Improvements in the treatment process

In response to stricter European regulations, water authorities have gradually upgraded their sewage treatment plants since the mid-1990s so that more and more nitrogen and phosphate compounds are removed from sewage. The introduction of biological forms of nitrogen and phosphate removal have contributed to this, in particular. Under these techniques, treatment processes are modified to create the optimum conditions for bacteria to break down and/or fix nitrogen and phosphorus compounds.

Other processes play a role in the removal of heavy metals. The removal of metals from sewage sludge, in particular, has improved over time due to the longer transit time of sewage through the treatment plant.

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