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Journal articles on the topic 'Drop manhole'

Author: Grafiati

Published: 4 June 2021

Last updated: 12 February 2022

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1

Camino, G. Adriana, David Z. Zhu, Nallamuthu Rajaratnam, and Manas Shome. "Use of a stacked drop manhole for energy dissipation: a case study in Edmonton, Alberta." Canadian Journal of Civil Engineering 36, no. 6 (June 2009): 1037–50. http://dx.doi.org/10.1139/l09-036.

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This paper reports on a laboratory investigation into the performance of a novel stacked drop manhole design where two identical rectangular manholes are stacked one beside the other but at different heights so that there is a drop in elevation from one to the other. The focus of the study was to estimate the energy dissipation that occurs in such stacked manholes during diverse inflow conditions. Flow regimes inside the structure were identified and the effectiveness of the design was assessed under variable inflow conditions. Total energy dissipation in the stacked manhole was found to range from about 50% to 90%, and the contribution of each manhole chamber to the overall energy dissipation was assessed. A relationship between water depths in the manhole chambers and the corresponding outflow conditions was established. In addition, an analysis of the flow patterns and flow regimes highlighted the relevant parameters involved in the mechanisms of energy dissipation.

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2

Zhu, Chunyue, Feidong Zheng, Genhua Yan, and Xianrui Shi. "Evolution of Water Conveyance Capacity through Hydraulic Transition Processes in Circular Drop Manholes." Water 13, no. 16 (August 20, 2021): 2277. http://dx.doi.org/10.3390/w13162277.

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Circular drop manholes are widely implemented for steep catchments in urban drainage networks. Poor downstream hydraulic transition processes of a manhole system, i.e., the formation of hydraulic jump near the outlet entrance, and the sudden transition from free surface to pressurized flow with bursts of air in the outflow pipe can severely constraint the capacity of water conveyance. In this paper, we defined four basic hydraulic stages that indicate where hydraulic transition processes begin and end. The measurements of typical manhole models with different drop heights were conducted under different inflow and outflow conditions. Three types of transition processes covering all flow patterns have resulted into a graphical visualization by analyzing two pairs of dimensionless parameters. The flow inside a circular drop manhole was considered to reach its discharge capacity when the abrupt drop of manhole water level is visible in the fully aerated flow pattern. Four empirical equations revealing the water level filling ratio and discharge efficiency at different hydraulic stages were also presented for further predictions of choking risks.

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3

Arao, Shinji, Tetsuya Kusuda, Katsumi Moriyama, Shunsuke Hiratsuka, Jyunsaku Asada, and Nozomu Hirose. "Energy losses at three-way circular drop manholes under surcharged conditions." Water Science and Technology 66, no. 1 (July 1, 2012): 45–52. http://dx.doi.org/10.2166/wst.2012.164.

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Energy loss at manholes is of importance in the design of storm sewer networks and in flood-analysis. Some researchers have already investigated the energy loss at three-way manholes under surcharged conditions. However, formulation to calculate the energy loss at manholes, including all variables of structural elements of the pipes and of the manhole has not yet been accomplished. Therefore, more study to formulate the energy loss at three-way drop manholes is needed. In this study, the ratio of the diameter between inflow pipes and an outflow pipe, the ratio of flow rates between those pipes, water depth in a manhole and the drop gaps between those pipes are considered and the energy loss at three-way circular drop manholes is examined. Finally, a modified formula, more accurate than that in the U.S. Federal Highway Administration's 2001 Urban Drainage Design Manual is proposed. The proposed formula takes the influence of the ratio of the diameter between inflow pipes and outflow pipe and drop gaps between those pipes into consideration. The calculated energy loss coefficients in both straight-through and lateral pipes successfully reproduce the measured values.

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4

Hasheminejad, Seyedreza, Mohammad-Javad Khanjani, and Gholam-Abbas Barani. "Effects of jet-breaker dimensional characteristics on drop manhole hydraulic performance." Canadian Journal of Civil Engineering 46, no. 6 (June 2019): 481–93. http://dx.doi.org/10.1139/cjce-2018-0227.

