Recovery during sludge processing

Waste water in the Netherlands is purified at 350 sewage water treatment plants. The plants are managed by Water Boards. Every year they produce approximately 1,500,000 tons of treatment sludge. The phosphate content of the Dutch sludge is approximately 30-40 grams per kilo of dry matter. Using the correct methods would enable the Dutch water boards to recover a total of 10,000 tons of phosphate from sludge every year.

Half of all Dutch sludge is incinerated at two mono incinerators: Slibverwerking Noord-Brabant (SNB) at the Moerdijk industrial estate and DRSH in Dordrecht. Another quarter goes to compost producers, and another quarter is incinerated in cement ovens. In 2008, SNB incinerated 430,000 tons of sludge. The phosphate in the sludge is concentrated by the incineration and absorbed by the ash at a concentration of 80 grams of phosphate per kg ash. In 2008, SNB produced 38.500 tons of ash. This means that the phosphate production of SNB is already at 3100 tons of phosphate per year.

An advantage of the recovery of phosphate at the incinerators is that half of all phosphate in the Netherlands is currently collected at two sites in the Netherlands. But naturally, the more incinerators, the more phosphate recovery. The recovery of phosphate at incinerators does not have to cost anything, in contrast to recovery at treatment plants or toilets. On the contrary, it can even produce money. Furthermore, if all sludge processors convert to mono incineration there is sufficient potential to recover almost all the phosphate from the waste water.