The Anaerobic Filter for
Waste Treatment
JAMES C. YOUNG, Graduate Student
PERRY L. McCARTY, Associate Professor
Civil Engineering Department
Stanford University
Stanford, California
INTRODUCTION
An entirely new anaerobic treatment process has been found to be particularly
effective for the treatment of low strength soluble organic wastes. This process,
termed the "anaerobic filter," is basically a rock-filled bed similar in appearance to an aerobic trickling filter. However, the waste is distributed across the
bottom of the anaerobic filter. Flow is upward through the bed of rocks so that the
filter is completely submerged. Anaerobic microorganisms accumulate in the void
spaces between the rocks so that the waste comes in contact with a large active
biological mass as it passes through the filter. A high degree of treatment results
even at nominal waste temperatures, and the effluent is essentially free of biological solids.
Historically, anaerobic systems have been used to stabilize high strength
wastes, primarily composed of the solid; produced by aerobic processes and removed from settling tanks. Conventional anaerobic processes have required long
detention times for good waste stabilization and have usually been uneconomical
for the treatment of waste containing less than about one per cent biologically
degradable organic material.
"Anaerobic activated sludge" and other similar anaerobic contact processes
can also efficiently treat low strength wastes. However, settling and recycle of
the effluent solids is required to maintain a sufficiently high biological mass for
efficient treatment. For wastes which are primarily soluble a significant fraction
of the microbial mass may remain dispersed; the biological solids are difficult to
settle and recycle, and high treatment efficiencies are difficult to maintain.
In comparing the anaerobic filter to these existing biological treatment processes a number of distinct advantages stand out:
1) The anaerobic filter is ideally suited for the treatment of soluble wastes.
2) No effluent or solids recycle is required with the anaerobic filter. The
biological solids remain in the filter and are not lost with the effluent.
3) The accumulation of high concentrations of active solids in the filter permits the treatment of dilute wastes even at nominal temperatures. Heating is not required as in most other anaerobic processes to maintain a high
treatment efficiency.
4) Very low volumes of sludge are produced by the anaerobic filter. The effluent is essentially free of suspended solids,  and sludge wasting, in some
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