ENERGY RECOVERY FROM THERMAL TREATMENT: TO DIGEST OR NOT TO DIGEST – IS THIS SUSTAINABLE?

Many wastewater utilities are developing or have recently developed biosolids management
plans (BMP) that provide a strategy for 20 to 25 years into the future. In developing BMPs,
wastewater utilities are faced with many challenges, such as satisfying the customer base,
satisfying internal and external stakeholders and developing a BMP that is affordable,
sustainable for the future and meets regulations. Traditionally, small, medium and some largesized
wastewater utilities have land applied anaerobically digested Class B biosolids either as
liquid or dewatered cake, while several of the larger wastewater utilities have thermally oxidized
their biosolids. With growing public pressure to reduce or cease land application, there has been
renewed interest in thermal oxidation as a management strategy, often raising the question: is it
sustainable? If the wastewater utility has existing digestion, is thermal oxidation compatible with
digestion or should digestion be stopped?
This paper presents a comparison of six different thermal oxidation process schemes with respect
to their economic, energy and carbon footprints for undigested and digested solids. The results of
the comparison provide wastewater utility staff and engineers with the positive answer to the
question “Is thermal oxidation of biosolids with energy recovery sustainable?”