Nitrogen critical loads and management alternatives for N-impacted ecosystems in California

Empirical critical loads for N deposition effects and maps showing areas projected to be in exceedance of the critical load (CL) are given for seven major vegetation types in California. Thirty-five percent of the land area for these vegetation types (99,639 km²) is estimated to be in excess of the N CL. Low CL values (3–8 kg N ha^?1 yr^?1) were determined for mixed conifer forests, chaparral and oak woodlands due to highly N-sensitive biota (lichens) and N-poor or low biomass vegetation in the case of coastal sage scrub (CSS), annual grassland, and desert scrub vegetation. At these N deposition critical loads the latter three ecosystem types are at risk of major vegetation type change because N enrichment favors invasion by exotic annual grasses. Fifty-four and forty-four percent of the area for CSS and grasslands are in exceedance of the CL for invasive grasses, while 53 and 41% of the chaparral and oak woodland areas are in exceedance of the CL for impacts on epiphytic lichen communities. Approximately 30% of the desert (based on invasive grasses and increased fire risk) and mixed conifer forest (based on lichen community changes) areas are in exceedance of the CL. These ecosystems are generally located further from emissions sources than many grasslands or CSS areas. By comparison, only 3–15% of the forested and chaparral land areas are estimated to be in exceedance of the NO₃^? leaching CL. The CL for incipient N saturation in mixed conifer forest catchments was 17 kg N ha^?1 yr^?1. In 10% of the CL exceedance areas for all seven vegetation types combined, the CL is exceeded by at least 10 kg N ha^?1 yr^?1, and in 27% of the exceedance areas the CL is exceeded by at least 5 kg N ha^?1 yr^?1. Management strategies for mitigating the effects of excess N are based on reducing N emissions and reducing site N capital through approaches such as biomass removal and prescribed fire or control of invasive grasses by mowing, selective herbicides, weeding or domestic animal grazing. Ultimately, decreases in N deposition are needed for long-term ecosystem protection and sustainability, and this is the only strategy that will protect epiphytic lichen communities.     

Treatment and toxicity evaluation of methylene blue using electrochemical oxidation,fly ash adsorption and combined electrochemical oxidation-fly ash adsorption

Treatment of a basic dye, methylene blue, by electrochemical oxidation, fly ash adsorption, and combined electrochemical oxidation-fly ash adsorption was compared. Methylene blue at 100 mg L^?1 was used in this study. The toxicity was also monitored by the Vibrio fischeri light inhibition test.When electrochemical oxidation was used, 99% color and 84% COD were removed from the methylene blue solution in 20 min at a current density of 428 A m^?2, NaCl of 1000 mg L^?1, and pH₀ of 7. However, the decolorized solution showed high toxicity (100% light inhibition).For fly ash adsorption, a high dose of fly ash (>20,000 mg L^?1) was needed to remove methylene blue, and the Freundlich isotherm described the adsorption behavior well.In the combined electrochemical oxidation-fly ash adsorption treatment, the addition of 4000 mg L^?1 fly ash effectively reduced intermediate toxicity and decreased the COD of the electrochemical oxidation-treated methylene blue solution. The results indicated that the combined process effectively removed color, COD, and intermediate toxicity of the methylene blue solution.     

Effect of salinity on metal-complex dye biosorption by Rhizopus arrhizus

In this study the biosorption of Yellow RL, a metal-complex anionic dye, by dried Rhizopus arrhizus, a filamentous fungus, was investigated as a function of initial solution pH, initial dye concentration and initial salt (sodium chloride) concentration. The fungus exhibited the maximal dye uptake at pH 2 in the absence and in the presence of salt. Dye uptake increased with the dye concentration up to 1000 mg l^?1 and diminished considerably in the presence of increasing concentrations of salt up to 50 g l^?1. The fungus biosorbed 85.4 mg dye g^?1of dried biomass at 100 mg l^?1 initial dye concentration in the absence of salt. When 50 g l^?1 salt was added to the biosorption medium, this value dropped to 60.8 mg g^?1 resulting in 28.8% reduction in biosorption capacity. The Redlich–Peterson and Langmuir–Freundlich were the most suitable adsorption models for describing the biosorption equilibrium data of the dye both individually and in salt containing medium. The pseudo-second-order and saturation type kinetic models depicted the biosorption kinetics accurately for all cases studied. Equilibrium and kinetic constants varied with the level of salt were expressed as a function of salt concentration.     

