Bio-electrochemical removal of nitrate from water and wastewater--a review.

Hydrogenotrophic denitrification of potable water: a review.

Nitrogen (N) is applied worldwide to produce food. It is in the atmosphere, soil, and water and is essential to all life. N for agriculture includes fertilizer, biologically fixed, manure, recycled crop residue, and soil-mineralized N. Presently, fertilizer N is a major source of N, and animal manure N is inefficiently used. Potential environmental impacts of N excreted by humans are increasing rapidly with increasing world populations. Where needed, N must be efficiently used because N can be transported immense distances and transformed into soluble and/or gaseous forms that pollute water resources and cause greenhouse effects. Unfortunately, increased amounts of gaseous N enter the environment as N2O to cause greenhouse warming and as NH3 to shift ecological balances of natural ecosystems. Large amounts of N are displaced with eroding sediments in surface waters. Soluble N in runoff or leachate water enters streams, rivers, and groundwater. High-nitrate drinking water can cause methemoglobinemia, while nitrosamines are associated with various human cancers. We describe the benefits, but also how N in the wrong form or place results in harmful effects on humans and animals, as well as to ecological and environmental systems.

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Nitrogen in the Environment: Sources, Problems, and Management

Overview of in-situ applicable nitrate removal processes

Biological denitrification was reviewed regarding its potential application to treating nitrate in industrial wastewater. Although heterotrophic denitrification is an efficient and well-developed process, some carbon content in wastewater is essential to maintain bacterial activity. Because of the high operating cost of heterotrophic denitrification caused by the required addition of a carbon source and potential “carbon breakthrough”, the study of autotrophic denitrification has attracted the interest of numerous researchers. Many advances in autotrophic processes have been made in the application of novel concepts and reaction schemes. While the main advantage of autotrophic bacteria rests on the reduction of operating costs by the replacement of an external carbon source with a cheaper electron donor, further decrease in cost requires additional refinement of these processes, including further improvement of reactor structure and optimization of reaction conditions. In the long term, new concepts are required for a compact wastewater treatment process. This review addresses the state of the art of each electron donor candidate for its potential application to the treatment of industrial wastewater containing nitrate.

Biological nitrate removal in industrial wastewater treatment: which electron donor we can choose

On-site nitrate removal of groundwater by an immobilized psychrophilic denitrifier using soluble starch as a carbon source.

To maximize nitrogen utilization rates during nitrification and denitrification in a simultaneous reaction for direct nitrogen removal from ammonia–nitrogen in a single reactor, two different carriers were applied that immobilized nitrifiers and denitrifiers separately. With the optimized DO concentration and mixing ratio of immobilization carriers, ammonium–nitrogen was successfully removed as designed until the middle phase of treatment where nitrogen removal rate was higher than 83% of the theoretical value, although an imbalance between nitrification and denitrification occurred at a later phase of treatment where residual nitrate–nitrogen concentration was less than 2 mg/l. The new approach using two different carriers to immobilize nitrifiers and denitrifiers separately was proved useful for controlling both nitrification and denitrification rates, enabling the utilization of maximum treatment ability of both nitrifiers and denitrifiers in a single reactor for direct nitrogen removal from ammonium–nitrogen.

Improved simultaneous nitrification and denitrification in a single reactor by using two different immobilization carriers with specific oxygen transfer characteristics

Simultaneous nitrification-denitrification under fixed constant dissolved oxygen (DO) condition in a single reactor was examined by using two different carriers, polyacrylamide-gel carrier and cellulose carrier immobilizing nitrifiers and denitrifiers, respectively. The DO condition enabling the highest simultaneous nitrification-denitrification rate was found between 0.5 and 0.75 mg/l. When DO concentration of culture broth was maintained at 0.5 mg/l, the simultaneous nitrification-denitrification was successfully realized in a single reactor as designed, resulting in the apparent nitrogen removal rate corresponding to 83% of the theoretical value.

Simultaneous Nitrification-Denitrification under Constant Dissolved Oxygen Condition by Using Two Different Immobilization Carriers with Specific Oxygen Transfer Characteristics

Tae-Jong Lee

Papers

On-site nitrate removal of groundwater by an immobilized psychrophilic denitrifier using soluble starch as a carbon source.

Improved simultaneous nitrification and denitrification in a single reactor by using two different immobilization carriers with specific oxygen transfer characteristics

Simultaneous Nitrification-Denitrification under Constant Dissolved Oxygen Condition by Using Two Different Immobilization Carriers with Specific Oxygen Transfer Characteristics