Presence Of DOC Research Articles

Reclamation of impacted urban phreatic water through nanofiltration technology: Insight on natural organic matter removal by fluorescence spectroscopy

Nanofiltration (NF) is a promising technology called to play a relevant role in water reclamation, which lies in the core of circular economy in the water sector. The aim of this study was to assess two aromatic polyamide-based NF membranes (the looser NF270 and the tighter NF90 ones) for the treatment of urban impacted phreatic water. The focus was centred on the removal of dissolved inorganic and organic solutes and on the differences observed between solutes. Membrane ions rejection was modelled by the Solution-Electro-Diffusion Film Model (SEDFM). DOC was tracked by Fluorescence Excitation-Emission Matrices (FEEM) coupled to Parallel Factor Analysis (PARAFAC) to get insight into the character of DOC rejected by or permeated through the membranes. Results showed that the NF90 membrane systematically achieved upper values in the rejection of ions than the looser NF270 one. Variations between ions could be interpreted by the mechanisms ruling their rejection, i.e. Donnan and dielectric exclusion phenomena. Experimental rejections were also satisfactorily fit by the SEDFM, indicating that that the presence of DOC in the phreatic water did affect modelling of ions transport through the membranes. DOC was rejected at very high percentages (>90%) by both membranes, but FEEM-PARAFAC analysis revealed that humic- and tryptophan- like components were more rejected (>90% for both membranes) than tyrosine-like compounds (45% for NF270 and 57% for NF90). The finding is of relevance from a point of view of disinfection practices, as it has been observed that humic-like substances are strongly correlated with DBPs formation.

The effects of soil properties and co-contaminants on sorption of perfluorooctane sulfonate (PFOS) in contrasting soils

Abstract Sorption plays an important role in controlling the fate and behaviour of per- and polyfluoroalkyl substances (PFAS) in soils. However, there is no consensus on the influence of key soil properties on sorption of perfluorooctane sulfonate (PFOS) in the current literature. In particular, the effects of soil mineral components on sorption have not been fully investigated. In this study the sorption isotherms of PFOS under different electrolytes (Na + and Ca2＋) was investigated using eight contrasting soils that varied in pH, total organic carbon (TOC) content, clay content and other physico-chemical properties. In addition the sorption behaviour of PFOS was studied at different pH values (3–9) and ionic strengths (0.03 and 0.3 M NaNO3) to determine the role of hydrophobic and electrostatic interactions on PFOS sorption. The effects of possible co-contaminants, lead (Pb) (20.8 mg/L Pb 2 + ) and dissolved organic carbon (DOC, 11.5 mg/L as humic acid) and perfluorooctanoic acid (114 μ g/L PFOA) on sorption of PFOS were also investigated. A strongly significant linear relationship (p + or Ca2＋. The presence of DOC, and other common co-contaminants like PFOA, and Pb 2 + in solution generally increased PFOS sorption by the soils. Sorption of PFOS at different ionic strengths and pH demonstrated that the sorption was dominated by hydrophobic interactions when the TOC content was high, but electrostatic interactions dominated at lower pH values and in soils with smaller TOC contents. This study demonstrates the role of both organic matter and surface chemical properties of soils as key factors influencing PFOS sorption. The use of multiple soil properties to explain the sorption is required.

Are dominant microbial sub-surface communities affected by water quality and soil characteristics?

Subsurface microorganisms must deal with quite extreme environmental conditions. The lack of light, oxygen, and potentially nutrients are the main environmental stresses faced by subsurface microbial communities. Likewise, environmental disruptions providing an unbalanced positive input of nutrients force microorganisms to adapt to varying conditions, visible in the changes in microbial community diversity. In order to test microbial community adaptation to environmental changes, we performed a study in a surface Managed Aquifer Recharge facility, consisting of a settlement basin (two-day residence time) and an infiltration pond. Data on groundwater hydrochemistry, soil texture, and microbial characterization was compiled from surface water, groundwater, and soil samples at two distinct recharge operation conditions.Multivariate statistics by means of Principal Component Analysis (PCA) was the technique used to map the relevant dimensionality reduced combinations of input variables that properly describe the system behavior. The methodology selected allows including variables of different nature and displaying very different range values. Strong differences in the microbial assemblage under recharge conditions were found, coupled to hydrochemistry and grain-size distribution variables. Also, some microbial groups displayed correlations with either carbon or nitrogen cycles, especially showing abundant populations of denitrifying bacteria in groundwater. A significant correlation was found between Methylotenera mobilis and the concentrations of NO3 and SO4, and also between Vogesella indigofera and the presence of DOC in the infiltrating water. Also, microbial communities present at the bottom of the pond correlated with representative descriptors of soil grain size distribution.

