an air-nanobubble (ANB) injection method was proposed for sulfide mitigation in gravity sewers, and its sulfide control efficiency was evaluated by long-term laboratory gravity sewer reactors. The results showed that an average inhibition rate of 45.36% for sulfide was obtained when ANBs were implemented, which was 3.75 times higher than that of the traditional air injection method, revealing the effectiveness and feasibility of the ANB injection method. As suggested by microbial community analysis of sewer biofilms, the relative abundance of sulfate-reducing bacteria (SRB) decreased 40.57% while that of sulfur oxidizing bacteria (SOB) increased 215.27% in the presence of ANBs, indicating that sulfide mitigation by ANB injection included both the inhibition of sulfide production and the oxidation of dissolved sulfide. The specific cost consumption of ANB injection was 1.7 $/kg-S, which was only 6.85% of that of traditional air injection (24.8 $/kg-S), suggesting that the sustainable supply of oxygen based on ANB injection is not only environmentally but also economically beneficial for sulfide mitigation. The findings of this study may provide an efficient sulfide mitigation strategy for the management of corrosion and malodour issues in the poorly ventilated gravity sewers.