November 2006, Vol. 18, No.11

Problem Solvers

Problem Solvers Biosolids Reuse as Clear as Glass

 

Problem: Chicago-area sanitary district was running out of landfill capacity.
Solution: Melt the biosolids into glass.

The North Shore Sanitary District (NSSD; Bedford Park, Ill.), located about 30 mi (48 km) north of Chicago, owns and operates more than 100 mi (160 km) of intercepting sewer lines and pumping stations that collect and convey wastewater from local sewer systems to wastewater treatment plants in Gurnee, Waukegan, and Highland Park, all in Illinois. These three plants, in turn, send their dewatered sludge to NSSD’s new Sludge Recycling Facility in Zion, Ill.

In 2001, NSSD was faced with a decision that many sanitary districts face: Should it continue its current biosolids management practice, or change directions and pursue a more sustainable alternative? At the time, NSSD landfilled its sludge and would have had to begin the process of licensing and construction of additional landfill capacity. After an extensive search and review of the best environmental practices used in the world, NSSD opted for a bioenergy technology, developed by Minergy Corp. (Neenah, Wis.), to vitrify, or melt, its biosolids into a reusable glass aggregate product that can be beneficially reused by the local construction industry.

First of Its Kind
The world’s first commercial application of Minergy’s GlassPack® technology, designed to vitrify municipal biosolids into glass aggregate at NSSD, is undergoing final commissioning and will be fully operational by year’s end. The facility will convert 170 tonne (187 ton) of biosolids the district produces per day into about 6.4 tonne (7 ton) of glass aggregate.

“The district’s choice of Minergy’s GlassPack vitrification process over the past practice of landfilling dewatered biosolids was due to the environmental benefits of the technology, particularly the beneficial reuse of the glass aggregate produced,” said Brian Dorn, NSSD general manager. “By recycling the district’s biosolids into an inert glass product that can be used for construction purposes, the district will preserve open lands. Instead of landfilling, open spaces can instead be promoted for use as nature preserves for wildlife, vegetation, family recreation, and education,” Dorn said.

Emissions Under Control
According to Bob Paulson, business development manager for Minergy, the GlassPack technology utilizes a patented closed-loop, oxygen-enhanced combustion process combined with traditional thermal energy recovery to harness the renewable energy contained in the biosolids. Heat energy, recovered from the melter flue gas using a thermal oil heat-transfer system, is used to pre-dry the 170 tonne (187 ton) of wet sludge into 31.8 tonne (35 ton) of granulate each day. 

The process uses oxygen-separated air to produce melter temperatures greater than 1260oC (2300oF) that completely destroy the organics and greatly reduce the amount of exhaust gas generated. The volume of exhaust from GlassPack is more than 90% lower than traditional biosolids incineration systems. The Sludge Recycling Facility, located in Lake County, received state emissions permits to operate as a minor source in a designated Moderate Non-Attainment Area for the 8-hour Ozone Standard without the need for additional NOx or VOC control equipment.

Glass Aggregate Uses
The glass aggregate produced by the vitrification process has multiple beneficial industrial applications, including roadbed construction, blended cements, backfill, blasting media, roofing shingles, and asphalt pavement. Minergy has received approval from the state environmental regulatory agencies in Illinois, Wisconsin, and Michigan to beneficially reuse the glass aggregate in the construction industry.

Preserving open land by reducing the need to landfill has been at the forefront of NSSD’s strategic and environmental objectives. Based on recent interest in the technology, Paulson believes the NSSD plant will be a model for other municipalities around the country and world seeking a sustainable solution to biosolids disposal challenges.  

For more information, visit www.minergy.com or send an e-mail to info@minergy.com. Contact Dorn at North Shore Sanitary District at (847) 623-6060.