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
