Startup strategy for partial nitritation treatment of anaerobically digested effluent of swine wastewater in a sand filter

• The PN process can be maintained in a sand filter without any forced aeration.
• The startup strategy for PN was to gradually increase influent ammonium and pH.
• The principal cause for nitrite accumulation was high free ammonia concentration.
• An effluent with the desired NO2−-N/NH4+-N ratio of 1.02 was obtained for ANAMMOX.

This research investigated the startup of the partial nitritation (PN) process in a sand filter at ambient room temperature (5.5–27 °C) to produce an effluent suitable for the subsequent anaerobic ammonium oxidation (anammox) process. A naturally ventilated sand filter was used to treat anaerobically digested effluent of swine wastewater. Startup strategy of gradual step increases in the influent ammonium nitrogen concentration and pH successfully achieved the PN process. The principal cause for nitrite accumulation was high free ammonia concentration (up to about 20 mg L−1). An effluent with a nitrite-to-ammonium ratio of 1.02 was obtained, with the optimal influent ammonium nitrogen concentration of 600.0 mg L−1 and pH of 8.09. Overall, the PN process can be maintained in a sand filter without forced aeration, and coupling with the subsequent anammox process to achieve completely unpowered autotrophic nitrogen removal.

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