A Bibliometric Analysis of Geosmin Removal and Treatment Technologies using Web of Science Database and VOSviewer.

In the last few years, the presence of geosmin (GEO) in water bodies has caused serious problems related to water consumption by the population. Many studies focus on its occurrence and detection, but little is discussed about the technologies for treatment and removal of this contaminant. In this way, the present work aims to present a bibliographic search and a bibliometric analysis carried out in the Web of Science database and in VOSviewer software about geosmin remediation, in the last 10 years. 100 articles were found, of which only one, from 2021, was a review. It was possible to assess that the subject has gained greater notoriety in the last 7 years, since the year 2016 marked the increase of publications on the subject, as well as an increasing number of citations. Among the most published countries is the People's Republic of China, with 53% of publications. Bibliometric analysis showed that GEO is directly related to 2-methylisoborneol (2-MIB), since both occur simultaneously in water bodies. In addition, it was possible to identify that adsorptive processes are the most used in the removal of these contaminants, followed by advanced oxidative processes and biological processes, in that order.

Study of the recovery of phosphorus from struvite precipitation in supernatant line from anaerobic digesters of sludge.

The goal of this work was to study the effective recovery of phosphorus from the supernatant of anaerobic digestion of sewage sludge by precipitation as struvite. The formation of struvite is envisioned as a promising process for nutrient removal and subsequent recovery, thus providing a strong incentive for its implementation, since the sewage is a renewable source of phosphorus. Struvite precipitation was obtained by controlled addition of Mg(OH)2 or MgCl2. We evaluated the removal of ammonia and phosphate under equimolar conditions of magnesium and magnesium stoichiometric excess of 100 to 200% relative to the limiting reagent, under a stirring speed of 300 rpm at pH 8, 9 and 10. The best condition was MgCl2 in 1:1 molar ratio to phosphate, considering the stoichiometric ratio [PO4(3-)]:[NH4(+)] of 0.13 (presented by raw sample). The results show the best cost-benefit ratio, removal of phosphate of 90.6% and ammonium removal of 29%, resulting in 23 mg l(-1) PO4(3-) and 265 mg l(-1) NH4(+) concentration in effluent.

Study of solar photo-Fenton system applied to removal of phenol from water.

This study evaluated the use of a Fenton's reaction in a falling film solar reactor (FFR), as a possible advanced oxidation process for the mineralization of the organic compound phenol in water. Preliminary tests were carried out to evaluate phenol degradation by photolysis and to select the optimal residence time in which to carry out the process using a solar photo-Fenton system. The variables studied were the initial phenol concentration (100 to 300 mg L(-1)), the [Phenol]:[H2O2] mass ratio (1.0 to 2.0) and the [H2O2]/[Fe2+] molar ratio (5 to 10). Phenol degradation of 99% and chemical oxygen demand (COD) reduction of 97% were obtained under the following reaction conditions: phenol concentration=200 mg L(-1), mass ratio [Phenol]:[H2O2]=1.5 and molar ratio [H2O2]/[Fe2+]=7.5. Overall mineralization was achieved using the solar photo-Fenton process to destroy phenol and COD. The solar photo-Fenton process using a FFR appears to be a viable method for removing phenols in wastewaters on an industrial scale.

Removal of boron from oilfield wastewater via adsorption with synthetic layered double hydroxides.

Hydrotalcite is a layered double hydroxide (LDH) consisting of brucite-like sheets of metal ions (Mg-Al). In this work, hydrotalcites were synthesized, and boron removal from oilfield wastewater was evaluated. LDHs were synthesized using the co-precipitation method. The calcined products (CLDHs) were obtained by heating at 500°C and characterized using X-ray diffraction, X-ray fluorescence, thermogravimetric analysis and the specific surface area (BET). The affinity of LDHs for borate ions was evaluated for calcined and uncalcined LDHs as a function of contact time, initial pH of the oilfield wastewater (pH ∼ 9) and the LDH surface area. The tests were conducted at room temperature (approximately 25ºC). The results indicated that 10 min were needed to reach a state of equilibrium during boron removal for calcined LDHs due to the high surface area (202.3 m(2) g(-1)) regardless of the initial pH of the oilfield wastewater, which resulted from the high buffering capacity of the LDHs. The adsorption capacity increased as the adsorbents levels increased for the range studied. After treatment of the oilfield wastewater containing 30 mg L(-1) of boron with Mg-Al-CO3-LDHs, the final concentration of boron was within the discharge limit set by current Brazilian environmental legislation, which is 5 mg L(-1). Pseudo-first-order and pseudo-second-order kinetic models were tested, and the latter was found to fit the experimental data better. Isotherms for boron adsorption by CLDHs were well described using the Langmuir and Freundlich equations.

Evaluation of pH, alkalinity and temperature during air stripping process for ammonia removal from landfill leachate.

