Anaerobic Digestion - Science topic

Ammonia (NH₃) is generated because of nitrogen in the feces and urine of pigs and cattle and the uric acid of poultry manure. Ammonia forms from the biological and chemical breakdown of manure protein, uric acid, and urea during manure storage and decomposition. Ammonia Recovery is an award-winning, low-cost, environmentally responsible method of recovering nitrogen, in the form of ammonia, from various dilute waste streams and converting it into concentrated ammonium sulfate. The most effective method for reducing ammonia emissions from manure application sites is to incorporate that manure into soil as quickly as possible. This drastically reduces volatilization losses resulting from exposure to air. Treating common ammonia odors in the home landscape may be done by the addition of carbon or simply applying liberal amounts of water to leach the soil and a lime treatment to increase the soil pH. Excessive ammonia discharged to receiving waters can cause serious ecological problems, such as eutrophication resulting in the depletion of dissolved oxygen, and excessive algal growth. Substantial concentrations of ammonia in wastewater can also cause toxicity to fish and wildlife.

Thank you all. I have gathered enough to choose from.

Warm regards,

C. Ugochukwu

There are several mathematical algorithms that can be used to estimate the flow of influent and effluent for anaerobic digestion and struvite precipitation processes. Some commonly used methods include mass balance equations, dynamic modeling, and process simulation.

One way to estimate the flow of influent and effluent for anaerobic digestion is to use mass balance equations. This involves determining the amount of organic matter entering and leaving the system, as well as the amount of biogas produced. This can be done by measuring the chemical oxygen demand (COD) or total solids (TS) of the influent and effluent, and using those values to calculate the mass balance.

Another approach is to use dynamic modeling, which involves creating a mathematical model of the system that can predict the behavior of the process over time. This can be done using software such as Aspen Plus or SuperPro Designer, which can simulate the process and predict the flow of influent and effluent.

Simulation is also another approach that can be used to estimate the flow of influent and effluent. This method involves creating a computer model of the system that can simulate the process and predict the flow of influent and effluent. This can be done using software such as MATLAB or Simulink, which can simulate the process and predict the flow of influent and effluent.

Ultimately, the specific algorithm or method that is chosen will depend on the available data, the specific requirements of the system, and the level of accuracy and precision desired.

The amount of magnesium, ammonium and phosphate in coffee waste digestate will vary depending on the specific source of the waste and the treatment process used. Factors such as the type of coffee beans used, the brewing method, and the type of wastewater treatment applied can all affect the concentration of these elements in the digestate.

In general, coffee waste digestate is known to have high levels of nutrients, such as nitrogen, phosphorus, and potassium, which are essential for plant growth. However, it's difficult to give a general amount of magnesium, ammonium and phosphate in the coffee waste digestate, as it can vary greatly depending on the specific source and treatment process.

It's important to conduct a chemical analysis of the coffee waste digestate to determine the exact concentrations of magnesium, ammonium, and phosphate. This can be done by a laboratory using methods such as inductively coupled plasma-optical emission spectroscopy (ICP-OES) or ion chromatography (IC). The results of the analysis will give you more information about the quantity of each element in the digestate and also how to use it as a fertilizer.

It is also important to note that the coffee waste digestate may contain other contaminants such as heavy metals, caffeine, and organic compounds, which should also be analyzed to determine their concentration and potential risks.

Magnesium oxide (MgO) is commonly used to control the pH and promote struvite precipitation in wastewater treatment systems. The amount of MgO needed to be added to a struvite precipitation reactor can be calculated using the following formula:

MgO (g) = (mg/L of Mg) x (volume of wastewater (L)) / 40

Where mg/L of Mg is the concentration of magnesium ions in the wastewater and 40 is the molecular weight of MgO.

For example, if the magnesium concentration in the wastewater is 10 mg/L and the reactor volume is 1000 L, the amount of MgO needed to be added to the reactor would be:

MgO (g) = (10 mg/L) x (1000 L) / 40 = 250 g

It's important to note that the amount of MgO needed to be added will also depend on the pH of the wastewater and the desired pH for struvite precipitation. In general, a pH range of 8.5 - 9.5 is optimal for struvite precipitation, so the pH of the wastewater should be adjusted to this range before adding the MgO.

