Sulfur transformation in rising main sewers receiving nitrate dosage

Methane mitigation via the nitrite-DAMO process induced by nitrate dosing in sewers

Nitrate or nitrite-dependent anaerobic methane oxidation (n-DAMO) is a microbial process that links carbon and nitrogen cycles as a methane sink in many natural environments. This study demonstrates, for the first time, that the nitrite-dependent anaerobic methane oxidation (nitrite-DAMO) process can be stimulated in sewer systems under continuous nitrate dosing for sulfide control. In a laboratory sewer system, continuous nitrate dosing not only achieved complete sulfide removal, but also significantly decreased dissolved methane concentration by ∼50 %. Independent batch tests confirmed the coupling of methane oxidation with nitrate and nitrite reduction, revealing similar methane oxidation rates of 3.68 ± 0.5 mg CH4 L-1 h-1 (with nitrate as electron acceptor) and 3.57 ± 0.4 mg CH4 L-1 h-1 (with nitrite as electron acceptor). Comprehensive microbial analysis unveiled the presence of a subgroup of the NC10 phylum, namely Candidatus Methylomirabilis (n-DAMO bacteria that couples nitrite reduction with methane oxidation), growing in sewer biofilms and surface sediments with relative abundances of 1.9 % and 1.6 %, respectively. In contrast, n-DAMO archaea that couple methane oxidation solely to nitrate reduction were not detected. Together these results indicated the successful enrichment of n-DAMO bacteria in sewerage systems, contributing to approx. 64 % of nitrite reduction and around 50 % of dissolved methane removal through the nitrite-DAMO process, as estimated by mass balance analysis. The occurrence of the nitrite-DAMO process in sewer systems opens a new path to sewer methane emissions.

Sulfur-containing substances in sewers: Transformation, transportation, and remediation

Sulfur-containing substances in sewers frequently incur unpleasant odors, corrosion-related economic loss, and potential human health concerns. These observations are principally attributed to microbial reactions, particularly the involvement of sulfate-reducing bacteria (SRB) in sulfur reduction process. As a multivalent element, sulfur engages in complex bioreactions in both aerobic and anaerobic environments. Organic sulfides are also present in sewage, and these compounds possess the potential to undergo transformation and volatilization. In this paper, a comprehensive review was conducted on the present status regarding sulfur transformation, transportation, and remediation in sewers, including both inorganic and organic sulfur components. The review extensively addressed reactions occurring in the liquid and gas phase, as well as examined detection methods for various types of sulfur compounds and factors affecting sulfur transformation. Current remediation measures based on corresponding mechanisms were presented. Additionally, the impacts of measures implemented in sewers on the subsequent wastewater treatment plants were also discussed, aiming to attain better management of the entire wastewater system. Finally, challenges and prospects related to the issue of sulfur-containing substances in sewers were proposed to facilitate improved management and development of the urban water system.

Long-term effects of thiosulfate on the competition between sulfur-mediated bacteria and glycogen accumulating organisms in sulfate-rich carbon-deficient wastewater

Sewage nutrient (e.g., nitrogen and phosphorus) biological removal performance is often limited by the deficient carbon source and undesirable glycogen accumulating organisms (GAOs), even in sulfate-containing wastewater. Thiosulfate (S2O32-) as a bioavailable, environmentally-benign, metastable and cost-effective agent has been regarded as electron carriers that induces high sulfur-mediated bacterial activity for nutrient removal from wastewater. In this study, the long-term effects of thiosulfate on the competition between sulfur-mediated bacteria (SMB, including sulfur-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB)) and GAOs were explored to further close the gap of our knowledge on the control of GAOs under carbon deficient wastewater. Three reactors were continuously operated for over 100 days and were fed with 200 mg acetate-COD/L and 20 (R1), 50 (R2) and 80 (R3) mg S/L thiosulfate respectively. The results revealed that adding thiosulfate at the beginning of the anoxic phase promoted sulfur metabolism and increased the proliferation of SRB (mainly Desulfobacter) and SOB (mainly Chromatiaceae). Correspondingly, the relative abundance of GAOs (mainly Candidatus_Competibacter) decreased. After the carbon source was reduced, the abundance of GAOs increased and the competitive activity of SRB was weakened, resulting in the reduced sulfate reduction, which could be attributed to the fact that GAOs had a higher carbon source competitiveness than SRB under low carbon source conditions. While SOB maintained a high abundance due to the addition of thiosulfate as an additional electron donor, which enhanced the denitrification efficiency. Additionally, the dominant SOB shifted from Thiobacillus to Chromatiaceae during the long-term operation, indicating that Chromatiaceae had a higher competitive advantage for reduced sulfur (e.g., S2O32-, Polysulfide (Poly-S)) and nitrate compared to Thiobacillus. Furthermore, microbial functional genes revealed that S metabolism was enhanced during long-term operation. The potential mechanism and optimization strategy regarding the competition between sulfur-mediated bacteria and GAOs were revealed.

Enhancement of bio-S0 recovery and revealing the inhibitory effect on microorganisms under high sulfide loading

Biodesulfurization is a mature technology, but obtaining biosulfur (S0) that can be easily settled naturally is still a challenge. Increasing the sulfide load is one of the known methods to obtain better settling of S0. However, the inhibitory effect of high levels of sulfide on microbes has also not been well studied. We constructed a high loading sulfide (1.55-10.86 kg S/m3/d) biological removal system. 100% sulfide removal and 0.56-2.53 kg S/m3/d S0 (7.0 ± 0.09-16.4 ± 0.25 μm) recovery were achieved at loads of 1.55-7.75 kg S/m3/d. Under the same load, S0 in the reflux sedimentation tank, which produced larger S0 particles (24.2 ± 0.73-53.8 ± 0.70 μm), increased the natural settling capacity and 45% recovery. For high level sulfide inhibitory effect, we used metagenomics and metatranscriptomics analyses. The increased sulfide load significantly inhibited the expression of flavin cytochrome c sulfide dehydrogenase subunit B (fccB) (Decreased from 615 ± 75 to 30 ± 5 TPM). At this time sulfide quinone reductase (SQR) (324 ± 185-1197 ± 51 TPM) was mainly responsible for sulfide oxidation and S0 production. When the sulfide load reached 2800 mg S/L, the SQR (730 ± 100 TPM) was also suppressed. This resulted in the accumulation of sulfide, causing suppression of carbon sequestration genes (Decreased from 3437 ± 842 to 665 ± 175 TPM). Other inhibitory effects included inhibition of microbial respiration, production of reactive oxygen species, and DNA damage. More sulfide-oxidizing bacteria (SOB) and newly identified potential SOB (99.1%) showed some activity (77.6%) upon sulfide accumulation. The main microorganisms in the sulfide accumulation environment were Thiomicrospiracea and Burkholderiaceae, whose sulfide oxidation capacity and respiration were not significantly inhibited. This study provides a new approach to enhance the natural sedimentation of S0 and describes new microbial mechanisms for the inhibitory effects of sulfide.

A critical review of chemical uses in urban sewer systems

Chemical dosing is the most used strategy for sulfide and methane abatement in urban sewer systems. Although conventional physicochemical methods, such as sulfide oxidation (e.g., oxygen/nitrate), precipitation (e.g., iron salts), and pH elevation (e.g., magnesium hydroxide/sodium hydroxide) have been used since the last century, the high chemical cost, large environmental footprint, and side-effects on downstream treatment processes demand a sustainable and cost-effective alternative to these approaches. In this paper, we aimed to review the currently used chemicals and significant progress made in sustainable sulfide and methane abatement technology, including 1) the use of bio-inhibitors, 2) in situ chemical production, and 3) an effective dosing strategy. To enhance the cost-effectiveness of chemical applications in urban sewer systems, two research directions have emerged: 1) online control and optimization of chemical dosing strategies and 2) integrated use of chemicals in urban sewer and wastewater treatment systems. The integration of these approaches offers considerable system-wide benefits; however, further development and comprehensive studies are required.

