Filling Materials

Filling materials: description and operations

The major source of wastewater pollution is organic matter. Nature reacts spontaneously to this form of pollution by developing bacteria that decompose organic wastes. However, these compete with other forms of aquatic life for oxygen requirements. If oxygen is lacking, the bacteria do not survive and water quality is severely affected.

Thus, the determinant of water health is oxygen, and consequently the degree of pollution is expressed in terms of BOD, or biological oxygen demand. Percolating filters are created to meet this biological oxygen demand before the water is discharged into receiving water bodies, thus avoiding harmful eutrophication effects on rivers, lakes and seas. This also gives rise to the need for biofilm-forming filling materials, which are useful in percolating filters.

MITA Water Technologies offers two types of biofilm media.

• Margherita filling for percolator beds is the result of the evolution of fills used in the past, such as crushed stone and wood. By using this new fill material, higher structures with much higher specific surface areas and reduced risk of clogging can be achieved.
• Bioset structured filling materials consist of an alternating series of flat and/or corrugated PVC sheets, bonded together to provide a lightweight, strong and rigid structure. Such modules are therefore capable of withstanding high loads.

These structures, the result of careful design, provide high active surface area for bacterial growth in a relatively small volume and possess sufficiently large free passage spaces to avoid bacterial accumulation such as to cause clogging of the filter. Percolating liquid flow can be vertical or cross-current, depending on the design.