Dear Adam,

Very good question. In theory, if the processes are realized in certain conditions: liquid media, anaerobiosis, high nitrogen and Phosphorus concentration and rather warm environment, the processes (Water treatment and manure or other organic waste treatment) should result in struvite precipitation.

This would discard, for example, composting, as temperature is lower and there is no liquid phase.

If I get more specific info, I will let you know.

Cheers

Hi, Sabarish Ravi

Designing a digester for AD, irrespective of the substrate, requires many things to be done prior. They are,

1. Digester/reactor size: Dependent on what scale the experimental design and substrate are to be addressed.

2. Substrate concentration: Decided by the strength of the substrate.

3. Substrate/Inoculum ratio: Generally, various ratios are experimented with, and the ideal one is finalised.

4. Co-digestate ratio: Based on the waste composition and type.

5. Reactor type: Equipment availability. Established laboratory facilities go for high-end reactor facilities, whereas the others go for traditional and basic reactors.

6. Analysis: Pre, during, and post-experiment analysis we are going to be done gives a clear idea about the requirements for the experiment and the work to be carried over.

From the question, it is clear that the substrate is organic and wet, so AD is the best approach. However, AD can be done with many techniques, which a clear idea for the process to be known well ahead.

I hope this answer helps.

Thanks!

Dear Rawan,

By "two-phase system", did you mean feeding a photo-bioreactor with the enriched CO2, and then using the yielded microalgal biomass to produce biogas?

You can add hot water with feed.

BITECO BIOGAS - Calculator Main (biteco-energy.com)

Gede Adi Wiguna Sudiartha

I agree with Abhijeet Singh and would like to add that the SOUR (specific oxygen uptake rate) represent the aerobic microbial activites. For anoxic and anaerobic microbial activities similar parameters can be defined and used.

You need to know the discharge as liter per day, then you can divide the number by the discharge to convert to g per liter.

Hello,

This paper may helps!

TAN (total ammoniacal nitrogen) refers to 'nitrogen' in ammoniacal form. The parameter being reported is nitrogen and hence the multiplying factor is 14. One way to remember it is: imagine someone is determining Organic Nitrogen or Total Kjeldahl Nitrogen in a wastewater sample. Which organic compound would he/she choose to decide the multiplying factor?

Nitrate reducing under anaerobic conditions where some bacteria utlilize Nitrate instead of Oxygen as terminal electrone acceptor is termed dissimilatory. Nitrate-reducing bacteria are mostly heterotrophic and often facultative anaerobic, with the ability to switch between oxygen and nitrate respiration depending on the environmental conditions.According to the electron acceptor, both oxygen and nitrate could be electron acceptor for the respiration for microorganisms in activated sludge. The oxygen is preferred over the nitrate because of its higher redox potential and more energy produced in respiration. an excessive increase in nitrate concentration (>10 mg l−1 NO3−-N) in the environment leads to nitrate pollution which has become a global environmental problem.Generally, the number of nitrate-reducing bacteria in deep crystalline bedrock groundwater have been predicted to be low, based on studies focusing on detection of essential genes (e.g., nitrate reductase, narG) for denitrification in deep crystalline bedrock environments . Nevertheless, these bacteria, otherwise below the detection limit, have been shown to significantly increase the transcription of narG genes in response to increased concentration of methane together with sulfate under N2 atmosphere in deep groundwater . In addition, it has been shown that certain ε-proteobacterial lineages couple reduction of nitrate to simultaneous oxidation of sulfide. Sulfur: Sulfur cycling, which is primarily driven by hydrogen sulfide and other reduced sulfur compounds serving as electron donors for sulfur-oxidizing microorganisms, is tightly interwoven with other important element cycles (carbon, nitrogen, iron, manganese) (Wasmund et al., 2017). Alternatively, sulfur (e.g., sulfate) can also act as a terminal electron acceptor, once more energetically favorable electron acceptors such as oxygen, nitrate/nitrite, and iron and manganese oxides are depleted.

