SewerGEMS Clonnect Edition: How to model a eastewater pumpiing system to calculate H2S concentration?

Question

Hi everyone 
 I am going to calculate H2S concetration in a wastewater pump station using SewerGEMS Connect Edition. 
 As I have learned it is just with the Explicit (SWMM Solvers) we can calculate concentration of H2S. Is it true? 
 Problem is, when I run the model I receive these notifications: 
 - 20171 "Base" "Pump" "37" "PMP-2" (N/A) "The upstream link of the pump is non-virtual. The SWMM engine will treat this link as virtual." SWMM Export Validation 
 - 800039 "Base" "Pump" "37" "PMP-2" (N/A) "When using the explicit solver, it is preferable that pumps should be connected immediately upstream and downstream to short, virtual links." SWMM Export Validation 
 But I would like to run a real pump station and real pressure pipe and trace the H2S and BOD of whole the system i connection with the rest of the network. 
 Do you khow any solouton for the above-mentioned? 
 Many thanks in advance. 
 Best regards, 
 Hasan Meihami

Sushma Choure · Accepted Answer

Hello Hasan, 
 It is true that t o analyze hydrogen sulfide formation in a SewerGEMS model, the SWMM solver must be used, see below wiki on modeling H2S, for your reference. 
 Modeling septicity / hydrogen sulfide (H2S) 
 About handling of pressure pipes in SWMM solver around pumps, a virtual pressure pipe is placed on both the suction and discharge side of the pump in case of Explicit solver, it is the way how Explicit solver works. It will model real pressure hydraulics only, virtual pipes will pass the flow from pumps to downstream nodes. 
 What is a virtual pressure pipe and how virtual pipes are handled by each solver?

Jesse Dringoli · Answer

Hasan, the assumption of virtual pipes only impacts the pressure pipe between the wetwell and the pump, which is typically short. Most likely any impact this would have on H2S would be very minimal and less than the margin of error introduced by other inaccuracies between the real system and the hydraulic model data input. 
 I have added a note about this and the user notifications in question to the related wiki article: What is a virtual pressure pipe and how virtual pipes are handled by each solver?

Jesse Dringoli · Answer

Hi Hasan, 
 The first user notification is saying that the upstream pipe between the wetwell and pump will automatically be treated as virtual. 
 The second notification is referring the downstream pressure pipe but is a suggestion (it does not automatically change it to virtual). It appears to be in reference to a typical case of multiple pumps in parallel where you would typically have a common downstream junction with another short pipe, like this: 
 
 Treating both the upstream and downstream short pipes as virtual tends to work better with the Explicit solver, hence the user notifications. Since they are typically quite short, they should not have a notable impact on hydraulic results. If you have a case where you have a single pump and there is a long pressure pipe on the downstream side, you can simply ignore the user notification. (again, only the suction-side pipe will automatically be treated as virtual). If you experience problems with the pump results in such a case, you can try inserting a junction on the downstream side of the pump by using the pressure junction layout tool to split the pipe, creating a short pressure pipe that you can try changing to be virtual. 
 
 Note that the H2S loss factor is not used in the case of pressure pipes because water is assumed to be pressurized, so the H2S gas cannot leave the liquid phase. See: Troubleshooting "N/A" results in H2S Modeling for pressure pipes 
 I have made some further edits to the related article based on the information above.

SewerGEMS Clonnect Edition: How to model a eastewater pumpiing system to calculate H2S concentration?

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