How does a biogas production plant work?
Using organic matter to produce energy
Biogas production consists of recovering organic matter (in our case, cow dung or plant residues) which, through fermentation, allows the production of green energy: biogas. This energy is sent directly to the gas network or transformed into electricity and sent to the electric grid or used by the farm itself. It is an effective solution for recycling organic waste on large farms.
Optimizing biogas production with Bicar®
Used as a preventive or curative measure in case of acidosis, the addition of Bicar® to the substrate stabilises the pH in the digester and thus ensures the production of biogas.
The advantages of Bicar® for biogas
Stabilization of the biological processes of biogas production
Bicar® increases the pH inside the digester thanks to its high buffering capacity (due to sodium bicarbonate). The biological processes of biogas production (hydrolysis, acetogenesis and methanogenesis) can thus be stabilised by avoiding the accumulation of volatile fatty acids in the digester which inhibit the biogas production process.
Better performance and fewer sediment layers
By buffering the added substrate, Bicar® improves the performance of the biogas plant. It also participates in the reduction of sediment layers in the digester and foam on the surface, which are recurrent phenomena.
A biogas production increased by 1.8% per day
The addition of Bicar® to the substrate (125 kg of Bicar® per day for 55 days) increased the volume of biogas produced each day by 115 m3, i.e. by 1.8% (test carried out on a 2500 m3 fermenter and for a retention time of 55 days).
Lime vs Bicar® for biogas production
|
Lime |
Bicar® |
|
Slightly soluble in water, resulting in deposits and clogging of the system. |
Good water solubility, no formation of sediment layers |
|
Difficult to make an accurate dosage, resulting in a high risk to the biological system in case of overdose. |
Very good performance of the biological process due to controlled buffering |
|
Very early inhibition of the biological system by calcium. |
Inhibition by sodium alone between 6 and 30 g/litre, in suitable systems even up to 60 g/l. |
|
No increase in buffer capacity thanks to HCO3. |
Increased buffer capacity due to HCO3 and increased pH value => higher yield and better biogas quality. |
|
Abrupt change in pH: extremely harmful to the microbial biological process (when quicklime or slaked lime is used). |
Reduced foam formation during the biogas production process. |
|
Lime being a more dangerous product, it is necessary to wear protective gloves and to pay attention to the legislation on chemicals . |
Natural buffer based on sodium bicarbonate, easy handling and dosage. |
Recommendations for the use of Bicar® for biogas production
Acidosis in the biogas plant manifests itself in the following ways:
- a drop in pH to below 6.8-7.0,
- a drop in buffering capacity to below 100-150 mmol/L or TAC* values below 6000-7000,
- a rapid increase in the FOS**/TAC ratio to over 0.7.
In the event of acidosis*** , it is strongly recommended that Bicar® be added according to the following doses:
- 5 to 10 T for facilities fed with liquid manure,
- 8 to 20 T for facilities fed with energy crops.
Changes of substrate are likely to result in imbalances in the flora in the digester and modify the acid-base equilibrium of the environment:
-
a drop in pH to below 7.0-7.2,
- a drop in buffering capacity to below 100-200 mmol/L and TAC values below 8000-10,000,
- a rapid increase in the FOS/TAC ratio to over 0.7.
When changing the substrate***, it is recommended that Bicar® be added in the following doses, 3 days before to 3 days after the change of substrate:
5 to 10 T in 2 to 3 doses over the course of the 6 days for facilities fed with liquid manure,
5 to 15 T in 2 to 3 doses over the course of the 6 days for facilities fed with energy crops.
Adding Bicar® allows the performance of the biogas plant to be improved. The quantities required*** depend on the retention time and the type of substrate:
- for a facility fed with 100% corn, add 100 kg Bicar® per day,
- for a facility fed with 70% maize and 30% liquid manure, add 50 kg Bicar® per day,
Generally, allow 1.5 T (one 25 kg bag per day for 60 days) to 7.5 T for the duration of the retention time (40 to 60 days).
* The TAC, or complete alkalinity titration, defines the buffering capacity of the environment. The lower the TAC, the less the ecosystem is able to buffer a drop in pH.
** The VOA value (standing for volatile organic acids, or FOS in German) represents the concentration of organic acids in the environment.
*** The recommended doses of Bicar® for biogas production are based on empirical observations of a biogas plant measuring 2500 m3, and for a retention time of 40 to 60 days. The use of Bicar® is the sole responsibility of the user. For further information, or for recommendations tailored to your facility, you can contact one of our experts in biogas.