17 DEC 2003
Most backwashing filters are intended to backwash on the basis of a certain
head loss through the filter that indicates that the collected solids have exceeded the
filter's optimum capacity. However, in practice, most manufacturers will activate the
backwash procedures based on a timer (e.g., once per day) regardless of head loss.
This more frequent washing prevents clogging and cuts down on maintenance cost.
Similarly, cartridge filters may need to be replaced on the basis of head loss
through the filter. However, such maintenance can be sporadic and lead to system up-
set and even breakthrough, if the need does not coincide with available personnel. It is
often preferable to have a head loss alarm activated through a transducer but to have
regularly scheduled filter replacement based on time (e.g., monthly or annually) or on
treatment volume (e.g., every million gallons).
Most manufacturers will have minimum required controls on their systems
with additional controls available as options. The cost effectiveness of manual vs. auto-
mated vs. telemetric controls will depend on the availability of operations and mainte-
nance personnel and the relative isolation of the treatment system site. Generally,
automated and remote sensing controls are preferred over manual operation.
MAINTENANCE. Capital costs are just one component of installing and
operating a filtration system. Cartridge and bag filtration systems have the lowest capital
costs, but when there are high solids loadings and frequent media element replace-
ments, the operating costs can become quite significant.
Similarly, systems that require a lot of pumps and air compressors can use a
great deal of energy and require additional maintenance.
The design professional should look at each of the energy components and
the recommended maintenance schedule for any filtration system being considered to
determine whether one alternative will entail greater operating costs than another.