Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Important issues for the local authorities are what to do with the sludge produced insewagetreatment plants. The tax for landfill leads to higher costs with 250 SEK/ton. On the 31December 2004 it will be forbidden to landfill sludge.
In Sweden the yearly production of sludge is 240 000 tons, counted as DS. The phosphorouscontent is 3 % in sludge. The total yearly production of sludge gives 6000 tons of phosphorous. (Andersson et al, 1999). During the last years about one third of this phosphorous has been used as fertilisers at fields and one third as fertilisers on outer areas, the rest to landfill. Värmdö is producing 2700 tons sludge from sewage treatment plant countedas DS. (Lidbjörk, 1999).
During the autumn in 1999 there has been a large number of alarming reports saying that the sludge in addition to heavy metals, toxic organic compounds, also contains brominatedcontaining flame retardants and dangerous infectious matter from hospital waste water. The alarming reports made the LRF in October 1999 to ban all spreading of sludge as fertilisers.Today it is not clear when and if this ban will be removed.
In this Master of Science it is shown that landfilling of sludge leads to serious environmental effects, for example global warming, eutrofication and acidification. This indicates that landfill of sludge is not good in an environmental perspective.
In this study in Värmdö sludge treatment has been studied with the simulation tool ORWARE(ORganic WAste REsearch). ORWARE is a system analysis model for waste planing with tools for lifecycle and substance flow analyses. The model is used for calculating emissionsand energy consumption for a waste system. It is thought as a tool for simulating different treatment methods for liquid and solid waste in a given area.
The alternatives to landfill that have been studied in this thesis is incineration, composting with sewage treatment sludge and garbage from household in an reactor compost, as well as composting of sewage treatment sludge and biowaste in string compost.
The study indicates that if it is possible to guarantee low concentrations of toxic substances in the sludge, the best alternative is to spread the sludge on fields. The uncertainty of the containing components in the sludge makes the incineration alternative a good alternative to guarantee destroy possible toxic components and bacteria that can exist in the sludge. The problem with incineration is that essential components like phosphor are destroyed and cannot be utilised. There are same methods today were you could utilise the phosphorous in incineration. These methods are very expensive and energy demanding and is therefore notused that much. With the discussion today about sustainable development incineration wherephosphorous is not utilised is only acceptable in the short term until the problems about the toxic components in the sludge have been solved.
2000. , 47 p.