Hydrogen sulfide control in sewer systems: A critical review of recent progress

In sewer systems where anaerobic conditions are present, sulfate-reducing bacteria reduce sulfate to hydrogen sulfide (H₂S), leading to sewer corrosion and odor emission. Various sulfide/corrosion control strategies have been proposed, demonstrated, and optimized in the past decades. These included (1) chemical addition to sewage to reduce sulfide formation, to remove dissolved sulfide after its formation, or to reduce H₂S emission from sewage to sewer air, (2) ventilation to reduce the H₂S and humidity levels in sewer air, and (3) amendments of pipe materials/surfaces to retard corrosion. This work aims to comprehensively review both the commonly used sulfide control measures and the emerging technologies, and to shed light on their underlying mechanisms. The optimal use of the above-stated strategies is also analyzed and discussed in depth. The key knowledge gaps and major challenges associated with these control strategies are identified and strategies dealing with these gaps and challenges are recommended. Finally, we emphasize a holistic approach to sulfide control by managing sewer networks as an integral part of an urban water system.

In-sewer decay and partitioning of Campylobacter jejuni and Campylobacter coli and implications for their wastewater surveillance

Campylobacter jejuni and coli are two main pathogenic species inducing diarrhoeal diseases in humans, which are responsible for the loss of 33 million lives each year. Current Campylobacter infections are mainly monitored by clinical surveillance which is often limited to individuals seeking treatment, resulting in under-reporting of disease prevalence and untimely indicators of community outbreaks. Wastewater-based epidemiology (WBE) has been developed and employed for the wastewater surveillance of pathogenic viruses and bacteria. Monitoring the temporal changes of pathogen concentration in wastewater allows the early detection of disease outbreaks in a community. However, studies investigating the WBE back-estimation of Campylobacter spp. are rare. Essential factors including the analytical recovery efficiency, the decay rate, the effect of in-sewer transport, and the correlation between the wastewater concentration and the infections in communities are lacking to support wastewater surveillance. This study carried out experiments to investigate the recovery of Campylobacter jejuni and coli from wastewater and the decay under different simulated sewer reactor conditions. It was found that the recovery of Campylobacter spp. from wastewater varied with their concentrations in wastewater and depended on the detection limit of quantification methods. The concentration reduction of Campylobacter. jejuni and coli in sewers followed a two-phase reduction model, and the faster concentration reduction during the first phase is mainly due to their partitioning onto sewer biofilms. The total decay of Campylobacter. jejuni and coli varied in different types of sewer reactors, i.e. rising main vs. gravity sewer. In addition, the sensitivity analysis for WBE back-estimation of Campylobacter suggested that the first-phase decay rate constant (k₁) and the turning time point (t₁) are determining factors and their impacts increased with the hydraulic retention time of wastewater.

Effects of sewer biofilms on the degradability of carbapenems in wastewater using laboratory scale bioreactors

Carbapenems are last-resort antibiotics used to treat bacterial infections unsuccessfully treated by most common categories of antibiotics in humans. Most of their dosage is secreted unchanged as waste, thereby making its way into the urban water system. There are two major knowledge gaps addressed in this study to gain a better understanding of the effects of their residual concentrations on the environment and environmental microbiome: development of a UHPLC-MS/MS method of detection and quantification from raw domestic wastewater via direct injection and study of their stability in sewer environment during the transportation from domestic sewers to wastewater treatment plants. The UHPLC-MS/MS method was developed for four carbapenems: meropenem, doripenem, biapenem and ertapenem, and validation was performed in the range of 0.5-10 μg/L for all analytes, with limit of detection (LOD) and limit of quantification (LOQ) values ranging from 0.2-0.5 μg/L and 0.8-1.6 μg/L respectively. Laboratory scale rising main (RM) and gravity sewer (GS) bioreactors were employed to culture mature biofilms with real wastewater as the feed. Batch tests were conducted in RM and GS sewer bioreactors fed with carbapenem-spiked wastewater to evaluate the stability of carbapenems and compared against those in a control reactor (CTL) without sewer biofilms, over a duration of 12 h. Significantly higher degradation was observed for all carbapenems in RM and GS reactors (60 - 80%) as opposed to CTL reactor (5 - 15%), which indicates that sewer biofilms play a significant role in the degradation. First order kinetics model was applied to the concentration data along with Friedman's test and Dunn's multiple comparisons analysis to establish degradation patterns and differences in the degradation observed in sewer reactors. As per Friedman's test, there was a statistically significant difference in the degradation of carbapenems observed depending on the reactor type (p = 0.0017 - 0.0289). The results from Dunn's test indicate that the degradation in the CTL reactor was statistically different from that observed in either RM (p = 0.0033 - 0.1088) or GS (p = 0.0162 - 0.1088), with the latter two showing insignificant difference in the degradation rates observed (p = 0.2850 - 0.5930). The findings contribute to the understanding about the fate of carbapenems in urban wastewater and the potential application of wastewater-based epidemiology.

Experimental and modeling investigations on the unexpected hydrogen sulfide rebound in a sewer receiving nitrate addition: Mechanism and solution

Biogenic hydrogen sulfide is an odorous, toxic and corrosive gas released from sewage in sewers. To control sulfide generation and emission, nitrate is extensively applied in sewer systems for decades. However, the unexpected sulfide rebound after nitrate addition is being questioned in recent studies. Possible reasons for the sulfide rebounds have been studied, but the mechanism is still unclear, so the countermeasure is not yet proposed. In this study, a lab-scale sewer system was developed for investigating the unexpected sulfide rebounds via the traditional strategy of nitrate addition during 195-days of operation. It was observed that the sulfide pollution was even severe in a sewer receiving nitrate addition. The mechanism for the sulfide rebound can be differentiated into short-term and long-term effects based on the dominant contribution. The accumulation of intermediate elemental sulfur in biofilm resulted in a rapid sulfide rebound via the high-rate sulfur reduction after the depletion of nitrate in a short period. The presence of nitrate in sewer promoted the microorganism proliferation in biofilm, increased the biofilm thickness, re-shaped the microbial community and enhanced biological denitrification and sulfur production, which further weakened the effect of nitrate on sulfide control during the long-term operation. An optimized biofilm-initiated sewer process model demonstrated that neither the intermittent nitrate addition nor the continuous nitrate addition was a sustainable strategy for the sulfide control. To minimize the negative impact from sulfide rebounds, a (bi)monthly routine maintenance (e.g., hydraulic flushing with nitrate spike) to remove the proliferative microorganism in biofilm is necessary.

Simultaneous use of nitrate and calcium peroxide to control sulfide and greenhouse gas emission in sewers

The sewer system is a significant source of hydrogen sulfide (H₂S) and greenhouse gases which has attracted extensive interest from researchers. In this study, a novel combined dosing strategy using nitrate and calcium peroxide (CaO₂) was proposed to simultaneously control sulfide and greenhouse gases, and its performance was evaluated in laboratory-scale reactors. Results suggested that the addition of nitrate and CaO₂ improved the effectiveness of sulfide control. And the combination index method further proved that nitrate and CaO₂ were synergistic in controlling sulfide. Meanwhile, the combination of nitrate and CaO₂ substantially reduced greenhouse gas emissions, especially the carbon dioxide (CO₂) and methane (CH₄). The microbial analysis revealed that the combined addition greatly stimulated the accumulation of nitrate reducing-sulfide oxidizing bacteria (NR-SOB) that participate in anoxic nitrate-dependent sulfide oxidation, while the abundance of heterotrophic denitrification bacteria (hNRB) was reduced significantly. Moreover, the presence of oxygen and alkaline chemicals generated by CaO₂ facilitated the inhibition of sulfate-reducing bacteria (SRB) activities. Therefore, the nitrate dosage was diminished significantly. On the other hand, the generated alkaline chemicals promoted CO₂ elimination and inhibited the activities of methanogens, leading to a decrease of CO₂ and CH₄ fluxes, which facilitated elimination of greenhouse effects. The intermittent dosing test showed that the nitrate and CaO₂ could be applied intermittently for sulfide removal. And the chemical cost of intermittent dosing strategy was reduced by 85 % compared to the continuous dosing nitrate strategy. Therefore, intermittent dosing nitrate combined with CaO₂ is probably an effective and economical approach to control sulfide and greenhouse gases in sewer systems.

