ABT aimed to increase the solid removal efficiency of the drum-filter by testing polymers in the wastewater before it enters the drum-filter.  All types of filtration provided water of the same quality with the same amount of dry matter, but with less solids when flocculation (with DR-3000GR) was practised.

Moreover, the 40μ mesh could hold 85% more solids from flocculated wastewater than non-treated wastewater. These quantities of total solids in the concentrated sludge, however, are still too low, to be used as  Bio-Based Fertilisers.

Finally, the time needed to achieve draining on the filters is significantly less with flocculation, indicating that drum-filters could produce more filtered water for re-use in the RAS.

Filter-bags were used to remove solids and slurries and were characterized by a high-rate pollution holding capacity.  When filter-bags of 1µ are used, there is a need to allow more time for filtration, while for the bags of 5µ most of the filtration takes place in the first five minutes. ​A lot of solids stay in the bags, as they cannot be emptied correctly and fully, and therefore it is not practical to integrate filter-bags before the drum-filters in this case.

Figure 1: A) Untreated wastewater and Flocculated wastewater 1 minute after treatment and B) After 30 minutes.

Figure 2: Turbidity and % of dry material of filtered water and upheld sludge, from treated (with flocculants) and non-treated wastewater of Atlantic salmon.  

The liquid/solid separation usually takes hours when left to gravity alone but can be achieved in minutes or seconds with properly prepared polymers. ​The polymers’ ability to flocculate solids is central to their role in water treatment and can be even more effective when combined with a coagulant.  ​These environmentally friendly polymers, could flocculate solid particles, increase their size and therefore increase the efficiency of the drum-filter. By applying filter-bags to the wastewater leaving the drum-filter after the backwash, farmers could even further decrease their environmental impact


Further information: https://aquaeas.org/Program/PaperDetail/40765