Acidic Streams Research Articles

Sulfur Reduction at Hyperthermoacidophilic Conditions with Mesophilic Anaerobic Sludge as the Inoculum.

Sulfur reduction at hyperthermoacidophilic conditions represents a promising opportunity for metal sulfide precipitation from hot acidic metallurgical streams, avoiding costly cooling down. The suitability of mesophilic anaerobic sludges as the inoculum for sulfur-reducing bioreactors operated at high temperature and low pH was explored. We examined sludges from full-scale anaerobic reactors for sulfur-reducing activity at pH 2.0–3.5 and 70 or 80 °C, with H2 as an electron donor. At pH 3.5 in batch experiments, sulfidogenesis started within 4 days, reaching up to 100–200 mg·L–1 of dissolved sulfide produced after 19–24 days, depending on the origin of the sludge. Sulfidogenesis resumed after removing H2S by flushing with nitrogen gas, indicating that sulfide was limiting the conversion. The best performing sludge was used to inoculate a 4 L gas-lift reactor fed with H2 as the electron donor, CO2 as the carbon source, and elemental sulfur as the electron acceptor. The reactor was operated in semibatch mode at a pH 3.5 and 80 °C, and stable sulfide production rates of 60–80 mg·L–1·d–1 were achieved for a period of 24 days, without formation of methane or acetate. Our results reveal the potential of mesophilic anaerobic sludges as seed material for sulfur-reducing bioprocesses operated at hyperthermoacidophilic conditions. The process needs further optimization of the volumetric sulfide production rate to gain relevance for practice.

Study of the operational parameters in the hollow fibre liquid-liquid membrane contactors process for ammonia valorisation as liquid fertiliser

The transformation of wastewater treatment plants (WWTPs) to resources recovery plants (nutrients and energy) is forcing the development of specific technologies for selective recovery. Ion-exchange and hollow fibre liquid-liquid membrane contactors (HF-LLMCs) appeared as promising technologies to reduce operation costs, at ambient temperature, on the N-recovery from main-streams of urban WWTPs. A concentrated ammonia stream (4.5 g/L), recovered from treated wastewater using zeolites and NaOH, was used to test different operational parameters on the performance of the HF-LLMC process for ammonia recovery. These tested parameters were HF-LLMC position (horizontal and vertical), HF-LLMC feed and acid streams inputs (shell and lumen), type of acid stripping solution (0.4 M H3PO4 and 0.4 M HNO3), membrane drying, flow rate for each stream (263–770 mL/min), number of steps (1 and 2) and number of membrane contactors (1 and 2 in series). The maximum ammonia recovery (>95%) was achieved by a one-step configuration using two vertical membrane contactors in series; using the shell side for feed stream and the lumen side for the acid stripping solution (HNO3); at 450 mL/min and 770 mL/min flow rates for feed and acid stripping solutions, respectively. The liquid fertiliser composition obtained was around 4.6% N (from NH4+). Additionally, the ammonia treated stream, rich in NaOH, had residual levels of NH3 (about 200 mg/L) that could be reused for the regeneration of the zeolites. This optimized HF-LLMC process allowed to recover ammonia from a tertiary treatment solution of an urban WWTP and at the same time to produce ammonium salts that could be used as liquid fertilisers in irrigation applications. Therefore, this technology promotes the circular economy concept for nutrient recovery in urban WWTPs.

Evaluation of an extreme acid-resistant sulphonamide based nanofiltration membrane for the valorisation of copper acidic effluents

