Short-term temperature impact on simultaneous biological nitrogen-sulphur treatment in EGSB reactor

Sulphides are present in many wastewater streams; their removal is important due to corrosiveness, toxicity and unpleasant odour, and can be carried out by anaerobic biological treatment. This study focuses on the temperature effect (25-10 °C) on an expanded granular sludge bed (EGSB) reactor for sulphide removal using nitrate as electron acceptor. The reactor was run at a NO₃^-/HS^- molar ratio of 0.35 and pH of 8.5-9.0. Samples were analysed by ion chromatography (NO₃^-, SO₄^2- and S₂O₃^2-), spectrophotometry (S^2-) and by scanning electron microscopy (SEM). S^2- and NO₃^- removal was 99.74 ± 0.04 and 99.5 ± 2.9%, respectively. Sulphur (S⁰) was found on the outer granule surface and struvite inside the granule, by SEM. Sulphide conversion to sulphur was up to 76%. Temperature transitions and levels influenced S₂O₃^2- and SO₄^2- concentrations.