Nitrates and nitrites are ubiquitous in the environment and commonly found in human diets. Nitrates are widely used as fertilizers in agriculture, resulting in high levels of nitrate accumulation in a variety of vegetables. Vegetables are the primary source of exposure to ingested nitrates, comprising nearly 80% of the total nitrate intake in a typical human diet.1 In contrast to nitrates.

Some microbes are capable of using nitrate as their terminal electron accepter. The ETS used is somewhat similar to aerobic respiration, but the terminal electron transport protein donates its electrons to nitrate instead of oxygen. Nitrate reduction in some species (the best studied being E. coli) is a two electron transfer where nitrate is reduced to nitrite. Electrons flow through the quinone pool and the cytochrome b/c1 complex and then nitrate reductase resulting in the transport of protons across the membrane as discussed earlier for aerobic respiration.

N03- + 2e- + 2H+N02-+ H20

This reaction is not particularly efficient. Nitrate does not as willingly accept electrons when compared to oxygen and the potential energy gain from reducing nitrate is less. If microbes have a choice, they will use oxygen instead of nitrate, but in environments where oxygen is limiting and nitrate is plentiful, nitrate reduction takes place.

While both are sources of acetate, which is readily digestible by methanogens, I think the difference in performance you're seeing could be due to the higher pH resulting from sodium, which increased the free ammonia levels that inhibit methanogens growth, especially aceticlastic methanogens. Some studies also suggest that high free sodium ions can cause inhibition of microbial growth.

Hope that helps!

Dear Sajjad Haghayegh,

A bottle of hydrogen gas is used which is connected to the digester. Between the two, we insert a mass flow controller followed by a gas pump. Indeed, a circulation pump with a subsequent venturi nozzle distributes the introduced hydrolyzate and the injected H₂. Hydrogen inflow is regulated by a mass flow controller. The produced biogas and injected hydrogen are recirculated via a gas pump.

Please refer to Figure 1 in the attached paper.

Regards

Please refer to the following link.

Regards

Hi, everyone, you should define them as pseudo components. then in the specification tab please insert MW, NBP, and density according to the file which I attached here.

Check out my articles, you might benefit from them

Fatihah Suja when you are talking about TS and VS improvements in the anaerobic digestion or in other words i can sum it up as What can you do to speed up anaerobic digestion and this is one and the same thing and we can surely get it by mixing Because mixing liquid manures with drier feedstock materials can raise the TS content of the digester feedstock, farmers must keep adequate moisture in the feedstock to keep anaerobic activity going, as well as evaluate the type of anaerobic digester they're using and how much TS it can tolerate.

Hafiz Adeel Ahmad most of the experts have explained in detail about the organic loading rate but when actual based on the figures I keep my designs of the digesters ranging between 2.5 - 3.1 and below these figures the digesters are not economical though the working is better but financially the projects are not feasible and when we consider above 3 then the monitoring and supervision would be on continuous 24*7 basis

The following RG link is also very good:

Depends on the size of the agitator and the digester I can help you at different sizes feel free to contact +91 8317585217 (whatsapp)

You can use in this case the C₁V₁ = C₂V₂ equation. Let's assume you have 100 mL sample with a TS concentration of 40%, if you want to achieve 7%, then the volume of your final "solution" has to be ~ 571.43 mL (meaning, you have to add 471.43 mL DW to your stock sample).

Many fungi produce acids but they are not normally a problem in anaerobic digesters specially if there is enough alkalinity available. Often fungal enzymes are more aggressive than many bacterial enzymes and may enhance the first step of methanogenesis (hydrolysis of macro molecules which is the slowest step.. AKA rate determining step)...so they can help instead of inhibit. However,

If pH drops below 7 for any reason (bacterial or fungal) the lower pH causes methanogens to be inhibited or die. If there is a very high increase of bacteria or fungi added suddenly, the hydrolysis step may increase too fast not allowing the next step of methanogenesis to catch up and to metabolize the organic acids produced in the hydrolysis step causing drop in pH.

The flow diagram

Cds and Zns

1. hydrogen and methane, both can't be produced together

2. methane is not formed by bacteria

3. isolation is just used for identification and characterization. From an application point of view, isolation is not at all required. Also, one can't isolate something unless they know what to isolate. Anaerobic digestion is a community job and not done by one or few microbes.