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Drop manholes prevent excessive flow velocity and provide energy dissipation in steep urban sewer and drainage systems. Their poor hydraulic performance under Regime R2, in which the inlet jet collides with the manhole outlet, was improved by the jet-breaker. However, this device should still be properly sized to efficiently enhance manhole operation. In this paper, effects of jet-breaker length, width, sagitta, angle, and inlet pipe filling ratio on drop manhole performance, were investigated experimentally. Two-level factorial design and dimensional analysis were both utilized to design the experiments to study drop manhole energy dissipation and air demand as responses. Statistical analysis of the results revealed both significant design factors and regression models for each response. Neither jet-breaker length nor width had significant effects. However, the responses were improved by increasing both jet-breaker angle and inlet pipe filling ratio. Jet-breaker sagitta had a different effect on each response; a flat plate was more appropriate for energy dissipation while a curved plate decreased air demand. Simultaneous analysis of regression models determined the proper levels of significant design factors as 80% filling ratio of the inlet pipe, jet-breaker angle at 70°, and its sagitta equal to 0.

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5

Hasheminejad, Seyedreza, Mohammad-Javad Khanjani, and Gholam-Abbas Barani. "Utilizing modern experimental methodology to quantify jet-breaker dimension effects on drop manhole performance." Water Science and Technology 78, no. 5 (September 5, 2018): 1168–78. http://dx.doi.org/10.2166/wst.2018.377.

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Abstract Drop structures and especially drop manholes are extensively employed in supercritical routes of sewer and drainage systems. Drop manholes remarkably affect hydraulic features of their downstream system, while their operation is dominated by the flow regime inside them. Poor hydraulic performance of these structures under Regime R2 was improved with the jet-breaker, yet its proper dimensions were needed to be precisely determined. In this paper, effects of the jet-breaker length, width, sagitta, and angle on drop manhole energy dissipation and air demand (as responses), under the inlet pipe 80% filling ration, were experimentally studied. The modern statistical design of experiment (DoE) methodology and dimensional analysis were utilized to design the experiments in accordance with the 24-1IV fractional factorial design. Ten specific jet-breakers were examined and more than 135 tests were performed. The statistical analysis of the results revealed that both responses were significantly improved when the jet-breaker length and width were 2 and 1.4 times the inlet pipe diameter, respectively; its sagitta was equal to 0, and its angle was at 70°. The use of DoE resulted in 21% reduction in experimental runs, straightforward data analysis, and unbiased concluding.

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6

Hasheminejad, Seyedreza, Mohammad-Javad Khanjani, and Gholam-Abbas Barani. "Utilizing Modern Experimentation Method to Quantify Jet-Breaker Dimension Effects on Drop Manhole Pool Height." Civil Engineering Journal 4, no. 12 (December 24, 2018): 2978. http://dx.doi.org/10.28991/cej-03091214.

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Drop manholes are commonly employed in sewer and drainage systems to reduce pipes slope. The operation of these structures is dominated by their flow regime. Poor hydraulic performance of them under Regime R2 was improved with the jet-breaker, which intersects the inlet jet; yet its proper dimensions were needed to be precisely determined. In this paper, effects of jet-breaker length, width, sagitta, and angle on drop manhole pool free-surface height were experimentally studied under 80% filling ratio of the inlet pipe. The modern statistical Design of Experiment (DoE) methodology and dimensional analysis were utilized to design the experiments in accordance with the 24-1IV fractional factorial design. Consequently, nine specific jet-breakers were built and examined at two different angles, and under various flow rates. The statistical analysis of the results shown that manhole pool height was significantly decreased when jet-breaker length, width, and sagitta were 1, 1.4, and 0.7 times the inlet pipe diameter, respectively, and its angle was at 70°. The use of DoE resulted in 21% reduction in experimental runs, cost, and time, while it provided comprehensive data analysis and objective conclusion.

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7

De Martino, Flavio, Corrado Gisonni, and Willi H. Hager. "Drop in Combined Sewer Manhole for Supercritical Flow." Journal of Irrigation and Drainage Engineering 128, no. 6 (December 2002): 397–400. http://dx.doi.org/10.1061/(asce)0733-9437(2002)128:6(397).

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8

Corsi, Richard L., Christopher J. Quigley, Henryk Melcer, and John Bell. "Aromatic VOC emissions from a municipal sewer interceptor." Water Science and Technology 31, no. 7 (April 1, 1995): 137–45. http://dx.doi.org/10.2166/wst.1995.0219.

