News from Schwing Bioset

Managing Cost, Air Quality and Odor Control with Schwing

Case Study: Ellsworth, WI

The West Central Wisconsin Biosolids Facility (WCWBF) is a regional biosolids processing facility in Ellsworth, Wisconsin, serving Ellsworth and over 20 neighboring communities. The biosolids are dewatered by centrifuges to 20-24% total solids. The dewatered sludge enters an alkaline stabilization system that mixes the sludge with lime and fly ash to yield a Class A product. The treated biosolids are stockpiled in a 37,000-square-foot covered storage building, and beneficially reused semi-annually by local farmers.

In 2008, WCWBF decided to upgrade the lime stabilization process, with the main goals being to contain cost and maintain air quality and odor control. The existing mixer used open hoppers; between that and the fly ash, the system generated a lot of dust. Furthermore, the facility received periodic complaints from neighbors about the odor.

WCWBF chose a Schwing-Bioset system employing a closed hopper, screw conveyors, and pressurized piping system to contain dust and odors. To avoid costly contract hauling charges, WCWBF had to achieve demolition of the old system and installation of the new Schwing-Bioset system within 10 days of shutting down the old system. Demolition and preparation took three days; Schwing Bioset's team installed the new equipment, including the electrical, within the remaining seven days.

With a few minor modifications to adapt it to the winter weather, the Schwing-Bioset system has performed within expectations since commissioning, achieving its goals of managing cost, dust, and odors.

Tags: Class 'A' Biosolids, Bioset Process, Alkaline Stabilization, Biosolids, Dewatering

What should we do with our biosolids?

As the children’s book has it, everyone poops. By and large, in the developed world, this means the toilet flush is our last contact with what might be our lowest common denominator.

But what comes next? That poo, after all, goes somewhere. And in America, it basically means that local municipalities make a choice: human waste can go to a landfill, a field, or an incinerator.

The landfill and the incinerator seem clear enough, but can we really put human waste on the fields where we grow our food, or play with our kids?

You bet!

Human waste becomes “sludge” when it passes through municipal water treatment facilities, and it can be treated and turned into Class A or Class B biosolids (as defined by the EPA). 

In terms of land application (spreading the biosolids on the ground as fertilizer), exceptional quality—Class A—biosolids can be used in small amounts with no buffer requirements or crop type/harvesting restrictions. These “exceptional quality” biosolids meet EPA requirements for low levels of metals and bugs.

If used in large quantities, Class A biosolids do have buffer requirements, but no crop harvesting restrictions. 

Class B biosolids, on the other hand, basically always have buffer requirements, public access, and crop harvesting restrictions (Class B biosolids are treated, but still contain detectible levels of metals/pathogens).

Contact Us, We Can Help Any City Produce Class A

Tags: Class 'A' Biosolids, Bisolids Handling, Wastewater Treatment

Class A Biosolids vs. Class B in Plain English

What’s Class A? What’s Class B?

The EPA provides A Plain English Guide to the EPA Part 503 Biosolids Rule, which is broken into ten chapters. Table 2-5 in Chapter 2 (PDF) summarizes the differences between the pathogen reduction requirements for Class A and Class B biosolids:

 class A biosolids, class B biosolids

Class A

Class B

In addition to meting the requirements in one of the six alternatives listed below, fecal coliform or Salmonella sp. Bacteria levels must meet specific density requirements at the time of biosolids use or disposal or when prepared for sale or give-away (see Chapter Five [PDF] of this guidance).

The requirements in one of the three alternatives below must be met.

Alternative 1: Thermally Treated Biosolids
Use one of four time-temperature regimens.

Alternative 1: Monitoring of Indicator Organisms
Test for fecal coliform density as an indicator for all pathogens at the time of biosolids use or disposal

Alternative 2: Biosolids Treated in a High pH-High Temperature Process
Specifies pH, temperature, and air-drying requirements

Alternative 2: Use of PSRP
Biosolids are treated in one of the Processes to Significantly Reduce Pathogens (PSRP) (see Table 5-7)

Alternative 3: For Biosolids Treated in Other Processes
Demonstrate that the process can reduce enteric viruses and viable helminth ova. Maintain operating conditions used in the demonstration.

Alternative 3: Use of Processes Equivalent to PSRP
Biosolids are treated in a process equivalent to one of the PSRPs, as determined by the permitting authority

Alternative 4: Biosolids Treated in Unknown Process
Demonstration of the process is unnecessary. Instead, test for pathogens—Salmonella sp. or fecal coliform bacteria, enteric viruses, and viable helminth ova—at the time the biosolids are used or disposed of or are prepared for sale or give-away.


Alternative 5: Use of PFRP
Biosolids are treated in one of the Processes to Further Reduce Pathogens (PFRP) (see Table 5-4)

Alternative 6: Use of a Process Equivalent to PFRP
Biosolids are treated in a process equivalent to one of the PFRPs, as determined by the permitting authority


Do you have more questions? CLICK HERE

Tags: Class 'A' Biosolids, Biosolids Process, EPA, Biosolids Handling



Class A biosolids are completely safe for a variety of land applications. The end product is basically aerated soil that has beneficial levels of nitrogen, phosphorus, and potassium. The Class A product from a Bioset System has slightly elevated levels of lime as a result of the alkaline stabilization process. The alkaline reaction is as follows:
    CaO + H2O => Ca(OH)2  + 490 Btu/lb of heat

The by products of the reaction between quick lime and water are lime and the heat used to kill pathogens. Acid is also used to create a secondary reaction with the lime (Ca(OH)2) that can make up to an additional 400 Btu/lb of heat to accelerate pathogen kill. The end product has a PH of greater than 11.5. Long term tests have shown that this process maintains its PH several months after processing. This is important because some process can only reduce pathogens to safe levels for a short period of time when the material is dry. If pathogens are not thoroughly killed by treating extensively, then rain water and moisture can reactivate the pathogens in the soil and make them unsafe.   

The end product is used as a fertilizer because it is safe with no pathogens and rich with nutrients. Nitrogen and Phosphorus are the sought after nutrients in the planting soil industry, creating value for this material as a soil additive. There are also benefits from organic components in the material resulting from the original biological material.

Having a basic material (PH is higher than 7) from the lime content is an advantage as a soil amendment to help balance out acidic soil as well as fertilize. Acidic soil is found across the U.S. as a result of acid rain and other natural or manmade conditions. There are small treatment plants that will give this material away to locals as a free fertilizer for gardening. Some moderately sized facilities have contracts with farmers that can use the material to balance out soil and fertilize without buying costly lime and fertilizer additives. Contracts have also been established to sell the end product to golf courses in Florida, a region known to have highly acidic soil. Balancing the PH and providing a healthy fertilizer for the greens, while reducing maintenance costs.     

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Tags: Class 'A' Biosolids, Biosolids, Bioset Class A, Fertilizer Replacement

Schwing Bioset featured on Fox Business News

Please be advised, due to technical difficulties experienced by the Fox Business Network the Schwing Bioset feature on 21st Century Business did not air on October 10, 2009, as scheduled. However, it will be re-aired on Saturday October 31st at 5:00 PM EST.

Tags: Class 'A' Biosolids, Fluid Bed Drying, Biosolids