I suggest you to use anaerobic treatment for the wastewater having biodegradable COD higher than 2000 mg/l.

Thank you Erkan. Been looking for recommended COD values from literatures but what I found are only descriptives and no specific values. I am actually doing batch anaerobic digestion of blackwater with high strength domestic wastewater as co-substrate and found that my methane yield appeared to be lower than when digesting with blackwater alone. One reason could be dilution or some inhibitions....

By the way, if you don't mind, are there any literatures that I can site for the COD recommendation? thank you.

Dear Ana,

The decreased methane yield may be due to the deficiency of some nutrients or methals like Fe or Co.

As for the reference for the COD concentration suitable for anaerobic treatment, you may use Metcalf and Eddy(2004). On the page 987 under the title of "Organic Concentration and Temperature" it is written that "Generally, COD concentration greater than 1500 to 2000 mg/L are needed to produce sufficent quentities of methane to heat the wastewater without an external fuel source. At 1300 mg/L COD or less, aerobic treatment may be the preffered selection".

I hope this will be helpful.

erkan

The COD is really not important parameter from anaerobic digestion efficiency point of view. The parameters like organic dry matter, N-NH4 content, C:N ratio, HM content play much more important role.

Btw. - the COD value for slurry (main substrate in agricultural biogas plants) is usually over 15000 mg/l.

Hi Jacek,

You may be correct. Of course, other parameters should be controlled as well. However, a minimum COD is also required at least to produce enough methane to heat the reactor. The COD value of dilute domestic wastewaters (300-500 mg/L) may be lower than the required minimum COD level. So the feasibility of the process is becoming more important than the process efficiency when you talk about the minimum COD requirement. But process efficiency seems to be more important for high COD contents as the process is, of course, become feasible.

If you utilize high rate reactor as UASB a daily rate of of 5 to 10 kg COD/m3 is possible.

Depends on your objective. If you main goal is to recover biogas from the wastewater, the high concentration from 1,000-50,000 mg/L or even higher will be OK. Considering solubility of methane in water (20-30 mg/L), a low concentration is not good for methane recovery. If you focus only on COD removal, low concentration even < 100 mg/L would be OK.

There is work being done right now on the concept of treating domestic strength dilute wastewater (COD as low as say 500 mg/l) anaerobically, with minimal-to-no heating (basically ambient temperature). Dr. Perry McCarty is one I know of (given Weimin Wu's answer and location I would not be surprised if they are working on just this) and there are others I'm sure. To me this is a promising potential future application to energy efficient wastewater treatment, and one I am watching for possible experimentation and maybe pilot scale work here.

Recommended range given current "mainstream" technology (UASB, etc) would work best with COD of at least 2,000+ mg/l; but if the question is at what level can it be treated, the concentration is much lower. So I guess it may help to know more about how you intend to operate (ie: ambient temperature? warm wastewater coming in? need to heat so you require enough methane to provide that heat?) and what your objectives are.

Anaerobic treatment of domestic wastewater may be feasible when anaerobic membrane bioreactors are used (Yoo et al., 2012(McCarty is one of the authors)). The reactor may be operated at ambient temperatures. But UASB type reactors may not be appropriate for that. Anaerobic membrane bioreactors may need further studies to use them for full scale applications. As far as I know, membrane fouling increases as the temperature decreases. Scouring type is also important (with gas or water recirculation). External or submerged membrane? At least half of the methane may remain in the treated effluent as dissolved methane, which was mentioned by Dr. Weimin Wu. So there are some unknowns.

It depends on the biodegradable portion of COD or BOD/COD ratio since the generated energy in the form of CH4 gas is what makes it feasible. Other parameters could be competing compound such as sufur comounds. Also, there could be low COD, but high organic loading rate which determined the loading rate of digester. Typical digesters loading aret is 1-10 gCOD/L.d.

.. go right ... higher than 1 gCOD/liter .... mostly biodegradable .....