4. to get a basic understanding of AD please have a look at this

This is a good question. Are there any peer reviewed papers that prove biochar improves AD in low C/N reactors, and what are the dosages used? I struggle to find clear numbers that prove such effect. At the same time, if there are such studies, are they carried out against robust controls and comparing with other alternatives? such as zeolites, etc,? I have tried biochar for ammonia adsorption and got no significant effect at all. I am honestly interested in finding what needs to be done to get a result. With biogas production did not get any effect at all. It is wrong to suggest biochar is readily available carbon when it is otherwise being offered as a way to fix carbon in soils ;)

Arthur Ribeiro Torrecilhas many are doing the same researches which have been done and optimising the same at the economic options and yes developing and working on the microbial development and robust systems are what everyone is eyeing on right now

Saba Gholizadeh There are many factors d on which the cost part depends right from the size of the plant, feedstock on daily basis, environment, end use of gas etc etc and to give you an example do we need based on the feedstock capacity or the digester volume.

Suppose we assume 100 cows and they produce approximately 10 kgs of cowdung per head which means the total cowdung available for gas generation is 1000 kgs and this typically has around 12-16% solids so assuming 1:1 water/recircualte/slurry we can go ahead with 2m3 * 25 days + gas volume digester design and this might roughly cost you approximately INR 4-7 lacs for the digester and other equipment and accessories separate.

Interesting question though we all know the answer but it would be tough to put it in words and yes even I would be waiting for the answer to this question

Dear Jack Rizvi ,

Hope you are doing great. I have been studying on the anaerobic digestion process and bio-digester for a couple of years; The most detailed model to estimate the amount of biogas is the ADM1 model without a shadow of a doubt, but if you do not need the exact amount of the produced biogas you won't need this model since it is quite complicated and requires detailed information that might not be found much easily. Besides the ADM1 model, the most accurate results would be obtained by conducting an experiment and measuring the amount of the produced biogas, afterwards you could measure the calorific value of the biogas yield.

Raegards

Hi guys. This is a great topic to discuss, in that way, to answer this question, I suggest reading the following articles:

and...

Let me know if they were helpful to you folks doing a recommendation and citation of them.

Best Regards.

Biogas recovery for sustainable ciities the critical review shared by Mariana Cardoso Chrispim is really good and am sure that might be of some help to you Dr Mohammad Javad Bardi and yes as I said it depends on personal basis and have loads of 20+ years of exp and yes I can share on individual basis whenever we can and would like to exchange ideas

+91 8317585217 (whatsapp)

Awais Aqib you have to consider the total solids content along with the organic dry matter

or dry matter and organic dry matter and based on the OLR of the digester just add water and homogenize it with water and ensure proper slurry is made and then feed it to the digester based on the design.

One can ensure that after feeding for 20-25 days without disturbing it the gas generation can be seen and further one can take the next course of action based on the feedstock the digester is designed for

if this is designed for animal manure then start feeding slowly and gradually increase the amount to the designed capacity

It is quite well known that the presence of sulfates is inhibitory to methanogenesis. The main reasons for this inhibitory effect are (i) microbial reduction of sulfate produces sulfide or free H2S, and (ii) sulfate-reducing bacteria (SRB) compete with methanogens for electron donors (Shende and Pophali, 2020). In your case, it is likely that the sulfate reducing bacteria have outcompeted the methanogens and are producing more H2S in a full-scale reactor. Generally, the inhibitory effect of sulfate on methane-producing bacteria is 1200 mg/L sulfate.

Hope it helps.

Tutorial is shared here in this link

As mentioned earlier depends on many factors but 15-30 days

Aldyon Azkarahman there are various ways one can check it either with the readily available pH paper testing paper or the pH meter or the sensors/probes which are available can be installed where the slurry comes in contact with the probe and online readings can be seen on the meters or the can also be connected to the the panels/plc

Yes it does and also depends on the technology where I always suggest if the waste has less than 4-5% Total solid content then always one should select UASB or modified version of UASB

William Anam you qeustion answerd by the expert Jim C Philp and Steven L Larson i do agree with them and their comments as ATCC is the source for a wide range of methanogens and I do use the same in my experiments.

