Research On Nitrification Kinetics Model Of Seawater Biofilter

The treatment and recycling of the wastewater are the core technologies in themarine Recirculating Aquaculture System （RAS）. Biological aerated filter （BAF）, animportant water treatment unit of a marine RAS, which is used to remove harmfulammonia and organics. In consideration of the characteristic of wastewater in marineculture and marine biofilter, a model about height of pack and COD/TAN wasestablished on the basis of the law of nitrification, the effect of hydraulic retentiontime （or flow rate） and changeable water quality to nitrification efficiency.The research, aim on the Regularity of Ammonia Transformation along MarineBiological Aerated, under the conditions (pH7.1-7.6, DO5-7mg L^-1, gas water ratioabout20:1, organic load about4g （m³·h）^-1) shows that the most ammonia isremoved under the10cm height of medium, while a little ammonia is removed duringthe10cm⁷0cm. Besides, the effluent ammonia concentration increases along witheither the increment of the influent ammonia concentration or the reduction of thehydraulic retention time.In different ratio of COD/TAN, the removal rate of ammonia always increasesalong with the increase of the flow rate, although the growth trend was gentle on theultimate. In the range of COD/TAN from1.57to8.28, the removal rate of ammoniawas increased along with a larger COD/TAN, while a reverse result in the range ofCOD/TAN from8.28to11.08. The effluent nitrite concentrate increases first, andthen decreases with the flow rate increasing. Thepeak value of effluent nitriteconcentrate curvewhen COD/TAN=2.82or3.57was much higher than it whenCOD/TAN=1.57，4.22or11.02.The model, established on the basis of the principle of adsorption and the firstorder reaction bio-film, predicts the ammonia concentration along the BAF accuratelywith a low influent ammonia concentration, but slightly lower than the true value witha high influent ammonia concentration. The model, based on Monod equation and interspecific competition, explainedclearly the changing regularity of biofilter efficiency. It willprovide scientific basisand theoretical guidance for the maintenance and emergency response of biofilter.