Improving anaerobic digestion performance after severe acidification: Unveiling the impacts of Fe3O4-bentonite composites in co-digestion of waste activated sludge and food waste.

Acidification recovery in anaerobic digestion of food waste is challenging. This study explored its in-situ recovery using a co-substrate of food waste and waste activated sludge. Fe3O4 and bentonite were used as conductor and carrier, respectively, to enhance AD performance under severe acidification. The application of Fe3O4-bentonite resulted in a 152% increase in cumulative methane in the Fe3O4-bentonite 10 digester, demonstrating its effectiveness in restoring the acidified AD system. In acidified systems, bentonite enhanced the diversity and richness of microbial communities due to its buffering capacity. The excessive non-conductive polysaccharides excreted by bacteria in extracellular polymeric substances reduced the possibility of electron transfer by Fe3O4. However, in the synergistic application of Fe3O4 and bentonite, this resistance was alleviated, increasing the possibility of direct interspecies electron transfer, and accelerating the consumption of volatile fatty acids. This approach of integrating carrier and conductive materials is significant for in-situ restoration of acidified systems.

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.

Reactivity of dissolved effluent organic matter (EfOM) with hydroxyl radical as a function of its isolated fractions during ozonation of municipal secondary effluent.

Dissolved effluent organic matter (EfOM) plays an important role in ozonation decomposition and hydroxyl radical (·OH) scavenging in ozonation for the degradation of trace organic contaminants (TrOCs) in municipal secondary effluents. The properties of EfOM have been considered a major concern in this process because EfOM fractions act differently as initiator, promoter or inhibitor of ozone decomposition and ·OH scavenging, which further impacts the degradation effectiveness of TrOCs. This study isolated EfOM from three wastewater treatment plants into six fractions (HoA, HoB, HoN, HiA, HiB and HiN) to understand the reaction kinetics as a function of EfOM and its isolated fractions. Their reaction rate constants with ·OH (kEfOM-·OH), and their roles as the initiator, promoter and inhibitor in the ·OH chain reactions in ozone decomposition were further quantified. The results showed that kEfOM-·OH of hydrophilic fractions (HiF) (accounting for 17%) reached up to 10 times as high as that for hydrophobic fractions (HoF) (accounting for 83%) (7.92 × 108 M-1 s-1 versus 0.78 × 108 M-1 s-1), suggesting the dominating role of HiF in ·OH scavenging. Hydrophilic base (HiB) was the most important fraction dominating the ozone decomposition and reaction with ·OH due to its highest rate constants of initiation and promotion. This study quantifies the kinetics and contribution of EfOM fractions in ·OH scavenging, which will guide the optimization implementation of ozonation and other ·OH-mediated AOPs toward wastewater effluents.

Corporate Social Responsibility and Energy-Related Pro-Environmental Behaviour of Employees in Hospitality Industry.

Tourism and hospitality are at a crossroads. The growth and developmental potential of these industries indicate the economic benefits for an associated nation at one end. However, the environmental issues related to tourism and hospitality create challenges for the administration at another end. In most cases, a sheer amount of carbon emission in hospitality lies with energy consumption, especially electrical energy. However, past studies on environmental management have mainly focused on the supply side of energy (production) and left the terrain of the demand side (consumption by individuals) unattended. Recently, behavioral scientists have indicated that corporate social responsibility (CSR) actions of a firm can promote sustainable behavior among individuals, including employees. We tend to spark this discussion from an energy consumption perspective by investigating the relationship between CSR and energy-related pro-environmental behavior of employees (EPB) in the hospitality sector of a developing country (Pakistan). To understand the underlying mechanism of this relationship, this study proposes the mediating role of green intrinsic motivation (GIM) and the moderating role of human emotions, e.g., employee admiration (ADM). We developed a theoretical model for which the data were gathered from different hotel employees with the help of a questionnaire. We used structural equation modeling for hypotheses testing. The empirical evidence indicated that CSR significantly predicts EPB, and there is a mediating role of GIM. The study also confirmed that ADM moderates this relationship. The findings of this study will be helpful for hotel administration to understand the profound importance of CSR-based actions to promote energy-related sustainable behavior among employees, e.g., EPB. Other implications for theory and practice have been highlighted in the main text of this draft.

Enhancement and mechanisms of micron-pyrite driven autotrophic denitrification with different pretreatments for treating organic-limited waters.

