The choice of treatment used in an intensive or recirculating tank system depends on
objectives determined by economical and environmental considerations and regulations. In
intensive flow-through tank systems, water treatment is normally limited to aeration,oxygenation, and solids removal. In contrast, recirculation systems include at least
biofiltration in addition to the processes mentioned above. Of these processes, solids
removal and nitrification can impact nutrient fluxes, while aeration and oxygenation may
only cause an increase in concentration resulting from the increased biomass carrying
capacity (Table 2). The influence of solids removal is by trapping and separating the
solids, in which a high proportion of the P and a small proportion of the N may be present;
that of biofiltration is by transforming one form of dissolved N (ammonia) to another
(nitrate).