Hexavalent chromium removal by Osage Orange

This study explores the sorption potential of Osage Orange (Maclura Pomifera) for the removal of Cr(VI) ion. The influence of contact time, solution pH, initial metal concentration, amount of biosorbent and ionic strength on the removal of Cr(VI) ion was studied. The biosorption of Cr(VI) with pulp and peel was investigated in a batch arrangement. The initial and equilibrium concentrations of Cr(VI) ions in aqueous phase were determined by spectrophotometry. The sorption process was pH and concentration dependent. The sorption of Cr(VI) ions increased with a decreasing pH until pH 2. The increase in initial Cr(VI) ions concentration in aqueous phase increased the sorption. The sorption data fitted well with the Langmuir sorption model within the concentration range studied. The observed maximum biosorption capacity by Langmuir sorption model at pH of 2 for M. Pomifera pulp was 0.92 mmol of Cr(VI)/g and for M. Pomifera peel was 0.55 mmol of Cr(VI)/g.     

Hexavalent chromium reduction by an actinobacterium Flexivirga alba ST13T in the family Dermacoccaceae

An isolated strain Flexivirga alba ST13(T) was examined for the reducing activity of hexavalent chromium (Cr(VI)). Strain ST13(T) grew in the liquid medium containing 0.33 mM Cr(VI) under aerobic cultivation, even though growth was inhibited on agar minimal media containing 0.31 mM Cr(VI). The growth in the liquid medium containing Cr(VI) at 3 mM was severely inhibited, and the concentration of Cr(VI) decreased below the detection limit within 13 days. Most of the Cr(VI) was eliminated from the liquid medium in the log phase and the stationary phase. XANES analysis of the precipitate shows the presence of Cr(OH)(3), indicating the bacterial reduction of Cr(VI) to trivalent chromium (Cr(III)). The bacterial Cr(VI) reduction was more efficient in minimal medium supplemented with molasses than with glucose. These results strongly suggest that the isolate F. alba ST13(T) is a novel actinobacterium with Cr(VI) reducing activity that is stimulated by molasses.     

Treatment of hexavalent chromium in chromite ore processing solid waste using a mixed reductant solution of ferrous sulfate and sodium dithionite

We investigated a method for delivering ferrous iron into the subsurface to enhance chemical reduction of Cr(VI) in chromite ore processing solid waste (COPSW) derived from the production of ferrochrome alloy. The COPSW is characterized by high pH (8.5-11.5) and high Cr(VI) concentrations in the solid phase (up to 550 mg kg(-1)) and dissolved phase (3-57 mg L(-1)). The dominant solid-phase minerals are forsterite (Mg2SiO4), brucite (Mg-(OH)2), and hydrocalumite [Ca4(Al, Fe)2(OH)12X x 6H2O), X = (OH)2(2-), SO4(2-), CrO4(2-)]. The method utilizes FeSO4 in combination with Na2S2O4 to inhibit oxidation and precipitation of the ferrous iron, thereby preventing well and formation clogging. Laboratory batch tests using a 0.05 M FeSO4 + 0.05 M Na2S2O4 solution indicated effective treatment of both dissolved and solid-phase Cr(VI). Contrary to treatments with FeSO4 and FeCl2 alone, the combination resulted in both complete removal of Cr(VI) from solution and sustained Fe(ll) concentrations in solution after a 24 h period. A field test involving injection of 5700 L of a 0.07 M FeSO4 + 0.07 M Na2S2O4 solution into a COPSW saturated zone (pH 11.5) indicated no well and formation clogging during injection. Examination of a core collected 0.46 m from the injection well following injection indicated effective treatment of the solid phase Cr(VI) based on analysis of water, phosphate solution, and high temperature alkaline extracts. The combined reductant solution also imparted a residual treatment capacity to the COPSW allowing for subsequent treatment of dissolved phase Cr(VI); however, dissemination of the iron in the highly alkaline environment appeared to be impeded by the inability to sufficiently lower the pH with distance from the injection well to avoid precipitation of Fe(OH)2 and likely also FeCO3. Injection of a 0.2 M FeSO4 + 0.2 M Na2S2O4 solution into another COPSW saturated zone (pH 9) indicated much more effective dissemination of the injected iron.     