Pyrite-driven autotrophic denitrification (PAD) represents a cheap and promising way for nitrogen removal from organic-limited wastewater, which has obtained increasing attention in recent years. However, the limited denitrification rate and unclear mechanism underlying the process have hindered the engineered application of PAD. This study aims to shed light on the impacts of different pretreatments (i.e., ultrasonication, acid-washing and calcination) on micron-pyrite surface characteristics, denitrification performance and biofilm formation during PAD in batch reactors. A series of solid-phase analyses revealed that all pretreatments could significantly promote biofilm attachment on pyrite granules, but impacted the proportion, distribution and chemical oxidation state of sulfur (S) and iron (Fe) at varying degrees. Batch tests showed that ultrasonication and acid-washing could enhance the total nitrogen reduction rate by 14% and 99%, and decrease the sulfate production rate by 51% and 42%, respectively, when compared with untreated pyrite. Microbial community analysis indicated that Thiobacillus and Rhodanobacter dominated in PAD systems. Two types of indirect mechanisms (i.e., contact and non-contact) for pyrite leaching may co-occur in PAD system, resulting in ferrous iron (Fe2+), thiosulfate (S2O32-) and sulfide (S2-) as the main electron donors for denitrification. A PAD mechanism model was proposed to describe the PAD electron transfer pathway with the aim to optimize the engineered application of PAD for nitrogen removal.

Enhancement of nitrogen removal by a modular design of vertical flow constructed wetlands with a plant carbon source: Optimization of carbon dosage for nitrogen removal, practicability evaluation and strategy exploration for water quality control.

The requirement of artificial aeration for increasing nitrogen removal in vertical flow constructed wetlands (VFCWs) brings extra energy consumption and complex maintenance. The feasibility of a modular design to replace artificial aeration for partially saturated VFCWs with palm bark as a carbon source (PSVFCW-pb) to achieve water quality control, especially nitrogen removal was evaluated. The PSVFCW-pb with a spatially separate structure and perforated peripheries for better oxygen diffusion had a promising total nitrogen removal (e.g., 66.4% at a dosage of 1.435 g/L of palm bark pretreated at 120 °C for 40 min) without additional aeration, while organic carbon removal was nearly unaffected. An appropriate increase of the palm bark dosage (≤1.435 g/L) resulted in higher nitrogen removal; however, a more palm bark (1.875 g/L) could not further increase nitrogen removal but caused color pollution. In addition, the removal of nitrogen by the modularized PSVFCW-pb was more sensitive to the ambient temperature than the removal of organic carbon and phosphorus, and the higher temperature was preferable. Notably, the more attractive property of the modular design is its great potential to improve nitrogen removal by conveniently altering the number and/or scale of oxic and oxygen-free modules. Finally, the relationships between the hydraulic load and inflow concentration were explored, by which the suitable hydraulic load could be flexibly adjusted based on real-time water quality to meet the specified surface water quality criteria in different seasons. This study provides a reliable CW design for controlling nutrient pollution in surface waters.

Shape optimization of egg-shaped sewer pipes based on the nondominated sorting genetic algorithm (NSGA-II).

Overflow pollution is an undesired issue that commonly occurs in combined sewers under wet weather conditions. There is a lack of existing studies on the structural optimization of sewers to prevent siltation, and no previous study on egg-shaped sewers with this purpose has confirmed satisfactory anti-sedimentation performance. To achieve reduced sedimentation and lower energy loss under low- and high-flow conditions, respectively, the nondominated sorting genetic algorithm (NSGA-II) was adopted in this study based on a constant full filling discharge capacity equal to that of a 300 mm (diameter) circular sewer. The results showed that egg-shaped sewers with bottom and top arc radii of 58.3 and 116.6 mm, respectively, and a height of 408.1 mm performed significantly better than circular sewers (d = 300 mm). Notably, at a low flow ratio below 0.2, the shear stress of the optimized egg-shaped sewer was 5.2%-20.6% higher than that of the circular sewer. At a flow ratio of 0.2-0.6, both the egg-shaped and circular sewers were capable of maintaining a balanced amount of sediment between deposition and erosion. As the flow ratio increased to 0.6-1, both types of sewers completely scoured sediments: in this situation, the shear stress of the egg-shaped sewer was 5.5%-10.1% lower than that of the circular sewer, thus exhibiting reduced energy loss. This study indicates that egg-shaped sewers have an attractive future in replacing circular sewers for sedimentation prevention and cost control.

