BIOLOGICAL, REMOVAL OF NITROGEN IN TOXIC INDUSTRIAL EFFLUENTS, HIGH IN AMMONIA

Industrial wastewaters with high ammonia concentrations, high toxicity and/or unfavourable COD/N ratio call for special attention and concer n with regard to design and operation of the wastewater treatment syst em. Two cases are described: wastewater from a rendering plant and fro m a coke oven plant. The precondition for obtaining and maintaining a nitrification process in both a rendering plant and a coke oven plant is close control and regulation of pH in the process tanks. Both high and low values of pH cause inhibition of the nitrifiers. pH should be kept in the range 6.5-7.0. The organic fraction at the rendering plant mainly consists of easily biodegradable organic acids. The BIO-DENITR O concept has been chosen for this application and proven to be very e fficient to obtain low effluent values for (NH3 + NH4)-N due to the fl exibility in adjusting the phase length under variation in loadings an d wastewater composition. Complete denitrification could be obtained w ith COD/N ratio larger than 5. Wastewater from a coke oven plant conta ins compounds that are extremely toxic to the nitrifiers as for exampl e phenol, cyanide, thiocyanate, sulphide and ammonia. Sufficient upstr eam buffering is essential to prevent shock loads. In order to obtain complete denitrification at the coke oven plant by using an internal c arbon source, it is necessary to have an efficient ammonia stripping a nd phenol must not be removed from wastewater. COD/N ratio must be lar ger than 8 to obtain complete denitrification.