Metagenomic analysis of microbial community and metabolic pathway of simultaneous sulfide and nitrite removal process exposed to divergent hydraulic retention times

The role of hydraulic retention time (HRT) on S⁰ production was assessed through metagenomics analyses. Considering comprehensive performance for the tested HRTs (0.25-13.33 h), the optimal HRT was 1 h, while respective sulfide and nitrite loading rate could reach 6.84 kg S/(m³·d) and 1.95 kg N/(m³·d), and total S⁰ yield was 0.36 kg S/(kg (VSS)·d). Bacterial community richness decreased along the shortening of HRT. Microbacterium, Sulfurimonas, Sulfurovum, Paracoccus and Thauera were highly abundant bacteria. During sulfur metabolism, high expression of sqr gene was the main reason of maintaining high desulfurization load, while lacking soxB caused the continuous increase of S⁰. Regarding nitrogen metabolism, the rapid decrease of nitrite transporter prevented nitrite to enter in cells, which caused a rapid decrease of nitrite removal under extreme HRT. Adjusting HRT is an effective way to enhance S⁰ production for the application of the simultaneous sulfide and nitrite removal process.

Development and validation of a sampling and analysis method to determine biogenic sulfur in a desulfurization bioreactor by gas chromatography coupled with a pulsed flame photometric detector (GC-PFPD)

Suspended biomass bioreactors can be operated to remove H₂S from biogas under anoxic conditions and produce elemental sulfur, the commercial value of which has been demonstrated. In the present paper, a novel methodology comprising the optimization of a determination method performed in a gas chromatograph equipped with a pulsed flame photometric detector (GC-PFPD), combined with a simple preparation based on filtration and extraction with toluene, is proposed. The injector temperature and carrier gas flow rate (Q_He) values were optimized using a response surface methodology based on a face-centred composite central design. This optimization revealed that the optimum conditions were an injector temperature and carrier gas flow rate of 222 °C and 7 mL min^-1, respectively. The chromatographic method shows an analysis time of 48 min, a detection limit of more than 5.9 mg L^-1, a relative standard deviation of less than 3.71%, and a sulfur recovery percentage of more than 98%. These values provide excellent linearity and a reasonable concentration range (10-200 mg L^-1). Finally, a measurement error of 4.45% was obtained when using the present method in a selectivity test.

Response difference of simultaneous sulfide and nitrite removal process to different cooling modes

The effects of various cooling modes (sudden cooling (25℃→10℃) and step cooling (25℃→20℃→15℃→10℃)) on the performance of simultaneous sulfide and nitrite removal process were reported. Regardless of cooling mode adopted, the process maintained good sulfide removal performance, and removal percentage was 100.00%. Considering nitrite removal percentage, the process was more sensitive to step cooling mode (k = 0.06707) in comparison to sudden cooling mode (k = 0.02760). Lowering temperature promoted the transformation from sulfate to elemental sulfur, and it was easier to increase the proportion of elemental sulfur (79.90%) by means of step cooling. The sulfide oxidation rate and nitrite reduction rate were 0.01540 mg /(L∙min) and 0.00354 mg /(L∙min), respectively, in the sudden cooling mode, and 0.01168 mg /(L∙min) and 0.00138 mg /(L∙min), respectively, in the step cooling mode. Low temperature reduced the diversity of microbial community, and Sulfurovum was still a dominant bacterial member in both cooling modes.

Corrosion mitigation by nitrite spray on corroded concrete in a real sewer system

Microbially influenced concrete corrosion (MICC) in sewers is caused by the activity of sulfide-oxidizing microorganisms (SOMs) on concrete surfaces, which greatly deteriorates the integrity of sewers. Surface treatment of corroded concrete by spraying chemicals is a low-cost and non-intrusive strategy. This study systematically evaluated the spray of nitrite solution in corrosion mitigation and re-establishment in a real sewer manhole. Two types of concrete were exposed at three heights within the sewer manhole for 21 months. Nitrite spray was applied at the 6th month for half of the coupons which had developed active corrosion. The corrosion development was monitored by measuring the surface pH, corrosion product composition, sulfide uptake rate, concrete corrosion loss, and the microbial community on the corrosion layer. Free nitrous acid (FNA, i.e. HNO₂), formed by spraying a nitrite solution on acidic corrosion surfaces, was shown to inhibit the activity of SOMs. The nitrite spray reduced the corrosion loss of concrete at all heights by 40-90% for six months. The sulfide uptake rate of sprayed coupons was also reduced by about 35%, leading to 1-2 units higher surface pH, comparing to the control coupons. The microbial community analysis revealed a reduced abundance of SOMs on nitrite sprayed coupons. The long-term monitoring also showed that the corrosion mitigation effect became negligible in 15 months after the spray. The results consistently demonstrated the effectiveness of nitrite spray on the MICC mitigation and identified the re-application frequencies for full scale applications.

Biogenic sulfide for azo dye decolorization from textile dyeing wastewater

Azo dye is the most versatile class of dyes used in the textile industry. Although the sulfidogenic process shows superiority in the removal of azo dye, the role of biogenic sulfide produced by sulfate-reducing bacteria (SRB) in the decolorization of azo dye is unclear. This study explored the mechanism of biogenic sulfide for removal of a model azo dye (Direct Red 81 (DR 81)) through biotic and abiotic batch tests with analysis of intermediates of the azo dye degradation. The results showed that biogenic sulfide produced from sulfate reduction directly cleaved two groups of azo bond (-NN-), thereby achieving decolorization. Moreover, the decolorization rate was enhanced by nearly 3-fold (up to 42 ± 1 mg/L-hr; removal efficiency > 99%) by adding an external carbon source or elevating the initial azo dye concentration. This study showed that biogenic sulfide plays an essential role in azo dye decolorization and provides a new avenue for the potential application of biogenic sulfide from the sulfidogenic system for the treatment of azo dye-laden wastewater.

Importance of thermodynamics dependent kinetic parameters in nitrate-based souring mitigation studies

Souring is the unwanted formation of hydrogen sulfide (H₂S) by sulfate-reducing microorganisms (SRM) in sewer systems and seawater flooded oil reservoirs. Nitrate treatment (NT) is one of the major methods to alleviate souring: The mechanism of souring remediation by NT is stimulation of nitrate reducing microorganisms (NRM) that depending on the nitrate reduction pathway can outcompete SRM for common electron donors, or oxidize sulfide to sulfate. However, some nitrate reduction pathways may challenge the efficacy of NT. Therefore, a precise understanding of souring rate, nitrate reduction rate and pathways is crucial for efficient souring management. Here, we investigate the necessity of incorporating two thermodynamic dependent kinetic parameters, namely, the growth yield (Y), and F_T, a parameter related to the minimum catabolic energy production required by cells to utilize a given catabolic reaction. We first show that depending on physiochemical conditions, Y and F_T for SRM change significantly in the range of [0-0.4] mole biomass per mole electron donor and [0.0006-0.5], respectively, suggesting that these parameters should not be considered constant and that it is important to couple souring models with thermodynamic models. Then, we highlight this further by showing an experimental dataset that can be modeled very well by considering variable F_T. Next, we show that nitrate based lithotrophic sulfide oxidation to sulfate (lNRM₃) is the dominant nitrate reduction pathway. Then, arguing that thermodynamics would suggest that S° consumption should proceed faster than S⁰ production, we infer that the reason for frequently observed S⁰ accumulation is its low solubility. Last, we suggest that nitrate based souring treatment will suffer less from S⁰ accumulation if we (i) act early, (ii) increase temperature and (iii) supplement stoichiometrically sufficient nitrate.

A novel granular sludge-based and highly corrosion-resistant bio-concrete in sewers

Bio-concrete is known for its self-healing capacity although the corrosion resistance was not investigated previously. This study presents an innovative bio-concrete by mixing anaerobic granular sludge into concrete to mitigate sewer corrosion. The control concrete and bio-concrete (with granular sludge at 1% and 2% of the cement weight) were partially submerged in a corrosion chamber for 6 months, simulating the tidal-region corrosion in sewers. The corrosion rates of 1% and 2% bio-concrete were about 17.2% and 42.8% less than that of the control concrete, together with 14.6% and 35.0% less sulfide uptake rates, 15.3% and 55.6% less sulfate concentrations, and higher surface pH (up to 1.8 units). Gypsum and ettringite were major corrosion products but in smaller sizes on bio-concrete than that of control concrete. The total relative abundance of corrosion-causing microorganisms, i.e. sulfide-oxidizing bacteria, was significantly reduced on bio-concrete, while more sulfate-reducing bacteria (SRB) was detected. The corrosion-resistance of bio-concrete was mainly attributed to activities of SRB derived from the granular sludge, which supported the sulfur cycle between the aerobic and anaerobic corrosion sub-layers. This significantly reduced the net production of biogenic sulfuric acid and thus corrosion. The results suggested that the novel granular sludge-based bio-concrete provides a highly potential solution to reduce sewer corrosion.

