Desulphurization is a difficult part for all biogas engineering projects. Normally, the chemical scrubber process consumes many NAOH with expensive operation cost.The dry type desulphurization requires frequent replacement of the filling mass with a lot of manpower at dangerous working condition EnvironTec has completed more than 800 projects with Biological Desulphurization (BDS). Using microbial metabolic principle without consuming any chemicals, BDS has proved its low operating cost and the Best Practice Technology. A typical project shows that the operating cost of biological scrubberis less than RMB 2 cent per m3 biogas.
A certain amount of air is added into the biogas. Then the mixture of raw gas passes through the EnvironTec BDS reactor for H2S removal. Inside this reactor a big amount of filling mass materials (10,000 ~ 40,000 pieces) are installed inside to provide sufficient growth area for bacteria. Nutrient and water solution is recycled over the package continuously. In most cases, the nutrient supply can be from natural source or man-made fertilizer i.e. :
Digested waste water
Liquid phase of digested sludge or manure
Artificial fertilizer NPKE
Special aerobic bacteria (i.e. Thiothrix or Thiobacillus), starts growing in the nutrient solution and also on the surface of the filling mass materials. The bacteria takes up the H2S from the gas and converts it into elemental sulfur and sulfuric acid according to the following chemical reaction:
H2S + 2O2 → H2SO4
2 H2S + O2→2 S + 2 H2O
S + H2O + 1.5 O2→H2SO4
The sulfuric acid is neutralized by the buffering capacity of the nutrient solution. It is then removed out of the system with liquid waste water automatically.