BOD modeling in sewerGems

Question

Hi to all, 
 1.in my project, I'm going to model quality of sewerage. I change active numerical solver from implicit to explicit and insert BOD local inflow for several manholes. after running the model, none of analyse on quality doesn't accomplish in model and BOD out not be represented. why does it occur? 
 2.for modeling BOD when we have data as person (50 gr/day), what process we must be do for modeling BOD in sewerGems? 
 
 Thanks in advance. 
 A.Ghasemi 
 MS in Civil engineering- Environmental engineering

Jesse Dringoli · Accepted Answer

Re: 2.what relationship is there between BOD inflow and BOD out? 
 Unless you have some kind of treatment in the manhole, BOD in to the manhole is equal to BOD out of the manhole. BOD can however change along a conduit. 
 Re: 3. how can BOD in conduits have pattern? 
 Patterns cannot be assigned to BOD because the equations behind the hydrogen sulfide modeling (Pomeroy equation) was developed on steady flow conditions and therefore works with average hydraulic conditions. For more on this, see the help topic "Hydrogen-Sulfide (H2S) Modeling". 
 Re: 4.BOD out decreased when sewer go ahead conduit so that after passed several conduits it became zero without treating. why was it occurred? 
 The decay rate may be too high. Check your Flux coefficient and H2S Loss coefficient. You cna read more about how these are used in the aforementioned Help topic. In ASCE MOP 69, flux refers to the creation of H2S as BOD breaks down and converts sulfate to sulfide. The "N" in the Pomerory-Parkhurst equation refers to the loss of H2S to the gas phase. 
 Re: 5.i didn&rsquo;t insert H2S inflow but I think when there are BOD inflow, part of BOD converted to H2S. and I expected, H2S produced in conduits but it wasn&rsquo;t occurred. Why? 
 Usually there is no H2S inflow. It is only created when BOD breaks down in anaerobic conditions. 
 Re: 6. what range is H2S flux coefficient in m/s considered? 
 Some typical values are mentioned in the aforementioned Help topic and in the sub-topic "Theory H2S Modeling Workflow". Also, note that H2S forms slowly over time and what really affects corrosivity is the long term average concentration. It is good to get some samples to calibrate those formation coefficients. 
 Re: about 5000 label need to combine, so it needs alot of time and after that perhaps some mistake occur. unless write a code that loads of same labels sum and then same labels convert to one. 
 After re-reading this thread and thinking about this some more, it appears that the units of your BOD may not match the expected units. In SewerGEMS, the "BOD (local inflow)" is a concentration - note the units, for example mg/L. Unless I'm misreading your posts, it appears that the data you have in your shapefiles is a volume of BOD per day, in grams. So, you can't simply enter that for the "BOD (local inflow)". This is another reason why patterns aren't used for BOD, because it is assumed to be an average concentration, which would not change as inflow changes over time. You may need to take a step back, examine your BOD data along with sanitary inflows to find the actual BOD concentration for different types of inflows, then assign them to the manholes accordingly. There is some information in the aforementioned H2S Help topic "Theory H2S Modeling Workflow" that mentions typical values for BOD concentration for domestic wastewater. However like with the Flux and Loss coefficients, the exact values may be different in your situation and for different types of sanitary inflows.

Sushma Choure · Answer

Hello Amir, 
 
 Do you mean that you are not getting results for BOD after modeling that using Explicit solver? 
 If that is the case then , could you please upload a copy of your model for our review? 
 There are two options for sharing your model files on Communities. If you would like the files to be visible to other members, compress the files into a zip file and upload them as an attachment using the &lsquo;Advanced Reply editor&rsquo; before posting. If your data is confidential, you can follow the instructions in the link below to send it to us via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley. 
 communities.bentley.com/.../7079.be-communities-secure-file-upload 
 If you send the model, please post here so we know it is available. 
 
 About your second question, 
 
 First, you should get the BOD data converted into say mg/L , as required by SewerGEMS. 
 As you have data per person, if you know the population that contributes to each manhole or to each ward which you could later distribute into manholes of that area. 
 
 So if you know population that contributes to each manhole you can multiply that population with BOD per person, and you could get BOD loading at manholes. 
 
 Regards, 
 Sushma.