Ultrasound-enhanced coagulation for cyanobacterial removal: Effects of ultrasound frequency and energy density on coagulation performance, leakage of intracellular organic matters and toxicity.

Ultrasound-enhanced coagulation is capable of effectively removing algal cells in algae-laden water. However, study differences in ultrasound settings, algal cell conditions and coagulant properties complicate the accurate evaluation of this technique for practical applications. No study has yet compared algae (and algal organic matters) removal among different frequencies of ultrasound in the ultrasound-coagulation process. In this study, the ultrasound at three typical frequencies, 29.4, 470 and 780 kHz, were applied for this purpose. The results showed that high-frequency ultrasound at 470 and 780 kHz had substantially greater improvement of coagulation than low-frequency ultrasound at 29.4 kHz (For example, the turbidity removal at 1 mg-Al/L of polymeric aluminum chloride increased by 204.2%, 571.9% and 563.2% under 29.4, 470 and 780 kHz ultrasound-coagulation, respectively, at 3.42 J/mL). Algal cells exhibited irreversible physical damage and the release of intracellular organic matters (such as odorous compounds) under low-frequency ultrasound with energy densities ≥ 3.42 J/mL, whereas high-frequency ultrasound was characterized by nonviolent impairment, including oxidative degradation and gas vacuole destruction (particularly reversible) resulting from ultrasound-induced radicals and cell resonance, respectively. Avoiding the severe destruction of algal cells is crucial for minimizing the toxicity and secondary pollution of the treated water. To achieve satisfactory removal, protected safety and better economy, the optimal energy density for each frequency was also determined. The findings from the analyses of the laboratory-cultured sample were confirmed via real eutrophic surface water. This study provides new insights and guidance for the ongoing study of harmful algal removal by ultrasound-enhanced coagulation.

Ultrasound-enhanced coagulation for Microcystis aeruginosa removal and disinfection by-product control during subsequent chlorination.

Ultrasound techniques have gained increased interest in environmental remediation because of their promising performance and reagent-free nature. This study investigated the effects of ultrasound-coagulation on Microcystis aeruginosa removal, disinfection by-product (DBP) formation during subsequent chlorination, and acute toxicity and DBP-associated toxicity variations in chlorinated effluents. Compared with coagulation using polymeric aluminum chloride (5 mg-Al/L) alone, ultrasound-coagulation showed significantly enhanced turbidity removal, with the removal ratio increasing from 51% to 87%-96%. Although the addition of ultrasound may not substantially improve and even deteriorate the coagulation removal of DOC following the leakage of intracellular organic matter, the significantly improved DBP control was achieved as the cells dominated DBP formation. With the addition of ultrasound, the chlorine demand, aggregate DBP concentration and total organic halogen concentration reductions in the chlorinated M. aeruginosa solution increased from 15%, 47% and 52% (coagulation alone), respectively, to 56%-78%, 56%-80% and 68%-89%. The enhanced DBP mitigation was mainly attributed to the enhanced algal removal. Similarly, the acute toxicity and DBP-associated toxicity of chlorinated effluents further decreased from 100% and 0.0092 (coagulation alone) to 30%-88% and 0.0029-0.0060. Therefore, ultrasound-enhanced coagulation is a promising strategy for urgent algal removal, DBP mitigation and toxicity abatement.

An investigation of mechanisms for the enhanced coagulation removal of Microcystis aeruginosa by low-frequency ultrasound under different ultrasound energy densities.

There is a lack of studies elaborating the differences in mechanisms of low-frequency ultrasound-enhanced coagulation for algae removal among different ultrasound energy densities, which are essential to optimizing the economy of the ultrasound technology for practical application. The performance and mechanisms of low-frequency ultrasound (29.4 kHz, horn type, maximum output amplitude = 10 µm) -coagulation process in removing a typical species of cyanobacteria, Microcystis aeruginosa, at different ultrasound energy densities were studied based on a set of comprehensive characterization approaches. The turbidity removal ratio of coagulation (with polymeric aluminum salt coagulant at a dosage of 4 mg Al/L) was considerably increased from 44.1% to 59.7%, 67.0%, and 74.9% with 30 s of ultrasonic pretreatment at energy densities of 0.6, 1.11, and 2.22 J/mL, respectively, indicating that low-frequency ultrasound-coagulation is a potential alternative to effectively control unexpected blooms of M. aeruginosa. However, the energy density of ultrasound should be deliberately considered because a high energy density (≥18 J/mL) results in a significant release of algal organic matter, which may threaten water quality security. The specific mechanisms for the enhanced coagulation removal by low-frequency ultrasonic pretreatment under different energy densities can be summarized as the reduction of cell activity (energy density ≥ 0.6 J/mL), the slight release of negatively charged algal organic matter from cells (energy density ≥ 1.11 J/mL), and the aggregation of M. aeruginosa cells (energy density ≥ 1.11 J/mL). This study provides new insights for the ongoing study of ultrasonic pretreatment for the removal of algae via coagulation.