The exhaustion of Cu reserves minable and processable with the available technology is forcing the hydrometallurgical copper industry to seek alternative sources. Following circular economy principles, researchers’ attention has focused on the recovery of valuable metals from the acidic waste streams generated. Nowadays, membrane technologies are being selected as the first alternative for the treatment and valorisation of such acidic waste streams. Among them, a new generation of high acidity resistance nanofiltration (NF) membranes offer the alternative for acid recovery while providing a metal-enriched stream. In this work, the extreme-acid resistant Duracid membrane was evaluated for the valorisation of different synthetic acidic waste streams from the hydrometallurgical Cu industry. These waters were characterised by a high acidity (pH 0.5–1.5) and the presence of Fe (11–14 g/L), Zn (0.7–1.4 g/L) and As (0.5–0.7 g/L), among others. Initially, the membrane was characterised by different techniques (SEM, FTIR-ATR, XPS). Experiments were performed under constant and varying permeate flux and feed water composition. Metals were effectively rejected (>90%), whereas H+ easily permeated through the membrane. The experimental results were adjusted to the Solution-Electro-Diffusion-Film (SEDF) model to determine the membrane permeances to species. Empirical mathematical equations were developed and validated to express the dependence of permeances on solution composition. Finally, the prediction capability of the SEDF model, together with the developed empirical equations for the permeances, was proposed as a tool for designing a NF unit to valorise acidic streams from the hydrometallurgical Cu industry. The model predicted gypsum scaling onto the membrane and therefore anticipated the need of applying antiscalants.

Effects of volcanic parent materials on the acid buffering capacity of forest soils on Yakushima Island, Japan

ABSTRACT Soil acidification is a natural pedogenetic process in forest ecosystems, but is accelerated by acidic deposition. Soils on Yakushima Island, in southwestern Japan, are derived from granitic bedrock and volcanic parent materials influenced by eolian dust inputs. Acid deposition and low acid-neutralizing capacity (ANC) of granite-derived soils are hypothesized to be the cause of acidic stream water that has been widely observed on Yakushima. It remains unclear, however, whether ANCs are also limited in volcanic soils, which contain weatherable minerals and have high buffering capacities. To compare acidification rates between granite-derived soils and volcanic soils, we estimated changes in ANCs between granite and volcanic parent materials and the resulting soils at a pedogenetic timescale, using the mass balance of titanium. After 7300 years of soil development following the eruption of the Kikai caldera, decreased ANCs and total base reserves were observed in both granite-derived and volcanic soils, compared to their respective parent materials. No difference in soil ANC was observed between granite and volcanic parent materials. Different cations contribute to acid neutralization in soils: decreasing ANC results primarily from the loss of Al in granite-derived soils, while acidity is neutralized by the loss of base cations from volcanic soils. In granite-derived soils, resistance to weathering and K retention in 2:1 type silicate clays limit the loss of bases while increasing the accumulation of exchangeable Al. In volcanic soil profiles, base leaching and the sorption of organic acids onto short-range order minerals can neutralize acidity, although erosion and admixing of granite or eolian dust-derived materials lead to a reduction of ANC in surface soil horizons.

Near-infrared imaging in a microfluidic channel of aqueous acid–base reactions

This paper presents a near-infrared imaging method to measure the concentrations of acid (HCl and H2SO4), base (NaOH), and produced salt (NaCl and Na2SO4) simultaneously during neutralization in a microfluidic channel. This method is based on spectral variations in the water absorption band observed in the wavelength range 1350–1600 nm. Linear correlation models using three characteristic wavelengths in the band are constructed to convert the absorbance to the concentrations. The images clearly show that at the interface between the acid and base solution streams, the concentrations decrease and salt is produced, diffusing in the transverse direction. The concentration range is 0–2 mol/L and the resolution is <0.1 mol/L. The concentrations were verified by comparison with numerical simulations and quantitative evaluation of influencing factors. From the images, the local production rates of salt were determined, which depended on the flow velocity and temperature. This study indicates the potential of the method for analyses of not only acid–base neutralizations but also other reactions, mixing, and separation between various aqueous components.

Enhanced removal of copper(II) from acidic streams using functional resins: batch and column studies

The adsorption behaviour of copper(II) ions in acidic streams using different polymeric adsorbents (Lewatit MonoPlus TP 220, Lewatit MonoPlus SR 7, Lewatit AF 5, Purolite A 830, Purolite S 984, Purolite A 400 TL, Dowex PSR 2, Dowex PSR 3) was studied, and the results were compared. The adsorbents were characterized by determination of the point of zero charge and the Fourier transform infrared spectroscopy method. The kinetic (effects of phases contact time) and equilibrium (effect of initial Cu(II) concentration) studies were also carried out. The effects of hydrochloric and nitric(V) acids on adsorption behaviour of Cu(II) were examined. The FTIR spectra after the Cu(II) adsorption were also obtained, and the mechanism of Cu(II) sorption was proposed. Of eight adsorbents, the best one was chosen and applied in further studies (column adsorption, column and batch desorption, reuse of adsorbent in cycles of sorption–desorption, selectivity in two-component solutions Pd(II)–Cu(II)). Cu(II) sorption efficiency was the highest using Lewatit MonoPlus TP 220. Its sorption is well described by the pseudo-second-order kinetic equation and the Langmuir isotherm model. Ion exchangers show also high affinity for noble metals, especially for gold(III): Au(III) > Pd(II) > Pt(IV) (the column test) from single- and two- or three-component solutions (the batch test).Graphic abstract

