 Welcome everyone to this IWA Masterclass III OVNR on Methane Monitoring, Modeling, and Mitigation. I'm Keshav Sharma and I'm currently in Brisbane, Australia, working at the University of Queensland. I'll be moderating this OVNR today. So before we start the OVNR, we have got some housekeeping matters. IWA has got a climate smart utility COP. You can find this on IWA Connect website. Please check the link at the bottom on the side there to visit this website. There's a very useful website where you can join and discuss participants in various discussions. This is a platform to exchange ideas. Talking about today's OVNR, this OVNR will be recorded and will be made available to all the participants on demand on the IWA website. Also, the speakers will have some responsibilities for securing copyright permissions for any work that they present here. And the views that are presented in this OVNR are the presenters' views and they don't necessarily reflect IWA opinion. During the presentation or after the presentation, you are welcome to have your questions to our panel. Please use Q&A box to send your questions to the panelists. We will answer these during the discussion and also towards the end of this OVNR. The chat box, please do not put any questions in chat box. This is for the general request only. We have got five presentations today. There are four presentations, five presenters. They are very good presentation and we'll go through this presentation and after each presentation, there will be a very brief Q&A session. So each presentation will last for 10 minutes and followed by five minutes Q&A. And also towards the very end, we'll have 20 minutes time for general discussion Q&A. This is the agenda for this OVNR. These are the panel members for today's webinar. Myself, Keisab Sharma, Wippert Evelen from Gend University, Belgium. We've got Anders from Karlstad, Westward treatment plant in Sweden. We've got Annett from the same Westward treatment plant in Sweden. We've got Oriel from the Catalonia Institute of Water Research in Spain. And we've got John Willis from Brown and Caldwell, USA. Before we start our webinar, there will be a poll on your screen. There are two questions on the poll. Please participate in the poll and share your answers with the panelists of this webinar. We'll wait for a few minutes before you complete the poll. Okay, we've got the results of this poll here. Number one question, do you think we can take action to reduce methane emission now? Almost everyone, 99% of the participants say yes to this. Yes, we can reduce the methane emission. Second question was, what would you find useful to make progress? Most popular answer, there are two answers. The most popular one was tools to better estimate emissions. And second one is experience with monitoring methods. So there's a result from the poll. Thank you very much for participating in this poll and expressing your views. Before we move into the webinar, please feel free to share your thoughts on social media. We have got this report on quantification and modeling of fugitive greenhouse gas emission from urban water system. That is published by IW recently. If you have any thoughts on the issues related to methane emissions from urban water systems, please share your thoughts on social media. Use tag at IWSQ on social media. And also tell us what action you are taking to reduce methane emissions. The hashtag you could use is IWA, etc. So today, the whole webinar is focusing on methane with an emission from urban water system. We are talking about monitoring, modeling, and mitigation. So these are the areas that will be covered in today's webinar. Why are we talking about methane is because methane is highly potent global greenhouse gas with the global warming potential of 21 over 100 years and 56 over 20 years. Our first speaker today is Evelyn from Gantt University, Belgium. Evelyn is a full professor at the Gantt University, leading the BIO-CEO research group. Our group has specific expertise in biological wastewater treatment, considering innovative techniques and sustainability aspects such as greenhouse gas emissions. They do process engineering, aim and get process optimization through physical based modeling and simulation, data treatment techniques, and experimental studies. With this introduction, I would like to invite Evelyn to give her presentation. Your time is 10 minutes. Thank you very much Sharma. I hope you can hear me well. Yes, good morning. Good afternoon. Good evening everybody around the globe. It will be my pleasure to talk to you today about methane emissions from wastewater treatment plants, more specifically the quantification and mitigation. As we all know wastewater treatment plants emit greenhouse gases. They emit CO2, which is associated to the plant's energy consumption, which is mainly for irrigation. They emit N2O, which is a very potent greenhouse gas and mainly emitted during nitrification and denitrification, as you have already seen in the May webinar of this series. And then today we will be dealing with methane emissions from wastewater treatment plants. About 10 years ago, we performed the first full-scale, long-term online monitoring campaign measuring both nitrous oxide and methane emissions from a municipal wastewater treatment plant. You see the plant here. It was the wastewater treatment plant from Plaring Severe near Rotterdam in the Netherlands. We measured for about one year. And if you look very well to this plant, of course, you immediately recognize the settlers. You also see a lot of white on the other equipment, which is because this was a specific plant which was covered. It's close to housing facilities and it was completely covered to be able to withdraw the off-cast for treatment and immediately understand that this gives us interesting perspectives for monitoring greenhouse gases. The configuration of the wastewater plant, we see on the next slide, and the wastewater treatment plant has a primary settler and then biological treatment. It has been revamped over the years. This is why it consists of a plug-flow reactor followed by a carousel reactor. And the plug-flow reactor has a pre-denitrification configuration. Both the primary and secondary sludges are sent to sludge treatment, which consists of the thickening process, anaerobic digestion, dewatering, and then cogeneration, so using the biogas for energy production. Since the whole plant was covered, we were able to analyze the off-cast of the entire plant using only two sampling points. This made our life much easier. The gas composition was measured with an online gas analyzer and the gas flow rates were measured with an animometer. In order to be able to identify the sources and sinks of methane on the plant, we also wanted to set up mass balances over the different unit processes. So for this purpose, we had to calculate the methane load in every single liquid and gas stream from the flow rate and the concentrations. For measuring dissolved methane, we used a method based on sorting out methane and analyzing the headspace of the recipient with gas chromatography. For the gas streams, we took the samples in gas bags and also analyzed them with the GC. And here, in the next slide, you see the overall results. Both the methane and the nitrous oxide emissions at this plant were quite high and they exceeded the indirect CO2 emissions that were related to electricity consumption, so not to be neglected. Also, the emission factors for both compounds were higher than the emission factors which are put forward by the IPCC. And then we quantified the methane mass flow rates over all unit processes and you can find details described in the publication corresponding to this. I want to draw your attention to a few specific sources and sinks of methane. First of all, the sources. The main sources of methane, which you see on the next slide, were the sewer system, which was responsible for 25% of the total methane emission. So sewer system 25% and then the unit processes related to anaerobic digestion, that was the other 75%. And you see the breakdown of the methane emissions for the individual unit processes mentioned on the slide. In fact, it was a lot, 75% of the methane emission comes from all the processes related to anaerobic digestion. This makes, if you make the calculation, that the amount of methane which is emitted from processes that are related to biogas production may be potentially even higher than the CO2 that you avoid by using biogas. So this gives us something to think about and definitely a reason to take care of the unit processes around anaerobic digestion, which is definitely one important point of mitigation. Besides methane sources, we also found a methane sink on the plant, namely the biological reactor. 