However sometimes I do take from the running commercial plants and on an average it depends on the size of the plant and the feed material and we do innoculate from the same plant on weekly basis for better experiments

William Anam nice question and i do agree with Kien Vu and there are standard testing parameters available with many laboratories

Kien Vu has already suggested the link and i do agree with him

Afnan Yasar yes it is quite possible and can be done easily

Thank you Sumathi Malairajan and Angel Luengos.

Dear Kasra,

The most important chemical parameter for an optimal AD process is the C/N ratio of the substrate, which must be in the range of 15-30. So, before calculating the quantities of materials you need to know the C/N and the humidity of each. The share of each material in the mixture will be decided so that C/N of the substrate be 15-30, then the mixture should be diluted with water (or with a slightly alkaline solution, if the mixture is acidic) to have a total solids content of 8-10% and a pH of 7-7.5. As far as I know, sewage sludge is a nitrogen-rich material (C/N <10), therefore, I think that a share of 90% sewage sludge according to your recipe could be too much, as only 10% of food waste cannot rise C/N enough. Also, many types of food waste (animal waste and wastewaters) are rich in nitrogen. In any case, at first C, N and humidity must be determined for each material. Regards.

Better to check this

Here you can find the cap assembly we use.

I suggest, try to fed settled residue (centrifuged) of the total volume of the feed sludge and discard the supernatant. This wii help to maintain the HRT without the impact of feed shock.

Thank you Sadib Bin Kabir for sharing the file and also thank you Ahmed Alengebawy for this interesting question

Yes possible but depends on the drying technique.... Thermal drying is the answer

There are many pre treatments available and particularly it depends on the feedstock/ rawmaterial and local conditions too. There are many factors depends on selection criterion and one has to do some feasibility study before getting or selecting the best that suits a particular feed stock.

Yes you can

As it is well explained by other researchers that any treatment plant is designed on the input parameters of influent and the desired output parameters / results.

Operating cost of an aerobic plant is always higher than an anaerobic one.

Why you want to add a 03rd anaerobic / aerobic digester when you already have 02 anaerobic digesters? Instead you should focus on the treatment efficiency of these digesters and do any rectification (if required).

I recommend you to check out agent-based modeling -- ABM -- it gives much better expressivity in the interaction of different bacterial species and their spatiotemporal dynamics.

This approach is routinely used in ecosystems, societies, markets, immune systems, pedestrian behavior, military combat, and similar areas.

PDEs are not so flexible in describing fine spatiotemporal disturbances and one to one interactions. They work with averages, which are not so suitable to describe fine, strictly local bacterial interactions.

Of course, you should add microorganisms to your reactor due to the dynamics of anaerobic processes. You feed the waste to the digesters such as rice husks, rice straws, rice bran as SUBSTRATES and actually they're the food for your microorganisms. You have your microorganisms in your SEED SLUDGE (you can call it also 'inoculum'). You can determine the amount of seed sludge you put to your reactors from the literature.

The lower heating value for pure methane is 35.8 MJ/m3. Note that it is per normal cubic metre (1 m3 at 0 C and 1 atm.).

The lower heating value of 100 ml CH4 at 0 C and 1 atmosphere equals 3.58 kJ.

If the temperature and pressure differ you can use the ideal gas law PV=nRT to calculate which volume it corresponds to at 0 C and 1 atm.

Dear Soufia, its a nice and interesting question you asked.

Please go through this article & DOI link for a broader knowledge.

"Bacterial growth kinetics: measurement and significance in the activated-sludge process"

Author links open overlay panelG.L.JonesShow morehttps://doi.org/10.1016/0043-1354(73)90120-6

Best Regards,

Md Osim Aquatar,

AcSIR,CSIR-NEERI,INDIA

Thanks @Giovana

Have you read the handbook I provided you in your last question? Please stop asking such questions if you don't understand the basics of anaerobic digestion and first focus on the handbook. Read it thoroughly and try to understand. Everything is written in a very easy and descriptive manner.

I know that faeces contains such microb, but addition of cow dung will facilitate the production of methane.

