A fertilizer plant effluent that contains high levels of ammonia was treated using a four-stage, fixed-film aerated bioreactor in a pilot plant design. Ammonia concentrations in the influent wastes were maintained up to 480 mg L−1 NH3-N and reactor hydraulic loading rates were varied up to 0.14 m m−2 d−1 during continuous operation. Process performance was satisfactory and nitrification rates were determined based on steady-state operation. Ammonia removal was not inhibited by the organic content and the high ammonia concentrations of the influent waste. Removal rates obtained at 20°C ranged between 0.49 to 3.23 NH3-N per day per g volatile solids of attached biomass, which are considerably higher than those reported for the activated sludge and RBC processes under similar operating conditions. This could be attributed to the good oxygen transfer capacity and the large quantity of attached biomass attained in the studied reactor. The rate of nitrification in this system apparently follows first-order kinetics. Design relationships were developed for nitrification of fertilizer effluent and an optimum design loading of 25 g NH3-N m−2d−1 is recommended to achieve higher than 90% ammonia removals.

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