Developments in Disinfection Using Advanced Alkaline Stabilization

Innovation in biosolids treatment can be a challenging process. The development of a new or innovative biosolids disinfection process not only has to function accordingly, but also must adhere to ever-increasing restrictions imposed by the federal government in addition to local and state governments. The purpose of this project was to conduct experiments to define an advanced alkaline process as PFRP by demonstrating the ability of the system to handle different sludge types and verifying the suggested optimum operating conditions indicated by previous tests. Prior to PEC approval, Class A was being achieved via the pasteurization option and Vector Attraction Reduction is still met via Option 6, pH 12 for 2 hours, pH 11.5 for an additional 22 hours. In order to achieve a Class A product, increased temperatures and/or ammonia addition is required to inactivate the highly resistant viruses, protozoan spores, and helminth eggs. The primary physical parameters of interest are pH, temperature and ammonia concentration with regard to disinfection. Studies at Tulane have observed disinfection under closed systems at 55°C instead of 70°C due to the containment of ammonia in a closed system (Reimers et al., 2004). In the disinfection of biosolids along with temperature caused by the exothermic reactions of quicklime and acid trimming, the non-charged disinfectants are a major player. For alkaline disinfection, ammonia is the primary constituent. The key parameters of interest to determine the efficacy of the process are the pathogens: Ascaris, fecal coliform and poliovirus. Aerobic endospores were also monitored as a potential indicator organism for alkaline processes. The data demonstrates the effectiveness of the closed alkaline system at inactivating helminth ova within 30 – 40 minutes resulting in a greater than 2 log reduction. Most importantly, a greater than 3 log reduction was noted for all samples with regard to poliovirus and fecal coliform. The resistance of the aerobic endospores again proved to be higher than that of the other pathogens of concern. The data for the final runs conducted in the summer of 2010 substantiated the results of the previous studies conducted by Tulane. This data indicates meeting the criteria for Class A disinfected biosolids. The data related to pathogen testing, the required reductions, and indicator organism usage, will be presented along with the major hurdles to be overcome in pathogen recovery.