Polysulfone/graphene quantum dots composite anion exchange membrane for acid recovery by diffusion dialysis

The advancement in membrane-based separation technologies offers advantages over traditional ways. Recovery of acid from acidic waste stream is an important issue to be solved by greener route. Diffusion dialysis using anion exchange membranes (AEMs) is an energy-intensive and environment friendly process to be taken forward. Herein, we report the eco-friendly route for chloromethylation of polysulfone using chloromethyl ethyl ether (CMEE). Effect of chloromethyl ethyl ether concentration, reaction temperature, and reaction time are investigated to get maximum tethered chloromethyl group and high yield of product. Series of chloromethylated polysulfone membranes are prepared with different concentrations of graphene quantum dots (GQDs) followed by quaternization using trimethylamine. The prepared membranes are characterized by their water content, transport properties, and stabilities. Composite membranes show enhanced water uptake, ion exchange capacity, and mechanical stability compared to that of pristine membrane. Interestingly, to address the environmental impact of acids present in industrial waste, AEMs are employed for acid recovery from model waste at higher concentrations of acid and salt using diffusion dialysis. For prepared membranes, 35.5–47.5% acid recovery has been achieved in presence of metal ions. SCE-1.0 (1.0 wt % GQD/ QPSU) membrane shows the highest acid recovery (47.5%) among the membranes. Composite membranes suggest their potential utility in acidic effluent treatment via diffusion dialysis.

Industrial Wastewater Treatment by Nanofiltration-a Case Study on the Anodizing Industry.

The anodizing industry generates several alkaline and acidic wastewater streams often with high concentrations of heavy metals. In this study, nanofiltration (NF) was used to treat wastewater from individual baths, i.e., wastewater from color rinse, alkaline pickling rinse, acidic pickling rinse and anodizing rinse, as well as a mixture of all the wastewater streams. The experiments were carried out by using a commercial membrane (NF99HF) exhibiting pure water permeability of 10 L/(m2·h·bar). For all wastewater streams except one, pH was adjusted to bring it within the recommended pH limits of the membrane, whereby part of the heavy metals precipitated and was removed. The NF of the color rinse offered high-quality permeate (heavy metals below detection limit) and high permeability (9 L/(m2·h·bar)), whereas the nanofiltration of the alkaline pickling rinse exhibited no permeability. The NF of the acidic pickling rinse showed a permeability of 3.1–4.1 L/(m2·h·bar), but low ion rejection (7–13%). NF of the neutralized mixed wastewater, after the removal of precipitate, produced high-quality permeate with a stable permeability of 1 L/(m2·h·bar). Treatment of the mixed wastewater is therefore the best option if the water has to be discharged. If the water has to be reused, the permeate conductivity in the color rinse and anodizing rinse baths have been reduced significantly, so the treatment of these streams may then be a better option.

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We describe a new periphytic eunotioid species, Eunotia itacueretabaensis sp. nov., found in a second order stream in Vila Velha State Park in Southern Brazil. We analyzed both size variation and external and internal morphological features under light and scanning electron microscopy. The new species is mainly characterized by large size and morphology variation, and by the presence of three slight undulations in the dorsal margin of the valve in larger individuals, while smaller ones feature a single undulation, making it distinct from other known species. Its morphology is compared with similar species, as Eunotia pectinalis and Eunotia silvae. Eunotia itacueretabaensis was found attached to submerged tree trunks and forming macroscopic colonies in a fast flow acidic stream. Besides representing a new addition to the present database of Brazilian diatom flora, our study highlights the important role of environmental conservation areas, which serve as important repositories for unexplored species.

