Overview
Green H₂S Scrubbers are designed for high gas flow sites and provide an environmentally friendly method for hydrogen sulfide (H₂S ) removal without the use of chemicals. Utilizing sulfur-oxidizing bacteria from the Thiobacillus family, these scrubbers effectively convert H₂S into sulfate through a series of oxidation processes. The system operates within an acid-proof tank filled with specially designed media and utilizes a liquid nutrient—such as NPK nutrient or digested sludge liquor—that is continuously recirculated and sprayed across the media. Maintaining a temperature of 35-40 degrees Celsius is crucial for optimal performance.
The effluent from the biological scrubber is diluted with the effluent stream from the digester, minimizing environmental concerns. Moreover, lower liquid recycle rates result in the need for low-capacity pumps, unlike the high-capacity pumps required in chemical scrubbers.
Main Features
Increased Purification Life: Enhances the operational lifespan of biogas purification systems.
Reduced Engine Maintenance: Lowers the maintenance needs of compressors and related equipment.
Minimal Operational Expenses: Nearly zero operational and maintenance costs.
Main Features
By reducing the concentration of hydrogen sulfide (H₂S ) in raw biogas, Green H₂S Scrubbers significantly enhance the operational life of compressors and towers used in biogas processing.
Process Description of Biological Scrubber
Biogas drawn from a biogas holder is fed into an acid-proof scrubbing tower equipped with active immobilized bacteria on specialized packing material. Controlled quantities of air are introduced into the scrubbing tower, where aerobic bacteria oxidize H₂S in the biogas. The scrubbing liquid, consisting of soft water or bio-methanated digester overflow (treated water), is sprayed onto the packing material from the top of the tower. This liquid is supplemented with a bacteria solution and nutrients to maintain healthy bacterial colonies.
To control the pH levels within the tower, a portion of the scrubbing liquid is continuously drained out. Internal circulation pumps, pipes, and fittings are constructed from PE or FRP to withstand the acidic scrubbing liquid. The temperature in the scrubber is maintained at approximately 40-50°C, allowing water-saturated biogas to exit the scrubber at the same temperature.
Performance of the Biological Scrubber
Several factors contribute to the effective performance of the biological H₂S scrubber, which employs a packed tower design:
Specialized Packing Design: The packing material provides a high surface area, facilitating significant bacterial attachment and effective H₂S mass transfer.
Air Velocity Management: Optimized air velocity creates a turbulent regime, increasing gas–film mass-transfer coefficients.
Micronutrient Supply: Continuous provision of micronutrients ensures that bacterial cultures do not experience limitations in H₂S degradation.
Homogeneous Distribution: Liquid and air are evenly distributed throughout the scrubber, preventing gas short-circuiting or the formation of dead zones in the packed bed, thus maximizing biological activity.
Startup and Performance Indicators
At startup, the reactor sump is inoculated with activated microorganisms. The efficiency of H₂S removal is indicated by a decline in pH, which occurs due to the production of H+ ions and sulfate from H₂S oxidation. Following acclimation, the scrubber can achieve over 99% H₂S removal for inlet concentrations.
The long-term performance is characterized by the Elimination Capacity (EC), defined as the amount of H₂S degraded per unit of time, normalized by the volume of the packed bed. The airflow is consistently adjusted according to changes in biogas flow. Typically, elimination efficiencies exceeding 99% are achievable for high inlet H₂S concentrations, even with gas contact times as short as 1.6–2.3 seconds—significantly outperforming chemical-based H₂S removal systems.
Use of Sulfate Effluent from the Biological Scrubbing System
The effluent exiting the biological scrubber contains sulfur in the form of sulfate. This sulfate can be mixed with post-digestion treated water for bio-composting, serving as an excellent source of sulfur for the compost and enriching its quality. The soluble nature of the separated sulfur allows for easy mixing with treated water for further treatment or disposal.
Advantages of Biological H₂S Removal Systems
Complete Microbiological Technology: A truly green solution, as no chemicals are used in the process.
Simplicity and Low Power Consumption: Achieves the lowest operational and maintenance costs for biogas sweetening.
High H₂S Removal Efficiency: Effectively reduces H₂S concentrations from 30,000 ppm to virtually non-detectable levels, prolonging the lifecycle of process equipment.
Minor Pressure Drops: Results in less operational strain, potentially eliminating the need for an additional blower.
Versatility: Suitable for cleaning biogas from any source at a low cleaning cost.
