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    Extracellular azo dye oxidation: Reduction of azo dye in batch reactors with biogenic sulfide
    (Taylor & Francis Ltd, 2022) Toprak, Dilan; Demir, Ozlem; Ucar, Deniz
    In this study, the sulfide-based reduction of azo dyes (Acid Blue 264) was investigated. Sulfate was reduced to sulfide with an ethanol-fed sulfate reduction reactor and the sulfide produced was used to reduce azo dyes in separate batch reactors using sulfide as the electron carrier. The Box-Behnken experiment design method was used to identify how operational parameters affect the decolorization efficiency. As independent variables, initial dye concentration, sulfide concentration and reaction time were selected while dye removal was considered as the response function. Based on the Box Behnken design, the higher regression coefficient (R-2=0.9397) shows that the experimental results are in good agreement with model predictions. At the initial dye concentration of 80 mg/L, the highest dye removal efficiency, about 82.39%, was obtained at the sulfide concentration of 50 mg/L and the reaction time of 25 h. This study showed that Box Behnken's model prediction was a suitable approach for identifying the best conditions for dye removal.
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    Impact of temperature and biomass augmentation on biosulfur-driven autotrophic denitrification in membrane bioreactors treating real nitrate-contaminated groundwater
    (Elsevier, 2022) Demir, Ozlem; Atasoy, Ayse Dilek; Calis, Bedia; Cakmak, Yakup; Di Capua, Francesco; Sahinkaya, Erkan; Ucar, Deniz
    Nitrate (NO3-) contamination of groundwater is a major health concern worldwide as it can lead to serious illnesses such as methemoglobinemia and cancer. Autotrophic denitrification is a smart approach for treating groundwater, being typically organic-deficient. Lately, biogenic sulfur (S-bio(0)) has emerged as a sustainable, free, and high-efficiency substrate to fuel membrane bioreactors (MBRs) treating contaminated groundwater. However, the effects of moderate temperature and biomass concentration on the performance and fouling of the S-bio(0)-fed MBR were not investigated previously. This study shows that biomass levels of similar to 1 g MLVSS/L limit membrane fouling but also denitrification efficiency. Biomass augmentation up to 3 g MLVSS/L enhanced denitrification but worsened fouling due to increase of extracellular polymeric substance (EPS) levels in the bulk liquid. Temperature decrease from 30 degrees C to 20 degrees C halved denitrification efficiency, which could be partially recovered through bioaugmentation. The mechanisms affected by temperature decrease, practical applications, and future research needs were discussed.