In-sewer stability of selected analgesics and their metabolites

Understanding the in-sewer stability of analgesic biomarkers is important for interpreting wastewater-based epidemiology (WBE) data to estimate community-wide analgesic drugs consumption. The in-sewer stability of a suite of 19 analgesics and their metabolites was assessed using lab-scale sewer reactors. Target biomarkers were spiked into wastewater circulating in simulated gravity, rising main and control (no biofilm) sewer reactors. In-sewer transformation was observed over a hydraulic retention time of 12 h. All investigated biomarkers were stable under control reactor conditions. In gravity sewer conditions, diclofenac, desmetramadol, ibuprofen carboxylic acid, ketoprofen, lidocaine and tapentadol were highly stable (0-20% transformation in 12 h). Valdecoxib, parecoxib, etoricoxib, indomethacin, naltrexone, naloxone, piroxicam, ketoprofen, lidocaine, tapentadol, oxymorphone, hydrocodone, meperidine, hydromorphone were considered as moderately stable biomarkers (20-50% transformation in 12 h). Celecoxib and sulindac were considered unstable biomarkers (>50% transformation in 12 h). Ketoprofen, lidocaine, tapentadol, meperidine, hydromorphone were transformed to 0-20% whereas diclofenac, desmetramadol, ibuprofen carboxylic acid, valdecoxib, parecoxib, etoricoxib, indomethacin, naltrexone, piroxicam were transformed up to 20-50% in 12 h in rising main reactor (RMR). These biomarkers were considered as highly stable and stable biomarkers in RMR, respectively. Sulindac, celecoxib, naloxone, oxymorphone and hydrocodone were transformed more than 50% in 12 h and considered as unstable biomarkers in RMR. This study provides the information for a better understanding of the in-sewer loss of the analgesics before using them in WBE biomarkers for estimating drug loads at the population level.

Diversion of food waste into the sulfate-laden sewer: Interaction and electron flow of sulfidogenesis and methanogenesis

Diverting food waste (FW) into the sulfate-laden sewer may pose a significant influence on the production of methane and sulfide in sewers. Identifying microbial electron utilization is essential to understanding the interaction of sulfidogenesis and methanogenesis in depth. Here, we reported sulfide and methane production from the sewer bioreactors receiving sulfate-laden wastewater (160 mg S/L), with and without FW addition. Long-term monitoring showed that the addition of FW (1 g/L) could boost both sulfide (by 39%) and methane (by 44%) production. As for the electrons used for sulfidogenesis and methanogenesis, about 98% flowed to sulfidogenesis. Cryosection-fluorescence in situ hybridization showed that high sulfate content suppressed the accumulation of methanogens in biofilm outer layer, whereas methanogens in the inner layer were enriched with FW addition. Moreover, the FW addition fostered the diversity of the fermentative bacteria and changed the type of methanogens in biofilms, and up-regulated the key enzymes expressions for sulfidogenesis and methanogenesis. A model-based investigation suggests that increased FW-to-sewage ratios would exert a significant impact on methane production than on sulfide production. The microbial electron flows were highly dependent on sulfate concentration and FW-to-sewage ratios. The findings of this study suggest that sulfate and substrate levels play a key role in microbial electron utilization for sulfide and methane production, and diverting FW into the sulfate-laden sewer may exert negative impacts on sewer management and the environment.

Emission characteristics of odorous volatile sulfur compound from a full-scale sequencing batch reactor wastewater treatment plant

Volatile sulfur compounds (VSCs) generated and discharged as air pollutants from wastewater treatment plants (WWTPs) pose a threat to human health and the environment. This study characterized VSC emissions from a full-scale sequencing batch reactor (SBR) WWTP at the water-air interface for one year. Results demonstrated that higher ambient temperatures and aeration contributed significantly to VSC emissions as the highest emissions occurred over summer during the feeding synchronous aeration period. VSC emissions were related to chemical oxygen demand and sulfate concentrations in wastewater, and empirical formulas based on these values were proposed that can be used to model VSC emission fluxes from SBR WWTP. VSC emission factors (μg·ton^-1 wastewater) throughout the SBR treatment process were: 361 ± 101 hydrogen sulfide (H₂S), 82 ± 76 methyl mercaptan (MT), 61 ± 31 dimethyl sulfide, 17 ± 5 carbon disulfide, and 46 ± 24 dimethyl disulfide. H₂S and MT were the dominant odors released. Findings from this study may be applicable for calculating VSC emissions during SBR wastewater treatment stages, and may be beneficial for determining methods and strategies to reduce VSCs.

Production and characteristics of elemental sulfur during simultaneous nitrate and sulfide removal

The production and characteristics of elemental sulfur were examined during simultaneous sulfide and nitrate removal, with abiotic assays as control. The biotic assay showed good sulfide and nitrate removal, with the respective removal percentage of which were 90.67-96.88% and 100%. Nitrate reduction resulted in the production of nitrogen gas, while sulfate formed due to sulfide oxidation. The concentration of elemental sulfur in the effluent was greater than that in the sludge, which accounted for 73.70-86.28% of total elemental sulfur produced. Furthermore, the elemental sulfur of the effluent and sludge from the biotic assays was orthorhombic crystal S₈. Elemental sulfur was normally distributed in the effluent, but its average diameter increased with the increasing influent sulfide concentration (60-300 mg S/L), where the average diameter increased from 10 (60 mg S/L) to 29 μm (300 mg S/L).

Simultaneous nitrate and sulfate dependent anaerobic oxidation of methane linking carbon, nitrogen and sulfur cycles

ANaerobic MEthanotrophic (ANME) archaea are critical microorganisms mitigating methane emission from anoxic zones. In previous studies, sulfate-dependent anaerobic oxidation of methane (AOM) and nitrate-dependent AOM, performed by different clades of ANME archaea, were detected in marine sediments and freshwater environments, respectively. This study shows that simultaneous sulfate- and nitrate-dependent AOM can be mediated by a clade of ANME archaea, which may occur in estuaries and coastal zones, at the interface of marine and freshwater environments enriched with sulfate and nitrate. Long-term (~1,200 days) performance data of a bioreactor, metagenomic analysis and batch experiments demonstrated that ANME-2d not only conducted AOM coupled to reduction of nitrate to nitrite, but also coupled to the conversion of sulfate to sulfide, in collaboration with sulfate-reducing bacteria (SRB). Sulfide was oxidized back to sulfate by sulfide-oxidizing autotrophic denitrifiers with nitrate or nitrite as electron acceptors, in turn alleviating sulfide accumulation. In addition, dissimilatory nitrate reduction to ammonium performed by ANME-2d was detected, providing substrates to Anammox. Metatranscriptomic analysis revealed significant upregulation of flaB in ANME-2d and pilA in Desulfococcus, which likely resulted in the formation of unique nanonets connecting cells and expanding within the biofilm, and putatively providing structural links between ANME-2d and SRB for electron transfer. Simultaneous nitrate- and sulfate-dependent AOM as observed in this study could be an important link between the carbon, nitrogen and sulfur cycles in natural environments, such as nearshore environments.

Ciprofloxacin-degrading Paraclostridium sp. isolated from sulfate-reducing bacteria-enriched sludge: Optimization and mechanism

Ciprofloxacin (CIP), one of the most widely used fluoroquinolone antibiotics, is frequently detected in the effluents of wastewater treatment plants and aquatic environments. In this study, a CIP-degrading bacterial strain was isolated from the sulfate reducing bacteria (SRB)-enriched sludge, identified as Paraclostridium sp. (i.e., strain S2). The effects of critical operational parameters on CIP removal by the strain S2 were systematically studied and these parameters were optimized via response surface methodology to maximize CIP removal. Furthermore, the pathway and kinetics of CIP removal were investigated by varying the initial CIP concentrations (from 0.1 to 20 mg/L). The CIP removal was characterized by rapid sorption followed by biotransformation with a specific biotransformation rate of 1975.7 ± 109.1 µg/g-cell dry weight/h at an initial CIP concentration of 20 mg/L. Based on the main transformation products, several biotransformation pathways have been proposed including piperazine ring cleavage, OH/F substitution, decarboxylation, and hydroxylation as the major transformation reactions catalyzed by cytochrome P450 and dehydrogenases. Acute toxicity assessment apparently shows that CIP biotransformation by strain S2 resulted in the formation of less toxic intermediates. To the best of our knowledge, this is the very first study in which a key functional microbe, Paraclostridium sp., highly effective in CIP biotransformation, was isolated from SRB-enriched sludge. The findings of this study could facilitate in developing appropriate bioaugmentation strategy, and in designing and operating an SRB-based engineered process for treating CIP-laden wastewater.

