Sand Filtration and UV Disinfection
The Mt.View Sanitary District utilizes a Dynasand® filter
system.
The system removes solids from the secondary effluent achieving a
clarity
that allows downstream disinfection with ultraviolet light. The
Dynasand®
filter is a continuous-backwash, upflow, deep-bed, granular-media
filter
system. The filter media is continuously cleaned by recycling the sand
internally through an airlift pipe and sand washing. The cleansed sand
is redistributed on top of the sand bed, allowing for continous,
uninterrupted
flow of filtrate and reject (backwash) water.
The Mt.View Sanitary District
utilizes the Trojan UV
3000™disinfection
system. The first POTW ( Public Owned Treatment
Works) operated
in Northern California to use ultraviolet light for disinfection on a
full
scale operation, MVSD has been able to totally eliminate the use of
gaseous
chlorine, sulphur dioxide and ammonia, all Acutely
Hazardous Materials (AHMs), which can be toxic
to both humans
and wildlife. The Trojan system uses the same UV found in sunlight, but
in a concentrated dose, to destroy harmful microorganisms present in
the
wastewater. The elimination of AHM's
from the plant premises has increased staff and public safety while
decreasing
District liability.
What
is ultraviolet light?
UV light is defined as
electromagnetic radiation
having a wavelength less than that of visible light (400 nm) and
greater
than that of X-Rays (100 nm). The unit of wavelength is a nanometer
(nm),
equal to 10-9 meters.The
optimum UV wavelength for
germicidal effect is 253.7nm, which is found only in small amounts in
the
solar radation because energy at these wavelengths is absorbed by the
atmosphere.
The source of UV energy
that MVSD utlitizes is
low pressure mercury arc lamps. The radation is generated by striking
an
electric arc through mercury vapor. Discharge of the energy generated
by
excitation of the mercury results in the emission of UV light.