An Economical Low-Energy Bio-oxidation Process
For The Treatment of High BOD Wastewaters
ARTHUR M. STERN, Manager
Environmental Research
Betz Laboratories, Inc.
Trevose, Pennsylvania 19047
LARRY L. GASNER, President
Gasner Engineering
Feasterville, Pennsylvania 19047
FRANCIS A. SANDERS, President
Betz. Environmental Engineering, Inc.
Plymouth Meeting, Pennsylvania 19462
INTRODUCTION
The most important reaction in the stabilization of wastes is oxidation. Conventional
waste treatment oxidation systems are generally arranged to balance out air flow with waste
loadings and, as a consequence, are characterized by low oxygen mass transfer rates. In
contrast, the fermentation industry has sought ways of increasing oxygen transfer into
fluids as a means ofachieving greater productivity per reactor (1,2,3,4, 5). This concept has
started to find acceptance in waste treatment programs as exemplified by the successful
substitution of molecular oxygen for air. The evidence available, thus far, strongly indicates
that increasing oxidation efficiency by improving mass transfer rates of oxygen reduces
aeration basin size requirements (by appreciably shortening detention times). This is of
particular importance in urban areas where land values are high.
The following is a detailed account of work carried out on a high BOD pharmaceutical
waste. The experimental aerator employed was designed to promote a much higher mass
transfer of oxygen into fluid feeds than the most efficient processes described thus far (3,6).
The aerator to be described is the result of intensive optimization studies and is the
prototype of a large pilot unit currently being evaluated.
EXPERIMENTAL
Description of Experimental Aerator
A schematic of the experimental aerator and ancillary equipment used to oxidize a
high BOD pharmaceutical waste is found in Figure 1. The unit was constructed of plexiglas
and consisted of two aerator chambers each of which was 11.5" x 8" x 48". These chambers
were arranged in series and fitted with baffles, perforated sparger tubes, pH, foam and
dissolved oxygen probes as shown. Effluent from the second aerator emptied into a settling
tank.
Raw waste was continually pumped into the first aerator chamber (volume: 63.8 liters)
and exited via a weir in the connecting wall into the second aerator chamber (volume: 62.5
liters). A weir in the outer wall of the latter allowed the oxidized waste to flow into a settling
tank from which the final effluent was led via a port in the top to a sampling vessel or the
sewer. Sludge from the bottom of the settling tank was pumped back to the first aerator
chamber and/or wasted if necessary. This pump, along with an agitator located in the
bottom of the settling tank, was turned on for one minute per 10 minute period to avoid
channeling. The nine minute quiescent period was found to be adequate for sludge settling.
881