Analysis of Nitrogen Sedimentation in the Advanced Integrated Wastewater Pond System (AIWPS) at Richmond Field Station, U.C. Berkeley Clement Hsieh Environmental Sciences Dept., U.C. Berkeley Abstract Wastewater systems are necessary for the reduction of limiting nutrients such as nitrogen. High levels of nitrogen flow into the wastewater system. After treatment, nitrogen is expected to flow out below limits set by government agencies. The nitrogen that is removed in the Advanced Integrated Wastewater Pond System (AIWPS) partially settles to the bottom of the various ponds after having been incorporated into algae. Currently, the AIWPS does not remove nitrogen below limits established by the EPA. The objective of this study is to determine the pathway in which nitrogen is removed so that future modifications to the AIWPS can be more effective in removing nitrogen. Once complete and fully operational, the AIWPS can be replicated in developing nations and remote locations in advanced countries as an effective, low-cost method of wastewater treatment. Anoxic conditions at the bottom of the ponds in the AIWPS rarely support nitrate and nitrite forms of nitrogen. Organic nitrogen appears to be the most abundant form of nitrogen present in the ponds. The amount of nitrogen measured in the sediment indicates that settling is not the primary method of nitrogen removal in the AIWPS. Total Kjeldahl Nitrogen analysis has revealed an average concentration of 49.5 mg TKN/g sediment in the advanced facultative pond (AFP), 40.4 mg TKN/g sediment in the high rate pond (HRP), and 34.7 mg TKN/g sediment in the settling basins (SB). Ammonia analysis has revealed a level of 9.27 mg NH3/g sediment in the advanced facultative pond (AFP), 1.54 mg NH3/g sediment in the high rate pond (HRP), and 4.30 mg NH3/g sediment in the settling basins (SB). Depth measurements of sediment along with known dimensions of the ponds allowed quantification of N-compound pathways: 4% of inflow settles into the sediment, 79.6% of which is removed by the AFP, 16.2% by the HRP, and 4.2% by the SBs.Introduction Nitrogen is usually abundant in raw sewage that first enters a wastewater facility (Lundquist 1999, pers. com.). Once inside a pond, nitrogen in its various forms can go to a gaseous state, become trapped in solids and settle, or be suspended in the wastewater pond (Horne and Goldman 1994). During the summer, some nitrogen is lost to the atmosphere at a higher rate (Lundquist 1999, pers. com.). Various algae can also obtain and incorporate nitrogen flowing into the pond (Horne and Goldman 1994). One purpose of wastewater systems is to remove potential limiting nutrients like nitrogen from the water to prevent eutrophication from occurring wherever treated wastewater flows. Nitrogen exists in various forms in water systems, including nitrate and nitrite, organic nitrogen (defined as “organically bound nitrogen in the trinegative oxidation state” (Standard Methods Committee 1994), and ammonia. Total oxidized nitrogen consists of nitrate and nitrite nitrogen. Of the specific forms of nitrogen, both nitrate and nitrite have been identified as growth-limiting nutrients, but have also been identified as toxic substances in high doses, known to cause methemoglobinemia in infants (SMC 1994). For these reasons, limits have been imposed on nitrate and nitrite concentrations in drinking water supplies. Limits have also been imposed on nitrogen levels from wastewater that flows back into the environment. Wastewater systems have been designed to reduce amounts of toxins, suspended solids, and potential limiting nutrients below limits set by local, state, and national governments (Frankenbach and Meyer 1999). Without wastewater management systems, excess nutrients can destabilize ecosystems, cause anoxia, and kill large populations of aquatic life (Horne and Goldman 1994). Also, lack of wastewater management systems can result in biological and chemical toxins entering drinking water sources such as groundwater (Palin 1950). The system currently being studied is monitored for nitrogen inflow and outflow. Using data collected over a period of time, it is possible to determine how much nitrogen the wastewater treatment system removes. Data regarding nitrogen attenuation at this facility does not yet exist. The purpose of this study is to determine if nitrogen is settling into the sediment at the bottom of the wastewater ponds and if so, in what quantity. Knowledge of this information is important in understanding how the overall system works to remove nitrogen in wastewater. More specifically, the study can potentially determine which sectionof the system performs nitrogen removal most efficiently. This determination can recommend future studies into making other ponds in the wastewater treatment system more efficient in nitrogen removal for improvement. Alternative, low-technology treatment centers such as this study site could become sufficiently effective at nitrogen removal to benefit developing communities that cannot afford current standard wastewater facilities. Study site. This study was located at the Richmond Field Station, under operation of the University of California at Berkeley. The study site contains a laboratory responsible for designing alternative wastewater systems that are cost-efficient and require little maintenance and advanced materials. These systems are intended for use in developing nations that have few resources to dedicate to wastewater management. The wastewater system known as the Advanced Integrated Wastewater Pond System (AIWPS) and the Algae Laboratory operate under Environmental Engineering and Health Sciences Laboratories (EEHSL) (Oswald, 1999). The AIWPS consists of two large ponds and a set of three settling bins. Wastewater from the city of Richmond enters the digester pit located at the center of the advanced facultative pond (AFP). The digester pit is surrounded by an octagonal wooden platform that also extends to the edge of the pond. The pit provides an anaerobic environment for bacteria. These anaerobic bacteria break down sewage through fermentation, reducing biological oxygen demand (BOD) and releasing methane. Water overflows from the digester pit into the AFP. The AFP serves as an aerobic environment for algae processes. Algae take up nutrients such as nitrogen and phosphorus released by bacterial processes. This treated sewage