Subsoil TPH contamination in two oil pipeline pumping stations and one pipeline right-of-way in north Mexico

This investigation deals with the characterization carried out in zones around two pipeline pumping stations and one pipeline right-of-way in the north of Mexico. In particular those areas where contamination was evaluated: (a) south area of the separation ditch in the Avalos station, (b) the area between the separation ditch at the Avalos station, (c) km 194 + 420 of the Moctuzma station, and (d) km 286 + 900 in the Candelaria station. Results of this investigation showed that only four samples showed TPH values higher than the Mexican limit for 2004: AVA 1B, with 21,191 mg kg^?1; AVA 1C, with 9348 mg kg^?1; AVA 2B, with 13,970 mg kg^?1; and MOC 2A, with 4108 mg kg^?1.None of the sampled points showed the presence of PAHs at values higher than those found in the Mexican or American legislations. PAH were detected in the range of 0.0004 and 13.05 mg kg^?1.It is suggested to implement surfactant soil washing as a remediation technique for the approximately 600 m³ that need to be treated.     

Closing the water cycle for industrial laundries: An operational performance and techno-economic evaluation of a full-scale membrane bioreactor system

To reduce the consumption of freshwater in the laundry industry, a new trend of closing the water cycle has resulted in the reuse/recycling of water. In this study, the performance of a full-scale submerged aerobic membrane bioreactor (9 m³) used to treat/reuse industrial laundry wastewater was examined over a period of 288 days. The turbidity and total solids (TS) were reduced by 99%, and the chemical oxygen demand (COD) effluent removal efficiencies were between 70% and 99%. The levels of COD removed by the membrane were significantly greater than the levels of biodegraded COD. This enabled the bioreactor to sustain COD levels that were below 100 mg/L, even during periods of low wastewater biodegradation due to bioreactor sludge. An economic evaluation of the membrane bioreactor (MBR) system showed a savings of 1.13 € per 1 m³ of water. The payback period for this system is approximately 6 years. The energy and maintenance costs represent only 5% of the total cost of the MBR system.     

Lead accumulation in different Chinese cabbage cultivars and screening for pollution-safe cultivars

Recently, the concept of pollution-safe cultivars (PSCs) was proposed to minimize the influx of pollutants to the human food chain. Variations in lead (Pb) uptake and translocation among Chinese cabbage (Brassica pekinensis L.) cultivars were investigated in a pot-culture experiment and a field-culture experiment to screen out Pb-PSCs for food safety. The results of the pot-culture experiment showed that shoot Pb concentrations under two Pb treatments (500 and 1500 mg kg^?1) varied significantly (p < 0.05) between cultivars, with average values of 3.01 and 6.87 mg kg^?1, respectively. Enrichment factors (EFs) and translocation factors (TFs) in cultivars were less than 0.50 and varied significantly (p < 0.05) between cultivars. Shoot Pb concentrations in 12 cultivars under treatment T₁ (500 mg kg^?1) were lower than 2.0 mg kg^?1. The field-culture experiment further confirmed Qiuao, Shiboqiukang and Fuxing 80 as Pb-PSCs, which were suitable to be cultivated in low-Pb (<382.25 mg kg^?1) contaminated soils and harmless to human health as foods.     

Analytical solution for Joule–Thomson cooling during CO2 geo-sequestration in depleted oil and gas reservoirs

Mathematical tools are needed to screen out sites where Joule–Thomson cooling is a prohibitive factor for CO₂ geo-sequestration and to design approaches to mitigate the effect. In this paper, a simple analytical solution is developed by invoking steady-state flow and constant thermophysical properties. The analytical solution allows fast evaluation of spatiotemporal temperature fields, resulting from constant-rate CO₂ injection. The applicability of the analytical solution is demonstrated by comparison with non-isothermal simulation results from the reservoir simulator TOUGH2. Analysis confirms that for an injection rate of 3 kg s^?1 (0.1 MT yr^?1) into moderately warm (>40 °C) and permeable formations (>10^?14 m² (10 mD)), JTC is unlikely to be a problem for initial reservoir pressures as low as 2 MPa (290 psi).     