Electrochemically Induced Precipitation Enables Fresh Urine Stabilization and Facilitates Source Separation.

Source separation of urine can enable nutrient recycling, facilitate wastewater management, and conserve water. Without stabilization of the urine, urea is quickly hydrolyzed into ammonia and (bi)carbonate, causing nutrient loss, clogging of collection systems, ammonia volatilization, and odor nuisance. In this study, electrochemically induced precipitation and stabilization of fresh urine was successfully demonstrated. By recirculating the urine over the cathodic compartment of an electrochemical cell, the pH was increased due to the production of hydroxyl ions at the cathode. The pH increased to 11-12, decreasing calcium and magnesium concentrations by >80%, and minimizing scaling and clogging during downstream processing. At pH 11, urine could be stabilized for one week, while an increase to pH 12 allowed urine storage without urea hydrolysis for >18 months. By a smart selection of membranes [anion exchange membrane (AEM) with a cation exchange membrane (CEM) or a bipolar membrane (BPM)], no chemical input was required in the electrochemical cell and an acidic stream was produced that can be used to periodically rinse the electrochemical cell and toilet. On-site electrochemical treatment, close to the toilet, is a promising new concept to minimize clogging in collection systems by forcing controlled precipitation and to inhibit urea hydrolysis during storage until further treatment in more centralized nutrient recovery plants.

Microbiome for the Electrosynthesis of Chemicals from Carbon Dioxide.

The price for renewable electricity is rapidly decreasing, and the availability of such energy is expected to increase in the coming years. This is a welcomed outcome considering that mitigation of climate disruption due to the use of fossil carbon is reaching a critical stage. However, the economy will remain dependent on carbon-based chemicals and the problem of electricity storage persists. Therefore, the development of electrosynthetic processes that convert electricity and CO2 into chemicals and energy dense fuels, perhaps even food, would be desirable. Electrochemistry has been applied to the manufacture of many valuable products and at a large industrial scale, but it is difficult to produce multicarbon chemicals from CO2 by chemistry alone. Being that the biological world possesses expertise at the construction of C-C bonds, it is being examined in conjunction with electrochemistry to discover new ways of synthesizing chemicals from electricity and CO2. One approach is microbial electrosynthesis. This Account describes the development of a microbial electrosynthesis system by the authors. A biocathode consisting of a carbon-based electrode and a microbial community produced short chain fatty acids, primarily acetate. The device works by electrolysis of water, but microbes facilitate electron transfer from the cathode while reducing CO2 by the Wood-Ljungdahl pathway possessed by an Acetobacterium sp. While this acetogenic microorganism dominates the microbiome growing on the cathode surface, 13 total species of microbes overall were ecologically selected on the cathode and genomes for each have been assembled. The combined species may contribute to the stability of the microbiome, a common feature of naturally selected microbial communities. The microbial electrosynthesis system was demonstrated to operate continuously at a cathode for more than 2 years and could also be used with intermittent power, thus demonstrating the stability of the microbiome living at the cathode. In addition to the description of reactor design and startup procedures, the possible mechanisms of electron transfer are described in this Account. While mysteries remain to be solved, much evidence indicates that the microbiome may facilitate electron transfer by supplying catalyst(s) external to the bacterial cells and onto the cathode surface. This may be in the form of a hydrogen-producing catalyst that enhances hydrogen generation by an inert carbon-based electrode. Through the enrichment of the electrosynthetic microbiome along with several modifications in reactor design and operation, the productivity and efficiency were improved. In addition to the intrinsic value of the current products, coupling the process with a secondary stage might be used to produce more valuable products from the acetic acid stream such as lipids, biocrude oil, or higher value food supplements. Alternatively, additional work on the mechanism of electron transfer, reactor design/operation, and modification of the microbes through synthetic biology, particularly to enhance carbon efficiency into higher value chemicals, are the needed next steps to advance microbial electrosynthesis so that it may be used to transform renewable electrons and CO2 directly into products and help solve the problem of climate disruption.

