Flow rate influence on sediment depth estimation in sewers using temperature sensors.

Enhancing sediment accumulation monitoring techniques in sewers will enable a better understanding of the build-up processes to develop improved cleaning strategies. Thermal sensors provide a solution to sediment depth estimation by passively monitoring temperature fluctuations in the wastewater and sediment beds, which allows evaluation of the heat-transfer processes in sewer pipes. This study analyses the influence of the flow conditions on heat-transfer processes at the water-sediment interface during dry weather flow conditions. For this purpose, an experimental campaign was performed by establishing different flow, temperature patterns, and sediment depth conditions in an annular flume, which ensured steady flow and room-temperature conditions. Numerical simulations were also performed to assess the impact of flow conditions on the relationships between sediment depth and harmonic parameters derived from wastewater and sediment-bed temperature patterns. Results show that heat transfer between water and sediment occurred instantaneously for velocities greater than 0.1 m/s, and that sediment depth estimations using temperature-based systems were barely sensitive to velocities between 0.1 and 0.4 m/s. A depth estimation accuracy of ±7 mm was achieved. This confirms the ability of using temperature sensors to monitor sediment build-up in sewers under dry weather conditions, without the need for flow monitoring.

The characteristics and in-sewer transport potential of solids derived from domestic food waste disposers.

This study aims to assess the transportability of food waste disposer particles within a sewer system. A series of laboratory studies has examined the physical characteristics of solid particles derived from domestic food waste disposers. Particle size distributions and maximum settling velocity characteristics were measured for 18 common food types, and stored in a publicly accessible database. Particle size distributions are shown to fit well with a 2-parameter Gamma distribution. Settling velocity is generally higher for larger particles, except when particle density and sphericity change. For most food types, particle specific gravity was close to unity. Egg shell particles had a significantly higher specific gravity. This information, combined with the particle size data have been used to show that there is a very low likelihood of food waste particle deposition in sewers during normal operational flows, other than temporary transient deposits of egg shell particles.

Potential influence of sewer heat recovery on in-sewer processes.

Heat recovery from combined sewers has a significant potential for practical renewable energy provision as sources of heat demand and sewer pipes are spread across urban areas. Sewers are continuously recharged with relatively hot wastewater, as well as interacting with heat sources from surrounding air and soil. However, the potential effects of modifying sewage temperature on in-sewer processes have received little attention. The deposition of fats, oils and greases (FOGs) and hydrogen sulphide formation are biochemical processes and are thus influenced by temperature. This paper utilises a case study approach to simulate anticipated temperature reductions in a sewer network due to heat recovery. A laboratory investigation into the formation of FOG deposits at temperatures varying between 5 °C and 20 °C provided mixed results, with only a weak temperature influence, highlighting the need for more research to fully understand the influence of the wastewater composition as well as temperature on FOG deposit formation. A separate modelling investigation into the formation of hydrogen sulphide when inflow temperature is varied between 5 °C and 20 °C showed considerable reductions in hydrogen sulphide formation. Hence, heat extraction from sewers could be a promising method for managing some in-sewer processes, combined with traditional methods such as chemical dosing.

Spatial Variability of Anaerobic Processes and Wastewater pH in Force Mains.

The present study focuses on anaerobic organic matter transformation processes in force mains for the purpose of improving existing sewer process models. Wastewater samples were obtained at 100 m intervals from a 1 km long pilot scale force main and measured for several wastewater parameters. Transformation rates for selected parameters were calculated and their spatial variability analyzed. In terms of electron transfer, fermentation was the most significant process, resulting in a net volatile fatty acid formation of 0.83 mmol/L. Sulfate reduction resulted in a production of 0.73 mmol/L of inorganic sulfide. Methanogenesis was negligable in all experiments despite an anaerobic residence time of more than 30 hours. As a result of the anaerobic processes, the wastewater pH decreased by approximately one pH unit, resulting in a corresponding increase in the fraction of molecular hydrogen sulfide. A significant spatial variablilty was observed for the average transformation rates of all parameters.