It depends more on the BOD and nitrogen content. The COD load can be high - up to 850 mg/g d.w. but if the COD load are moderate toxic and if BOD content reach at least 10% of COD it can work. Be aware of the nitrogen, during degradation ammonia and nitrite levels can reach toxic levels. Hope that answered your questions.

COD is an important parameter for anaerobic digestion, if the COD is too low the methane production will be low too. it is also important take into account the kind of reactor, the retention time, the temperature. Usually for wastewater the reactors most appropriate are UASB or EGSB, working at low HRT, because the COD of urban wastewater usually is lower than 1000 mg COD/L.

In my opnion the range of COD suitable for anaerobic process will depend on the type of reactor that you will operate. There are reactors that support high load a larger amount of COD / L / day (oragnica volimetria load) and may even be used reactors in series for higher loads. However, other factors must be taken into account as biodegradilidade effluent (relationship BOD / COD), relation between nitrogen and carbon and flow applied to the system.

The Oct 2012 issue of Water21 has a good review article of successful use of anaerobic treatment of ordinary domestic sewage with COD of 500 to 800 mg/L in Brazil. They are getting methane/energy production, but there are some complications at those low levels, such as much of the methane may still be dissolved in the treated wastewater when it is discharged due to the relatively short HRT.

COD or BOD is not the real point that you need to consider in anaerobic digestion. The most important point, assuming that the organic source is non-toxic and biodegradable, is the loading rate. In classical anaerobic digestion processes, the load is very limitated because of the subsequent stage of clarification/recovering of sludge. In high-efficiency anaerobic technologies, like UASB-like reactors, biofilm reactors, biomass-attached reactors or MBR reactors, the hydraulic retention time can be decreased substantially. In some cases, the HRT could be gone down to several minutes! There are a lot of newflanged applications of these kind of technologies for treating low-strenght wastewaters, like domestic wastewaters, the only problem is the real possibility of losing methane dissolved in water, but it stronlgy depends on the goal of the treatment (energy or non-energy recovering process). On the contrary, you could increase the hydraulic retention time just by adding some kind of mixing method, both hydraulic or gaseous. In this way, there are some examples of treatments of wastewaters of very high loads (I have seen up to 150 g COD/L)

It is true that organic loading rate (OLR) is an important operating parameter, however, if COD is too low, anaerobic digestion may not be feasible. For instance for low COD, in order to have feasible operation in terms of energy recovery, OLR needs to be increased which requires low retention time in the reactor. This may not be practical in terms of adequate digestion time or reactor design and configuration and/or operational conditions.

Hello Mahmood,

Yes, what you comments is true for a conventional anaerobic digestion process, but for high efficiency processes, where the biomass concentration is maximized, the final result strongly depends on the biomass concentration, so in these cases it is important to talk about specific loading rate. If this parameter is lower than the specific activity of the biomass, it will be feasible. Of course, the problem of very low HRT affects a lot to the methane recovery, but some times energy recovery is not needed, for example in tropical countries where heating is not neccesary.

Greetings!

the amenability of biological trreatment process depends on the BI ratio.The biodegradability index (BI) is a measure of the extent to which a waste is amenable to biodegradation. BI can be expressed as a ratio of BOD5: COD. For good biodegradability of any wastewater, a minimum BOD: COD ratio (BI) of 0.3-0.4 is considered to be ideal, with a ratio of ≥0.3 desirable for coupling with aerobic treatment and ≥0.4 for anaerobic treatment (Metcalf & Eddy, 2nd ed., 1979). that means out of your total COD there should be at least 40 % BOD in waste water to be treated with Anaerobic process.

Dear Virendra,

A lot of things have changed since the Metcalf&Eddy publication. This book dealed with anaerobic technologies as an alternative for treating biodegradable and non-toxic wastewater, mainly anaerobic digestion of sludge from WWTP. However, there are a lot of applications for anaerobic digestion in which conventional biodegradability tests are not representative of the applicability os such technologies. For example, wastes from bleaching paper have low biodegradability and high toxicity and there are plenty of cases of succesful application of high-rate anaerobic reactors. The only thing that needs to be considered is whether the anaerobic sludge is capable of adaptation to treat this kind of wastes. Sometimes, the adaptation period is so long (up to several months), but finally the biodegradability of the waste increases considerably. You can take a view on these two papers:

http://www.ncbi.nlm.nih.gov/pubmed/21041023?dopt=Abstract

http://onlinelibrary.wiley.com/doi/10.1002/jctb.3753/abstract

Thank you

Dear Ana,

If you used UASB reactor the biological charge is 0.05 to 0.15 g COD/gSSV during start up at 2 g COD/gSSV in operation.

