Advances in Biosolids Disinfection/Stabilization Utilizing Sulfuric Acid

An increased application of sulfuric and other acids for the inactivation of pathogens and enhancement of stabilization of biosolids has been observed in the last 15 years. Using sulfuric acid, some 3 to 5 log inactivation of fecal coliform and 60 % reduction of viable helminth eggs at ambient temperature in a pH range of 1.5–3.0 was observed. In order to enhance sludge disinfection at room temperatures (20–25 °C), nitrous acid (a non-charged biocidal agent) and ozone/chlorine dioxide (oxidizing disinfecting agents) were added to inactivate helminth eggs, viruses, and bacteria and to keep the nitrous acid thermodynamically stable in the ORP range of 50 to 700 mV. This work has been noted in studies conducted on the Neutralizer and Synox process. Disinfection can also be enhanced by exothermic reactions between ammonia and sulfuric acid, phosphoric acid, or nitric acid, which is developed by commercial processes such as Unity and VitAG Process. Such reactions can increase the biosolids temperature up to 130°C. This has been observed with the exothermic ammonium sulfate process (Unity and VitAG Processes). Further data will be coming from final PEC study for the Neutralizer process and EVT study for the Unity process.