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<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

4.11.2 Oxidation ditch

Plant Name: Streator Wastewater Treatment Facility
Location: Streator, Illinois
Service Population: 14,800
Flow: Design - 12.49 ML/d; peak - 40.88 ML/d.
Contact: 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.

Plant Description

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.

Effluent Quality

Permit levels are as follows:

  Monthly average Daily maximum
CBOD5 10 mg/L 20 mg/L
SS 12 mg/L 24 mg/L
400 CFU/100 ml  
pH 6 - 9  
Ammonia 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.

Sludge Handling

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.

Stormwater Management

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 plant sludge.

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.

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