Waste water resulting from the production of polyethyleneimine production and cyclohexanone production contain high concentrations of ammonia, organic carbon, oligomers and sodium sulfate and are unusually resistant to two sludge waste water treatment processes. A two sludge treatment system includes a denitrification step and a nitrification step. Denitrification removes carbon from waste water with the use of carbon metabolizing bacteria. Nitrification is the removal of ammonia from the waste water by bacterial oxidation of ammonia to nitrate (NO.sub.3.sup.-). Nitrification is carried out by a limited number of bacterial species and under restricted conditions, including a narrow range of pH and temperature. Nitrifying bacteria grow slowly and nitrogen oxidation is energy poor in relation to carbon oxidation. In addition, nitrification is inhibited by the presence of a large number of compounds, including ammonia and nitrite ion (NO.sub.2.sup.-). Also, nitrifying bacteria subsist only under aerobic conditions and require inorganic carbon (CO.sub.3.sup.-) for growth.
The nitrification process met with recurring failure. Failure is exhibited by the change from nearly complete ammonia removal where no polyethyleneimine waste is present in the waste water, to essentially no ammonia removal, where 6 percent polyethyleneimine waste is present in the waste water, within a period of 48 hours.
The present invention is identification of the factors causing the failure of the polyethyleneimine waste water treatment process and development of a process to treat the waste water.
It was found that biological pre-treatment of the polyethyleneimine waste stream, in order to reduce the inhibitory effect of the polyethyleneimine waste water on the nitrification process, is not feasible since the high content of sodium sulfate in the stream prevents biological activity.
To solve this problem a waste water treatment process including removal of sodium sulfate from the waste water in conjunction with biological pre-treatment, denitrification and nitrification was devised.