Reduced sulfide and methane in rising main sewer via calcium peroxide dosing: Insights from microbial physiological characteristics, metabolisms and community traits

Performance and mechanistic study of biochar and magnesium-enhanced phytoremediation in cadmium-contaminated soil by alfalfa

Recently, phytoremediation has been regarded as a green and environment friendly technique to treat metals contaminated soils. Thus, in this study, pot experiments were designed to investigate the combine effects of biochar and magnesium (MPs) to purify cadmium (Cd)-contaminated soils by Medicago sativa L. (alfalfa). The results showed that the combined use of biochar and Mg significantly increased the accumulation of Cd and promoted the transport of Cd from root to shoot in alfalfa, simultaneously. Importantly, the combined use of biochar and Mg could increase the accumulation of Cd in shoot and whole plant (shoot + root) of alfalfa up-to 59.1% and 23.1%, respectively. Moreover, the enhancement mechanism can be analyzed from several aspects. Firstly, the photosynthesis was enhanced, which was beneficial to plant growth. The product of photosynthesis provided energy for uptake and transport of Cd. Meanwhile, its transport in phloem could promote the transport of Cd. Secondly, the enhancement of antioxidant capacity of alfalfa effectively protected the membrane structure of alfalfa, which indicated that Cd could enter alfalfa from the channel on the cell membrane. Lastly, the chemical form of Cd and microbial community structure in soil were changed. Overall, these changes reduced the Cd toxicity in soil, enhanced the resistance capability of alfalfa, increased the Cd uptake by alfalfa and promoted the growth of alfalfa. Thus, the obtained results suggested that the combined use of biochar and Mg is an effective approach to enhance phytoremediation performance for purifying Cd-contaminated soils.

Ferrate(VI)-based oxidation for ultrafiltration membrane fouling mitigation in shale gas produced water pretreatment: Role of high-valent iron intermediates and hydroxyl radicals

Ultrafiltration (UF) is increasingly used in the pretreatment of shale gas produced water (SGPW), whereas severe membrane fouling hampers its actual operation. In this work, ferrate(VI)-based oxidation was proposed for membrane fouling alleviation in SGPW pretreatment, and the activation strategies of calcium peroxide (CaO2) and ultraviolet (UV) were selected for comparison. The findings indicated that UV/Fe(VI) was more effective in removing fluorescent components, and the concentration of dissolved organic carbon was reduced by 24.1 %. With pretreatments of CaO2/Fe(VI) and UV/Fe(VI), the terminal specific membrane flux was elevated from 0.196 to 0.385 and 0.512, and the total fouling resistance diminished by 52.7 % and 76.2 %, respectively. Interfacial free energy analysis indicated that the repulsive interactions between pollutants and membrane were notably enhanced by Fe(VI)-based oxidation, thereby delaying the deposition of cake layers on the membrane surface. Quenching and probe experiments revealed that high-valent iron intermediates (Fe(IV)/Fe(V)) played significant roles in both CaO2/Fe(VI) and UV/Fe(VI) processes. Besides, hydroxyl radicals (•OH) were also important reactive species in the UV/Fe(VI) treatment, and the synergistic effect of Fe(IV)/Fe(V) and •OH showed a positive influence on SGPW fouling mitigation. In general, these findings establish a theoretical underpinning for the application of Fe(VI)-based oxidation for UF membrane fouling mitigation in SGPW pretreatment.

Biofiltration of gaseous mixtures of dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide: Effect of operational conditions and microbial analysis

The efficient removal of volatile sulfur compounds (VSCs), such as dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), is crucial due to their foul odor and corrosive potential in sewer systems. Biofilters (BFs) offer promise for VSCs removal, but face challenges related to pH control and changing conditions at full scale. Two BFs, operated under acidophilic conditions for 78 days, were evaluated for their performance at varying inlet concentrations and empty bed residence times (EBRTs). BF1, incorporating 4-6 mm marble limestone for pH control, outperformed BF2, which used NaHCO3 in the nutrient solution. BF1 displayed better resilience, maintained a stable pH of 4.6 ± 0.6, and achieved higher maximum elimination capacities (ECmax, 41 mg DMS m-3 h-1 (RE 38.3%), 146 mg DMDS m-3 h-1 (RE 83.1%), 47 mg DMTS m-3 h-1 (RE 93.1%)) at an EBRT of 56 s compared to BF2 (9 mg DMS m-3 h-1 (RE 7.1%), 9 mg DMDS m-3 h-1 (RE 4.8%) and 11 mg DMTS m-3 h-1 (RE 26.6%)). BF2 exhibited pH stratification and decreased performance after feeding interruptions. The biodegradability of VSCs followed the order DMTS > DMDS > DMS, and several microorganisms were identified contributing to VSCs degradation in BF1, including Bacillus (14%), Mycobacterium (11%), Acidiphilium (7%), and Acidobacterium (3%).

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.

