Challenge

An eastern U.S. municipality was using two centrifuges for dewatering 80 to 100,000 gallons-per-day of product from the sludge thickeners.  They had routinely treated the sludge for odor control by adding approximately 100 pounds per day (126 mg/L) of potassium permanganate (KMnO4) prior to the two centrifuges.  Dosage of potassium permanganate was based on the presence of hydrogen sulfide (H2S) in the liquid phase from the centrifuges.  Sulfide levels of 0.1 mg/L were common while using this treatment protocol.  The customer was concerned with the cost of the program and continued to look for alternative chemical treatment solutions to control the odor.

Solution

VX-456, a proprietary mixed oxidant liquid product as an alternative to potassium permanganate was recommended.  To allow a side-by-side comparison, one centrifuge feed was dosed with VX-456 and the other with potassium permanganate.

Results

Initially, VX 456® was dosed (126 mg/L) on an equal dry weight basis to the potassium permanganate used by the customer.  Samples of the liquid centrate were analyzed for hydrogen sulfide by the methylene blue method.  Following treatment, the potassium permanganate stream had 0.1 mg/L sulfide residual, while the VX 456® side had none.  The dose rate of VX 456® was reduced to 63 mg/L (half) and then to 42 mg/L (one-third of the original dose) with the centrate remaining sulfide-free. 

VX 456® not only performed better than potassium permanganate but actually reduced the customer's odor control expenses.  An added benefit was the residual control of odor obtained with the VX 456®.  Due to the excellent performance and cost savings realized by the VX 456® program, the customer made a decision to switch to VX 456® for odor control of their sewage sludge. 

VX 456 is a registered trademark of Occidental Chemical Corporation