混凝-动态膜深度处理印染废水

应用混凝-动态膜工艺，对印染废水的二级出水进行深度处理。通过考察单独投加不同的混凝剂对废水COD去除率的效果，确定了混凝剂投加范围；在此基础上考察不同混凝剂以及不同过滤方式对渗透通量和COD去除率的影响。研究表明，投加混凝剂能提高渗透通量，且分体式混凝-动态膜工艺的渗透通量比一体式大33％左右；但一体式混凝-动态膜工艺的COD去除率更高，硫酸铝的使用效果比聚合氯化铝好，最佳投量下COD去除率达到57％左右，能保证印染废水的达标回用。     

In situ chemical reduction of Cr(VI) in groundwater using a combination of ferrous sulfate and sodium dithionite: a field investigation

A field study was conducted to evaluate the performance of a ferrous iron based in situ redox zone for the treatment of a dissolved phase Cr(VI) plume at a former industrial site. The ferrous iron based in situ redox zone was created by injecting a blend of 0.2 M ferrous sulfate and 0.2 M sodium dithionite into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. Monitoring data collected over a period of 1020 days after more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from initial concentrations between 4 and 8 mg/L to less than 0.015 mg/L. Sustained treatment is assumed to be primarily due to the reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron (hydr)oxide solid surfaces within the treatment zone. Precipitated phases likely include FeCO3 and FeS based on saturation index considerations and SEM/EDS analysis. The detection of solid phase sulfites and thiosulfates in aquifer sediments collected from the treatment zone more than 2 years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI).     

Nitrate reduction by zerovalent iron: effects of formate, oxalate, citrate, chloride, sulfate, borate, and phosphate

Recent studies have shown that zerovalent iron (Fe0) may potentially be used as a chemical medium in permeable reactive barriers (PRBs) for groundwater nitrate remediation; however, the effects of commonly found organic and inorganic ligands in soil and sediments on nitrate reduction by Fe0 have not been well understood. A 25.0 mL nitrate solution of 20.0 mg of N L(-1) (1.43 mM nitrate) was reacted with 1.00 g of Peerless Fe0 at 200 rpm on a rotational shaker at 23 degrees C for up to 120 h in the presence of each of the organic acids (3.0 mM formic, 1.5 mM oxalic, and 1.0 mM citric acids) and inorganic acids (3.0 mM HCl, 1.5 mM H2SO4, 3.0 mM H3BO3, and 1.5 mM H3PO4). These acids provided an initial dissociable H+ concentration of 3.0 mM available for nitrate reduction reactions under conditions of final pH < 9.3. Nitrate reduction rates (pseudo-first-order) increased in the order: H3PO4 < citric acid < H3BO3 < oxalic acid < H2SO4 < formic acid < HCl, ranging from 0.00278 to 0.0913 h(-1), corresponding to surface area normalized rates ranging from 0.126 to 4.15 h(-1) m(-2) mL. Correlation analysis showed a negative linear relationship between the nitrate reduction rates for the ligands and the conditional stability constants for the soluble complexes of the ligands with Fe2+ (R2 = 0.701) or Fe3+ (R2 = 0.918) ions. This sequence of reactivity corresponds also to surface adsorption and complexation of the three organic ligands to iron oxides, which increase in the order formate < oxalate < citrate. The results are also consistent with the sequence of strength of surface complexation of the inorganic ligands to iron oxides, which increases in the order: chloride < sulfate < borate < phosphate. The blockage of reactive sites on the surface of Fe0 and its corrosion products by specific adsorption of the inner-sphere complex forming ligands (oxalate, citrate, sulfate, borate, and phosphate) may be responsible for the decreased nitrate reduction by Fe0 relative to the chloride system.     

NOM removal by adsorption and membrane filtration using heated aluminum oxide particles

Heated aluminum oxide particles (HAOPs) are a newly synthesized adsorbent with attractive properties for use in hybrid adsorption/membrane filtration systems. This study compared removal of natural organic matter (NOM) from water by adsorption onto HAOPs with that by adsorption onto powdered activated carbon (PAC) or coagulation with alum or ferric chloride (FeCl3); explored the overlap between the NOM molecules that preferentially adsorb to HAOPs and those that are removed by the more conventional approaches; and evaluated NOM removal and fouling in hybrid adsorbent/membrane systems. For equivalent molar doses of the trivalent metals, HAOPs remove more NOM, and NOM with higher SUVA254, than alum or FeCl3. Most of the HAOPs-nonadsorbable fraction of the NOM can be adsorbed by PAC; in fact, that fraction appears to be preferentially adsorbed compared to the average NOM in untreated water. Predeposition of the adsorbents on a microfiltration membrane improves system performance. For the water tested, at a flux of 100 L/m2-hr, predeposition of 11 mg/L PAC and 5 mg/L HAOPs (as Al3+) allowed the system to operate 5 times as long before the transmembrane pressure increased by 1 psi and to remove 10-20 times as much NOM as when no adsorbents were added.     

