74    TREATMENT OF A STEEL WORKS EFFLUENT
WITH A CONVENTIONAL SINGLE-SLUDGE SYSTEM
BUILT IN CASCADES
Dipl.-Biol. Bernd Zacharias, Research Assistant
Prof. a. D. Dr.-Ing. Rolf Kayser, Former Head
Department of Sanitary Engineering
Technical University of Braunschweig
Braunschweig, Germany
INTRODUCTION
Wastewater from steel producing plants or from cokery facilities contains a lot of substances
like phenols or cyanides which need to be degraded. The requirements on the effluent quality
have increased during the last years. Besides the elimination of the organic pollutants, of free
cyanide, and of heavy metals, low concentrations of inorganic nitrogen in the effluent are required.
In the past, many researchers concentrated on the degradation of the major pollutants such as
phenols and cyanides without considering the degradation of nitrogen.1"1 Degradation of nitrogen was investigated with two- or more-step biological plants5"8 or dealt with after several preconditioning processes.910 Other researchers described treatment of coke-oven wastewater for
carbon and/or nitrogen elimination with a single-sludge system.""13 The applied sludge ages exceeded 40 days in all investigations. A synthetic wastewater containing phenols and cyanide was
treated by Shieh and Richards, applying a single-sludge system with a sludge age of 15 days.14
Sund and Wotrubez" described a single-sludge system with nitrification for a technical scale
pilot-plant but did not mention the applied sludge age.
Besides the elimination of the pollutants, the security in performance is an important requirement for a wastewater treatment plant treating steel works effluent.
In this study, we concentrated on the treatment of the complete wastewater stream of a steel
work instead of cleaning single streams in order to minimize high peak concentrations of inhibitory substances in the influent. Moreover, wastewater from diffuse sources is gathered and
lead to the complete stream and these pollutants are treated as well.
Treatment was achieved in a single-sludge system built in cascades. Because of the very low
nitrogen concentrations in the effluent required by the controlling authorities, a post-denitrifica-
tion step was mandatory. The only choices were a single-sludge or at least a three-sludge system.
Of these, the first one was favored.
For performance security, a two-step process is advantageous, if on one hand inhibitory substances in the influent are degraded in the first step or on the other hand, can be eliminated by
the excess sludge removal of the first step. The main inhibitory substances in this specific wastewater are phenols and cyanides which are both water-soluble. Therefore adsorption and subsequent removal with the excess sludge is not possible. Peak concentrations on the other hand
would reach the second step and there inhibit the nitrification process, even if the biomass in the
first step is able to degrade the inhibitory substances.
For these reasons, a single-sludge system built in cascades was considered to be the most adequate alternative. A one-step process is easy to handle since there exists only one return sludge
flow. Peak concentrations of inhibitory substances may lead to increased effluent concentrations
but the pollutants will be quickly reduced to a non-inhibitory level due to the presence of degrading bacteria in the sludge.
50th Purdue Industrial Waste Conference Proceedings, 1995, Ann Arbor Press, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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