80%, so that's quite a lot of the methane, which entered the biological reactor was converted. And we could identify that the conversion took place in the irated part of the biological tank. It was performed by aerobic methane oxidizing bacteria, which I will further refer to as methanotrophs. So that is great. Methane can be converted. And this is definitely something we want to exploit. Therefore, in the next part of our study, we investigated which operational and design conditions could promote methane conversion over stripping. And we did this through mathematical modeling and simulation. We started from the activated sludge model number one that most of you know, at least the ones who are modeling. ASM1 describes COD and nitrogen removal in activated sludge, and we extended it with aerobic growth and decay of methanotrophs. We assumed that they followed monokinetics and we took parameter values from literatures. We call the resulting model ASM1M. ASM1M was then implemented in BSM1, which is a virtual waste water treatment plant with a pre-unitrification configuration. It consists of two anoxic reactors and three aerobic reactors in series, mimicking a plug flow system. For the reference case in the study, we replaced the three aerobic tanks by a single continuous stirred tank reactor, which is thus completely mixed. We also included in the model an appropriate description of the gas liquid transfer. And then the results. First of all, we compared two process configurations. The single aerobic tank, which is completely mixed, CSTR. And then the plug flow modeled as three completely mixed tanks in series, which had the same aerobic volume in total as the CSTR had. The graphs show the percentage of the incoming methane, which is stripped in blue, which is emitted in reddish and converted in green. So this is what we want. We want the green. We see it for the overall plans in the pie chart, and we also see the results for the separate reactors as bar charts. And you see in the pie chart that the completely mixed configuration performs much better with regard to methane conversion. That's the green part in the pie chart on the top, much better than the one for the plug flow reactor. The plug flow reactor is less good. How can we explain this? Well, in fact, a plug flow configuration has a higher inlet substrate concentration. So higher substrate concentration, that inlet means that you need higher oxygen at that point. So you will provide more aeration air. This also makes that you have higher, so that the aim is to provide more oxygen, higher gas liquid transfer rate of oxygen. But it also makes that you have a higher liquid gas transfer rate of methane, so more stripping. As a result, in the plug flow reactor, you have more stripping and less methane conversion than in a completely mixed reactor. In terms of methane conversion, this is less good. This is, by the way, also something that we examined later on for SBR types of systems, like in granular sludge, where you also have this plug flow system and high oxygen demand at the beginning is then not very beneficial. As a next parameter, we investigated the effect of the aeration intensity as such. The upper graph shows the percentage of the income in methane, which is stripped, converted and discharged with the effluent. The lower graph shows the effluent concentrations in terms of organic carbon, COD, ammonium and methane. And we see that the optimal aeration intensity for methane conversion corresponds with the one for ensuring a good effluent quality in terms of COD and ammonium. So this is very good news. Of course, a small fraction of the air that you use for aeration will also be used for methane conversion. We calculated that this was about three and a half percent. And then last, we investigated the effect of the depth of the aeration equipment. The graph shows the percentage of the entering methane again, which is stripped in blue, converted in green, and discharged with the effluent in red for different depths of the aeration equipment. If zero meter means that you have surface aeration, four meter, quite regular, and eight meter, then a very deep reactor. The equation which was used to calculate the gas-liquid transfer of methane and oxygen takes into account different effects, which are counteracting. First of all, you have a higher partial pressure at greater depths, which means that you have a better solubility of methane and oxygen. Second effect is that there is depletion as the gas level rises, so there is less oxygen present to convert the methane. So quite some interactions, which you can ideally describe with modeling. But overall, we found that for deeper aeration, you get less methane stripping and a higher methane conversion efficiency. That brings me to my take-home messages of today. We have quantified methane emissions from wastewater treatment plants, the magnitude I presented, the dynamics I didn't present today, but in fact for methane, there were not so much seasonal dynamics. What we did to this end, we've used fit-for-purpose monitoring methods, and I was happy to see that you all agreed that good monitoring methods are really key for us to mitigate methane emissions. I definitely agree with that. So what we described in one of these papers is a refinement of a sorting out method for measuring dissolved methane, in case you need that. We also identified sinks and sources of methane, and we have proposed some mitigation options. Thank you for your attention. Before I leave the floor, I want to also thank in particular Matej's Daama, who is the joint Ph.D. student who has performed most of the work that I have been presenting today. It was my pleasure to guide Matej's together with Markan Rossekt from TU Delft. Thank you. Thank you. I have been for a nice presentation, very informative one. We got a few minutes for a question and answer. Abdel, there's a question on Q&A board. Yes, I've seen that from whom, boy. Is anaerobic and anaerobic CSTR a good way to model the methane emissions from the sludge storage tanks, or are there better ways? Well, first of all, in what I presented today, we did not model this storage tank, but we did it in other studies. It's definitely something relevant. It is indeed so that 75% of methane emissions that you get from sludge treatment is mainly due to the storage before and after the anaerobic digestion. So if you could cover those storage tanks, that would already solve a lot of problems in terms of mitigation. If you want to model how much is there, I would say, yeah, depending on the configuration that you have, if it is an oxy, usually you don't provide any oxygen there. So it would say indeed it is anaerobic. Is it a CSTR? In most cases, I would say probably yes, this depends on the mixing there. It is definitely also the way that I would model it. And what you typically do is then you take an anaerobic digestion model, and you model it as if it's an anaerobic digestion process. If there would be some oxygen present, you could include a bit of gas liquid transfer there, indeed. Okay, I hope that answers the question. I will go to the next one that I see. Please, Keshav, tell me when to stop. And the results only corresponds to covered facilities, right? If not, could you please comment? But first of all, indeed the fact that the facility was covered made our life much easier in terms of quantifying the overall emissions. That's clear. We could simply use one of the off-gas pipes and measure. Otherwise, what you would need to do is to use a floating hood and then preferably also measure at different places in the plant and try to make some overall calculation in that way. However, the results that we presented for the unit process are completely independent of the process being covered or not. It's a bit easier to measure the off-gas, but otherwise you could also measure dissolved oxygen concentrations in different unit processes. And as for the conclusions, since and sources of methane emissions, I would say there is no reason to believe, no reason whatsoever why they would be different for non-covered facilities. So the fact that methane sludge storage contributes to methane, that's a clear one. The fact that you have conversion in the aerobic tank is also not related to the fact that this tank is covered. It has to do with the amount of dissolved methane that enters the biological reactor. There are a few more questions. Yes, do you have a preference? Yes, that's a bit of a technical one. I'm just answering them in chronological questions. How was the methane produced in anaerobic processes sent back to the aerobic reactors? If you look at the slide, I'm not sure if I can go there, the slide of the plant configuration, you will see that there is an off-gas withdrawal from the plants. And then it's sent back to the previous slide. Well, it's also discussed in detail in the paper, but it's so that the whole off-gas of the plant is taken and it is then sent to the biological reactors where it is used for aeration. And then afterwards it's taken from the aerobic reactors and then sent to a compost filter before it is released. I'm afraid that we are running out of time now, so we may have to wait until we have got another session for question and answer at the end. Thank you, Evelyn, for your presentation. There are some questions coming in chat box as well. I would like to remind everyone that please put your questions in Q&A box so that it's easier for us to monitor and follow. There are some outstanding questions still there, so we'll come to that question later in the session. Thank you, Evelyn. Thank you. Now we'll move to our next presentation on monitoring within EggMet. We have a two-presenter here, Anders and Annette. Anders is a consultant at NetoBase, AV. He has been appointed responsible for EggMet, the Swedish voluntary system for monitoring methane from biogas facilities. He's also a methane measurement consultant within EggMet and for biogas plants that needs to measure under the environmental code. Annette is a compliance manager at a biogas facility situated at a municipal