Dissolved Organic Research Articles

Trihalomethanes in finished drinking water in relation to dissolved organic carbon and treatment process for Alberta surface waters

Abstract Disinfection by‐products are formed when the disinfectant (often a strong oxidizer) reacts with bulk dissolved organics in the water during treatment and distribution. The relationship between trihalomethanes (THMs) and bulk dissolved organics (DOC) in the finished drinking water for municipal treatment plants in Alberta using surface waters has been summarized. Treatment processes considered included chlorination with filtration alone, chlorination with complete treatment (coagulation, sedimentation and filtration [CSF], with or without additional treatment such as aeration and activated carbon), and chloramination with CSF. Trihalomethane levels were significantly correlated with the content of DOC as would be expected. For complete treatment systems using chlorination, the average THM yield was approximately 11 μg THM per mg of DOC. These data suggest that if the DOC level of the treated water exceeds 4 mg L‐1, the average THM will likely exceed 50 ug L‘1 if chlorination is used. For chloramin...

Contribution of humic substances to the dissolved nitrogen pool in the Greenland Sea

The concentration and distribution of dissolved nitrogenous compounds was studied in the Greenland Sea in June 1991. Dissolved organic (DON) and inorganic nitrogen (DIN) were determined in seawater of different origin and depth. Dissolved organic matter was isolated on XAD-2 resin and fractionated into its non-humic hydrophilic (H1), and so-called humic components (hydrophobic acid, HbA, and hydrophobic neutral, HbN). From all fractions the DON content was subsequently determined. Total DON concentrations were about 5 μmol Ni −1 in the surface and 3 μmol NI −1 below depths of 150–200 m. DIN varied between 1.5 and 1.6 μmol NI −1. There was a highly significant inverse correlation ( r = −0.75) between DON and DIN suggesting a close coupling in the uptake and release of the different forms of nitrogen. The mean DON concentrations of the XAD-fractions were for HI = 2.3 μmol Ni −1, for HbA = 0.8 μmol NI − and for HbN = 1.0 μmol NI −1. The average percentage contributions were, respectively, 56%, 19% and 25%. This means that about 56% of the total DON does not belong to the ‘humic fraction’. The HbN fraction was evenly distributed in the water column, without any obvious relationship with water masses, depth, or nutrient status. In contrast, the HbA fraction showed a significant correlation with total DON.

Chemical regeneration of granular activated carbon from an operating water treatment plant

Granular activated carbon (GAC) from an operating water treatment plant was used to study the effectiveness of a chemical regeneration procedure. The ability of new, used and regenerated carbon to remove dissolved organic (DOC) and taste and odour causing compounds from water was established using simple column experiments. Surface properties of the carbon were studied using X-ray photoelectron spectroscopy, surface titrations and microelectrophoresis. The results have been interpreted in terms of surface characteristics caused by variation in pH.

Dissolved Organic and Inorganic 14C Concentrations and Ages for Coastal Plain Aquifers in Southern Maryland

The Aquia (Paleocene) and Magothy (Late Cretaceous) Formations of the Atlantic Coastal Plain represent two well-characterized (hydrodynamically and geochemically) aquifers in southern Maryland. 14C measurements of the dissolved organic (DOC) and inorganic carbon (DIC) of Aquia and Magothy groundwaters have been made using accelerator mass spectrometry (AMS). Both DI14C and DO14C concentrations in the initial flow path are unexpectedly low. As the water progresses farther from the recharge area, the DI14C percent modern carbon (pMC) is consistently lower than the DO14C pMC; this difference stays constant for all samples. The 14C-derived ages for an Aquia water sample downgradient at Site 4 are 17 ka and 12 ka for DI14C and DO14C, respectively. Radiocarbon ages have been compared to ages determined by two other independent dating methods: computer-simulated hydrodynamic modeling and age estimates based on changes in Cl−, 18O and 2H distributions, which are interpreted to be influenced by sea level and climate.

Kinetics and mechanisms of dissolved organic carbon retention in a headwater stream

Freeze-dried aqueous extracts of autumn-shed maple leaves, birch leaves, and spruce needles were added to a third-order reach of Bear Brook, New Hampshire at concentrations similar to those predicted to occur during peak leaf fall. Leachate from each species was rapidly removed from solution. With initial concentrations of added leachate of approximately 5 mgl−1, dissolved organics (DOC) uptake ranged from 73 to 130 mg m−2 h−1 for the first five hours of travel downstream from the point of addition. There was no preferential removal of DOC of low molecular weight, or of monomeric carbohydrates relative to phenolics or unidentified DOC. Stream sediments and organic debris rapidly removed DOC from solution in laboratory experiments. No significant flocculation or microbial assimilation of sugar maple leachate occurred in stream water alone. Stream sediments showed small increases in respiration with addition of leaf leachate, but no increase in respiration occurred upon addition of leachate to organic debris. Abiotic adsorption due to the high concentrations of exchangeable iron and aluminium in stream sediments may be responsible for much of the rapid removal of leaf leachate observed in field experiments. Abiotic processes appear to retain DOC within the stream, thereby allowing subsequent metabolism of dissolved organic carbon by stream microflora.

Nutrient and particulate fluxes in a salt marsh ecosystem: Tidal exchanges and inputs by precipitation and groundwater 1

Waterborne nutrients enter Great Sippewissett Marsh through groundwater, rain, and tidal flooding. The ebb of tidal water removes nutrients. During summer, uptake by marsh biota leads to net import of nutrients. The increased export of ammonium in August may be due to leaching from senescent marsh plants. There is a net annual export of ammonium, nitrate, nitrite, dissolved organic (DON) and particulate (PN) nitrogen, particulate carbon (PC), and phosphate. Ammonium, DON, and PN are the major forms of nitrogen exported. Nutrient concentrations in coastal and marsh water are correlated, and marsh exports could contribute substantially to nutrient supplies of coastal waters.Groundwater entering the marsh provides primarily NO3‐N and DON. Nutrient inputs through precipitation consist primarily of DON, NO3‐N, and NH4‐N. Particulate materials in rain have a high C:N ratio, contributing little to enrichment of the nitrogen‐limited salt marsh. Groundwater carries over 20 times the amount of nutrients brought in by rain. The nitrogen provided by both sources is more than enough to support annual plant growth. Inputs of nitrogen by groundwater arc therefore important to the nitrogen economy of a salt marsh.About half the dissolved inorganic nitrogen brought into the marsh by groundwater is converted to and exported as PN. The marsh thus transforms the nitrogen that would have been used by primary producers into a form suitable for consumers such as shellfish. Large amounts of apparently refractory DON enter the marsh in groundwater and similar amounts are exported by tides. PC exported to coastal water is equivalent to 40% of the net annual production of Spartina alterniflora, the dominant marsh plant.