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Municipal and industrial sewers have come under increased regulatory scrutiny as sources of volatile organic compound (VOC) emissions to the ambient atmosphere. A well-ventilated municipal sewer interceptor that receives significant quantities of VOC-laden industrial wastewater was studied to quantify VOC emissions. Headspace outgassing rates across four manhole covers were as high as 2300 m3/h. Emissions were greatest for toluene, approaching 100 g/h from a single manhole cover at the mid-point of the 24-hour event. Significant diurnal and weekday/weekend trends were observed. Emissions from a single manhole cover rivaled or exceeded those summed over aerated grit chambers and aeration basins at four large municipal wastewater treatment facilities in Southern Ontario. The primary source of VOC stripping was observed to be a series of large drop structures, with aromatic VOC stripping efficiencies ranging from 25 to 38% across two drops. Finally, an existing model that predicts VOC emissions from sewers was observed to reasonably predict measured stripping efficiencies. An important conclusion of this study is that large fractions of VOCs may be removed from wastewater and emitted to the ambient atmosphere prior to entering a downstream treatment facility.

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9

ARAO, Shinji, and Tetsuya KUSUDA. "FORMULA ON ENERGY LOSSES AT TWO-WAY CIRCULAR DROP MANHOLE." Doboku Gakkai Ronbunshuu G 62, no. 1 (2006): 162–70. http://dx.doi.org/10.2208/jscejg.62.162.

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10

Carvalho, Rita F., and Jorge Leandro. "Hydraulic Characteristics of a Drop Square Manhole with a Downstream Control Gate." Journal of Irrigation and Drainage Engineering 138, no. 6 (June 2012): 569–76. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0000437.

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11

ARAO, Shinji, Shunsuke HIRATSUKA, and Tetsuya KUSUDA. "FORMULA ON ENERGY LOSSES AT THREE-WAY CIRCULAR DROP MANHOLE UNDER SURCHARGE FLOW." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 69, no. 2 (2013): 105–22. http://dx.doi.org/10.2208/jscejhe.69.105.

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12

ARAO, Shinji, Shunsuke HIRATSUKA, and Tetsuya KUSUDA. "FORMULA ON ENERGY LOSSES AT THREE-WAY CIRCULAR DROP MANHOLE UNDER SURCHARGE FLOW." Journal of JSCE 4, no. 1 (2016): 19–37. http://dx.doi.org/10.2208/journalofjsce.4.1_19.

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13

Granata, Francesco. "Dropshaft cascades in urban drainage systems." Water Science and Technology 73, no. 9 (February 1, 2016): 2052–59. http://dx.doi.org/10.2166/wst.2016.051.

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Dropshaft cascades are typical elements of sewer systems in steep urban catchment basins. The design of a dropshaft cascade, which is generally addressed as an optimization problem, also needs to consider the subsequent effects induced on the flow by the different elements of the cascade. Experimental research has been performed at the hydraulic engineering laboratory of the University of Cassino and Southern Lazio in order to investigate the basic flow patterns in a dropshaft cascade, with particular reference to energy dissipation and air entrainment. This research has shown that, regarding these aspects, a dropshaft cascade proved to be a more efficient solution of the single drop manhole with the same total drop height.

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14

Ayub, Nabende, Twaibu Semwogerere, and Richard O. Awichi. "Mathematical Modelling of Sewage Overflow Through Pipe-Manhole Drainage Sewer Systems Using CFD: A Case of Mbale City, Eastern Uganda." East African Journal of Engineering 2, no. 1 (November 23, 2020): 33–45. http://dx.doi.org/10.37284/eaje.2.1.239.

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The major objective of this study was to design a model to optimize sewage flow through pipe-manhole drainage systems using Computational Fluid Dynamics (CFD). Multi-phase flows like two-phase flow in transport pipes is a common occurrence in many industrial applications such as sewage, water, oil, gas transportation and power generation. Accurate prediction of fluid velocity and pressure drop is of utmost importance to ensure effective design and operation of fluid transport systems. Numerical simulations were performed at different pipe inclinations and fluid flow velocities. A two-dimensional pipe of 0.5 m in diameter and 20 m long was used with a Standard k−ε turbulence and the volume of fraction (VOF) free surface model to solve the turbulent mixture flow of air and water. The CFD approach is based on the Navier-Stokes equations. Results show that the flow pattern behaviour and numerical values of liquid velocities and pressure drop compare reasonably well. It is concluded that the most effective way to optimize a sewer network system in order to minimize the overflows through Pipe-manhole drainage system for Mbale Municipality conditions is by considering minimum and maximum sewer velocities in the range 0.67 ms−1 to 5.5 ms−1 respectively, sewer diameters, slope gradients for optimal sewer design and expanding the number of sewer network connections of household, municipal and industries.