Regards

usually > 1000-2000 mg/L can be used by anaerobic processes

The primary goal of anaerobic digestion is recovery of energy (methane) and the secondary goal is volume reduction and waste stabilisation. Assuming that the target waste is biodegradable and non-toxic in nature, in my opinion and experience the COD of the waste should be at least in the range of 1200 to 2000 mg/l for the generation of biogas and its further utilization and also for the process to become economically viable. Anaerobic treatment/digestion should not be carried out just for the sake of doing it. One should be able to generate some value added byproducts out of such operations. Generation of biogas from sewage/domestic wastewater (having BOD 150-300 mg/l and COD 250-650 mg/l), in my opinion, is not at all economically viable considering the amount of biogas being generated. However, one can generate significant amount of biogas from the biogas plant specifically running on night soil. Its simple, higher the COD of waste (biodegradable and non-toxic) higher will be the biogas generation and the process will be economically viable.

300ppm to 1500ppm

Greater than 1500 to 2000mg/L is suitable for Anaerobic treatment

Actually, high concentration wastewater from palm oil processing with up to 10,000 to 25,000 mg COD/L has been successfuly treated in upflow reactor. How to treat high COD wastewater, careful design of reactor configuration is important.

Mr Wu,

The production of biogas appears to be your primary objective; but to stop there is insufficient. I hope you would look at methods of processing the sludge into viable products. What were you thinking about the use of the sludge.

I completely agree with Dr. Daniel Puyol. The biodegradability of the wastewater under investigation is the key issue. If you are dealing with a wastewater that is recalcitrant under anaerobic conditions, then you should try other sorts of treatment methods. COD/BOD ratio will not give you a sound idea about the biodegradability of your wastewater. Often due to acclimation and inhibition problems you obtain a BOD value that is lower than the actual organic content. And you have no idea about how your BOD deviates from the actual amount. You can get a BOD that represents 10 % of the organics or 85 % of the organics. Then if you use this parameter with COD in the form of a ratio, and try to depend on this ratio to find out the biodegradability of the wastewater under question your research may end up in a pitfall.

thanks

HI Fatos,

Have you ever used SBOD data? Did you find it to be a more accurate representation of the organic content? If no; then why?

Jon Cloud

Soluble BOD or BOD can not give even a rough idea about the organic content of a wastewater.The concept of BOD depends on assessing the pollution potential of a wastewater that contains an available organic carbon source for aerobic organotrophic microorganisms by measuring the amount of oxygen utilized during growth of the organisms on a sample of wastewater. Lower BOD values than the actual values are obtained when the microorganisms used as the seed in the test are not acclimated to the substrate in the effluent (which is the case in almost all industrial wastewaters as sewage is used as the origin of seed) or when the effluent contains inhibitors that slow down the biological growth (industrial wastewater streams very often carry inhibitors). Furthermore the BOD parameter tends to underestimate the organic concentration as the conditions in the test bottle are too different from those prevailing in the biological reactor: static culture, low organic matter concentration, low microorganism concentration, diminishing concentrations of dissolved oxygen, etc. Because of these restrictions and disadvantages the usage of BOD parameter alone, indicating only an unknown fraction of the total organic content, in wastewater management, is not recommended.

If the wastewater has high temperature, say above 30 °C, anaerobic treatment may be suitable even at low COD concentrations (domestic waste water). Under cold or moderate climate conditions, COD concentrations should be high enough to allow heating the feed to at least 37 °C with the biogas produced.