Enumeration of sulphate-reducing bacteria for assessing potential for hydrogen sulphide production in urban drainage systems.

Urban drainage structures have increasing demands which can lead to increasing hydrogen sulphide related problems forming in places where they have not previously been prevalent. This puts pressure on the methods currently used to monitor and diagnose these problems and more sophisticated methods may be needed for identifying the origin of the problems. Molecular microbiological techniques, such as quantitative polymerase chain reaction, offer a potential alternative for identifying and quantifying bacteria likely to be causing the production of hydrogen sulphide, information that, when combined with an appropriate sampling programme, can then be used to identify the potentially most effective remediation technique. The application of these methods in urban drainage systems is, however, not always simple, but good results can be achieved. In this study bacteria producing hydrogen sulphide were quantified in three small combined sewer overflow storage tanks. Bacterial counts were compared between wastewater, biofilms and sediments. Similar numbers were found in the wastewater and biofilms, with the numbers in the sediments being lower. If remediation methods for hydrogen sulphide are deemed necessary in the tanks, methods that target both the wastewater and the biofilms should therefore be considered.

The effect on the birth experience of women and partners of giving birth in a "birth environment room": A secondary analysis of a randomised controlled trial.

OBJECTIVE: To evaluate women and partners' experience of birth in a "birth environment room" compared to a standard birth room. DESIGN: A single centre parallel randomised controlled trial. Women and partners were enrolled during a 3-year period (May 2015 to March 2018). SETTING: The Department of Obstetrics and Gynaecology at Herning Hospital, Denmark. PARTICIPANTS AND INTERVENTION: A total of 680 Danish speaking nulliparous women, more than 18 years old, with a singleton pregnancy in cephalic presentation, and a spontaneous onset of labour, and their partners were randomly assigned to give birth in a "birth environment room" (n = 340) or in a standard birth room (n = 340) on arrival at the birth unit. MEASUREMENTS AND FINDINGS: Outcomes were the overall birth experience and overall satisfaction with care, measured on a Likert scale, obtained in the postpartum questionnaire sent to the women 6 weeks after birth and to their partners 1/2 weeks after birth. Other outcomes were "staff support for partner", "undisturbed contact with new-born", "feeling of being listened to", "level of information", "attention to psychological needs", "suggestions for pain-relief", "participation in decision-making", "midwife present when wanted", "support from midwife", "birth wishes were met", "loss of internal control" (only women), "loss of external control", "support from partner" (partners: "being supportive for partner"), "importance of physical environment for birth" and "importance of physical environment for staff´s ability to involve the women" (only women). All outcomes were prespecified. We applied Mann Whitney U test for comparing the two groups. Data were collected from 326 women and 236 partners in the intervention group and from 315 women and 209 partners in the control group. The intention-to-treat analysis revealed no difference in the overall experience of birth for women or partners (p 0.81 and p 0.17, respectively). Partners in the intervention group reported more overall satisfaction with care compared to partners in the control group (p 0.048). In the intervention group, fewer women and partners responded they had not had the opportunity for undisturbed contact with their new-born in the first hours after birth (RR 0.19 (95% CI 0.04-0.87) and OR 0.00 CI (0.00-0.83), respectively). Otherwise, there were no differences between groups. The thematic analysis revealed that many women and partners felt they were not able to benefit from the features in "the birth environment room" in the most intense hours of birth. KEY CONCLUSION AND IMPLICATIONS FOR PRACTICE: "The birth environment room" did not improve the overall experience of birth for women and partners. Partners in the intervention group were overall more satisfied with care. These findings are of importance in the developing of physical birth environments that support the mental/emotional process of labour.

Profiling Bispebjerg Acute Cohort: Database Formation, Acute Contact Characteristics of a Metropolitan Hospital, and Comparisons to Urban and Rural Hospitals in Denmark.