Mechanism of microbial metabolic responses and ecological system conversion under different nitrogen conditions in sewers

Nitrogen plays a central role in the sewer ecosystem, and the bioconversion of nitrogen can significantly affect bioreactions in sewers. However, the mechanisms underlying the involvement of nitrogen-associated pollutants in sewer ecosystems remain unknown. In this study, the effects of two typical nitrogen ratios (organic/inorganic nitrogen: 7/3 (Group A) and 3/7 (Group B)) on carbon, nitrogen, and sulfur bioconversions were investigated in a pilot sewer. The distribution of amino acids, such as proline, glycine and methionine, was significantly different between Groups A and B, and carbon-associated communities (based on 16S rRNA gene copies) were more prevalent in Group A, while sulfur and nitrogen-associated communities were more prevalent in Group B. To explore the effect of nitrogen on microbial response mechanisms, metagenomics-based methods were used to investigate the roles of amino acids involved in carbon, nitrogen, and sulfur bioconversion in sewers. Proline, glycine, and tyrosine in Group A promoted the expression of genes associated with cell membrane transport and increased the rate of protein synthesis, which stimulated the enrichment of carbon-associated communities. The transmembrane transport of higher concentrations of alanine and methionine in Group B was essential for cell metabolism and nutrient transport, thereby enriching nitrogen and sulfur-associated communities. In this investigation, insights into carbon, nitrogen and sulfur bioconversions in sewer ecosystems were revealed, significantly improving the understanding of the sewer ecosystem within a community context.

Effect of influent feeding pattern on municipal tailwater treatment during a sulfur-based denitrification constructed wetland

This work studied three parallel pilot-scale constructed wetlands based on sulfur-based autotrophic denitrification (SAD-CWs) with horizontal, vertical-horizontal and integrated vertical inflow for nitrogen removal of municipal tailwater. SAD system played the predominant role for nitrate removal and the integrated vertical inflow pattern was the most efficient pattern with 96.1% NO₃^--N and 44.3% total phosphorus (TP) removal efficiency, respectively, at the condition of 3.5 h hydraulic retention time (HRT) and 18.5-23.5 °C. Although no great and serious change for microbial community structure was observed among these systems, the diversity in term of abundance of microbes and certain function species was observed. Proteobacteria, Ignavibacterae and Chloroflexi were the dominant phyla and accounted for over 59.1%, 7.5%, and 6.0% in SAD-CWs, respectively. Moreover, the richness and diversity of denitrifies in SAD-CWs with integrated vertical inflow were both higher than that in the other two reactors, especially sulfur autotrophic denitrifying bacteria.

Full-scale investigation of ferrous dosing in sewers and a wastewater treatment plant for multiple benefits

This study demonstrates the full scale application of iron dosing in a metropolitan wastewater treatment plant (WWTP) and the upstream sewer system for multiple benefits. Two different dosing locations, i.e., the WWTP inlet works (Trial-1) and upstream sewer network (Trial-2) were tested in this study. Both dosing trials achieved multiple benefits such as sulfide control, phosphate removal and improved sludge dewaterability. During Trial-1, a sulfide reduction of >90% was achieved at high dosing rates (>19 kgFe ML^-1) of ferrous chloride in the inlet works and in Trial-2 the in-sewer ferrous dosing had significant gas phase hydrogen sulfide (H₂S) concentration reduction in the sewer network. The ferrous dosing enhanced the phosphate removal in the bioreactor up to 76% and 53 ± 2% during Trial-1 & 2, respectively. The iron ending up in the anaerobic sludge digester reduced the biogas H₂S concentration by up to 36% and 45%, respectively. The dewaterability of the digested sludge was improved, with relative increases of 9.7% and 9.8%, respectively. The presence of primary clarifier showed limited impact on the downstream availability of iron for achieving the afore-mentioned multiple benefits. The iron dosing enhanced the total chemical oxygen demand removal in the primary clarifier reaching up to 49% at the high dose rates during Trial-1 and 42 ± 1% during Trial-2. This study demonstrated that multiple benefits could be achieved independent of the iron dosing location (i.e., at the WWTP inlet or in the network). Further, iron dosing at both locations enhances primary settling, beneficial for bioenergy recovery from wastewater.

Dewaterability enhancement and sulfide mitigation of CEPT sludge by electrochemical pretreatment

Dewatering and sulfide control are the key challenges in treating chemically enhanced primary treatment (CEPT) sludge. In this study, an electrochemical pretreatment (EPT) approach with the input of 10 V/800 mA was explored for simultaneously improving the dewaterability of CEPT sludge and eliminating its sulfide production. The effects of different electrode materials (carbon and titanium) and EPT durations (from 5 to 15 min) were documented to reveal the underlying EPT mechanism. EPT with titanium electrodes (titanium-EPT) led to limited improvement in dewaterability and sulfide control. EPT with carbon electrodes (carbon-EPT) for 15 min, however, led to decreases in capillary suction time and specific resistance in filtration of over 80% and the suppression of about 99% of hydrogen sulfide (H₂S_(g)) production over 5 days of anaerobic storage. Analysis of the characteristics of treated CEPT sludge revealed that carbon-EPT disintegrated sludge flocs with ∼70% reduction in sludge particle sizes and release of aromatic and tyrosine protein-like substances, thus enhancing sludge dewaterability. The sulfur balance in the liquid and gaseous phases showed that most of the sulfur-containing compounds remained in the solid phase as aliphatic sulfur and sulfonic acid after carbon-EPT, thereby mitigating sulfide emission. While the pattern of sulfur distribution in sludge with titanium-EPT was dominated by sulfide, it was similar to the control sample. Reduction in bacteria associated with sulfide production (i.e., Lachnospiraceae) in CEPT sludge after carbon-EPT also contributed to sulfide elimination. This study demonstrates that EPT can be a superior option for simultaneously enhancing the dewaterability of CEPT sludge and mitigating its sulfide production.

Sulfur Cycle in a Wetland Microcosm: Extended 34S-Stable Isotope Analysis and Mass Balance

The sulfur cycle is an important part of constructed wetland biogeochemistry because it is intimately intertwined with the carbon, nitrogen, and iron cycles. However, to date, no quantitative investigation has been conducted on the sulfur cycle in constructed wetlands because of the complexity of wetland systems and the deficiencies in experimental methodology. In this study, ³⁴S-stable isotope analysis was extended in terms of the calculation for the enrichment factor and the kinetic analysis for bacterial sulfate reduction. With this extended method, we attempted for the first time to assess the true rate of bacterial sulfate reduction when sulfide oxidation co-occurs. The joint application of the extended ³⁴S-stable isotope and mass balance analyses made it possible to quantitatively investigate the primary sulfur transformation in a wetland microcosm. Accordingly, a sulfur cycle model for constructed wetlands was quantified and validated. Approximately 75% of the input sulfur was discharged. The remainder was mainly removed through deposition as acid volatile sulfide, pyrite, and elemental sulfur. Plant uptake was negligible. These findings improve our understanding of the physical, chemical, and biological transformations of sulfur among plants, sediments, and microorganisms, and their interactions with carbon, nitrogen, and iron cycles, in constructed wetlands and similar systems.

Increased Resistance of Nitrite-Admixed Concrete to Microbially Induced Corrosion in Real Sewers

Microbially induced concrete corrosion is a major deterioration process in sewers, causing a huge economic burden, and improved mitigating technologies are required. This study reports a novel and promising effective solution to attenuate the corrosion in sewers using calcium nitrite-admixed concrete. This strategy aims to suppress the development and activity of corrosion-inducing microorganisms with the antimicrobial free nitrous acid, which is generated in situ from calcium nitrite that is added to the concrete. Concrete coupons with calcium nitrite as an admixture were exposed in a sewer manhole, together with control coupons that had no nitrite admixture, for 18 months. The corrosion process was monitored by measuring the surface pH, corrosion product composition, concrete corrosion loss, and the microbial community on the corrosion layer. During the exposure, the corrosion loss of the admixed concrete coupons was 30% lower than that of the control coupons. The sulfide uptake rate of the admixed concrete was also 30% lower, leading to a higher surface pH (0.5-0.6 unit), in comparison to that of the control coupons. A negative correlation between the calcium nitrite admixture in concrete and the abundance of sulfide-oxidizing microorganisms was determined by DNA sequencing. The results obtained in this field study demonstrated that this novel use of calcium nitrite as an admixture in concrete is a promising strategy to mitigate the microbially induced corrosion in sewers.

