Abstract

Partial nitrification of ammonia to nitrite was studied as a shortcut process to reduce the oxygen consumption during nitrification and the necessities of organic carbon compounds for denitrification in wastewater treatment plants (WWTP). This process is specially recommended for the treatment of wastewater containing low total organic carbon to nitrogen ratios (C/N) like the effluents of anaerobic digesters from the fish canning industry. These effluents contain residual carbon compounds and in some cases high salt concentrations. In the present study the effects of acetate and different salts present in the feeding of a SHARON reactor have been evaluated. When acetate was added, concentrations up to 0.2 g TOC/L did not exert significant effect on the ammonia oxidation to nitrite. Values higher than 0.3 g TOC/L (C/N = 0.3 g/g) resulted in competition between heterotrophs and autotrophs with a detrimental effect over the latter. Results indicate that the decrease in ammonia oxidising activity was due to a competition for substrates between both groups of bacteria. When the presence of NaCl, KCl and Na2SO4 was tested in batch experiments similar inhibitory effects were measured. Molar concentrations of 100 mM caused 40% of inhibition on the maximum specific ammonia oxidising activity. The effect of NaCl on the operation of a SHARON reactor was tested at concentrations between 0 and 513 mM. The ammonia oxidation activity increased in the presence of 85 mM, while higher salt concentrations up to 425 mM provoked a slight decrease of activity and when 513 mM where added the activity was reduced to 10%. A strategy based on the pH control was applied in order to maintain the stability of the SHARON operation. Effluents from an anaerobic digester treating wastewater from a fish cannery were partially nitrified to be further used in the Anammox process.