Nitrogen and DOC removal from wastewater streams of the metal-working industry

In pilot plant studies, permeates of ultrafiltration of boron- and ethanola mine-containing coolants were used as a carbon source for denitrification o f NO2-N and NO3-N in the wastewater from electrochemical deburring after me tal ion precipitation. Treatment of the two wastewater streams in a cascade of submerged fixed bed reactors at increasing pH-values revealed that a mo re alkaline pH resulted in a lower denitrification rate and an increasing n itrite concentration in the effluent. The DOC-removal efficiency was about 70% for pH values of 7.8-9. It was not possible to establish a nitrificatio n. The biomass in the treated wastewater was fine-particulate and could har dly be separated. For evaluation of the maximal biodegradability of the DOC of the permeates in batch experiments, the long-term BOD instead of the BOD5 was more suitab le. Results of BOD21-detenminations corresponded with the DOG-removal effic iency of the immobilized population in the pilot plant at HRTs ranging from 3.9-13.5 d. Whereas the nitrate content of the EC-wastewater could be redu ced completely, even at high loading rates, about 30% of the COD of the per meates remained undegraded. A COD of <300 mg O-2/l could only be obtained a fter chemical oxidation of the effluent by UV-activated H2O2. Production-related Variations of the boron- and DOG-concentrations in the p ermeates of ultrafiltration of cooling lubricants apparently prevented the establishment of a nitrification of ammonia, that was released during denit rification with ethanolamines as a carbon source. Only when both wastewater streams were co-treated with a, only slightly polluted third, non-toxic wa stewater stream of the factory, elimination of nitrate and ammonia from EC- wastewater and permeate, respectively, was successful. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.