Cyanobacterial blooms control with CaO2 in different stages: Inhibition efficiency, water quality optimization and microbial community changes

This study explored the feasibility of calcium peroxide (CaO2) to inhibit cyanobacterial blooms of the outbreak and dormancy stages. Our previous studies have found that CaO2 has a high inhibitory effect on cyanobacteria. In order to explore the application effect of CaO2 in actual cyanobacteria lake water, we conducted this study to clarify the effect of CaO2 on inhibiting cyanobacteria in outbreak and dormancy stages. The results showed that CaO2 inhibited the growth of cyanobacteria in the outbreak and dormancy stages by 98.7% and 97.6%, respectively. The main inhibitory mechanism is: (1) destroy the cell structure and make the cells undergo programmed cell death by stimulating the oxidation balance of cyanobacteria cells; (2) EPS released by cyanobacteria resist stimulation and combine calcium to form colonies, and accelerate cell settlement. In addition to causing direct damage to cyanobacteria, CaO2 can also improve water quality and sediment microbial diversity, and reduce the release of sediment to phosphorus, so as to further contribute to cyanobacterial inhibition. Finally, the results of qRT-PCR analysis confirmed the promoting effect of CaO2 on the downregulation of photosynthesis-related genes (rbcL and psaB), microcystn (mcyA and mcyD) and peroxiredoxin (prx), and verified the mechanism of CaO2 inhibition of cyanobacteria. In conclusion, this study provides new findings for the future suppression of cyanobacterial bloom, by combining water quality, cyanobacterial inhibition mechanisms, and sediment microbial diversity.

Enhancement of sewer sediment control and disruption of adhesive gelatinous sediment structure using low-dose calcium peroxide

Large quantities of sediments in urban sewer systems pose significant risk of pipe clogging and corrosion. Owing to their gel-like structure, sewer sediments have strong resistance to hydraulic shear stress. This study proposed a novel approach to weaken the erosion resistance of sewer sediments by destroying viscous gel-like biopolymers in sediments with low doses of calcium peroxide (CaO2). After treatment with 10-50 mg g-1 TS of CaO2, the critical erosion shear stress was significantly reduced by 25.7%-59.9%. The sediment aggregates gradually disintegrated into small diameter particles with increasing CaO2 dosage. Further analysis showed that the strong oxidizing and alkaline environment induced by CaO2 treatment led to cell lysis and changes in the composition and property of extracellular polymeric substances (EPS). After CaO2 treatment, aromatic proteins and humic acid-like substances associated with adhesion translocated from the inner EPS layers to outer layers while being disintegrated into small organic molecules. Concomitantly, CaO2 treatment disrupted the main functional groups (-OH, COO-, C-N, CO, and CN) in inner EPS layers, thus weakening EPS adhesion. Analysis of protein secondary structure and zeta potential reflected the reduced aggregation capacity of sediment microorganisms and loosening of sediment structure after CaO2 treatment. Thus, CaO2 treatment facilitated fragmentation and disaggregation of the gelatinous structure of sewer sediments. Such green strategy decreased the cost of sewer sediment disposal by 42.10-68.95% when compared to water flushing, and it would improve the self-cleaning capacity of sewer system and efficiency of dredging equipment.

In-situ sewer sediment self-cleaning by plant ash-driven hydrolysis: Impairing adhesion and hydraulic erosion resistance from gelatinous biopolymer molecule deconstruction

The gelatinous structure and adhesion of sediments induced strong hydraulic erosion resistance and bottom siltation, which brought about serious challenges in sewer management. The in-situ sediment self-cleaning technology with low energy and labor consumption has become urgent demand. This study proposed an innovative plant ash-triggered molecule hydrolysis strategy for driving sewer sediment self-cleaning. Plant ash treatment at the optimal dosage of 0.10 g/g SS promoted molecular deconstruction and dissolution of aromatic proteins (tryptophan-like and tyrosine-like proteins), humic acids (fulvic acid-like and humic acid-like substances) and carbohydrates with secondary structure deflocculation (α-helix to β-turn), meanwhile numerous microbial cells were lysed, contributing to linkage breakage in extracellular polymeric substance (EPS). The gelatinous EPS disruption and outward migration with cohesion reduction were achievable. Sediment adhesion was vulnerable to EPS structural damage, which was degenerated by 91.14 %. Correspondingly, the sediment matrix structure was observably disintegrated into dispersive and small fragments, with increased surface electronegativity and eliminated adhesive bio-agglomeration. Thereby, the sensitivity of sediments to hydraulic erosion was greatly improved. In this case, substantial organic and inorganic sediment particles were solubilized and downstream transported by gravity sewage flow. Such plant ash-triggered hydrolysis provided a sustainable strategy for sediment self-cleaning in "waste control by waste" pattern, which improved sediment floating by 7.25-9.57 times. Considerable economic benefits of 35.56-123.46 CNY/(sewer meter length) were obtained compared with traditional mechanical flushing approaches. The findings might provide theoretical and engineering inspirations for solving sewer sediment issues.

