Suwannee River NOM
IHSS has recently used reverse osmosis to isolate more than 1000g of natural organic matter (NOM) from the Suwannee River. The sample was collected from the same site that was used originally to collect the standard Suwannee River humic and fulvic acids. The new NOM sample is now available from the IHSS for $20 per 100mg. The elemental composition of dry Suwannee River NOM is: 48.8 %C; 3.9 %H; 39.7 %O; 1.02 %N; 0.60 %S; 0.02 %P; 7.0 %Ash (Total 101.0%). A brief description of the sampling trip and isolation procedure follows.
From May 1 through May 9, 1999, a group representing the International Humic Substances Society (IHSS) visited the Suwannee River in south Georgia, U.S.A. to collect a new reference sample of natural organic matter (NOM). This reference NOM sample will complement the standard and reference humic and fulvic acids that were previously collected from the Suwannee River. The members of this group included Dr. James Alberts and Dr. Monika Takács of the University of Georgia Marine Institute at Sapelo Island and Dr. Michael Perdue and Ms. Lili Ding of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.
The sample was collected at the first dam on the Suwannee River sill, on the southwestern edge of the Okefenokee Swamp near Fargo, GA. The project was authorized by the Board of Directors of IHSS, and access to the sill was granted by the Okefenokee National Wildlife Refuge in Folkston, GA. During the nine-day project, 33 concentrated samples were collected. For each sample, a 120-gallon aliquot of Suwannee River water was prefiltered successively through 1 µm and 0.4 µm polypropylene filters and concentrated to about six gallons using a RealSoft PROS/2S portable reverse osmosis system. After a concenrated sample was obtained, its temperature was maintained at or below the temperature of the river. Overall, 3960 gallons of water (about 14,990 liters) were concentrated to a final volume of 199 gallons (about 753 liters).
Because the chemical composition of the Suwannee River was expected to vary during the time required to collect the entire sample, a volume-weighted composite sample of the prefiltered Suwannee River water was prepared by collecting and combining 10-mL aliquots at periodic intervals (every 40 gallons). The composite sample, which was stored on ice at all times, had a pH of 3.93 and a TOC concentration of 39.2 mg/L (3.27 mmol/L).
While a sample was being concentrated, it was circulated continuously through a cation exchange resin (H+-form) to remove most major cations. The "field-desalted" concentrated samples had pH values of 2.8 ± 0.1, well below the average pH of 3.93 for the prefiltered water. During the operation of the reverse osmosis system, the permeate flow rate gradually decreased due to adsorption of organic matter on the reverse osmosis membranes. At the low pH values of the concentrated samples, the adsorbed organic matter was probably enriched in humic acids. To recover this organic matter and to increase the permeate flow rate, a single 12-liter solution of 0.01 M NaOH was used on three occasions (about once every three days) to rinse the reverse osmosis membranes. Its final pH was about 6.5.
The samples were transported to Dr. Perdue's laboratory at Georgia Tech on May 10, 1999. In the laboratory, the reverse osmosis membranes were rinsed a final time with 10 liters of 0.01 M NaOH to recover some additional adsorbed organic matter. The two NaOH rinse solutions were desalted using a cation exchange resin (H+-form) and then mixed into the other 33 concentrated samples. The concentrated samples were then desalted for a final time, using 250-ml columns of cation exchange resin (H+-form) at a flow rate of about 100 ml/min. A volume-weighted composite sample was prepared from the desalted, concentrated samples. Its pH was 2.54 and its TOC concentration was 725 mg/L (60.4 mmol/L). From the volumes and TOC concentrations of the prefiltered water and the final concentrated samples, the percent recovery of organic carbon was calculated to be 92.9%.
During the three weeks that the samples were being processed in Dr. Perdue's laboratory at Georgia Tech, they were stored in a cold room at 4-6 °C. For two days, while the cold room was not operational, the samples were cooled with ice.
On May 31, the 31 carboys of desalted, concentrated samples were shipped by truck to Van Drunen Farms in Momence, IL, where they were stored in a cold room until an IHSS representative could arrive to supervise the freeze-drying process. Finally, on June 7-9, the samples were freeze-dried under the supervision of Dr. Perdue. Approximately 1060 g of freeze-dried natural organic matter was obtained. The freeze-dried product was transferred back to Georgia Tech for pulverization, homogenization, and final drying.
Nordic Reservoir NOM
This sample was obtained from a drinking water reservoir at Vallsjøen, Skarnes, Norway on October 29 to November 3, 1997 under the direction of Egil Gjessing. The reservoir is at 225 m above sea level and has a maximum depth of depth of about 14 m. The sample was obtained from the Sør-Odal County Waterworks intake pipe that draws water from at depth of 10m (pH = 5.6, EC = 2.1 mS/m and DOC = 10.7 mg/L). The water temperature was 4o C.
The initial concentration was done using a RealSoft PROS/2S portable reverse osmosis system (Serkiz & Perdue). The water was first pumped through a sodium saturated Dowex -50 cation exchanger. No filtration was used. The permeate was discarded and the retentate was recirculated back to the sample reservoir. For every 1 m3 of water isolated, the RO membrane and the cation exchanger were back washed with 0.006 M NaOH.
The resulting 130 L of RO-isolate was concentrated further by roto evaporation. The temperature of the concentrate did not at any time exceed 25o C during this low-pressure evaporation. The remaining 10 L of concentrate containing about 250 mg of C was filtered under 7 atmospheres of pressure through 142 mm Sartorius membrane filters with nominal pore size of 0.45 µm. The filtered concentrate was freeze dried.
The Nordic Chapter of the IHSS distributed the Nordic NOM sample until 2001 when it became part of the IHSS collection.
Reference:
Serkiz, S.M. and Perdue, E.M. (1990) Isolation of dissolved organic matter from
Suwannee River using reverse osmosis. Water Res. 24,
911 - 916.