Treatment of landfill leachates by nanofiltration

Landfill leachate contains high concentrations of organic matter, color, heavy metals and toxic substances. This study presents the feasibility of a commercial nanofiltration membrane (NF-300) in the removal of pollutants from a landfill leachate generated from the Treatment Stabilization and Disposal Facility in Gujarat state of India. Two different leachate samples (Leachates A and B) were collected from the downstream side of closed landfill cells A and B. The average quality of the leachate was 67 719 mg/L COD, 217 mg/L ammonical nitrogen, 22 418 mg/L BOD, 3847 mg/L chlorides and 909 mg/L sulphate. The operating variables studied were applied pressure (4–20 atm), feed flowrate (5–15 L/min) and pH (2, 4, 5.5 and 6.7). It was observed that the solute rejection (R_O) increased with increase in feed pressure and decreased with increase in feed concentration at constant feed flowrate. In the present study, the rejection of cations followed the sequence: R_O (Cr³⁺) > R_O (Ni²⁺) > R_O (Zn²⁺) > R_O (Cu²⁺) > R_O (Cd²⁺) for leachates A and B. The order of solute rejection sequence is inversely proportional to the diffusion coefficients. The rejection of sulphate ions by the NF-300 membrane was 83 and 85%, while the rejection of chlorides was 62 and 65% for leachates A and B, respectively. The NF-300 membrane was characterized by using the combined-film theory-Spiegler–Kedem (CFSK) model based on irreversible thermodynamics and the ion transport model based on the extended Nernst–Planck equation. The membrane transport parameters were estimated using the Levenberg–Marquadt method. The estimated parameters were used to predict the membrane performance and the predicted values are in good agreement with the experimental results.     

Airborne manganese concentrations on the Korean peninsula from 1991 to 2006

In this study, the distribution of airborne manganese (Mn) bound with particulate matters (PM) was investigated using data sets collected from 15 major cities in Korea over a 16-year time span (1991–2006). The mean Mn concentration measured from all the major cities in Korea throughout the entire study period was 71 ng m^?3, while the annual mean values of different cities ranged from 10.5 ng m^?3 in Yeosu (2003) to 615 ng m^?3 in Wonju (2006). The Mn levels were considerably larger in industrialized areas than in other land-use types. The Mn concentrations in the major industrial cities of Pohang, Incheon, and Ansan averaged 255, 98.2, and 84.6 ng m^?3, respectively; these values were far higher than those measured typically at most cities, e.g., 20–60 ng m^?3. Seasonal patterns characterized by the peak occurrence in spring and the noticeable drop in summer reflected the effects of the massive PM inflow from China (spring) and effective washout by summer monsoon in East Asia, respectively. Examination of Mn data over a long-term period indicated that the temporal trends of Mn seen in most cities were fairly constant through time since the 1990s, although some abnormalities were observed in cities of strong man-made activities (e.g., Pohang and Wonju). In light of the severity of airborne Mn pollution in many urban areas, it is desirable to establish an abatement strategy that can help effectively reduce Mn levels.     

Butyltin occurrence and risk assessment in the sediments of the Iberian Peninsula

The occurrence of butyltin (BT) compounds in more than 50 recent sediment samples of the Iberian Peninsula, collected in the harbours of the western Mediterranean Sea (Spain) and the North Atlantic Ocean (Portugal), including domestic and industrial sewage disposal sites, has been assessed. The highest levels of tributyltin (TBT) (7673 μg kg^?1 dry wt.) were detected in commercial harbours associated with inputs from large vessels. However, relatively high TBT values (about 2150 μg kg^?1 dry wt.) were also detected in fishing and recreational boating areas. Spanish marinas and harbours are more polluted in terms of TBT (5–7673 μg kg^?1 dry wt.) compared to those in Portugal (4–12 μg kg^?1 dry wt.). Generally, the Mediterranean sediments show a BT distribution characterized by the predominance of TBT over the degradation products dibutyl (DBT) and monobutyltin (MBT), indicating the presence of recent inputs, in contrast to the Portuguese coastal distribution. Calculation of butyltin degradation indexes (BDI) confirmed a different trend, depending on the area. Furthermore, a comparative study of the occurrence of BT in different sewage sludge disposal sites shows that domestic primary sewage sludge effluents can contribute to coastal BT pollution, but to a lesser extent when compared with harbours. Historical trends (1995–2003) for Barcelona harbour reveal that BT regulations on the use of TBT-based antifouling paints have not been fully effective. Finally, a comparison against the existing sediment quality guidelines (SQGs) indicated that acute toxic effects could only be expected for TBT in some Mediterranean harbours; conversely, in every North Atlantic Ocean station, a lesser environmental threat for the harbour benthic community is expected.     