As to the upper limit: There is no limit. I treated a waste water with 60.000 ppm of COD without any biological problems. Problems observed were encrustations by CaCO3 precipitation.

Generally high BOD (>1000mg/L) is preffered for anaerobic digestion to produce the collectable biogas. However, increasing BOD is only one option. The key factor determining the methane production is the ratio of food and microorganism (F/M). The higher F/M, the higher methane coversion from BOD. Once keeping F/M above the certain value via appropriate process design, even low strength wastwater (like domestic wastewater) can be possible for significant methane recovery.

The answer depends on reactor configuration. Attached film or UASB reactors can treat much lower strength wastewaters than a basic anaerobic digester. A more dilute flow is obviously more difficult to treat efficiently, but actually has the advantage of providing a higher methane content: this is due to the greater solubility of CO2 and higher water flow per gas generated in a dilute waste. A literature search will find the appropriate values.

Incidentally, I disagree with the previous statement that "the primary goal of anaerobic digestion is recovery of energy (methane) and the secondary goal is volume reduction and waste stabilisation." Anaerobic digestion has been used for many decades solely for stabilization because this is essential for many end uses. The value of energy generation may be offset by costs of subsequent sludge management problems if the digested sludge is not sufficiently stable. Reductions in biodegradable fraction, pathogen content, odor potential, and vector attraction should be considered as high priorities.

Recalcitrant wast-water such as leachate has significant efficiency to run the system with high COD (50,000-60,000) mg/L using biological process. HRT and Zone Temperature should be concern based on your research objectives.

Normally it was >750mg/l

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Generally it should be more than 2000mg/L.

Important factor for selection of anaerobic treatment is wastewater alkalinity, water temperature and degree of treatment (Final BOD). Typically BOD of 1400 to 1500 mg/L give you break point after which anaerobic treatment is more economically viable. Refer to Metcalf & Eddy book chapter on Anaerobic treatment. Though, high HRT in anaerobic system to achieve the same degree of treatment. If space is not the constraint, then look for this option or make a hybrid systems (combination of anaerobic-anoxic and aerobic system).

I think that you should obtain BOD of wastewater and biodegrability index (BOD/ COD). if this index is less than 0.3, it is not suitable for biologic digestion.

COD alone will not be a good indicator. VFA profiles need to be carried out for COD more than 2500 mg.L.

Complementary comment to Arthur's experimental observation of " I treated a waste water with 60.000 ppm of COD without any biological problems. Problems observed were encrustations by CaCO3 precipitation."

Extreme high COD means large concentration in DOC, which always accompany with oversaturation of Ca2+. The fermentation of such wastewater will result in decreased value in DOC, and gradual precipitation of Ca2+ in terms of Calcite. This behavior is ubiquitous in landfill leachate collection systems. We have a recent theoretical study about the DOC-Ca oversaturated solution and its evolution with enhanced clogging. Please see the following link:

https://www.researchgate.net/publication/261581085_Modeling_precipitate-dominant_clogging_for_landfill_leachate_with_NICA-Donnan_theory

Article Modeling precipitate-dominant clogging for landfill leachate...

Hey. Are there some normal reference ranges for COD and BOD that someone can use to make a national policy from? Which is the most preferred method for COD and BOD measurements? Are there country-to-country differences in COD and BOD values? In a normal biomedical laboratory, what are the expected COD and BOD values considering that a normal waste water sewerage is functional?

What is the recommended amount of COD necessary for biogas production from winery effluent.

For how long the anaerobic sludge can be kept unfed while stabilizing the sludge in the reactor? What could be COD range below which it needs to be fed? Thanks.

thank you all for your good recommend! my sample was food waste from canteen in china ,the total COD was 9000 mg/l. then I use them in Microbial Fuel Cell (MFC) reactor as substrate.

Dear Sir need source paper for high COD value mentioned by you for study @weimin wu

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Domestic sewage has low COD which is not suitable for methane biogas production because the energy to heat the reactor will exceed what you recover as methane. And as you may know anaerobic process and is relatively slow and less efficient (70%) than aerobic process (up to 95%)