FerroSorp® DG

Powdered desulphurization reagent for binding hydrogen sulfide in biogas plants

General

Biogas is produced by anaerobic conversion of biomass. In addition to the main components of methane and carbon dioxide, biogas often contains hydrogen sulfide which has to be removed prior to use to prevent odor and corrosion problems. Different desulphurization technologies that can be applied include oxygenation, addition of iron salts, subsequent removal with fixed-bed iron hydroxide based absorbers, flue gas scrubbers and biological oxidation of hydrogen sulfide.

Digesters of WWTP Braunschweig / Wastewater Association Braunschweig

Problem

Oxygenation of the fermentation chamber using ambient air often has only minor effect on formation of hydrogen sulfide but leads to a dilution of the biogas and thus to a reduced caloric content. While downstream desulfurization technologies are used to circumvent this effect, they require a high capital investment. Furthermore, the formation of hydrogen sulfide in the bioreactor is not prevented, which has a well-known inhibiting effect on methane production. Dosages of highly acidic iron salts lead to precipitation of sulfide. The disadvantages of this method is the reduced buffering capacity of the fermentation substrate and the requirements for the storage and handling of iron salts due to their water hazard class restrictions.

Solution

Specifically to solve the problems mentioned above, HeGo Biotec GmbH developed a desulfurization reagent based on iron hydroxide. The precipitation of hydrogen sulfide in the fermenter can be described by the following chemical reaction:

FerroSorp DG - equation

Procedure

The iron hydroxide contained in FerroSorp® DG binds hydrogen sulfide immediately during formation. In a first reaction, trivalent iron is reduced under anaerobic conditions to divalent iron. In so doing, hydrogen sulfide can be oxidized to elemental sulfur. In a subsequent reaction, divalent iron reacts with hydrogen sulfide forming finely dispersed iron sulfide which can be observed in the blackening of the fermenting residue. Using FerroSorp® DG, no additional anions are introduced into the substrate. In FerroSorp® DG, contained calcium compounds increase the buffer capacity of the fermentation substrate and thus counteract acidification. Co-precipitation of trace elements with hydrogen sulfide is reliably prevented; thus, methanogenesis can proceed uninhibited resulting in optimal biogas yield and high methane levels.

Mikroskopische Darstellung von methanosarcina acetivorans | HeGo Biotec

Microscopic view of methanosarcina acetivorans

Application

FerroSorp® DG can be added easily to the fermenting substrate in the receiving station. FerroSorp® DG is classified as “non-hazardous to waters” and safe due to its chemical properties. There are no specific regulations concerning storage and handling of FerroSorp® DG.

Advantages at a glance

  • Highly active reagent for hydrogen Sulfide removal in biogas plants
  • Optimum yield of biogas with high methane content
  • Effective protection against acidification of the fermenting substrate by increasing the buffer capacity
  • Cost effective compared to downstream hydrogen sulfide removal techniques due to higher biogas yield
  • Easy application
  • No increase in acidity of the fermenting substrate
  • No impairment of the fermenting residue considering material recycling and waste management