Deniz Ucar

Sulfidogenic fluidized bed treatment of real acid mine drainage water.

The treatment of real acid mine drainage water (pH 2.7-4.3) containing sulfate (1.5-3.34 g/L) and various metals was studied in an ethanol-fed sulfate-reducing fluidized bed reactor at 35°C. The robustness of the process was tested by increasing stepwise sulfate, ethanol and metal loading rates and decreasing feed pH and hydraulic retention time. Highest sulfate reduction rate (4.6g/L day) was obtained with feed sulfate concentration of 2.5 g/L, COD/sulfate ratio of 0.85 and HRT of 12 h. The corresponding sulfate and COD removal efficiencies were about 90% and 80%, respectively. The alkalinity produced in sulfidogenic ethanol oxidation neutralized the acidic mine water. Highest metal precipitation efficiencies were observed at HRT of 24 h, the percent metal removal being over 99.9% for Al (initial concentration 55 mg/L), Co (9.0 mg/L), Cu (49 mg/L), Fe (435 mg/L), Ni (3.8 mg/L), Pb (7.5 mg/L) and Zn (6.6 mg/L), and 94% for Mn (7.21 mg/L).

Performances of anaerobic and aerobic membrane bioreactors for the treatment of synthetic textile wastewater.

This study aims at comparatively evaluating anaerobic and aerobic MBRs for the treatment of azo-dye containing synthetic wastewater. Also, the filtration performances of AnMBR and AeMBR were compared under similar operating conditions. In both MBRs, high COD removal efficiencies were observed. Although almost complete color removal was observed in AnMBR, only partial (30-50%) color removal was achieved in AeMBR. AnMBR was successfully operated up to 9 L/(m(2)h) (LMH) and no chemical cleaning was required at 4.5 LMH for around 50 days. AeMBR was operated successfully up to 20 LMH. The filtration resistance of AnMBR was generally higher compared to AeMBR although reversible fouling rates were comparable. In both MBRs, offline chemical cleaning with NaOCl and sulfuric acid almost completely removed irreversible fouling and the resistances of chemically cleaned membranes were close to those of new membranes.

Sulfidogenic biotreatment of synthetic acid mine drainage and sulfide oxidation in anaerobic baffled reactor.

The treatment of synthetic acid mine drainage (AMD) water (pH 3.0-6.5) containing sulfate (3.0-3.5 g L(-1)) and various metals (Co, Cu, Fe, Mn, Ni, and Zn) was studied in an ethanol-fed sulfate-reducing 4-compartment anaerobic baffled reactor (ABR) at 32°C. The reactor was operated for 160 days at different chemical oxygen demand (COD)/sulfate ratios, hydraulic retention times (HRT), pH, and metal concentrations to study the robustness of the process. The last compartment of the reactor was aerated at different rates to study the bio-oxidation of sulfide to elemental sulfur. The highest sulfate reduction efficiency (88%) was obtained with a feed sulfate concentration of 3.5 g L(-1), COD/sulfate mass ratio of 0.737, feed pH of 3.0 and HRT of 2 days without aeration in the 4th compartment. The corresponding COD removal efficiency was about 92%. The alkalinity produced in the sulfidogenic ethanol oxidation neutralized the acidic mine water from pH 3.0-4.5 to pH 7.0-8.0. Effluent soluble and total heavy metal concentrations were substantially reduced with removal efficiencies generally higher than 99%, except for Mn (25-77%). Limited aeration in the 4th compartment of ABR promoted incomplete oxidation of sulfide to elemental sulfur rather than complete oxidation to sulfate. Depending on the aeration rate and HRT, 32-74% of produced sulfide was oxidized to elemental sulfur. This study demonstrates that by optimizing operating conditions, sulfate reduction, metal removal, alkalinity generation, and excess sulfide oxidation can be achieved in a single ABR treating AMD.