Purpose: To present a metropolitan cohort, Bispebjerg acute cohort (BAC), and compare patient characteristics and outcomes with patients from urban and rural hospitals in Denmark. Patients and Methods: We linked data from seven Danish nationwide registries and included all acute contacts to non-psychiatric hospitals in the years 2016-2018. Acute hospital contacts to Bispebjerg and Frederiksberg Hospital constituted BAC, representing a solely metropolitan/urban catchment area. Patient characteristics and outcomes were compared to the rest of Denmark in an urban cohort (UrC) and a rural cohort (RuC), stratified by visit and hospitalization contact types. Results: We identified 4,063,420 acute hospital contacts in Denmark and BAC constituted 8.4% (n=343,200) of them. BAC had a higher proportion of visits (65.1%) compared with UrC (52.1%) and RuC (45.3%). Patients in BAC more often lived alone (visits: BAC: 34.8%, UrC: 30.6%, RuC: 29.2%; hospitalizations: BAC: 50.8%, UrC: 36.7%, RuC: 37.2%) and had temporary CPR number (visits: BAC: 4.4%, UrC: 1.9%, RuC: 1.6%; hospitalizations: BAC: 1.5%, UrC: 0.9%, RuC: 0.8%). Visit patients in BAC were younger (BAC: 36, UrC: 42, RuC: 45 years, median), more often students (BAC: 18.0%, UrC: 14.0%, RuC: 12.5%), and had more contacts due to infectious diseases (BAC: 19.8%, UrC: 14.1%, RuC: 6.2%) but less due to injuries (BAC: 40.0%, UrC: 43.8%, RuC: 60.7%). Hospitalized patients in BAC had higher median age (BAC: 64, UrC: 61, RuC: 64 years) and fewer were in employment than in UrC (BAC: 26.1%, UrC: 32.1%, RuC: 28.1%). BAC Hospitalizations had a lower death rate within 30 days than in RuC (BAC: 3.0% [2.9-3.1%], UrC: 3.1% [3.0-3.1%], RuC: 3.4% [3.3-3.4%]), but a higher readmission-rate (BAC: 20.5% [20.3-20.8%], UrC: 17.3% [17.2-17.4%], RuC: 17.5% [17.5-17.6%]). Conclusion: Significant differences between BAC, urban, and rural cohorts may be explained by differences in healthcare structure and sociodemographics of the catchment areas.

Effect of temperature on the substrate utilization profiles of microbial communities in different sewer sediments.

Sewer systems represent an essential component of modern society. They have a major impact on our quality of life by preventing serious illnesses caused by waterborne diseases, by protecting the environment, and by enabling economic and social development through reducing flood risk. In the UK, systems are normally large and complex and, because of the long lifespan of these assets, their performance and hence their management are influenced by long-term environmental and urban changes. Recent work has focussed on the long-term changes in the hydraulic performance of these systems in response to climate change, e.g. rainfall and economic development. One climate-related driver that has received little attention is temperature, which may in itself have a complex dependence on factors such as rainfall. This study uses Biolog EcoPlates to investigate the effect of different temperatures (4 degrees C, 24 degrees C and 30 degrees C) on the carbon substrate utilization profiles of bacterial communities within sewer sediment deposits. Distinct differences in the metabolic profiles across the different temperatures were observed. Increasing temperature resulted in a shift in biological activity with an increase in the number of different carbon sources that can be utilized. Certain carboxylic and amino acids, however, did not support growth, regardless of temperature. Distinct differences in carbon utilization profiles were also found within sewers that have similar inputs. Therefore, this study has demonstrated that the carbon utilization profile for microbial communities found within sewer sediment deposits is dependent on both temperature and spatial variations.

Effect of a variable organic loading rate on process kinetics and volatile solids destruction in synthetic food waste-fed anaerobic digesters.