Jesse Dringoli · Answer

Hello Amir, 
 Just to be sure - are you saying that you have a polygon shapefile in which each polygon has an area and a population density, or just the area and population density of the entire study area? For the former, one idea is to use Loadbuilder (Tools > Loadbuilder) > Population/land use data > Load Estimation by Population. Create and select a Thiessen polygon as the service area layer, select your shapefile as the "population layer", select the population density field, then in the table at the bottom, enter your "bod per person". If your model already had other loading on your manholes, you may need to set up a unique Pattern to assign to the loads, so you can later filter out the "real" loads. 
 After the Loadbuilder run has completed, either go through each manhole, open the Sanitary Load Collection and copy/paste the base load value to the BOD field, or use Modelbuilder to Sync out/in with a spreadsheet. Meaning, set up a blank spreadsheet with column headers for manhole label, base load, load type and Pattern. Connect to the spreadsheet with Modelbuilder, using "Manhole, Sanitary Loads" as the Table Type, mapping the label as the key field, the base load coumn to the Base Flow field, the Load Type column to the "Load Definition (label)" field and the Pattern column to the "pattern (label)" field. At the end of the Modelbuilder run, choose "no" when asked if you want to build the model. Then, back in the Modelbuilder manager, select the connection you just configured and click the Sync Out button at the top. This will export the information to the spreadsheet. If you had "real" loads already in the model, open the spreadsheet and delete all the rows related to those real loads. If you used a unique pattern in Loadbuilder then this should be easy. 
 Now, set up another Modelbuilder connection to the same spreadsheet, this time using the "Manhole" table type, mapping Label as the key field and mapping the Base Load column to the BOD field. This will import the "loads' from Loadbuilder into the BOD field. Lastly, you'll need to delete the loads from the model. You can do this in the Sanitary Load Control Center (tools menu). Filter by pattern if needed, select the rows, then delete. 
 Regarding hydrogen sulfide modeling in general: you can read more about it in the help and in the below article: 
 http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/16217.what-s-new-in-sewergems-and-civilstorm-v8i-selectseries-4 
 You can also watch the below Webinar: 
 http://pages.info.bentley.com/video-details/?video=CO_VID_OCT22&videoDBID=2de5febb-f911-4358-92a8-b6358c7e6564 
 Make sure you have the calculation option "Run Hydrogen Sulfide Analysis" set to "true".

Jesse Dringoli · Answer

Re: units in Loadbuilder - Don't worry about that - remember that you're just bringing it in as a load as a workaround to be able to populate the BOD. So, after Loadbuilder has been completed, as long as the load unit in the sanitary load collection matches the unit you used in Loadbuilder (L/day for L/capita/day for example) then the value shown in the sanitary load collection will be the BOD. I'd suggest doing a few spot checks to confirm, after the Loadbuilder run. 
 
Re: "other loading mean quantity of sewer? how does quality parameter (flow) add to quantity parameter(BOD)??" 
 
I'm not sure what you're asking - can you explain in more detail? 
 
Re: "I can’t filter out the "real" loads and don’t know about it. How can I do it?" 
 
You can filter by pattern. Before running loadbuilder, create a new pattern (Components > Patterns > Hydraulic) that you will use to assign to the loads that you will bring in through Loadbuilder (the ones that are actually BOD). When you set up the loadbuilder run to import the BOD values, use that pattern. Then when the Loadbuilder run is complete, you can distinguish the BODs that you just imported from the "real" loads that were already on your manholes, by way of that pattern. The Sanitary Load Control Center can be filtered by pattern.

Re: "What you said first paragraph doesn’t accomplish the modeling of BOD? Why do we do paragraph 2& 3?" 
 
The first three paragraphs of my previous response are all related to your question about importing BOD from your shapefiles/polygons. Once the entire process is complete, you will have the BOD in your manholes and will be able to model hydrogen sulfide (assuming the rest of the model setup is correct such as setting up the calculation option to run H2S). 
 
Re: "Can you say easier for my understanding to fulfill the model?" 
 
If you're unclear on something after reading my above answers, let me know. It is difficult for me to get more specific without a deep understanding of your modeling situation and structure of your files. 
 
Apologies for the broken link to the H2S Webinar - I've corrected it in my previous post. Here's a link to the main list of Webinars for Haestad products: 
 
 pages.info.bentley.com/videos

Jesse Dringoli · Answer

I'm having some difficulty following your question. When you say "mapping", I assume you are referring to the use of Modelbuilder to sync-out the data to a spreadsheet, and then sync-in to the BOD field. 
 
For the units to use - see the last part of my previous response (and the first reply by Sushma) - it sounds like you have BOD data as a volume, but SewerGEMS expects a concentration. So, I would re-examine your data to make sure it is truly a BOD and if so, convert it to the expected unit (such as mg/l) before importing it back into the BOD field of the manhole (using Modelbuilder). 
 
Some of your message above appears to be asking about this conversion, but I'm not sure I understand all of it, and it is something that you will need to do (if the data you have is indeed correct). If you have a pattern of BOD volume over time and sanitary loading over time, you may be able to take this information in Excel to calculate the BOD concentration to enter in SewerGEMS. 
 
Regarding the field to select when mapping to the BOD field in SewerGEMS - as seen in the properties of a manhole (and when using the Explicit (SWMM) solver), the input field for BOD concentration is "BOD (Local Inflow)", so that is indeed the one you would need to map to. The field "BOD (out)" is a calculated result field. 
 
Regarding "on the other hand, we know For domestic wastewater, the BOD concentration may be on the order of 200 to 300 mg/L. then how do we consider this case?" 
 
Can you clarify what you are asking here? If you want to model a BOD concentration of 200 or 300 mg/L, enter that in the "BOD (Local Inflow)" field. You can add this field to the manhole flextable and global edit it if needed.