The fate of selenium in an algal-bacterial system in the San Joaquin Valley of California, public health considerations

The fate of selenium in an Algal-Bacterial Selenium Removal (ABSR) Facility was studied during the period November 1998 through November 1999 in the Panoche Drainage District of the San Joaquin Valley of California. The facility consists of two pond systems running in parallel each utilizing a different organic material as a reducing agent, a molasses-fed North ABSR System and an algae-fed South ABSR System.; The main objectives of this study were: (1) to develop and validate a method for selenium determination in treated agricultural drainage water, (2) to validate a method for selenium determination in sediment samples, and (3) to characterize the potential hazard to wildlife of the ABSR Facility and to evaluate the minimization of selenium exposure to wildlife.; The standard method (APHA et al. 1995) for the digestion of water samples and subsequent determination of total soluble selenium by hydride generation atomic absorption spectrometry (HGAAS) was modified and validated. The amount of 2% (w/v) persulfate added for digestion of water samples from the ABSR Facility was higher than that recommended in the APHA Standard Methods. The need for higher 2% persulfate doses appears to be associated with the presence of organic compounds in the water.; Accuracy of total selenium determinations in sediment samples was assessed by comparison of two digestion methods during the process of sample preparation. The two digestion methods, the Martens and Suarez Method (1997a) and the LBNL Method (1998), were compared. Significant differences were found in 30% of the samples. Assessment of those differences found that the Martens and Suarez Method is more suitable to digest sediment samples collected at the ABSR Facility. Selenium levels in sediments of the reduction ponds were the highest found in the literature (400 to 895 μg g−1).; The drainage water selenium load that entered the facility during the study period was estimated at approximately 8.6 kg (>99% as selenate). Of that load, 5.5 kg were applied to the molasses-fed system while 3.1 kg were applied to the algae-fed system. The molasses-fed system removed approximately 63% of the applied selenium load while the average selenium removal by the algae-fed system was 11%.; Projections for a full-scale ABSR Facility treating 470 L s−1 (17 cfs) of agricultural drainage water are promising, and such a facility would remove up to 932 kg of total selenium annually. The minimization of selenium exposure to wildlife comes accompanied by the projection to remove >90% of the nitrate influent load thereby reducing the potential for further eutrophication of the San Joaquin River and the Delta.