In contrast to bacterial degradation, nutrient
assimilation by plants is limited by surface, as
photosynthesis is dependent on solar radiation.
Therefore, to achieve maximum nutrient recycling
rates, trickling filter systems should provide
a large surface area for plant growth and
photosynthesis in relation to their volume. In
theory, a planted trickling filter could double
its nutrient recycling capacity when constructed
halve as deep and with a surface twice as large.