wastewater treatment plant in Karlstad, Sweden. She is responsible for the production of biomethane as vehicle fuel. Earlier, she has worked with landfill gas at a municipal waste facility. With this introduction, I would like to invite Anders and Annette to give your presentation. Thank you and I will start and Annette will take over in a little while. You can take the next slide. EggMet is a system that all biogas plants in Sweden is invited to join, where we try to make a system out of measuring methane and mitigate its emissions in a systematic way. It is Sönsdvarten and Afall Sverige trade organizations for waste and for wastewater treatment that has started this system. And they have appointed me. I'm a consultant from Kornitoves to manage the system. I also do measuring quantifications within EggMet as part of my work. Next slide, please. This system, as of right now, about half of the production of biogas is done by plants that is member of the EggMet system. And we've been active for about two years. So, of course, we hope to have more facilities joined so we include all the facilities, of course. What we do within the system is try to systematically reduce methane emissions by, first, systematic leak detection and helping plants do this in do leak detection and repair in a systematic way. This is performed by the staff, but they get support from EggMet in their efforts. Next, we'll be describing how they do this in the plant. The next part of EggMet is emission quantification, which is done by an external consultant. I'm one of those. And we do this. So I will be talking more about emission quantification later on. Next slide, please. A little bit about the leak detection, the rules within the system so that you know what we try to achieve. We want our members to do a very thorough check on the facility every year. This is not very often, but we think it is enough to do a thorough check every year. Because we then do a less check that is more in specific points where we can detect if there is, has risen leakages during the period from the last check. And if there is leakages, then of course we detect it and we go in and try to remediate and find the exact sources and produce the emissions, of course. And this is done by the facilities. What we do as a consultant is to check the measurements and see if it corresponds to the values we achieved when we do the quantification, which I will be describing later. One tool that is very efficient, we think, is to use the right equipment. I would be describing what kind of leakage instruments we prefer in EGMET. But also to do these simple measures, like knowing what you have, rust and stuff, that you know that here we might have an emission and search for it more thoroughly in those places. And the upper picture that we encourage our members to do as the picture says to have simple ways of easily monitoring leakages. And I have already kind of talked about this looking, looking for rust, leak detection spray, leak detection instruments. And if you have a big company and big many leakages, you can employ the IR camera as a way to visualize where you have your leakages. The facilities themselves, we encourage them to use the semiconductor sensor because it has a low detection limit. It is therefore possible to measure in a room and see if you have a high, if the amount of gases have recent, from recent measurements, then you can detect it with the semiconductor sensor because they have low detection limit and they have a short time frame for reaching the value that is accurate. So choose a good leak detection instrument and you will save time. Now on it. So now I'm going to talk a little bit about how we do it here on site with the leak detection and repair. And this slide shows a part of one of the protocols we have for leak detection. And according to regulations, we are obliged to do this at least four times a year. But in reality, we do it more often, but we don't, we don't put it in a document like this. It's not loaded in a protocol. But every time we have had a stop somewhere and we start all over again, we go all over to find leaks and stop again and start all over until it is a seat. So the leak detection as Andes has talked about is carried out with a handheld instrument with a semiconductor sensor on a flexible measuring hose. You've seen pictures and leak detection spray is also used. And we do measuring at where there are gas couplings, flanges, valves and also sludge hatches. And if we find any leakage, we mark it as red in the protocol. And if it's somewhere not so obvious, a nameplate is put up and as close as possible to the leakage point. And when suitable repair is done with sealants of different kinds. And when tightening is needed, we have spark free tools for that. So here's the second slide shown with pictures of two measuring places. And to the left you see a condensation or condensation vessels with the couplings, flanges and valves. And to the right you see the sludge hatches on top of the digester where there can be leakage around the edges. And that is repaired by using sealant or thread blocking. And thanks for me back to you Andes. Thank you Annette. My part of this process is the condensation done in all the plants every third year. And we've already talked with the issue of standardization with the issue of choosing the right methods. We have a book called Handbook Metal Metal. I don't think it's in English, but it is the book that describes how we are supposed to carry out our measurements. We have different firms doing quantification but all use the same standardized method. We also use the same standardized reporting and calculation. And we try to, when we do the measurements differ between pre-treatment measurements, measurements on pre-treatment processes, measurements on gas systems and measurements on digestate treatment. Because the reporting then can be used in the statistics in a more efficient way. And it is also possible to use the data to report back to the facilities where we compare with other facilities. And what kind of missions they have in these three areas. And then of course we do a summary of the total and we deliver a measure reducing measures to the facilities. And what we think from our experience is the best way to reduce methane in their facility. And quantification of course means that we have to measure the concentration and the flow. And we do it over time. We take our equipment with us. We don't measure short periods. We measure up to an hour in each point to be certain that any variations is caught in the measurement. And if there are processes that could result in varying degrees of emissions, then we include this in our measurement. As you can see here, just one example of a measurement where it was important to measure difference passes in the process to be able to calculate the right mission over time. Next piece. And as I said, we bring our equipment with us to be able to measure over time. And the method that we have chosen within a moment is the feed and ionization detector with the cutter for methane. So it filters away all the hydrocarbons. The feed measures all as the instrument measures all hydrocarbons, but we filter away all other with the filter. And then we get the result in methane. There are other good measures, but we chose and said that within a moment we should use the feed, the flame ionization detector. Next piece. And of course, we have to measure flow, which is often the most difficult part to get a good result. We do with differential pressure gig or clockwise sensor to different methods that we are allowed to use. Sometimes it is impossible. We have explosion zones, for instance, where we cannot bring our measurement equipment by law. And then we have to use time data or for some instances where we have low flows, it is allowed to use standard values within the handbook. So what we reach is the method emission factors that was presented in the earlier presentation. Also, the percentage of methane related to the amount of methane produced at a facility and this makes it possible to compare different facilities with each other. Next, this is an example. This is the quantification protocol and the numbers are, of course, examples from a facility, but it shows you that this is standardized all the way through. The mathematics is done by a certain protocol. All the participant quantifier consultants do the same way. So we put in the concentration value, the differential pressure from the differential gauge and the pipe diameter and some constants. And then we calculate the amount of gas, amount of methane that is emitted from this specific source. And then with the facilities total methane produced over the year, we calculate the percentage, the methane emission factor. We have different kind of emission sources that we measure. We have point emissions and we have diffusion emissions. Point emissions is often, we often try to measure in ventilation charts, different kind, general ventilation and process ventilation is two different kinds. The general ventilation, we must measure of course and then the process ventilation where we, for instance, is connected to a certain centrifuge or something where we think that we have emissions. Diffuse emissions, then we need to have a hood for some kind of collection device to be able to measure. We have also understood that these emissions cannot be easily compared between facilities