To protect the water supply for the Metropolitan Chicago area, the Illinois legislature, in 1889, created the Metropolitan Sanitary District of Greater Chicago. To insure the quality of the water supply, the Sanitary District collected and diverted the wastes of 750,000 people away from Lake Michigan. Today, the Sanitary District collects and treats the wastes from a domestic population of 5% million people and an industrial waste load equivalent to 4% million people. The District serves Chicago and 120 other cities and sub-urbs in an 858 square mile area.
The wastewater enters the treatment plant through underground sewers, some as large as 24′ in diameter. The wastewater passes through screens which remove coarse debris such as rags, branches, bits of wood, etc. before being pumped to ground elevation. After pumping, the wastewater flows by gravity thru grit tanks which remove grit and sand particles by sedimentation. After grit removal, the wastewater flows into a primary settling tank where from 40% to 50% of the organic and inorganic solids settle out and are pumped to anaerobic digesters. The wastewater then flows to aeration tanks where it is mixed with another flow containing microorganisms which feed on the organic matter remaining in the wastewater. Diffused air provides mixing and supplies oxygen to the microorganisms as they convert the soluble and insoluble organic matter into cell mass, multiplying in size and number.
In the anaerobic digesters, the solids from the primary and final settling tanks are digested by other forms of bacteria and are partially converted into methane gas and carbon dioxide. The methane gas produced is collected and used to heat the digesters to maintain a temperature of 95°F, the optimum temperature for the metabolism of the bacteria. After a 14 day digestion period, the solids are removed in a slurry which is approximately 4% solids.
The final disposition of solids generated in wastewater treatment processes has histroically been one of the major concerns of wastewater facility operators. Many methods have been utilized and the Metropolitan Sanitary District, in generating solids quantities equivalent to 700 dry tons per day currently, has pursued many of the most practical methods.
Major methods of solids disposal practiced prior to 1965 were:
- Heat drying to produce a type of commercial fertilizer
- Anaerobic digestion with subsequent lagoon disposal
- Air drying on sand beds with disposal by land fill
- Wet air oxidation
U of I Research Project
Dr. Thomas Hinesly of the Agronomy Department of the University of Illinois conducted the most sophisticated of the research projects relative to the “Solids-On-Land” Program. Aided by a grant from the Bureau of Solid Waste Management and the Metropolitan Sanitary District of Greater Chicago, the University of Illinois constructed a research facility at the Northeast Agronomy Research Center near Elwood, Illinois. This facility includes 44 plots 10 feet by 50 feet, buried tanks to store fertilizer and water, and pumps and piping to move the fertilizer and the water from the storage tanks and apply them to the plots.
Both NH4+-N and NO3-N in the surface waters decreased with rainfall intensity but increased with liquid fertilizer application and accumulation. Phosphorus in the surface waters correlated highly with liquid fertilizer applications. While rainfall intensity and liquid fertilizer applications and accumulations did not affect the NH4+-N or PO4-³ concentration of the groundwater, the NO3-N which is mobile in the soil, highly correlated with rainfall intensity and liquid fertilizer application and accumulation.
Additional research by the University of Illinois showed that fecal coliforms in impounded liquid fertilizer reduced from 40,000 per ml to 200 in 32 days, and they reduced from 3,000 per ml to 0 in the supernatant during the same period.
A study relating fecal coliform reduction to soil moisture in Plainfield sand showed that when the soil moisture is 10% or more 99.9% of the fecal coliforms die in 30 days after application and incorporation of the liquid fertilizer to the soil. Fecal coliform in the cake on the soil surface resulting from liquid fertilizer application decreased from 3,680,000 per gram one day after application to 700 per gram 12 days after application.
Reclamation of Acid Strip-Mined Waste Land
During November of 1970, the Sanitary District trucked 36,000 gallons of liquid fertilizer to the Shawnee National Forest southwest of Harrisburg, Illinois. The Forest Service applied this liquid fertilizer to three of four plots at the rates of 100, 58, and 25 dry tons per acre. The fourth plot which is the check plot – received no liquid fertilizer.
During March 16, 1971, the Forest Service planted a mixture of 20 pounds of K-31 fescue and 7 pounds of weeping lovegrass on all four plots. By June all plots but the control plot supported vegetative cover, the higher the liquid fertilizer application rate the more vigorous the grass growth. The grass on the check plot failed to germinate.
Constructing the plots to allow capture of the subsurface drainage water permitted sampling the water for analysis on all 4 plots before liquid fertilizer application. Table 3 shows the percent concentration of 5 heavy metals in the drainage water before treatment and 7 months after application for each plot. This indicates the liquid fertilizer application and the vegetative growth retarded the rate of acid production which keeps these ions in solution.
Encouraged by the results of its own demonstration program and the results of research by the University of Illinois, the Sanitary District to date has purchased approximately 10,000 acres of land in Fulton County, Illinois, much of which had been strip-mined for coal.
The Sanitary District is in Fulton County at the invitation of the Fulton County Board of Supervisors. Concerned about the progress of strip-mining, they sought a method of reclaiming the land to return it to agricultural production. At the same time the Sanitary District sought a place to utilize its liquid fertilizer production.