Behavior of selected pharmaceuticals in subsurface flow constructed wetlands: a pilot-scale study

Subsurface flow constructed wetlands (SSFs) constitute a wastewater treatment alternative to small communities due to the low operational cost, reduced energy consumption, and no sewage sludge production. Although much information is available about conventional water quality parameters in SSF constructed wetlands, few data are available regarding specific contaminants. In this paper, we focus on the behavior of three widely used pharmaceuticals (clofibric acid, ibuprofen, and carbamazepine) in two pilot SSF constructed wetlands planted with Phragmites australis and characterized by different water depths (i.e., 0.3 and 0.5 m). These SSFs partially treat the urban wastewater from a housing development (ca. 200 inhabitants). The three pharmaceuticals and bromide were continuously injected into the two SSFs during a period of 150-200 h, and the effluent concentration was simultaneously measured as 6 h composite samples. Their removal efficiency was calculated from the injected concentration, and the hydraulic parameters were evaluated and compared to bromide as tracer. In this regard, the behavior of clofibric acid was similar to that of bromide, and no sorption into the gravel bed occurred. On the other hand, carbamazepine showed a higher sorption than bromide and clofibric acid, which is attributable to its interaction on the gravel bed. Accordingly, the use of clofibric acid as a hydraulic tracer is proposed, taking into account its low residence time. Ibuprofen removal was 81% in the shallow SSF and 48% in the deep one. Differences in removal efficiency could be explained by the less anaerobic environment of the shallow wetland.     

In situ metal precipitation in a zinc-contaminated, aerobic sandy aquifer by means of biological sulfate reduction

The applicability of in situ metal precipitation (ISMP) based on bacterial sulfate reduction (BSR) with molasses as carbon source was tested for the immobilization of a zinc plume in an aquifer with highly unsuitable initial conditions (high Eh, low pH, low organic matter content, and low sulfate concentrations), using deep wells for substrate injection. Batch experiments revealed an optimal molasses concentration range of 1-5 g/L and demonstrated the necessity of adding a specific growth medium to the groundwater. Without this growth medium, even sulfate, nitrogen, phosphorus, and potassium addition combined with pH optimization could not trigger biological sulfate reduction. In column experiments, precipitation of ZnS(s) was induced biologically as well as chemically (by adding Na2S). In both systems, zinc concentrations dropped from about 30 mg/L to below 0.02 mg/L. After termination of substrate addition the biological system showed continuation of BSR for at least 2 months, suggesting the insensitivity of the sulfate reducing system for short stagnations of nutrient supply, whereas in the chemical system an immediate increase of Zn concentrations was observed. A pilot experiment conducted in situ at the zinc-contaminated site showed a reduction of zinc concentrations from around 40 mg/L to below 0.01 mg/L. Termination of substrate supply did not result in an immediate stagnation of the BSR process, but continuation of BSR was observed for at least 5 weeks.     

Role of aluminum speciation in the removal of disinfection byproduct precursors by a coagulation process

Humic acid (HA) was extracted and separated into different molecular weight (MW) fractions, then coagulated by aluminum chloride and polyaluminum chloride (PACl). The removal of disinfection byproduct (DBP) precursors and the aluminum speciation variation of the coagulants were investigated in detail. In particular, the role of aluminum speciation in the removal of DBP precursors was discussed. During the coagulation process, AlCl3 hydrolyzed into dominating in situ Al13 species at pH 5.5. The in situ Al13 species exhibited better removal ability for haloacetic acid (HAA) precursors than PACl. At pH 7.5, in situ hydrolyzed Al13 species of AlCl3 decomposed into dimeric Al species. In this case, preformed Al13 of PACl had a high removal ability of HAA precursors. Specially, the greatest reduction of HAA precursors with a low MW (<30 kDa) was through charge neutralization at pH 5.5, and that of HAA precursors in high MW (> 30 kDa) fractions was through adsorption at pH 7.5. Different from HAA precursors, the in situ Al13 species did not have a high removal ability of trihalomethane (THM) precursors. Therefore, PACl exhibited a better removal ability of THM precursors than AlCl3 at different pH values. In the different MW fractions, the greatest reduction of THM precursors was through charge neutralization at pH 5.5.     