Effect of passive ventilation on the performance of unplanted sludge treatment wetlands: heavy metal removal and microbial community variation.

Sludge treatment wetlands (STWs) have been applied worldwide to treat excess sludge; however, the performance of STWs is generally limited by weather partly due to the plants vegetated on the STWs. In this study, ventilation is suggested to assist unvegetated STWs. Solid samples from different depths were analysed. Additionally, the variation of microbial community in STW unit was analysed and the fate of heavy metals in the sludge was determined. Results indicate that the STW unit with suitable parameters has better performance in stabilising and maturing the sludge than planted STW, which may contribute to the variation of the microbial community; additionally, ventilation exerts a positive influence on these bacteria during the variation of microbial community and on heavy metal removal through the substrate and positively impacts the Cd and Pb in reduction state. Furthermore, ventilation decreases the bioavailability of Cr. With ventilation in STWs, Bacillus and Streptomyces play a necessary role in enhancing the possibility of sludge to be used as microbial inoculants.

A comparative study on the use of palm bark as a supplementary carbon source in partially saturated vertical constructed wetland: Organic matter characterization, release-adsorption kinetics, and pilot-scale performance.

In this study, a comparative investigation of palm bark and corncob (a well-investigated material) for enhancing nitrogen removal efficiency in partially saturated vertical constructed wetland (PSVCW) was performed to evaluate an effective and cost-effective supplementary carbon source. The characteristics of the released organic matter and the release processes were analyzed through optical property characterization and a first-order release-adsorption model, respectively, and the nitrogen removal performance was evaluated in a series of pilot-scale PSVCWs. Results showed that the amount of organic matter released per unit mass of corncob was larger than that released per unit mass of palm bark under the same pretreatment conditions (control, heat, and alkaline pretreatment). The organic matter released from corncob has a higher apparent molecular weight and a higher degree of aromatic condensation than those of the organic matter released from palm bark, whereas the organic matter released from palm bark has higher and more stable bioavailability. Moreover, palm bark showed a more significant improvement of release capacity with the heat and alkaline pretreatment methods. Pilot-scale studies revealed that PSVCW using palm bark as the supplementary carbon source has a longer replacement cycle and higher total nitrogen (TN) removal efficiency than that using corncob, indicating that palm bark can be considered an effective and inexpensive supplementary carbon source. This study provides initial guidance for the ongoing research on supplementary carbon sources for improving nitrogen removal efficiency in constructed wetlands.

Cohesive strength changes of sewer sediments during and after ultrasonic treatment: The significance of bound extracellular polymeric substance and microbial community.

Sewer flushing is widely used to remove sewer sediment from drainage systems; however, its performance and cleaning efficiency are limited by the cohesive strength of sewer sediment. To address this, ultrasound, as a clean technology, is proposed to reduce the cohesive strength of sewer sediment. This study investigated the variations in the cohesive strength, extracellular polymeric substances (EPSs), and microbial community of sewer sediment with ultrasonic treatment. During ultrasonic conditioning, the degradation process of the cohesive strength followed the first-order kinetic model and was positively related to the degradation of bound-EPSs. Field emission scanning electron microscopy, particle diameter, and three-dimensional excitation emission analyses suggested that ultrasound reduced the cohesive strength by decreasing the bound-EPS concentration, which reduced the particle size of sewer sediment, and by destroying the structure of tryptophan proteins, which impaired the stability of agglomerated particles. Following ultrasonic treatment, the cohesive strength of the treated sediment was reduced to 69.3% of that of the raw sewer sediment after storage for 21 days; this result could be ascribed to the improvements in polysaccharide transport, amino acid transport, and the cell wall biogenesis functions of the microbial community, as indicated by PICRUSt. Furthermore, next-generation sequencing studies suggest that the proportions of Syntrophomonadaceae, Bacteroidetes_vadinHA17, Synergistaceae, and Syntrophaceae, which are associated with anaerobic digestion and methane production in sediment, improved conspicuously after ultrasonic conditioning.

