Organic and nitrogenous matter effects on the denitrification of saline and protein-rich effluents

The separate effect of protein concentration, nitrate concentration and carbon/nitrogen (C/N) ratio on the rate and efficiency of nitrate reduction was studied in batch reactors fed with a mixture of a synthetic substrate and a saline protein-rich salmon-plant effluent. At a constant nitrate concentration (40 mg L-1), the specific rate of nitrate removal decreased by 60% with increasing initial protein concentration (392 to 1900 mg L-1) and ammonification prevailed under these conditions; meanwhile at a constant protein concentration (1104 mg L-1), the specific rate of nitrate removal increased 58 times with increasing nitrate concentrations (0.5 to 78 mg L-1) and denitrification was the main route for nitrate reduction. The C/N ratio had an inverse effect on the specific rate of denitrification; the latter ranged from 227 to 563 [mg NO3 - N (g VSS·d)-1] for a C/N ratio of 163 to 16 [mg TOC (total organic carbon) (mg NO3 - N)-1], respectively. On the other hand, the ammonia production rate was proportional up to a C/N ratio of 150.