Biological Biogas Scrubber – Biological DeSulphurization Process
The Biological Biogas Scrubber by AquaThane is an efficient biological process for removing hydrogen sulphide (H₂S) from biogas with minimal chemical usage.
The process involves a vertical scrubber column and an aeration tank with sulfur-oxidizing bacteria.
Key process steps:
1. H2S absorption in scrubber:
- The biogas is introduced into a vertical scrubber column, where it flows counter-currently with a mildly alkaline washing liquid that absorbs H₂S, cleaning the biogas:
(1) H2S + NaOH ↔ NaHS + H2O
2. Biological Sulfide oxidation in aeration tank:
- The sulphide rich washing liquid is forwarded to the aeration tank. where a controlled supply of air provides oxygen for sulfur-oxidizing bacteria (Thiobacillus).
- These microorganisms convert the dissolved sulfide into elemental sulfur (S⁰) and a small amount of sulfuric acid (H₂SO₄) through the following reactions:
(2) NaHS + ½O2 ↔ S0 + NaOH
(3) 2 NaHS + 4O2 ↔ Na2SO4 + H2SO4
3. Process balancing and by-product management:
- The alkalinity consumed during H2S absorption in the scrubber is largely restored by the oxidation reaction forming elemental sulfur.
- The small amount of generated H2SO4 is neutralized using caustic dosing.
- To prevent salt accumulation (e.g., Na2SO4), a controlled bleed stream is maintained.
- The produced sulphur (in the reactor tank) is separated from the bleed stream in a settler unit, allowing for safe disposal or reuse.
- The scrubber operates within a closed reactor system, significantly reducing the odour, toxicity, and corrosiveness of the biogas.
Key advantages:
- The selective biological process ensures that hardly any additional nutrients are needed.
- The system requires minimal energy to operate efficiently.
- Minimal caustic consumption helps keep operating expenses low.
- With no hazardous chemicals involved or created, the system is simple to manage and ensures operator safety.
