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3.3.2        Sewage sludge production

The annual production of sewage sludge in the EU-32 was about 11.1 million tonnes in 2018 – about 17 kg per person (Anderson et al, 2021).  94% of this sludge was “disposed”. According to the Eurostat data used in that report, 27 % of the sewage sludge was used in agriculture, 25 % was incinerated, 21 % in compost and other applications, 9 % landfilled, and 19 % is used in another way.

Fig 3.2 shows a wide variation in the destinations for sewage sludge. Some countries have a high reliance on sending treated sewage to land, others incineration. Decisions are based partly on geography (e.g. availability of land) and also on the level of concern about pollutant loads in the sludge. There is a lack of data on sludge destinations for a number of European countries.

Figure 3.2 Sewage sludge management approaches in Europe

The cost for treatment + disposal of sludge in European countries has been estimated to reach, on average, approximately 200 per tonne of dry mass, according to the type of treatment and disposal.

With regards to sludge production, the treatment can have two objectives:

• recovery of materials or energy from sludge, utilising its resource potential;
• reduction of the amount of sludge produced, minimising waste.

The increase of the solid content in sludge by dewatering significantly reduces the volume of wet sludge for disposal. The reduction of dry mass of sludge leads to the reduction of solid content and volume. Methods are based on physical, mechanical, chemical, thermal and biological treatments. Most of them are aimed at solids solubilisation and disintegration of bacterial cells in sludge.