ADVANCES IN ALKALINE STABILIZATION/DISIFECTION OF MUNICIPAL BIOSOLIDS

This paper explores the advances and future directions in alkaline biosolids stabilization and disinfection. Over the past ten years, the main factors addressed with regards to controlling disinfection are pH, temperature, free ammonia concentration, total solids content and exposure time. The primary parameters directly relating to this inactivation of the pathogens are specific ammonia content at temperatures up to 55°C and temperature above 55°C. In this paper, the range focused on lies at temperatures above 45°C, but below 55°C with the purpose of achieving a stabilized product at lower temperatures for the long-term. The other factors assist in this inactivation. For example, the thermophilic process is controlled by exothermic reactions of anhydrous lime and/or acid trimming agents such as sulfuric, phosphoric and sulfamic acid. The stabilization of alkaline processes is based on (1) high alkaline dosages, (2) the composting of alkaline biosolids, which is explained in this paper and (3) chemical alteration/destruction of the degradable organics. The effect of alkaline dosing was assessed at levels ranging from 0.05% to 2% ammonium as nitrogen with different types of biosolids (raw and anaerobic). The information for this paper comes from work conducted at Tulane University, the University of Manitoba, Bioset, Inc. and N-Viro International Corporation.Various biosolids respond differently to similar doses of alkaline agents due to the inherent acidity generated in the stabilization. An aerobically-digested sludge will require a much higher dose of lime to neutralize the acidity generated during stabilization than a similar sludge produced by anaerobic digestion. In the next few years, it is expected that alkaline stabilization/disinfection of biosolids will be optimized in relation to pH, suspended solids, ammonia content, temperature and exposure time. In addition, the end products will become more viable as value-added products. In other words, it is anticipated that the value of the generated product would absorb the cost of treatment, which is important for small municipalities and the agricultural community that cannot afford the more expensive processes.