Long-term effect of water diversion and CSOs on the remediation of heavy metals and microbial community in river sediments.

Untreated combined sewer overflows (CSOs) cause serious water pollution problems. In this study, the effects of CSO-induced heavy metals and the remediation practice of installation of a long-term water diversion (LTWD) on the microbial environment in river sediments were analyzed in an inland river. The Zn, Cd, Cr, and Cu contents in sediments and water were analyzed. DNA extraction and polymerase chain reaction analysis were conducted based on the Illumina MiSeq platform. The results showed that CSOs have a significant adverse impact on the diversity of microbial populations in river sediments. The LTWD is helpful in improving the richness of microorganisms and the proportion of Gram -ves, but it is challenging to reduce the accumulation of heavy metals in the sediment. The correlation analysis shows a strong relationship between some metabolic pathways and Zn and Cd accumulation in river sediments. Some detoxification compound metabolisms are also promoted at these sites. Thus, chronic exposure to environmental heavy metals from CSOs decreases the river microbial community, and further affects the ecological environment of the river. Therefore, without eliminating CSOs or reducing overflow frequency, it is difficult to alleviate the accumulation of heavy metals in river sediments and improve river ecology via water diversion alone.

Effects of extracellular polymeric substances and microbial community on the anti-scouribility of sewer sediment.

Sewer sediment is the main source of overflow pollution, and the anti-scouribility of sewer sediment directly determines the amount of the discharged contaminants. In this study, sewer sediments of different depths were collected from combined and storm sewers in Shanghai, China. The anti-scouribility, represented by the shear stress of each layer of sewer sediment, was detected in situ. The microbial community and extracellular polymeric substances (EPS), including carbohydrates and proteins present in the sewer sediments were characterized. The results indicated that the distribution of the anti-scouribility of sewer sediment is regulated. There were positive correlations between the content of EPS, proteins, and carbohydrates, and the anti-scouribility of sediments (Pearson Corr. = 0.604, sig. = 0.219; Pearson Corr. = 0.623, sig. = 0.234; Pearson Corr. = 0.727, sig. = 0.359, respectively). Furthermore, the microbial community had a positive influence on anti-scouribility. In particular, the gram-positive bacterial phyla of Bacteroidetes and Firmicutes may be important and influential for the improvement of anti-scouribility of sediment owing to their production of cellulose.

Runoff simulation of two typical urban green land types with the Stormwater Management Model (SWMM): sensitivity analysis and calibration of runoff parameters.

The characteristics of surface runoff and the infiltration properties of urban green land are important to determine the effects of runoff reduction by low-impact development (LID) facilities. In this paper, two typical types of urban green land (lawn and shrub) in Shanghai were selected to study the runoff characteristics under eight rainfall events. The sensitivity of the runoff parameters was analyzed, and then, the optimal parameters were determined using the Stormwater Management Model (SWMM). The results showed that the interception and infiltration capacities of shrub were greater than those of lawn. The rainfall intensity and rainfall pattern were the major factors that influenced the interception and infiltration of rainwater. The threshold value that generates runoff varied across the eight rainfall events ranged from 1.6 to 28.5 mm for lawn and 4.5 to 32.0 mm for shrub. The maximum reduction ratios of runoff and peak flow for shrub were 52 and 57% higher than them for lawn, respectively. The parameters for shrub were more sensitive to runoff and peak flow compared with those for lawn. Under light rainfalls with a short duration, the maximum infiltration rate and depression storage were more sensitive than those under heavy rainfalls with a long duration. Antecedent dry weather period was not found to be a sensitive parameter except for the shrub under light rainfalls. The relative errors of runoff and dynamic mean runoff (60 min) for lawn and shrub were within ± 9.5%. The errors of peak flow ranged between - 21 and 16.6%. The dynamic runoff characteristics and the parameters for lawn and shrub determined in this study can provide references for simulating urban runoff and planning LID areas.

Identification of sewage markers to indicate sources of contamination: Low cost options for misconnected non-stormwater source tracking in stormwater systems.