Electrochemical Pretreatment for Sludge Sulfide Control without Chemical Dosing: A Mechanistic Study

Sulfide is a toxic and corrosive odorant generated in various sludge treatment and disposal systems. We developed an electrochemical pretreatment (EPT) approach to eliminate sludge sulfide production without adding chemicals. Biochemical sulfide potential (BSP) test was used to evaluate the effectiveness of EPT on sludge sulfide production. The sulfide control was effective with EPT, and we determined the underlying mechanism of EPT. EPT which was operated at 12 V for 720 s eliminated 99% of dissolved sulfide and 100% of gaseous H₂S_(g). In comparison, the dissolved sulfide reached 104 ± 1 mg S/L in the control BSP test. A sulfur mass balance analysis in the BSP test showed that 90% of the produced sulfide was removed via metal precipitation. Metal distribution results confirmed that metals (i.e., Fe, Mn, and Ni) in the sludge became soluble after EPT and were released from their residual and organically bound fractions. EPT which was operated at 15 V solubilized around 73, 92, and 72% of Fe, Mn, and Ni, and these metals precipitated the sulfide that was produced from biological sulfate reduction. Sludge analysis revealed that EPT disintegrated sludge flocs and disrupted metal-binding functional groups. Specifically, reduction of 17% C═O functional groups in the sludge was found, which could be associated with metal release. The impact of oxidants (e.g., chlorine) generated from EPT on sulfide oxidation was minimal. The findings of this study broadened up our understanding of the electrochemical process for sulfide control during saline sludge digestion.

Current status and future prospects of sewer biofilms: Their structure, influencing factors, and substance transformations

With rapid urbanization, sewer systems are extensively being constructed for the collection and transportation of sewage to minimize the severe environmental and health issues, especially relating to the spread diseases. The existence of abundant biofilms on the inner walls of sewers could lead to potential risks such as sewer explosions, poisonous gas leaks, and pipe corrosions with the transformations of various kinds of pollutants. Therefore, it is urgent to clarify their inner mechanisms to safely govern sewer systems. In this study, the characteristics of sewer biofilms including their structure, influencing factors, and substance transformations were analyzed in-depth. The results reveal that sewer biofilms (1.0 mm depth approximately) consist of large quantities of inorganic and some organic substances, while the abundant functional genus of the bacteria and archaea are summarized. Sewer biofilms influencing factors were determined to be sewer operation mode, sewage characteristics, and shear stress. Further, the transformation of organics, sulfur, and nitrogen as well as emerging micropollutants (such as, biomarkers, antibiotic resistance genes, and engineered nanoparticles) was investigated to guarantee sewer security and public health. Therefore, the current review could be considered as guidance for researchers and decision-makers.

A new method to overall immobilization of phosphorus in sediments through combined application of capping and oxidizing agents

A new method has been developed for improving the overall immobilization efficiency of phosphorus (P) in sediment. A capping agent (lanthanum modified bentonite, LMB) was sprinkled on the sediment surface to prevent the release of P in the top sediment layer. Meanwhile, an oxidizing agent (calcium nitrate, CN) was injected into the sediment layer (~5 cm) to immobilize labile P in deep sediment layers. High-resolution sampling techniques, including diffusive gradients in thin films (DGT) and high-resolution dialysis (HR-Peeper) were employed to investigate the fine-scale changes of labile and/or soluble nitrogen, P, sulfide and iron in sediments, respectively. The results showed that the combined application of LMB and CN had significant advantages over the individual treatments. The average concentrations of soluble reactive phosphorus (SRP) (0.01 mg/L) in the overlying water after a 68-day incubation were only 10%, 21% and 4% for the CK, LMB and CN treatments, respectively. Furthermore, the immobilization effect caused by the combined treatment reached from the sediment-water interface to a depth of 60 mm in the sediment, and the effective depth was much >20 mm caused by LMB treatment. The concentrations of SRP in the sediment profile were also lower than those of the other treatments. The results of this work indicate that the combined application of capping and oxidizing agents is a promising method to control water eutrophication by preventing the release of P from both the top and deep sediment layers.

Intracellularly stored polysulfur maintains homeostasis of pH and provides bioenergy for phosphorus metabolism in the sulfur-associated enhanced biological phosphorus removal (SEBPR) process

Sulfur-associated enhanced biological phosphorus removal has recently been developed for the removal of biological nutrients. In this new bioprocess, the polymeric sulfur compound (poly-S) is crucial to connecting sulfur conversions and polyphosphate accumulation; however, its mechanisms are still elusive. This study investigated the role of poly-S in maintaining the system stability by operating a lab-scale reactor for 720 d and conducting batch experiments with various initial pH values. The main findings were as follows: i) intracellular poly-S increased from 30 to 95 mg S (g VSS)^-1, whereas polyhydroxyalkanoates increased from 8 to 22 mg C (g VSS)^-1; ii) glycogen increased from 7.5 to 12.5 mg C (g VSS)^-1 during the first 520 d before decreasing; and 3) P removal could be maintained at 8-12.5 mg P (L)^-1. The decrease in glycogen was likely because the accumulation of enough poly-S could replace glycogen to provide reducing power and buffer the inner pH. The results of batch tests confirmed that poly-S could adjust the intracellular protons under anaerobic conditions (pH always returned to neutral or neutral levels at the end of anaerobic phase) and provide cellular bioenergy (adenosine triphosphate, for P uptake, thereby maintaining net P removal). The predominant microbial communities were facultative denitrifying Thauera (11%), sulfide-oxidizing Thiobacillus (8%), and sulfate-reducing Desulfobacter (9%). However, the conventional polyphosphate-accumulating organisms were detected at very low abundance (e.g. Tetrasphaera at only 0.02%). Overall, poly-S could regulate intracellular protons and energy balance and reduce glycogen accumulation, keeping good biological P removal performance.

Continuous sulfur biotransformation in an anaerobic-anoxic sequential batch reactor involving sulfate reduction and denitrifying sulfide oxidization

The pathways and intermediates of continuous sulfur biotransformation in an anaerobic and anoxic sequential batch reactor (AA-SBR) involving sulfate reduction (SR) and denitrifying sulfide oxidization (DSO) were investigated. In the anoxic phase, DSO occurred in two sequential steps, the oxidation of sulfide (S^2-) to elemental sulfur (S⁰) and the oxidation of S⁰ to sulfate (SO₄^2-). The oxidation rate of S^2- to S⁰ was 3.31 times faster than that of S⁰ to SO₄^2-, resulting in the accumulation of S⁰ as a desired intermediate under S^2--S/NO₃^--N ratio (molar ratio) of 0.9:1. Although, approximately 60% of generated S⁰ suspended in the effluent, about 40% of S⁰ retained in the sludge, which could be further oxidized or reduced in anoxic or anaerobic phase. In anoxic, S⁰ was subsequently oxidized to SO₄^2- under S^2--S/NO₃^--N ratio of 0.5:1. In anaerobic, S⁰ coexist with SO₄^2- (in fresh wastewater) were simultaneously reduced to S^2-, and the reduction rate of SO₄^2- to S^2- was 3.17 times faster than that of S⁰ to S^2-, resulting in a higher production of S⁰ in subsequent anoxic phase. Microbial community analysis indicated that SO₄^2-/S⁰-reducing bacteria (e.g. Desulfomicrobium and Desulfuromonas) and S^2-/S⁰-oxidizing bacteria (e.g. Paracoccus and Thermothrix) co-participated in continuous sulfur biotransformation in the AA-SBR. A conceptual model was established to describe these main processes and key intermediates. The research offers a new insight into the reaction processes optimization for S⁰ recovery and simultaneous removal of SO₄^2- and NO₃^- in an AA-SBR.