The effect of organic sources on the electron distribution and N2O emission in sulfur-driven autotrophic denitrification biofilters

Sulfur-driven autotrophic denitrification (SAD) is considered as an effective alternative to traditional heterotrophic denitrification (HD) due to its cheap, low sludge production and non-toxicity. Nitrous oxide (N2O) as an intermediate product inevitably was generated at the limited supply of electron donor or unbalanced electron distribution condition during the denitrification process. Recently, autotrophic denitrification biofilters were conclusively implemented for advanced nitrogen removal in wastewater treatment plant (WWTP). However, residual organic sources after wastewater treatment could affect the electron distribution among denitrifying reductases and few studies are known about this issue. In this study, several lab-scale biofilters packed with elemental sulfur slices were applied to explore the electron distribution characteristics of autotrophic denitrification through the combination of different nitrogen oxides (NOx). The results clearly delineated that the different combination of nitrogen oxides had a remarkable effect on the electron distribution. In any case, the electrons likely flow toward nitrate reductase (Nar) under a single nitrogen oxide combination, followed by nitrite reductase (Nir) and nitrous oxide reductase (Nos). The concurrent presence of multiple electron acceptors resulted in most electrons flowing toward Nar, and least toward Nos. Compared to traditional SAD, the reduction rate of nitrogen oxide in the sulfur-driven autotrophic denitrification with influent of organic source (OSAD) was greatly improved. The maximum value of the true specific rates of NO3- in OSAD process was 9.43 mg-N/g-VSS/h. It was increased by 8.26 folds higher than that in traditional SAD. The electrons were more easily distributed to Nos with the addition of sodium acetate, which further promoted the N2O reduction. This study will provide theoretical support for controlling N2O release in SAD biofilters.

Impact of sertraline on biohydrogen production from alkaline anaerobic fermentation of waste activated sludge: Focusing on microbial community and metabolism

Nowadays, antidepressants are massively consumed worldwide, inevitably bringing about the concern for their latent hazard to the natural environment. This research focused on exploring the effect of sertraline (SET, a typical antidepressant) on hydrogen yields from alkaline anaerobic fermentation of waste activated sludge (WAS). The hydrogen accumulation reached the peak of 14.73 mL/g VSS (volatile suspended solids) at a SET dosage of 50 mg/kg TSS (total suspended solids), i.e., 1.90 times of that in the control fermenter. The data of Illumina high-throughput sequencing demonstrated that SET promoted the expression of genes regulating the membrane transport. Microbial community analysis suggested that some species that could degrade refractory substances were enriched after SET exposure. Finally, metabolic pathways of hydrogen production and consumption were found to be significantly affected with SET addition. This study would deepen the concept of typical antidepressants influencing energy recovery from WAS.

Peracetic acid activated by ferrous ion mitigates sulfide and methane production in rising main sewers

Iron-based peracetic acid (PAA) advanced oxidation process (AOP) is widely used in water purification because of its high efficiency and low toxicity. In this study, for the first time, ferrous iron (Fe2+) and PAA were dosed jointly into the rising main sewer reactor, to verify the feasibility of sulfide and methane control as well as investigate the comprehensive mechanism of Fe2+/PAA on sewer biofilm. Results demonstrated the superior biocidal effect of Fe2+/PAA dosing than that of PAA alone. Intermittent Fe2+/PAA dosing showed that the average inhibitory rate of sulfide production rate (SPR) and methane production rate (MPR) was 52.0% and 29.9%, respectively, at a Fe2+/PAA molar ratio of 1:1 and PAA concentration of 3 mmol/L (i.e., the mass-based concentrations of Fe2+ and PAA were 6.79 mg-Fe/L and 228 mg/L, respectively). Beside, sewer biofilm was found to be resistant to PAA during repeated dosing events. However, resistance could be alleviated by introducing sulfide in situ in the Fe2+/PAA process, and SPR and MPR were further reduced to 27.39% and 67.32% of the control, respectively. LIVE/DEAD Staining showed that Fe2+/PAA exhibited a strong destructive effect on microbial cells, with the proportion of viable cells being 26.34%. Electron paramagnetic resonance (EPR) and free radical quenching results indicated that the inhibitory order was R-O• > •OH > Fe(IV), which led to the disruption of cellular integrity (i.e., 17.24% increase in LDH) and intracellular enzyme system (i.e., cellular metabolic disorders). Microbial analysis revealed that long-term Fe2+/PAA dosing decreased the sulfate-reducing bacteria (SRB) abundance, and the dominant genus of methanogenic archaea (MA) shifted from Methanofastidiosum, Methanobacterium to Methanosaeta. The cost of Fe2+/PAA dosing on methane and sulfide control in rising main sewers was $1.81/kg-S, economically and environmental-friendly attractive for practical applications.