Sea Water Formation Research Articles

A Molecular Dynamics Study of the Influence of Low-Dosage Methanol on Hydrate Formation in Seawater and Pure Water Metastable Solutions of Methane

The behavior of low concentrations of methanol (0.5 and 1.0 wt% of water) as a promoter for hydrate formation in seawater or pure water metastable solutions of methane was investigated using the classical molecular dynamics method at moderate temperature and pressure. The influence of methanol on the dynamics of the re-arrangement of the hydrogen bond network in seawater and pure water solutions of methane was studied by calculating order parameters of the tetrahedral environment and intermolecular torsion angles for water molecules, as well as by calculating the number of hydrogen bonds, hydrate, and hydrate-like cavities. It was found that hydrate nucleation can be considered a collective process in which the rate of hydrate growth is faster in systems with low concentrations of methanol, and confident hydrate growth begins earlier in a metastable solution without sea salt with a small amount of methanol than in systems without methanol.

Novel Antifouling Coatings by Zwitterionic Silica Grafting on Glass Substrates.

Zwitterionic silica coatings for surface functionalization are greatly prominent because of their simple and fast preparation, high availability, and effective antifouling properties. In this work, two zwitterionic sulfobetaine silane coatings, i.e., mono-SBSi and tris-SBSi, were deposited on glass surfaces and tested for antifouling of biological material and biofilm using human cancer cell and seawater, respectively. The used zwitterionic precursors mono-SBSi and tris-SBSi differ by the number of hydrolyzable silane groups: mono-SBSi contains one trimethoxysilane group, whereas tris-SBSi contains three of these functions. First, X-ray photoelectron spectroscopy indicates the successful grafting of zwitterionic coatings onto a glass surface. Characterization using atomic force microscopy shows the different morphologies and roughness of the two coatings. The glass surface became more hydrophilic after the grafting of zwitterionic coatings than the bare glass substrate. The antifouling properties of two coatings were evaluated via human cancer cell adsorption. Interestingly, the tris-SBSi coating displays a significantly lower level of cell adsorption compared to that of both mono-SBSi coating and the non-modified control surface. The same trend was observed for biofilm formation in seawater. Finally, the toxicity of mono-SBSi and tris-SBSi coatings was evaluated on zebrafish embryos, indicating the good biocompatibility of both coatings. Our results indicate interesting antifouling properties of zwitterionic coatings. The chemical constitution of the used precursor has an impact on the antifouling properties of the formed coating: the tris-SBSi-based zwitterionic silica coatings display improved antifouling properties compared to those of the mono-SBSi-based coating. Besides, the use of trisilylated precursors should result in the formation of more resistant and robust coatings due to the higher number of grafting functions. For all these reasons, we anticipate that tris-SBSi coatings will open new perspectives for antifouling applications for biological environments and implants.

Seawater-based sII hydrate formation promoted by 1,3-Dioxolane for energy storage

Solidified natural gas (SNG) via clathrate hydrates offers a promising solution to overcome the challenges faced by both liquified natural gas (LNG) and compressed natural gas (CNG), enabling the storage of natural gas in a secure, large-scale, and long-continued fashion. Herein we utilized seawater to synthesize sII methane hydrate to reduce the raw material cost and evade the issue of water scarcity. Comprehensive experiments were performed to investigate the effects of temperature, pressure, and amino acids on mixed CH4/DIOX hydrate formation in seawater. Elevating the temperature from 283.2 K to 293.2 K resulted in a decrease in both the hydrate formation rate and methane storage capacity. Conversely, increasing the initial pressure from 7.2 MPa to 11.2 MPa enhanced both parameters. Hydrate morphology was presented to understand the evolution of hydrate systems under different experimental conditions. In-situ Raman analysis identified the structure of synthesized hydrates and unveiled the unique occupancy of guest molecules (DIOX and CH4) within the hydrate cages. The findings of this study contribute to the advancement of economically viable SNG technology through the direct utilization of seawater.

