Abstract:
Douglas-fir bark, 3/4 inch and 1 1/2 inch in size, was tested in recirculating
trickling filters 1, 2, and 3 feet in depth, hydraulically loaded at 2.27, 4.54, and
9.08 gallons per minute per square foot (gpm/sq.ft.) with 2 and 4 percent poultry
manure slurry at 70° F. Preliminary tests indicated the necessity of allowing
the heavier waste particles to settle by gravity. Samples collected at the beginning
and at intervals during the run indicated that the reduction of biological
oxygen demand (BOD) followed close to the formula BODt = BODo10-tt. Also,
as the depth of filter and the rate through the filter increased, the rate of removal
of total solids increased. However, the rate of flow through the filter had little
effect upon nitrogen removal, as this was influenced by the length of time circulated
and the depth of the filter bed. BOD and total solids concentrations lowered
at a faster rate when the larger bark was used. There was no indication that
the bark increased in either nitrogen or phosphorous during the tests. The turbidity
on an average improved from 75 to 4.3 JTU (Jackson turbidity units) for
the 2 percent concentrations and from 157 to 16.4 JTU for the 4 percent concentrations
in 23 hours.