Knowing the daly biogas volume production and CH4% and CO2 % mean values.On using CH4 and CO2 densities, you can then calculate the digested mass by adding m(CH4) and m(CO2) : which are the main biogas content.

agree with Mustafa Vohra

Good afternoon and apologies but I had not seen this conversation.

Regarding Lea's cons we think they do not detract from the data quality and overall ease of use of the machines and, yes we are always working on upgrades that do not leave behind our previous customers. That is our commitment:

1. Program not user friendly. We have had an issue with the commas in the csv data files which temporarily we address adding a suitable laptop to ensure this is no difficulty to using the machines seamlessly. We did learn from our experience in Ireland. Also, we learn to make the modifications in Excel on comma and colon delimiters. As well as that, we are developing a totally new software that will take care of that, and will be free download.

2. Ease of cleaning. This really is a matter of getting used to and having some simple cheap tools, such as a toilet brush and ....that's it. I have just prepared 4 complete sets (60 reactors) and it does take time, because of the quantity, but the wide mouths make it very easy to clean well inside. You are correct, the bottles can be autoclaved, and also apart from not breaking easily are standard bottles you can buy directly from scientific suppliers such as VWR. This was our intention from design: to ensure durability, avoid damage and have something that can be replaced easily in the worst case. Regarding the staining, this is one thing we can not eliminate. We have thought about using gas bottles, and might use them at some point in the future; but hand in heart, the benefit in the context of a BMP test of seeing through in a dark liquid submerged in a water bath is limited. I get shaky hands every now and then and knowing I can't break those bottles even if I dropped them, especially when preparing lots, reassures me. Our biggest client now have 26 Nautilus machines in one single lab and they work them non stop. To address Lea's comment we are actually developing at this very moment something we call: AD Survival Pack. It contains those little things that make using any BMP machine extremely easy and efficient. You are right Lea, sometimes even not having a right size beaker, or a suitable spatula can mess slow us down. The pack will include, precisely even some buckets we have found ideal for the clean up process, and we are also making hose disconnections much easier.

3- Manual calibration of gas flow meter. On this one I will be a little defensive, but it is for a good, honest reason. We tested several designs of gas flow meter by our own means and found, reasonably, that even if a cell has a "calibrated value" this is not consistent and it really is not possible to guarantee all cells in a 15 cell gas flow meter will be exactly the same volume. Because we believe that the integrity of data is paramount in research we provide the ability to manually calibrate the cells and for the user to see directly what their machines is actually measuring. We are developing new methods of fabrication that should reduce the need to do calibrations and keep them closer. But, please do not feel bad, calibrating is painful but so important for us all to trust data.

On this point, please keep this in mind, today 16 July 2020, I tell all our existing clients, you will hear good news from us next year for you. I can not disclose this at the moment, but we are not in the business of gimmicks, it will be to the benefit of all. Be sure we work with all of you, because we need funds to survive, but money is not what drives us really, we love research :)

Vincent, as soon as conditions allow and it is convenient to you, we will visit you.

Thank you for your comments, they are not ignored and in fact, even though I just saw them now, I can tell you we have been working on all these fronts. However, the machines do the job, and do it consistently for many years.

Take care

There are (basically) two categories of anaerobic metabolism: (1) fermentation and (2) oxidative phosphorylation that does not use oxygen to make ATP. However, many people are incorrectly taught that fermentation is the only type of anaerobic metabolism. So, when folks say "anaerobic organisms do not have the TCA cycle" what they really mean is "fermentative organisms do not have the TCA cycle". In contrast, it is quite common for non-fermentative anaerobic organisms to use the TCA cycle, such as sulfate reducers, nitrate reducers, iron reducers, etc.

From a more generalized viewpoint, the promising kinds of feedstock for renewable fuels should:

Thank you for your answer! Meanwhile, I have also tried to use a pitched blade agitator and it is doing the work (the total suspension volume is only around 7 L). It can even easily resuspend sedimented starch, in case the stirring is not active all the time.

Following

you can check my article, it was about liquid phase using ADM1.

Good luck

+1 Edwin Zea Escamilla .

