D2.1 - EU Project Neptune

NEPTUNE · Contract-No. 036845 Deliverable 2.1
However, the sludge contains harmful heavy metals (Table 4.1b) and the nowadays more
and more observed and investigated micropollutants:
o Polynuclear aromatic hydrocarbons
(PAH)
o Herbicide residues
o Polychlorinated biphenyls (PCB)
o Organo-tin compounds
o Polychlorinated terphenyls
o Phthalate esters
o Phenol
o Petroleum hydrocarbons
o Chlorinated hydrocarbon solvents
and phenols
o Surfactants
o Organochlorine insecticides
o Aromatic amines
o Organophosphorus compounds
Since sludge consists of the material which had to be removed from the water due to
potential risk for the people and the environment, sewage sludge itself has to be treated
before it is finally disposed of in some form. Therefore, while demands on wastewater
treatment are increasing, the techniques for the sewage sludge treatment have to be
improved due to the more strict legislations in this area as well. The cost for sludge treatment
contributes up to 50% to the overall costs of the WWTP (Khiari et al., 2004). Nowadays, at
the most WWTP the mixture of primary and secondary sludge goes to stabilization and
disinfection if used in agriculture (aerobic or anaerobic digestion, composting, pasteurization
etc.) followed by dewatering and drying. The result is stabilized dewatered or dried sewage
sludge that has to be finally disposed of. The major ways for sludge use and disposal are:
application to agricultural land, landfill, sea disposal and incineration. The sea dumping of
sewage sludge was completely abandoned in 1980’. Land filling is also recognized as an
environmental hazard in some countries (banned in Switzerland since 2000 and in Sweden
since 2005). Use in agriculture is in discussion because of the increased amount of organic
micro pollutants and heavy metals in the sludge. Incineration is still thought the best
alternative in terms of volume and hazardous impact reduction as well as energy reuse. The
amount of produced sludge, as well as the methods commonly used for sludge treatment
and disposal, is given in the next table.
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