With the increasing installation of weather-dependent renewable sources such as solar and wind power, the ability to produce electricity on demand to balance any shortfall in supply is becoming more important. Anaerobic digestion is a low-carbon energy source with the potential to be flexible to meet this need. An investigation was conducted into the response of two laboratory-scale anaerobic digesters at loading rate of 2.5 gVS L-1 day-1 over five months using a synthetic food waste as a substrate. One digester was consistently fed at the same rate, whereas the other digester was fed with periods of varying organic loading rate, from 0.1 to 7 gVS L-1 day-1, using a feed pattern derived from a record of restaurant food waste. The digester that had been fed at a variable rate showed a pronounced increase in biogas production after feed events and a 9.6% higher VS breakdown than the steady-feed digester (81% compared to 74%), with no effect on digester stability, volatile fatty acid concentration, overall biogas output or biogas quality. These findings support and encourage the use of variable-rate feeding to balance the electricity demand.

Does giving birth in a "birth environment room" versus a standard birth room lower augmentation of labor? - Results from a randomized controlled trial.

OBJECTIVE: In the last decade, there has been an increased interest in exploring the impact of the physical birth environment on midwifery practice and women's birth experiences. This study is based on the hypothesis that the environment for birth needs greater attention to improve some of the existing challenges in modern obstetric practice, for example the increasing use of augmentation and number of interventions during delivery. STUDY DESIGN: A randomized controlled trial was carried out to study the effect of giving birth in a specially designed "birth environment room" on the use of augmentation during labor. The study took place at the Department of Obstetrics and Gynecology, Herning Hospital, Denmark and included 680 nulliparous women in spontaneous labor at term with a fetus in cephalic presentation. Women were randomly allocated to either the "birth environment room" or a standard birth room. The primary outcome was augmentation of labor by use of oxytocin. Secondary outcomes were duration of labor, use of pharmacological pain relief, and mode of birth. Differences were estimated as relative risks (RR) and presented with 95% confidence intervals. RESULTS: No difference was found on the primary outcome, augmentation of labor (29.1% in the "birth environment room" versus 30.6% in the standard room, RR 0.97; 0.89-1.08). More women in the "birth environment room" used the bathtub (60.6% versus 52.4%, RR 1.18; 1.02-1.37), whereas a tendency to lower use of epidural analgesia (22.6% versus 28.2%) did not reach statistical significance (RR 0.87; 0.74-1.02). The chance of an uncomplicated birth was almost similar in the two groups (70.6% in the "birth environment room" versus 72.6% in the standard room, RR 0.97; 0.88-1.07) as were duration of labor (mean 7.9 hours in both groups). CONCLUSIONS: Birthing in a specially designed physical birth environment did not lower use of oxytocin for augmentation of labor. Neither did it have any effect on duration of labor, use of pharmacological pain relief, and chance of birthing without complications. We recommend that future trials are conducted in birth units with greater improvement potentials.

Optimization of mycoremediation treatment for the chemical oxygen demand (COD) and ammonia nitrogen (AN) removal from domestic effluent using wild-Serbian Ganoderma lucidum (WSGL).

The fungi-based technology, wild-Serbian Ganoderma lucidum (WSGL) as myco-alternative to existing conventional microbial-based wastewater treatment is introduced in this study as a potential alternative treatment. The mycoremediation is highly persistent for its capability to oxidatively breakdown pollutant substrates and widely researched for its medicinal properties. Utilizing the nonhazardous properties and high degradation performance of WSGL, this research aims to optimize mycoremediation treatment design for chemical oxygen demand (COD) and ammonia nitrogen (AN) removal in domestic wastewater based on proposed Model 1 (temperature and treatment time) and Model 2 (volume of pellet and treatment time) via response surface methodology (RSM). Combined process variables were temperature (0C) (Model 1) and the volume of mycelial pellets (%) (Model 2) against treatment time (hour). Response variables for these two sets of central composite design (CCD) were the removal efficiencies of COD (%) and AN (%). The regression line fitted well with the data with R2 values of 0.9840 (Model 1-COD), 0.9477 (Model 1-AN), 0.9988 (Model 2-COD), and 0.9990 (Model 2-AN). The lack of fit test gives the highest value of sum of squares equal to 9494.91 (Model 1-COD), 9701.68 (Model 1-AN), 23786.55 (Model 2-COD), and 13357.02 (Model 2-AN), with probability F values less than 0.05 showing significant models. The optimized temperature for Model 1 was at 25 °C within 24 h of treatment time with 95.1% COD and 96.3% AN removals. The optimized condition (temperature) in Model 1 was further studied in Model 2. The optimized volume of pellet for Model 2 was 0.25% in 24-h treatment time with 76.0% COD and 78.4% AN removals. Overall, the ascended sequence of high volume of pellet considered in Model 2 will slow down the degradation process. The best fit volume of pellet with maximum degradation of COD and AN is equivalent to 0.1% at 25 °C in 24 h. The high performance achieved demonstrates that the mycoremediation of G. lucidum is highly potential as part of the wastewater treatment system in treating domestic wastewater of high organic loadings.

