Can we predict biogas production? Which will be those parameters influencing more?
Dear Guruprasad Ji,
Organic loading rates of 3.2 to 32 Kg COD/m3.d may be used for anaerobic process ,Expected methane production 0.35m3/Kg COD removed.,influencing parameters as below
Characteristic of waste water for example waste water have COD concentration ranging from 3000 to 30000 ppm,
Flow and loading variation
wide variation in in fluent flow and organic loads can upset the balance between acid fermentation and methanogenesis in anaerobic process for soluble and easily degradable subtracts such as sugar,soluble starches,the acidogenic reactions can be much faster at high loading rates and may increase the reactor volatile fatty acids (VFA) and hydrogen concentration and depress the Ph. higher hydrogen concentration can inhibit propionic and butyric acid conversion.The lower Ph can inhibit methanogenesis .
Organic concentration and temperature.
The feasibility of Anaerobic treatment depends on waste water strength and temperature ,reactor temperature of 25 to 35 deg C are generally preferred to support more optimal biological reactions rates ,Can be applied at lower temperature and has been sustained at 10 to 20 deg C in suspended and attached growth reactors.At the lower temperature slower reaction rates occurs and longer SRTs,larger reactor volumes and lower organic COD loading rates are needed ,At temperature in the rage of 10 to 20 deg C the degradation of long chain fatty acids is often rate limiting .if long chain fatty acids accumulate foaming may occur in the reactor .
Fraction of Non-dissolved Organic material
The composition of the waste water in terms of its particular and soluble fractions effects the type of anaerobic reactor selected and its design.
waste water Alkalinity
with the high CO2 content (Typically in the range of 30 to 50%) in the gas produced in anaerobic treatment ,Alkalinity concentration in the range from 2000 to 4000 ppm as CaCO3 are typically required to maintain the Ph at or near 7.
Hi Guruprasad Anaokar, you need to take into account the total COD to calculate the expected methane production.
surely @Asif Latif , But how to measure it on site...i mean to say which readings i need to record?
Methane yield is 0.35 m3/kg COD degraded. However, this is the theoretical value. The actual value will be less since not all of the COD inlet will be degraded.
In any case, you can use temporarily gas detection procedures for on-site measurements, for instance the Dräger gas detection.
Which other parameters need to be considered keeping biogas production rate as a focus?
Dear Rajeev,
Typically, 1 g of COD removed = 0.25 g of CH4 produced, which is equivalent to 1.4 L of CH4 at STP. Usually, about 90% of the COD is converted to CH4. However, the percentage of CH4 in biogas depends on the pH in the anaerobic digestion reactor, which is affected by the equilibrium CO2.
Volatil solids also should be an indicator. Depending of the kind of organic matter that feed the process, many data are avalaible in the scientific litterature to indicate the biogas or the CH4 rate for each kg VS destroy by the process.
In complement of the information added bye Rajeev Gupta, ammonia concentration in link with the pH ihnibit the process. Finally the lipidic load also affect the process.
Yann
we can predict the biogas production from the COD removal. stoicheometrically speaking 16 grams of methane is equal to 64 grams of COD. a small fraction (10 to 17%!) of the COD removed in the anaerobic digestion process is utilized in the anaerobic sludge generation and the rest can be taken as converted into methane/biogas. At STP 1 kg COD converted into biogass can produce 0.35 Nm3 of methane.
any comment on effect of humidity on Biogas generation rate please.
Dear Guruprasad,
you will have to characterize your influent wastewater into its biodegradable and unbiodegradable COD fractions. The Biogas you'll obtain is based on the amount of biodegradable COD into your digester. it's not just the COD fed to the digester because some of it is unbiodegradable. it depends entirely on the nature of the wastewater fed to the digester. Please see a step by step model that can help you quantify the amount of biogas you will get. including the stoichiometric model part of the Anaerobic digester design.
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