Dear Hillary,Good ...
Published by Prem Baboo, Researcher at www.researchGate.net
Dear Hillary,
Good question,
Biological methods for the removal of sulphur containing compounds from wastewater In the case of biological treatment, sulphate, sulphite and other sulphur compounds are reduced in an anaerobic step to sulphide, which in turn can be oxidized to elemental sulphur by way of limited oxidation For reducing sulphur compounds to sulphide, an electron donor is necessary, as follows from the reaction:
SO4--- + 5 5H2O + 8e ==HS- + H20-
Sulphide is oxidised very readily in aerobic conditions Biotechnological processes for sulphide removal consist in the conversion of sulphide into elemental sulphur by colourless sulphur bacteria according to the following reaction:
2HS + O2 = 2S + 2OH
or by genera of anaerobic photosynthetic bacteria from the families Chlorobiaceae and Chromaticeae that catalyse the photosynthetic van Niel reaction.
2n H2S + n CO2 = 2n S + (CH2O)n + n H2O
light radiated to a photosynthetic reactor is coupled to the conversion of sulphide to elemental sulphur using the reverse citric acid cycle . The advantage of such a method is that only small waste streams remain because the sulphur, that is, formed can be reused. However, the disadvantage is that, especially when the effluent contains little organic matter, electron donors (methanol, ethanol, glucose and other saccharides, organic acids, H2 and CO have to be added in order to provide sufficient reducing equivalents for the SRB. This, as a result, increases the costs of this method substantially . Organic compounds that have more than two carbon atoms that degrade under anaerobic conditions give H2 and acetate. H2 can be used as an electron donor for the reduction of sulphate and sulphite.
Oxidation Reduction Potential (ORP) can be a valuable tool for seeing what is happening in unit processes like anoxic and anaerobic tanks.