An Overview of Electron Acceptors in Microbial Fuel Cells

Microbial fuel cells (MFC) have recently received increasing attention due to their promising potential in sustainable wastewater treatment and contaminant removal. In general, contaminants can be removed either as an electron donor via microbial catalyzed oxidization at the anode or removed at the cathode as electron acceptors through reduction. Some contaminants can also function as electron mediators at the anode or cathode. While previous studies have done a thorough assessment of electron donors, cathodic electron acceptors and mediators have not been as well described. Oxygen is widely used as an electron acceptor due to its high oxidation potential and ready availability. Recent studies, however, have begun to assess the use of different electron acceptors because of the (1) diversity of redox potential, (2) needs of alternative and more efficient cathode reaction, and (3) expanding of MFC based technologies in different areas. The aim of this review was to evaluate the performance and applicability of various electron acceptors and mediators used in MFCs. This review also evaluated the corresponding performance, advantages and disadvantages, and future potential applications of select electron acceptors (e.g., nitrate, iron, copper, perchlorate) and mediators.

A novel elemental sulfur-based mixotrophic denitrifying membrane bioreactor for simultaneous Cr(VI) and nitrate reduction.

This study aims at investigating the simultaneous nitrate and chromate reduction by combining the advantages of sulfur-based autotrophic denitrification, heterotrophic denitrification and membrane bioreactor (MBR) technologies. A laboratory-scale MBR equipped with hydrophilic flat sheet polyethersulfone (PES) membranes (0.45μm) was used to evaluate the performance of mixotrophic denitrification at varying nitrate and Cr(VI) concentrations. Methanol was supplied at C/N (mg methanol/mg NO3--N) ratio of 1.33. In the absence of Cr(VI), almost complete denitrification of 50mg/L NO3--N was obtained and the methanol requirement (3.60±0.9mg COD/(mg NO3--N)) for heterotrophic denitrifiers, was quite close to the theoretical value (3.7mg COD/(mg NO3--N)). Around 54% of the influent nitrate was denitrified by heterotrophs and the rest (56%) was denitrified by autotrophic sulfur oxidizers. The effluent sulfate averaged around 200mg/L, which was below than the theoretical sulfate concentration if autotrophic denitrification process was used alone. Autotrophic denitrification activity completely ceased at 5mg/L Cr(VI), but heterotrophic denitrification did not show any inhibition. Almost complete chromate and nitrate reduction was observed at 1mg/L Cr(VI). MBR was operated for around 200days and a weekly physical membrane cleaning was enough at a flux of 15 LMH.

Biosolubilisation of Metals and Metalloids

The solubilisation of metals and metalloids is catalysed by a variety of microorganisms in natural and engineered environments. Biosolubilisation has a number of undesired implications, such as the generation of acid mine drainage and the formation of acid sulfate soils, which have harmful environmental impacts. Biosolubilisation also contributes to the corrosion of man-made structures causing significant economic losses. On the other hand biosolubilisation has been harnessed by the mining industry to recover valuable metals and uranium from low-grade ores and concentrates in large scale. This allows the utilisation of ores the processing of which would not be economically feasible through traditional mining methods. Biosolubilisation holds also potential for the recovery of resources from waste and clean-up of metal contaminated environments. This chapter reviews the role that microorganisms have in the solubilisation of various metals and metalloids, the mechanisms through which biosolubilisation occurs and microbial groups mediating the solubilisation. The environmental implications and industrial applications of biosolubilisation are also discussed. Microorganisms can catalyse biosolubilisation through oxidative and reductive dissolution, mediated by the oxidation and reduction of ferrous and ferric iron, respectively. Moreover, biosolubilisation can be achieved through the production of biogenic acids, alkali and ligands, such as cyanide, thiosulfate, organic acids and iodide. Mechanisms contributing to microbially influenced corrosion of metallic iron and steel include differential aeration cells, galvanic cells, attack by microbial oxidants, acids, sulfides and other metabolites, cathodic depolarisation and direct microbial extraction of electrons from steel. A wide range of microorganisms are able to facilitate solubilisation reactions, including bacteria, archaea and eukaryotes. Bioleaching has been explored for recovering metals from e.g. a variety of sulfide ores, metallurgical waste, electronic scrap, sludge from municipal and industrial wastewater treatment, municipal solid waste incineration fly ash and contaminated sites. Large-scale biosolubilisation has been mainly used for copper-, cobalt-, nickel-, zinc-, uranium- and gold-containing sulfidic ores through oxidative bioleaching, whereas reductive bioleaching is yet to be implemented at industrial scale.

