Abstract
Sulfide produced by sulphate-reducing bacteria in anaerobic reactors can seriously affect biogas quality. Microaeration has become a reliable way to remove sulfide, by promoting its oxidation. However, limited research is available regarding its application in upflow anaerobic sludge bed (UASB) reactors. In this research, silicon membranes were studied as a mechanism to dose oxygen in USAB reactors. Two configurations were tested: the membrane placed inside the reactor or in an external module. Our results show that the external membrane proved to be a more practical alternative, providing conditions for sulfide oxidation. This led to a reduction in its concentration in the liquid effluent and biogas. External membrane configuration achieved a sulfide conversion rate of 2.4 g-S m2 d−1. Since the membrane was not sulfide-selective, methane losses were observed (about 9%). In addition, excessive oxygen consumption was observed, compared to the stoichiometric requirement. As is the case for many membrane-based systems, membrane area is a key factor determining the correct operation of the system.
Highlights
High sulfate concentrations can be found in the wastewater from different industries, including pharmaceutical, food, tannery, edible oil refinery, among others [1,2,3,4]
A t-student test confirmed no statistical difference between values with and without membrane micro-oxygenation for Reactor 1
Most of reported research and applications have been focused on microaeration of continuous stirred-tank reactors, where air/oxygen is normally injected into the headspace of the digester, and less research has been dedicated to the application of microaeration in granular reactors [14]
Summary
High sulfate concentrations can be found in the wastewater from different industries, including pharmaceutical, food, tannery, edible oil refinery, among others [1,2,3,4]. Sulfate is generally found in nature and is chemically inert, nontoxic, and nonvolatile. It could affect the anaerobic digestion process during (waste) water treatment, by promoting competition between methanogens archaea and sulphate-reducing bacteria (SRB). SRB can oxidize hydrogen and various organic compounds, using sulfate as the electron acceptor, and producing hydrogen sulfide (H2 S) [4,5,6]. Maintaining a chemical oxygen demand (COD)/sulfate ratio over 10 prevents inhibiting sulfide concentrations being reached in anaerobic reactors, which, depending on the pH, can be between 50 and 800 mg L-1 [7,8]
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