Cleaner Technology Transfer to the Polish Textile ... - Miljøstyrelsen

86
One digester was operated as a reference digester fed with municipal sewage
sludge. The three parallel digesters were operated with a mixture of municipal
sewage sludge and up to 20% by volume of metal salt dye-stuff precipate,
polymer dye-stuff precipate, and membrane filtered dye-stuff concentrate,
respectively.
The results from the experimental work showed that the digesters fed with
dye-stuff remanences performed with similar COD reduction and gas production
as the reference digester fed with sewage sludge alone. Thus no disturbance
of the anaerobic digestion could be detected.
The experimental work was also tested for breakdown and possible redissolution
of dye-stuff during the anaerobic treatment. In figure 4 are shown results
from spectrophotometric scanning measurements of filtered feed samples and
filtered effluent samples from the digesters. From the figure (left) it can be
seen that in the feed samples no dye-stuff was present in the dissolved phase,
except for the feed containing membrane remanence, which as expected
showed significant amounts of dissolved dye-stuff.
Figure 4.
Results from spectrophotometric scanning measurements of filtered digester feeds (left) and filtered digester
effluents (right).
From figure 4 it can be seen that no dissolved dye-stuff was found in the filtered
effluent samples, except for the sample from the digester fed with polymer
precipitate, in which a small concentration of dissolved dye-stuff could be
observed. The dissolved dye-stuff in the membrane remanence thus was
degraded through the anaerobic digestion. The small amount of dye-stuff
observed in the effluent from the digester fed with polymer precipitate indicated
release of some precipitated dye-stuff caused by degradation of the
applied polymer. The released dye-stuff concentration is small and will be
invisible when possibly returned into the sewage with the reject after sludge
dewatering.