Effect of sulfate removal in a high sulfate volumetric loading micro-aerobic bio-reactor and study of subsequent bio-sulfur adsorption by iron-modified activated carbon

Removal of sulfide from a micro-aerobic bio-reactor was studied at 10 000 mg L−1 chemical oxygen demand (COD) of inlet water, with the sulfate volumetric loading 0.75, 1.0, 1.5 and 2.0 kg (m−3 d−1), respectively. Tentatively, activated carbon (AC) as an adsorbent was modified in positively charged iron to adsorb bio-sulfur through electrostatic interaction. At an O2/S molar ratio of 8–10, the reactor was sufficient to decrease the sulfide in the effluent and biogas to low levels at the sulfate volumetric loading of 2 kg (m−3 d−1). After iron-modified, the specific surface area of AC was form 32.4 m2 g−1 to 65.0 m2 g−1, and the zeta potential was 25.3 mV at pH 7.0. The XRD pattern of the iron-modified activated carbon (FeAC) explained that the metal species of iron was Fe3O4. It could be clearly seen that there was Fe3O4 on the surface of the FeAC, and sulfur particles with a large particle size were adsorbed by the FeAC on the SEM figures. And the XRD pattern of the bio-sulfur explained that the bio-sulfur was made up of S8 (91.444%), C3H4N2OS (1.491%) and CH5N3S (7.075%). The zeta potential of bio-sulfur was −25 mV and the particle size was mainly distributed at the average diameter of 1935 nm at pH 7.0.