The rapid chemically induced corrosion of concrete sewers at high H2S concentration

Concrete corrosion in sewers is primarily caused by H₂S in sewer atmosphere. H₂S concentration can vary from several ppm to hundreds of ppm in real sewers. Our understanding of sewer corrosion has increased dramatically in recent years, however, there is limited knowledge of the concrete corrosion at high H₂S levels. This study examined the corrosion development in sewers with high H₂S concentrations. Fresh concrete coupons, manufactured according to sewer pipe standards, were exposed to corrosive conditions in a pilot-scale gravity sewer system with gaseous H₂S at 1100 ± 100 ppm. The corrosion process was continuously monitored by measuring the surface pH, corrosion product composition, corrosion loss and the microbial community. The surface pH of concrete was reduced from 10.5 ± 0.3 to 3.1 ± 0.5 within 20 days and this coincided with a rapid corrosion rate of 3.5 ± 0.3 mm year ^-1. Microbial community analysis based on 16S rRNA gene sequencing indicated the absence of sulfide-oxidizing microorganisms in the corrosion layer. The chemical analysis of corrosion products supported the reaction of cement with sulfuric acid formed by the chemical oxidation of H₂S. The rapid corrosion of concrete in the gravity pipe was confirmed to be caused by the chemical oxidation of hydrogen sulfide at high concentrations. This is in contrast to the conventional knowledge that is focused on microbially induced corrosion. This first-ever systematic investigation shows that chemically induced oxidation of H₂S leads to the rapid corrosion of new concrete sewers within a few weeks. These findings contribute novel understanding of in-sewer corrosion processes and hold profound implications for sewer operation and corrosion management.

Experimental and modelling evaluations of sulfide formation in a mega-sized deep tunnel sewer system and implications for sewer management

Mega-sized deep tunnel sewer systems are indispensable infrastructures to convey the sewage and/or stormwater to the centralized sewage treatment works in large cities with dense populations and limited land. The rapid urbanization in China and other countries is boosting the construction of the deep tunnel sewer systems. However, the formation of sulfide, which induces serious odor nuisance and sewer corrosion, has not been investigated in such sewer systems. Taking a real Sewage Conveyance System (SCS) with 23.3 km-long and 70-160 m-deep interconnected tunnels in Hong Kong as a representative example, this study conducted experimental and modelling investigations to evaluate the sulfide formation in the mega-sized deep tunnel sewer systems. The field investigation revealed that the daily sulfide production rate in the SCS was up to 1410 kg S/d, suggesting the substantial sulfide production during the long-distance and long-time sewage conveyance. Using a validated Biofilm-Initiated Sewer Process Model (BISM), the sulfide formation in the SCS under the influences of various factors, which are relevant to the situations in China and other countries, were simulated. The simulation results showed that 89% of the total sulfide production in the SCS was generated in the two tunnels with long hydraulic retention times (HRT) and large flowrates. The specific sulfide formation rates exhibited a linear relationship with HRT (R² = 0.61), but the linear relationship with the sewer diameter was weak. The sulfide production rate increased with increasing temperature (12 °C-32 °C) by 3.5 times, and it only decreased by 50% when the sulfate concentration decreased from 309 to 17 mg S/L, indicating that serious sulfide pollution could still happen in the sewers with a low concertation of sulfate in sewage. Increasing the organic levels in sewage would also promote the sulfide production in sewers. The flowrate would not influence the sulfide production rate significantly, but a storm event could remarkably reduce the sulfide production in rainy days. The findings unveil the potential serious sulfide problems in the mega-sized deep tunnel sewer systems, which are being increasingly constructed in China and other countries. To mitigate the odor and corrosion problems in the deep tunnel sewer systems, the sulfide control strategies should be considered during the sewer design and management.

Removal of Pharmaceuticals and Illicit Drugs from Wastewater Due to Ferric Dosing in Sewers

Ferric (Fe³⁺) salt dosing is an efficient sulfide control strategy in the sewer network, with potential for multiple benefits including phosphorus removal in the biological reactors and sulfide emission control in the anaerobic digesters of wastewater treatment plant (WWTP). This paper extends the knowledge on the benefit of iron dosing by exploring its impact on the fate of organic micropollutants (MPs) in the wastewater using sewer reactors simulating a rising main sewer pipe. The sulfide produced by the sewer biofilms reacted with Fe³⁺ forming black colored iron sulfide (FeS). Among the selected MPs, morphine, methadone, and atenolol had >90% initial rapid removal within 5 min of ferric dosing in the sewer reactor. The ultimate removal after 6 h of retention time in the reactor reached 93-97%. Other compounds, ketamine, codeine, carbamazepine, and acesulfame had 30-70% concentration decrease. The ultimate removal varied between 35 and 70% depending on the biodegradability of those MPs. In contrast, paracetamol had no initial removal. The rapid removal of MPs was likely due to adsorption to the FeS surface, which is further confirmed by batch tests with different FeS concentrations. The results showed a direct relationship between the removal of MPs and FeS concentration. The transformation kinetics of these compounds in the reactor without Fe³⁺ dosing is in good agreement with biodegradation associated with the sewer biofilms in the reactor. This study revealed a significant additional benefit of dosing ferric salts in sewers, that is, the removal of MPs before the sewage enters the WWTP.

Investigation of multiple polymers in a denitrifying sulfur conversion-EBPR system: The structural dynamics and storage states

Polyhydroxyalkanoates (PHAs), polyphosphate (poly-P) and polysulfide or elemental sulfur (poly-S) are the key functionally relevant polymers involved in the recently reported Denitrifying Sulfur conversion-associated Enhanced Biological Phosphorus Removal (DS-EBPR) process. However, little is known about the structural dynamics and storage states of these polymers. In particular, investigating the poly-S generated in this process is quite a superior challenge. This study was thus aimed at simultaneously qualitative-quantitative investigating poly-S and associated poly-P and PHAs through the integrated chemical analysis and Raman micro-spectroscopy coupled with multiple microscopic methods (i.e. optical microscopy, confocal laser scanning microscopy, and differential interference contrast microscopy). The chemical analytical results displayed a stable DS-EBPR phenotype in terms of sulfur conversion, P release/uptake and the dynamics of relevant polymers. The multiple microscopic images and Raman spectrum profiles further clearly demonstrated the existence of the polymers and their dynamic changes under alternating anaerobic-anoxic conditions, consistent with the chemical analytical results. In particular, Raman analysis for the first time unraveled the co-existence of S⁰/S_n^2- species stored either intracellularly or extracellularly; and the dynamic conversions between S⁰/S_n^2- and other sulfur species suggest that there might be a universal pool of bioavailable sulfur. The results reveal the mechanisms underlying the structural dynamics and changes in storage states of the relevant polymers that are functionally relevant to the carbon/phosphorus/sulfur-cycles during different metabolic phases. These mechanisms would otherwise not be obtained only using a traditional chemical analysis-based approach.

Systematic evaluation of a dynamic sewer process model for prediction of odor formation and mitigation in large-scale pressurized sewers in Hong Kong

To evaluate and mitigate odor formation and emission in sewers, several sewer models have been developed. Although these models can predict the immediate effects of chemical dosing on odor emission control, the long-term effects due to the variation of biofilm dynamics were generally underestimated. Therefore, in this study, we developed a dynamic model to simulate sewer processes initiated by sewer. The dynamic sewer process model was calibrated and validated with experimental data collected from two pressurized mains in actual operation in Hong Kong (TCS and MH17). The results show that the dynamic model can satisfactorily predict the dynamic concentrations of sulfide and ammonium (with measured and simulated values differing by less than 6%). The model was employed to systematically assess the long-term effects of three commonly used control strategies, i.e. addition of nitrate salts, addition of biocides, and hydraulic flushing, on sulfide formation and to predict sewer biofilm compositions. The modeling results reveal that the effect of odor mitigation measures on sulfide control varied with time due to the re-establishment of sulfate-reducing bacteria community in sewer biofilm. The long-term effect of nitrate addition would be diminishing because of the growth of heterotrophic denitrifies in sewer biofilms (increased from 7% to 21% after 55 days of nitrate addition) to consumed more nitrate. After dosing biocide or hydraulic flushing in sewers, sulfide production would rebound in the following several days due to the regrowth of sewer biofilms, indicating that the optimization of odor mitigation strategies is necessary. This study highlights that the biofilm dynamics shall be involved in the simulation of odor formation and emission, to evaluate and optimize the long-term effects of mitigation measures.

