生物脱硫技术的原理为：通过营造脱硫菌适宜的工作环境，使沼气中H2S在脱硫菌的生物氧化还原作用下生成单质硫被去除。脱硫系统属开放系统，微生物种群随环境改变而变化。在大多数生物发酵罐中，微生物种类以细菌为主、真菌为次，极少有酵母菌；常用的细菌是硫杆菌属的氧化亚铁硫杆菌、脱氮硫杆菌及排硫杆菌，最成功的代表是氧化亚铁硫杆菌，其生长的最佳pH值为2.0～2.2。从沼气发酵罐内导出的气体进入生物脱硫塔，同时从发酵罐内抽出部分发酵液，用泵将发酵液从生物脱硫塔的底部抽到顶部进行淋洒，发酵液的作用是发酵液当中含有很多微生物，与沼气中的H2S作用后，能够生成含有硫单质的细菌，存在于生物脱硫塔内部的填充层里，这种细菌是好氧性细菌，因此，在进行生物脱硫前，沼气应预先通过鼓风机注入微量的空气(O2)，使其处于好氧状态。如果没有与H2S相遇，可以消耗自身成为H2SO4，通过发酵液的循环而排放出去；发酵液经过循环后，当其pH值降到2时，需要重新更换，原来的废水则流到贮液池等待好氧处理。利用注入的空气和营养液中的水分发生以下氧化还原反应：
The principle of biological desulfurization technology is: by building the suitable working environment of desulfurizing bacteria, we can remove H2S from biogas under the biologic oxidation-reduction effect of desulfurizing bacteria. The desulphurization system is an open system, and the microbial population changes with the environment. In most biological fermentation, microbial species dominated by bacteria, fungi, and few yeasts; common bacteria, Thiobacillus ferrooxidans of Thiobacillus denitrificans and Thiobacillus thioparus, on behalf of the most successful is the Thiobacillus ferrooxidans, the optimum pH value of 2 to 2.2 growth. Enter the bio desulfurization tower from the gas in the methane fermentation tank is derived, and from the fermentation tank out of fermentation liquid, the fermentation liquid from biological desulfurization tower bottom to the top for sprinkling pump pump, fermentation liquid is fermented liquid which contains many microorganisms, and in biogas after H2S, can generate a sulfur bacteria, the filling layer exists in the internal biological desulfurization tower, this bacterium is aerobic bacteria, therefore, in biological desulfurization, biogas should advance by injecting air blower (O2), which is in the aerobic condition. If there is no encounter with H2S, it can consume itself as H2SO4, and it will be discharged through fermentation cycle. After fermentation, when the pH value of the fermentation liquor is reduced to 2, it needs to be renewed. The original wastewater will flow to the liquid storage tank and wait for aerobic treatment. The following redox reaction occurs by the use of the water in the injected air and the nutrient solution:
2H2S+O2→2H2O+2S
2H2S+O2 - 2H2O+2S
2S+3O2+2H2O→2H2SO4
2S+3O2+2H2O - 2H2SO4
H2S在脱硫菌的作用下进行氧化还原反应后，生成单质硫和H2SO4，贮存于塔内填料和营养液内，通过填料上生物膜的脱落和营养液的定期外排净化。
Under the action of desulphurizing bacteria, H2S produces sulfur and H2SO4, which are stored in the fillers and nutrient solutions, and are removed by biofilm on the fillers and regularly discharged by nutrient solution.
优势：运行费用低，无需催化剂或氧化剂，无需更换滤料，脱硫效率高。
Advantages: low operating cost, no catalyst or oxidant, no need to replace filter material, high desulfurization efficiency.
劣势：一次性投资高，过程不易控制，沼气中氧残留量不易控制。
Disadvantages: high one-time investment, the process is not easy to control, oxygen residue in biogas is not easy to control.