Advent of Neutralizer Process for Municipal Residuals Disinfection and Stabilization

In the late 1980's, Tulane researchers developed the Synox process, which utilized ozone, sulfuric acid and nitrous acid to disinfect biosolids (Reimers 1991). From this work, it was noted that nitrous acid was the primary disinfecting agent to inactivate helminth eggs. The process was observed to be effective and would produce a Class A biosolids within 4 to 24 h depending upon the dosage of nitrous acid in the range of 1500 to 400 mg/L, respectively. The Synox process was approved as a PFRP process by EPA's PEC in the early 1990's. The problem with this process was related to the utilization of ozone to hold the ORP at >100 mV. The ozone process was very costly and made the process not viable economically. The Neutralizer Process is able to control the ORP with chlorine dioxide, which is much less expensive and more reliable in a municipal sludge environment. This process utilizes chlorine dioxide and nitrous acid under acidic conditions to meet Class A biosolids requirements for disinfection and is also able to stabilize raw sludge.