There has been increasing research focusing on the detection and occurrence of wastewater contamination in urban water systems. To find suitable markers to indicate industrial and domestic sewage flows inappropriately entering storm drains, this study investigated the occurrence and fate of 52 chemical markers through wastewater treatment facilities of manufacturers of agricultural and sideline products, beverage products, and pharmaceutical products, which are also consumed in our daily life. Of the 52 candidate markers, sodium, chloride, potassium, isomalto-oligosaccharide, acesulfame, theanine, glycerol, and clarithromycin were found to be conservative markers, with an average change in concentrations through the wastewater treatment processes of <30%. These markers are useful in identifying industrial and domestic sewage flow contamination in urban sewers. Specially, sodium, chloride, potassium, isomalto-oligosaccharide, acesulfame, and clarithromycin exhibited higher concentrations in blackwater than in greywater, with detected average concentrations of 43.8 mg/L, 189 mg/L, 37.3 mg/L, 123 µg/L, 37.2 µg/L, and 0.99 µg/L in blackwater, respectively. In contrast, theanine and glycerol were observed with higher concentrations in greywater than in blackwater (average 10.1 µg/L and 19.5 µg/L in greywater, respectively). The benchmark concentrations to discriminate between industrial and domestic sewage were also presented. A study in a storm drainage system of downstream Taihu catchment, China demonstrated the usefulness of the markers as low-cost options to trace and quantify misconnected wastewater entries into storm drains, while denoting priority areas for misconnected entries correction.

Characterizing heavy metals in combined sewer overflows and its influence on microbial diversity.

This study characterized the pollution levels and potential ecological risk of heavy metals in combined sewer overflows (CSOs) and their effects on microbial diversity in nearby riparian sediments. The chemical fractionations of Zn, Cd, Cr, and Cu in dry-weather flows, wet-weather flows (CSO discharges), sewer sediments, and surface runoffs were determined. Geo-accumulation (Igeo) and ecological risk (RI) indexes were employed for metal risk assessment. DNA extraction and polymerase chain reaction (PCR) amplification on the Illumina MiSeq platform were conducted. The results show that heavy metals contents in fine-sized fractions have higher values than those in coarse-sized fractions. Chemical fractionation analysis suggests that Zn and Cd are two of the most bioavailable metals impacted by anthropogenic activities. Cr and Cu contents in CSOs are relatively stable and could exist for extended periods. According to the RI analysis, CSOs pose a considerable risk (RI-G2) to receiving waters due to the higher bioavailability of Cd, which was consistent with the Igeo index. Furthermore, under the stress of the highly-bioavailable Cd and Cu, Gram +ves in the riparian benthic sediment gradually became dominant with metal-tolerance property. Therefore, long-term exposure to highly bioavailable metals could exhibit great impacts on microbial diversity.

Different erosion characteristics of sediment deposits in combined and storm sewers.

To investigate the different erosion patterns of sediments in combined and storm sewers, sediments from three separate sewer systems and two combined sewer systems in urban Shanghai were collected for the flushing experiments. These experiments were conducted with different consolidation periods and shear velocities. As the consolidation period increases, dissolved oxygen exhibits a positive effect on the microbial transformations of organic substrates. Potential structural changes and separations of the surface and bottom layers of sediments are observed. The results also reveal that the organic matter, particle size and moisture have different effects on the erosion resistance of sediments. Furthermore, illicit connections behaved as an important factor affecting the viscosity and static friction force of particles, which directly alter the erosion resistance of sewer sediments.

Influences of rainfall variables and antecedent discharge on urban effluent concentrations and loads in wet weather.

For storm drainages inappropriately connected with sewage, wet weather discharge is a major factor that adversely affects receiving waters. A study of the wet weather influences of rainfall-discharge variables on storm drainages connected with sewage was conducted in the downtown Shanghai area (374 ha). Two indicators, event mean concentration (EMC) and event pollutant load per unit area (EPL), were used to describe the pollution discharge during 20 rain events. The study showed that the total rainfall and discharge volume were important factors that affect the EMCs and EPLs of the chemical oxygen demand, total phosphorus, and especially those of NH4+-N. The pollutant concentrations at the beginning of the discharge and the discharge period were also major factors that influence the EMCs of these three pollutants. Regression relationships between the rainfall-discharge variables and discharge volume/ EPLs (R2 = 0.824-0.981) were stronger than the relationships between the rainfall-discharge variables and EMCs. These regression equations can be considered reliable in the system, with a relative validation error of less than ±10% for the discharge volume, and less than ±20% for the EPLs. The results presented in this paper provide guidance for effectively controlling pollution in similar storm drainages.