Arsenic-enriched aquifers: Occurrences and mobilization of arsenic in groundwater of Ganges Delta Plain, Barasat, West Bengal, India

Hydrogeochemical characteristics and elemental features of groundwater and core sediments have been studied to better understand the sources and mobilization process responsible for As-enrichment in part of the Gangetic plain (Barasat, West Bengal, India). Analysis of water samples from shallow tubewells (depth 24.3-48.5m) and piezometer wells (depth 12.2-79.2m) demonstrate that the groundwater is mostly the Ca-HCO3 type and anoxic in nature (mean EhSHE=34mV). Arsenic concentrations ranged from <10-538μg/L, with high concentrations only present in the shallow to medium depth (30-50m) of the aquifer along with high Fe (0.07-9.8mg/L) and relatively low Mn (0.15-3.38mg/L) as also evidenced in core sediments. Most groundwater samples contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V), exhibiting the reducing condition. Results show lower concentrations of NO3, SO4 and NO2 along with higher values of DOC and HCO3, indicating the reducing nature of the aquifer with abundant organic matter that can promote the release of As from sediments into groundwater. Positive correlations of As with Fe and DOC were also observed. The presence of DOC may actively drive the redox processes. This study revealed that reduction processes of FeOOH was the dominant mechanism for the release of As into the groundwater in this part of the Ganges Delta plain.

A ToxR-dependent role for the putative phosphoporin VCA1008 in bile salt resistance in Vibrio cholerae El Tor N16961

The putative phosphoporin encoded by vca1008 of Vibrio cholerae O1 is expressed in vivo during infection and is essential for the intestinal colonization of infant mice. In vitro, its expression is induced under inorganic phosphate (P(i)) limitation in a PhoB/R-dependent manner. In this work we demonstrated that VCA1008 has a strain-specific role in the physiology and pathogenicity of V. cholerae O1. Disruption of vca1008 led to a growth defect, an inability to colonize and a high susceptibility to sodium deoxycholate (DOC; the major bile compound) in the El Tor biotype strain N16961, but did not affect the classical strain O395 in the same way. Furthermore, vca1008 promoter activity was higher in N16961 cells grown under a low P(i) supply in the presence of DOC than in the absence of the detergent. In the P(i)-limited cells, vca1008 was positively regulated by PhoB, but when DOC was added to the medium, it negatively affected the PhoB-mediated activation of the gene, and enhanced vca1008 expression in a ToxR-dependent manner. These findings reveal for the first time a complex strain-specific interplay between ToxR and PhoB/R systems to control porin genes, as well as the influence of DOC on the expression of PhoB- and ToxR-regulated genes and pathogenesis in pandemic strains of V. cholerae.

RETRACTED: Hydrogeochemical behavior of arsenic-enriched groundwater in the deltaic environment: Comparison between two study sites in West Bengal, India

Groundwaters have been collected from deltaic areas of West Bengal (Chakdaha and Baruipur blocks) to record their hydrogeochemical characteristics, and to verify the mechanism of arsenic (As) release. The data reveals that shallow (<70 m) groundwaters in both areas are of Ca-Mg-HCO(3) type; however deeper (>70 m) groundwaters in Baruipur areas are slightly enriched with Na, Cl and SO(4), indicating possible saline water intrusion. The groundwater is anoxic (mean Eh: -124 and -131 mV) with high levels of As (mean: 116 and 293 microg/L), Fe (mean: 4.74 and 3.83 mg/L), PO(4) (mean: 3.73 and 3.21 mg/L) and Mn (mean: 0.37 and 0.49 mg/L), respectively for Chakdaha and Baruipur areas. The observed values of As and bicarbonate (mean: 409 and 499 mg/L) in the shallow aquifer are indicative of redox processes (e.g., oxidation of organic matter) favouring the release of As. Moreover, the presence of DOC in the shallow aquifer suggests that organic matter is young and reactive, and may actively engage in redox driven processes. Our study further confirms that both Fe- and Mn-reduction processes are the dominant mechanisms for As release in these groundwaters.

