Mechanical Screens

These screens remove sticks, rags(paper products like toilet paper), large solids and other debris that would be harmful to other the rest of the treatment plant.  The next screen will show the materials removed.

Waste From Screens

The waste from the screens is compacted to removed organic materials and dewater prior to final disposal into a dumpster, where it is taken to the landfill.

Grit Removal

Aerated tanks are used to remove grit from the water after it has passed through the screens.  The aeration keeps organic materials in suspension to continue through the treatment process.  Heavier materials sink and are placed in a dumpster.

Grit Disposal

The grit from from the bottom of the grit tank is brought up in a dumpster by an auger.  Allowing the water to continue through the treatment process.  Grit is taken to the landfill for disposal.

Primary Clarifers

Suspended solids still in the waste water will go into a 50-foot diameter clarifier basin and allow the larger organic materials to settle to the bottom.  Those materials pumped to a sludge blend tank.

Secondary Clarifiers

This clarifier will remove the biomass from activated sludge that settles to the bottom.  Sludge can be recycled back into the aeration tanks or wasted into the sludge blend tank for final treatment.

Sludge Blend

The solids to be sent to the digesters in the sludge blend tank are run through these rotational drum thickeners.  A polymer is added to help remove excess water before the sludge is pumped to the digester.

Primary Digesters

The primary digesters are kept within a degree of 90 degrees F to keep specific micro-organisms at the correct temperature for breaking down the solids.  Methane and hydrogen sulfide are produced by the process and the gas is captured and used to heat the digesters.

Thickener Building

After the solids are through treatment in the digesters, they are run over a belt thickener to remove excess water again, by using a polymer.  Once thickened the solids are moved to the blue storage tank onsite.

Land Application

In the Spring and Fall the solids are taken out of the blue tank and applied to the farm land around the wastewater treatment plant.  The nutrients are low but the carbon in the waste help build soil structure.  This is the end of the Solids Treatment.


The solids (sludge) generated from the various processes are further processed to stabilize them before final disposal.  Air-diapragm  pumps are used to pump sludge from the primary clarifiers into the sludge blend tank.  The sludge blend tank holds primary sludge and waster activated sludge (WAS).

Rotary Drum Thickeners

Rotary Drum Thickeners

The WAS is pumped from the secondary clarifiers into a holding tank.  When a sufficient quantity of WAS has been collected, it is thickened in the sludge blend tank.  Rotary drum thickeners  use polymer to thicken the WAS from 0.5 percent solids to 4.5 percent; which removes some for the water from the sludge and correspondingly reduces the quantity to be handled.

The excess water is then returned to the plant influent flow to be processed again.  The sludge blend tank is mixed with a vertical chopper-typle pump to make a more homogeneous sludge blend.  Any scum removed from the primary clarifiers is also mixed in the blend tank.  Progressing cavity pumps are used to pump the blended sludge to the existing anaerobic digesters for treatment.

Anaerobic digestion is the process used to stabilize and treat the blended sludge.  Stabilization reduces pathogens and also reduces the potential for the stabilized sludge (biosolids) to attract "vectors".

Anaerobic Digesters

Anaerobic Digesters

Vectors are organisms such as rodents or insects that can spread disease by transferring pathogens.  The IGLSD digestion process includes two primary digesters with fixed concrete covers and two secondary digesters with floating steel gasholder covers.  The primary digesters heat the sludge to 95 degrees F to complete the stabilization process. The primary digesters are mixed with internal draft tube mixers mounted on the covers.  A by-product on anaerobic digestion is methane, or digester gas.  The digester gas is collected and stored under the secondary digester gas holder covers and used in the boilers to provide heat for the digesters.

Primary Sludge Pumps

Primary Sludge Pumps

The biosolids resulting from stabilization are thickened with an existing gravity belt thickener to increase the solids content to approximately 6%.  Once ticketed, solids are pumped to a large storage tank on-site.  Biosolids are land-applied as fertilizer on local cropland in the spring before planting and in the fall after harvest.