Influence of Microbial
Waste Products on Metabolic
Activity of High Solids Activated Sludge
DONALD R. WASHINGTON, Professor
Bio-Environmental Engineering Division
LENORE S. CLESCERI, Research Associate
Biology Department
JOHN C. YOUNG, Graduate Assistant
FREDERICK W. HARDT, Graduate Assistant
Bio-Environmental Engineering Division
School of Engineering
Rensselaer Polytechnic Institute
Troy, New York
INTRODUCTION
Studies on the kinetics of the activated sludge process have led to an inquiry
concerning the applicability of the model to concentrated microbial systems (1).
In the pursuit of this end, problems of oxygen transfer (2) and solids separation (3)
have been investigated. Ultrafiltration which is pressurized filtration through polymeric membranes has proven suitable as a solids separation device for this system
(high solids activated sludge).
Okey (4) has observed that the high solids ultrafiltration system removes about
25 per cent of the influent organic phosphate under certain operating conditions.
Since solids separation by ultrafiltration can result in complete removal of all dissolved solids, a certain amount of unused waste and metabolic end products of
activated sludge will recirculate in the whole system. The aim of this study was to
determine the influence of the increasing concentration of metabolic waste end products in the system. The approach taken was to evaluate the relative change in carbon,
phosphate, nitrogen, glucose and oxygen uptake rate due to ultrafiltration and recirculation.
APPARATUS
The reactor was built from a large diam acrylic cylinder. The base and top
plates were made from the same materials as the cylinder. The base plate was attached by tie rods and sponge rubber gaskets. The top plate was put on without
sealing. There were several holes on the top plate which offered enough spaces for
exhaust, cooling coil, sparger, substrate additions and thermometer. The internal
diam of the aeration vessel was 7-3/4 in. The height of the reactor was 16 in.
Figure 1 shows the reactor, the feeding system, and the cooling system. The simple
aerator was a stainless steel tubing with six holes on the internal side of the bottom
loops. There was a large magnetic mixer and a 1-1/2 in. magnetic stirring bar to
maintain the homogeneity of the mixed culture. The cooling coil was also made with
stainless steel tubing. This coil was seven in. in diam and three in. in height. The
coolant was Troy tap water, with which the temperature of the reactor could be
maintained at about 20 C in the summer.
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