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    Biological denitrification for water detoxification: A review
    (Elsevier Science Sa, 2025) Ucar, Deniz; Sahinkaya, Erkan; Sabba, Fabrizio; Di Capua, Francesco
    Biological denitrification is an established process for nitrate (NO3-) removal that is typically applied in wastewater treatment plants (WWTPs) and sometimes for drinking water treatment. In WWPTs, conventional denitrification is driven by the oxidation of the organic matter existing in the influents of municipal and/or industrial origin. Alternatively, some inorganic compounds, including sulfur, hydrogen, and iron, can act as electron acceptors for denitrification purposes. In industrial wastewater and in water from contaminated water bodies, toxic compounds including heavy metals such as chromium, arsenic, uranium, and manganese as well as other pollutants such as sulfide, thiocyanate, perchlorate, and aromatic compounds can be present. Interestingly, these compounds can also act as energy sources for denitrifying bacteria and/or be co-reduced with NO3 - and other denitrification intermediates. In this way, their toxicity can be partially or totally removed, which demonstrates the potential of biological denitrification for the detoxification of both water and wastewater. This work reviews the toxicity, degradation pathways, and impacts on denitrification steps, microorganisms, and bioreactor operation of eight types of toxic compounds that can be detoxified via biological denitrification. The role of the different compounds on nitrous oxide (N2O) emissions during denitrification is also discussed to provide useful information for the minimization of greenhouse gas emissions.
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    Co-removal of P-nitrophenol and nitrate in sulfur-based autotrophic and methanol-fed heterotrophic denitrification bioreactors
    (Elsevier Sci Ltd, 2023) Yenilmez, Aylin Ebru; Ertul, Selin; Yilmaz, Tulay; Ucar, Deniz; Di Capua, Francesco; Sahinkaya, Erkan
    P-nitrophenol (PNP) can co-occur with nitrate (NO3-) in industrial and municipal wastewater due to effluent discharges from industry and agricultural activities. In this study, the simultaneous removal of PNP and NO3- was investigated under autotrophic and heterotrophic denitrifying conditions in two bioreactor columns at laboratory scale. Autotrophic denitrification with elemental sulfur showed efficient elimination of both PNP (85 % on average for 5-50 mg/L) and NO3- (99 % on average) even at feed PNP concentration of 50 mg/L. In contrast, the heterotrophic column showed significantly lower PNP removal (53 % on average for 5-50 mg/L) despite denitrification efficiency being >= 95 %. ORP was identified as a possible control parameter to modulate PNP removal efficiency. The autotrophic column showed better resiliency than the heterotrophic one under intermittent feeding of 50 mg/L of PNP. Absorbance spectra and HPLC results revealed no accumulation of PNP by-products, i.e., aminophenol, in the autotrophic column during transient feeding conditions.
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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.
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    Perchlorate reduction in a thiosulfate-based denitrifying membrane bioreactor
    (Elsevier, 2023) Yilmaz, Tuelay; Yurtsever, Adem; Sahinkaya, Erkan; Ucar, Deniz
    Reductive removals of perchlorate and nitrate, which can be present simultaneously in groundwater, were investigated in a novel thiosulfate-based denitrifying lab-scale membrane bioreactor (MBR) equipped with a polyethersulfone membrane module. Complete denitrification at a hydraulic retention time (HRT) as low as 3 h and a rate of 800 mg NO3--N/(L.d) was accomplished. Simultaneous with nitrate, complete perchlorate reduction was also detected at the feed concentration of 3000 mu g/L and at 12 h HRT. Although further rise in perchlorate loading caused its incomplete reduction, the reduction rate reached up to 38 mg/(L.d). Hence, the developed process is promising for simultaneous perchlorate and nitrate reduction from contaminated groundwater. Sus-tainable filtration performance was observed up to a flux of 12.5 L/(m2.h) (LMH) at which the fouling rate was 85.32 +/- 19.65 mbar/d. However, when the flux was raised further to 25 L/(m2.h), the TMP drastically increased to a rate of 393 +/- 40 mbar/d.
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    Performance of a pilot-scale reverse osmosis process for water recovery from biologically-treated textile wastewater
    (Academic Press Ltd- Elsevier Science Ltd, 2019) Sahinkaya, Erkan; Tuncman, Selen; Koc, Ibrahim; Guner, Ali Riza; Ciftci, Suheyla; Aygün, Ahmet
    Textile industry generates a high volume of wastewater containing various type of pollutants. Although high color and chemical oxygen demand (COD) removals are achieved with the combination of biological and chemical treatment processes, reverse osmosis (RO) process is generally needed for water recovery due to high conductivity of the textile wastewater. In this study, a pilot scale RO process containing one spiral wound membrane element was operated under three different operational modes, i.e. concentrated, complete recycle and continuous, to collect more information for the prediction of a real-scale RO process performance. It was claimed that complete recycle mode of operation enabled mimicking the operational conditions exerted on the first membrane, whereas continuous mode of operation created conditions very similar to the ones exerted on the last membrane element in a real scale RO process train. In the concentrated and continuous mode of operation, water recovery and flux were around 70% and 19 L/m(2)/h (LMH). Permeate produced in the RO process can be safely reused in the dyeing process as the feed and permeate conductivities were around 5500 mu S/cm and 150 mu S/cm, respectively, at 70% water recovery. However, color concentration in the concentrate exceeded the discharge limits and would need further treatment. The RO performance was accurately predicted by ROSA simulations.
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    Sequential sulfur-based denitrification/denitritation and nanofiltration processes for drinking water treatment
    (Academic Press, 2021) Asik, Gulfem; Yilmaz, Tulay; Di Capua, Francesco; Uçar, Deniz; Esposito, Giovanni; Sahinkaya, Erkan
    Efficient and cost-effective solutions for nitrogen removal are necessary to ensure the availability of safe drinking water. This study proposes a combined treatment for nitrogen-contaminated groundwater by sequential autotrophic nitrogen removal in a sulfur-packed bed reactor (SPBR) and excess sulfate rejection via nanofiltration (NF). Autotrophic nitrogen removal in the SPBR was investigated under both denitrification and denitritation conditions under different NO3− and NO2− loading rates (LRs) and feeding strategies (NO3− only, NO2− only, or both NO3− and NO2− in the feed). Batch activity tests were carried out during SPBR operation to evaluate the effect of different feeding conditions on nitrogen removal activity by the SPBR biofilm. Bacteria responsible for nitrogen removal in the bioreactor were identified via Illumina sequencing. Dead-end filtration tests were performed with NF membranes to investigate the elimination of excess sulfate from the SPBR effluent. This study demonstrates that the combined process results in effective groundwater treatment and evidences that an adequately high nitrogen LR should be maintained to avoid the generation of excess sulfide.