The BioChemical DeSulphurization Process (BCSP) from HydroThane is a simple biological process that removes hydrogen sulphide (H₂S) from biogas with a minimal use of chemicals.

The biogas is fed into vertical scrubber column(s) with packing media inside. In counter current flow, a slightly alkaline washing liquid is used for absorbing the H2S and cleaning the biogas (reaction 1).

(1) H₂S + NaOH ↔ NaHS + H₂O

The HydroThane STP ^® BCSP can be seen as a combination of a conventional chemical scrubber and a biological oxidation step. The sulphide rich washing liquid is forwarded to the aeration tank. A controlled amount of air is pumped in to provide sufficient oxygen for the sulphur oxidizing bacteria.

The sulphur oxidizing micro-organisms (thiobacillus) in the aeration tank metabolize the dissolved sulphide into S (elemental sulphur) mainly and some H₂SO₄ (sulphuric acid) following:

(2) NaHS + ½O2 ↔ S0 + NaOH
(3) 2 NaHS + 4O2 ↔ Na₂SO₄ + H₂SO₄

The main part of the alkalinity consuming H₂S absorption in the scrubber (reaction 1) is compensated by the oxidation reaction to elemental sulphur (reaction 2). The small amount of generated H₂SO₄ (from side reaction 3) needs to be neutralized by means of caustic dosing. Preventing accumulation of salts (e.g. Na₂SO₄) a small bleed stream is required. The produced sulphur (in the reactor tank) is separated from this effluent bleed stream by means of a settler unit. These separated, harmless, residual products can be directly discharged or reused.

The HydroThane STP^® BCSP is accomplished in a closed reactor system and reduces the odour, toxicity and corrosiveness of the biogas.

The benefits from the HydroThane STP^® BCSP are:
• Extreme low operational costs (limited caustic consumption)
• Hardly no nutrient requirement (selective biological process)
• Low energy requirement
• Simple and safe to operate (no hazardous chemicals used/formed)
• Low maintenance