GusChem: Coatings in the wastewater system

Wastewater treatment is perceived as only a necessary sub-area that does not contribute to value creation. It has to work and the costs should be as low as possible. Some of the problems that can occur here have their origins in microorganisms, so it makes sense to look at them from this perspective.

Nature is everywhere, even in the most inhospitable areas it tries to spread again. In the process water sector, both in the waste water pipes and in the reaction tanks, this cannot be avoided. In general, two strains of microorganisms can already be distinguished here: aerobic (require oxygen) and anaerobic (without oxygen) microorganisms. Accordingly, microorganisms can multiply in a closed area, i.e. in the absence of oxygen, and other microorganisms spread everywhere in the presence of oxygen. But even here there is mixing, for example the aerobic microorganisms live on the surface of a slime layer and the anaerobic microorganisms live deep inside this slime layer; in between there is dead biomass and mineral components.

This leads us to the most common problems caused by microorganisms. Coatings and crusts form which restrict the cross-section, limit the effectiveness of gravel filters and ion exchanger resins and can even lead to blockages (Fig. 1/cover picture). Furthermore, thin sludge that is heavily interspersed with biology is difficult to dewater and the metabolic products of the microorganisms can also lead to limit value problems, in particular increased nitrite values, sulphide exceedances (smell of rotten eggs) or excessively high COD values.

These biofilms and deposits can also accumulate heavy metals, which can lead to limit values being exceeded again when they are later removed (Fig. 2). By "detoxifying" the wastewater, the conditions for nature become more and more favorable the closer the wastewater flow is to the final control. A recommendation on how to proceed always depends on the case and should be adapted to the local conditions.