86    BIOLOGICAL REMOVAL OF NITROGEN
FROM COKING PLANT EFFLUENTS
Christina Sund, Vice-President
I. Kriiger Engineering AS, Denmark
Herbert Wotrubez, Engineer
Kriiger-Holter Wassertechnik GmbH
INTRODUCTION AND BACKGROUND
Wastewater from coking plants, which is mostly condensate from coke gas cleaning, contains high
concentrations of many toxic compounds, including phenol, cyanide, thiocyanate, sulphide and
ammonia. Furthermore, compounds such as fluoren, pyren, acenaphtehene, phenanthren and
fluoranthen can be found in concentrations between 0.1 to 0.5 mg/L.
Wastewater composition varies slightly between different types of coking plants. The compounds
present are mainly the same, but due to the operation mode of coking batteries and chosen gas
treatment options, the final composition will vary.
In 1992, a new European Community (EC) directive regarding municipal waste treatment facilities
was released, limiting, among other things, the discharge of nitrogen in environmentally sensitive
areas.
The directive focuses on municipal wastewaters, but, in connection with national legislation, it is
unavoidable not to limit industrial discharges. Considering the new directive, and that coking wastewater contains many compounds classified by the EC as harmful to the environment (List 1 compounds), the national authorities have proposed a tightening of water licenses for coking plants.
For example during 1987, in Germany, a remarkable tightening of the regulation occurred, and in
June of last year, further tightening was proposed.
Table I summarizes the development of regulations in Germany. As can be seen, the conditions for
wastewater treatment regarding effluent quality have dramatically changed during the last 10 years.
Furthermore, at the latest revision, special measures regarding nitrogen removal were requested, as
the traditional methods applied in coking plants with steam stripping of ammonia at elevated pH,
were no longer sufficient. Furthermore, restrictions on micropollutants were introduced, (AOX,
PAH, etc.) and a remarkable reduction in toxicity allowance was requested.
All together this meant that traditional treatment of coking wastewater (high loaded activated
sludge) was insufficient.
Biological wastewater treatment has been applied for coking plant wastewater for the last thirty
years. These plants have been designed to degrade organic constituents such as phenol, and to limit
cyanide discharge. Many of these plants have suffered from operational problems due to design errors
as for example inadequate equalisation, pretreatment upstream, or lack of understanding for ongoing
processes in the treatment system.
Biological Nitrogen Removal
Biological nitrogen removal has proven to be a reliable process in many municipalities, and also for
industrial wastewater treatment plants. As for industrial facilities, success has been dependent on the
understanding of specific requirements for the individual types of wastewater, and how these should
be taken into consideration during plant design and operation.
Biological nitrogen removal comprises oxidation of ammonia in the presence of oxygen in two steps
to nitrate, by means of the bacteria nitrosomonas and nitrobacter.
Nitrate is further biologically reduced to nitrogen gas by bacteria, also in two steps, where nitrate is
first reduced to nitrite, and then finally to nitrogen gas.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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