In stream dynamics of acid mine drainage and untreated sewage

Both acid mine drainage (AMD) and untreated sewage are serious water quality issues faced by poor, rural communities both within the United States and worldwide. In Appalachia, it is common for these water quality issues to coincide. The aim of this study was to investigate the interaction between AMD and untreated sewage in stream. The study area, Murray City, Ohio, was conflicted, blocking construction of a mine water treatment system to maintain sewage ‘treatment’ by the AMD. Data collected over 5 months from Snow Fork Creek in Murray City, Ohio, show that during low flow, high net acidity portions of a water year, the acidity is sufficient to limit fecal indicator bacteria populations below regulatory limits. During high flow, low net acidity portions of the water year, bacterial populations thrive above the regulatory limits until a point where dilution by water of good quality leads to a decrease in fecal indicator bacteria concentrations to near the regulatory limit of 126 CFU/100 mL for primary contact recreation. This study shows that AMD limits the survival of fecal indicator bacteria and suggests that traditional fecal indicator bacteria are insufficient for detecting untreated sewage in acidic streams despite both visual and olfactory evidence.

Comparison of acid-resistant ceramic and polymeric nanofiltration membranes for acid mine waters treatment

Acid-resistant ceramic and polymeric nanofiltration (NF) membranes have been identified as relevant materials for sustainable management of acidic streams. NF properties such as a high passage of single-charged ions and high rejection of multi-charged ions make NF membranes suitable for acid recovery and metal concentration. In this work, the performance of two acid-resistant membranes: TiO2 ceramic and MPF–34 (proprietary layer) was tested with solutions mimicking acidic mine waters. Model solutions were composed by Al(III), Fe(III), Ca(II), Cu(II), Zn(II) and rare earth elements (REEs(III)) such as La(III), Dy(III), Sm(III), Nd(III), Pr(III) and Yb(III). The effect of acidity (from pH 1.5 to 1.0), Al(III) (from 0.6 to 1.8 g/L) and Fe(III) (from 0.5 to 2.1 g/L) concentrations was studied. Both membranes allowed the transport of H+ (negative rejections were obtained), but exhibited differences related to the metallic ions transport. While MPF–34 presented metal rejections around 80% and independent on the concentration of the major components (Al(III) and Fe(III)), the TiO2 membrane provided a sequence of rejection values from 5 to 30%, with highest values for trivalent transition metals. These differences in the sequence of rejections suggested that the chemical properties of the TiO2 layer played a relevant role, and that they could only be explained by dielectric effects. From the observed rejections, it was estimated that MPF–34 provided concentration factors for metals up to 4.2 and <1 for the H2SO4.

Enhancing Bioremediation Potential of Pseudomonas putida by Developing Its Acid Stress Tolerance With Glutamate Decarboxylase Dependent System and Global Regulator of Extreme Radiation Resistance.

The extensive use of acids in a variety of manufacturing industries results in the increase of discharged acidic waste stream into the environment. Such co-pollution of acids and other organic pollutants limits the biodegradation capability of neutrophilic degraders. With high-throughput genetic techniques, we aim to improve the acid tolerance of a pollutant-degrading bacterium, Pseudomonas putida S16 by genetically engineering it with the glutamate decarboxylase (GAD)-dependent system and the global regulator (IrrE) of extreme radiation resistance. The engineered strains holding either GAD system or irrE regulator could grow under pH 4.5, compared to the wild type. They could also degrade over 90% of a selected pollutant (benzoate or nicotine) under pH 5.0 in 48 h, while no biodegradation was detected with the wild type under the same conditions. We conclude that acid stress tolerance by the possession of the GAD system or IrrE regulator in pollutant-degrading bacteria would be a promising approach to enhance their viability and biodegrading activities in bioremediation of acidic wastes.

In Situ Photophysical Characterization of π-Conjugated Oligopeptides Assembled via Continuous Flow Processing.

