UAV-based RGB and TIR imaging for geothermal monitoring: a case study at Kestanbol geothermal field, Northwestern Turkey.

Kestanbol is one of the most important geothermal fields in NW Turkey. This study conducted the first-ever surveys over a 10 ha reach of the Kestanbol geothermal field using an unmanned aerial vehicle (UAV) equipped with visible (RGB) and thermal infrared (TIR) cameras. Low-altitude flights below 40 m above the ground were operated above the Kestanbol geothermal field. Approximately 3500 RGB and TIR images were captured using the UAV. We recorded high-resolution RGB and TIR data of the Kestanbol geothermal field and applied the structure from motion (SfM) algorithm to identify the distribution of geothermal springs and seeps. The Kestanbol geothermal field was monitored to create a georeferenced RGB orthophoto, RGB 3D surface model, thermal anomaly map, and digital surface model (DSM) of the area with centimeter-level accuracy. In the TIR orthophoto, the surface temperature in the geothermal field was found to be between 15 and 75 °C. All the thermal anomalies revealed by the survey were verified by field observations. The geothermal springs and seeps were parallel to the NE-SW regional tectonic trends. The results of this study demonstrate an effective technique for monitoring and assessing geothermal water using UAV-based RGB and TIR imaging and provide an accurate basis for geothermal development projects. RGB and TIR imaging using UAVs are considered promising methods for improving the assessment of the effects of geothermal water on the environment.

Metal removal from acid mine lake using ultrasound-assisted modified fly ash at different frequencies.

Acid mine drainage/lakes (AMD/AMLs) have a low pH with high concentrations of metals and sulfate and have been a major environmental problem in the Can Coal Basin, in northwestern Turkey. In this study, metal removal from Hayirtepe AML by using fly ash (FA) and modified fly ash (MFA) was investigated in batch experiments. The effects of various parameters, such as ultrasonic frequency, dose, contact time, pH, and temperature, were examined to determine the optimum conditions for metal removal from AML. This study also focused on the application of ultrasound-assisted modification by using a 20-kHz ultrasonic probe and a 40-kHz ultrasonic bath to increase the FA surface and improve its adsorption capacity for metal removal. FA modification at 20 kHz showed better results than that at 40 kHz because it produced rapid bubble implosion with acoustic cavitation. The FA and MFAs selectivity for metal removal was 98%-99% for Fe, 96%-99% for Al, 94%-97% for Zn, 90%-95% for Co, 88%-94% for Ni, 77%-92% for Cu, and 74%-92% for Mn according to the determined optimum parameters. Scanning electron microscopy coupled with the energy-dispersive X-ray spectroscopy (SEM/EDX) and X-ray diffractometry of the solid residues (SRs) identified gypsum as a new mineral phase from sulfate removal from the AML. Inductively coupled plasma mass spectrometry and SEM/EDX analysis revealed that the metal content of the SRs increased. The adsorption process fitted the pseudo-second order kinetic model. Thermodynamic parameters showed that the process was exothermic and the randomness of the solid/solution interface increased during adsorption. Reuse experiments indicated that the MFAs were reused more effectively for metal removal from AML compared with the FA. This study showed that the use of MFAs with a high adsorption capacity and surface area is economic and efficient for metal removal from AML.

Generation of Acid Mine Lakes Associated with Abandoned Coal Mines in Northwest Turkey.

A total of five acid mine lakes (AMLs) located in northwest Turkey were investigated using combined isotope, molecular, and geochemical techniques to identify geochemical processes controlling and promoting acid formation. All of the investigated lakes showed typical characteristics of an AML with low pH (2.59-3.79) and high electrical conductivity values (1040-6430 µS/cm), in addition to high sulfate (594-5370 mg/l) and metal (aluminum [Al], iron [Fe], manganese [Mn], nickel [Ni], and zinc [Zn]) concentrations. Geochemical and isotope results showed that the acid-generation mechanism and source of sulfate in the lakes can change and depends on the age of the lakes. In the relatively older lakes (AMLs 1 through 3), biogeochemical Fe cycles seem to be the dominant process controlling metal concentration and pH of the water unlike in the younger lakes (AMLs 4 and 5). Bacterial species determined in an older lake (AML 2) indicate that biological oxidation and reduction of Fe and S are the dominant processes in the lakes. Furthermore, O and S isotopes of sulfate indicate that sulfate in the older mine lakes may be a product of much more complex oxidation/dissolution reactions. However, the major source of sulfate in the younger mine lakes is in situ pyrite oxidation catalyzed by Fe(III) produced by way of oxidation of Fe(II). Consistent with this, insignificant fractionation between δ(34) [Formula: see text] and δ(34) [Formula: see text] values indicated that the oxidation of pyrite, along with dissolution and precipitation reactions of Fe(III) minerals, is the main reason for acid formation in the region. Overall, the results showed that acid generation during early stage formation of an AML associated with pyrite-rich mine waste is primarily controlled by the oxidation of pyrite with Fe cycles becoming the dominant processes regulating pH and metal cycles in the later stages of mine lake development.