Pathogen Inactivation by a Closed Alkaline System

The efficiency of advanced alkaline disinfection in closed systems has been demonstrated to depend on the balance of ammonia concentration, pH, exposure time, temperature, total solids content, post-treatment storage time and mixing effectiveness. When the alkaline system is a closed one, an additional pathogen stressor is added: pressure. The effect of the alkaline dosing has been assessed for raw, aerobically, and anaerobically digested biosolids that produce un-ionized ammonia at concentrations of 0.05% to 2%. Overall, the addition of pressure as a factor in disinfection increased the inactivation of Ascaris egg to Class A levels by 50 to 99%, at the temperature range of 40 – 55°C. The systems studied were compared to an alkaline process operated under open conditions, which limited the concentrations of ammonia available due to the Henry's gas law. Under a closed pressurized system, the impact of un-ionized gaseous ammonia was greatly increased and the resulting time required for inactivation reduced from hours/days to minutes. Also, the use of ferrate in alkaline treatment is an emerging technology that has recently gained interest due to a new synthesis method, making it a more cost effective option. In the next few years, it is expected that alkaline disinfection of biosolids will be optimized in relation to the factors stated above, at much lower doses of the alkaline agents. The closed-system alkaline processes that will be developed will be more energy-efficient, cost-effective, and have full control of potential odorous emissions.