Victor Hugo Argentino de Morais Vieira you have yourself included the answer to your question in the end. Here is my take on your points:

- Calculation (not modelling) in excel is possible but has its own limitations. With the help of characterization factors you can at the most calculate carbon and energy footprints but not other impacts. Plus it will not be possible to create all the background processes in excel as mentioned by Edwin.

- You can write to the SimaPro distributor in Brazil who can make the academic version available to you free of cost.

- Yes, excel is easy but would you want the policy makers to see the results and your recommendations or give them the excel to understand ?!

- Unit based (not system based) processes in SimaPro are extremely transparent and you can see every input and output of all the background processes. You can copy and create your own processes if the local inputs are different. I would not be worried about the code and simulations as long as I have all the inventories of background processes in front of me.

- Finally your last point is the key.....Yes it will not be technically accurate to conduct LCA in excel as your results will give the incomplete and biased picture. Plus it will be difficult for you to answer all the queries in case you go for ISO /third party review of your report.

Since you want to conduct it for policy makers, I would suggest to go for a complete and technically correct LCA as per the ISO guideline. All the best!

The Italian norm on BMP test (UNI/TS 11703:2018) states that the inoculum/substrate ratio must be comprised between 2 and 3 for general biomass digestion (i.e. 0.5 to 0.33 if you define as substrate/inoculum). Nevertheless, it also states that some substrates (glycerol, fats, industrial effluents containing inhibitors like olive mill wastewater, etc.) may require teh test to be performmed with I/S >= 5. This must be established by the lab operator and stated in the report of the test. For a discussion on the pros and cons of the Italian , German and IWA draft on BMP assay, please see chapter 6 of my book https://www.crcpress.com/Managing-Biogas-Plants-A-Practical-Guide/Rosato/p/book/9781138626614

Well , I don't think u can loose any of ur reactors in as much as all the operational conditions are in order e.g maintaining ur operating temperature, constant agitation and ur digesters are air tight. Once there is a control, duplicates may not be necessary.

Anaerobic digestion

You (can) measure how much feed you put into your reactor in terms of VS and COD. You (can) also measure how much methane you produce.

Thus you can calculate / know how much methane you produce per gVS or per g COD.

We know that 1 gram of COD can theoretically produce 350 mL methane (or to put it differently: the COD of methane is 64 gram oxygen per mol of methane, which is 22.4 L at standard temperature and pressure). Using this value you can calculate the efficiency with which the COD in the feed is converted into methane.

I am not sure what you are feeding your reactors, but if you additionally measure the concentration of volatile fatty acids (VFAs) in your reactors you can additionally calculate the fraction of the feed that is degraded/converted into VFAs (make sure that you take the VFAs in the feed into account when you do this). Using the theoretical COD of VFAs, you can now additionally calculate the fraction of COD in the feed that is hydrolysed (remember to also take methane into account in this calculation). Indeed, adding the COD of the VFAs formed and the COD of the methane formed, you can calculate the efficiency with which the COD in the substrate is degraded.

And by comparing the methane formed in the system with the methane formed in the BMP tests you evaluate how efficient your continuous system is in terms of methane recovery.

Doing all this you should be aware that some of the methane will leave your system via the water phase, so you should take this methane (production) also into account.

It goes without saying that all measurements and subsequent calculations are ultimately expressed per reactor and day; (feed in on a daily basis, methane and VFAs out on a daily basis).

Hope this helps.

Zhenming Zhou, Qingxiang Meng, Zhongtang Yu. 2011. Effects of Methanogenic Inhibitors on Methane Production and Abundances of Methanogens and Cellulolytic Bacteria in In Vitro Ruminal Cultures. Applied and Environmental Microbiology, 77 (8) 2634-2639

A.S.K. Chan, T.B. Parkin. 2000. Evaluation of potential inhibitors of methanogenesis and methane oxidation in a landfill cover soil. Soil Biology and Biochemistry. 32 (11–12) 1581-1590

Kari Wolff, I am not familiar with your experimental setup (T, P, feed/biogas compositions, or process set up) or what you are trying to achieve/investigate. If you are looking for a research collaboration, there seem to be some interesting questions in this space.