Metropolitan Water Reclamation District of Greater Chicago, Chicago, IL

This will be referred to as MWRDGC for the rest of the discussion  
 

Overview

This project services 872 square miles and collects from a population of over 5.2 million and an additional 4.5 million equivalent industrial wastewater.  This results in wastewater for over 9.7 million people.  The waste is pretreated to remove the industrial loads released into the system.  The 7 wastewater treatment facilities produce over 550 dry tons of anaerobically digested biosolids daily.  Fifty percent of the biosolids are lagooned and the air dried to around 60 % solid concentration.  The remaining 25 to 30 percent is air dried to around 65 % solids.  The majority of these biosolids are used on the 15,528 acres of abandoned strip-mined land and prairie land in Fulton County purchased by MWRDGC.

Three forms of biosolids have been applied here: liquid biosolids, sludge cake, and currently dewatered biosolids. Fields are prepared by leveling  and creating berms and runoff basins around the perimeter of each field.  These basins are used to collect the treated water and to test it.  If it meets the regulations of 100 mg/L of suspended solids, less than 34 mg/L BOD, and a ph of between 6 and 10,  the waters are released into the local watershed.

The biosolids are spread using side-unloading spreaders and loaded by front-end loaders.  After the sludge is applied the soils are disked to incorporate the sludge.  The application rate is calculated by measuring the amount delivered each day.  This causes a great deal of compaction which has been a problem in the past.

Corn, Wheat, and soybeans are grown here and nitrogen loading rates are controlled by the needs of these crops.  Average rates are between 20 and 40  dry tons per acre.  The group is trying to reduce the extent of the farming operation by leasing the fields to private farmers that are located in the area.
After 40 years of attempts, the acid mined areas still will not promote vegetation.  Currently,  1,000 dry tons of biosolids and 70 tons of lime per acre  are used for the mined lands.
 
 

Monitoring

Air:
Air quality samples are taken to measure the amount of ammonia lost to volatilization from the holding tanks and lagoons.  no environmental impact has been observed.

Groundwater:
24 ground monitoring wells were installed throughout the site since 1971 at depths of 35 to 70 feet.  There has been no violations due to the application of biosolids on these sites.  There is still a problem with the acid mine drainage from the abandoned mine from 40 years ago.

Soil and crop samples:
Soil sampling started in 1972 with samples taken from the surface to a depth of 6 inches.  Crop residues have been taken on the grains grown on these lands including the corn ears produced on site.
 

Results

Metal concentrations here are higher than most municipalities studied in the country.  This is due to the large industrial supplies generated at the treatment plants.  In the 1980's, Chromium, Nickel, and Lead all exceed the regulations set out in the 503 regulations.  Today the metals are all below the federal standards.  This is due in part to better pretreatment and deregulation in the late 1980's after the ban on ocean dumping.

The values of metals found in the corn ear leaf samples are listed for Cadmium, Zinc, and Chromium  in the table below.  All measurements are in mg/kg.
 

This table shows how the metal concentration is extremely variable using these industrial wastewaters.
There was little difference between the control and the biosolid amended soils.  The average yields are much lower on the amended soils than on the control soils with commercial fertilizers.  The average yields on the amended soils were 57 bushels  per acre verses an average yield on the commercial fertilized fields with 73 bushels per acre.  The average yields on normal farms in the area is upwards of 160 to 180 bushels per acre.  This proves that the mined soils around the test area are contributing greatly to the low ph which lowers the yields of these crops.

Some accumulation of metals has been found in the test soils.  In the upper 6 inches of soil, the applied metals are showing different rates of accumulation.  These are the percentages of the applied metals still in the soil system.

• 79% cadmium
• 11% chromium
• 49% copper
• 15% nickel
• 26% lead
• 67% zinc

This shows that as a treatment process, this site is failing by accumulating the trace metals in the upper soils with a high potential of run off into the surrounding surface waters.
 

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