Optimization of biogenic sulfur flocculation from an anoxic desulfurization bioreactor using response surface methodology

Elemental sulfur is an interesting byproduct obtained in the anoxic biodesulfurization of biogas. However, the colloidal properties of this biogenic elemental sulfur (S0) make its efficient recovery difficult. The present study investigated the flocculation of S0 produced in an anoxic bioreactor for biogas desulfurization using cationic (Sedifloc 40L4 C, Lizaflock 853 M), anionic (Innoflock 201) and non-ionic flocculants (NI-1009) and a coagulant (polyaluminum chloride). Cationic-type flocculants showed the highest flocculation efficiency, which led to its selection for further evaluation using the response surface methodology of the effects and interactions of its dose, stirring speed and pH on the biogenic sulfur flocculation rate. Optimum S0 flocculation conditions were observed using Lizaflock 853 M at a dose of 0.82 mg L−1, a stirring speed of 30 rpm and a pH of 8.0. A S0 flocculation rate of 97.05% was achieved for an initial concentration of 1730 mg S0 L−1. The Zeta potential of the settled sulfur particles increased after the flocculation process.