Aerobic and anaerobic biofiltration in an aquaculture unit—Nitrite accumulation as a result of nitrification and denitrification

pH-decrease in nitrifying biofilms

Nitrate removal characteristics of high performance fluidized-bed biofilm reactors.

raw wastewater provides the energy source and serves as the electron donor for the denitrification reaction. Full-scale in dustrial experience16 and cost comparisons based on municipal systems17 have indicated the potential of the pre-denitrification process for nitrogen control. The process flowsheet of the coupled, two-stage fluidized bed pilot plant is shown in Figure 1. The pilot plant consisted of an anoxic denitrification fluidized bed reactor, 150 mm in di ameter, and an oxygenic nitrification fluidized bed reactor, 290 mm in diameter. The initial empty bed reactor volumes were 58.5 L and 210 L for the anoxic and oxygenic beds, respectively. However, the bed heights and reactor volumes were adjustable by relocating the position of the sand-biomass separation systems. Pure oxygen was supplied to the nitrification reactor through a proprietary oxygen transfer device (Dorr-Oliver Inc.). High internal recycle rates were necessary for both reactors to maintain the required fluidization fluxes, to ensure an adequate oxygen supply to the nitrification process and to return nitrate and nitrite to the denitrification reactor. The support media in both reactors was quartzite sand with an effective size of 0.48 mm and a uniformity coefficient of 1.23.

Two-stage biological fluidized bed treatment of coke plant wastewater for nitrogen control

The authors discuss fixed-film nitrification studied in a pilot-scale fluidized bed treating municipal secondary effluent. A mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence-time distribution, was developed to predict the steady-state and short-term dynamic performance of the reactor. The model equations were solved using orthogonal collocation with trial functions tailored to the spherical-shell biofilm geometry, and a semi-implicit third-order Runge-Kutta integration technique. The steady-state model closely fit measured concentration profiles using the maximum specific growth rates for Nitrosomonas and Nitrobacter as adjustable parameters. The dynamic model predicted observed responses to set and impulse changes in ammonium and nitrite concentrations to within 3 mg/L without further parameter adjustment. The fluidization model predicted the observed fluidized bed height within 1 cm.

Dynamic model of nitrification in fluidized bed

Experiments were conducted to describe the kinetic performance of a pilot scale biological fluidized bed reactor for municipal wastewater denitrification. A half-order kinetic model (8 to 48 mg·1 –1 NO 3 +NO 2 -N), coupled with an Arrhenius temperature dependence relationship (4 to 27°C) was adequate to describe denitrification. Neither biofilm support media (granular activated carbon and sand) or hydraulic flux (0.25 to 1.7 m 3 ·m –2 ·min –1 ) were found to be significant factors in controlling the denitrification rate. Under similar influent wastewater conditions, the fluidized bed process provided equivalent NO 3 +NO 2 -N removal at volumetric denitrification rates approximately ten times as fast as suspended growth or submerged rotating biological contactor (RBC) processes. Temperature dependency of the removal rate was less than for suspended growth or submerged RBC processes, but similar to the dependency in a packed column.

K.L. Murphy

Papers

Kinetics of biological fluidized bed wastewater denitrification