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15

Gargano, Rudy. "Discussion of “Drop in Combined Sewer Manhole for Supercritical Flow” by Flavio De Martino, Corrado Gisonni, and Willi H. Hager." Journal of Irrigation and Drainage Engineering 130, no. 2 (April 2004): 171–72. http://dx.doi.org/10.1061/(asce)0733-9437(2004)130:2(171).

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16

De Martino, Flavio, Corrado Gisonni, and Willi H. Hager. "Closure to “Drop in Combined Sewer Manhole for Supercritical Flow” by Flavio De Martino, Corrado Gisonni, and Willi H. Hager." Journal of Irrigation and Drainage Engineering 130, no. 2 (April 2004): 172. http://dx.doi.org/10.1061/(asce)0733-9437(2004)130:2(172).

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17

Granata, F., G. de Marinis, R. Gargano, and W. H. Hager. "Discussion of “Hydraulic Characteristics of a Drop Square Manhole with a Downstream Control Gate” by Rita F. Carvalho and Jorge Leandro." Journal of Irrigation and Drainage Engineering 139, no. 7 (July 2013): 593–94. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0000583.

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18

Carvalho, Rita F., and Jorge Leandro. "Closure to “Hydraulic Characteristics of a Drop Square Manhole with a Downstream Control Gate” by Rita F. Carvalho and Jorge Leandro." Journal of Irrigation and Drainage Engineering 139, no. 7 (July 2013): 594–95. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0000608.

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19

Fereshtehpour, Mohammad, and Mohammad R. Chamani. "Flow Characteristics of a Drop Manhole with an Internal Hanging Baffle Wall in a Storm Drainage System: Numerical and Experimental Modeling." Journal of Irrigation and Drainage Engineering 146, no. 8 (August 2020): 04020022. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0001490.

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20

Christodoulou, George C. "Drop Manholes in Supercritical Pipelines." Journal of Irrigation and Drainage Engineering 117, no. 1 (January 1991): 37–47. http://dx.doi.org/10.1061/(asce)0733-9437(1991)117:1(37).

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21

Granata, F., G. de Marinis, R. Gargano, and W. H. Hager. "Hydraulics of Circular Drop Manholes." Journal of Irrigation and Drainage Engineering 137, no. 2 (February 2011): 102–11. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0000279.

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22

Camino, G. Adriana, David Z. Zhu, and Nallamuthu Rajaratnam. "Hydraulics of Stacked Drop Manholes." Journal of Irrigation and Drainage Engineering 137, no. 8 (August 2011): 537–52. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0000327.

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23

Kim Chung, Dwayne Chung, So Hung Huynh, Shufen Wang, Xuchuan Jiang, Oi Wah Liew, Murat Muradoglu, and Tuck Wah Ng. "A superhydrophobic manhole for drops." Journal of Materials Chemistry A 5, no. 3 (2017): 914–18. http://dx.doi.org/10.1039/c6ta09459g.

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24

Ma, Yiyi, David Z. Zhu, Nallamuthu Rajaratnam, and Bert van Duin. "Energy Dissipation in Circular Drop Manholes." Journal of Irrigation and Drainage Engineering 143, no. 12 (December 2017): 04017047. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0001241.

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25

Granata, Francesco, Giovanni de Marinis, and Rudy Gargano. "Air-water flows in circular drop manholes." Urban Water Journal 12, no. 6 (April 14, 2014): 477–87. http://dx.doi.org/10.1080/1573062x.2014.881893.

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26

Granata, Francesco, Giovanni de Marinis, and Rudy Gargano. "Flow-improving elements in circular drop manholes." Journal of Hydraulic Research 52, no. 3 (April 14, 2014): 347–55. http://dx.doi.org/10.1080/00221686.2013.879745.

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27

Banisoltan, Sahar, Nallamuthu Rajaratnam, and David Z. Zhu. "Experimental Study of Hydraulics of Drill-Drop Manholes." Journal of Hydraulic Engineering 141, no. 10 (October 2015): 04015021. http://dx.doi.org/10.1061/(asce)hy.1943-7900.0001042.

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28

Helmi, Ahmed M., Heba T. Essawy, and Ahmed Wagdy. "Three-Dimensional Numerical Study of Stacked Drop Manholes." Journal of Irrigation and Drainage Engineering 145, no. 9 (September 2019): 04019017. http://dx.doi.org/10.1061/(asce)ir.1943-4774.0001414.

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29

Crispino, Gaetano, Pasquale Contestabile, Diego Vicinanza, and Corrado Gisonni. "Energy Head Dissipation and Flow Pressures in Vortex Drop Shafts." Water 13, no. 2 (January 12, 2021): 165. http://dx.doi.org/10.3390/w13020165.