because there are so many factors involved in how much emissions we actually measure at one time. And at another time, it can be a completely different value. So we have more difficulties in how to use the data from diffusion emissions sources, but we are working on it next piece. Ventilation, here we have the kind of measurements that are quite easy to do. We measure from pre-treatment, from buildings, from ventilation, from buildings where sludge is handled, from hydrogenization units, hydrogenization units can vary very much over time. So we have to measure them quite early. We do in gas equipment rooms, often quite low values, but some facilities we can detect very high values, but generally very low values. Gas holders are the same thing. Some gas holders emit enormous amounts of methane, actually. Others don't. And therefore it's a good idea to monitor the gas holders thoroughly to be able to mediate. Here we have often the big sources of emissions, but also the sources that are difficult to have good measures to reduce. As I said, the emissions of diffusion emissions is a big problem for us in a way that we think that as of today, we have only done measurements. And the data should be used in a different way than we have done so far. And therefore we don't do anything including our statistics, because we need to use the data in a different way. And I think we believe that mathematic modeling with the data is a way to go forward, but we haven't reached that yet, unfortunately. It's the next focus area of ours. Sources where we have found big emissions is the post-treatment. If there are systems that are not connected to the gas system, then we can have very big emissions from post-treatment. Another area where we have seen historically big emissions is from gas upgrading units. The residual gas can vary very much between facilities. It can vary both within certain techniques because of process disturbances, and it's therefore important to measure quite often. These facilities often measure more often than every third year because of environmental code. But we have also seen that during the years that IgMAT and previous systems have been existing, that we have reached lower and lower emissions from gas purification and gas upgrading units. Here are some examples of how we present our data to the facilities first. I won't go into detail, but you can see that we measure for quite a long time, up to an hour, and we will measure different ventilation within the facilities. Then we use the data to measure the flow of methane, and the percentage part, the methane emission factors, as it's called, also for these different areas in the facility. On the bottom row you see the upgrading unit, the results from the upgrading unit ventilation and the process gases. Process gases have historically been the big issue, but we also see that many plants, may be not as thorough with their leaked detections and can have quite a big emission from ventilation. This is a compilation of results, and I will leave it to you to study it if you want to, but I can take some pieces out of it to show you. You have the biggest emissions noted here in non-gas type storage tanks. This is post-treatment, as I talked about, a big emission source. You also have quite a lot from water scrubbing. This is known historically, and it's just a fact. It's also from CHP units, when you produce electricity from the gas. The EU stands for gas upgrading, and the EU stands for electricity-producing units. Leakages, as you see, can be quite high numbers in certain areas, but often it is when you have an upgrading unit. Higher pressures, more emissions. This is a compilation of results from the EU units and shows you a little bit about how different kind of upgrading units stand with regards to emissions. We can see that the chemical scrubber, the chemical scrubber are quite good with regard to emissions, but within them you can have quite big differences because of how they are from them, how they use them over time. We have the water scrubber on the other end, quite large emissions, and there it is also possible to mediate the emissions by the way you run the facility. The PSR has had very quite numbers previously, but gone down quite a bit in the Swedish measurements because new processes, better processes. And that was all for me. Thank you. Thank you, Anders and Annette for the great presentation. We didn't really have much time left, but I think we can probably take one or two questions if there are any. I don't really see any questions in the Q&A box at the moment, so we'll wait until we come to that discussion at the end of this webinar. Okay, so we move to the next presentation. This presentation is on methane generation and quantification from Suez. The speaker is Oriel Guterres. Oriel is a research fellow at the Catalan Institute of Water Research in Ziruna. He is an expert in urban sanitation systems, including urban sewerage and drainage, development of innovative solutions and digitization of urban water systems. Oriel has more than 15 years of experience and research leadership in sewer systems. With this brief introduction, I would like to invite Oriel to give a presentation. Oriel. Thank you very much, Keshia, for the introduction. In my presentation today, I will talk a little bit about what happened with the methane in sewer systems. The outline of the presentation has these different points, the first a little bit of context of sewer systems, the biological reactions that occur and they produce the methane in this specific section of the room wastewater system, which factors affect the methane production and a little bit of introduction of quantification because John Willis in the next presentation will elaborate a little bit further on this topic. But let's start with this slide, which is one of the slides that is on the report that we published. And I encourage you to read the report because all the information of this presentation is a little bit more extended. So we've seen that methane is being produced in different places of the urban wastewater systems. Eveline has explained which are the different contribution and it was good to see that in her case 25% comes from this initial part, which is the sewer systems, 25% is not neglectable. So my presentation is going to be focusing on these sections of the urban wastewater system, which is the sewer systems. Sewer systems, by definition, it's a crucial section of the urban wastewater system that its main function is to transport the wastewater that is generated in so many different places down to the wastewater treatment plan. Well, depending on the configuration of this sewer network, there are sections where the methane can be formed and stripped. And just for you to have a number or a sense of the magnitude of these installations, in Spain, the length of the sewer network is this number here, 189,000 kilometers. Like if you put all the sewer networks, all the pipes, pumps, stations, manholes, everything all together in one line, it can have like this extension, which for you to take as a reference is two times the equator line. Okay, so two times a look in the whole planet. And that's only for Spain, like different countries like the United States, Germany, developed countries, it's case-based, it can change a little bit, but it has a big, big magnitude and transport a lot of sewage, and it has a big, big value in terms also in asset value for the urban wastewater systems. So what happens in this transport the wastewater from its origin to the wastewater treatment plans? So in some sections of the sewer systems, they can prevail on Arabic conditions and Arabic conditions can occur. And then these biological reactions that they are the ones that transport the organic matter that is contained in the wastewater down to biogas. And as I said, this is already more well explained in the book, but there's this four step where the organic matter, the big compounds are break down and transform to methane and CO2 at the end. Okay, so in sewer systems, we can this thing happen in specific places. But as I said, it's a biological transformation of organic matter to methane. And this process, this biological process is very much linked with another process that happens in sewer systems, which is the reduction of sulfate to sulfide H2S. Okay, so these two different biological reactions happen simultaneously. And the two different biological communities help each other to produce these two different compounds. Also in this slide, we have like a small simplification of how the sewer systems and the sewer networks work. We have mainly two different depending on the slope and the configuration of the network have two different cases. The first one is this sections where we call usually rising mains and it's where the wastewater is transport from a lower point to a higher point. And this is characterized to be like pipes fully full with no headspace. And in these conditions, there is no oxygenation, there's no radiation, so under every conditions can happen. And when this happened is one of the primary spots, one of the primary places where the biofins that they can produce methane and sulfide, they grow. And in this slide, we can see that these biofins, they grow attached to the sewer walls inside the pipes. And it is a physical support, so they attach to the pipes and they take the sulfate and the organic matter that is in the wastewater to perform