Summary and conclusions

Spildevandsslam fra kommunale og private renseanlæg i 2005

This report specifies the amounts of sewage sludge from municipal and private wastewater treatment plants for 2005.

For 2005 the amount of produced sewage sludge was approximately 132.600 tons, estimated in dry net weight. The total amount of sludge specified in dry matter has fluctuated between 133.000 tons and 165.000 tons in the period from 1995 to 2005. The Danish EPA reckons that the total sludge amounts have been relatively stable since 2002.

The distribution of sludge quantities according to treatment methods, specified in dry matter content, was unchanged from 1995 to 2005. However, since 1999 it has been a tendency that the share of sludge drained with a centrifuge has increased at the expense of other methods, including the belt filter pressing method.

Generally, the share of dry matter used for agriculture, etc. decreased until 2001. A possible explanation of the decreased use in agriculture could be the uncertainty that existed because of stricter quality requirements concerning the disposal of sludge on agricultural land. The amount of sludge disposed on agricultural land, etc. nevertheless increased from 2001 to 2002. The main reason that the disposal category “Others” increased considerably in those particular years were partly the incineration of dried sewage sludge in cement kilns and partly the inclusion of sludge as raw material in a combustion process which produced sand blasting agents.

The Danish EPA assesses that recycling of sewage sludge has increased since 2002 at the expense of sludge “used for other purposes”. This is probably due to the closing in 2005 of a significant company that utilised sewage sludge in the manufacturing of sand blasting agents. Today the amounts that were previously used at this facility are recycled as fertiliser in Denmark or its neighbouring countries. Further, since 2002 there has been a general expansion of mineralisation facilities, hence it is to be expected that the amounts of sludge used for that purpose will increase. The amount of sludge incinerated in Denmark is assessed to be constant compared to 2002 levels.

The amounts of nutrient salts in sludge are estimated to amount to 6,305 tons of nitrogen, 4,144 tons of phosphorus and 719 tons of potassium. From this it is estimated that 3,910 tons of nitrogen, 2,310 tons of phosphorus and 78 tons of potassium have been disposed on agricultural land.

For heavy metals there is an over-all decreasing tendency in the weighted average concentrations from 1995 to 2005. This is also the case for environmental xenobiotic substances.

For NPE the decrease in the weighted average concentration from 1997 to 2005 has been approximately 80 percent. This is in part due to the voluntary agreements made with Industry in the late eighties aimed at reducing the use of NPE in products. Likewise, there has been a drastic decrease in the weighted average concentration of LAS, with the largest decrease taking place since 2000. For 2005 there are no reports of analyses where the limit values for the environmental xenobiotic substances DEHP and LAS have been exceeded.