Denitrification Abstracts
|
Denitrification in Aquatic Life
Support Systems: Options and Overview Hunter Ryan, California Science Center Watch Video (Login required) Full Abstract
In recirculating aquatic systems, nitrate accumulates as a byproduct of the mineralization and oxidation of nitrogenous compounds produced by the metabolic processes of fishes and other system inhabitants. Nitrate is less toxic than ammonia or nitrite but, in high concentrations, nitrate can pose a health threat to numerous aquatic organisms. In the past, aquarium and aquaculture facilities have relied on partial water changes to control nitrate levels; however, the cost incurred by replacing significant volumes of water in large-scale aquariums can be problematic. In recent years, many facilities have employed methods of biological denitrification to reduce and manage nitrate levels in aquaria. Biological denitrification can be accomplished through autotrophic or heterotrophic processes. Heterotrophic methods contribute to alkalinity and have higher nitrate removal rates than autotrophic methods. Autotrophic denitrification has lower energy yields, but does not require the addition of an external carbon source, produces less sludge and sulfide, and has a higher tolerance for oxygen. There are several common denitrification reactor designs including batch reactors, continuous flow reactors, and mixed design reactors. Additionally, packed bed/column and moving bed reactor configurations are frequently utilized as microbial growth/electron donor substrates. Critical design factors include hydraulic loading rate, nitrogen production rate, hydraulic residence time, and nitrate removal rate. |
Solid Phase Denitrification: A
Sustainable Technology for Reducing Nitrate and Phosphate Concentrations Timothy A. Hovanec, Ph.D., DrTim's Aquatics Watch Video (Login required) Full Abstract
Nitrification, the oxidation of ammonia to nitrite and nitrite to nitrate, while a fundamental process in marine aquaria, is nevertheless poorly understood in terms of the organisms responsible. Recent research shows a much greater diversity of organisms responsible for nitrification than previously believed, especially for the ammonia-oxidizing bacteria (AOB). In marine systems water temperature and organic load play a major role in determining AOB species composition of the nitrifying bacteria consortium. The significance of ammoniaoxidizing Archaea (AOA) has been the subject of much recent research; however, the importance of AOA in marine systems has not yet been definitively answered. |
Recirculating Autotrophic Denitrification for High Removal Rates and User-Friendly Operation
Andrew Aiken, National Aquarium Watch Video (Login required) Full Abstract
Advances in denitrification systems continue to be made, however risks associated with systems that must work within narrow tolerances, and which are susceptible to mismanagement of operational complexity, have prevented their widespread use. Heterotrophic, e.g. methanol-based, systems can be problematic due to high levels of bio-growth and biofouling, as well as erratic nitrate removal rates resulting in production of hydrogen sulfide. Autotrophic, e.g. sulfur-based systems for large aquaria can be too large to suitably fit in mechanical rooms due to inefficient removal rates. The National Aquarium in Baltimore employs an efficient sulfur-based autotrophic denitrification system that attains a peak removal rate of 7 kg NO3-/m3 S-day, which is more than three times greater than the removal rate of common autotrophic sulfur denitrification systems. The total footprint of the system is <8 m2. Nitrate removal rates are high while bio-growth and bio-fouling remain low. Annual seawater savings is 855 m3 for each system. Operation of the system does not require elaborate control equipment such as ORP sensors or modulating valves. Operation is user-friendly, and consists of only three operator functions: manual adjustment of system flow rates, filter backwashing and purging of nitrogen gas. |