Bioinspired materials have been developed with the aim of harnessing natural self-assembly for precisely engineered functionality. Microfluidics is poised to play a key role in the directed assembly of advanced materials with ordered nano and mesoscale features. More importantly, there is a strong need for understanding the kinetics of continuous assembly processes. In this work, we describe a continuous microfluidic system for the assembly and alignment of synthetic oligopeptides with π-conjugated cores using a three-dimensional (3D) flow focusing of inlet reactant streams. This system facilitates in situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM), which can be used in unprecedented capacity to characterize the integrity of peptides during the assembly process. To achieve continuous assembly, we integrate chevron patterns in the ceiling and floor of the microdevice to generate a 3D-focused sheath flow of the reactant peptide. Consequently, the peptide stream is directed toward an acidic triggering stream in a cross-slot geometry which mediates assembly into higher-order fiber-like structures. Using this approach, the focused peptide stream is assembled using a planar extensional flow, which ensures high degrees of microstructural alignment within the assembled material. We demonstrate the efficacy of this approach using three different synthetic oligopeptides, and in all cases, we observe the efficient and continuous assembly of oligopeptides. In addition, finite element simulations are used to guide device design and to validate 3D focusing. Overall, this approach presents an efficient and effective method for the continuous assembly and alignment of ordered materials using microfluidics.

Integration of selectrodialysis and solvent-impregnated resins for Zn(II) and Cu(II) recovery from hydrometallurgy effluents containing As(V)

The main challenge for copper smelters is to ensure product quality under the constant increase in impurities (As, Se, Mo, Co, Zn, Sb, and Pb) in copper ores that has occurred over the years. The presence of toxic elements, such as As(V), in acidic streams rich Cu(II) and Zn(II) (pH 2.0–2.5) limits the valorisation of both metals. In this study, a novel combination of the following two ion-exchange-based processes were proposed: i) membrane selectrodialysis (SED) for the selective separation of Zn(II)/Cu(II) from As(V) and ii) solvent-impregnated ion-exchange (IX) resins for the selective separation of Zn(II) from Cu(II). The selective separation of As(V), which is present in solution as H3AsO4/H2AsO4–, is achieved using a combination of monocharge and non-monocharge selective cation-exchange membranes to avoid the co-precipitation of As(V) when IX resins are used for Cu(II)/Zn(II) recovery. This combination of processes represents the novelty of the present study since it could be used in hydrometallurgical industries to remove As(V) and, at the same time, to valorize two value-added metals [Cu(II) and Zn(II)]. At the moment, only single-stage processes have been proposed. Using SED, a Cu(II)/Zn(II)-rich stream [97 ± 2% Cu(II) and 82 ± 3% Zn(II)] was obtained, and 60 ± 4% of As(V) was removed from the initial feed stream. Then, the separation of Zn(II) from Cu(II) was proposed using Lewatit VP OC 1026 resin at pH = 2.2 and 4.3, respectively. In this IX resin process, it was possible to recover 70 ± 3% of Zn(II) and 98 ± 2% of Cu(II) and to concentrate Zn(II) and Cu(II) around 30- and 23-times, respectively.

A split pH direct liquid fuel cell powered by propanol or glycerol

A split pH fuel cell was constructed using an alkaline fuel stream containing NaOH and an alcohol fuel (glycerol, 1-propanol, or 2-propanol) with an acidic oxidant stream containing H2SO4 and 3% H2O2; the electrodes were Pd black anode and Pt black or carbon black cathode separated by a cation exchange membrane with Na+ substituted for H+. The split pH environment improves the thermodynamics of the fuel cell by creating a large potential difference between electrodes, and it provides improved kinetics by lowering the pH of the anode to optimum conditions for alcohol oxidation. When the fuel cell was constructed with a carbon black cathode, significant performance was observed, with maximum power density as high as 115 mW cm−2 for 1-propanol, 105 for glycerol, and 101 for 2-propanol. When the cathode was constructed with Pt black, the power densities increased as high as 275 mW cm−2 for glycerol, 241 for 1-propanol, and 228 for 2-propanol. This performance with Pt is the highest to our knowledge for these fuels in the open literature.

