Impact of ionic composition of groundwater on oxidative iron precipitation

In the Netherlands, approximately 60% of drinking water is obtained from (generally anaerobic) groundwater. This requires aeration followed by rapid sand filtration (RSF) to remove iron, manganese, arsenic and ammonium. The mechanisms responsible for their removal or the clogging of RSFs and breakthrough of colloidal iron or manganese oxides have not been fully elucidated in previous studies. In this work, factors affecting iron precipitation have been studied in an aerated, continuously stirred bench scale jar experiments to simulate the supernatant layer of submerged sand filters. Time series data of filtered iron concentration and precipitate size have been collected in experiments with synthetic groundwater with and without P, Si, HCO3 and Ca at neutral pH. We show that precipitate growth is not influenced by different HCO3 concentrations but is reduced drastically when NOM is present and, to lesser extent, Si as well. The addition of P appears to hamper precipitate growth to some extent, but requires more research. We also observe that addition of Ca improves the growth of Fe precipitates in the presence of Si and especially NOM. These results have great significance for improving Fe removal efficiency of groundwater treatment plants in Netherlands and abroad.

Comparative Analysis of Aminopolycarboxylate Chelants Improves Iron Control in Acidizing Operations

Aminopolycarboxylate-based chelants are used to control iron precipitation during acidizing operations by interacting directly with the iron, resulting in water-soluble complexes. This paper highlights that, in order to improve the effectiveness of iron control during acidizing operations, the type and the concentration of the chelants should be based on the formation properties and the well characteristics by comparing the cheltors’ performance as iron-control agents at different temperatures and pH environments with different levels of iron concentrations and chelant to iron molar ratios in acid (HCl). This study also addresses the interactions between the tested iron-control additives and acid, as well as the performance of the chelants in carbonate cores. Laboratory experiments were conducted to investigate the performance of nitrilotriacetic acid (NTA), glutamic acid, N, N-diacetic acid (GLDA), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine-tetraacetic acid (EDTA), and hydroxyethylethylenediaminetriacetic acid (HEDTA) as iron control additives in 5 wt% HCl at pH values 0 to 4.5 to simulate carbonate acidizing at temperatures of 70 to 300°F, and initial iron concentrations of 2000 ppm. The performance of NTA and EDTA was also compared at higher initial iron concentration (4000 ppm). This work also quantified the effects of acid additives such as corrosion inhibitor and non-ionic surfactant on the chelation performance. Coreflood experiments using carbonate cores in acid with chelant helped determine its influence on permeability. Testing chelant-to-acid molar ratios of 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, and 2:1 relative to iron concentration yielded optimal values. Additional tests monitored iron precipitation in solution using an inductively coupled argon plasma (ICAP) emission spectroscopy. Precipitates were filtered and analyzed using X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Without chelant, at 70°F and 2000 ppm initial iron concentration, precipitation began at pH 1.45 and completed by pH 2.42. At 150 and 210°F, iron precipitated at pH 0.68 and 0.3 and completed by pH 1.3 and 1, respectively. At 70°F, NTA showed a minimum of 98% chelation at pH 4.3; however, its performance declined at 150°F to 74% chelation at pH 4.24, and at 210°F to 53% chelation at pH 4.0. Although DTPA dissolves completely in live acid, precipitations occurred at partially spent acid. At pH 0.15, SEM-EDS showed that the precipitate contains as much as 13 wt% iron. Thus, DTPA is not a suitable iron-control agent. HEDTA showed a 90% chelation at 210°F and pH 4.8. GLDA's performance declined to less than 50% at 150°F. At higher iron concentrations of 4000 ppm, Na3NTA kept all iron in solution in a 5 wt% HCl up to pH 4.0 at 70°F and its performance declined to a minimum of 97% at pH 4.7 at same temperature. At 150°F, and 210°F, Na3NTA started to gradually decline at pH values greater than 3.9, and 3.5, respectively. The minimum chelation reached by NTA was 91% at pH 4.4, at 150°F, and 73% at pH 4 at 210°F. Upon comparing the NTA's results at high iron concentrations to the popular EDTA, Na4EDTA at 1-to-1 mole ratio with iron exceeded its maximum solubility in 5 wt% HCl and precipitated in the original solution. For NTA, a molar ratio of 1.4:1 is optimal at 70 and 150°F, showing chelation performance of 95% and 94%, respectively, while a molar ratio of 1.5:1 is optimal at 210°F, showing a chelation performance of 87%. This study's results improve field operations by identifying NTA and HEDTA as having the best iron-control chelation performance of the five additives tested, thus reducing guesswork and streamlining production. The work also provided recommendations for choosing the best type of iron-control agent based on solubility and coreflood analysis. The results can be used to design more efficient acidizing fluids. This work won second place in the Masters division of the 2020 Gulf Coast Regional Student Paper Contest, April 2020.

Improvement of Solar Photo-Fenton by Extracts of Amazonian Fruits for the Degradation of Pharmaceuticals in Municipal Wastewater

Extracts of copoazu (Theobroma gramdiflorum), canangucha (Maurita Flexuosa), and coffee (coffea arabica) were explored as enhancers of the solar photo-Fenton process to eliminate acetaminophen, sulfamethoxazole, carbamazepine, and diclofenac. The process performance, at pH 6.2 and 5 mg L− 1 of iron without the extracts, has a very limited action (~ 35% of the pollutants degradation at 90 min of treatment) due to the iron precipitation. Interestingly, the extracts addition increased the soluble iron forms but only copoazu extract improved the pollutants degradation (~ 95% of elimination at 90 min of the process action). The copoazu extract acted as a natural complexing agent, maintaining the soluble iron up to 2 mg L− 1 even after 90 min, and consequently enhancing the pollutants degradation. The effect of copoazu extract dose on the process performance was also assessed, finding that an iron: copoazu extract molar ratio equal to 1:0.16 was the most favorable condition. Then, the process improved by copoazu extract was applied to municipal wastewater. Remarkably, the process led to ~ 90% of total pharmaceuticals degradation at 20 min of treatment. This work evidences the feasibility of amazonian fruits extracts to improve the solar photo-Fenton process to degrade pharmaceuticals in aqueous matrices at near-neutral pH.