INFLUENCE OF MECHANICAL
BLENDING ON AEROBIC DIGESTION
OF WASTE ACTIVATED SLUDGE
SHYAM D. BOKIL and J.K. BEWTRA
Department of Civil Engineering, University of Windsor, Windsor, Ontario, Canada
The present study was undertaken to determine the influence of mechanical blending
on aerobic stabilization of waste activated sludge. Simultaneous influence of blending on
settleability, pH, oxygen uptake rate, and total plate count were studied also.
Materials and Methods
Sludge samples were collected from the activated sludge treatment plant at Windsor,
Ontario. This plant receives a variable amount of industrial wastes and, during a part of
this study, alum and lime were added to raw sewage to reduce phosphates in the effluent.
Mixed liquor samples were collected near the outlet end of the aeration tank and were
allowed to settle for 40 to 50 minutes. The supernatant was then siphoned off and
discarded.
Eight to twelve litres of thickened sludge were continuously aerated in jars for a period
of 9 to 11 days at a room temperature ranging between 21 to 23°C. The sludge in onfe or
more jars was blended periodically in an Osterizer Blender provided with variable speed
control. The blending of sludge in the blender was done either in a batch operation or in a
continuous operation. In batch operation the entire contents of the aeration jar were
removed periodically and blended; whereas in continuous operation, the jar contents were
circulated continuously through the blender. The operation of the blender was controlled
by a timer so as to switch it on for one minute in every 5, 10, or 15 minutes. Parallel tests
were conducted on unblended sludge so as to act as controls.
The parameters varied were the intensity and frequency of blending and the aeration
rates. The effect of washing the sludge either with 0.05M phosphate buffer of pH 7.45 or
with distilled water was determined also. The digested sludge characteristics were
determined in terms of progressive biodegradation of volatile suspended solids, VSS, and
its settleability in 30 minutes. Each day the volume of liquid lost from the jars due to
evaporation was made up by addition of tap water. Tests for the suspended solids, SS,
VSS and settleability of sludge were carried out according to the Standard Methods
(1965). Oxygen uptake rates were measured polarographically with YSI Biological
Oxygen Monitor, Model 53. Generally, the sample for oxygen uptake measurement was
withdrawn from the jar about 30 minutes after the blending had been completed and the
sludge had been aerated. A 25 ml sample of the sludge was placed in the probe chamber
421
BLENDING ON AEROBIC DIGESTION
OF WASTE ACTIVATED SLUDGE
SHYAM D. BOKIL and J.K. BEWTRA
Department of Civil Engineering, University of Windsor, Windsor, Ontario, Canada
The present study was undertaken to determine the influence of mechanical blending
on aerobic stabilization of waste activated sludge. Simultaneous influence of blending on
settleability, pH, oxygen uptake rate, and total plate count were studied also.
Materials and Methods
Sludge samples were collected from the activated sludge treatment plant at Windsor,
Ontario. This plant receives a variable amount of industrial wastes and, during a part of
this study, alum and lime were added to raw sewage to reduce phosphates in the effluent.
Mixed liquor samples were collected near the outlet end of the aeration tank and were
allowed to settle for 40 to 50 minutes. The supernatant was then siphoned off and
discarded.
Eight to twelve litres of thickened sludge were continuously aerated in jars for a period
of 9 to 11 days at a room temperature ranging between 21 to 23°C. The sludge in onfe or
more jars was blended periodically in an Osterizer Blender provided with variable speed
control. The blending of sludge in the blender was done either in a batch operation or in a
continuous operation. In batch operation the entire contents of the aeration jar were
removed periodically and blended; whereas in continuous operation, the jar contents were
circulated continuously through the blender. The operation of the blender was controlled
by a timer so as to switch it on for one minute in every 5, 10, or 15 minutes. Parallel tests
were conducted on unblended sludge so as to act as controls.
The parameters varied were the intensity and frequency of blending and the aeration
rates. The effect of washing the sludge either with 0.05M phosphate buffer of pH 7.45 or
with distilled water was determined also. The digested sludge characteristics were
determined in terms of progressive biodegradation of volatile suspended solids, VSS, and
its settleability in 30 minutes. Each day the volume of liquid lost from the jars due to
evaporation was made up by addition of tap water. Tests for the suspended solids, SS,
VSS and settleability of sludge were carried out according to the Standard Methods
(1965). Oxygen uptake rates were measured polarographically with YSI Biological
Oxygen Monitor, Model 53. Generally, the sample for oxygen uptake measurement was
withdrawn from the jar about 30 minutes after the blending had been completed and the
sludge had been aerated. A 25 ml sample of the sludge was placed in the probe chamber
421