Validation of spectral gas radiation models under oxyfuel conditions. Part A: Gas cell experiments

Combustion of hydrocarbon fuels with pure oxygen results in a different flue gas composition as combustion with air. Standard CFD spectral gas radiation models for air combustion are out of their validity range. The series of three articles provides a common spectral basis for the validation of new developed models. In part A of the series gas cell transmissivity spectra in the spectral range of 2.4–5.4 μm of water vapor and carbon dioxide in the temperature range from 727 to 1500 ° C and at different concentrations were compared at a nominal resolution of 32 cm^?1 to line-by-line models from different databases, two statistical-narrow-band models and the exponential wide band model. The two statistical-narrow-band models EM2C and RADCAL showed a good agreement with a maximal band transmissivity deviation of 3%. The exponential-wide-band model showed a deviation of 6%. The new line-by-line database HITEMP2010 had the lowest band transmissivity deviation of 2.2% and was recommended as a reference model for the validation of simplified CFD models.     

Experimental investigation of the CO2 sealing efficiency of caprocks

Using a combination of experimental (petrophysical and mineralogical) methods, the effects of high-pressure CO₂ exposure on fluid transport properties and mineralogical composition of two pelitic caprocks, a limestone and a clay-rich marl lithotype have been studied. Single and multiphase permeability tests, gas breakthrough and diffusion experiments were conducted under in situ p/T conditions on cylindrical plugs (28.5 mm diameter, 10–20 mm thickness).The capillary CO₂ sealing efficiency of the initially water-saturated sample plugs was found to decrease in repetitive gas breakthrough experiments on the same sample from 0.74 to 0.41 MPa for the limestone and from 0.64 to 0.43 MPa for the marl. Helium breakthrough experiments before and after the CO₂ tests showed a decrease in capillary threshold (snap-off) pressure from 1.81 to 0.62 MPa for the limestone.Repetitive CO₂ diffusion experiments on the marlstone revealed an increase in the effective diffusion coefficient from 7.8 × 10^?11 to 1.2 × 10^?10 m².Single-phase (water) permeability coefficients derived from steady-state permeability tests ranged between 7 and 56 nano-Darcy and showed a consistent increase after each CO₂ test cycle. Effective gas permeabilities were generally one order of magnitude lower than water permeabilities and exhibit the same trend. XRD measurements performed before and after exposure to CO₂ did not reveal any distinct change in the mineral composition for both samples. Similarly, no significant changes were observed in specific surface areas (determined by BET) and pore-size distributions (determined by mercury injection porosimetry). High-pressure CO₂ sorption experiments on powdered samples revealed significant CO₂ sorption capacities of 0.27 and 0.14 mmol/g for the marlstone and the limestone, respectively.The changes in transport parameters in the absence of detectable mineral alterations may be explained by carbonate dissolution and further precipitation along a pH profile across the sample plug which would not be subject to quantitative mineral alteration.     

Effect of gas composition in Chemical-Looping Combustion with copper-based oxygen carriers: Fate of light hydrocarbons

Chemical-Looping Combustion (CLC) is an emerging technology for CO₂ capture because separation of this gas from the other flue gas components is inherent to the process and thus no energy is expended for the separation. Natural or refinery gas can be used as gaseous fuels and they may contain different amounts of light hydrocarbons. This paper presents the combustion results obtained with a Cu-based oxygen carrier using mixtures of CH₄ and light hydrocarbons (LHC) (C₂H₆ and C₃H₈) as fuel. The effect on combustion efficiency of the fuel reactor temperature, solid circulation flow rate and gas composition was studied in a continuous CLC plant (500 W_th). Full combustions were reached at 1073 and 1153 K working at oxygen to fuel ratios, ? higher than 1.5 and 1.2 respectively. Unburnt hydrocarbons were never detected at any experimental conditions at the fuel reactor outlet. Carbon formation can be avoided working at 1153 K or at ? values higher than 1.5 at 1073 K. After 30 h of continuous operation, the oxygen carrier exhibited an adequate behavior regarding attrition and agglomeration. It can be concluded that no special measures should be taken in a CLC process with Cu-based OC with respect to the presence of LHC in the fuel gas.     