Elemental abundances and isotopic composition of Italian limestones: Glimpses into the evolution of the Tethys

Biogenic limestones from three sections (north, central, and south) across peninsular Italy have been analysed for major and trace elements and Nd, Pb, and Sr isotopic ratios. These data are used to monitor the evolution of the Tethys Ocean from the Triassic through to the Miocene. Limestones’ major, trace, and REE elements contents are consistent with their formation in seawater with little sign of crustal, volcanic, or hydrothermal input. V/Cr and Ce/Ce* ratios indicate their deposition in oxygenated waters. Rb-Sr-Ba discrimination diagram, consistent with the immobile trace element distribution, indicates that limestone deposition took place in either marginal or open ocean environments. Ages based on stratigraphy are in good agreement with the chronostratigraphic Sr curves implying that the Tethys ocean, throughout its history, was in contact with the open, global, ocean system. Although the isotopic values of Sr and Nd are relatively restricted, Pb is extremely variable and highly radiogenic. High Pb isotope ratios characterise limestones deposited during the rifting of the southern Tethyan ocean in the Lower Jurassic and in the Lower Cretaceous, suggesting stronger crustal inputs in small basins. The weighted average, present-day, isotope values (AIL = average Italian limestone) for the Italian limestones, excluding anomalous samples, are 87Sr/86Sr = 0.70785, 143Nd/144Nd = 0.51227, and 206Pb/204Pb = 18.94, 207Pb/204Pb = 15.69, 208Pb/204Pb = 38.66. These values are useful in monitoring the fate of limestones during orogenesis and the role that they may have played in magma genesis.

Studies on Methane Gas Hydrate Formation Kinetics Enhanced by Isopentane and Sodium Dodecyl Sulfate Promoters for Seawater Desalination

Methane hydrate applications in gas storage and desalination have attracted increasing attention in recent years. In the present work, the effect of isopentane (IP), sodium dodecyl sulfate (SDS), and IP/SDS blends as promoters on methane hydrate formation kinetics, in terms of the pressure–temperature (P-T) profile, gas uptake, hydrate induction time (HIT), and water-to-hydrate conversion ratio (WHCR), were studied for distilled water and seawater samples with an IP/water sample ratio of 3:10 (by volume) and an SDS/water sample ratio of 1:1000 (by mass). Each solution was tested in a stirred tank at 600 rpm at a temperature and pressure of 2 °C and 5.2–5.3 MPa. In the case of methane hydrate formation in distilled water, the highest WHCR attained was 9.97% without additives, and 45.71% and 72.28% for SDS and isopentane additives, respectively. However, when using seawater at a salinity of 3.9%, the highest WHCR attained was 2.26% without additives and 9.89% and 18.03% for SDS and IP promoters, respectively, indicating the inhibiting effect of salinity on hydrate formation. However, the HIT was longer for seawater hydrate formation, with an average of 13.1 min compared to 9.90 min for methane hydrate formation. Isopentane enhances the HIT for methane hydrate formation in seawater by 2.23 times compared to SDS. For methane hydrate formation in seawater, the presence of IP shortened the HIT by 15.6 min compared to the seawater sample without promoters. Additionally, a synergistic effect was observed when IP and SDS were combined and used in methane hydrate formation in distilled water and seawater systems. The positive effect of IP on methane hydrate formation is possibly due to the binary hydrate formation mechanism, which improves the hydrate formation thermodynamic and kinetic parameters.

