BALTIC SEAENVIRONMENT PROCEEDINGS No. 59 - Helcom

It is particularly important to record influent quantities
and the quality of BOD-5/P and BOD-5/N ratios as well as
the biological degradability before and after
sedimentation. The COD/BOD5 ratio is also important in
that it has a crucial influence on the dimensions of the
nitrogen-removal equipment.
Our experience in Germany shows that pilot tests to
determine wastewater composition should last at least one
week and include periods of maximum load capacity.
As a further tool for determining the dimensions of sewage
treatment plants with nutrient-removal stages, a computer
program called DENIKA has meanwhile been developed by
German scientists. Using this program, the optimum
dimensions can be determined for each plant based on the
measured pollution load values and the given processes.
Compared with this procedure, the figures calculated only
from the tables are far higher. Pilot plants, therefore,
can greatly reduce investment and running costs.
For large sewage treatment plants, f. ex. for a
population-equivalent of 50,000, the operation of a pilot
plant is recommended. This is especially the case when the
composition of the wastewater is different from that
usually recieved from households. It is only through the
use of pilot plants that optimum processes and tank
construction can be determined. Operating a pilot plant,
however, requires a lot of time and personnel. The test
period usually lasts one year because all operating
conditions are to be recorded. The time and effort
involved in running a large pilot plant certainly pay off
in that there are no surprises later during full-scale
operation and it is known which results can be expected.
In Schleswig-Holstein, four such pilot plants have been in
operation simultaneously over the past few years. The
plants are transportable systems that were specially
designed at universities and then made available to the
town councils and local authorities to carry out the test
205