On-Site Wastewater Treatment and Disposal Systems - Forced ...

for larger, centralized systems can be found in the "Manual of Practice
- Operation of Wastewater Treatment Plants" (36) and "Process Control
Manual for Aerobic Biological Wastewater Treatment Facilities" (37).
Major mechanical maintenance problems for onsite treatment units are
with blower or mechanical aerator failure, pump and pipe clogging,
electrical motor failure, corrosion and/or failure of controls, and
electrical malfunctions (35). Careful attention to a maintenance
schedule will reduce these problems to a minimum, and will also
alleviate operational problems due to the biological process upset.
Emphasis should be placed on adequate maintenance checks during the
first 2 or 3 months of operation.
6.4.2.7 Considerations for Multi-Home Application
The extended aeration process may be well suited for multiple-home or
commercial applications. The same requirements listed for single onsite
systems generally apply to the larger scale systems (20)(36)(37)(38).
However, larger package plant systems may be more complex and require a
greater degree of operator attention.
6.4.3 Fixed Film Systems
6.4.3.1 Description
Fixed film systems employ an inert media to which microorganisms may
become attached. The wastewater comes in contact with this fixed film
of microorganisms either by pumping the water past the media or by mov-
ing the media past the wastewater to be treated. Oxygen may be supplied
by natural ventilation or by mechanical or diffused aeration within the
wastewater. Fixed film reactors are normally constructed as packed tow-
ers or as rotating plates. Figure 6-12 depicts three types of onsite
fixed film systems - the trickling filter (gravity flow of wastewater
downward), the upflow filter (wastewater pumped upward through the
media), and the rotating biological contractor.
The trickling filter has been used to treat wastewater for many years.
Modern filters today consist of towers of media constructed from a vari-
ety of plastics, stone, or redwood laths into a number of shapes (honey-
comb blocks, rings, cylinders, etc.). Wastewater is distributed over
the surface of the media and collected at the bottom through an undrain
system. Oxygen is normally transferred by natural drafting, although
some units employ blowers. Treated effluent is settled prior to being
discharged or partially recycled back through the filter.
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