Properties of Sulfur Particles Formed in Biodesulfurization of Biogas

Annemerel Mol,Cees Buisman,Renata Van Der Weijden,Johannes Klok

doi:10.3390/min10050433

Abstract

In the biodesulfurization (BD) process under halo-alkaline conditions, toxic hydrogen sulfide is oxidized to elemental sulfur by a mixed culture of sulfide oxidizing bacteria to clean biogas. The resulting sulfur is recovered by gravitational settling and can be used as raw material in various industries. However, if the sulfur particles do not settle, it will lead to operational difficulties. In this study, we investigated the properties of sulfur formed in five industrial BD facilities. Sulfur particles from all samples showed large differences in terms of shape, size, and settleability. Both single crystals (often bipyramidal) and aggregates thereof were observed with light and scanning electron microscopy. The small, non-settled particles account for at least 13.6% of the total number of particles and consists of small individual particles with a median of 0.3 µm. This is undesirable, because those particles cannot be removed from the BD facility by gravitational settling and lead to operational interruption. The particles with good settling properties are aggregates (5–20 µm) or large single crystals (20 µm). We provide hypotheses as to how the differences in sulfur particle properties might have occurred. These findings provide a basis for understanding the relation between sulfur particle properties and formation mechanisms.

Highlights

Biogas, natural gas, and other gases originating from anaerobic degradation of organic matter usually contain corrosive and toxic hydrogen sulfide (H2 S) [1,2,3]
The particle morphology different seen with light microscopy in the original
We investigated the properties of sulfur formed in five industrial BD facilities

Summary

Introduction

Natural gas, and other gases originating from anaerobic degradation of organic matter usually contain corrosive and toxic hydrogen sulfide (H2 S) [1,2,3]. Biodesulfurization (BD) of gas under halo-alkaline conditions is an attractive process, because it (i) utilizes naturally occurring bacteria instead of chelating chemicals to catalyze sulfide oxidation, (ii) operates at ambient pressure and temperature, (iii) has a high H2 S removal efficiency, (iv) produces re-usable biological sulfur, and (v) does not require stabilizers and solvents for sulfur in the process solution [6,7]. In the process (Figure 1), H2 S is removed from the gas stream by absorption into a mildly alkaline buffered process solution (pH 8–10), where it dissociates into bisulfide (HS− ; Equation (1)). In the subsequent process step, a mixed culture of halo-alkaline sulfide oxidizing bacteria (HA-SOB) oxidizes bisulfide to elemental sulfur (S0 ) in a micro-aerophilic bioreactor (Equation (2)).

Methods

Results

Conclusion