R. Méndez

Treatment of saline wastewater in SBR aerobic granular reactors

Fish canning effluents characterized by their salt content, up to 30 g NaCl/L, were treated, previously diluted to desired concentration, in a SBR where aerobic granular sludge was produced. The formation of mature aerobic granules occurred after 75 days of operation with 3.4 mm of diameter, SVI of 30 mL/g VSS and density around 60 g VSS/L-granule. Treated organic loading rates were up to 1.72 kg COD/(m3.d) with fully organic matter depletion. Ammonia nitrogen was removed via nitrification-denitrification up to 40% when nitrogen loading rates were of 0.18 kg N/(m3.d). The presence of salt in the treated effluent did not cause a detrimental effect on the operation of the reactor once the aerobic granules were formed.

N2O Production by Nitrifying Biomass Under Anoxic and Aerobic Conditions

The capacity of nitrifying biomass, grown in biofilms or in suspension, to reduce NO2- and NO3− under anoxic conditions was tested in batch experiments. The estimated reduction rates were 5 and 25xa0mg N per gram volatile suspended solids (VSS) per day for nitrate and nitrite, respectively, in the case of the nitrifying biofilms. Activity tests carried out with successive feedings indicated that no acclimation of the biomass to the tested conditions occurred, as the obtained reduction rates remained almost constant. Another series of activity assays was carried out with nitrifying suspended biomass, and the reduction rates for nitrate and nitrite were 30.4 and 48.9xa0mg N per gram VSS per day, respectively. N2O and N2 were the final gaseous products, and their percentages depended on the source of nitrogen feed. The specific production of nitrous oxide during nitrification was investigated during continuous experiments in a biofilm airlift suspension reactor. Specific production rates up to 46xa0mg N2O–N per gram VSS per day were measured. The percentage of N2O produced represented up to 34.4% of the ammonia oxidized. Nitrite accumulation, low dissolved oxygen concentrations, and the presence of organic matter favored the production of nitrous oxide. N2O gas was not detected during the oxidation of nitrite even when organic matter was present. To prevent N2O gas production in nitrifying systems, the operation at low dissolved oxygen concentrations, nitrite presence, or organic matter content should be avoided.