Influence of phosphate dosing on biofilms development on lead in chlorinated drinking water bioreactors.

Phosphate dosing is used by water utilities to prevent plumbosolvency in water supply networks. However, there is a lack of knowledge regarding biofilm formation on lead and plastic materials when phosphate concentrations are modified in drinking water systems. In this study, biofilms were grown over lead coupons and PVC tubes in bioreactors supplied with local drinking water treated to provide different phosphate doses (below 1, 1 and 2 mg/L) over a period of 28 days. A range of commercial iron pellets (GEH104 and WARP) were tested aiming to maintain phosphate levels below the average 1 mg/L found in drinking water. Changes in biofilm community structure in response to three different phosphate treatments were characterised by Illumina sequencing of the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Scanning electron microscopy was used to visualise physical differences in biofilm development in two types of materials, lead and PVC. The experimental results from the kinetics of phosphate absorption showed that the GEH104 pellets were the best option to, in the long term, reduce phosphate levels while preventing undesirable turbidity increases in drinking water. Phosphate-enrichment promoted a reduction of bacterial diversity but increased that of fungi in biofilms. Overall, higher phosphate levels selected for microorganisms with enhanced capabilities related to phosphorus metabolism and heavy metal resistance. This research brings new insights regarding the influence of different phosphate concentrations on mixed-species biofilms formation and drinking water quality, which are relevant to inform best management practices in drinking water treatment.

Micronutrient deficits in patients with chronic pancreatitis: prevalence, risk factors and pitfalls.

OBJECTIVE: We investigated the prevalence of micronutrient deficiencies and associated patient and disease-related risk factors in patients with chronic pancreatitis (CP). METHODS: We enrolled 115 consecutive CP outpatients. Micro-nutritional assessments included plasma levels of fat-soluble vitamins (A, D and E) and trace elements (magnesium and zinc). Bioelectrical impedance and muscle function tests were used to characterize the macro-nutritional status (sarcopenia and phase angle). Prevalence of micro-nutritional deficiencies was estimated and associated with a number of patient and disease characteristics including presence of exocrine pancreatic insufficiency (EPI) and diabetes mellitus. In an additional analysis, we explored the association between micronutrient levels and macro-nutritional status. RESULTS: The mean age of patients was 57.9 ± 13.0 years, 71% were men and 50% had an alcoholic aetiology. Vitamin D deficiency (22%) was the most common micronutrient deficit followed by zinc deficiency (20%) and magnesium deficiency (17%). Vitamin A deficiency (10%) and vitamin E deficiency (7%) were only seen in patients with EPI (P ≤ 0.03), while the presence of trace element deficits was associated with plasma albumin levels (P ≤ 0.006). Plasma zinc levels were decreased in sarcopenic patients (P < 0.001) and positively correlated to phase angle (coefficient 0.28; P < 0.001). CONCLUSION: Various micronutrient deficits were observed in CP outpatients, and associated risk factors were diverse and distinct for the individual nutrients. Taken together, our findings highlight the complexity of micronutrient assessment in patients with CP and emphasise the importance of simultaneous evaluation of plasma protein levels, inflammatory activity and macro-nutritional status.

Modeling of hydrogen sulfide oxidation in concrete corrosion products from sewer pipes.