The Calcium Isotope (δ44/40Ca) Record Through Environmental Changes: Insights From the Late Triassic

AbstractCalcium isotopes (δ44/40Ca) are particularly useful in palaeo‐environmental studies due to the key role of carbonate minerals in continental weathering and their formation in seawater. The calcium isotope ratio can provide hints on past changes in the calcium fluxes, environmental shifts, ecological factors and alternatively diagenesis of carbonate rocks. The investigation of the Late Triassic calcium isotope record offers a great opportunity to evaluate such factors in a time interval that witnessed important environmental and ecological turnovers, such as the first appearance of calcareous nannoplankton, ocean acidification and periods of elevated extinction rates. In this study, we present a δ44/40Ca data set from the upper Norian (Upper Triassic) through the lower Hettangian (Lower Jurassic) interval. The isotope records reveal two globally significant signals: a ∼ 0.20‰ decrease through the early Rhaetian (Upper Triassic) and a small, negative (∼0.14‰) excursion corresponding to the emplacement of the Central Atlantic Magmatic Province, at the end of the Triassic. The possible explanations for these signals are changes in the isotopic ratio of the continental calcium influx to the ocean due to the high chemical weathering rate of carbonates and possibly ocean acidification, respectively. The considerable (∼0.15–0.30‰) offset in δ44/40Ca between study areas is likely the combined result of local differences in lithology and early marine diagenesis. The major evolutionary step represented by the first occurrence of calcareous nannoplankton did not have at this time a determining role on the calcium isotopic signature of the marine carbonates.

Seawater desalination by coupling cyclopentane hydrate formation and capacitive deionization processes in the presence of Fe3O4 nanoparticles and magnetic field

This study investigates seawater desalination by coupling cyclopentane hydrate formation and capacitive deionization processes. High induction time, low conversion of water to hydrate, and low ion removal efficiency are the challenges of the hydrate desalination process. In order to reduce the cost of hydrate formation, cyclopentane was used as a hydrate former. Also, the promotion effects of Fe3O4 nanoparticles and magnetic field on the cyclopentane hydrate formation in pure water, seawater, and synthetic saline waters containing NaCl, KCl, CaCl2, and MgCl2 at different concentrations were investigated. The results showed that the Fe3O4 nanoparticles and magnetic field could improve the hydrate formation and the effect of Fe3O4 nanoparticles is greater than the magnetic field. However, the promoting effect on the induction time and removal efficiency was intensified when the Fe3O4 nanoparticles and the magnetic field were used simultaneously. The results of hydrate formation in seawater showed that the induction time in the presence of 0.07 wt.% Fe3O4 nanoparticles, magnetic field, and simultaneous use of both of them were reduced by 89, 22, and 92%, respectively. The ion removal efficiency reached 79% for Na+ and higher than 99% for K+, Ca2+, and Mg2+ when capacitive deionization was used as post-treatment.

An atomic force microscopy study of calcite dissolution in seawater

We present the first examination of calcite dissolution in seawater using Atomic Force Microscopy (AFM). We quantify step retreat velocity and etch pit density to compare dissolution in seawater to low ionic strength water, and also to compare calcite dissolution under AFM conditions to those conducted in bulk solution experiments (e.g. Subhas et al., 2015, Dong et al., 2018). Bulk dissolution rates and step retreat velocities are slower at high and mid-saturation state (Ω) values and become comparable to low ionic strength water rates at low Ω. The onset of defect-assisted etch pit formation in seawater is at Ω ∼ 0.85 (defined as Ωcritical), higher than in low ionic strength water (Ω ∼ 0.54). There is an abrupt increase in etch pit density (from ∼106 cm−2 to ∼108 cm−2) occurring when Ω falls below 0.7 in seawater, compared to Ω ∼ 0.1 in low ionic strength water, suggesting a transition from defect-assisted dissolution to homogeneous dissolution much closer to equilibrium in seawater. The step retreat velocity (v) does not scale linearly with undersaturation (1-Ω) across an Ω range of 0.4 to 0.9 in seawater, potentially indicating a high order correlation between kink rate and Ω for non-Kossel crystals such as calcite, or surface complexation processes during calcite dissolution in seawater.