Whey filtration: a review of products,application, and pretreatment with transglutaminase enzyme

In the cheese industry, whey, which is rich in lactose and proteins, is underutilized, causing adverse environmental impacts. The fractionation of its components, typically carried out through filtration membranes, faces operational challenges such as membrane fouling, significant protein loss during the process, and extended operating times. These challenges require attention and specific methods for optimization and to increase efficiency. A promising strategy to enhance industry efficiency and sustainability is the use of enzymatic pre-treatment with the enzyme transglutaminase (TGase). This enzyme plays a crucial role in protein modification, catalyzing covalent cross-links between lysine and glutamine residues, increasing the molecular weight of proteins, facilitating their retention on membranes, and contributing to the improvement of the quality of the final products. The aim of this study is to review the application of the enzyme TGase as a pretreatment in whey protein filtration. The scope involves assessing the enzyme's impact on whey protein properties and its relationship with process performance. It also aims to identify both the optimization of operational parameters and the enhancement of product characteristics. This study demonstrates that the application of TGase leads to improved performance in protein concentration, lactose permeation, and permeate flux rate during the filtration process. It also has the capacity to enhance protein solubility, viscosity, thermal stability, and protein gelation in whey. In this context, it is relevant for enhancing the characteristics of whey, thereby contributing to the production of higher quality final products in the food industry. © 2023 Society of Chemical Industry.     

Evaluating behavior of oxygen,nitrate, and sulfate during recharge and quantifying reduction rates in a contaminated aquifer

This study evaluates the biogeochemical changes that occur when recharge water comes in contact with a reduced aquifer. It specifically addresses (1) which reactions occur in situ, (2) the order in which these reactions will occur if terminal electron acceptors (TEAs) are introduced simultaneously, (3) the rates of these reactions, and (4) the roles of the aqueous and solid-phase portions of the aquifer. Recharge events of waters containing various combinations of O2, NO3, and SO4 were simulated at a shallow sandy aquifer contaminated with waste fuels and chlorinated solvents using modified push-pull tests to quantify rates. In situ rate constants for aerobic respiration (14.4 day(-1)), denitrification (5.04-7.44 day(-1)), and sulfate reduction (4.32-6.48 day(-1)) were estimated. Results show that when introduced together, NO3 and SO4 can be consumed simultaneously at similar rates. To distinguish the role of aqueous phase from that of the solid phase of the aquifer, groundwater was extracted, amended with NO3 and SO4, and monitored overtime. Results indicate that neither NO3 nor SO4 was reduced during the course of the aqueous-phase study, suggesting that NO3 and SO4 can behave conservatively in highly reduced water. It is clear that sediments and their associated microbial communities are important in driving redox reactions.     

Relative importance of charge neutralization and precipitation on coagulation of Kaolin with PACI: effect of sulfate ion

The effect of the sulfate ion on coagulation with polyaluminum chloride (PACl) was investigated by using an optical monitoring technique together with the conventional jar test procedure and electrophoretic mobility (EM) measurements. The effect of the SO4(2-)/Al ratio, dosage, and pH were examined in detail. The experimental results show that sulfate has a significantly different effect on PACl coagulation as a result of preformed hydrolysis products, where charge neutralization and precipitation play different parts in the coagulation process. The increased rate of coagulation with increasing SO4(2-)/Al ratio can be partially explained by charge neutralization effects, through increased adsorption and complexation of sulfate, thus giving increased particle collision efficiency. Different PACl samples were prepared with different values of B ([OH]/[Al]). For B = 0 (i.e., AlCl3) with mainly monomers, hydroxide precipitation tends to be accelerated in the presence of sulfate, giving significant turbidity removal. The high charge neutralization ability remains for samples with B = 1.5 and 2.0, with large proportions of preformed oligomers and polymers. Sulfate promotes aggregation of hydrolyzed species for B= 2.5, causing significantly improved coagulation efficiency through an electrostatic patch effect. The results illustrate further that particle charge plays a less important role in coagulation after reaching a certain value, while precipitate formation improves coagulation significantly.     

Protein hydrolysis by protease isolated from tuna spleen by membrane filtration: A comparative study with commercial proteases

Membrane filtration is considered to be a low-cost and large scale method for recovery and purification of enzymes. The trypsin-like serine protease (TSP) was recovered and purified by microfiltration and ultrafiltration from the extract of the spleen of the yellowfin tuna (Thunnus albacores). The partially purified TSP has the activity of 96.5 U/mL and purity of 74.2 U/mg protein based on casein digesting unit. It has the molecular weight of 24 kDa proved by SDS-PAGE. The potential application of TSP in the protein hydrolysis was investigated in comparison to the use of two commercial proteases, i.e. Alcalase^® 0.6 L and Delvo-Pro under their optimal hydrolysis conditions. The effects of enzymes, substrates and enzyme to substrate ratio on the degree of hydrolysis (DH) were studied. Alcalase showed the highest DH for both casein and soybean isolate. TSP showed higher DH than Delvo-Pro when casein was employed as the substrate. However, TSP showed the lowest DH when soybean protein was used as the substrate. The present study proved that TSP recovered and purified from the tuna canning waste by membrane filtration can be used for protein hydrolysis as well as other commercial proteases.     

