Developments in Stabilization and Disinfection in Alkaline Systems

This paper is a compilation of experimental data obtained from Tulane University studies, field operations, projects at University of Manitoba, and Cornell University studies on the influence of ammonia disinfection in alkaline stabilization. The main parameters that are utilized in developing nomographs on disinfection related to ammonia content include: (1) ammonia concentration, (2) exposure time, (3) temperature, (4) suspended solids content, and (5) mixing. From the data, the inactivation of helminth eggs such as Ascaris have been enhanced by 50% to 99% at temperature ranges of 35°C to 50°C as compared to the time required for pathogen inactivation related to just the time/temperature phenomenon alone. The effect of the alkaline dosing has been assessed for raw, aerobically, and anaerobically digested biosolids that produce ammonia at concentrations of 0.05% to 2%. This data is incorporated in a fashion related to achieve a design that will ultimately gain approval by governmental agencies such as USEPA Pathogen Equivalency Committee. This data is usable for any alkaline stabilization process. In the next few years, it is expected that alkaline disinfection of biosolids will be optimized in relation to the factors stated above. Once this relationship is clearly defined and the most advantageous combination established, it would allow the development of a process that will be not only more energy efficient, but also more cost effective. In addition, stabilization with regard to alkaline systems using oxygen uptake as an indicator of stability was assessed. This phase of research is currently underway at Tulane University using the Respirometer system. The stabilization of alkaline treated biosolids can be based on both short-term and long-term basis. The data in this paper illustrates that the SOUR test may be a better indicator of stabilization than just holding pH with time.