Inactivation of Ascaris suum eggs in digested and dewatered biosolids with lime and fly ash at bench scale and full scale

Abstract

The feasibility of inactivating Ascaris suum eggs spiked into digested and dewatered biosolids from Winnipeg, Manitoba to class A levels (as per USEPA 1993) by storing the biosolids treated with lime (CaO) and (or) fly ash under anoxic conditions was investigated. The study was comprised of two phases. The first phase involved mixing the biosolids with various quantities of lime and (or) fly ash in a Hobart mixer and storing the mixed product in 16 L buckets at 4–6 °C. Phase two involved full-scale mixing of lime and (or) fly ash using a Lödige mixer. The mixed product was buried in trenches and stored for 356 d at naturally occurring environmental temperatures that ranged from –1 to 33 °C in the trench. The lowest lime dose capable of inactivating Ascaris suum eggs to class A levels was 50 g of lime — amended with 1000 g of fly ash per kilogram of dry biosolids. Storage for 291 d at environmentally occurring temperatures was required to meet the class A criteria. Maintaining the higher temperatures for a longer duration would have reduced the time necessary to achieve the target inactivation. Key words: Ascaris suum, biosolids, eggs, fly ash, helminth, inactivation, lime.