莫里斯抽提器中微乳化作用 除去制革废水中铬的研究

本实验研究中，用植物油（椰子油）合成的表面活性剂除去制革厂废水中的铬。在这个抽提过程中采用莫里斯抽提器。包括搅拌速度，溶解率及总流率在内的重要变量用于工艺的优化，实验采用23因素设计，根据实验设计得到的结果，分析计算了各个变量的作用大小，并证明它们之间是相互影响的。我们用反应界面方法研究变量的作用。最佳反应条件：搅拌速度，428转／分；溶解率，0．37；总流率，2．0升／小时。在一次抽提以后，进行了二次抽提，结果表明可以用盐酸和硫酸从微乳相中除去铬，这就可以使水在制革生产中循环利用。     

Kinetics of soluble chromium removal from contaminated water by zerovalent iron media: corrosion inhibition and passive oxide effects

Permeable reactive barriers containing zerovalent iron are being increasingly employed for in situ remediation of groundwater contaminated with redox active metals and chlorinated organic compounds. This research investigated the effect of chromate concentration on its removal from solution by zerovalent iron. Removal rates of aqueous Cr(VI) by iron wires were measured in batch experiments for initial chromium concentrations ranging from 100 to 10 000 microg/L. Chromate removal was also measured in columns packed with zerovalent iron filings over this same concentration range. Electrochemical measurements were made to determine the free corrosion potential and corrosion rate of the iron reactants. In both the batch and column reactors, absolute rates of chromium removal declined with increasing chromate concentration. Corrosion current measurements indicated that the rate of iron corrosion decreased with increasing Cr(VI) concentrations between 0 and 5000 microg/L. At a Cr(VI) concentration of 10 000 microg/L, Tafel polarization diagrams showed that chromium removal was affected by its diffusion rate through a passivating oxide film and by the ability of iron to release Fe2+ at anodic sites. In contrast, water reduction was not mass transfer limited, but chromium did decrease the exchange current for the hydrogen evolution reaction. Even at the most passivating concentration of 10 000 microng/L, effluent Cr(VI) concentrations in the column reactors reached a steady state, indicating that passivation had also reached a steady state. Although chromate contributes to iron surface passivation, the removal rates are still sufficiently fast for in situ iron barriers to be effective for Cr(VI) removal at most environmentally relevant concentrations.     

Arsenic removal from groundwater by household sand filters: comparative field study, model calculations, and health benefits

Arsenic removal efficiencies of 43 household sand filters were studied in rural areas of the Red River Delta in Vietnam. Simultaneously, raw groundwater from the same households and additional 31 tubewells was sampled to investigate arsenic coprecipitation with hydrous ferric iron from solution, i.e., without contact to sand surfaces. From the groundwaters containing 10-382 microg/L As, < 0.1-48 mg/L Fe, < 0.01-3.7 mg/L P, and 0.05-3.3 mg/L Mn, similar average removal rates of 80% and 76% were found for the sand filter and coprecipitation experiments, respectively. The filtering process requires only a few minutes. Removal efficiencies of Fe, phosphate, and Mn were > 99%, 90%, and 71%, respectively. The concentration of dissolved iron in groundwater was the decisive factor for the removal of arsenic. Residual arsenic levels below 50 microg/L were achieved by 90% of the studied sand filters, and 40% were even below 10 microg/L. Fe/As ratios of > or = 50 or > or = 250 were required to ensure arsenic removal to levels below 50 or 10 microg/L, respectively. Phosphate concentrations > 2.5 mg P/L slightly hampered the sand filter and coprecipitation efficiencies. Interestingly, the overall arsenic elimination was higher than predicted from model calculations based on sorption constants determined from coprecipitation experiments with artificial groundwater. This observation is assumed to result from As(lll) oxidation involving Mn, microorganisms, and possibly dissolved organic matter present in the natural groundwaters. Clear evidence of lowered arsenic burden for people consuming sand-filtered water is demonstrated from hair analyses. The investigated sand filters proved to operate fast and robust for a broad range of groundwater composition and are thus also a viable option for mitigation in other arsenic affected regions. An estimation conducted for Bangladesh indicates that a median residual level of 25 microg/L arsenic could be reached in 84% of the polluted groundwater. The easily observable removal of iron from the pumped water makes the effect of a sand filter immediately recognizable even to people who are not aware of the arsenic problem.