their metabolism. And they expulse, they create this sulfide and methane that then it's dissolved in the wastewater that is being transferred. Okay, so here in this in this rising mains sections is the specific place where these compounds are generated. But these compounds, they are problematic when they are released to the atmosphere and that happens in these next sections, when we have like minecalls or gravity sewers or what will discharge menstrual when the pipe moves from being completely full to have a gas phase. There is a little bit of gas phase and those compounds are stripping. This is where their contribution is like a detrimental. Okay, so we have two different situations, the gravity sewers and the rising mains sewers or pressure pipes. So generation of these compounds occur here and release the stripping and when these compounds create the troubles are here in this gravity sections or what one manholes. So, and how does that happen? We performed studies already a few years ago and to see how these two different biofilms and biological communities interact. And we saw that this methane production was possible thanks to a thing called that we call it stratification. So which is the different location of these communities within the biofilm. Okay, I'm going to try to explain this in this slide so here on the left hand side we have a section of a pipe and this brown here is like the sewer biofilm which is all about a few millimeters thick. Okay, so in this part of the slide we have like a section of this biofilm. This is the substatum. This is the pipe and this top part here is the water. Okay, so all these things is this phenomenon that the biofilm. So what happened with this biofilm is like the sulfide reducing bacteria sulfate reducing bacteria sorry the bacteria that is able to use this sulfate. They tend to sit on the outer parts of the biofilm. Okay, on the external parts and the sulfate has been consuming these parts and it's been released back to the liquid phase in terms of sulfide. Okay. And in the lower parts in the inner parts of the biofilm. They are the methanogens the methanogen archaea they tend to be there because they are more sensible they are not as strong as the sulfide bacteria. So this is specific configuration. This helps to protect the methanogen archaea. And because of the solubility and the transfer of organic matter can go all the way through the biofilm they're still there and they are able to get their food. And they transform this organic matter back to me then which is exposed in the in the liquid phase. Okay. Here on the lower part of the screen we have like a couple of images where we perform experiments to quantify which are the where they were sitting the different sulfide reducing bacteria which is this part and methanogens. And here you can see this is like the biofilm surface and how the deeper that we go to the biofilm so divided in five different layers. And we see that the higher the intensity of the green color is the higher it's the presence of this sulfide reducing bacteria. So as I was explaining here they tend to sit on the top part on the outer sections of their sections of the biofilms and the methanogens with different methanogenic archaea that we analyze. We saw that they were going to sit in the lower part. So this combination and this stratification have to be there simultaneously and produce these two different compounds at the same time. Okay. Yes, I will go past with this one because the main message of this slide is like not only in the sewer biofilm walls is where the sulfide and methane can be produced. There is places in the in the sewer systems where the sediments tend to sit and the same conditions of anaerobic conditions and release of methane can happen. And there are also spots, hot spots for methane production in from sewer systems. So which are the factors that affect the methane generation from sewers. So we have them listed in this slide. And I'm going to explain a little bit one by one very briefly. The first one is the dissolved oxygen. Obviously the methane generation happens in anaerobic conditions. So any access or any exposure to oxygen to the methanogenic archaea is not good for them. They don't like it. So that's why they tend to sit on the lower parts of the biofilm. And that's that allows them to to perform this methanogenic activity to have methane production. So and that's why methane production happens more in rising main systems because there is no oxygen there is no headspace. There is no radiation. There are more favorable conditions for them. The second one also is very obvious. We need to have organic matter in the reservoir. That's something that happens everywhere. There is no limitation of organic matter. So they need to have COD or volatile fatty acids. Depending volatile fatty acids are more easily biodegradable. So it's their favorite food. The third factor is the something that we call hydraulic retention time. And this is the time of contact between the biofilms and the wastewater which is moving through the pipe. So the higher the time that the wastewater is in contact with these biofilms, the more methane that we will have in this dissolved wastewater because the methanogens, they are taking organic matter and bringing back the methane. So if the water goes past in the sewer systems, the final concentration of methane is going to be lower than if the water stays there and sits for a longer time and the concentrations increase. So that's a logic, quite simple. So that's about the hydraulic retention time. The second last factor is what we call also the area to volume ratio and that is related to the diameter of the pipes. So in small diameter pipes, we have a volume of water which sits here and this small volume of water can be in contact of the area of the biofilm. So the biofilm can access to mostly of the wastewater that is there. And that happens in upstream sections of the sewer systems when we have smaller pipes, connections from the households, etc. But as we go down to the sewer systems and we have like bigger diameters of pipes, big pipes, the area to volume ratio decreases. And we have, even though we have a little bit more area, there is a big volume of wastewater that is not directly exposed to the biofilms. So the ratio of this is another factor that makes that we have more methane or less methane in the sewer systems. And finally, another factor which is very obvious is like the temperature and even though it's very obvious, it has not been thoroughly studied yet. And the logic is that the biofilms they grow in like in, they like warm temperatures. Okay, that's commonly known, but we don't know the extent of this higher and lower temperatures. It influences the production of methane, but that's definitely one of the main factors that affects the production in sewer systems. Okay, and finally, just one slide to talk about this methane quantification from sewers. Okay, as you might guess, the quantification of methane in sewer systems, it's complicated because of the extension and the different points of emissions and generation and all of these things that I have just introduced in my presentation. Okay, here in this slide, I'm showing you like the ideal sampling points and the ways that all the places that you should measure methane if you want to have like a good assessment and close the mass balance to see how much methane is being produced in one section. So in rising main stations, you will have to sample here, sample here, know the stretch of the pipe and the flows, etc. Which is maybe a little bit more easier, but in gravity sections, the complication is much, much higher and you have multiple sample points with air flow measurements, water flow measurements. So it's not tricky. And in addition to this, there is no, yet, still a method that allows us to measure directly dissolved sulphide. So we have to take samples, just the samples as also I have already mentioned in that methodologies, and then bring the samples to the GC and have the results and calculate back what was the concentration in the dissolves. So there is still a lot of limitations on this place and we are working hard to address on this knowledge gaps and limitations. So the conclusions of my presentation to that is like sewer systems are sections of the urinary water system where methane is being produced, we have seen this and we are studying this. We saw the difference between the generation and the expression of these places in the network. We explained the biopharmus stratification influence and which are the factors that affect the methane production. And as I said, the quantification is as tricky as possible, but we are studying and we are developing new tools and new assessment based on modeling and comprehensive monitoring to perform this, have more accurate quantifications and emissions assessment. John will elaborate a little bit more in his presentation next. So that's it for me. If you have any questions, I will be happy to reply. Thank you very much. Thank you for your very informative presentation. We have a few minutes left. So we got a few questions waiting for you. Yes. So I should go down to this. The questions are the, can you help a little bit with the questions? Can you read it because I don't know about the Q&A, which are the ones that I should get into. Currently IPCC, yes, the last two. Thank you. Okay, we definitely underestimate emissions