Biological denitrification of fertiliser wastewater at high chloride concentration

Wastewater from the fertiliser industry is characterised by high chloride concentration, normally varying between 60 and 76 g/ l. Experiments with biological denitrification were performed in laboratory-scale ‘fill and draw’ reactors with synthetic fertiliser wastewater, with chloride concentrations up to 96.7 g Cl/l at 37°C; the pH was controlled in the range 6.8 to 7.2. Potassium acetate was added as carbon source for the suspended cultures. The results of the experiments showed that biological denitrification was feasible at the extreme environmental conditions prevailing in undiluted fertiliser wastewater. However, the extreme conditions affected the denitrification rates. The volumetric rates were reduced by a factor of ten between chloride levels of 4.8 to 96.7 g/l. The results from the performed tests can also be applied to other wastewaters with similar characteristics as that of the fertiliser industry, i.e. with high salinity. As an example, the pharmaceutical and aquacultural industries can be mentioned.