News from Schwing Bioset

Lime Stabilization-Fact vs. Fiction(myth-busted)

As you can imagine, working with sludges and biosolids brings up a number of concerns, from the basic to the technical. At the very basic, there’s “does it have an awful smell?” It’s a natural enough concern—we’re working with human waste, after all. But is there a terrible smell?

Class A Biosolids
Not at all, thanks to the Schwing Bioset process. A pinch valve flattens the sludge flowing out of the reactor, creating additional surface area to allow the ammonia and other compounds to be released and subsequently captured and scrubbed under the collection hood. The smell, overall, is akin to wet concrete (because of the lime content). In fact, in many instances the Class AA product produced by the Schwing Bioset process is stored outdoors on the edge of town with residential homes within sight.
At the more technical end, other lime stabilization systems are plagued by poorly mixed lime and sludge. Schwing Bioset solves this with a twin auger mixer that ensures the lime and sludge are thoroughly combined.
Another common concern is that the lime/sludge dust will make for a tough work environment. But the Schwing Bioset process is a closed system with a sealed mixing hopper—and that ensures the dust stays inside the machine, and not your lungs.


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