Some years ago when the costs of chemical sludge disposal sky-rocketed, it became necessary to do it a better way for one of my clients.
Previously on a controlled schedule, sludge was pumped into trailers from a third party service provider and was hauled off to its facility. Typically, this occurred three days a week. The chemical sludge is generated from a dissolved air flotation system and pumped into one of two sludge storage tanks.
Once the sludge was on this third party’s property, samples were collected and analyzed for moisture. Based upon the moisture percentage of the sludge and the weight of the sludge, a cost per ton would be generated.
Over five years, the cost had increased from $24 to $36 per ton. The weekly volume remained 15 tons per week for approximately 50 weeks each year.
Knowing this 50 percent cost increase was prohibitive for the company, we started looking at solids handling equipment and realized tackling the problem that way would involve a significant capital expenditure.
First, we looked at the operators’ current procedures to see if changes there would allow the disposal of sludge in a landfill instead of it being hauled off by a third party.
We contacted landfills and found a local one interested in receiving our sludge. Landfills are regulated by local authorities, so to send the sludge there, we needed to follow state regulatory provisions.
After the sampled sludge met the Toxicity Characteristic Leaching Procedure lab analysis, we learned the landfill required a specific moisture content and odor control.
Achieving the moisture levels required involved specific, rigorous handling procedures. The sludge storage tanks had open tops where rain could get in, so we put covers on top. A pulley system on the covers opens them during the day, but closes them in the event of rain.
We also optimized the chemistry for solids separation using a polymer. We mixed a polymer solution and pumped it into the sludge as it was pumped into the storage tanks. We usually pump the sludge every 2 hours and decant the water every 3 to 4 hours to remove it from the tanks.
A full tank is emptied the next day, so the schedule of storing, pumping, decanting and emptying completes a 2- to 3-day cycle depending on volume atmospheric conditions that ultimately allows us to control moisture.
The company experimented with odor control chemicals. It first analyzed the sludge and evaluated the source of the odor, and then it developed an odor control program using three chemicals and two injection points.
The chemicals are purchased in concentrated form and then mixed in water to be further mixed into the sludge at a controlled rate. The first chemical is injected where the sludge is pumped into the storage tanks, and the second as the sludge is pumped into the trailer to haul it off to the landfill.
After making these changes, we stopped using the third party. Twelve years later, the landfill still accepts our sludge. We controlled the moisture as we pumped it into the storage tank, and we controlled the age with chemicals to reduce its odor. All in all, more than $200,000 was saved, the result of cutting $24 per ton at 15 tons per week for 50 weeks a year.
Known in the industry as "Wastewater Dan," Dan Theobold, proprietor of Environmental Services, is a professional wastewater and safety consultant/trainer. He has more than 24 years of hands-on industry experience operating many variants of wastewater treatment processing units and is anxious to share his knowledge with others.