Summary
In the production of motor vehicle components (e.g. transmissions, axles), certain metal parts are electrochemically deburred before final assembly. The resulting “electrochemical wastewaters” contain high concentrations of nitrate and nitrite, which it has not been possible to remove to a sufficient extent using the processes applied hitherto.
The object of this research project was the development of a treatment process in which nitrogen is removed from the wastewater stream ahead of its discharge into the receiving water course by means of denitrification. The carbon required for this purpose was to be supplied by permeate from the ultrafiltration of cooling lubricants. The combined process has been tested in a fixed bed denitrification reactor with a secondary aerobic treatment stage.
Results:
- In trial operation, 75% degradation of the dissolved organic carbon content (DOC) has been achieved.
- Trials for the chemical oxidation of residual DOC have revealed that a process of this type would be too expensive.
- Using permeate diluted to a ratio of 1:5 with further pre-treated industrial wastewater, denitrification has increased degradation rates for DOC and total nitrogen to over 90%. Sludge recirculation has produced a significant acceleration in conversion.
- Constituents of cooling lubricant emulsions, such as boron, are specifically responsible for the inhibition of nitrification. Contaminants from external sources have no significant influence upon residual DOC in the permeate.
