Conditions for successful nitrogen removal from source-separated urine by partial nitritation/anammox

Abstract

Partial nitritation/anammox (PN/A) of source-separated urine is less energy-intensive and potentially cheaper and more environmentally friendly than conventional nitrogen removal from mixed sewage. However, PN/A of undiluted source-separated urine has not yet been established. In this study, the feasibility of PN/A for source-separated urine (total nitrogen ≈ 2 to 3 g-N L-1). To evaluate the influence of different factors, one- and two-stage configurations were operated using different influents, i.e. source-separated urine, synthetic urine, and urine with additional divalent cations. While partial nitritation was successfully achieved in both configurations with digester supernatant and urine, anammox activity was lost shortly after switching from digester supernatant to the urine influents. Toxic organic compounds or pharmaceuticals and the high monovalent to divalent cation ratio were suspected as causes of anammox failure, but were ruled out due to the different reactor configurations and influent compositions tested. Other suspected factors such as COD/N ratio, phosphate and sulfate inhibition, nitrogen compound inhibition, metal inhibition, pH and dissolved oxygen were also systematically excluded. Instead, the high salt concentration in urine compared to the digester supernatant most likely caused the reactor to fail due to the disintegration of large flocs, and the resulting challenge of biomass retention. The shortcomings of the floccular sludge system were overcome by using biofilm carriers, resulting in successful PN/A. This hybrid system ran for 140 days with nitrogen removal rates of up to 1000 mg-N L-1d-1with an average of 410 ± 220 mg-N L-1d-1, and a nitrogen removal efficiency of 93 ± 3% at 30°C.

Resource-Efficient Nitrogen Removal from Source-Separated Urine with Partial Nitritation/Anammox in a Membrane-Aerated Biofilm Reactor

“…The obtained NRRs are within the range of typical volumetric (between 0.3 and 2.0 mg N L –1 d –1 − ) and membrane area-specific (1500–2500 mg N m –2 d –1 ) rates for PN/A in side-stream conditions, at high (>25 °C) temperatures. Compared to previous works of PN/A on urine, the rates and efficiencies obtained are more than double and maintained for much longer. ,, …”

“…Biofilms instead of suspended flocs could overcome the stability issues on diluted urine as they are known for their ability to produce extracellular polysaccharide substances (EPS) that provide a protective barrier against fluctuations in (potentially) toxic compounds, salinity, N levels, and so forth. Biofilm systems have demonstrated the ability to overcome washout effects and operate successfully in highly saline conditions, even up to seawater, 50–60 mS cm –1 . , In a moving bed biofilm reactor (MBBR), a longer operation span on diluted urine with rates up to 1000 mg N L –1 d –1 could be reached . Yet, significant rate fluctuations and eventual failure were observed as a result of limited control between oxic/anoxic zoning and subsequent imbalances in capacity after load fluctuations.…”