Abiotic and biotic oxidation of hydrogen sulfide related to concrete corrosion was studied in corrosion products originating from a sewer manhole. The concrete corrosion products were suspended in an acidic solution, mimicking the conditions in the pore water of corroded concrete. The removal of hydrogen sulfide and dissolved oxygen was measured in parallel in the suspension, upon which the suspension was sterilized and the measurement repeated. The results revealed the biotic oxidation to be fast compared with the abiotic oxidation. The stoichiometry of the hydrogen sulfide oxidation was evaluated using the ratio between oxygen and hydrogen sulfide uptake. The ratio for the biotic oxidation pointed in the direction of elemental sulfur being formed as an intermediate in the oxidation of hydrogen sulfide to sulfuric acid. The experimental results were applied to suggest a hypothesis and a mathematical model describing the hydrogen sulfide oxidation pathway in a matrix of corroded concrete.

Study protocol for a randomised trial evaluating the effect of a "birth environment room" versus a standard labour room on birth outcomes and the birth experience.

INTRODUCTION: In the last decade, there has been an increased interest in exploring the impact of the physical birth environment on birth outcomes. The birth environment might have an important role in facilitating the production of the hormone oxytocin that causes contractions during labour. Oxytocin is released in a safe, secure and confidence-inducing environment, and environments focused on technology and medical interventions to achieve birth may disrupt the production of oxytocin and slow down the progress of labour. An experimental "birth environment room" was designed, inspired by knowledge from evidence-based healthcare design, which advocates bringing nature into the room to reduce stress. The purpose is to examine whether the 'birth environment room', with its design and decor to minimise stress, has an impact on birth outcomes and the birth experience of the woman and her partner. MATERIALS AND METHODS: A randomised controlled trial will recruit 680 nulliparous women at term who will be randomly allocated to either the "birth environment room" or a standard room. The study will take place at the Department of Obstetrics and Gynecology at Herning Hospital, with recruitment from May 2015. Randomisation to either the "birth environment room" or standard room takes place just before admission to a birth room during labour. The primary outcome is augmentation of labour, and the study has 80% power to detect a 10% difference between the two groups (two-sided α = 0.05). Secondary outcomes are duration of labour, use of pharmacological pain relief, mode of birth, and rating of the birth experience by women and their partners. TRIAL REGISTRATION: NCT02478385(10/08/2016).

Performance of wild-Serbian Ganoderma lucidum mycelium in treating synthetic sewage loading using batch bioreactor.

The fluctuation of domestic wastewater characteristic inhibits the current conventional microbial-based treatment. The bioremediation fungi has received attention and reported to be an effective alternative to treat industrial wastewater. Similar efficient performance is envisaged for domestic wastewater whereby assessed performance of fungi for varying carbon-to-nitrogen ratios in domestic wastewater is crucial. Thus, the performance of pre-grown wild-Serbian Ganoderma lucidum mycelial pellets (GLMPs) was evaluated on four different synthetic domestic wastewaters under different conditions of initial pH (pH 4, 5, and 7) and chemical oxygen demand (COD) to nitrogen (COD/N) ratio of 3.6:1, 7.1:1, 14.2:1, and 17.8:1 (C3.6N1, C7.1N1, C14.2N1, and C17.8N1). The COD/N ratios with a constant concentration of ammonia-nitrogen (NH3-N) were chosen on the basis of the urban domestic wastewater characteristics sampled at the inlet basin of a sewage treatment plant (STP). The parameters of pH, COD, and NH3-N were measured periodically during the experiment. The wild-Serbian GLMPs efficiently removed the pollutants from the synthetic sewage. The COD/N ratio of C17.8N1 wastewater had the best COD and NH3-N removal, as compared to the lower COD/N ratio, and the shortest treatment time was obtained in an acidic environment at pH 4. The highest percentage for COD and NH3-N removal achieved was 96.0% and 93.2%, respectively. The results proved that the mycelium of GLMP has high potential in treating domestic wastewater, particularly at high organic content as a naturally sustainable bioremediation system.

Influence of pipe material and surfaces on sulfide related odor and corrosion in sewers.

