Section 14.    FOOD WASTES
THE TREATMENT OF APPLE PROCESSING WASTEWATER
BY THE ANAEROBIC FILTER PROCESS
Mark J. Laquidara, Laboratory Supervisor
Department of Civil Engineering
Northeastern University
Boston, Massachusetts 02115
Charles R. Ott, Professor
Department of Civil Engineering
University of Lowell
Lowell, Massachusetts 01854
INTRODUCTION
Biological treatment of waste streams containing BOD's ranging between 800 and 8,000 mg/l may
present problems in conventional processes, i.e., they are too strong for conventionally designed aerobic processes and too weak for conventional anaerobic digestion. Because there are many industrial
waste streams that fall in this range of concentrations, McCarty and co-workers developed the anaerobic filter process [1].
The anaerobic filter is not applicable to all waste streams with BOD's in this range, but finds its
greatest utility in the processing of wastes whose organic content is primarily in a soluble form and
contains low suspended solids concentrations. In addition to its ability to treat wastes of this type, the
filter possesses the advantage of requiring very little energy input. Aside from heat required to maintain proper operation, thoughtful plant outlay can reduce energy inputs to almost negligible amounts.
Even the external heat input may be small in some installations.
The study reported here was concerned with application of the anaerobic filter to the treatment of
wastes generated by a local apple processing firm. After a short settling period, the waste stream satisfied the process requirements of low suspended solids concentration and moderate organic strength
(see Table I).
Objectives of the study were to determine the treatment capabilities of the anaerobic filter process
when fed this waste as a function of: (1) operating temperature; (2) nutrient content; and (3) hydraulic
detention time. With respect to nutrients, the waste was found to have abundant phosphorus but was
severely limited in nitrogen.
DESCRIPTION OF THE ANAEROBIC FILTER PROCESS
The anaerobic filter process consists of a rock filled bed similar in appearance to an aerobic trickling filter. However, the waste is distributed across the bottom of the filter. The flow is upward
through the bed of rocks so 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 flows through the filter. A high degree of treatment results at nominal waste temperatures,
and the effluent is essentially free of suspended solids due to interception by the rocks.
Satisfactory loading rates have been found to range between 0.427 to 3.40 kg COD/day/m3 (26.5
to 212 lbs COD/day/1000 ft3) of total filter volume, and respective efficiencies range from 93% to
60%. Adequate liquid detention times range from 4.5 to 72 hours [2,3]. Previous work with the
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