Bioprecipitation of Metals and Metalloids

Heavy metals are toxic, carcinogenic and unlike organic contaminants are not biodegradable, and thus accumulate in organisms. Approximately 60% of the polluted areas in the world, suffer from the harmful effects of metals including Cd, Ni, Cu, Pb, Zn, Hg and Co. Mining, fertilizer, tanneries, paper, batteries and electroplating industries are the main sources of heavy metal containing waters. For example, in China, the annual amount of heavy metal containing electroplating industry wastewater has exceeded 4 billion tons. Up to 1000 mg/kg heavy metal concentration in sediments has been reported due to repeated discharges. We reviewed the sources of heavy metal containing water and metal precipitation techniques including metal sulfide, hydroxide, ferrihydrite, geothite, jarosite as well as schwertmannite precipitation. Metal sulfide precipitation relies on the biological generation of H2S and near complete metal removal is possible with both organic (i.e. ethanol) and inorganic (i.e. hydrogen) electron donors. The utilization of soluble electron donors provides high rate and dense metal precipitates with metal recovery of over 80% (usually 100%). Additionally, metals can be recovered separately as various metal sulfides by adjusting pH. Biological oxidation/reduction processes facilitate the formation of insoluble metal precipitates for uranium (U6+ to U4+); chromium (Cr6+ to Cr3+) or iron (Fe2+ to Fe3+). The major points extracted from the study are: (1) metal sulfide precipitation is fast, results in low residual metal concentrations and allows for selective recovery of various metals with a wide variety of different reactor configurations, (2) high rate biological metal recovery is possible with cultures which use metals as electron acceptors which eliminates the drawbacks such as chemical costs and huge sludge volume production in chemical reduction, (3) animal manure, leaf mulch, sawdust, wood chips, sewage sludge, cellulose could be used in passive treatment systems and therefore operational costs could be optimized, (4) some heavy metals can be precipitated through biological oxidation (i.e. Fe2+ to Fe3+) and (5) possible iron precipitates include hematite (Fe2O3); geothite (FeOOH); ferric hydroxide Fe(OH)3; jarosite Fe3(SO4)2(OH)6; schwertmannite Fe16O16(SO4)2(OH)12.n(H2O) and scorodite (FeAsO4.2H2O).

Sequential Precipitation of Heavy Metals Using Sulfide-Laden Bioreactor Effluent in a pH Controlled System

ABSTRACT Sulfide produced in an ethanol fed anaerobic baffled reactor, was utilized to precipitate metals separately in a pH controlled system. Sulfide produced in the reactor (780±27 mg/L S2–) was transported with N2 gas to the metal precipitation chamber at pH 2.5 to precipitate Cu2+ separately from Fe2+. Cu precipitation was completed at 98% efficiency within 5 min. The remaining Fe2+ was then precipitated at elevated pHs by mixing the reactor effluent. XRD patterns of the precipitates showed that copper was precipitated in the form of CuS with a particle size of 14–22 nm whereas iron was precipitated as FeS with 32-85 nm particle size.

An Approach for Sustainable Management of The Balikligol Lakes, Turkey

The Balikligol Lakes in Sanliurfa, Turkey (Lake Ayn-i Zeliha and Lake Halil-ur Rahman) are freshwater lakes, which possess not only environmental value but also touristic value due to their natural aquarium look and their historical and sacred status in the past and present. The fish deaths have been encountered in these lakes from time to time. Deteriorating water quality can harm the health of the fish in the water. Therefore, the water quality in both the lakes needs to be monitored and proper management strategies should be developed. The pollution in the lakes exceeding the acceptable levels endangers the sustainable management of the biodiversity. With the advent of the measurement technology, it is now possible to set-up permanent monitoring and management systems in a cost-effective way. The objective of this study is to establish an online water quality monitoring and management system to protect the water quality in the Balikligol Lakes. In all eight measuring stations were selected at random for keeping track of the pollution levels. The applicable system units were determined. Each station will make predetermined measurements and send data to the Environmental Administration Center of Sanliurfa Governorship via wireless internet connection. The closeness of these Lakes to the city center makes the wireless internet access available. Moreover, the measuring station locations were geocoded on a digital map, and information tables for each station linked to the digital map using Geographic Information System (GIS) software. The basic approach of the system is that the collected data at the Environmental Administration Center will be analyzed with the support of GIS enabled software, and the action plan will be determined according to the guidelines established for the surface water quality standards. This whole process will create a management system for “The Balikligol Lakes” which receives real-time data continuously and respond promptly according to the guideline.