Analysis of Total Suspended Solids and Dissolved Oxygen Concentrations of the Algal- Bacterial Selenium Removal (ABSR) system

The Algal-Bacterial Selenium Removal (ABSR) system has been very effective at removing Selenium from agricultural drainage water that enters the water systems of the San Joaquin Valley, CA. Although selenium levels are significantly lower in the effluent of the ABSR system, Dissolved Oxygen (DO) levels in effluent water have been found to be significantly lower than normal. If DO levels dip under 5mg/L saturation, aquatic life is put under stress. At levels 1-2mg/L saturation, fish would likely start to die off. The purpose of this study was to examine the affect the ABSR system has on the DO levels in its effluent. Water samples were collected from two ABSR pond systems in Panoche, CA, where there are two systems with different pathways. The Low-cost system has influent going into a high rate pond (HS) and then goes into a reduction pond (RS), so anoxic bacteria uptake the selenium. The High-efficiency system has influent water going into a reduction pond (RN), and then put through as sand filter (NSSF). The effluent of both systems were tested for Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) levels, which are related to DO saturation levels in water. In the Low-cost system, levels from the effluent showed increases in both BOD and TSS levels. In the High-efficiency system, there are increases in BOD and TSS levels as well. Although increases in both BOD and TSS levels were found, the High-efficiency system was able to stay within EPA limits. The Low-cost system failed to meet EPA standards for TSS levels. In conclusion, the effluent coming out of the High-efficiency systems will not substantially lower DO saturation levels to dangerous limits. Introduction Much of the drainage water in the San Joaquin Valley is contaminated by runoff from land that is used for agricultural purposes (Green 2001). Agricultural waste and chemicals are often found in high concentrations in the discharge from agricultural drainage systems (Oswald 1988). The discharge enters the San Joaquin River by way of sloughs that lead directly to the river (Green 2001). The runoff from the agricultural land negatively affects the water quality of the river, which then affects the wildlife surrounding the river (Green 2001 and Zarate 1999). Dissolved oxygen (DO) plays a vital role in determining water quality. Like organisms on land, fish and other aquatic organisms require oxygen in order to survive. Oxygen enters the aquatic system through several pathways. One way is from the photosynthesis process of aquatic plants (Water Shedds: Dissolved Oxygen, elect. Comm. 2002). During photosynthesis plants release oxygen, aquatic plants release this oxygen into the water. Another way for oxygen to enter is through the water-air interface where oxygen from the atmosphere is dissolved into the water. Gas solubility increases as water temperature and salinity decrease (Water Shedds: Dissolved Oxygen, elect. Comm. 2002). There are also processes that will use up the dissolved oxygen in the water. These include the respiration of organisms, and the decomposition of organic material by bacteria. If DO levels drop under 5mg/L saturation, aquatic life is put under stress. At levels or 1-2mg/L fish would likely suffocate to death (Water Shedds: Dissolved Oxygen, elect. Comm. 2002). The site in the Panoche Drainage District, in the San Joaquin Valley uses the ABSR system. The purpose of the ABSR is to remove Selenium (Se), on top of Nitrate. It consists of three ponds. The first is a reduction pond (RP) where Anoxic Bacteria are used to uptake the selenium, which is often in the form of selenate (SeO6) (Quinn). In the RP organic carbon in the form of Molasses is added to promote bacteria activity. The second pond is an HRP, similar to the one in the AIWPS. Here Algae grows and assimilating carbon dioxide, ammonium and phosphates. There are two different pond systems within the Panochec system. One is the Highefficiency system, and the other is Low-cost system. The differences between the two include a different arrangement of the different ponds, and molasses is added to the High-efficiency pond as a nutrient for bacteria. Table 1. The Panoche ABSR systems. There have been prior research projects that have looked at the affects and usefulness of these systems. In 2001, Diana Stuart researched the ABSR system in Panoche for its effectiveness in removing Selenium (Stuart, D. 2001). Stuart sought to show whether or not the ABSR system would effectively remove the bioavailability of Selenium in the effluent water. Stuart concluded that although the system was effective in removing selenate, it did not remove Organic Selenium effecitively (Stuart 2001). Another project by Atsushi Hatano in 2001 focused on Nitrogen removal in the AIWPS in Delhi and Panoche. Hatano’s goal was to find out transformation pathways and the removal rates of nitrate, nitrite and ammonium nitrogen in the AIWPS (Hatano 2001). Hatano also wanted to determine if pH, DO, and temperature had on affect on the transformation pathways and the removal rates. Hatano concluded that the AIWPS in Delhi was more effective at removing Nitrogen than a similar system in Panoche (Hatano 2001). Also, it was found that only temperature had a substantial affect on the transformation pathways and removal rates. Previous research was also done on the cost effectiveness and efficiency of the AIWPS technology. In a study by Zarate and his group, the application of the AIWPS technology to chemically contaminated agricultural drainage water was studied using a demonstration plant. The study concluded that the technology was efficient, removing enough selenium and nitrates to High Efficiency System Low Cost System Effluent Sand Filter Algae Removed High Rate Pond Molasses Removed Algae Grows CO2 Consumed Reduction Pond Molasses Added Selenate and Nitrate Reduced Effluent Reduction Pond Algae Settles Selenate and Nitrate Reduced High Rate Pond CO2 and Nutrients Added Nitrate Assimilated by Growing Algae Influent Agricultural Waste Water