Experimental Investigation and Modeling of the Transformation of Illicit Drugs in a Pilot-Scale Sewer System

In-sewer stability of illicit drug biomarkers has been evaluated by several reactor-based studies, but less has been done in sewer pipes. Experiments conducted in sewer pipes have advantages over lab-scale reactors in providing more realistic biomarker stability due to the flow and biological dynamics. This study assessed the transportation and transformation of seven illicit drug biomarker compounds in a pilot-scale rising main and a gravity sewer pipe. Biomarkers presented diverse stability patterns in the pilot sewers, based on which a drug transformation model was calibrated. This model was subsequently validated using transformation data sets from the literature, aiming to demonstrate the predictability of the pilot-based transformation coefficients under varying sewer conditions. Furthermore, transformation coefficients for five investigated biomarkers were generated from four studies, and their prediction capabilities under the pilot-sewer conditions were jointly assessed using performance statistics. The transformation model was successful in simulating the in-sewer stability for most illicit drugs. However, further study is required to delineate the sources and pathways for those compounds with potential formations to be simulated in the transformation model. Overall, the transformation model calibrated using the pilot-sewer data is a credible tool for the application of wastewater-based epidemiology.

Physiological and transcriptomic analyses reveal CuO nanoparticle inhibition of anabolic and catabolic activities of sulfate-reducing bacterium

The widespread use of CuO nanoparticles (NPs) results in their continuous release into the environment, which could pose risks to public health and to microbial ecosystems. Following consumption, NPs will initially enter into sewer systems and interact with and potentially influence sewer microbial communities. An understanding of the response of microbes in sewers, particularly sulfate-reducing bacteria (SRB), to the CuO NPs induced stress is important as hydrogen sulfide produced by SRB can cause sewer corrosion and odour emissions. In this study, we elucidated how the anabolic and catabolic processes of a model SRB, Desulfovibrio vulgaris Hidenborough (D. vulgaris), respond to CuO NPs. Physiological analyses indicated that the exposure of the culture to CuO NPs at elevated concentrations (>50 mg/L) inhibited both its anabolic and catabolic activities, as revealed by lowered cell proliferation and sulfate reduction rate. The antibacterial effects of CuO NPs were mainly attributed to the overproduction of reactive oxygen species. Transcriptomic analysis indicated that genes encoding for flagellar assembly and some genes involved in electron transfer and respiration were down-regulated, while genes for the ferric uptake regulator (Fur) were up-regulated. Moreover, the CuO NPs exposure significantly up-regulated genes involved in protein synthesis and ATP synthesis. These results suggest that CuO NPs inhibited energy conversion, cell mobility, and iron starvation to D. vulgaris. Meanwhile, D. vulgaris attempted to respond to the stress of CuO NPs by increasing protein and ATP synthesis. These findings offer new insights into the bacterial-nanoparticles interaction at the transcriptional level, and advance our understanding of impacts of CuO NPs on SRB in the environment.

Real-time prediction of rain-impacted sewage flow for on-line control of chemical dosing in sewers

Chemical dosing is a commonly used strategy for mitigating sewer corrosion and odour problems caused by sulfide production. Prediction of sewage flow variation in real-time is critical for the optimization of chemical dosing to achieve cost-effective mitigation of hydrogen sulfide (H₂S). Autoregressive (AR) models have previously been used for real-time sewage prediction. However, the prediction showed significant delays in wet weather conditions. In this paper, autoregressive with exogenous inputs (ARX) models are employed to reduce the delays with rainfall data used as model inputs. The model is applied to predicting sewage flows at two real-life sewage pumping stations (SPSs) with different hydraulic characteristics and climatic conditions. The calibrated models were capable of predicting flow rates in both cases, much more accurately than previously developed AR models under wet weather conditions. Simulation of on-line chemical dosing control based on the predicted flows showed excellent sulfide mitigation performance at reduced cost.

Incorporating sulfur reactions and interactions with iron and phosphorus into a general plant-wide model

Sulfur causes many adverse effects in wastewater treatment and sewer collection systems, such as corrosion, odours, increased oxygen demand, and precipitate formation. Several of these are often controlled by chemical addition, which will impact the subsequent wastewater treatment processes. Furthermore, the iron reactions, resulting from coagulant addition for chemical P removal, interact with the sulfur cycle, particularly in the digester with precipitate formation and phosphorus release. Despite its importance, there is no integrated sulfur and iron model for whole plant process optimization/design that could be readily used in practice. After a detailed literature review of chemical and biokinetic sulfur and iron reactions, a plant-wide model is upgraded with relevant reactions to predict the sulfur cycle and iron cycle in sewer collection systems, wastewater and sludge treatment. The developed model is applied on different case studies.

Population histamine burden assessed using wastewater-based epidemiology: The association of 1,4‑methylimidazole acetic acid and fexofenadine

Systematic sampling and analysis of wastewater has become an important tool for monitoring consumption of drugs and other substances, and has been proposed as a method to evaluate aspects of population health using endogenous biomarkers. 1,4‑methylimidazoleacetic acid (MIAA) is an endogenous biomarker and metabolite of histamine turnover. Its urinary excretion is elevated in conditions such as mastocytosis, hay fever, hives, food allergies and anaphylaxis. The aim of this study was to develop and apply methods for MIAA in wastewater and compare its occurrence with antihistamine use in wastewater. Consecutive daily samples were collected from seven catchments serving populations from 3000 to 2 million and covering rural and urban communities during the 2016 Census in Australia. MIAA and the antihistamines (ranitidine, fexofenadine, cetirizine) were quantified consistently. Per capita excretion of MIAA (mg/d/capita) estimated from the WW concentrations were consistent with findings from previous clinical studies. We found significant positive correlations between loads of MIAA and fexofenadine (R² = 0.68, p < 0.0001) and cetirizine (R² = 0.25, p = 0.03) across the various catchments. Sewer reactor experiments on the degradation of MIAA and the antihistamines found that fexofenadine is stable for at least 24 h while MIAA, ranitidine and cetirizine are subject to degradation, and this should be considered in interpretations. To the best of our knowledge, this study is the first wastewater study to introduce and monitor an endogenous metabolite of histamine, and the first study to monitor and relate proxies of disease and treatment of disease.

Improved sulfide mitigation in sewers through on-line control of ferrous salt dosing

Water utilities worldwide spend annually billions of dollars to control sulfide-induced corrosion in sewers. Iron salts chemically oxidize and/or precipitate dissolved sulfide in sewage and are especially used in medium- and large-size sewers. Iron salt dosing rates are defined ad hoc, ignoring variation in sewage flows and sulfide levels. This often results in iron overdosing or poor sulfide control. Online dosing control can adjust the chemical dosing rates to current (and future) state of the sewer system, allowing high-precision, stable and cost-effective sulfide control. In this paper, we report a novel and robust online control strategy for the dosing of ferrous salt in sewers. The control considers the fluctuation of sewage flow, pH, sulfide levels and also the perturbation from rainfall. Sulfide production in the pipe is predicted using auto-regressive models (AR) based on current flow measurements, which in turn can be used to determine the dose of ferrous salt required for cost-effective sulfide control. Following comprehensive model-based assesment, the control was successfully validated and its effectiveness demonstrated in a 3-week field trial. The online control algorithm controlled sulfide below the target level (0.5 mg S/L) while reducing chemical dosing up to 30%.

A novel approach to quantifying elemental sulfur (S0) in environmental samples

The quantification of elemental sulfur (S⁰) is an important part of monitoring and controlling sulfur-involving processes. Existing methods of S⁰ detection either require significant time or involve the use of toxic chemicals. We have developed and validated a new method to determine S⁰ in environmental samples using calorimeter-ion chromatography (IC), in which S⁰ is fully oxidized to sulfur trioxide (SO₃) with pure oxygen at 20 atm in a calorimeter. The resulting SO₃ is then absorbed by a sodium bicarbonate (NaHCO₃) solution and analyzed using IC. To verify this method, standard samples with various sulfur contents (5-200 mg S), possible interfering substances (SO₄^2-, SO₃^2-, S₂O₃^2- and S^2-), and mixed environmental samples were tested and compared. The high correlation of R² = 0.999 between the examined and theoretical values was obtained with a high recovery rate of ≥95% and a low relative standard deviation (RSD) of ≤1%. Samples containing at least 25 mg of S⁰ were accurately measured (recovery error < 5%). Thiosulfate was identified as the main interfering substance, and pretreatment was needed to eliminate it. This new method is more efficient, cost-effective, easier to operate, and more secure and accurate than existing methods.