Understanding the effect of ventilation, intermittent pumping and seasonality in hydrogen sulfide and methane concentrations in a coastal sewerage system

Matos, Rita Ventura; Ferreira, Filipa; Gil, Carla; Matos, José

doi:10.1007/s11356-018-3856-3

Cited by 19 publications

(10 citation statements)

References 25 publications

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“…This is also visible when C-2 MH cover is open (Figure 7b). This effect is most likely due to the constricted downstream boundary, which causes sewer pressurization and air movement toward the upstream end, as observed in Matos et al [16]. While this is sometimes visible in the measured velocity oscillations, the low air velocities, the somewhat limited anemometer sensitivity and the fact that the anemometer does not retrieve direction, may mask this effect.…”

Section: Effect Of Downstream Pressurization (Full Flowing Pipe)mentioning

confidence: 76%

“…The experimental apparatus and equipment was followed as described in Matos et al [16]. It involved continuous monitoring of several gas phase parameters, namely headspace air velocity (±0.03 m s −1 )-v_air, air velocity through the venting stack-v_exit, barometric pressure (±0.05 Pa)-P_atm, pressure difference between sewer headspace and outside atmosphere (±0.05 Pa)-dP, temperature (±0.3 • C)-T, relative humidity (±2%)-R.H., H 2 S (±0.1 ppm), and O 2 (±0.01%) concentrations.…”

Section: Field Monitoring and Samplingmentioning

confidence: 99%

“…The theoretical framework, namely fluid mechanics theory and other studies [13,14,16], establishes that dP and air movement are related, therefore it was considered that, under these circumstances, the correlation holds valid for this data set. This allowed obtaining a simple empirical correlation (through ordinary least squares-OLS regression) between those variables (Figure 2b), which allows for an expedite prediction of airflows emitted to the outside atmosphere (Equation (1)), with a coefficient of determination of 0.77: v_exit = 0.0241 × dP + 0.1072 (1) where v_exit (m s −1 ) refers to air velocity exiting the venting stack and dP to the pressure differential between sewer and exterior atmosphere (Pa).…”

Section: Relationship Between Pressure Differences and Air Velocity Tmentioning

confidence: 99%

“…Matos et al [16] assessed the influence of different ventilation and operating conditions on H 2 S and CH 4 horizontal and vertical movement, in a section of a small gravity sewer under intermittent conditions. The results evidenced the effect of headspace temperature and ventilation in R.H. content, in sewer pressurization and gas movement within confined boundaries of the trunk sewer.…”

Section: Introductionmentioning

confidence: 99%

“…The observed pressure gradients induced by pumping events (peaking at approximately 100 Pa) were significantly higher than those measured in other systems, for much smaller inflows. As an example, in the Ericeira (Portugal) gravity sewer, described in Matos et al [16], the pumping of 6 L s −1 of wastewater originated pressure differentials of 9 Pa, roughly 10 times lower than those measured at the Meco pipe. This indicates that the magnitude of gas pollutant emissions may rely heavily on the headspace impacts of hydraulic flows and pumping characteristics.…”

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confidence: 97%

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Influence of Intermittence and Pressure Differentials in Hydrogen Sulfide Concentration in a Gravity Sewer

Matos

Ferreira

Matos

2019

Water

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The work presented herein was carried out to assess the effect of intermittent pumping events in sewer headspace pressure differentials, as well as their relationship with hydrogen sulfide gas concentration. A full scale gravity sewer in Portugal, located downstream of several pumping stations, was used as the guiding case study. Under normal system operation, pressure difference between the outside atmosphere and the sewer headspace seemed to influence the in and out-gassing of gas pollutants emitted through the venting stack. Wastewater pumping cycles generated maximum pressure differentials of roughly 100 Pa, which in turn originated maximum air velocities of 1.76 m s−1 exiting the venting stack. Each pumping event was followed by a pressure drop of about 50 Pa, quickly attaining null concentrations of H2S at the venting stack. A statistically significant relationship between pressure differentials and air exit velocity was observed, which allowed obtaining an empirical equation for expedite prediction of airflows emitted to the outside atmosphere (R2 = 0.77). Conversely, the same effect was not observed along the length of the sewer pipe, unlike the findings of other studies. The effect of a full flowing pipe at the downstream end of the gravity trunk sewer was also noticeable in downstream sewer pressurization and gas build-up. It was concluded that the magnitude of the gas pollutant emissions may heavily depend on the impacts of hydraulic flows and pumping characteristics in headspace pressure differences, denoting the need for better approaches when designing and installing venting stacks.

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Section: Effect Of Downstream Pressurization (Full Flowing Pipe)mentioning

confidence: 76%

Section: Field Monitoring and Samplingmentioning

confidence: 99%