LOW–DOSE ALKALINE DISINFECTION OF DEWATERED BIOSOLIDS

Bench-scale experiments were conducted to establish the effect of low-dose alkaline treatment of Winnipeg dewatered, anaerobically digested biosolids and determine the abiotic factors leading to pathogen inactivation over a long-term anoxic storage with various additions of alkaline materials. Technical-grade lime and fly ash from a nearby power plant were used as alkaline agents. The stored biosolids were mixed with soil to test for pathogen regrowth.The tests were designed to find optimum doses that would bring the pH to a level high enough to convert most of the indigenous ammonia from ammonium ion (NH4 +) to free ammonia gas (NH3). Various doses of lime and power plant fly ash showed significant evolution of free ammonia from digested, dewatered biosolids at the lowest doses of addition.Anoxic storage of lime-applied biosolids was effective in reducing levels of fecal coliform and Salmonella sp. bacteria well below those required to regard the biosolids as U.S. EPA's Class A within one day. The minimum effective lime dose was 30 g CaO/kg TS. There was no significant pH change at doses higher than 60 g CaO/g TS even after 6 months of storage.Fly ash doses had to be 10 times greater than lime doses to achieve the same level of fecal coliform reduction. When combined, lime and fly ash resulted in a greater pH increase in biosolids than either used individually.Fecal coliform regrowth in topsoil formulations was limited to the mixtures containing raw biosolids and biosolids treated with 30, and 60 g CaO/kg TS, and remained below the Class A limit. There was no Salmonella regrowth observed in any of the topsoil formulations.