Feasibility of packed-bed trickling filters for partial nitritation/anammox: Effects of carrier material, bottom ventilation openings, hydraulic loading rate and free ammonia.

This study pioneers the feasibility of cost-effective partial nitritation/anammox (PN/A) in packed-bed trickling filters (TFs). Three parallel TFs tested different carrier materials, the presence or absence of bottom ventilation openings, hydraulic loading rates (HLR, 0.4-2.2 m3 m-2 h-1), and free ammonia (FA) levels on synthetic medium. The inexpensive Argex expanded clay was recommended due to the similar nitrogen removal rates as commercially used plastics. Top-only ventilation at an optimum HLR of 1.8 m3 m-2 h-1 could remove approximately 60% of the total nitrogen load (i.e., 300 mg N L-1 d-1, 30 °C) and achieve relatively low NO3--N accumulation (13%). Likely FA levels of around 1.3-3.2 mg N L-1 suppressed nitratation. Most of the total nitrogen removal took place in the upper third of the reactor, where anammox activity was highest. Provided further optimizations, the results demonstrated TFs are suitable for low-energy shortcut nitrogen removal.

One-stage partial nitritation/anammox at 15 °C on pretreated sewage: feasibility demonstration at lab-scale.

Energy-positive sewage treatment can be achieved by implementation of oxygen-limited autotrophic nitrification/denitrification (OLAND) in the main water line, as the latter does not require organic carbon and therefore allows maximum energy recovery through anaerobic digestion of organics. To test the feasibility of mainstream OLAND, the effect of a gradual temperature decrease from 29 to 15 °C and a chemical oxygen demand (COD)/N increase from 0 to 2 was tested in an OLAND rotating biological contactor operating at 55-60 mg NH4(+)-N L(-1) and a hydraulic retention time of 1 h. Moreover, the effect of the operational conditions and feeding strategies on the reactor cycle balances, including NO and N2O emissions were studied in detail. This study showed for the first time that total nitrogen removal rates of 0.5 g N L(-1) day(-1) can be maintained when decreasing the temperature from 29 to 15 °C and when low nitrogen concentration and moderate COD levels are treated. Nitrite accumulation together with elevated NO and N2O emissions (5% of N load) were needed to favor anammox compared with nitratation at low free ammonia (<0.25 mg N L(-1)), low free nitrous acid (<0.9 µg N L(-1)), and higher DO levels (3-4 mg O2 L(-1)). Although the total nitrogen removal rates showed potential, the accumulation of nitrite and nitrate resulted in lower nitrogen removal efficiencies (around 40%), which should be improved in the future. Moreover, a balance should be found in the future between the increased NO and N2O emissions and a decreased energy consumption to justify OLAND mainstream treatment.