Control of halophenol formation in seawater during chlorination using UV/TiO2 pre-treatment

Abstract Seawater is a valuable water resource in coastal regions. However, during seawater chlorination, a group of halophenols (HPs) may be formed. These HPs have lower odor and taste detection thresholds than other disinfection by-products (DBPs), however these are usually more toxic than most of the abundantly detected DBPs. Hence, an effective approach for control of HP formation during seawater chlorination is required to minimize highly toxic HP formation. Pretreatment using TiO2 photocatalysis was applied in this study to assess its ability for removal of HP precursors. Seawater samples with external addition of 1 mg/L phenol were spiked with TiO2 from 0.1 to 10.0 g/L and exposed under UV light for 2 to 120 min. The UV absorbance at 254 nm and the excitation–emission matrix fluorescence of dissolved organic matter were measured for each treated sample. It was observed that the optimal treatment condition to achieve the highest UV254 removal was 4.0 g/L TiO2 with UV exposure of 30 min. By pretreatment using this method and stated dose and exposure, only two types of HPs were detected during chlorination, compared with four types of HPs formed in the untreated samples. Moreover, the pretreatment greatly reduced the concentration of 2,4,6-TBP from more than 400 μg/L to less than 1 μg/L. The significance of this research study is to identify the effectiveness of UV/TiO2 in reducing DBP formation by analyzing the mechanisms during the process, which indicates the use of UV/TiO2 pretreatment for control of HP formation in seawater during chlorination.

Vertical Water Exchange in the Caspian Sea Assessed by the Distribution of Transient Tracers

The reliability of various scenarios of vertical structure formation in Caspian Sea water was analyzed based on the distribution of transient tracers (CFC-11, CFC-12, 3H, and 3He) at deep-water stations in the Middle and Southern Caspian in the course of international comprehensive isotope-geochemical studies in the period of maximal sea level rise in 1995–1996. The available hydrometeorological data and the specifics of water dating with the use of transient tracers suggested the conclusion that, after the large-scale gravitational convection in the Middle Caspian, caused by anomalous cooling of surface water in the Northern Caspian in the late winter of 1976, a structure of water masses has formed, barring the ventilation of deep water in the Middle and Southern Caspian up to the mid-1990s.

Contrasting initial events of localized corrosion on surfaces of 2219-T42 and 6061-T6 aluminum alloys exposed in Caribbean seawater

Abstract Aluminum alloy samples, 6061-T6 and 2219-T42, were exposed to Caribbean seawater for 90 d. The fluctuations of open circuit potential, considered as electrochemical noise (EN), were used to characterize and compare initial pitting events, which appeared on their surfaces. EN analysis was carried out using the power spectral density (PSD) vs frequency. The decrease of the β exponent in PSD graphs indicated a release of spontaneous energy with the progress of pit formation in seawater. The fluctuations were associated with the breakdown and formation of new corrosion layers. The values of β exponent in PSD graphs suggest that corrosion process of AA2219-T42 alloy occurs as a persistent non-stationary process, the dynamics of which is controlled by fractional Brownian motion (fBm), while on AA6061-T6 alloy the corrosion process was dominated by stationary and weakly persistent features, with the contribution of fractional Gaussian noise (fGn). After the exposure in seawater, SEM-EDX analysis revealed insoluble intermetallic particles on the alloys, rich in Cu or Fe and irregularly distributed. The preferential dissolution of Mg and Al occurs from the S-phase (Al2CuMg) of AA2219-T42 alloy.

Atmospheric CO2 captured by biogenic polyamines is transferred as a possible substrate to Rubisco for the carboxylation reaction

