Aerobic Stabilization of Primary
Wastewater Sludge
JOSEPH F. MAUN A, JR., Assistant Professor
of Environmental Health Engineering
University of Texas
Austin, Texas
HERMAN N. BURTON, Engineer
W. F. Turney and Associates
Consulting Engineers
Sante Fe, New Mexico
INTRODUCTION
The volume of primary and biological sludges resulting from the treatment of
domestic wastewater that must be treated and disposed of continues to increase.
The poor drainability and the putrescibility of primary sludges have resulted in the
use of biological treatment schemes to stabilize a portion of these complex organic solids prior to disposal. The microbial population utilizes the constituents
of the sludge as a source of energy, carbon, nitrogen, special growth factors, inorganic nutrients, and trace elements which are required for microbial metabolism. Most metabolites must be in solution before these materials can permeate
the cell membrane and become available for microbial utilization. Therefore,
the organic solids must be liquified and hydrolized by extracellular enzymes secreted by some microorganisms. Consequently, the mechanism of aerobic stabilization of primary sludge is a sequential biological process. The data presented
in this paper provide some insight into the breakdown of organic solids, the fate of
nitrogenous compounds, and the characteristics of the environment during aerobic
stabilization of primary sludge.
LITERATURE REVIEW
Aerobic stabilization of organic wastes is not a new process. Over 30 years
ago Heukelekian (1) reported that wastewater solids were stabilized aerobically
at a greater rate than during anaerobic digestion.
The primary objective of many of the earlier studies (2,3,4) in which aerobic
stabilization of organic solids was evaluated involved improving the drainability of
sludges. The data recorded during studies (2,3) designed to evaluate the extent to
which anaerobically digested sludge could be further stabilized aerobically indicated that the volatile solids content was reduced from 2.98 per cent to 1.08 per
cent after 47 days of aeration. Organic nitrogen was oxidized during aerobic treatment. The aerobically treated sludge was stable and showed no signs of decomposition when left without aeration.
Aeration of a mixture of activated and primary sludges for three hrs at 15 C
resulted in a decrease of alkalinity of 80 per cent (4).
An organic loading of approximately 0.1 lb VS/day/cu ft was suggested as
the maximum practical loading when only volatile solids destruction was considered in the aerobic stabilization of a mixture of primary and activated sludges
(5).    The destruction of volatile solids expressed in terms of lbs destroyed per day
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