Denitrification of wastewater containing high nitrate and calcium concentrations.
The removal of nitrate from rinse wastewater generated in the stainless steel manufacturing process by denitrification in a sequential batch reactor (SBR) was studied. Two different inocula from wastewater treatment plants were tested. The use of an inoculum previously acclimated to high nitrate concentrations led to complete denitrification in 6h (denitrification rate: 22.8mg NO3- -N/gVSSh), using methanol as carbon source for a COD/N ratio of 4 and for a content of calcium in the wastewater of 150mg/L. Higher calcium concentrations led to a decrease in the biomass growth rate and in the denitrification rate. The optimum COD/N ratio was found to be 3.4, achieving 98% nitrate removal in 7h at a maximum rate of 30.4mg NO3- -N/gVSSh and very low residual COD in the effluent.