Biogenic polyamines are involved in a wide range of plant cellular processes, including cell division, morphogenesis and stress responses. However, the exact roles of biogenic polyamines are not well understood. We recently reported that biogenic polyamines that have multiple amino groups can react with CO2 and accelerate calcium carbonate formation in seawater. The ability of biogenic polyamines to capture atmospheric CO2 prompted us to examine their roles in photosynthesis. Here, we demonstrated that atmospheric CO2 captured by biogenic polyamines is a candidate substrate for the carboxylation reaction of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is an enzyme involved in the first major step of carbon fixation during photosynthesis, and that biogenic polyamines can accelerate the carboxylation reaction of this enzyme because of their specific affinity for CO2. Moreover, the results of our nuclear magnetic resonance (NMR) analysis showed that putrescine, which is the most common biogenic polyamine, reacts with atmospheric CO2 and promotes the formation of carbamate derivatives and bicarbonate in aqueous environments. A sufficient amount of CO2 is well known to be produced by carbonic anhydrase from bicarbonate in vivo. The present study indicates that CO2 would be also produced by the equilibrium reaction from carbonate produced by biogenic polyamines and would be used as a substrate of Rubisco, too. Our results may suggest a new photosynthetic research strategy that involves CO2-concentrating mechanisms and also possibly constitutes a potential tool for reducing atmospheric CO2 levels and, consequently, global warming.

Control of halophenol formation in seawater during chlorination using pre-ozonation treatment.

The reverse osmosis process is widely used for seawater desalination, whereas the pre-chlorination step for controlling membrane biofouling results in undesirable disinfection by-products, such as halophenols (HPs) which are not yet regulated but of increasing concerns. The formation and speciation of HPs during chlorination of three filtered seawater samples (SA, SB, and SC) with various phenol concentrations (0.25, 0.5, 1.0mg/L) were evaluated. 4-Bromophenol (4-BrP), 2,4,6-trichlorophenol (2,4,6-TClP), 2,4-dibromophenol (2,4-DBrP), and 2,4,6-tribromophenol (2,4,6-TBrP) were identified during chlorination, with 2,4,6-TBrP as the predominant HP. Ozone as a common oxidant in water and wastewater treatment was subsequently applied to assess its effect in dissolved organic matter (DOM) and its ability of reducing HP precursors in the seawater samples. An initial ozone dose of 5mg O3/L was capable of reducing dissolved organic carbon (DOC) in SA, and UV absorbance at 254nm (UV254) in SB, whereas it induced an elevation of UV254 in SC. When ozone dose increased to 10mg O3/L, the DOC and UV254 levels in all seawater samples were reduced. Ozone was more powerful on degrading DOM with molecular weight (MW) of near 1000Da than those with MW of 20-100Da, both of which composed the majority of DOM in the seawater samples. As determined by excitation emission matrix fluorescence spectroscopy, the most ozone-susceptible fraction of DOM was soluble microbial by-product-like substances, while the least was tryptophan-like aromatic proteins. Despite that the initial ozone of 5mg O3/L was less effective in DOM degradation than the higher dose, it successfully degraded HP precursors. By pre-ozonation at 5mg O3/L, no chlorophenol was detected during chlorination, and the mean reductions of the three bromophnols formed were above 92% in all seawater samples, with the reduction of 2,4,6-TBrP being the highest of 99.7, 99.6, and 99.1% in SA, SB, and SC, respectively.

Elemental mercury (Hg(0)) in air and surface waters of the Yellow Sea during late spring and late fall 2012: Concentration, spatial-temporal distribution and air/sea flux

The Yellow Sea in East Asia receives great Hg input from regional emissions. However, Hg cycling in this marine system is poorly investigated. In late spring and late fall 2012, we determined gaseous elemental Hg (GEM or Hg(0)) in air and dissolved gaseous Hg (DGM, mainly Hg(0)) in surface waters to explore the spatial-temporal variations of Hg(0) and further to estimate the air/sea Hg(0) flux in the Yellow Sea. The results showed that the GEM concentrations in the two cruises were similar (spring: 1.86±0.40ngm−3; fall: 1.84±0.50ngm−3) and presented similar spatial variation pattern with elevated concentrations along the coast of China and lower concentrations in the open ocean. The DGM concentrations of the two cruises were also similar with 27.0±6.8pgL−1 in the spring cruise and 28.2±9.0pgL−1 in the fall cruise and showed substantial spatial variation. The air/sea Hg(0) fluxes in the spring cruise and fall cruise were estimated to be 1.06±0.86ngm−2h−1 and 2.53±2.12ngm−2h−1, respectively. The combination of this study and our previous summer cruise showed that the summer cruise presented enhanced values of GEM, DGM and air/sea Hg(0) flux. The possible reason for this trend was that high solar radiation in summer promoted Hg(0) formation in seawater, and the high wind speed during the summer cruise significantly increased Hg(0) emission from sea surface to atmosphere and subsequently enhanced the GEM levels.