from seawars. In the previous IPCC reports, they were not considered, but I'm not sure about the last one, but definitely with the work that we are getting out, we are showing that this is not a neglectable number. I'm going to say it, like 25% in that case, it was at the inlet of the wastewater treatment plan, and we don't know what happened a little bit upstream in the sections of the network. So that could be a part of the extra contribution. So definitely we are underestimating this. And there was another question about the higher rate to volume ratio within more or less of making emissions. Okay. So with the smaller diameter pipes, you have more contact between the biofilms and wastewater, but because they are smaller, they tend to have like lower also methane production. Even though all the wastewater is in contact with the biofilms, they get produced methane, but they tend to be like small pipes in the upstream parts of the sections. In the lower pipes and with higher diameters, they have less contact between the water and the volume, but because biofilm is like, we have more area of biofilm, like in overall numbers, they put up also major contribution in terms of the absolute numbers of methane. So that's a little bit, it depends a lot in case of specific situations also, but the rule of thumb is more or less what I just replied. Thank you. I'm afraid we have to stop here because we are running out of time. We still have one more presentation to go. The next presenter is John Willis. He will be talking about significance of sewer methane. And then some opportunities to quantify and reduce recover of methane from sewers. So that's his topic. John is Vice President with Brown and Caldwell and he's a WEF fellow with 32 years experience in attacking waste for energy and unrecovered resources within the wastewater space. He recently chaired WEF's VA Solid Committee and vice chaired WEF's PFAS Task Force, recently completed five years of service on WRF's Research Advisory Council. And now he's a chair of WEF's New Energy Management Task Force. With this introduction, I would like to invite John to give this presentation. Thanks, Keshav. Appreciate it. I do want to let folks know I did put a copy of my dissertation, but Keshav actually helped me out with, we did a fair amount of work together when we were pulling that together. But it goes through a lot of the detail on the sewer methane methods and how we did our analysis. So that's worth looking into. The one last thing that I wanted to say, and this is following up on a question that Oriole answered. IPCC says that if you're in the developed world, you can ignore sewer methane. The reason is because if you're in the developed world and realize IPCC is talking to countries, they're telling countries how they should do their carbon footprint. And if you're in a place like the United States, we use so much fossil fuel for power and transportation that sewer methane is not significant. But when you get to smaller operations like a city government or a county government or even smaller operations like a sewage utility, methane could be huge. IPCC is not talking to them. The problem is that a lot of the protocols have adopted that IPCC said it doesn't. It's interpreted that if you're in the developed world, you don't need to count it to mean that it doesn't exist. And it's not the same answer. So I'm going to just tell you what we've done. So I've got a really quick overview here. We're going to talk about sewer methane and some of the analysis we've done. We have an invention that we're working on piloting right now that could be a solution. We've got a project that we're pulling together where we're soliciting involvement from utilities to have us develop a better method, estimate your sewer methane, and then to come up with a method for everybody. So we'll talk about that. So just a few things. This is going back to some of the things that Oriole talked about. So our methodology assumes that all of the methane is produced by slimes. There are septic systems and slow moving sewers where you deposit a lot of solids. But sort of like a digester, if those solids aren't there for 10 days, they're not going to be stimulating a bunch of growth. The slimes on the wall of a pipe stay there for a long, long time and you can get those detention times where you're not wasting the methanogens faster than they're growing. So we assume it's produced by slimes. It's not carbon limited, unless you're below about 50 milligrams per liter COD. Our assumption in our model is if methane is produced, it's emitted. Evelyn was talking earlier about methanotrops, they exist. But some of the research at the University of Queensland and other places have had trouble finding them in significant quantities either on the headspace of the sewers or in the bulk phase of the liquid. So it'd be nice if they were there, but so our assumption right now is it all gets emitted. This is a mass balance that is a way to think about the collection system. So one of the toughest parts as Oriole mentioned is how much air is emitted from a gravity sewer. It's really difficult and there's been very few verification efforts because it's tough to know. The way to know is if you have a ventilated section, you know how much air flows coming here and you can measure the concentrations. And that's what we did as part of my PhD dissertation. The rest of it is that it could be that the upstream area brings methane into the foul air fan area that's exhausted. So we'll talk about some of these things. A sink could be that you wouldn't measure in this could be fugitive methane going to the atmosphere. You wouldn't measure it with your foul air fan. It could also be dissolved methane that's still dissolved when it goes down the sewer. So the model estimates what's in the known systems, but a lot of regional sewers may have contributions from local sewers who are bringing methane into their system as well. It's emitted under their control. This goes to show you a similar situation. This is a it's about an 80 plus mile collection system that goes into Washington DC and is treated by DC water. This blue section is the section served by a foul air fan that we were able to measure the emissions from what we did as part of this was to essentially model the known collection system and estimate how much methane it would produce. All of these dead ends here aren't dead ends at all their collection systems upstream from local governments who feed to the system. So we didn't know, but we did estimate how much methane was coming from here. So these are sample data and they're in the presentation. So I encourage you to look at them. The important here, the green concentrations are the measured methane concentrations that we saw at the foul air fan. And what you're seeing is that the concentrations here are 350, 400, as high as 600 parts per million by volume. This is the winter testing. The scales are the same and it doesn't disappear. It's about half as much. And that correlates with some of the temperature things that Oriole was talking about where every 10 degrees C you get about half as much methane and that's proven by these graphs. So these are interesting, but it is how we quantified the mass flux. So if we know how much methane is pulled out of this section of the gravity sewer or the blue one. And we modeled how much methane all of this pipe and this is 60 miles of large diameter sewer. This is five miles that we were ventilating and generated a negative pressure on. And we know how much methane we got here. All of the methane produced in this entire system upstream will only half of the mass that we measured at this foul air fan. Now, what we did in the paper to correlate that or sort of close the mass balance was to assume that all of the rest was imported from these jurisdictional sewers. Now, the other thing that's almost certainly false is that there's no methane emissions anywhere upstream of this foul air fan. That just couldn't be true. So we think that our methodology why it's the best best methodology we could do could be low by a factor of two to two and a half or three. And the idea is to try and develop a better methodology to quantify that. So despite the fact that we have a method and it's bigger than zero. It's still probably low. This is another paper that actually wrote with cardiac Chandran who's done a lot more nitrous oxide work than I have. And it's sort of reconciled it, but our estimate was for the US that 24% of the scope one greenhouse gas emissions are from process nitrous oxide. 13% of 6% are from effluent nitrous oxide and sewer methane is almost half. So I think this is significant. It's a big deal. It's a bigger deal if you're warm climates and it's definitely a bigger deal if you have a lot of force mains or surcharge pipes. How could we solve this. This is a project that we're working on now. If you have a force main coming into a pumping station or your treatment plant. The idea is to intercept it and to put in a siphon. And so the discharge level in the pumping station. The high point here could be it's probably nine meters higher than the water grade. So this isn't a little vacuum. It's a big vacuum. And in order to prime this siphon, you have to pull all the headspace gas out. But at point one atmospheres of absolute pressure, the sewage can't hold any any dissolved gases. 