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Vortex drop shafts are special manholes designed to link sewer channels at different elevations. Significant energy head dissipation occurs across these structures, mainly due to vertical shaft wall friction and turbulence in the dissipation chamber at the toe of the shaft. In the present study two aspects, sometimes neglected in the standard hydraulic design, are considered, namely the energy head dissipation efficiency and the maximum pressure force in the dissipation chamber. Different physical model results derived from the pertinent literature are analyzed. It is demonstrated that the energy head dissipation efficiency is mostly related to the flow impact and turbulence occurring in the chamber. Similarly to the drop manholes, a relation derived from a simple theoretical model is proposed for the estimation of the energy head loss coefficient. The analysis of the pressures measured on the chamber bottom allows to provide a useful equation to estimate the pressure peak in the chamber as a function of the approach flow energy head.

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30

Matias, N. M., J. S. Matos, and F. Ferreira. "Hydrogen sulfide gas emission under turbulent conditions – an experimental approach for free-fall drops." Water Science and Technology 69, no. 2 (October 21, 2013): 262–68. http://dx.doi.org/10.2166/wst.2013.702.

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Odor nuisance and sulfide corrosion in sewers carrying septic wastewater are accelerated at points of turbulence such as drops in manholes, but accurate methods or empirical expressions to evaluate the gas stripping rate at those particular sites are still missing. With the aim of improving the current knowledge on the influence of free-fall drops on the release of hydrogen sulfide gas, an experimental set-up was built allowing different free-fall drops heights and flows. Three types of experiments were carried out: reaeration tests without sulfide; sulfide oxidation tests; and hydrogen sulfide release tests. With the increase of the free-fall drop height or of the flow, a higher rate of air-to-water mass oxygen transfer was observed. Results regarding sulfide oxidation tests with reaeration through the free-fall have shown that the oxidation rate was correlated with flow. In the hydrogen sulfide release tests, the maximum concentration in the atmosphere reached 500 ppm. Results also showed that increasing the flow rate decreased the time at which the maximum concentrations in the atmosphere were observed.

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31

Hasheminejad, Seyedreza, and Wuyi Wan. "Debris Residence Time in Circular Drop Manholes: Experimental Perspective." Journal of Pipeline Systems Engineering and Practice 12, no. 4 (November 2021): 04021058. http://dx.doi.org/10.1061/(asce)ps.1949-1204.0000606.

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32

Tamura, Shiro, Osamu Matsushima, and Shizuo Yoshikawa. "Helicoidal-Ramp Type Drop Shaft to Deal with High Head Drop Works in Manholes." Proceedings of the Water Environment Federation 2010, no. 12 (January 1, 2010): 4991–5002. http://dx.doi.org/10.2175/193864710798182583.

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33

Yang, Zhi, David Z. Zhu, Tong Yu, Stephen Edwini-Bonsu, Adam Shypanski, and Yanchen Liu. "Case study of H2S release and transport in a trunk sewer with drops." Water Science and Technology 82, no. 11 (October 5, 2020): 2271–81. http://dx.doi.org/10.2166/wst.2020.475.

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Abstract Field work was performed to investigate the release of hydrogen sulphide (H2S) and its transport in the sewer trunk with drops in the Bonnie Doon area in Edmonton, Alberta, Canada, in order to develop a proper odor control strategy. The liquid sulfide concentration in the upstream trunk was low (less than 1.0 mg/L), and no H2S gas was detected in the head space under this low concentration. However, high H2S gas concentration was detected in the middle reach of the trunk due to the stripping effect of the three drops (2.7 m, 5.2 m and 2.0 m) along the trunk. The released H2S at drops was then transported in the sewer system and emitted at various locations and caused odor concerns. These drops played an important role in H2S release, and the overall H2S mass transfer coefficient at drops was much higher than that in normal gravity sewers. The overall oxygen and H2S mass transfer coefficient (KLa) was estimated to be around 200 h−1 and 300 h−1 at the first two drops, respectively. Field sampling of biofilm indicates that Desulfomicrobium was identified as the sulfate-reducing bacteria (SRB) responsible for sulfide generation in sewer wall biofilm and Thiobacillus was the only predominant member in manhole wall biofilm contributing to sewer manhole corrosion.