Effects of different levels of ozone on ammonia, nitrite, nitrate, and dissolved organic carbon in sterilization of seawater

Ozone is applied to the recirculation aquaculture system to reduce bacteria and parasites. Besides the sterilization effects, it is known that ozone has oxidizing effects on some water quality parameters. Therefore, oxidizing effects of ozone on ammonia (NH4-N), nitrite (NO2-N), nitrate (NO3-N), and dissolved organic carbon were tested in this study. During the test, ozone effects on pH, dissolved oxygen (DO) and bromination were also monitored. Ozone concentrations were originally set to 0.05, 0.1, 0.15, 0.2, and 0.25 ppm, but actual treatment concentrations were maintained at 0.04, 0.11, 0.15, 0.19, and 0.23 ppm. The 5 ppm of NH4-N was oxidized within 12 h in all concentrations of ozone treatments, with the average oxidizing rate of 0.65±0.28 mg NH4-N/L per h. The 5 ppm of NO2-N was oxidized within 1.5 h in all concentrations of ozone treatments at a rate of 4.5 mg NO2-N/L per h. One of 5 ppm NO3-N was oxidized by all concentration of ozone treatment after 24 h. In addition, ozone also oxidized dissolved organic carbon and maintained the concentration at about 2.9±0.77 ppm from the 15 ppm of initial concentration by 12 h. DO was increased from 5.9 to 9.4 ppm within 30 min in all ozone treatment and stabilized thereafter. Bromate concentrations increased sharply within the first 6 h of ozonation at the rate of 7.3±2.4 mg/L per h in almost all ozone treatments; the rate decreased to 2.5±0.15 mg/L per h thereafter. However, bromate concentration was not increased in the ammonia experiment until all ammonia was oxidized. Therefore, further studies are needed to determine the relationship between NH4-N concentration and bromate formation in seawater.

Precipitation of barite by marine bacteria: A possible mechanism for marine barite formation

Barite (BaSO 4 ) is found throughout the ocean, yet seawater is undersaturated with respect to barite, and organisms that could account for the abundance of barite have not yet been identifi ed. The mechanism for barite formation in seawater is not fully understood. Here we show that marine bacteria have the ability to precipitate barite through a metabolically mediated biomineralization process. We precipitated barite in laboratory experiments in the presence of several strains of marine bacteria grown on yeast media enriched with barium (Ba); barite did not precipitate under identical conditions in killed-bacteria controls. The crystals develop from amorphous, phosphorous-rich spherical precursors with fi brous internal textures, common in bacterial mineral precipitation. Bacterial mediation of barite precipitation can explain the distribution of barite in the water column and the occurrence of barite crystals in organic-rich sinking aggregates where bacteria are concentrated. This fi nding has implications for the use of barite and Ba proxies in paleoceanographic research.

TEM Investigations of Amorphous Calcium Carbonate Formation in Seawater

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Polymer dynamics of DOC networks and gel formation in seawater

