What are Biosolids?

Biosolids are created throughout the treatment process of wastewater.  They consist of  a combination of materials present in the wastewater stream as it enters the facility and the biological growth generated by the secondary treatment process within the facility.  Biosolids contain pathogens that are harmful to public health so they are pasteurized and treated with lime and heat and are deregulated before they finally leave the wastewater facility. 


Process of Biosolids

The Saint Peter Wastewater Treatment Facility processes biosolids in a "Class A exceptional quality" by first pumping in liquid form at two percent solid, from the clarifiers to a sludge storage tank.  From there, biosolids are pumped to the belt filter presses, which squeeze the water from the liquid biosolids to produce a “cake” that is 25-30 percent solid material.  The cake then travels by conveyor to the lime-heat treatment system, where lime is added to the cake to raise the temperature to 150° Fahrenheit.  After that temperature has been maintained for a minimum of 30 minutes, the cake is dropped to another conveyor that transports it to a storage bunker for finished biosolids.  The finished biosolids are 40-45 percent dry solid and the bunker where they are stored can hold up to 180 days of biosolids production.  After being processed the final material is classified as a deregulated "Class A exceptional quality" biosolid that can be easily disposed to agricultural land where they are used as fertilizer because they contain many nutrients that are beneficial for soil conservation and recycling.