90% of the saturated content in a ideal regime would come out. So we're going to test this and see how well it works. But this could be a solution. The other thing that you might be asking, well, won't this push back on my pumps? They're not designed to pump, you know, nine meters more static head. But it doesn't create that static head. The only energy required on this process is the energy to compress the headspace gas from point one atmospheres of pressure back to atmospheric pressure. And then when you do that, it's a siphon so that the pumps are still pumping against this hydraulic grade, despite the fact that you're lifting the water and extra nine meters. This is our demonstration facility at Miami-Dade, and these are mostly just shown to share that we're making progress. This is the biogas harvester on the top where we expect for the pressures to be like point one to point two atmospheres of absolute pressure. These are the sampling points where we can measure what's in the gas, how effective was the sampling, measure the dissolved methane and other things going in and out. The only problem we've got, the whole thing's assembled, but this is a 54 inch diameter force pane. What is that? That's probably at least a meter and a half, maybe a little more. And this is the venturi that we're trying to tie into. But in order to make this connection, they have to shut down this treatment plant treating 100 mgd. And I don't know what 100 meter mgd is in metric, but it's a big plant that serves most of the sewage from downtown Miami, Florida. So when they make that connection, we'll be able to test this out and see how it works. We have another project and I'm asking for volunteers. And if you're interested, get in touch with me, get in touch with Oriole who's working on this proposal with us and we'll get you included. But what the project would do is to have anybody who can do the work sample dissolved methane in their collection system. There's a method to do this. It does take more sophisticated analytical work. But if you're interested and want to do this, we want to know what the dissolved methane is. That's part of the mass balance. And then the idea is for us to develop two new methodologies. One of them is going to be more area based than the current methodology that we have. And to compare these methods against, again, the Potomac Interceptor data and possibly one other new gravity sewer verification project that would be done at King County, which is Seattle, Washington. Anyway, we'd like to get your output files from your hydraulic sewer models at average conditions for each plant. If we get 10 to 15 utilities, we're hoping to get hydraulic models for 30 to 50 sewer sheds. And what we're then able to do is to use this methodology that we developed to estimate what everybody's sewer methane is within their collection systems. We would then use those data to come up with a really simple methodology that would ask and it could be in local protocols. We could ask what's your temperature on average? How many people do you serve or some other size criteria? The part of this analysis will be should we use population equivalent? Should we use miles of sewer or kilometers of sewer? Or should we use area of sewer shed? Those would all represent size or maybe even total flow. Whatever that is, we should go that way and figure out what it is. And then everybody could include sewer methane in their inventory. This is part of the problem. The folks who are willing to do the hard work and estimate it for their system don't want to say, oh, I've got this twice as much a mission that nobody else is counting. So this would have let everybody and put it into, actually, IKLE is on our team. I know there's an IKLE Europe based in Germany. This is IKLE North America who would include it as part of their protocols. What we're asking for is a $20,000 cash contribution. And this is US dollars. What you get, though, is a detailed analysis and the equation for what each of your plants produce in sewer methane as a function of temperature and flow. You would allow you to contribute and helping us pick the best methodology and reviewing the data. It closes what I think is hands down the biggest gap in everybody's greenhouse gas emissions inventory, which gives you a better picture on what you can affect and what you can solve. And you also help everybody else add it to their sewer methane inventory. So this is a list of everybody on our team. So Keshub is going to be doing some heavy lifting. Oriole is going to be doing some heavy lifting. And we've also included Osborne Hanning Nielsen with Alberg University, who has done the rest of the bulk of the sewer methane research in our industry. So I am excited about pulling this together. If you're interested, please get in touch with me soon. This is my email. You can also text me on my cell phone. So that information is available. And with that, I'll open it for questions. If I have time for questions, Keshub. Yeah. Thanks a lot, John, for a nice informative presentation. We got a lot of questions regarding the sewer methane here. Please check Q&A box. A lot of questions to John and Oriole. Quick one out that's your favorite, Keshub. Oh, there's a question here about mitigating it. So generally, and this is aligned with what Oriole said, if you have a force main or you have sewers that are running full, which happens a lot. So if the pipe is entirely full, there's no oxygen in the headspace. There's no, and your slime layer goes all the way around. So if you could operate your sewer system by pulling down the hydraulic grades and making there be more gravity sewers, you would just produce less methane. And that's certain, but you sort of need to do this modeling and remodel it to quantify how much less methane there was. So there's a question here about the modeling equation. There will be modeling equations. There's is one in my PhD that I shared that you could use today. But there's also a long discussion about how it's probably low by a factor of two. So you could use that. We're hoping to get different equations that will allow you to apply them to a collection system model. There is one question also from asking about measures to reduce emissions from sewers. Definitely there's measures and usually these measures, they involve the dosage of several different chemicals and different approaches. And they have been traditionally first aimed at control the sulfide because sulfide was it creates problems like toxicity, other problems and corrosion. And but in our research, we demonstrated that these compounds that they are currently those that could affect also the metanogens in different degrees and different configurations, but there are definitely options to mitigate this. Yeah. Well, but good. There is a long list of papers and research on that topic. The question from the question from Jihan Lee. Yeah. Do you find differences of gas generation quite quantity of methane depending on the sewer types? Difference of gas generation quantity of methane depending on the sewer types. I don't understand exactly like sewer types. I think the question is whether you produce the same amount of methane from gravity sewers and rising mains or they are different. Okay, that's a tricky question because as I said in gravity sewers and John also highlighted this is gravities are more complex than rising mains and so far we don't have like enough data to have a proper comparison for this. We have been studied and as you to quantify in gravity we still have a lot of work to do on to be able to reply to this question. It does happen, but we don't know exactly the extent and also is that it depends a lot on the on the configuration of the sewer systems. If you have one sewer one sewer network with a lot of rising mains, then might the contribution of rising mains might be more important. But if you have like more gravity sections and the wastewater flows naturally to the wastewater treatment plants, then you would have like less methane production. So it depends a lot of the of the geographical extension and geographical distribution of your systems. Yeah, and we so Keshav and I did some modeling work on the difference and full flowing pipes as opposed to gravity sewers can produce. I mean, big pipes produce three to four times more methane if they're force mains the gravity sewers and small pipes could produce six to eight times more methane. So it really is and when you think about the factors. A lot of it is the area of the slimes, but a lot of it is that there's no oxygen transfer right you're not bringing oxygen into the sewage, which could inhibit it to some degree. Oh, so one of the one other thing that we wanted to check is if we do do those 30 to 50 sewer sheds. The other factor that I think goes into that is what do you think the percent of surcharged or force mains are compared to the total sewer network. So when we did DC water, it's like 5% are surcharged or force mains. And what this would do is give us default numbers. If we looked at 30 sewer sheds, then we could say, Oh, well, the default is 10% if you don't have any idea. But if you do have an idea, use your better estimate. And there are places, especially like in Florida where all the sewers are flat and all the ground is sand and full of water, where they're completely full all the time. I mean, I think Miami-Dade's collection system is probably 95% force mains, not force mains, but full flowing pipes. So depending on where it is, that's, you