Abstract The ocean plays a major role in global biogeochemical carbon cycling; it holds an important reservoir of reduced organic carbon, mostly in the form of dissolved organic carbon (DOC), and processes about one-half of the total primary production of the planet. Dissolved molecules present between living and assimilable size extremes (∼1000 nm -1 nm), constitute the most abundant form of remnant biochemicals in the ocean, outweighing the total living biomass by a factor of roughly 200. Because DOC is the fundamental substrate for marine microorganisms, and is primarily composed by small refractory biopolymers, this prompted the idea that the ocean might function as a huge repository of recalcitrant carbon. The missing link that elucidates this paradox and explains how the rich and vast stock of DOC becomes available to bacteria was the discovery that DOC throughout the water column remains in reversible assembly/dispersion equilibrium forming porous microscopic gels (Chin et al., Nature 391, 568-572, 1998). This abiotic DOC-POM shunt yields a microgel pool containing ∼70 gigatons of carbon forming discrete patches of high nutrient concentration that can be readily colonized by microorganisms. The presence of this huge gel mass in seawater extending far into the dark ocean has ramifications that might well scale nonlinearly through the microbial loop to the World Ocean and global climate system and it is fundamentally changing how oceanographers think about processes linking the microbial loop and biological pump to the rest of the biosphere and the geosphere. Even if a small fraction of DOC remains self-assembled, marine scientists will have to revise the rationale of established aquatic paradigms ranging from trace metal chelation, size–reactivity relationships, the microbial loop, the biological pump, colloid pumping, and humification. A ubiquitous, reversible DOC assembly/dispersion process implies a dynamic “patchiness” spanning from the molecular to the micron scale, where the assignment of static bulk features including dimension, concentration, functionalities and vertical fluxes can be open to question. This brief revision illustrates two case studies that show how simple methods and principles of polymer networks theory can be used to advance the understanding of one of the most intriguing and significant processes taking place in the ocean. Namely, the kinetics and thermodynamics of: (a) Ca-driven DOC self-assembly, and (b) hydrophobic bond-driven self assembly of DOC by amphiphilic exopolymers released by marine bacteria.

Rate of phosphoantimonylmolybdenum blue complex formation in acidic persulfate digested sample matrix for total dissolved phosphorus determination: Importance of post-digestion pH adjustment

Acidic persulfate oxidation is one of the most common procedures used to digest dissolved organic phosphorus compounds in water samples for total dissolved phosphorus determination. It has been reported that the rates of phosphoantimonylmolybdenum blue complex formation were significantly reduced in the digested sample matrix. This study revealed that the intermediate products of persulfate oxidation, not the slight change in pH, cause the slowdown of color formation. This effect can be remedied by adjusting digested samples pH to a near neural to decompose the intermediate products. No disturbing effects of chlorine on the phosphoantimonylmolybdenum blue formation in seawater were observed. It is noted that the modification of mixed reagent recipe cannot provide near neutral pH for the decomposition of the intermediate products of persulfate oxidation. This study provides experimental evidence not only to support the recommendation made in APHA standard methods that the pH of the digested sample must be adjusted to within a narrow range of sample, but also to improve the understanding of role of residue from persulfate decomposition on the subsequent phosphoantimonylmolybdenum blue formation.

Bromate ion formation in dark chlorination and ultraviolet/chlorination processes for bromide-containing water

Bormate (BrO 3 −) is a carcinogenic chemical produced in ozonation or chlorination of bromide-containing water. Although its formation in seawater with or without sunlight has been previously investigated, the formation of bromate in dilute solutions, particularly raw water for water treatment plant, is unknown. In this article, the results of bench scale tests to measure the formation rates of bromate formation in dilute solutions, including de-ionized water and raw water from Yangtze River, were presented in dark chlorination and ultraviolet (UV)/chlorination processes. And the effects of initial pH, initial concentration of NaOCl, and UV light intensity on bromate formation in UV/chlorination of the diluted solutions were investigated. Detectable bromate was formed in dark chlorination of the two water samples with a relatively slow production rate. Under routine disinfecting conditions, the amount of formed bromate is not likely to exceed the national standards (10 μg/L). UV irradiation enhanced the decay of free chlorine, and, simultaneously, 6.6%–32% of Br − was oxidized to BrO 3 −. And the formation of bromate exhibited three stages: rapid stage, slow stage and plateau. Under the experimental conditions (pH = 4.41–11.07, C Cl 2= 1.23–4.50 mg/L), low pH and high chlorine concentration favored the generation of bromate. High light intensity promoted the production rate of bromate, but decreased its total generation amount due to acceleration of chlorine decomposition.