Biological Treatment of a Toxic Industrial Waste —
Performance of an Activated Sludge and
Trickling Filter Pilot Plant
ROBERT J. STRACKE, Research Trainee
E. ROBERT BAUMANN, Professor
Department of Civil Engineering
Iowa State University
Ames, Iowa 50010
INTRODUCTION
The adoption of stricter Water Quality Standards and the issuance of federal discharge
permits for each wastewater discharge has forced many communities to initiate preliminary
investigations aimed at upgrading their wastewater treatment facilities because the effluent
quality discharged from their present facilities exceeds permit allocations. The primary
objective of this study was to conduct an analysis of the treatment facilities operated by a
medium-sized Iowa community and to recommend a feasible solution for improving its
effluent quality. This particular city was confronted with a challenging treatment problem
because about 30 percent of the total flow received at the city treatment facilities originates
from a chemical manufacturing industry located within the city.
MUNICIPAL WASTEWATER TREATMENT FACILITIES
General
The city involved in this study operates a single-stage, trickling filter treatment plant,
as shown in Figure 1. The combined industrial and municipal wastewater flows into a wet
well and is pumped to two primary settling tanks. From the primary tanks, the sewage flows
to a single covered trickling filter and then to a final settling tank. The combined primary-
secondary sludge from the primary settling tanks flows into a sludge-collection well and is
pumped to an aerobic digester. The aerobically-digested sludge is transferred to a second
digester for solids separation. Supernatant from the secondary digester is returned to the
wet well and the sludge is disposed of by spreading onto surrounding farmland. The effluent
from the final clarifier is discharged into a nearby river. The river flow (7-day, 10-year low
flow) provides a normal dilution ratio of 11:1 under average wastewater flow conditions.
Present Operating Conditions
Since the effluent quality discharged from the existing city treatment plant exceeded
Iowa's present Water Quality Standards, the Iowa Department of Environmental Quality
(IDEQ) issued a schedule of compliance which requires that the city effluent meet the
discharge quality limitations summarized in Table I by April 1, 1978.
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