know, that's the last factor. So it does matter. Now I know I just went way over Keshav. So I'll be quiet. Yeah. Thank you. There was a question regarding whether we can develop some equation, you know, taking a break on the factors like temperature and others. I think your ability answered this question. We definitely have a temperature and by the way, the guy who developed the equations is Keshav. So there you go. Okay. So we got definitely have a lot of equations there to estimate methane emission from sewers under different conditions. So I'll start. I think I'll go to the top and see what questions remains to be answered. The one we have got is do you have any fugitive emissions results information for membrane type BUU. I know the best possible answer this question. Any volunteers? I did some measurements on membrane BUU by I guess upgrading units, but unfortunately I cannot share data yet because they have to be compiled first. I cannot share specific data from specific utility. And so these will be compiled into one or two years, I think, for no numbers. Sorry. Thank you. Another question. What concentration of methane is generally required to so that it is, it uses feasible. So does anyone has got any answer to this? I don't have an exact answer. But the gas that the units that produce from, I think about if you could use gas to burn it if you get quite low, it's just a matter of putting your equipment right, so to speak, sorry about my English. So you could burn quite low, low gas quality. Thank you again. Okay, the higher every gives higher production of methane that's I think a lot of answer that question. Right. Yeah. Yeah. What could be the best technologies for delivering our onsite disposal system and wastewater? I'm not sure if this is this question is related to the topic today. And I don't think there's a, there's a one answer to this question as well. It would depend upon the individual situations. Okay, the other question here about source, any recommendation on how sewer system should be designed to mitigate methane and S2S production to capture it so it can be mitigated. Yeah. Good one. Well, the problem is that most of the sewers they're already there, like we, we have to work with what's on the other ground and it's sometimes it's difficult to to implement things. So with the new sewer systems, we could incorporate sections like exact exactly like John mentioned in the project solutions where the cyclones would able to get this biogas outside and it will be for it goes. And in effect, so it gets released into the atmosphere but that's for new construction and things need to be considered upfront and plan with enough time to apply it for the rest of the sewers that it's being there it's, it's quite limited limited leverage of places to work. Yeah. One of the ways. I was just to second it. I mean I do like the idea of this biogas harvester idea and the vacuum depressurization to collect the gas. One of the challenges will be if you do collect that gas, what do you do with it. And we don't know yet because we haven't pilot tested it, but our impression is we can collect a lot of methane. But what we're also going to collect is tons of carbon dioxide carbon dioxide is so much more soluble and if it turns out I'm going to get 90% of all the dissolved gas. My gas could be 75% carbon dioxide, and it might only be 10% methane. And that's the case I can't burn it. So maybe I want to be next to my plant with my digesters when I get that gas. And then I could burn it with the digester gas. And then it all becomes CO2, which is good as we could do with it. But the other thing that I think about that, and this gets to where are we going to be doing in 50 years or 30 years. So I think that device, if you put it between your aeration basins and your clarifiers allows us to extract biogenic CO2, put it back into spent oil fields for less energy than any other way to get CO2. It would be a lot easier than pulling it out of the atmosphere. So, you know, one of the things I think resource recovery facilities are going to be doing is sequestering biogenic CO2. Now, it's not a priority like reducing our methane emissions, which is worth a lot more today. But I think those kinds of systems could be used to get us there. Thank you. Evelyn, there's one question to you. Very last question. Can you please have a look? Second last question. Very interesting. How does methane mitigation affect N2O mitigation? I would say they are not that much connected, because we see that main methane sources are all related to the digestion and mainly to the storage, anaerobic conditions, whereas N2O production is related to denunification and denunification, so not anaerobic conditions, but aerobic and anoxic conditions. So in that sense, we're lucky. Well, lucky in the sense that at least doing something for one doesn't harm the other. We could think further, maybe we would find some connections anyway, but at least they do not negatively interfere at first sight. That's what I would say. Yes, please, John. While and on there Evelyn, we did measure, so the protocols say assume 1% of your produced biogas methane is released to the atmosphere. And yet all the digesters were designed today are fixed cover, they've got alarms on the relief valves that, you know, it doesn't emit gas. But where almost all of that gas is emitted is when you do water the biosolids. Yes, that's what they show. And I think that's great, but we've got to do something about that. So if we can recover that, that's something you could do today. An obvious one, it was also asked in the Q&A, I answered it in a written way. We saw in detail in the plant that I showed most of the emissions from anaerobic treatment were related to the dewatered sponge storage. If you could cover that, and that's too diluted to burn directly, but you could you but still a relatively low flow rate. So you could send it to the biogas engine, use it as combustion air, and in that sense get rid of part of it. Yes, definitely. That's a low hanging fruit indeed. We should do that. We should do the things that are easy, right? Yes, and that bring a lot of gain and not so much extra cost probably. Of course, yeah, depends how far your biogas engine is from the dewatered sponge storage. Is it already covered as well? There's a question in relation to post digestion stories. The second last question again, if anyone can answer that. In post digestion storage, is there an influence of mixing the tank or not mixing it? Well, mixing for sure will create more gas-liquid transfer and probably does not bring in a lot of oxygen. If you would have oxygen, you would prevent the methane formation will not be sufficient for that. It will be sufficient to strip the dissolved methane. So it's not a good thing. Also, what we've seen that in some digester, that was the state storage tanks, you have a crust. And if there's a crust formation, this is also advantages because it counteracts the stripping. And I would encourage anybody who is odor controlling their digested biostallid storage tank to make it a digester gas atmosphere and collect the methane off the tank. Don't add air to it, right? Make it another digester. Yeah. Okay, we didn't have much time left now. Last question, John, there's one question on sewer. The second last question again. Can you please have a look? Yeah, so I think the off-gassing from force mains is, I think that solution that I presented is a good one. The vacuum harvester, and I expect that that's going to work just fine on almost any force main. The other thing about that is if it turns out that I remove 80 to 90% of the dissolved gases, there's a really good chance I'm not going to have odor problems from sulfide in my head works. Which wouldn't that be a great thing? Or maybe that my head works equipment will last longer than 10 years. So, you know, I think there are coincidental benefits for some of these things. And I think we're going to do it. And the neat thing is it's not a widget you buy, it's pipe. And we're trying this first one. I think we have to stop here now. We're running out of time. Okay. Okay. So now a few announcement before we wrap up this webinar. Old Water Congress 11 to 15 September 2020 in Denmark, Copenhagen registration is now open and early bird registry discount ends on 30th of June. So please register before 30th of June to take advantage of the discount. And also for this we got another announcement. This seminar, this webinar was part of the masterclass series organized by IWA climate smart utilities initiatives that were taught in this series. And the last webinar of the masterclass series will be organized in few months time. That will be mostly on mitigation of greenhouse gas emission from urban water systems. That will be held before the World Water Congress, but to the date has not been finalized. Please keep an eye on the announcement. Okay. With this, I think we have come to the end of this webinar. I would like to thank all the presenters or the participants for the lively discussions presented very good presentations here. I would like to thank IWA team to allow us to take this opportunity to talk about the greenhouse gas, especially methane emission from urban water system. And also would like to thank all the supporting team from IWA. Okay, wherever you are. Good morning. Good afternoon. Good night. It's by from all the panel members from this webinar series. Thank you.