Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
4.11.2 Oxidation ditch
||Streator Wastewater Treatment Facility
||Design - 12.49 ML/d; peak - 40.88 ML/d.
||Greg Garbs, Project Manager. 815-672-2653
Streator is a former mining town, built over shallow coal mines. Industries
originally discharged to the mines to prevent the mines from collapsing and
because the previous wastewater plant, a secondary treatment facility built in
1955, did not have the capacity to treat all flows. In 1986, a process began to
prevent dwellings and industries from discharging sewage to the old mine sites.
Rainwater can still flow into the old mine sites under normal conditions.
The new plant, operating since late 1991, consists of a main influent pump
station followed by a mechanical bar screen, a grit chamber with chain and
bucket grit removal, and an orbal oxidation ditch operated in extended aeration
mode. The oxidation ditch has a high buffering capacity for toxic contaminants,
and features energy efficient operation. The mixed liquor from the oxidation
ditch flows to two secondary clarifiers, and the clarified effluent is
chlorinated then dechlorinated before discharge to the Vermilion River, which
supports small-mouth bass for sport fishing.
Permit levels are as follows:
|400 CFU/100 ml
||6 - 9
||April to Oct 1.5 mg/L Nov to March 4.0 mg/L
The oxidation ditch process results in effluent with less than 1 mg/L BOD5
and TSS. The ditch eliminated the need to add tertiary filters, which saved the
city more than $2.5 million U.S. in capital costs and more than $50,000 U.S. per
year in operating costs.
Waste secondary sludge is thickened either by gravity, or using a mechanical
gravity belt thickener. The thickened sludge is lime stabilized using a ration
of 1 part lime to five parts sludge by weight. The resulting biosolids are land
applied using wet hauling and subsurface injection in the spring and fall. 898
dry tonnes of sludge are handled a year.
The plant is designed for a peak flow of 40.88 ML/d, however flow from the local
combined sewers has been measured at 52.23 ML/d. The majority of the combined
flow is handled using two on site lagoons upstream of the main pumping station.
Each lagoon has a capacity of 3.78 ML, and is fitted with subsurface coarse
bubble aeration and mechanical mixers. The lagoons overflow to the old primary
treatment facility. The effluent from the primary clarifiers is chlorinated,
dechlorinated and discharged to the Vermilion River. BOD5 of the effluent ranges
from 20 to 100 mg/L, depending on flow. There are no permit requirements for
this discharge. Sludge removed from this system is processed with the secondary
Flow to the plant is controlled using a vortex regulator, which does not require
electrical controls or mechanical equipment. Should water levels in the
collection system rise too high, even with the on site lagoons in operation,
emergency combined sewer overflows discharge to the old mines. From there, the
wastewater percolates through the ground into the groundwater system.
The plant employs 5 people, and had an annual operating cost in 1998 of $500,000
U.S. The plant uses an MP2 Datastream maintenance software package, Opspack for
Windows, to generate and record operations and maintenance data.