The objective of this research was to evaluate the air stripping technology for the removal of ammonia from landfill leachates. In this process, pH, temperature, airflow rate and operation time were investigated. Furthermore, the relationship between the leachate alkalinity and the ammonia removal efficiency during the process was studied. The leachate used in the tests was generated in the Gramacho Municipal Solid Waste Landfill (Rio de Janeiro State, Brazil). The best results were obtained with a temperature of 60(o)C, and they were independent of the pH value for 7 h of operation (the ammonia nitrogen removal was greater than 95%). A strong influence of the leachate alkalinity on the ammonia nitrogen removal was observed; as the alkalinity decreased, the ammonia concentration also decreased because of prior CO2 removal, which increased the pH and consequently favored the NH3 stripping. The air flow rate, in the values evaluated (73, 96 and 120 L air.h(-1).L(-1) of leachate), did not influence the results.

Phosphorus recovery from aqueous solutions using Bioclastic Granules (Lithothamnium calcareum).

Against the growing world demand for food and the possibility of recovering some nutrients, this work focused on the evaluation of the use of Bioclastic Granules (BG) from the algae Lithothamnium calcareum as sorbent material for the removal/recovery of phosphorus from aqueous solutions. The main variables that affect the sorption process, pH, initial concentration of phosphate, and GB, as well as the contact time, were evaluated. The effect of pH was very significant, obtaining the best results of PO43- removal at pH 5. In the coarser granulometric fractions (+ 106 - 150 and + 210 - 300 µm), the best removals were observed (around 75%). Regarding the initial PO43- concentration in the solutions, the highest removal (in the range of 74 to 78%) was observed in the lowest concentrations (5 to 70 mg L-1) and the best uptake (10 to 14 mg g-1) at higher concentrations (200 to 420 mg L-1). The PO43- sorption data fitted the Freundlich model well, with kF of 1.35 L mg-1 and n of 2.43. A qmax of 14.35 mg g-1 was obtained using the Langmuir model. Regarding the sorption data over time, a better fit to the pseudo-first-order kinetic model was observed, obtaining a calculated qeq of 6.56 mg g-1 and a k1 of 0.0073 min-1. The incorporation of PO43- ions in the GB structure was confirmed through the characterization results before and after the sorption experiments using X-ray fluorescence (FRX) and scanning electron microscopy (SEM) techniques.

Cadmium removal by bioclastic granules (Lithothamnium calcareum): batch and fixed-bed column systems sorption studies.

The potential of Bioclastic Granules - BG (calcium-carbonate-based material) using the algae Lithothamnium calcareum as sorbent for the removal of Cd(II) from aqueous solutions by sorption was evaluated through batch and continuous systems tests using a fixed-bed column. Sorption process variables, in particular pH (2-7), particle size (<38-300 µm), initial BG concentration (0.1-1.0 g L-1), initial Cd(II) concentrations (5-400 mg L-1) and contact time (5-240 min), were evaluated. Adsorption isotherm profiles of Cd(II) per BG were similar to an L-type, or Langmuir type, with the adsorption forming a monolayer of approximately 0.61 µm, with a qmax of 188.74 mg g-1 and kL of 0.710 L mg-1. Thomas's model considers that sorption is not limited to a chemical reaction but is controlled by mass transfer at the interface. In the present study, the obtained value of kTh was 0.895 mL h-1 mg-1, reaching a sorption capacity qo of 124.4 mg g-1. For the Yoon-Nelson model, it was possible to obtain two important parameters to describe the behavior of the column, the rate constant (kYN), obtaining a value of 0.09 h-1 and an τ of 82.12 h corresponding to the time required for sorption to occur of 50% of the solute in the rupture curve. X-ray diffraction and scanning electron microscopy analyses coupled to the X-ray dispersive energy system (SEM/EDS) of the BG after the Cd(II) ion sorption tests evidenced the formation of crystals with the prevalence of a new mineral phase (otavite).

Evaluation of the mercaptobenzothiazole degradation by combined adsorption process and Fenton reaction using iron mining residue.

The present study investigated the degradation of mercaptobenzothiazole (MBT), evaluating homogeneous and heterogeneous systems. An iron mineral residue from the desliming step of iron mining was used as a source in the Fenton-like reaction (advanced oxidation process). A granulometric analysis of the residue was performed and yielded fractions with high hematite (Fe2O3) and low quartz content in sieves from 74 to below 44 mm. In this particle size range, the hematite content from 58.9% to 67.4% and the Brunauer-Emmett-Teller area from 0.1345 to 1.3137 m2 g-1 were obtained. The zeta potential curves as a function of pH were obtained for the residue, the MBT solution and mixtures thereof. The adsorption of MBT in the residue and its degradation through the Fenton-like reaction were investigated. Adsorption tests and the Fenton-like reaction were carried out, where the MBT species and the residue are oppositely charged, yielding, respectively, 10% MBT adsorption on the surface of the residue and 100% MBT degradation by the Fenton-like reaction at pH 3, hydrogen peroxide concentration of 25 mg L-1, residue concentration of 3 g L-1, 200 rpm and 25°C, from a 100 mg L-1 MBT solution. MBT degradation was found to occur mainly by the heterogeneous Fenton-like process.