Stabilization of furanics to cyclic ketone building blocks in the vapor phase

Furanics are produced in high abundance from the decomposition of biomass. The thermal and chemical instability of these species leads to the formation of humins upon condensation. The ring rearrangement of furfural to form 2-cyclopentenone and cyclopentanone is known to occur in the condensed aqueous phase, but this requires operation in condensed acidic media where humin formation readily occurs. High hydrogen pressures are typically used to offset rapid polymerization reactions, limiting the yields of stable unsaturated products that result. Here we report that furfural can be selectively converted to 2-cyclopentenone and cyclopentanone in a single step over supported TiO2 catalysts with both model compounds and real biomass-derived streams in the vapor phase. Selectivity for ring rearrangement vs. CO cleavage over TiO2 supported Ru and Pd catalysts can be tuned by manipulating the water partial pressure. The formation of these products in the absence of a condensed acidic stream also enables the tuning of reaction environments to favor the selective formation of unsaturated ketones, which could be valuable diolefin precursors. The incorporation of a TiO2 support in the catalysts tested leads to the suppression of CC hydrogenolysis/decarbonylation and enhancement of ring rearrangement reactions. The nature of the active sites for selective CO cleavage as well as vapor phase ring rearrangement are discussed.

Hollow fiber gas membrane-based removal and recovery of ammonia from water in three different scales and types of modules

Ammonia present in many industrial process streams and effluent streams is beginning to be recovered by means of microporous hydrophobic hollow fiber-based membrane contactor devices with gas-filled pores; the process is often characterized as supported gas membrane (SGM) process. Ammonium sulfate is usually obtained in a sulfuric acid stream on the other side of the membrane. It is useful to develop a quantitative basis for the extent of ammonia removal in such devices. Unlike deoxygenation of aqueous streams in such devices, membrane resistance is quite important for ammonia transport. Ammonia transport modeling in such devices is hampered by the complexity of feed liquid flow in the shell side of commercially used devices and lack of information on membrane resistance where membrane tortuosity introduces considerable uncertainty. The approach adopted here involves studying ammonia transport with the feed solution flowing through the hollow fiber bore where the fluid mechanics is simpler than shell-side flows. Comparison of model-based predictions of overall mass transfer coefficient (ko) with experimentally observed values allows estimation of the membrane mass transfer coefficient (km). One can use such estimates of km to model the observed ammonia transport in small crossflow devices and develop an empirical guidance of the dependences of the shell side mass transfer correlations. Guided by such information and deoxygenation SGM literature, a model was developed for large modules used for ammonia recovery via SGM. Model predictions of performances of the large modules are likely to be useful for various process considerations including the effect of temperature and feed flow rate variations on ammonia removal.

Extremely acidic environment: Biogeochemical effects on algal biofilms

The biological responses of acidobiontic species to extremely acidic waters, as those related with Acid Mine Drainage (AMD) processes, are relevant not only to understand the toxicological degree of the waters as well as the mechanisms responsible for the survival and adaptation of such organisms.Therefore, the objective of this study was to evaluate the effect of acidic pH and metals in biofilms collected in two sites a lentic permanent acid pond (AP) and a temporary acid stream (AS) affected by Acid Mine Drainage (AMD), and taking as control (C), an uncontaminated site with circumneutral pH. The results showed typical conditions of AMD-contaminated waters in sites AS and AP (pH < 3 and high concentrations of Al, Cu, Fe, Mn, Pb and Zn), which are responsible for a substantial decrease in biomass and biodiversity of biofilms (with a dominance of acidobiontic species, such as Pinnularia aljustrelica and Eunotia exigua, comparing to the control site. Also expressed by low values of photosynthetic pigments and reduced amount of proteins. In addition, such extreme acidic conditions also induced biofilms’ stress, increasing antioxidant [catalase (CAT), superoxide dismutase (SOD) and biotransformation glutathione S-transferases (GSTs)] enzymes activity and also membrane damage (peroxidized lipids). However, despite the quite similar physico-chemical conditions of both AMD-contaminated sites, differences in the toxicity status between them were indirectly detected through some of the biochemical parameters [GSTs, SOD and CAT], indicating site AS has the most toxic, which fact was attributed to the higher concentrations of Pb2+ in this water. This element is recognized to be highly toxic for biota, and in such acidic conditions remains in solution, easily available to the aquatic organisms. Since pH is similar in the acid sites, the different concentrations of heavy metals in the waters might be responsible for the observed changes in the biological community at these two sites.This fact was translated in a higher capacity of this site's biofilm to cope with the negative effects of the toxicants, evidenced in a higher positive correlation with GSTs, CAT and SOD when compared to biofilms of sites AP and C.