City of Columbus Utilizing Wastewater “Sludge”

Many times I have wondered what actually happens with the sludge that cities collect during the wastewater treatment process.  Most of the time, the sludge is dumped into city landfills at a very high cost.  The city of Columbus, OH, on the other hand, has taken a different approach over the years, where they’ve incinerated the sludge and turned it into ash.

Where does the sludge come from?  Wastewater sludge is the solid waste that travels through the city’s sewer system, and ends up at a treatment plant to be conditioned for future use.  The plants then send the water back into the area’s watershed, but keep the sludge (often heavily polluted) to be further cleaned before disposing of it in a landfill, or turning it into compost.

However, new rules from the U.S. Environmental Protection Agency governing air quality and emissions at these treatment plants will go into effect in March 2016, so cities are trying to figure out how they will meet those standards.  This being the case, the city of Columbus plans to spread its wastewater sludge across farm fields, rather than burn it and/or dump it into landfills. 

Although there is still some environmental concern in doing this, the city already has special permits from the Ohio EPA to compost some of its sludge and to spread some of it on farmland.  However, the sludge can only be used as a fertilizer on specific types of farmland, in specific places, and at specific times.  It cannot be spread onto farmland before a rainstorm because it would then wash into the watershed, resulting in contamination of rivers and streams.  The sludge also cannot be spread over frozen ground.

This being the case, the city must be able to store the sludge until it can be spread appropriately.  To achieve that, Columbus plans on spending $3.2 million to design storage tanks to hold the sludge during times where it cannot be used.  This is where Dwyer Instruments can be a go to instrumentation solution.

With Dwyer’s wide range of submersible level transmitters, tank level can be accurately monitored from a remote location.  There are two different products that are manufactured specifically for this application: Series PBLT2 and Series FBLT submersible level transmitters.  The PBLT2 features an extremely robust “birdcage” design to keep the unit stable and protected in the harshest environments.  The FBLT features a slimmer construction, yet is still strong enough to meet the most demanding applications.

The PBLT2 features a large diameter 316SS diaphragm seal, which is non-clogging and damage resistant to floating solids.  On the other hand, the FBLT features a robust FKM fluoroelastomer diaphragm that is PTFE coated for a stick resistant surface that will hold up in aggressive fluids.  The diaphragm cavity is filled with a gel that will not leak out versus oil or grease that is used by our competitors.

For more information on Dwyer Instruments products that service the water/wastewater industry, please visit