Electrocoagulation of blue reactive,red disperse and mixed dyes,and application in treating textile effluent

This study investigated the efficiency of electrocoagulation in removing color from synthetic and real textile wastewater. Two representative dye molecules were selected for the synthetic dye wastewater: a blue reactive dye (Reactive Blue 140) and a disperse dye (Disperse Red 1). The electrochemical technique showed satisfactory color removal efficiency and reliable performance in treating both individual and mixed dye types. The removal efficiency and energy consumption data showed that, for a given current density, iron was superior to aluminum in treating both the reactive dye and the disperse dye. With an initial dye concentration of 100 mg L^?1, the energy cost in achieving >95% color removal was on the order of 1 kWh m^?3 for both dyes. The effect of changing the initial pH of the samples on the removal efficiency and energy consumption was also studied. It was found that the design parameters used for the synthetic wastewater were less effective for treatment of real textile wastewater, with 1 in 5 tests on real wastewater failing.     

CO2 removal using membrane gas absorption

The objective of this study is to investigate the potential process for the removal of carbon dioxide (CO₂) from flue gas using fundamental membrane contactor, which is a membrane gas absorption (MGA) system. The experiments consisted of microporous polyvinylidenefluoride (PVDF) flat sheet membrane with 0.1 μm (as module I) and 0.45 μm (as module II) pore size. 2-Amino-2-methyl-1-propanol (AMP) solution was employed as the liquid absorbent. The effect of AMP concentration was studied with variation in the range 1–5 M. In addition, the experiments were carried out with 10%, 20%, 30% and 40% gas ratio of CO₂ to N₂ and pure CO₂ as well. Through contact angle measurement, membranes for module I and module II were obtained with CA values of around 130.25° and 127.77°, respectively. The mass transfer coefficients for module II are lower than those of module I for 1–5 M of AMP. Furthermore, the increase in CO₂ concentration in the feed gas stream enhanced the CO₂ flux as the driving force of the system was increased in sequence from 1 M to 5 M of AMP. However, after the particular percentage (40%) of CO₂ inlet concentration, the CO₂ fluxes seem saturated. The combination of AMP as liquid absorbent and PVDF microporous membrane in MGA system has shown the potential to remove the CO₂ from flue gas. In addition, the higher AMP concentration gave higher mass transfer coefficient at low liquid flow rates.     

Transfer characteristics of cobalt from soil to crops in the suburban areas of Fujian Province,southeast China

The bioavailability of cobalt and its transfer from soil to vegetables and rice were investigated. Among 312 soils collected from vegetable and paddy fields in the suburban areas of some major cities of Fujian Province, southeast China, total soil Co ranged from 3.5 to 21.7 mg kg^?1, indicating a slight accumulation compared with the background value of the province. DTPA extracted 0.1–8.5% of soil total Co. Total and DTPA-extractable Co correlated with soil pH, CEC, free Fe, total Mn, clay and silt content more significantly in paddy soils than in the soils from vegetable fields. The average Co concentrations in the edible parts of vegetables and rice were 15.4 μg kg^?1 and 15.5 μg kg^?1, respectively. The transfer factor (the ratio of plant Co to soil DTPA-extractable Co, TF_DTPA) ranged from 0.003 to 0.126 with a median of 0.049. The TF_DTPA decreased in the order of leafy vegetables > fruit vegetables > root vegetables > rice. The TF_DTPA of all crops decreased with increasing DTPA-extractable Co. Increase in pH, CEC, organic matter, clay, silt, free iron and total Mn limited the soil-to-plant transfer of Co to varying degrees. The transfer of Co from the soils to the edible parts of the crops was lower than that of Zn, Cu and Cd, but higher than that of Pb in the same areas. The concentrations of Co in rice and vegetables in the study areas were considered to be safe for the local residents because of the slight anthropogenic input and the low transfer potential to the edible parts of Co from the soils.     