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34

Zheng, Feidong, Yun Li, Jianjun Zhao, and Jianfeng An. "Energy Dissipation in Circular Drop Manholes under Different Outflow Conditions." Water 9, no. 10 (September 30, 2017): 752. http://dx.doi.org/10.3390/w9100752.

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35

Nakamura, Makoto, Shintaro Sugi, Makoto Ishikawa, and Hiroshi Kouchiwa. "CFD Analysis of Helicoidal-Ramp Type Drop Shaft to Deal With High Head Drop Works in Manholes." Proceedings of the Water Environment Federation 2015, no. 17 (January 1, 2015): 3828–37. http://dx.doi.org/10.2175/193864715819539443.

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36

ARAO, Shinji, Kyosuke OGAWA, Takuma YAMANE, Hiroshige IWASAKI, Shunsuke HIRATSUKA, and Tetsuya KUSUDA. "ENERGY LOSSES AT THREE-WAY CIRCULAR DROP MANHOLES WITH OPPOSED INFLOW PIPES." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 71, no. 4 (2015): I_541—I_546. http://dx.doi.org/10.2208/jscejhe.71.i_541.

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37

Movahedi, Azin, Ali Delavari, and Massoud Farahi. "Designing Manhole in Water Transmission Lines Using Flow3D Numerical Model." Civil Engineering Journal 1, no. 1 (December 5, 2015): 19. http://dx.doi.org/10.28991/cej-030987.

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Using cascades and drops existing in flow path has a history of 3000 years. Particularly, Roman engineers employed stepped spillways with the same idea in several countries; however, there are few information about the hydraulic performance of aqueducts. Most of these channels have flat long cross sections with low torsions (variable slope) such that they can encompass cascade and steep spillways or dopshaft. Given that there are few studies conducted on dropshafts, the present paper attempted to discuss about such structures in flow path and water transmission lines as well as introducing the existing principles and relations and present, the obtained results of designing though Flow3D. The obtained error percentage was about 20% which is acceptable for numerical studies.

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38

ARAO, Shinji, Sayaka MIHARA, Ryoya OBARA, Yuichiro SAKI, Shunsuke HIRATSUKA, and Tetsuya KUSUDA. "ENERGY LOSSES AT THREE-WAY CIRCULAR DROP MANHOLES WITH TWO OPPOSED INFLOW PIPES HAVING DIFFERENT DIAMETER." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 73, no. 4 (2017): I_685—I_690. http://dx.doi.org/10.2208/jscejhe.73.i_685.

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39

Hager, Willi H. "Discussion of “ Drop Manholes in Supercritical Pipelines ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)." Journal of Irrigation and Drainage Engineering 118, no. 5 (September 1992): 832. http://dx.doi.org/10.1061/(asce)0733-9437(1992)118:5(832).

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40

Christodoulou, George C. "Closure to “ Drop Manholes in Supercritical Pipelines ” by George C. Christodoulou (January/February, 1991 Col. 117, No. 1)." Journal of Irrigation and Drainage Engineering 118, no. 5 (September 1992): 833–34. http://dx.doi.org/10.1061/(asce)0733-9437(1992)118:5(833).

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41

Matias, Natércia, Rita Ventura Matos, Filipa Ferreira, Jes Vollertsen, and José Saldanha Matos. "Release of hydrogen sulfide in a sewer system under intermittent flow conditions: the Ericeira case study, in Portugal." Water Science and Technology 75, no. 7 (January 25, 2017): 1702–11. http://dx.doi.org/10.2166/wst.2017.040.

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The presence and fate of hydrogen sulfide in wastewater systems were studied in two stretches of an intercepting sewer system located in a coastal village, in Portugal. A range of hydraulic parameters were obtained and liquid and gas phase measurements were carried out, both continuously and through intensive sampling campaigns. Upstream, where flow rates were relatively low, dissolved sulfide concentrations around 12 mg S L−1 and hydrogen sulfide gas concentrations above 250 ppm were observed, along with limited corrosion damage. It is believed this is due to the low relative humidity detected along the atmosphere of the studied sewer system. Downstream, gas concentrations were always below 40 ppm. Despite that, high signs of corrosion were detected, particularly in manholes with drop structures. It is thought that condensation of spray produced by the fall is the main cause of the phenomenon. Another relevant observation was the rapid decline in dissolved sulfide contents along gravity trunk sewers following the discharge of rising mains, with loss rates as high as 40 mg S L−1 h−1. Air-flow velocities corresponded to 15–50% of wastewater flows, an observation which agrees with other authors' publications addressing relatively small pipes and moderate water flows.

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