8    RECYCLE AS AN ALTERNATIVE TO ALGAL TSS
AND BOD REMOVAL FROM AN INDUSTRIAL WASTE
STABILIZATION POND SYSTEM
E.M. Davis, Professor
Environmental Sciences
T. D. Downs, Professor
Biometry
Y. Shi, Graduate Research Assistant
A. A. Ajgaonkar, Graduate Research Assistant
School of Public Health
The University of Texas
Houston, Texas 77225
INTRODUCTION
Reuse of wastewater is acquiring a more important role in the overall concept of water conservation management. Increasingly, reports of new applications or methods for reclaiming this
vital resource appear to confirm this subject. Industrial wastewater reuse is among those sources
being considered more frequently.1-2 Information on industrial waste stabilization pond (WSP)
effluent recycling or reuse for cooling water purposes is virtually nonexistent. Oswald3 has
shown that, with proper design, industrial WSPs can achieve tertiary or even quaternary level effluent quality. An earlier study4 demonstrated that degradation enhancement could be achieved in
a series of industrial WSPs by recycling a portion of the secondary pond to the primary WSP influent with pH adjustment and phosphorus addition.
This paper presents data from investigations that were conducted to determine the feasibility
of recycling a WSP series effluent back within the system for BOD and total suspended solids
(TSS) reduction, which were algal in origin, and separately, to evaluate whether recycling the
final WSP effluent to the industry's cooling water ponds would show corrosion compatibility.5
The second part of this paper contains data developed from analyses of the settling characteristics of the algal standing crop in the industrial WSPs in question to determine the extent to which
autosedimentation could occur.
Details of the industrial WSPs were presented earlier with performance capabilities and algal
genera content.6 Since that report was published the two in-plant primary WSPs were replaced
with a double lined and covered anaerobic treatment reactor having 5.5 surface acres, 18 ft depth
and a hydraulic retention time (HRT) of about 20 days. The flow then goes to an aeration tank
with 6-8 hr. HRT, and then to a clarifier with sludge recycle to the influent to the aeration tank.
This system decreased primary WSP treatment HRT from that reported6 to have been -60 days to
20 days. The secondary (2°ry) and tertiary (3°ry) WSPs have not been altered since the referenced report. They are about 162 acres (5.5' depth) and 267 acres (3.5' depth) with HRTs, at 4.5
mgd flow, of 55-60 and 60 days, respectively. Therefore, these large HRTs achieve, at least, tertiary level treatment of organics, but do generate large algal populations which contribute to elevated BOD and TSS concentrations. Those elevated parameters, despite being nonhazardous and,
in fact, beneficial in the respective receiving waters, pose problems when permitting is under
consideration. At a 5.6 mgd effluent rate a proposed permit lowered the 30-day average TSS to
38 mg/L and BOD to 25 mg/L.
50th Purdue Industrial Waste Conference Proceedings. 1995, Ann Arbor Press, inc.. Chelsea, Michigan 48118.
Printed in U.S.A.
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