Application of polyacrylamide to reduce phosphorus losses from a Chinese purple soil: A laboratory and field investigation

Use of anionic polyacrylamide (PAM) to control phosphorus (P) losses from a Chinese purple soil was studied in both a laboratory soil column experiment and a field plot experiment on a steep slope (27%). Treatments in the column study were a control, and PAM mixed uniformly into the soil at rates of 0.02, 0.05, 0.08, 0.10, and 0.20%. We found that PAM had an important inhibitory effect on vertical P transport in the soil columns, with the 0.20% PAM treatment having the greatest significant reduction in leachate soluble P concentrations and losses resulting from nine leaching periods. Field experiments were conducted on 5 m wide by 21 m long natural rainfall plots, that allowed collection of both surface runoff and subsurface drainage water. Wheat was planted and grown on all plots with typical fertilizer applied. Treatments included a control, dry PAM at 3.9 kg ha^?1, dry PAM at 3.9 kg ha^?1 applied together with lime (CaCO₃ at 4.9 t ha^?1), and dry PAM at 3.9 kg ha^?1 applied together with gypsum (CaSO₄·2H₂O at 4 t ha^?1). Results from the field plot experiment in which 5 rainfall events resulted in measurable runoff and leachate showed that all PAM treatments significantly reduced runoff volume and total P losses in surface runoff compared to the control. The PAM treatments also all significantly reduced water volume leached to the tile drain. However, total P losses in the leachate water were not significantly different due to the treatments, perhaps due to the low PAM soil surface application rate and/or high experimental variability. The PAM alone treatment resulted in the greatest wheat growth as indicated by the plant growth indexes of wheat plant height, leaf length, leaf width, grain number per head, and dried grain mass. Growth indexes of the PAM with Calcium treatments were significantly lesser. These results indicate that the selection and use of soil amendments need to be carefully determined based upon the most important management goal at a particular site (runoff/nutrient loss control, enhanced plant growth, or a combination).     

Optimization of Fenton oxidation pre-treatment for B. thuringiensis – Based production of value added products from wastewater sludge

Fenton oxidation pretreatment was investigated for enhancement of biodegradability of wastewater sludge (WWS) which was subsequently used as substrate for the production of value- added products. The Response surface method with fractional factorial and central composite designs was applied to determine the effects of Fenton parameters on solubilization and biodegradability of sludge and the optimization of the Fenton process. Maximum solubilization and biodegradability were obtained as 70% and 74%, respectively at the optimal conditions: 0.01 ml H₂O₂/g SS, 150 [H₂O₂]₀/[Fe²⁺]₀, 25 g/L TS, at 25 °C and 60 min duration. Further, these optimal conditions were tested for the production of a value added product, Bacillus thuringiensis (Bt) which is being used as a biopesticide in the agriculture and forestry sector. It was observed that Bt growth using Fenton oxidized sludge as a substrate was improved with a maximum total cell count of 1.63 × 10⁹ CFU ml^?1 and 96% sporulation after 48 h of fermentation. The results were also tested against ultrasonication treatment and the total cell count was found to be 4.08 × 10⁸ CFU ml^?1 with a sporulation of 90%. Hence, classic Fenton oxidation was demonstrated to be a rather more promising chemical pre-treatment for Bt - based biopesticide production using WWS when compared to ultrasonication as a physical pre-treatment.     

Degradation of aqueous piperazine in carbon dioxide capture

Concentrated, aqueous piperazine (PZ) is a novel solvent for carbon dioxide (CO₂) capture by absorption/stripping. One of the major advantages of PZ is its resistance to thermal degradation and oxidation.At 135 and 150 °C, 8 m PZ is up to two orders of magnitude more resistant to thermal degradation than 7 m monoethanolamine (MEA). After 18 weeks at 150 °C, only 6.3% of the initial PZ was degraded, yielding an apparent first order rate constant for amine loss of 6.1 × 10^?9 s^?1. PZ was the most resistant amine tested, with the other screened amines shown in order of decreasing resistance: 7 m 2-amino-2-methyl-1-propanol, 7 m Diglycolamine^®, 7 m N-(2-hydroxyethyl)piperazine, 7 m MEA, 8 m ethylenediamine, and 7 m diethylenetriamine. Thermal resistance allows the use of higher temperatures and pressures in the stripper, potentially leading to overall energy savings.Concentrated PZ solutions demonstrate resistance to oxidation compared to 7 m MEA solutions. Experiments investigating metal-catalyzed oxidation found that PZ solutions were 3–5 times more resistant to oxidation than MEA. Catalysts tested were 1.0 mM iron (II), 4.0–5.0 mM copper (II), and a combination of stainless steel metals (iron (II), nickel (II), and chromium (III)). Inhibitor A reduced PZ degradation catalyzed by iron (II) and copper (II).