Hydrogen sulfide oxidation on sewer pipe surfaces was investigated in a pilot scale experimental setup. The experiments were aimed at replicating conditions in a gravity sewer located immediately downstream of a force main where sulfide related concrete corrosion and odor is often observed. During the experiments, hydrogen sulfide gas was injected intermittently into the headspace of partially filled concrete and plastic (PVC and HDPE) sewer pipes in concentrations of approximately 1,000 ppm(v). Between each injection, the hydrogen sulfide concentration was monitored while it decreased because of adsorption and subsequent oxidation on the pipe surfaces. The experiments showed that the rate of hydrogen sulfide oxidation was approximately two orders of magnitude faster on the concrete pipe surfaces than on the plastic pipe surfaces. Removal of the layer of reaction (corrosion) products from the concrete pipes was found to reduce the rate of hydrogen sulfide oxidation significantly. However, the rate of sulfide oxidation was restored to its background level within 10-20 days. A similar treatment had no observable effect on hydrogen sulfide removal in the plastic pipe reactors. The experimental results were used to model hydrogen sulfide oxidation under field conditions. This showed that the gas-phase hydrogen sulfide concentration in concrete sewers would typically amount to a few percent of the equilibrium concentration calculated from Henry's law. In the plastic pipe sewers, significantly higher concentrations were predicted because of the slower adsorption and oxidation kinetics on such surfaces.

Corrosion of concrete sewers--the kinetics of hydrogen sulfide oxidation.

Hydrogen sulfide absorption and oxidation by corroding concrete surfaces was quantified in a test rig consisting of 6 concrete pipes operated under sewer conditions. The test rig was placed in an underground sewer monitoring station with access to fresh wastewater. Hydrogen sulfide gas was injected into the pipe every 2nd hour to peak concentrations around 1000 ppm. After some months of operation, the hydrogen sulfide became rapidly oxidized by the corroding concrete surfaces. At hydrogen sulfide concentrations of 1000 ppm, oxidation rates as high as 1 mg S m(-2) s(-1) were observed. The oxidation process followed simple nth order kinetics with a process order of 0.45-0.75. Extrapolating the results to gravity sewer systems showed that hydrogen sulfide oxidation by corroding concrete is a fast process compared to the release of hydrogen sulfide from the bulk water, resulting in low gas concentrations compared with equilibrium. Balancing hydrogen sulfide release with hydrogen sulfide oxidation at steady state conditions demonstrated that significant corrosion rates--several millimeters of concrete per year--can potentially occur at hydrogen sulfide gas phase concentrations well below 5-10 ppm. The results obtained in the study advances the knowledge on prediction of sewer concrete corrosion and the extent of odor problems.

Modeling the formation and fate of odorous substances in collection systems.

A conceptual model that simulates the formation and fate of odorous substances in branched collection systems is presented. The model predicts the activity of the relevant biomass phenotypes under aerobic, anoxic, and anaerobic conditions in force mains and gravity sewers. The formation and fate of individual, malodorous substances in the bulk water, biofilms, and sediments are modeled. The release of odorous compounds from the bulk water to the sewer gas phase, their fate in the gas phase, and their subsequent release into the urban atmosphere is simulated. Examples of model application include the prediction of hydrogen sulfide and malodorous fermentation products from force mains and gravity sewers.

Aerobic and anaerobic transformations of sulfide in a sewer system--field study and model simulations.

The formation and fate of sulfide in a force main and a downstream-located gravity sewer were investigated in an extensive field study. Sulfide formation in the force main was significant. However, during 14 minutes of transport in the gravity sewer, the sulfide concentration decreased 30%, on average. An application of a conceptual sewer process model for simulating the formation and fate of sulfide was demonstrated. Overall, the model predicted that approximately 90% of the decrease of the sulfide concentration in the gravity sewer was the result of sulfide oxidation and that only a small fraction entered the sewer atmosphere, causing odor and corrosion. Even so, the model predicted concrete corrosion rates of up to 1.2 mm/y in the gravity sewer section.