Efficient and industrial production of H₂SO₄ from sulfur sludge by acidophilic cells in a membrane bioreactor via optimizing process

A large amount of sulfur-bearing hazardous wastes, including sulfur sludge, are generated in the production and processing of oil/natural gas/coal gas/biomass gas, which are difficult to dispose of with traditional processes, such as incineration or landfills. In the present work, a homemade membrane bioreactor (MBR) with an efficient volume of 10 m³ was utilized to continuously and efficiently remove sulfur (S⁰) from sulfur sludge and produce sulfuric acid (H₂SO₄) by using chemoautotrophic acidophilic cells on an industrial scale for the first time. The bio-oxidation process was also modelled and optimized by using response surface methodology. The quadratic models describe the causal relationships between the production rate of H₂SO₄ at pH 1.0 or the time required for the pH to decrease to 1.0 and three important control parameters (temperature, aeration rate and stirring velocity). The MBR maintained high-density growth of cells (≈2.1 × 10⁹/mL) throughout the entire operational period due to the excellent interception performance, establishing a basis for efficient sulfur removal and H₂SO₄ production. Under the optimized process controls of 33.6 °C for the temperature, 3.1 m³/min for the aeration rate and 83 rpm for the stirring velocity, a high production efficiency of H₂SO₄ at pH 1.0 (≈850 L/h) is obtained. Accordingly, the sulfur removal efficiency and sulfur residual concentrations reached 93% and 4.1% after 20 days of contact, respectively. The current study demonstrates that the MBR is suitable for industrial scale operations, for continuous and efficient sulfur removal and for production of H₂SO₄ from sulfur-bearing hazardous wastes. The green microbial means not only save very expensive disposal expense of sulfur-bearing hazardous wastes but also gain benefits through the manufacture of valuable H₂SO_4, displaying great business value and wide application prospect.