Abstract

The source of wastewater with high salinity is mining, oil and gas, seafood processing, tanning, and management of leachate from landfills. As water reuse and brine concentration increase, water treatment becomes more significant. High salt concentration may slow down nitrifying and anammox bacteria, making it difficult to obtain stable operation of these two processes, sometimes using different processes that require more energy or chemical dosing. In this research, we investigated partial nitritation (PN) and anaerobic ammonium oxidation (anammox) processes under gradually increased salinity using sequencing batch reactors (SBRs). We used reactor performance, including nitrogen speciation over time, removal rates, stoichiometry, and suspended solids (TSS/VSS).
The PN reactor operated on NaCl concentrations between 0.5 and 10 g/L for 350 days. The mean ammonia removal decreased as salinity increased. The removal efficiency was 75% at 3 to 5 g/L, 69% at 6 to 7 g/L, and 44% at 8 to 10 g/L. The nitrite selectivity was still good, with NAR above 84%. The decrease in PN power corresponded to a major decrease in biomass, as TSS reduced by about 90%. For the anammox reactor, it operated on NaCl concentrations between 1.0 and 6.5 g/L for 350 days. The average influent concentrations were 90 mg NH4-N/L and 119 mg NO2-N/L. The maximum total nitrogen removal efficiency occurred at mid-range salinity, at which time it was 66% at 4.0 g/L. The efficiency reduced at 6.5 g/L, to 44%. The stoichiometric ratios were steady during all phases, which equaled 1.35 for (ΔNO2)/(ΔNH4 ) and 0.23 for (ΔNO3)/(ΔNH4 ). TSS concentrations were steady during mid-range and high salinity, suggesting that the decrease in efficiency at 6.5 g/L may not be because of biomass. The results indicate that PN-anammox can be applied cautiously at moderate salinity concentrations up to 5 g/L, but it may increase the risk of reduced efficiency at higher concentrations.