Nitrogen Recovery in WasteWater Treatment - Term Paper Example

Nitrogen in domestic wastewater consists of approximately 60 to 70 percent ammonia?nitrogen and 30 to 40 percent organic nitrogen (Tchobanoglous et al. 2003; Crites and Tchobanoglous 1998). Environmental Effects Health Effects from Drinking Groundwater Contaminated with Nitrates- Human health concerns from nitrates in groundwater used as a drinking water source primarily focus on methemoglobinemia, however some studies suggest that nitrates may increase the risk of birth defects and development of certain cancers in adults.

Surface Water Pollution with Nitrogen- The harmful effects of eutrophication due to excessive nitrogen concentrations in the aquatic environment have been well documented. Algae and phytoplankton growth can be accelerated by higher concentrations of nutrients, leading to harmful algal blooms, hypoxia, and loss of submerged aquatic vegetation (SAV). In addition to stimulating eutrophication, nitrogen in the form of ammonia can exert a direct demand on dissolved oxygen (DO) and can be toxic to aquatic life.

Even if a wastewater treatment plant (WWTP) converts ammonia to nitrate by a biological nitrification process, the resultant nitrate can stimulate algae and phytoplankton growth. Removal of nitrogen from wastewater is a complex process, even for large wastewater treatment plants. Quality control of nitrogen removal processes from individual onsite wastewater systems is even more difficult to manage. Most of the nitrogen is released as nitrate (NO3-), which is highly mobile in the soil water. Wastewater treatment has generally been defined as containing one or more of the following four processes: (1) preliminary, (2) primary, (3) secondary, and (4) advanced (or tertiary) treatment.

Preliminary treatment consists of grit removal, which removes dense inert particles, and screening to remove rags and other large debris. Primary treatment involves gravity settling tanks to remove settleable solids, including settleable organic solids. The performance of primary settling tanks can be enhanced by adding chemicals to capture and flocculate smaller solid particles for the precipitation and removal of phosphorus. Secondary treatment follows primary treatment in most plants and employs biological processes to remove colloidal and soluble organic matter.

EPA classifies advanced treatment as “a level of treatment that is more stringent than secondary or produces a significant reduction in conventional, non?conventional, or toxic pollutants present in the wastewater” (U.S. Public Health Service and USEPA 2008). Effluent filtration and nutrient removal are the most common advanced treatment processes. Nitrogen Removal Processes The biological removal of nitrogen is carried out through a three-step process: (1) the conversion of ammonia from organic nitrogen by hydrolysis and microbial activities, called ammonification; (2) the aerobic conversion of ammonia to nitrate by reacting the ammonia with oxygen in a process called nitrification; and (3) the conversion of nitrate to nitrogen gas by reacting the nitrate with organic carbon under anoxic conditions in a process called denitrification.

The nitrification process is accompanied by the destruction of alkalinity (e.g., bicarbonate, HCO3-, is neutralized to carbonic acid, H2CO3). Alkalinity is recovered as part of the denitrification process with the generation of hydroxide. The chemical equations involved in the biological conversion of nitrogen are as follows: 1. Formation of ammonia fro