Direct determination of hydrophobic organic compounds in aqueous solution in the presence of dissolved organic carbon by high-performance liquid chromatography

A simple and quick method using high performance liquid chromatography is presented to determine hydrophobic organic compounds in aqueous solutions containing dissolved organic carbon. The analytical procedure does not require an extraction or purification step unlike conventional analytical approaches. It was used to measure the water solubility of dibenzofuran (4.55 mg l −1), acenaphthene (3.30 mg l −1), fluoranthene (0.23 mg l −1) and 4-chlorobiphenyl (1.47 mg l −1). The results were compared with those obtained by gas chromatographic quantification. The method was applied successfully to the direct determination of the water solubility of these compounds in the presence of DOC. In a solution of Aldrich humic acid, the water solubility of dibenzofuran, acenaphthene and 4-chlorobiphenyl increased linearly with increasing DOC concentration. The water extractable organic matter from peat led to a smaller solubility of dibenzofuran comparing to the Aldrich humic acid in the same concentration range of DOC.

ADSORPTION OF FLUOMETURON AND NORFLURAZON: EFFECT OF TILLAGE AND DISSOLVED ORGANIC CARBON

Adsorption is an important process that influences the fate and behavior of herbicides in soil. The herbicide adsorption process is influenced by both the dissolved and the solid soil organic carbon (DOC and SOC) content of soil. Both properties are affected by tillage management and biosolid utilization. This study was undertaken to examine the influence of tillage practice and various DOC sources and concentrations on the adsorption and desorption of fluometuron (N, N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea) and norflurazon (4-chloro-5(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone) in the Lexington silt loam (fine-silty, mixed, thermic, Typic Paleudalf). Batch adsorption/desorption studies were performed in the presence and absence of DOC extracted from poultry litter, dairy manure, and no-till surface soil. Herbicide adsorption is influenced strongly by soil organic carbon (SOC) content, with all soils having a greater affinity for norflurazon, relative to fluometuron. Average Koc values of 100 and 500 were determined for fluometuron and norflurazon. The influence of DOC on herbicide adsorption was a function of DOC source and concentration. Poultry litter DOC, characterized as having greater hydrophobicity and high-molecular-mass organic compound content, and dairy manure DOC (containing both low- and high-molecular-mass organic compounds) reduced herbicide adsorption. No-till DOC (hydrophilic with low molecular mass organic compounds) did not influence herbicide adsorption. In general, herbicide desorption was completely reversible. However, the equilibration period required to achieve reversibility varied with herbicide type, adsorption condition (DOC vs. no DOC), and DOC source and concentration in the desorption system. The reduction in herbicide adsorption in the presence of DOC could be attributed to the formation of soluble herbicide-DOC complexes. Further, herbicide desorption from mineral surfaces (low SOC soil) was observed to be more kinetically restricted relative to desorption from SOC (high SOC soil).

Significance of dissolved organic carbon in the prediction of thermocline depth in small Canadian shield lakes

Empirical models used to predict thermocline depths of lakes have typically been based on physical and morpho-metric variables. However, lakes with appreciable levels of dissolved organic material, including those found on the Canadian Precambrian Shield (DOC levels 1.4-12.41 mg/l), have seldom been included in these models. Our analysis suggests that for such lakes, thermocline depth is linked strongly to light penetration (Secchi depth r = 0.83, light extinction r = 0.85) which is strongly related to DOC concentration (Secchi depth r = 0.91, light extinction r = 0.97). A multivariate regression based on small Canadian Shield lakes suggests that DOC is the most important predictor of thermocline depth. Maximum effective length, maximum depth, and chlorophyll a contribute significantly to the prediction power of the regression model, but are of secondary importance in the presence of DOC.

Some Properties and Surface Localization of a Mg2+-ATPase in Microsomal Vesicles of Wheat Seedlings

Summary Microsomal membranes isolated from etiolated wheat seedlings were centrifuged on a discontinuous sucrose density gradient. A band of ionophore-stimulated and nitrate-sensitive ATPase activity was found in low density peak (1.09-1.11 g · ccm-1). There is an evident correlation between the degree of fluorescence quench and ATPase activity, proving that this enzyme acts as a proton pump. The enzyme (opt. ρH 6.2-6.8) preferentialy hydrolysed ATP and was strongly stimulated by gramicidin and nigericin. It was inhibited by DES, DCCD, Dio-9 and KN0 3 and to a slight extent by vanadate, oligomycin and sodium azide. With the use of affinity chromatography on a column with lectin-Sepharose 6 MB it was demonstrated that membrane vesicles are oriented right-side-out, i.e. that their cytoplasmic side is turned outside. Activity measurement of ATPase of microsomal vesicles digested with trypsin in the absence or presence of DOC, as well as upon use of Ca 2+ -ions and ATP (protecting the catalytic centre) permit the assumption that either the whole ATPase molecule or only its catalytic centre occurs on the extracytoplasmic side of microsomal membranes.